Dissertations / Theses on the topic 'Tree water use'

A general paradigm in semi-arid and arid systems is that woody plants with dimorphic root systems will exhibit preferential use of deeper soil water because it represents a more stable source of water than short duration pulses of shallow soil moisture derived from summer rainfall. However, whether this holds across all woody species and whether use of deeper soil water interacts with use of shallow soil water is not determined for many species in different ecosystems. Understanding the amount of water plants derive from groundwater and shallow soil water is critically important to accurate calculations of local and regional water balance. The focus of this research was to determine if dominant woody species in semi-arid riparian ecosystems used shallow soil water and how depth to groundwater and defoliation might affect root proliferation and water uptake. This research found that the functional grouping "phreatophytes" encompasses a variety of responses to environmental variation. Stable isotopic analyses determined that Prosopis velutina Woot. (Velvet mesquite) and Populus fremontii Wats. (Fremont cottonwood) used shallow soil water derived from summer rainfall, and the proportion of shallow soil water was higher at sites with greater depth to groundwater. In contrast Salix gooddingii Ball (Goodding willow) did not use shallow soil water at any location regardless of depth to groundwater. Field experiments using defoliation treatments, to limit carbon assimilation and reduce plant photosynthate pools, confirmed that Prosopis velutina exhibited flexible response in water uptake patterns in response to defoliation. Defoliation, which presumably reduced available photosynthate, increased the reliance of this species on shallow soil water; contrary to predictions that woody species should maintain extensive deep root systems to buffer themselves from seasonal drought. Greenhouse experiments with Populus fremontii and Prosopis velutina also indicated changes in belowground biomass of fine roots, which were associated with changes in water-source use for Populus fremontii, but not for Prosopis velutina. These results imply that in terms of predicting plant response to changes in future climates, or modeling fluxes of water from the soil to the atmosphere that are largely controlled by plant transpiration, intra- and interspecific variability will need to be considered.

Native plant communities and agricultural land are commonly converted to urban areas as cities across the Western United States continue to grow and expand. This expansion is typically accompanied by afforestation where a common goal among communities is to maximize shade tree composition. Planted forests in these regions are commonly composed of introduced tree species native to mesic environments and their ability to persist is dependent on consistent irrigation inputs. Many potential ecosystem services may be derived from planting trees in urban and suburban areas; however, there are also costs associated with extensive afforestation, and shade tree cover may have significant implications on municipal water budgets. In this study I evaluate variation in daily and seasonal water use of regionally common suburban landscape tree species in the Heber Valley (Wasatch County, Utah). I had two primary objectives: (1) to identify and understand the differences in transpiration between landscape tree species in a suburban setting and (2) to assess the sensitivity of sap flux and transpiration to variation in vapor pressure deficit, wind speed, and incoming shortwave radiation. I used Granier's thermal dissipation method to measure the temperature difference (ΔT) between two sap flux probes. The empirical equation developed by Granier was used to convert ΔT into sap flux density (Jo) measurements, which were then scaled to whole-tree transpiration. There were consistent and substantial differences in sap flux between tree species. I found that Picea pungens under irrigated growing conditions, on average, had Jo rates that were 32% greater and whole tree water use (ET) rates that were 550% greater than all other species studied. The findings of Jo may be partially explained by xylem architecture and physiological control over stomatal aperture. However, the rate of water flux in the outermost portion of sapwood does not necessarily determine the magnitude of whole tree transpiration. Rather, ET in this study was largely explained by the combined effects of irrigation, tree size, and sapwood to heartwood ratio.

Efficient use of irrigation and nutrients are becoming increasingly important in commercial orchards in the Hawkesbury area. Proper irrigation scheduling practices can help in the better use of irrigation water and reduce environmental impacts. Field experiments were conducted during February 1999 to June 2000 to understand soil-water use, and to evaluate farmer’s irrigation practice under an alley cropping system consisting of turf and stone fruits. The study was carried out at Atlas Farm, 3.5 km from the University of Western Sydney, Hawkesbury campus. The experimental site is a floodplain of the Hawkesbury River. The river flows within 1 km of the farm boundaries. The study was conducted under the farmer’s existing irrigation water and nutrient management practices. The main aims of the thesis were to study the movement and redistribution of soil-water and soil-moisture dynamics in the turf and stone fruit alley cropping system and to understand deep percolation losses and nitrogen leaching using the water balance approach. The study indicated that drainage occurred mainly after heavy rainfall and when there was rainfall for a few consecutive days. Thus irrigation application should be delayed if there is a likelihood of rain in a few consecutive days to prevent loss of water due to deep drainage. Furthermore, the study showed irrigation scheduling was essential to reduce nitrate leaching in the field; that irrigation depths should be varied according to the stage of crop growth, and the proper timing of irrigation application could help reduce deep percolation and runoff losses.<br>Master of Science (Hons) (Agriculture)

Exploring how drought influences growth, performance, and survival in different species is crucial to understanding the impacts of climate change on forest ecosystems. Here, we investigate the responses of two co-occurring pines (Pinus nigra and Pinus sylvestris) to interannual drought in east-central Spain by dendrochronological and wood anatomical features integrated with isotopic ratios of carbon (delta C-13) and oxygen (delta O-18) in tree rings. Our results showed that drought induces both species to allocate less carbon to build tracheid cell-walls but increases tracheid lumen diameters, particularly in the transition wood between early and latewood, potentially maximizing hydraulic conductivity but reducing resistance to embolism at a critical phase during the growing season. The thicker cell-wall-to-lumen ratio in P. nigra could imply that its xylem may be more resistant to bending stress and drought-induced cavitation than P. sylvestris. In contrast, the higher intrinsic water-use efficiency (iWUE) in P. sylvestris suggests that it relies more on a water-saving strategy. Our results suggest that narrower cell-walls and reduced growth under drought are not necessarily linked to increased iWUE. At our site P. nigra showed a higher growth plasticity, grew faster and was more competitive than P. sylvestris. In the long term, these sustained differences in iWUE and anatomical characters could affect forest species performance and composition, particularly under increased drought stress.

La biodiversité favorise un grand nombre de fonctions et services écosystémiques des écosystèmes forestiers tels que la production de bois ou la résistance aux attaques d’insectes et aux maladies. Cependant l’impact de la diversité sur l’acquisition et l’utilisation de l’eau et du carbone reste largement méconnu dans ces écosystèmes. De plus, dans le contexte actuel de changement climatique, l’influence de la diversité sur la réponse des écosystèmes forestiers à des événements climatiques extrêmes tels que la sécheresse reste à étudier. L’objectif de ce travail est donc de déterminer l’impact de la diversité en espèces d’arbre sur d’importantes fonctions du cycle de l’eau et du carbone telles que la transpiration, la composition isotopique du carbone ou la profondeur d’extraction de l’eau à l’échelle de l’arbre et de l’écosystème sous des conditions contrastées dedisponibilité en eau du sol. Ce travail a été réalisé dans le cadre du projet FunDivEUROPE sur un réseau de parcelles forestières ainsi que dans des plantations expérimentales le long d’un gradient Nord-Sud en Europe afin de couvrir une importante gamme de conditions climatiques. Nos travaux ont montré une importante variabilité de la réponse à la diversité à l’échelle de l’arbre et de l’écosystème en termes de relations hydriques et carbonées à travers l’Europe. La diversité en espèces ne semble pas influencer les relations hydriques et carbonées des espèces et des écosystèmes forestiers dans des conditions non limitantes de disponibilité en eau. Cependant, un fort effet de la diversité a été observé en conditions de sécheresse pour certains types forestiers. A partir de ces résultats, je discute des mécanismes d’interaction entre espèces qui peuvent expliquer les effets observés. Nos données ont montré que l’influence de la diversité en espèces est fortement dépendante du contexte et peut êtremodifiée par les conditions environnementales locales et les conditions climatiques. En terme de gestion forestière, je suggère que pour certaines régions en Europe, promouvoir la diversité en espèces ainsi que contrôler la densité des parcelles doit être recommandé afin d’adapter les écosystèmes forestiers aux futures conditions climatiques<br>Biodiversity is known to support and boost a wide range of forest ecosystem functions and services like productivity and resistance against insect pests and diseases. However, whether tree species diversity also promotes water and carbon acquisition and use in forest ecosystems is still unclear. Furthermore, in the current context of global warming, information on how tree species diversity can influence the response of forest ecosystems to extreme climatic events such as drought are urgently needed. In this framework, the objective of my PhD thesis was to determine how tree species diversity influences important functions of the water and carbon cycle including transpiration, carbon isotope composition and water extraction depth at the tree- and ecosystem-Scale under contrasting soil water conditions. My work was conducted within the FunDivEUROPE project in a network of permanent forest stands and tree plantations across a North-South gradient in Europecovering a wide range of climatic conditions. I found considerable variability among species or forest types in the response of transpiration and carbon isotope composition at the tree- and ecosystem-Scale across Europe. Species diversity did not affect the water and carbon relations of tree species and forest ecosystems under non-Limiting soil water conditions. However, a strong effect of species diversity was observed under drought conditions in some forest types. Based on these data, I discuss the potential mechanisms of species interactions that may explain the observed patterns. I also point out that the influence of species diversity is highly context-Dependent, and changes with local environmental and climatic conditions. In terms of forest management applications, I suggest that, at least in some regions, controlling for tree species diversity along with stand density and total basal area could be recommended to help forests adapt to drier conditions

Generally, the growth of all forests accelerate as canopies develop as in young forests and declines substantially soon after maximum leaf area is attained. The causes of this decline trend are multiple. However, age and size are normally coupled growth. Therefore, an experimental manipulation has been done to separate the effects of size from those of age by using traditional grafting techniques. Genetically identical grafted seedlings were produced from scions taken from trees of four different age classes ranged from 4 to 162 years. The aim of this study is to investigate the effects of tree age and tree size on growth, physiology and water use of two broadleaf species by conducting three major experiments. Growth characteristics such as relative growth rate and growth efficiency were measured together with leaf-level gas exchanges and sap flow studies. Comparisons were established among results observed in the field with the ones obtained in the grafted seedlings. The results showed that relative growth rate and growth efficiency decreased substantially with increase in age of donor trees in the field. In contrast, these parameters seemed almost constant on grafted seedlings which are scions taken from different meristematic ages did not show the age-related trend after they were grafted onto the rootstocks. Similar patterns were also observed in net photosynthesis from leaf-level gas exchange and sap-flow-based parameters in both species. In general, these results suggested that size limitation to water and nutrient transport to the top of the canopy is a primary cause that triggered the declination in production of photosynthate and reduced growth of the trees, and/or increase in maintenance respiration with increasing in tree size rather than controlled by meristematic age.

