Artigos de revistas sobre o tema "Tress gradient hypothesis"

Longleaf pine - wiregrass (Pinus palustris Mill. - Aristida stricta Michx.) woodlands occupy sites ranging from deep, xeric sandhills to the edge of wetlands in the southeastern United States. Aboveground net primary productivity (ANPP) of the overstory and understory were determined for three replicate sites of three site types (xeric, intermediate, and wet-mesic) that span a wide environmental gradient. In addition, soil moisture (at 30 and 90 cm) and N mineralization (in situ buried bag incubations) were measured through an annual cycle. Longleaf pine - wiregrass ecosystems varied by nearly twofold in ANPP across complex gradients. Overstory and understory and total (overstory and understory) ANPP were positively correlated to soil moisture at 30 and 90 cm. The proportion of understory ANPP relative to the total ANPP did not increase across the environmental gradient as predicted by hypotheses that invoke niche differentiation in rooting habits of grasses and trees. Contrary to expectations, cumulative net N mineralization was negatively related to soil moisture. All ANPP estimates were significantly and negatively related to cumulative N-mineralization. Further work is needed to explore the mechanisms by which soil moisture regulates productivity across space, time, and for individual species. Additional experimentation through resource addition would allow for investigations into multiple resource limitations and how resource limitations vary depending on gradient position.

Trees and other plants growing in stressful environments can display adaptive strategies such as sprouting, which is considered to be a functional trait for the persistence niche. For example, inselbergs are rocky outcrops that impose limitations on many plant forms through selective pressure to adapt to these environments. The present research tested the hypotheses that environmental harshness enhances sprouting, and that multi-stemmed trees have different persistence dynamics compared with single-stemmed trees. We sampled vegetation in 2006 and 2011 across a soil depth gradient in three areas: riparian forest, inselbergs and a corridor between the first two areas. Trees with a diameter at the breast height (dbh) ≥5 cm were sampled, and sprouts were counted. Results showed that the inselberg had more sprouted individuals and a larger amount of sprouts than the other areas. Thus, sprouting as a survival strategy was efficient in dealing with the environmental harshness and may be considered an adaptive strategy of trees to enable them to persist in such environments. The dynamic of multi-stemmed trees differed from single-stemmed ones, and the inselberg was distinct from the other areas. Over the 5 years of the present study, sprouting proved to be a strategy of persistence in this habitat, a finding that is in accordance with our hypothesis. Factors contributing to the environmental harshness, such as soil depth, may be the cause of sprouting in trees.

Understanding how genetic identity influences community structure is a major focus in evolutionary ecology, yet few studies examine interactions among organisms in the same trophic level within this context. In a common garden containing trees from a hybrid system (Populus fremontii S. Wats. × Populus angustifolia James), we tested the hypothesis that the structure of establishing understory plant communities is influenced by genetic differences among trees and explored foliar condensed tannins (CTs) and photosynthetically active radiation (PAR) as mechanisms. Several findings support our hypothesis: (i) Understory biomass and cover increase along the genetic gradient from P. angustifolia to P. fremontii. (ii) Along the same hybridization gradient, species richness decreases and species composition shifts. (iii) Populus foliar CT concentrations and PAR decrease from P. angustifolia to P. fremontii. (iv) Understory species richness increases with foliar CTs; however, biomass, cover, and composition show no relationship with CTs, and no understory variables correlate with PAR. (v) Structural equation modeling suggests that foliar CTs are a primary mechanism linking overstory tree genetics with understory richness. Using an experimental system dominated by naturally colonizing exotic species, this study demonstrates that a genetic gradient created by tree hybridization can influence understory plants.

Among the hypotheses invoked to explain high species richness in tropical forests, the niche differentiation hypothesis has received observational and experimental support (Ashton 1969, Chesson 2000, Clark et al. 1999, Souza & Martins 2004, Svenning 2001, Terborgh & Mathews 1999). Habitat specialization with regard to edaphic factors and topography has been observed in several plant groups including trees, lianas, shrubs, ferns and palms (Clark et al. 1999, Ibarra-Manriquez & Martinez-Ramos 2002, Svenning 1999, Tuomisto & Ruokolainen 1993). Treefall gaps and light gradients have also been found to be important ecological factors affecting plant distribution and niche differentiation in the understory (Chazdon 1986, Poorter & Arets 2003, Terborgh & Mathews 1999). It is suggested that such habitat heterogeneity may not only maintain biodiversity but also may lead to the origin of new species through the process of parapatric speciation (Gentry 1989, Haffer 1997, Patton & Smith 1992).