The arrival of the North American Monsoon System (NAMS) terminates a presummer hyperarid period in the southwestern United States (U.S.), providing summer moisture that is favorable for forest growth. Montane forests in this region rely on winter snowpack to drive much of their growth; the extent to which they use NAMS moisture is uncertain. We addressed this by studying stable carbon and oxygen isotopes in earlywood and latewood from 11 sites along a latitudinal gradient extending from Arizona and New Mexico to Utah. This study provides the first regional perspective on the relative roles of winter versus summer precipitation as an ecophysiological resource. Here we present evidence that Ponderosa pine uses NAMS moisture differentially across this gradient. C-13/C-12 ratios suggest that photosynthetic water use efficiency during latewood formation is more sensitive to summer precipitation at the northern than at the southern sites. This is likely due to the fact that NAMS moisture provides sufficiently favorable conditions for tree photosynthesis and growth during most years in the southern sites, whereas the northern sites experience larger summer moisture variability, which in some years is limiting growth. Cellulose O-18 and C-13 values revealed that photoassimilates in the southern sites were produced under higher vapor pressure deficit conditions during spring compared to summer, demonstrating a previously underappreciated effect of seasonal differences in atmospheric humidity on tree ring isotope ratios. Our findings suggest that future changes in NAMS will potentially alter productivity and photosynthetic water use dynamics differentially along latitudinal gradients in southwestern U.S. montane forests.

Measurements of the stable carbon isotope ratio (delta C-13) on annual tree rings offer new opportunities to evaluate mechanisms of variations in photosynthesis and stomatal conductance under changing CO2 and climate conditions, especially in conjunction with process-based biogeochemical model simulations. The isotopic discrimination is indicative of the ratio between the CO2 partial pressure in the intercellular cavities and the atmosphere (c(i)/c(a)) and of the ratio of assimilation to stomatal conductance, termed intrinsic water-use efficiency (iWUE). We performed isotope-enabled simulations over the industrial period with the land biosphere module (CLM4.5) of the Community Earth System Model and the Land Surface Processes and Exchanges (LPX-Bern) dynamic global vegetation model. Results for C3 tree species show good agreement with a global compilation of delta C-13 measurements on leaves, though modeled C-13 discrimination by C3 trees is smaller in arid regions than measured. A compilation of 76 tree-ring records, mainly from Europe, boreal Asia, and western North America, suggests on average small 20th century changes in isotopic discrimination and in c(i)/c(a) and an increase in iWUE of about 27% since 1900. LPX-Bern results match these century-scale reconstructions, supporting the idea that the physiology of stomata has evolved to optimize trade-offs between carbon gain by assimilation and water loss by transpiration. In contrast, CLM4.5 simulates an increase in discrimination and in turn a change in iWUE that is almost twice as large as that revealed by the tree-ring data. Factorial simulations show that these changes are mainly in response to rising atmospheric CO2. The results suggest that the downregulation of c(i)/c(a) and of photosynthesis by nitrogen limitation is possibly too strong in the standard setup of CLM4.5 or that there may be problems associated with the implementation of conductance, assimilation, and related adjustment processes on long-term environmental changes.

Assessment of forest water-use (WU) is undoubtedly important and necessary, especially in water scarcity areas that are already suffering the main negative impacts of climate change. However, instead of just determining how much water is used by a forest, it is also important to evaluate how forest-WU responds to forest management practices such as thinning, a widely recognized alternative to promote improvements in the hydrologic balance while maintaining or improving forest resilience. Thus, this thesis proposes three integrated studies performed in an area of Aleppo pine subject to experimental thinning in Eastern Spain. The first study was modelling an artificial neural network (ANN) to estimate daily WU independently of forest heterogeneity provided by thinning. Stand WU was accurately estimated using climate data, soil water content and forest cover (correlation coefficient, R: 0.95; Nash-Sutcliffe coefficient, E: 0.90 and rootmean-square error, RMSE: 0.078mm/day). Then the ANN modelled was used for gapfilling when needed and those results were used in the following studies. The secondly study addressed the question of how tree-growth, WU and water balance changed as a consequence of thinning. To this end, the influence of thinning intensity and its effect at short-term (thinned in 2008) and at mid-term (thinned in 1998) on the water-balance components and tree-growth were investigated. The high-intensity thinning treatment showed significant increases in mean annual tree-growth from 4.1 to 17.3 cm2 yr -1 , a rate which was maintained in the mid-term. Mean daily WU ranged from 5 (control) to 18 (high intensity thinning) l tree-1 . However, when expressed on stand basis, daily WU ranged from 0.18 (medium intensity thinning) to 0.30 mm (control plot), meaning that in spite of the higher WU rates in the remaining trees, stand WU was reduced with thinning. Large differences were found in the water balance components between thinning plots and control. These differences might have significant implications to maintain forest resilience, and improve forest management practices. The third study, brings forth two interesting points and their responses to thinning, WU and intrinsic water-use efficiency (WUEi). First, the relationships between growth and climate were studied at mid-term in order to identify if thinning can improve forest resilience. Second, the relationships between WU and WUEi was explored to identify how these factors were affected by thinning at short-term. A substantial limitation of tree-growth imposed by climatic conditions was observed, although thinning changed the tree-growth-precipitation relationships. Significant differences in WUEi were found after thinning at mid-term, however no significant difference was observed at short-term. Despite this, in general WUEi decreased when precipitation increased, with different slopes for each thinning intensity. Different patterns of the relationship between WU and WUEi were found, being positive for thinned plots and negative for control plot at short-term. Finally this thesis suggest that thinning in Aleppo pine plantations is effective in changing the relationships between WU and WUEi, furthermore, this thesis introduces a novel contribution by looking at the inter-related effects on growth, WU, WUEi and water balance in Mediterranean forest subject to thinning.<br>Gualberto Fernandes, TJ. (2014). Water-oriented management in forest plantations: combining hydrology, dendrochronology and ecophysiology [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/48476<br>TESIS

[Truncated abstract] Insufficient water use by annual crop and pasture species leading to costly rises in saline watertables has prompted research into potentially profitable deep-rooted perennial species in the Western Australian wheatbelt. Native mallee eucalypts are currently being developed as a short-rotation coppice crop for production of leaf oils, activated carbon and bio-electricity for low rainfall areas (300—450 mm) too dry for many of the traditional timber and forage species. The research in this study was aimed at developing a knowledge base necessary to grow and manage coppiced mallee eucalypts for both high productivity and salinity control. This firstly necessitated identification of suitable species, climatic and site requirements favourable to rapid growth, and understanding of factors likely to affect yield of the desirable leaf oil constituent, 1,8-cineole. This was undertaken using nine mallee taxa at twelve sites with two harvest regimes. E. kochii subsp. plenissima emerged as showing promise in the central and northern wheatbelt, particularly at a deep acid sand site (Gn 2.61; Northcote, 1979), so further studies focussed on physiology of its resprouting, water use and water-use efficiency at a similar site near Kalannie. Young E. kochii trees were well equipped with large numbers of meristematic foci and adequate root starch reserves to endure repeated shoot removal. The cutting season and interval between cuts were then demonstrated to have a strong influence on productivity, since first-year coppice growth was slow and root systems appeared to cease in secondary growth during the first 1.5—2.5 years after cutting. After decapitation, trees altered their physiology to promote rapid replacement of shoots. Compared to uncut trees, leaves of coppices were formed with a low carbon content per unit area, and showed high stomatal conductance accompanied by high leaf photosynthetic rates. Whole-plant water use efficiency of coppiced trees was unusually high due to their fast relative growth rates associated with preferential investments of photosynthates into regenerating canopies rather than roots. Despite relatively small leaf areas on coppice shoots over the two years following decapitation, high leaf transpiration rates resulted in coppices using water at rates far in excess of that falling as rain on the tree belt area. Water budgets showed that 20 % of the study paddock would have been needed as 0—2 year coppices in 5 m wide twin-row belts in order to maintain hydrological balance over the study period. Maximum water use occurred where uncut trees were accessing a fresh perched aquifer, but where this was not present water budgets still showed transpiration of uncut trees occurring at rates equivalent to 3—4 times rainfall incident on the tree belt canopy. In this scenario, only 10 % of the paddock surface would have been required under 5 m wide tree belts to restore hydrological balance, but competition losses in adjacent pasture would have been greater

[Truncated abstract. Please see the pdf format for the complete text. Also, formulae and special characters can only be approximated here. Please see the pdf version for an accurate reproduction.] This thesis examines the water use, ecophysiology and hydraulic architecture of Eucalyptus marginata (jarrah) growing on bauxite mine rehabilitation sites in the jarrah forest of south-western Australia. The principal objective was to characterise the key environment and plant-based influences on tree water use, and to better understand the dynamics of water use over a range of spatial and temporal scales in this drought-prone ecosystem. A novel sap flow measurement system (based on the use of the heat pulse method) was developed so that a large number of trees could be monitored concurrently in the field. A validation experiment using potted jarrah saplings showed that rates of sap flow (transpiration) obtained using this system agreed with those obtained gravimetrically. Notably, diurnal patterns of transpiration were measured accurately and with precision using the newly developed heat ratio method. Field studies showed that water stress and water use by jarrah saplings on rehabilitation sites were strongly seasonal: being greatest in summer when it was warm and dry, and least in winter when it was cool and wet. At different times, water use was influenced by soil water availability, vapour pressure deficit (VPD) and plant hydraulic conductance. In some areas, there was evidence of a rapid decline in transpiration in response to dry soil conditions. At the end of summer, most saplings on rehabilitation sites were not water stressed, whereas water status in the forest was poor for small saplings but improved with increasing size. It has been recognised that mature jarrah trees avoid drought by having deep root systems, however, it appears that saplings on rehabilitation sites may have not yet developed functional deep roots, and as such, they may be heavily reliant on moisture stored in surface soil horizons. Simple predictive models of tree water use revealed that stand water use was 74 % of annual rainfall at a high density (leaf area index, LAI = 3.1), high rainfall (1200 mm yr-1) site, and 12 % of rainfall at a low density (LAI = 0.4), low rainfall (600 mm yr-1) site, and that water use increased with stand growth. A controlled field experiment confirmed that: (1) sapling transpiration was restricted as root-zone water availability declined, irrespective of VPD; (2) transpiration was correlated with VPD when water was abundant; and (3) transpiration was limited by soil-to-leaf hydraulic conductance when water was abundant and VPD was high (> 2 kPa). Specifically, transpiration was regulated by stomatal conductance. Large stomatal apertures could sustain high transpiration rates, but stomata were sensitive to hydraulic perturbations caused by soil water deficits and/or high evaporative demand. No other physiological mechanisms conferred immediate resistance to drought. Empirical observations were agreeably linked with a current theory suggesting that stomata regulate transpiration and plant water potential in order to prevent hydraulic dysfunction following a reduction in soil-to-leaf hydraulic conductance. Moreover, it was clear that plant hydraulic capacity determined the pattern and extent of stomatal regulation. Differences in hydraulic capacity across a gradient in water availability were a reflection of differences in root-to-leaf hydraulic conductance, and were possibly related to differences in xylem structure. Saplings on rehabilitation sites had greater hydraulic conductance (by 50 %) and greater leaf-specific rates of transpiration at the high rainfall site (1.5 kg m-2 day1) than at the low rainfall site (0.8 kg m-2 day1) under near optimal conditions. Also, rehabilitation-grown saplings had significantly greater leaf area, leaf area to sapwood area ratios and hydraulic conductance (by 30-50 %) compared to forest-grown saplings, a strong indication that soils in rehabilitation sites contained more water than soils in the forest. Results suggested that: (1) the hydraulic structure and function of saplings growing under the same climatic conditions was determined by soil water availability; (2) drought reduced stomatal conductance and transpiration by reducing whole-tree hydraulic conductance; and (3) saplings growing on open rehabilitation sites utilised more abundant water, light and nutrients than saplings growing in the forest understorey. These findings support a paradigm that trees evolve hydraulic equipment and physiological characteristics suited to the most efficient use of water from a particular spatial and temporal niche in the soil environment.