The dichotomy of the earliest ecosystems into deltaic and floodplain forests was a long-standing view in paleobotany. The morphological traits such as nonbranching rootlets, bifurcating rhizomes, and bulbous bases of the primitive trees such as Eospermatopteris and lycopsids were considered adaptations to the lowland deltaic environments. In contrast, the traits of Archaeopteris trees such as wood, hierarchical branching networks of roots, and true leaves are an adaptation to the upland floodplain environments. The discovery of the Town of Cairo Highway Department (TCHD) fossil site in Upstate New York, where all major clades occupied a floodplain environment casts doubt on the validity of the environmental partition by the earliest trees at the higher taxonomic levels. This study aims to test the hypothesis of the environmental partition at the local scale by reconstructing the fossilized forest-floor landscape, the changes in the landscape over time, and the distribution patterns of the trees along the local environmental gradient at the TCHD site. To reconstruct the fossilized forest floor and to determine the environmental variations at the local scale, seven parallel cross-sections were drawn from south to north at THCH. The outcrop at the quarry floor measured 300 m in the north-south, and varied around 100–150 m in east-west direction. Primary sedimentary structures, the thickness of the sedimentary deposits that formed the forest floor and the surrounding quarry walls, paleosol features, and mega-fossils were measured, recorded, described, and mapped. Up to 3 meters deep drill-cores were extracted from the forest floor. The data was used to correlate the sedimentary deposits, and reconstruct the preserved landscape. Three dominant landscape features including an abandoned channel, an old-grown forest, and a local depression were recognized. These landscape features influenced greatly the pattern of local drainage, slope-gradients, patterns and durations of seasonal water pooling, paleosol developments, fossil distribution, and depositional environments. There is no evidence of environmental partitioning by trees at higher taxonomic levels at the local scale. The size and morphology of the root systems didn’t determine the distribution of the trees along the local environmental gradient such as drainage patterns but played important roles in tree stabilization. Forests would go through self-thinning as they matured. Upon comparison, it was found that the forests in unstable environments showed greater resiliency compared to forests established in the stable environments.

Abstract. The response of tropical trees and tree communities to climate change is crucial for the carbon storage and biodiversity of the terrestrial biosphere. Trees in tropical montane rain forests (TMFs) are considered particularly vulnerable to climate change, but this hypothesis remains poorly evaluated due to data scarcity. To reduce the knowledge gap in the response of TMF trees to warming, we established a field experiment along a 1300–2400 m elevation gradient as a proxy for warming in Rwanda. Seedling-size trees of 20 species native to montane forests in eastern and central Africa were planted in multi-species plots at three sites along the gradient. They have overlapping distributions but primarily occur in either transitional rain forests (∼ 1600–2000 ma.s.l.) or mid-elevation TMFs (∼ 2000–3000 ma.s.l.), with both early- (ES) and late-successional (LS) species represented in each elevation origin group. Tree growth (diameter and height) and survival were monitored regularly over 2 years. We found that ES species, especially from lower elevations, grew faster at warmer sites, while several of the LS species, especially from higher elevations, did not respond or grew slower. Moreover, a warmer climate increased tree mortality in LS species, but not much in ES species. ES species with transitional rain forest origin strongly increased proportional to stand basal area at warmer sites, while TMF species declined, suggesting that lower-elevation ES species will have an advantage over higher-elevation species in a warming climate. The risk of higher-elevation and LS species of becoming outcompeted by lower-elevation and ES species due to a thermophilisation response in a warmer climate has important implications for biodiversity and carbon storage of Afromontane forests.

The latitudinal gradient of species richness has frequently been attributed to higher diversification rates of tropical groups. In order to test this hypothesis for mammals, we used a set of 232 genera taken from a mammalian supertree and, additionally, we reconstructed dated Bayesian phylogenetic trees of 100 genera. For each genus, diversification rate was estimated taking incomplete species sampling into account and latitude was assigned considering the heterogeneity in species distribution ranges. For both datasets, we found that the average diversification rate was similar among all latitudinal bands. Furthermore, when we used phylogenetically independent contrasts, we did not find any significant correlation between latitude and diversification parameters, including different estimates of speciation and extinction rates. Thus, other factors, such as the dynamics of dispersal through time, may be required to explain the latitudinal gradient of diversity in mammals.