Windbreaks have been promoted as a means of arresting degradation of agricultural lands in the Sahel resulting from deforestation, but competition for water between windbreak trees and adjacent crops must be minimised if windbreaks are to be successfully established in areas where crop production is threatened by loss of trees. Research was done, consequently, between 1991 and 1993 in southern Niger, in West Africa, to aid development of strategies for the deployment of windbreaks in the Sahel which minimise competition for water. The objectives of this research were to: (1) quantify water use by windbreak trees; (2) determine the source of water utilised by windbreaks; and (3) identify the environmental and physiological variables controlling transpiration by windbreak trees. The heat-pulse method was used to measure water use during the cropping season by three tree species growing in windbreaks and patterns of water extraction from soil adjacent to windbreaks of each species were assessed from soil moisture contents measured by neutron attenuation. <I>Azadirachta indica </I>transpired less water than either <I>Acacia holosericea </I>or <I>Acacia nilotica </I>and extracted less water from the rooting zone of nearby crops, and was thus shown to be the least competitive of these tree species. Naturally-occurring variations in the ratio of the stable isotopes of oxygen (<SUP>18</SUP>O/<SUP>16</SUP>O) in water were utilised to trace the sources of water transpired by <I>Azadirachta indica </I>trees in windbreaks and adjacent crops of pearl millet (<I>Pennisetum glaucum</I>) at two locations with contrasting water table levels. Where groundwater could be accessed by the trees, they obtained large proportions of their water from surface layers of the soil only when water there was plentiful, for example after rain. Where groundwater was not accessible, the trees fulfilled their requirements for water from the surface layers of the soil profile throughout the year. Thus, competition for water between windbreaks and crops is more severe at locations where trees cannot utilise groundwater.

Les plantations d’hévéa (Hevea brasiliensis) s’étendent vers des zones non traditionnelles de production en Thaïlande où des conditions plus sèches ont pu conduire à une diminution de la croissance des arbres et de la production de latex. Des paramètres physiologiques utiles pour sélectionner des génotypes adaptés sont nécessaires, comme l’efficience d’utilisation de l’eau (WUE). La discrimination isotopique du carbone est largement utilisée comme proxy pour WUE et peut être aisément utilisée dans des programmes de sélection pour la tolérance à la sécheresse. δ13C des feuilles et les échanges gazeux foliaires ont été mesurés sur de jeunes plants de dix clones d’hévéa cultivés en pot dans une pépinière. La gamme de δ13C des feuilles entre ces dix clones était restreinte et la corrélation entre δ13C et WUEi était significative que sous fort déficit de pression de vapeur saturante, ce qui signifie que la prédiction de WUE par δ13C serait peu précise. Il y avait une large gamme de δ13C entre les génotypes dans une collection de 49 génotypes sauvages d’hévéa cultivés dans le nord-est de la Thaïlande en saison sèche et en saison des pluies. δ13C était relativement stable avec une bonne corrélation entre les saisons. Cette étude montre que la variabilité génétique de δ13C est prometteuse pour des futurs programmes de sélections si une bonne corrélation entre δ13C et WUE peut être établie. L’absence de corrélation entre de δ13C du latex (δ13C-L) et des composés solubles extraits des feuilles (δ13C-S) prélevées sur des arbres saignés et non saignés âgés de 20 ans suggère que photosynthétats récemment produits se mélangent à un stock important d’hydrate de carbone impliqués dans la régénération du latex après la saignée. Donc, δ13C du latex n’est pas un indicateur pertinent de WUE<br>The rubber (Hevea brasiliensis) plantations extend to non-traditional area in Thailand where dryer conditions has been reported to impair the growth of rubber trees and latex production. Physiological parameters helpful for breeding adapted genotypes are required, such as water use efficiency (WUE). Carbon isotope discrimination is widely used as a proxy for WUE that can easily be used for selection and breeding programs for drought tolerance. Leaf δ13C and leaf gas exchange were measured on young saplings of 10 rubber clones growing in pot in a common garden. The range of leaf δ13C among 10 clones was narrow and the correlation between δ13C and WUEi was significant under high vapour pressure deficit only, which means the prediction of WUE by δ13C would have low precision. There were large δ13C variations among the genotypes at all seasons in a collection of 49 wild genotypes of rubber in Northeastern Thailand. δ13C was rather stable with a good correlation between rainy and dry season. The genetic variability of δ13C is promising for breeding if a good correlation between δ13C of leaf and WUE can be established. The lack of correlation between δ13C of latex (δ13C-L) and of leaf soluble compounds (δ13C-S) collected from tapped and untapped 20 year-old rubber trees suggests that recent photosynthates are mixed in the large pool of stored carbohydrates that are involved in latex regeneration after tapping. Thus δ13C of latex is not a relevant indicator of WUE of rubber trees

During my three academic years, I focused on the effects of N fertilization on growth and function of plants and forest stands. The study had the dual objective of estimating the effects of atmospheric N deposition and evaluating the potential management value of N fertilization itself. In particular, the analysis took into account the changes induced in water use and intrinsic transpiration efficiency (ITE), an aspect often overlooked in world literature but of great importance especially in Mediterranean environment, where the positive effects of N fertilization may be denied by the parallel increased transpiration and exacerbated water stress.

Water conservation and pollution concerns from nutrient runoff will very likely dictate precise irrigation regimes for nursery managers in Virginia. Maximum plant growth with minimum input of water and fertilizer is becoming increasingly important. Therefore, water use and growth of red and sugar maple (Acer rubrum L. 'Franksred' and Acer saccharum Marsh.) were studied during two years of pot-in-pot (P+P) production and during three years after transplanting to field soil. Three major experiments were completed. The first experiment studied the effect of frequent irrigation (three-times-a-day) versus standard once-a-day irrigation and found that frequent irrigation increased trunk diameter growth of sugar maples in the second production cycle and for red maples in both production cycles. Height growth of neither species was affected by frequent irrigation. A study of sap flow pattern indicated that late day water stress of red maples was partially alleviated by frequent irrigation. In the second experiment, red and sugar maples were transplanted to field soil after one (1-yr) or two (2-yr) years of P+P production. Irrigation frequency requirement decreased as the trees grew and depended on environmental conditions, size at planting, source of water (rainfall versus irrigation) and species. Height and trunk diameter of 1-yr red maple was equal to that of 2-yr trees after only one year. Height and trunk diameter differences between 1-yr and 2-yr sugar maple trees persisted three years after transplanting. In the third experiment water use of 1-yr and 2-yr red and sugar maple while in P+P production was investigated. Four models of daily water-use were developed. A simple model that is suitable for growers includes species, trunk cross-sectional area (BA) and air temperature (TA) observations. An environmental model was developed using the Penman-van Bavel estimate of evapotranspiration (ET). ET required modifications based on tree characteristics, air temperature, windspeed and relative humidity to be an effective predictor of water-use. A complex model was based on a sine-cosine function of day-of-the-year. This model fits water-use data well for each species and production cycle and includes BA, ET and TA. An alternate simpler model requires only day-of-the-year, TA and BA, offering growers a relatively simple and accurate model of water use.<br>Ph. D.

A urbanização acelerada e mal planejada pode ocasionar diversas alterações e consequências para o ambiente, como a sistemática impermeabilização do solo, que pode ocasionar aumento do escoamento superficial da água e redução do tempo de escoamento, gerando problemas como enchentes, alagamentos, aumento do risco de desastres naturais, entre outros. A criação de mais áreas verdes pode ser considerada uma alternativa adequada para reduzir esses fenômenos, frente à rápida e crescente expansão urbana. Como os benefícios hidrológicos das árvores em ambiente urbano ainda são pouco explorados por pesquisadores, sobretudo no Brasil, existe a necessidade de se determinar o quanto a cobertura arbórea é capaz de influenciar na redução das consequências de eventos extremos para os ambientes urbanos. O i-Tree Hydro é um programa pioneiro em relacionar explicitamente os efeitos das árvores nas águas pluviais em área urbana, fornecendo diretrizes para o planejamento do espaço em áreas sensíveis à fenômenos ambientais. Portanto, este trabalho pretende aplicou o programa em uma bacia hidrográfica da cidade de São Paulo, com o objetivo de melhor compreender como a disposição das árvores podem influenciar em uma área densamente urbanizada. Foi possível concluir utilizando o programa i-Tree Hydro que se aumentamos a cobertura arbórea e diminuímos a impermeabilização da bacia a uma queda de 12% na vazão média anual. Enquanto, fazendo o processo oposto e aumentando a impermeabilização e diminuindo a cobertura arbórea o volume médio anual da bacia aumenta cerca de 6%. Também foi possível concluir neste trabalho que apenas aumentando a cobertura arbórea da bacia de estudo sem alterar a impermeabilização é possível uma redução de 4% na vazão média anual da bacia e que a remoção de toda cobertura arbórea da mesma provoca um aumento de cerca de 21% , aumentando a média anual em aproximadamente 700 m³.<br>Accelerated and poorly planned urbanization can cause a number of changes and consequences for the environment, such as systematic soil sealing, which can lead to increased water runoff and reduced run-off time, generating problems such as flooding, flooding, natural disasters, among others. The creation of more green areas can be considered an adequate alternative to reduce these phenomena, in front of the rapid and increasing urban expansion. As the hydrological benefits of trees in urban environments are still little explored by researchers, especially in Brazil, there is a need to determine how much tree cover is capable of influencing the reduction of the consequences of extreme events for urban environments. The i-Tree Hydro is a pioneering program to explicitly relate the effects of trees to rainwater in urban areas, providing guidelines for space planning in areas sensitive to environmental phenomena. Therefore, this work intends to apply the program in a river basin of the city of São Paulo, in order to better understand how the use of permeable pavements and the quantity and arrangement of trees can influence in a densely urbanized area. It was possible to conclude by using the i-Tree Hydro program that we increased the tree cover and decreased the waterproofing of the basin to a fall of 12% in the average annual flow. Meanwhile, by doing the opposite process and increasing waterproofing and decreasing tree cover the average annual volume of the basin increases by about 6%. It was also possible to conclude in this work that only increasing the tree cover of the study basin without altering the waterproofing is possible a reduction of 4% in the average annual flow of the basin and that the removal of all the tree cover of the same causes an increase of about 21 %, increasing the annual average by approximately 700 m³.