Abstract. We present results of a detailed study of drip rate variations at 12 drip discharge sites in Glory Hole Cave, New South Wales, Australia. Our novel time series analysis, using the wavelet synchrosqueezed transform, reveals pronounced oscillations at daily and sub-daily frequencies occurring in 8 out of the 12 monitored sites. These oscillations were not spatially or temporally homogenous, with different drip sites exhibiting such behaviour at different times of year in different parts of the cave. We test several hypotheses for the cause of the oscillations, including variations in pressure gradients between karst and cave due to cave breathing effects or atmospheric and earth tides, variations in hydraulic conductivity due to changes in viscosity of water with daily temperature oscillations, and solar-driven daily cycles of vegetative (phreatophytic) transpiration. We conclude that the only hypothesis consistent with the data and hydrologic theory is that daily oscillations are caused by solar-driven pumping by phreatophytic trees which are abundant at the site. The daily oscillations are not continuous and occur sporadically in short bursts (2–14 days) throughout the year due to non-linear modification of the solar signal via complex karst architecture. This is the first indirect observation leading to the hypothesis of tree water use in cave drip water. It has important implications for karst hydrology in regards to developing a new protocol to determine the relative importance of trends in drip rate, such as diurnal oscillations, and how these trends change over timescales of weeks to years. This information can also be used to infer karst architecture. This study demonstrates the importance of vegetation on recharge dynamics, information that will inform both process-based karst models and empirical estimation approaches. Our findings support a growing body of research exploring the impact of trees on speleothem paleoclimate proxies.

Pseudomonas syringae is a genetically diverse bacterial species complex responsible for numerous agronomically important crop diseases. Individual P. syringae isolates are assigned pathovar designations based on their host of isolation and the associated disease symptoms, and these pathovar designations are often assumed to reflect host specificity although this assumption has rarely been rigorously tested. Here we developed a rapid seed infection assay to measure the virulence of 121 diverse P. syringae isolates on common bean (Phaseolus vulgaris). This collection includes P. syringae phylogroup 2 (PG2) bean isolates (pathovar syringae) that cause bacterial spot disease and P. syringae phylogroup 3 (PG3) bean isolates (pathovar phaseolicola) that cause the more serious halo blight disease. We found that bean isolates in general were significantly more virulent on bean than non-bean isolates and observed no significant virulence difference between the PG2 and PG3 bean isolates. However, when we compared virulence within PGs we found that PG3 bean isolates were significantly more virulent than PG3 non-bean isolates, while there was no significant difference in virulence between PG2 bean and non-bean isolates. These results indicate that PG3 strains have a higher level of host specificity than PG2 strains. We then used gradient boosting machine learning to predict each strain’s virulence on bean based whole genome k-mers, type III secreted effector k-mers, and the presence/absence of type III effectors and phytotoxins. Our model performed best using whole genome data and was able to predict virulence with high accuracy (mean absolute error = 0.05). Finally, we functionally validated the model by predicting virulence for 16 strains and found that 15 (94%) had virulence levels within the bounds of estimated predictions. This study strengthens the hypothesis that P. syringae PG2 strains have evolved a different lifestyle than other P. syringae strains as reflected in their lower level of host specificity. It also acts as a proof-of-principle to demonstrate the power of machine learning for predicting host specific adaptation.

Background: Seed banks, an important element in the natural regeneration of plant communities, are regulated mostly by granivores along an altitudinal gradient.
 Question/Hypothesis: Pinus hartwegii forms transient and probably persistent seed banks along an altitudinal gradient. Seed removal will vary according to the removing agents, the altitude and the season.
 Species under study/Data description/Mathematical model: The formation of seed banks and the removal of Pinus hartwegii (Pinaceae) seeds along an altitudinal gradient were evaluated in different seasons using a linear model with two factorial variance analyses. 
 Site and years of study: The study was conducted at the Cofre de Perote National Park, Veracruz, Mexico, over an altitudinal gradient (at 3,400, 3,600, 3,800 and 4,000 m a.s.l.) in July-September 2015 (rainy season), and January-March 2016 (dry season). 
 Methods: In order to understand seed bank formation and identify the removal agents along an altitudinal gradient, two experiments were conducted with seeds from 10 trees at each altitudinal tier.
 Results: The results of the first experiment, after one year, demonstrated the formation of transient and probably persistent seed banks along an altitudinal gradient (P < 0.0001). The results of the second experiment showed significant variations in seed removal according to the removal agents and the seasons (P < 0.0001).
 Conclusions: Pinus hartwegii forms transient and probably persistent seed banks along an altitudinal gradient. Seed removal varies according to altitude and season.