Airborne lidar (light detecting and ranging) is a useful tool for probing the structure of forest canopies. Such information is not readily available from other remote sensing methods and is essential for modern forest inventories. In this study, small-footprint lidar data were used to estimate biophysical properties of young, mature, and old cottonwood trees in the Upper San Pedro River Basin, Arizona, USA. The lidar data were acquired in June 2003 and 2004, using Optech's 1233 ALTM (Optech Incorporated, Toronto, Canada). Canopy height, crown diameter, stem diameter at breast height (dbh), canopy cover, and mean intensity of return laser pulses from the canopy surface are estimated for the cottonwood trees from lidar data. The lidar estimates show a good degree of correlation with ground-based measurements. This study also demonstrates that other parameters of young, mature, and old cottonwood trees such as height and canopy cover, when derived from lidar, are significantly different (p &lt; 0.05). These lidar-derived canopy metrics provided the basis for a supervised image classification of cottonwood age categories, using a maximum likelihood algorithm. The results of classification illustrate the potential of airborne lidar data to differentiate age classes of cottonwood trees for riparian areas quickly and quantitatively.In addition, four metrics (tree height, height of median energy, ground return ratio, and canopy return ratio) were derived by synthetically constructing a large footprint lidar waveform from small-footprint lidar data (we summed up a series of Gaussian pulses that vertically stacked at the elevations produced by the small-footprint elevation data to create a modeled large-footprint return waveform and compared the synthetic waveforms with ground-based Intelligent Laser Ranging and Imaging System (ILRIS) scanner images in cottonwood trees). These four metrics were incorporated into a stepwise regression procedure to predict field-derived LAI for different age classes of cottonwoods.Additionally, this study applied the Penman-Monteith model to estimate transpiration of the cottonwood clusters using lidar-derived canopy metrics, such as height and LAI, and compared it with transpiration measured by sap flow, so that improved riparian water use estimates could be made.

Avui dia a Espanya i en moltes regions del món s'enfronten al problema d'escassetat d'aigua i la disminució de les seves ofertes. D'altra banda, les projeccions dels models climàtics preveuen que l'escassetat d'aigua es convertirà en un dels problemes més importants en moltes zones del món. Aquest seriòs problema fa que sigui urgent millorar l’eficiència en l’ús d’aigua. Considerant aquest aspecte, l'objectiu general d'aquesta tesis ha estat millorar l'eficiència del reg mitjançant la utilització de nous protocols de reg en dos espècies d’arbres, cirerers (Prunus avium) i de platan d’ombra (Platanus x hispanica) per a produir fusta. Mitjançant l'aplicació de diferents estratègies de reg deficitari basades en mesures de la màxima contracció diària del diámetre del tronc (MCD) combinat amb la mesura de l'estat de l'aigua al sòl. Els assajos van ser realitzats els anys 2009 i 2010, en un hivernacle (primer capítol) i en camp obert (segon i tercer capítol) a les instal•lacions de l'IRTA a Torre Marimon. Els objectius del primer capítol van ser avaluar si la MCD és un bon indicador de l’estat hídric del cirerer a partir de les relacions amb altres indicadors fisiològics i ambientals; així mateix, es va obtenir un valor llindar d'aquesta variable per a utilitzar-lo en la programació de reg. Com s'esperava els arbres ben regats i els arbres estressats van presentar diferències significatives en les variables fisiològiques: conductància estomàtica foliar (gs), potencial hídric foliar de migdia (md) i el flux de saba diari (Qd); el potencial matricial del substrat (s) va disminuir a valors de - 33 kPa i el corresponent valor de MCD va ser aproximadament de 0.30 mm. Aquests valors són considerats llindars potencials per a planificar el reg cirerers joves. Aquests valors corresponen a un md de -2.3 MPa i una gs de 50 mmol m-2 s-1, els quals indiquen estrès sever. En la part B del primer capítol, l'objectiu era explorar si la sequera afecta el patró diàri i horari dels dos indicadors de l’estat hídric mesurats en continu com son la variació del diàmetre del tronc i el flux de saba. Els arbres estresats mostren un increment significatiu de la MCD i un decrement del flux de saba respecte als arbres ben regats. La MCD és més sensible que el SF diàri front l'estrès per sequera, principalment a causa de la variabilitat més gran del SF entre arbres. En els cicles diàris, la variació del diàmetre del tronc i el flux de saba estan relacionats per un bucle que es comporta diferent quan estàn ben regats o estan estressats. La variació del pendent de la relació entre les dues varibles entre les 8 i les 16 hores en situacions de sequera pot ser un indicador d’estrés. Els objectius del segon capítol van ser intentar millorar la gestió de reg en arbres, cirerer i plàtan d’ombra, mitjançant la implantació de nous protocols de reg deficitari regulat (RDImds) basat en el valor absolut de la MCD i el potencial matricial del sòl (s), també es va combinar amb l’us d’aigua regenerada en cirerers . Els resultats indiquen que no va haver cap efecte negatiu associat amb l’aplicació del tractament RDI en el creixement en diàmetre, alçada i cobertura verda relativa, ni en la conductància estomàtica en ambdues especies. La qualitat d’aigua de reg tampoc va afectar al creixement dels cirerers El tractament RDImds ha estalviat aigua sense cap efecte negatiu sobre el creixement de l'arbre, amb el mateix comportament quan s’ha regat amb aigua regenerada o aigua de pou. El protocol aplicat en 2009 podria ser recomanat per a cirerers joves, i el protocol aplicat en 2010 podria ser recomanat per als plàtans. En el tercer capítol, l'objectiu va ser evaluar un protocol de programació de reg basat en el s i la señal de laMCD (MCDRDI/MCD100%Etc) en cirerer i en plàtan d’ombra. Els resultats van indicar que tractaments de RDI basats en la señal de MCD no van tenir efecte negatiu en els indicadors de creixement dels arbres, ni en la MCD ni en la gs. El tractament RDIsenyal va estalviar el 20-30% de l'aigua en les dues espècies. Així com en el tractament RDImds, el protocol aplicat en 2009 es podria recomanar per als cirerers joves i el protocol utilitzat en 2010 es podria recomanar per a plàtans d’ombra. Aquest darrer tractament té la desventatja que es necessita un control, però a la vegada evita els problemes de la influència de les condicions ambientals en la MCD del tractament RDImds.<br>Hoy en día en España y en muchas regiones del mundo se enfrentan al problema de la escasez de agua y la disminución de sus suministros. Por otra parte, las proyecciones de los modelos climáticos preveen que la escasez de agua se convertirá en uno de los problemas más importantes en muchas zonas del mundo. La gravedad de problema hace que sea necesario mejorar la eficiencia del uso del agua. Considerando lo anterior, el objetivo general de esta tesis es mejorar la eficiencia del riego mediante la utilización de nuevos protocolos de gestión de riego en dos especies de árboles: cerezos (Prunus avium) y plátano de sombra (Platanus x hispanica) para producir madera. Mediante la aplicación de diferente estrategias de riego deficitario basadas en las medidas de la máxima contracción diaria del tronco (MCD) combinado con la medida del estado hídrico del suelo. Los ensayos se realizaron los años 2009 y 2010, en un invernadero (primer capítulo) y en campo (segundo y tercer capítulo) en las instalaciones del IRTA en Torre Marimon. Los objetivos del primer capítulo fueron evaluar si la MCD es un buen indicador del estado hídrico del cerezo a partir de las relaciones con otros indicadores fisiológicos y ambientales; asimismo, se obtuvo un valor umbral de esta variable para utilizarlo en la programación del riego Como se esperaba, los árboles bien regados y los estresados presentaron diferencias significativas en todas las variables fisiológicas: conductancia estomática (gs), potencial hídrico de la hoja al mediodía ( md) y flujo de savia diario (Qd); el potencial matricial del substrato ( s) disminuyó hasta -33, y el correspondiente valor de MCD fue aproximadamente 0.30 mm. Estos valores se consideran umbrales potenciales para la programación del riego de árboles jóvenes de cerezos. Estos valores se corresponden a un -2 -1 md de -2.3 MPa y una gs de 50mmol m s , los cuales indican estrés hídrico severo. En la parte B del primer capítulo B, el objetivo fue explorar si la sequía afecta al patrón diario y horario de dos indicadores continuos del estado hídrico como son la variación del diámetro del tronco y el flujo de savia. Los árboles estresados mostraron un incremento significativo de la MCD y un decremento del SF diario respecto a los bien regados. La MCD es más sensible a la sequía que el SF diario, debido principalmente a la mayor variabilidad entre árboles del segundo. En los ciclos diarios, la variación del diámetro del tronco y el flujo de savia horario están relacionados por un bucle que se comporta diferente cuando está regado o estresado. La variación de la pendiente de la relación entre las dos variables entre las 8 y las 16 horas en situaciones de sequía puede ser un indicador de estrés. Los objetivos del segundo capítulo fueron intentar mejorar la gestión del riego en árboles, cerezo y plátano de sombra mediante la implantación de nuevos protocolos de riego deficitario regulado basados en el valor absoluto de MCD (RDImds) y el potencial matricial de suelo ( s), también se combinó con el uso de agua regenerada en cerezos. Los resultados indicaron que no hubo ningún efecto negativo relacionado con los tratamientos de RDI en el crecimiento en diámetro y altura del tronco ni en la cobertura verde, ni en la conductancia estomática en ambas especies. El tratamiento RDImds ha ahorrado agua sin ningún efecto en el crecimiento de los árboles, con el mismo comportamiento cuando se ha regado con agua regenerada o agua de pozo. El protocolo aplicado en 2009 podría ser recomendado para cerezos jóvenes, y el protocolo aplicado en 2010 podría recomendarse para plátanos. En el tercer capítulo, el objetivo fue evaluar un protocolo de riego basado en el s y la señal de la MCD (MCDRDI/MCD100%Etc). Los resultados indicaron que tratamientos de RDIseñal no tuvieron ningún efecto negativo sobre los indicadores de crecimiento de los árboles ni en la MCD ni en la gs. El tratamiento RDIseñal ahorró un 20 - 30% de agua en las dos especies. Així com en el tractament RDImds, el protocolo aplicado en 2009 se podría recomendar para cerezos jóvenes y el protocolo utilizado en 2010 se podría recomendar para plátanos. Este último tratamiento tiene la desventaja que necesita un control, pero a su vez evita los problemas de la influencia de las condiciones ambientales en la MCD del tratamiento RDImds.<br>Nowadays in Spain and many regions in the world face the problem of water scarcity and decreasing of its supplies. Moreover, climatic model projected that water scarcity will become one of the most important problems in many areas of the world. This serious problem supposes an urgent need to improve water use efficiency. Considering this problems, the general objective of this work was to improve irrigation efficiency by using new irrigation management protocol in two different species cherry trees (Prunus avium) and plane trees (Platanus x hispanica) for timber production. By applying different deficit irrigation strategies, based on the dendrometry measurements and other plant based water status indicators combined by soil water status measurements. The essays were conducted in 2009 and 2010; the first parts were conducted in one greenhouse and the second and third parts in the open field at IRTA Torre Marimon facilities. The objectives of the first chapter were to evaluate if MDS is a reliable indicator of cherry plants water status through its relationship with physiological and environmental variables; moreover, to study from these relationships the possibility of derivation a threshold value of MDS that indicated maximum water stress level in order to use it for irrigation scheduling. As expected well irrigated and stressed trees presented significant differences in all physiological variables: stomatal conductance (gs), midday leaf water potential ( md) and daily sap flow (Qd); substrate water potential ( s) decreased till -33kPa and the corresponding MDS value about 0.30 mm. Those values could be considered potential threshold for irrigation scheduling of young cherry trees. Those values corresponded to md of -2.3 MPa and gs of 50 mmol m-2 s-1, indicative of severe water stress. In part B of this chapter, the objective was to explore if drought affected the daily and hourly pattern of two continuous indicators of water status, trunk diameter variation and sap flow. Stressed trees showed a significant MDS increase and SF decrease respect to irrigated trees. MDS was more sensitive than SF in front of drought stress, mainly due to the higher variability of SF from tree to tree. In the daily cycle values, trunk diameter variation and sap flow were related to each other via a loop that differs according to tree water status. The change in the slope of the relationship between the two varibles between 8 and 16 hours in drought conditions can be an indicator of stress. The aims of the second chapter were to improve managing irrigation in woody trees, cherry and plane tree, by applying a regulate deficit irrigation protocols based on the absolute value of MDS (RDImds) and soil water potential ( s), combined by reclaimed water in cherry trees. Results indicated no negative effect related with RDI treatments was noticed on cherry or plane trees growth as no any significant differences was noticed in trunk diameter growth rate (TGR), height and relative green cover (RGC)neither in stomatal conductance in both species. Water quality neither affected the grothw of cherry trees. The RDImds treatment combined with s saved water without any negative effect on tree growth, with the same behavior when irrigated with reclaimed water or well water. The protocol applied in 2009 would be recommended for young cherry trees, and the protocol applied in 2010 would be recommended for plane trees. In the third chapter, the objective was to evaluate an irrigation scheduling protocol based on the information obtained from soil status s and MDS signal (MDSRDI/MDS100%Etc) as precision tools for automated adjustment of deficit irrigation in cherry and plane tree. Results indicated that RDIsignal and s protocols had no negative effect on tree growth indicators TGR and RGC; also no clear differences were noticed between well irrigated and RDIsignal trees in MDS and gs. Our irrigation scheduling protocol based on MDSsignal and s can be considered a valid protocol for schedule irrigation in woody trees as it helped us to save about 20- 30% of water in both species without any negative effect on the trees growth. As well as in the treatment RDImds, the protocol applied in 2009 could recommend for young cherry and protocol used in 2010 could recommend bananas for shade. The latter treatment has disadvantage it takes control, yet avoid the problems of the influence of environmental conditions on MCD treatment RDImds.

Magister Scientiae - MSc (Earth Science)<br>The increasing expansion of Acacia longifolia trees along the riparian zones in South Africa demands an urgent intervention as the species is listed in the National Environmental Management: Biodiversity Act (2004). This list includes species that are prohibited from growing, or being imported into South Africa. The detrimental effects of alien vegetation have been observed on the hydrology of the ecosystems invaded. However, the actual water use by Acacia longifolia has never been quantified. Therefore, there is inadequate knowledge of the actual rates and the differences in water use rates by A. longifolia occurring in the riparian zones and hillslopes. This study addresses this gap in knowledge by quantifying the diurnal and seasonal transpiration dynamics of hillslope and riparian A. longifolia. The variations of climate and soil water content on the hillslope and riparian zones were also examined in this study. The study was conducted on the Spanjaardskloof hills and along the Nuwejaars River (Moddervlei) in the Heuningnes Catchment, Cape Agulhas.

L'olivier est un agrosystème pérenne clé pour l'économie du pourtour méditerranéen avec des pratiques culturales contrastées (sec épars/irrigué intensive, co-planté...). Connu pour ses mécanismes d'adaptations au stress hydrique et sa capacité de survivre durant de longues périodes à conditions limitantes en eau de sol, l'oléiculture pluviale est dominante dans cette zone, notamment en Tunisie et l'écartement entre les arbres est une fonction de la distribution de la pluviométrie (un nombre important de pieds à l'hectare au Nord (6 m) et des oliveraies très éparses au Sud (25 m)) assurant un volume de sol exploré par les racines supposé être suffisant pour satisfaire les besoins en eau des oliviers. Il est cependant soumis à une forte pression climatique du fait des sécheresses récurrentes dont la fréquence et l'intensité risquent de s'accentuer dans les décennies qui viennent. La réponse de ces couverts épars, où l'eau est un facteur limitant, à ces changements climatiques est méconnue. Dans ce contexte, ce travail vise à améliorer notre connaissance des processus physiques régissant le cycle hydrologique et le développement de la végétation dans une oliveraie pluviale au centre de la Tunisie. L'objectif de cette thèse est double : i/tester la vulnérabilité de ces oliveraies éparses face aux conditions extrêmes futures et ii/proposer des solutions aux agriculteurs à court (par exemple l'irrigation localisée de complément) et à long termes (notamment la diminution des écartements entre les arbres ou l'extension des périmètres irrigués). Pour répondre à ces objectifs, nous avons besoin de bien caractériser le fonctionnement thermo-hydrique des oliviers, d'identifier la possibilité de suivre leur état hydrique actuel et de prédire leurs réponses à des conditions hydriques futures plus sévères. Dans un premier temps, un protocole expérimental dédié qui comprend des mesures par la méthode de fluctuations turbulentes et la méthode de flux de sève a été mis en place. Les données collectées qui renseignent sur les échanges d'énergie et de matière au sein du continuum sol-plante-atmosphère, ont été analysées et leur cohérence a été vérifiée à travers une étude des différentes composantes des bilans hydrique et énergétique à différentes échelles spatiales et temporelles. En plus de mesures directes, des mesures de proxidétection ont été sélectionnées afin d'analyser l'apport de cet outil puissant. Des relations entre les indices de stress hydrique estimés (par exemple l'écart entre la transpiration réelle et potentielle) et les indicateurs de proxidétection (la température de surface et le photochemical reflectance index) ont été donc établies pour détecter les seuils critiques au-delà des quels un apport en eau devient indispensable pour la survie de la plante. Dans un second temps, un modèle d'échanges sol-plante-atmosphère ISBA a été calé et validé en s'appuyant sur l'important jeu de données observé pour reproduire le fonctionnement des oliviers. Cette étude souligne que le caractère épars des oliviers est néanmoins un défi pour l'application de ces outils car la fraction de couverture de végétation (moins de 7 % pour notre site de Nasrallah) est telle que la surface est dominée par le fonctionnement du sol nu. Des ajustements ont été donc proposés voire apportés aux méthodes utilisées pour les adapter à ce faible taux de couvert végétal. La base de données utilisée pour cette étude est publiée sous le DOI : 10.6096/MISTRALS-SICMED.1479<br>The olive tree is a key perennial agrosystem for the economy of the Mediterranean basin with contrasting farming practices (rainfed sparse/intensive irrigated, co-planted ...). Known for its mechanisms of adaptation to water stress and its ability to survive for long periods under soil water limiting conditions, rainfed olive cultivation is dominant in this area, especially in Tunisia and the spacing between trees is a function of the distribution of the precipitation (from high density of plantation in the North (6 m) to very sparse in the South (25 m)) ensuring a volume of soil explored by the roots that is assumed to be enough to satisfy the water needs of the olive trees. However, it is subject to severe climatic pressure due to widespread dry spells, for which the frequency and intensity is likely to increase in the coming decades. The response of these sparse covers, where water is a limiting factor, to these climatic changes is unrecognized. In this context, this work aims to improve the current understanding of the physical processes governing the hydrological cycle and the development of vegetation in rainfed groves in central Tunisia. There is a twofold purpose: I / to test the vulnerability of these sparse olive groves to future conditions and ii / to make a decision support to farmers for the short (i.e., localized supplementary irrigation) and in the long term (in particular a decrease of the spacing between trees or the extension of irrigated area). To meet these goals, it is necessary to characterize the thermo-hydric functioning of olive trees, to identify the possibility of monitoring their current water status and to predict their responses to more severe future water conditions. As a first step, a dedicated experimental set up that includes eddy covariance and sap flow measurements has been installed. The collected data, which provide information on the exchange of energy and matter within the soil-plant-atmosphere continuum, were analyzed and their consistency was verified through a study of the different components of the water and energy balances at different spatial and time scales. In addition to direct measurements, proxidetection measurements are available and allow investigating the benefit of this powerful tool. Relationships between the estimated water stress indices (e.g., the difference between actual and potential transpiration) and the proxidetection indicators (surface temperature and photochemical reflectance index) were therefore established to detect critical thresholds beyond which a water supply becomes essential for the survival of the plant. In a second step, a soil-plant-atmosphere ISBA exchange model was calibrated and validated based on the large data set observed to reproduce the functioning of olive trees. This study emphasizes that the sparse nature of olive trees is nevertheless a challenge for the application of these tools because the fraction of vegetation cover (less than 7% for our Nasrallah site) is such that the surface is dominated by the bare soil functioning. Adjustments have therefore been proposed or even applied to these methods to adapt them to this low fraction vegetation cover. The database used in this study is published under the DOI: 10.6096/MISTRALS-SICMED.1479

Made available in DSpace on 2014-07-29T15:01:47Z (GMT). No. of bitstreams: 1 DissertacaoAbneFigueiredoNeto.pdf: 3315403 bytes, checksum: fa71315e1c2d245dfe9bb258f5291ad0 (MD5) Previous issue date: 2011-09-02<br>Disposal of sludge from Water Treatment Plants (WTP) in the environment is very harmful and can cause deterioration of water supplies. Existing methods for treatment of waste produced in ETA are few applied because the costs involved with operation and maintenance. Several alternatives are suggested for the disposal of these wastes, including the application of sludge in agricultural soils can generate several benefits. In this work we evaluated the development of crops with different dosages of WTS (0%, 18.75%, 37.50%, 56.25%, 75%). The sludge used in the study was collected in the ETA Eng. Rodolfo José da Costa, located in Goiânia/GO, which is used in aluminum sulphate (Al2 (SO4) 3) as a primary coagulant. For the study we used five treatments (T1: 25% substrate, 75% land, 0% sludge, T2: 25% substrate, land 56.25%, 18.75% sludge, T3: 25% substrate, 37.50 % land, 37.50% sludge, T4: 25% substrate, land 18.75%, 56.25% sludge, T5: 25% substrate, 0% land, 75% sludget) for four species of native plants occurring in cerrado (Padu-de-óleo; Gonçalo-alves; Canafístula and Ipe-brando). We adopted the completely randomized design (CRD) with four repetitions, totaling 400 plants. The data collections were performed at 30, 60, 90, 120 and 150 days after planting. Parameters such as the collar diameter, height, weight and chlorophyll were evaluated. Some relationships were used to determine the level of quality seedlings, as the ratio of shoot height and diameter of the collar, the relationship between height and dry weight of shoots and the ratio of dry weight of shoots and dry weight of roots. The largest number of dead individuals was found for Ipê-branco (Tabebuia roseo-alba), regardless of the treatment he underwent. The morphological parameters showed little variation among treatments. Compared to quality, some species showed the best 4 and subjected to treatment with 56.25% of sludge. In the treatments with higher amounts of sludge, the levels of nitrogen (N), potassium (K), calcium (Ca) and magnesium (Mg) in leaves were reduced. It was found that the allocation of the WTS nursery can be an alternative available and also an economic advantage to commercial nurseries. It is expected not only to encourage the commercial use of residue in crops that require specific concentrations of metals such as aluminum, abundant in the mud, the greater concern is the environmental and ecological nature, as tons of waste are discarded altogether, causing pollution and occupation of space unnecessarily.<br>O descarte do lodo das Estações de Tratamento Água (ETA) no meio ambiente é bastante nocivo, podendo provocar a deterioração dos mananciais. Os métodos existentes para tratamento dos resíduos produzidos em ETA são poucos aplicados em virtude dos custos envolvidos com operação e manutenção. Várias alternativas são sugeridas para a disposição destes resíduos, entre elas a aplicação do lodo em solos agrícolas pode gerar diversos benefícios. Neste trabalho foi avaliado o desenvolvimento de plantas cultivadas com diferentes doses de lodo de ETA (0%; 18,75%; 37,50%; 56,25%; 75%). O lodo utilizado no estudo foi coletado na ETA Eng. Rodolfo José da Costa, localizada em Goiânia/GO, na qual é utilizado o sulfato de alumínio (Al2(SO4)3) como coagulante primário. Para o estudo utilizaram-se 5 tratamentos (T1: 25% substrato, 75% terra, 0% lodo; T2: 25% substrato, 56,25% terra, 18,75% lodo; T3: 25% substrato, 37,50% terra, 37,50% lodo; T4: 25% substrato, 18,75% terra, 56,25% lodo; T5: 25% substrato, 0% terra, 75% lodo) para 4 espécies de plantas nativas com ocorrência no cerrado (Pau-de-óleo; Gonçalo-alves; Canafístula e Ipê-branco). Adotou-se o delineamento experimental inteiramente casualizado (DIC), com 4 repetições, num total de 400 plantas. As coletas de dados foram realizadas aos 30, 60, 90, 120 e 150 dias após o plantio. Parâmetros como o diâmetro do coleto, altura, peso e clorofila foram avaliados. Algumas relações foram utilizadas para a determinação do índice de qualidade das mudas, como a relação altura da parte aérea e o diâmetro do coleto, a relação da altura e o peso de matéria seca da parte aérea e a relação entre o peso de matéria seca da parte aérea e o peso de matéria seca das raízes. O maior número de indivíduos mortos foi encontrado para o Ipê-branco (Tabebuia roseo-alba), independente do tratamento a que foi submetido. Os parâmetros morfológicos apresentaram poucas variações significativas entre os tratamentos. Em relação aos índices de qualidade, algumas espécies apresentaram os melhores valores quanto submetidas ao tratamento 4, com 56,25% de lodo. Nos tratamentos com maior quantidade de lodo, os teores de nitrogênio (N), potássio (K), cálcio (Ca) e magnésio (Mg) nas folhas foram reduzidas. Verificou-se que a destinação de lodo de ETA para viveiros pode ser uma alternativa de disposição e ainda uma vantagem econômica para os viveiros comerciais. Espera-se não somente incentivar o uso comercial do resíduo em plantios que requeiram concentrações específicas de metais, tais como o alumínio, abundante no lodo; o maior interesse é de cunho ambiental e ecológico, visto que toneladas desse resíduo são completamente descartadas, gerando poluição e ocupação de espaços desnecessariamente.

Wasserverfügbarkeit ist in Wäldern Mitteleuropas wie auch in anderen Regionen der Welt oftmals ein limitierender Faktor für die Produktivität eines Bestandes. Ebenso wurde bereits in zahlreichen Studien untersucht, inwiefern Biodiversität einen Einfluss auf die Produktivität von Pflanzengemeinschaften hat. Es gibt jedoch nur wenig Informationen darüber, wie sich Baumartenvielfalt auf die Wassernutzung eines Waldbestandes auswirkt. Die Wassermenge, die für Transpiration und Zuwachs unter gegebenen Umweltbedingungen zur Verfügung steht ist davon abhängig, wie gut Pflanzen den vorliegenden Wasservorrat nutzen können. Es wird angenommen, dass Wasserverfügbarkeit für den Bestand durch komplementäre Wasseraufnahme zwischen gemeinsam auftretenden Pflanzenarten steigt. Daher zählt eine komplementäre Nutzung von Resourcen in ökologischen Studien allgemein zu den wichtigen funktionellen Effekten von Artenvielfalt. Jedoch setzt Komplementarität vorraus, dass funktionale Eigenschaften bestimmter Arten es diesen ermöglichen, entweder für andere Arten nicht verfügbare Resourcen zu nutzen, oder aber die selbe Resource räumlich und/ oder zeitlich getrennt voneinander zu nutzen. In gemischten Pflanzengemeinschaften ist oftmals eine erhöhte Produktivität im Vergleich zu Monokulturen zu beobachten, welche häufig durch Aufteilung von Resourcen und eine damit verbundene effektivere Nutzung erklärt wird. Im mitteleuropäischen Raum hat die Einrichtung von gemischten Laubwäldern in den letzten Jahrzehnten deutlich zugenommen. Gleiches gilt für die Umwandlung von Monokulturen (z. B. Fichte) in Bestände mit höherer Artenvielfalt, insbesondere von Arten die an die jeweiligen Standortbedingungen angepasst sind. Dieses Konzept der „naturnahen“ Forstwirtschaft zielt auf eine nachhaltige Produktion, erhöhte Stabilität angesichts möglicher extremer klimatischer Verhältnisse und eine Verbesserung der Erholungsfunktion von Wäldern ab. Infolgedessen ist es jedoch möglich, das Bestände mit erhöhter Baumartenzahl ebenso einen vergleichsweise höheren Verbrauch an Wasser aufweisen, was wiederum in erhöhtem Stress bei Trockenperioden resultieren könnte. Ein derartiger Effekt wäre demnach gegensätzlich zu den Zielen einer naturnahen Forstwirtschaft. Das Ziel dieser Studie war, die Auswirkung von Baumartenvielfalt (-mischung) auf die Wassernutzung eines temperaten Laubmischbestandes zu untersuchen und einen Beitrag zum besseren Verständnis dieser Zusammenhänge zu leisten. Hierfür wurden Untersuchungen innerhalb kleiner Baumgruppen durchgeführt, so genannter „Cluster“, die aus drei Bäumen der Kronenschicht bestanden, welche der potenziellen natürlichen Vegetation im Waldgebiet Hainich angehören (Fagus sylvatica, Tilia sp., Fraxinus excelsior, Acer pseudoplatanus, and Carpinus betulus). Die Cluster (n = 100) beinhalteten alle theoretisch denkbaren Kombinationen der 5 Untersuchungsarten in Ein- Zwei- und Dreiart Baumgruppen (25 Artkombinationen auf drei Diversitätsstufen), wobei jede Kombination in vier Wiederholungen vorlag (20 Einart-, 40 Zweiart- und 40 Dreiart-Cluster). In der ersten Studie wurde getestet, ob stabile Isotope von Wasser (2H und 18O) unter den gegebenen Bodenbeschaffenheiten im Hainich genutzt werden können, um die Wasseraufnahmetiefe von Bäumen zu identifizieren. Stabile Isotope von Wasser werden mittlerweile immer häufiger eingesetzt, um die Tiefe der Wasseraufnahme von Pflanzen festzustellen. Dabei wird ein Isotopengradient, der sich im Boden als Folge von Evaporation bildet, genutzt. Damit sich ein solcher Gradient bilden kann, benötigt es daher eine ausgedehnte Periode der Bodenaustrockung. Durch einen Vergleich der Isotopensignatur zwischen Wasserproben aus dem Stammxylem und verschiedenen Bodentiefen lässt sich die Tiefe der Wasseraufnahme der Bäume ermitteln. Allerdings lässt sich aus bisherigen Studien entnehmen das Bodeneigenschaften (z. B. Textur) die Signatur von 2H und 18O im Bodenwasser beeinträchtigen können. In Laborversuchen wurde daher getestet, ob eine Variation der Bodenfeuchte, des Tongehalts oder des Vorkommens von Calciumcarbonat im Boden eine Auswirkung auf die Isotopensignatur von extrahiertem Bodenwasser hat. Im ersten Versuch wurden getrocknete Bodenproben unterschiedlichen Tongehalts mit unterschiedlichen Mengen Wasser bekannter Isotopensignatur wiederbefeuchtet. Im zweiten Versuch wurde außerdem vor der Wiederbefeuchtung das Carbonat aus Teilproben des Bodens chemisch entfernt (Kontrollproben blieben unbehandelt), um den Effekt von Carbonat zu ermitteln. Für die Extraktion des Wassers aus den Proben wurde die kryogene Vakuum-Extraktion angewandt. Die Versuchsergebnisse deuteten darauf hin, dass mit abnehmendem Wassergehalt und zunehmendem Tongehalt in der Bodenprobe eine deutliche Veränderung von δ2H and δ18O im extrahierten Wasser auftrat. Weiterhin bewirkte die Anwesenheit von Carbonat im Boden eine Abreicherung von δ18O im Bodenwasser, wohingegen δ2H nicht verändert wurde. Den Ergebnissen Zufolge könnte der Einfluss eines hohen Carbonatgehalts im Boden so stark sein, dass eine unabhängige Anwendung von δ2H and δ18O zu widersprüchlichen Ergebnissen bei der Schätzung der Wasseraufnahmetiefe in hydrologischen Studien führen kann. Daher ist es zu empfehlen, deratige Analysen nicht nur auf einem, sondern auf beiden Isotopen zu stützen und auch die physikalischen sowie chemischen Bodeneigenschaften zu untersuchen. Da die erste Studie gezeigt hat, dass insbesondere 18O durch den Carbonatgehalt im Boden beeinflusst werden kann, wurde in der zweiten Studie ausschließlich die natürliche Abundanz von 2H genutzt, um die Wasseraufnahmetiefe einzelner Baumarten (Fagus sylvatica, Tilia sp. and Fraxinus excelsior) und deren Mischung während einer Periode der Bodenaustrocknung zu untersuchen. Hierbei sollte die Hypothese getestet werden, dass die Tiefe der Wasseraufnahme sich zwischen den Baumarten unterscheidet, was zu einer komplementären Wassernutzung in den Mehrart-Clustern führt. Weiterhin wurde angenommen, dass die Wasseraufnahmetiefe mit zunehmendem Baumdurchmesser ebenfalls ansteigt. Um die Tiefenverteilung der Wasserentnahme sowie mögliche Auswirkung der Baumgröße auf diese zu identifizieren, wurde die isotopische Zusammensetzung von Xylem- und Bodenwasserproben aus Einart- und Mehrart-Clustern analysiert und miteinander verglichen. Dafür wurden Bodenproben aus fünf Tiefenintervallen (0-0.1, 0.1-0.2, 0.2-0.3, 0.3-0.5, 0.5-0.7 m) in Stammnähe jedes untersuchten Baumes zusammen mit jeweiligen Stammproben entnommen. Mittels eines Isotopen Mischungsmodels konnte ermittelt werden, dass die relative Wasseraufnahmetiefe zwischen den Baumarten in Einart- sowie in Mehrart-Clustern variierte. Zusätzlich beeinflusste der Baumdurchmesser die Hauptaufnahmetiefe von Wasser in Mehrart-Clustern. Mit zunehmendem Durchmesser entnahmen die Bäume unabhängig von der Baumart Wasser vorwiegend aus vergleichsweise höheren Bodenschichten. Diese Resultate deuten auf eine Komplementarität in Bezug auf die relative Wasseraufnahme während einer Trockenperiode hin. Aufgrund des vorangegangenen Methodentests zu stabilen Isotopen wurde in dieser Studie lediglich 2H genutzt, um die Tiefe der Wasseraufnahme zu ermitteln. Zur Vollständigkeit wurde die Analyse jedoch auch mittels δ18O durchgeführt. Ebenso wie bei δ2H zeigte sich ein deutlicher Zusammenhang zwischen der Signatur der Hauptaufnahmetiefe und den Durchmessern der Bäume. Obwohl bei direktem Vergleich (grafische Analyse) und in der Modelberechnung δ2H and δ18O gegensätzliche Resultate zur relativen Wasseraufnahmetiefen der Bäume ergaben, ist der Zusammenhang zwischen Baumdurchmesser und Hauptiefe der Wasserentnahme gleich. Der letzte Teil der Studie befasste sich mit dem Einfluss unterschiedlicher Baumartenkombinationen, Artenvielfalt, Bestandesstruktur und klimatischen Bedingungen auf die Menge der täglichen Bodenwassernutzung während der Austrockungsperiode. Die Hypothese für diese Studie war, dass sich die Menge der täglichen Wasseraufnahme zwischen den Baumarten unterscheidet und mit ansteigender Baumartenvielfalt zunimmt (gemessen auf Einart- Zweiart-und Dreiart-Clustern). Die tägliche Wassaufnahme (mm Tag-1) wurde mittels eines einfachen Modelansatzes für die Bodentiefe von 0-0.3 m auf allen 100 Clustern und für die Tiefe 0-0.7 m auf 16 Clustern berechnet. Bis auf eine geringfügig höhere Wasseraufnahme in Einart-Clustern von Fraxinus excelsior im Zeitraum von Juni bis Mitte September 2009, konnte weder ein Einfluss der Artidentität der Bäume noch der Artenvielfalt auf die Menge der Wasseraufnahme in den Clustern festgestellt wurden. Die An- oder Abwesenheit der fünf untersuchten Baumarten in den Clustern zeigte ebenfalls kein Einfluss auf die Menge der Wasseraufnahme. Es lässt darauf schließen, dass unter den gegebenen Umständen Arteingenschaften und Artenvielfalt einen untergeordneten Einfluß auf die Nutzung von Bodenwasser haben, welcher möglicherweise auch von anderen Faktoren überdeckt wurde. Denkbar wäre hierbei ein Einfluss der Krautschicht oder die räumliche Anordnung der Bäume im Bestand, wobei die wichtigste Einflussgröße die vorherrschende Globalstrahlung war. Obwohl innerhalb der Cluster keine deutlichen Unterschiede gefunden wurden, die durch Arteigenschaften oder Artenvielfalt bedingt wurden, ist es dennoch möglich, dass diese auf einer größeren räumlichen Skala auftreten können. In Bezug auf die Wassernutzung eines Bestandes lässt sich demnach schliessen, dass Artenvielfalt alleine keine geeignete Vereinfachung für ein sehr komplexes Netzwerk aus verschiedenen Interaktionen zwischen Arteigenschaften innerhalb und zwischen Arten, sowie Bestandeseigenschaften und Umweltbedingungen ist. Jeder dieser Bestandteile könnte sich auf zeitlicher und räumlicher Ebene unterschiedlich auf die Wassernutzung eines Waldbestandes, unabhängig von der Biodiversität des Bestandes auswirken. Weiterhin ist es für Altbestände, mit geringem menschlichen Eingriff denkbar, dass sich Bäume im Laufe der Zeit gemäß der ihnen zur Verfügung stehenden Resourcen räumlich verteilen, wodurch ausgeglichene Nachbarschaftsbeziehungen entstehen könnten. Diese Arbeit zeigte, dass sich die physikalische und chemische Beschaffenheit des Bodens auf die Isotopensignatur von Wasser auswirkt. Dennoch können Isotopenversuche zur Ermittlung der Tiefenverteilung der Wasseraufnahme in temperaten Wäldern angewandt werden. Die Wasseraufnahmetiefe der Baumarten unterschied sich zwischen Ein- und Mehrart-Clustern, und deutete in Mehrart-Clustern auf eine Komplementarität hin, die durch Durchmesserunterschiede bedingt war. Baumartenvielfalt per se erhöhte jedoch nicht die Menge der absoluten Wasseraufnahme in den Clustern. Demnach gab es auch keinen Hinweis darauf, dass eine erhöhte Wassernutzungseffizienz zu einer deutlich verstärkten Ausnutzung der Bodenwasserresourcen während einer Austrocknungsperiode führt.

Uncertainties were analyzed in three areas (remote sensing, dendroclimatology, and climate modeling) relevant to current water resources management. First, the research investigated the relationships between remotely sensed and in situ Snow Water Equivalent (SWE) datasets in three western U.S. basins. Agreement between SWE products was found to increase in lower elevation areas and later in the snowpack season. Principal Components Analysis (PCA) revealed two distinct snow regions among the datasets and Singular Value Decomposition (SVD) was used to link both data products with regional streamflow. Remotely sensed SWE was found to be sufficient to use in statistically based forecast models in which magnitude did not affect results. Second, the research investigated the dendroclimatic potential of a critical flood control and hydropower region in the southeastern U.S. (Tennessee Valley) using climate division precipitation and regional tree-ring chronology datasets. Tennessee Valley May–July precipitation was reconstructed from 1692 to 1980 (289 years) using a stepwise linear regression model (R2 = 0.56). Weibull analysis illustrated that the Tennessee Valley reconstruction model developed generally underestimated extreme precipitation and overestimated average precipitation. The longest May–July drought occurred over 10 consecutive years (1827–1836). Instrumental records indicated that the two most recent droughts (1985–1988 and 2006–2008) ranked second and third in severity in the past three centuries. Third, past, present, and future patterns and extremes in streamflow within the North Platte River Basin were investigated. A streamflow reconstruction dating back to 1383 using tree rings was created to provide a proxy for the long-term variability in the region. Projected streamflow datasets from the Community Climate System Model (CCSM) were gathered to acquire future insight of the hydroclimatic variability within the North Platte River Basin (NRPB). Drought analysis revealed that 2002–2008 was one of the driest periods in the past 600 years. Multiple CCSM projections suggest that in the future, drier (5th percentile) years will become wetter relative to 1970–1999 CCSM hindcasts. Future average (50th percentile) and wet (95th percentile) years may yield statistically higher streamflow compared to those seen in the historical (1383–1999) record, suggesting potential anthropogenic influence beyond the historic natural variability.

University of Technology, Sydney. Faculty of Environmental Sciences.<br>This thesis presents the results of work undertaken to examine daily, seasonal and annual patterns of water use by a native remnant woodland in temperate Australia. The focus of the study was on the two dominant tree species of the woodland, but limited assessments of understorey and soil evapotranspiration were also undertaken. One of dominant species was Eucalyptus crebra, a broad-leaved tree and the other was Callitris glaucophylla a needle-leaved tree. At the start of the study, much of the eastern seaboard of Australia experienced a severe and prolonged drought but towards the end of the field work, rainfall at the site was significantly larger than the long-term average. This provided a fortuitous opportunity to compare the responses of vegetation water use to drought and nondrought periods. The study was conducted on the Liverpool Plains, of western New South Wales, Australia. Principle methods applied were (a) use of heat-pulse technology to measure rates of sap flow through trees; (b) open-top chambers to measure understorey and soil evapotranspiration; (c) application of the Penman-Monteith equation to estimate canopy conductance and transpiration rates; (d) two methods to scale spatially from measurements of individual trees to estimates of stand water use; (e) three methods to scale temporally from measurements conducted over a few weeks each year to provide annual estimates of stand water use; (f) a simple water balance was constructed to approximate the rate of deep drainage of water (rate of recharge). An annual water budget for the site was estimated for the drought and post-drought periods. The relationship between tree water use and diameter at breast height (DBH) was similar for the two species in each season, but the relationship for both species differed between seasons and years. In contrast, the relationships amongst DBH, sapwood area and leaf area differed between species at all times. This suggests that the same rate of water use by the eucalypt and Callitris (at a common size) was achieved through different mechanisms. Daily rates of stand water use showed significant intra- and inter-seasonal variation, with the lowest rates observed in winter and largest rates in summer. A simple model based upon solar radiation and vapour-pressure deficit was able to account for approximately 80 % of variation of stand water use under summer conditions with wet soil. Estimates of stand water use derived from the Penman-Monteith equation generally agreed well with those based upon measurements of sap velocity, with a slope of the regression of the two estimates being 1.03. In the drought-year, stand water use was approximately 59 % of rainfall and recharge was approximately 2% but in the post-drought year, when rainfall doubled compared to the drought year, stand water use was also 59 % whereas recharge was 4 %. This showed that despite the impact of an extensive and pronounced drought, the trees were able to rapidly adjust to more favourable conditions and maintain a low rate of recharge. These results are discussed in relation to the management of water resources for human consumptive use and in relation to the development of dryland salinity across Australian landscapes that have been cleared of trees.

Farmers in developing countries are struggling to feed families due to low crop yields resulting from land degradation, land use pressures and unsustainable use of water resources. While deliberate integration of trees into farming systems (agroforestry) has been practiced traditionally in the Mt. Elgon region of Uganda since time immemorial, with modernisation of society and commercialisation of agriculture, many farmers are motivated to dismantle agroforestry systems in favour of monocultural farming systems. The science needed to improve agroforestry in the Mt Elgon region should focus on tree-crop water interactions because the competition for light and water is one of the main reasons that farmers remove trees in favour of annual crops. Additionally, long-term adoption of agroforestry has been negatively affected by an underlying culture of financial expectancy and highly subsidized extension by research and development programmes, leading to ‘pseudo adoption’. I contend that modernised agroforestry practices, informed by science generated in a participatory manner, have the promise of improving household food security, livelihoods and resilience. The study is aligned to a pragmatic interdisciplinary research approach to embrace the domains of both biophysical science (tree-water use and crop productivity studies) and social science (farmer motivations and perceptions). It generally demonstrates effective application‐oriented research and farmer decision-making, with a specific case of managing trees in a relevant agroforestry system. The study seeks to understand how farmers’ knowledge and attitudes towards agroforestry change in response to exposure to the generation of scientific information from biophysical experiments. The four central research questions for this research are: (i) what influences the intentions of smallholder farmers in Mt. Elgon region to plant and retain trees on their farms?; (ii) what factors influence farmers’ perceptions of the impact of trees on common bean and coffee productivity?; (iii) what are the impacts of trees and their management on crop productivity and water use across a range of farm contexts?, and; (iv) what is the impact of biophysical information on farmers’ perceptions about agroforestry tree management in coffee-bean systems? A conceptual framework integrating the biophysical and social components of the study has been developed to inform the key agricultural technology adoption pathways of smallholder farmers. The study had an initial phase of in-depth, semi-structured farmer interviews and generation of biophysical information on impact of tree canopy pruning on tree water use and crop productivity from two selected farms with Cordia africana and Albizia coriaria trees integrated with coffee and common beans. The information from the biophysical data (collected over a 20-month period) was then reported to farmers through a series of extension events that were followed by a second phase of farmer interviews. Lastly, all the data and information collected from the second phase of farmer interviews and the biophysical experiment were used to establish the potential impact of incorporating C. africana and A. coriaria on soil water resources and sustainable crops productivity that would result from farmer adoption of biophysical information. Results from the biophysical component of the study show that C. africana and A. coriaria exhibit contrasting patterns of seasonal tree water use across leaf shedding stages, characterised by episodes of reverse flow in A. coriaria at specific periods of the year. While tree canopy pruning altered the synchrony in the vegetative phenology of Albizia trees, the pruned Cordia and Albizia trees respectively used 22.8% and 50.1% less water than unpruned trees whose average daily water use was 76.5L day-1 and 133.7L day-1. Coffee trees growing under pruned Cordia and Albizia trees used more water than coffee growing under unpruned trees, which could have resulted from more transpiration pull in coffee resulting from increased radiation with reduced shading. Canopy pruning also reduced the water demand of the tree component and resulted in recharge in the crop-rooting zone. In terms of crop productivity, yields of parchment coffee were highest under pruned Albizia (949 kg/ha), followed by coffee under unpruned Albizia (792 kg/ha). Unshaded coffee produced the least yield at 402 kg/ha and 422 kg/ha in the Albizia and Cordia sites, respectively. The highest common beans yields (708 and 688 kg/ha) were obtained from common beans planted in open field sites, followed by those grown under unshaded coffee sites. The low yields from coffee and common beans under unpruned trees is attributed to below and above ground competition consistently outweighing the benefits of shade. The social component of the study applied a Structural Equation Modeling (SEM) technique to assess the psychological drivers of smallholder farmers’ intention and their motivation to integrate trees in their farming systems based on the Theory of Planned Behavior (TPB). The findings indicate that psychological factors are key drivers to the farmers’ internal decisionmaking process in agroforestry technology adoption and can be context specific. The adoption behaviour of smallholder farmers is mainly shaped by existing community social norms and beliefs that tend to promote knowledge exchange, as opposed to the conventional knowledge transfer extension approaches. While I provide evidence that attitude and perceived behavioural control are reliable predictors of farmer tree planting behaviour, farmer perceptions and knowledge of the impact of trees on farm and their management varies across the farmer categories studied, where the intended purpose of trees on farm is perceived differently. This study argues that bridging local and scientific knowledge through participatory research and extension is fundamental to enhance agricultural technology adoption among smallholder farmers. Therefore, the final phase of the study drew upon knowledge generated from biophysical component on impact of pruning on tree water use and crop productivity to assess farmers’ perceptions and willingness to adopt practices emanating from the study following exposure of 394 farmers to the research outputs. The extension events facilitated dialogue between the researcher and the farmers, and the results show that the information delivered through extension events was better understood by majority of the farmers directly interacting with the project. However, overall, only 184 farmers of the 394 participants (47%) were convinced that higher coffee yield could be obtained from shaded coffee. Therefore, over 50% of these farmers are still hesitant to change, as the majority of them prune their trees only when there is need for fuelwood and or poles. In the African context, agroforestry is strongly promoted via development projects, that provide incentives to farmers in form of free planting materials, tree nursery inputs and capacity building on planting and management of agroforestry components. There is always a likelihood that what appears as adoption is in fact trialling of the new practice, which masks actual longterm adoption. I therefore suggest that adoption information exchange through social networks and general community interactions may enhance long-term agroforestry adoption. These complex interaction processes should be applied at the early stages of technology adoption and would facilitate introduction of socially and biophysically appropriate agroforestry interventions into local realities. In conclusion, the results from the biophysical component of the study have demonstrated that agroforestry tree canopy pruning is an important on-farm management decision for controlling competition and subsequently increasing crop yields, while prolonging the period of intercropping in intensive farming systems. However, farmers may be hesitant to adopt such useful information due to an underlying culture of financial expectancy leading to ‘pseudo adoption’, underutilization of existing social networks during research and extension, limitations in the period of exposure to a technology, and constraints in measuring and predicting adoption. The study has generally demonstrated that adoption is not merely related to the technology, socio economic and behavioural factors, and the research and extension methods applied, but also a result of complex interactions between people, technologies and institutions. For effective extension, there needs to be a lot more visibility of the research itself and over a long period of time rather than the formal short-term interactions between farmers and extension agents. The impacts resulting from effective application-oriented research, understanding farmer decision making and successful adoption of biophysical information can be essential for informing policy decisions relating to agricultural technology adoption pathways of smallholder farmers and household food security.<br>Thesis (Ph.D.) -- University of Adelaide, School of Agriculture, Food and Wine, 2021

碩士<br>國立中興大學<br>水土保持學系<br>87<br>This study is experimented in the native-tree garden of Huisun Experimental Forest in Guoshing in Nantou County. The weather type of this area is warm heavy-humid type with average temperature 21℃ and average relative humidity 80%. We select ten dominant tree species to measure their leaf photosynthesis and transpiration. Four of them were chosen to probe into the relationships among photosynthetic gas exchange rate and measured meteorological factors. Results were summarized as follows: 1.Formosan Ash had the highest net photosynthetic rate in ten tested species and Ring-cupped Oak was the lowest. Net photosynthetic rates of Laurel family species were higher than those of Beech family species. Leaf conductance and transpiration rate showed the same results. The seasonal variation of the photosynthetic rate for the species of Nanto Actinodaphne and Incense Nanmu were lowest, but that for the species of Formosan Apple, Chinese Cork Oak and Formosan Nato Tree were highest. The seasonal variations of water use efficiency (WUE) for ten tested plants were low. The WUE of Laurel family species were higher than that of Beech family species. 2.In the analysis of the relationships among photosynthetic gas exchange rate, the VPD had negative significant correlation with net photo-synthetic rate and leaf conductance. The VPD had positive significant correlation with transpiration rate. The PPFD and leaf temperature had low correlation with net photosynthetic rate and leaf conductance but positive significant correlation with transpiration rate. 3.In the analysis of the relationships among net photosynthetic rate and stomatal respondence, the net photosynthetic rate increase with leaf conductance and showed positive significant correlation. The leaf conductance had positive significant correlation with non-stomatal factor (Ci/Ca) besides Incense Nanmu. The effect between net photosynthetic rate and stomatal factor was small. 4.The leaf number and net photosynthetic had low correlation among the tested plants except Nanto Actinodaphne. The SPAD and net photo-synthetic also had low correlation among all the tested plants.