<strong>ABSTRACT</strong> Tree community is the structural and functional basis of forest ecosystems. Forest ecosystem on hills is influenced by elevation due to variation in temperature, aspect and topographic features. Can the understanding of tree species occurrence guided by altitude help in finding the distributional pattern in different elevational bands? Gandhamardan hills belong to Eastern Ghats in Bargarh and Balangir districts of Odisha, India (20&deg;53<strong>&#39;</strong>29.7<strong>&#39;&#39;</strong>N, 82&deg;49<strong>&#39;</strong>57.8<strong>&#39;&#39;</strong>E). One hundred quadrates of 20m&times;20m size were laid during the year 2008 to study tree community&nbsp; with trees &ge; 15cm GBH in the 100ha protected forest. Relative frequency, relative density and relative abundance of tree species were calculated and summed up to get importance value index (IVI). Abundance to Frequency (A/F) ratio of each species was determined to get distribution pattern as regular (&lt;0.025), random (0.025-0.050) and contiguous (&gt;0.050). Dominance-Diversity (D-D) curves were plotted taking species rank on abscissa axis and IVI value on ordinate axis for the determination of species correlationship. Spearman&rsquo;s rank correlation (<em>&rho;</em><em>)</em> of IVI to relative frequency, relative density and relative abundance were calculated using Spearman&rsquo;s Rank formula. A total of 49 species belonging to 42 genera and 29 families were recorded throughout ten elevational bands within 300m to 550m.&nbsp; Species occurring at only single altitude range are <em>Cochlospermum religiosum</em> (L.) Alston (425-450m), <em>Dalbergia latifolia </em>Roxb.(400-425m), <em>Diospyros montana </em>Roxb. (500-525m),<em> Ficus benghalensis </em>L.(500-525m), <em>Garuga pinnata </em>Roxb. (350-375m), <em>Morinda pubescens </em>Sm. in Rees (425-450m), <em>Wrightia arborea </em>(Dennst) Mabb. (400-425m) and <em>Ziziphus mauritiana </em>Lam. (450-475m). All these species show contiguous type of distribution. Five species viz. <em>Buchanania lanzan </em>Spreng., <em>Cleistanthus collinus </em>(Roxb.) Benth. Ex Planch., <em>Diospyros melanoxylon </em>Roxb., <em>Terminalia alata </em>Heyne ex Roth and <em>Haldinia cordifolia</em> (Roxb.) Ridsdak were found in all the studied altitude bands. Out of 272 occurrences of species across all altitude bands, 136 occurrences of species are contiguous distribution type while the rest 136 occurrences are of regular (48 numbers) and random (88 numbers) distribution type. Random and contiguous distribution increase from lower altitude to mid altitude and again decrease from mid to higher altitudes whereas the opposite trend is observed for regular distribution. In the mid altitude band (400-425m) highest thirty eight species are observed. The Spearman&rsquo;s rank correlation value (<em>&rho;</em><em>)</em> shows that IVI is highly correlated with RD (<em>&rho;</em> =0.90 to 0.98) compared to that of RF (<em>&rho;</em> =0.66 to 0.85) and RA (<em>&rho;</em> =0.68 to 0.92). The theory of mid-domain effect with hard boundary concept for plant species distribution along altitude appears to be valid for Gandhamardan hill ecosystem. <strong>Key words :</strong> Eastern Ghats; Gandhamardan hill; Tree species; Dominance-Diversity; Mid-domain effect <strong>REFERENCES</strong> Andel, T.V. (2001). Floristic composition and diversity of mixed primary and secondary forests in northwest Guyana. <em>Biodiversity and conservation</em>.10:1645-1682. Armesto, J.J., Mitchell, J.D. and Villagran, C. (1986). A comparision of spatial pattern of trees in some tropical and temperate forests. <em>Biotropica </em>18: 1-11. Aubert, M., Alard, D. and Bureau, F. (2003). Diversity of plant assemblages in managed temperate forests: a case study in Normandy (France)<em> Forest Ecology and</em> <em>Management</em>. 175:321-337. Bhattarai, K.R. and Vetaas, O.R. (2005).&nbsp; Do fern and fern-allies show a similar response along the ecological gradient in the Himalayas? <em>Bulletin Department of Plant Resources</em>. 26:24-29. Bhattarai, K.R. and Vetaas, O.L. (2003). Variation in plant species richness of different life forms along a subtropical elevation gradient in the Himalayas, east Nepal. <em>Global Ecology and Biogeography</em>.12:327-340. Bhattarai, K.R., Vetaas, O.R. and Grytnes, J.A. (2004). Fern species richness along a central Himalayan elevation gradient, Nepal. <em>Journal of Biogeography</em>.31:398-400. Brown, J.H. (2001). Mammals on mountainsides, elevational patterns of diversity. <em>Global Ecology and Biogeography.</em>10:101-109. Cannon, C.H., Peart, D.R. and Leihton, M. (1998). Tree species diversity in commercially logged Bornean rainforest. <em>Science</em>. 28:1366-1368. Carpenter, C. (2005). The environmental control of plant species density on a Himalaya elevation gradient. <em>Journal of Biogeography</em>. 32:999-1018. Champion, H.G. and Seth, S.K. (1968). <em>A</em> <em>Revised survey of the forest types of India</em>. Manager of Publications, Government of India, New Delhi. Chiarucci, A., Dominics, V.D. and Wilson, J.B. (2001).Structure and floristic diversity in permanent monitoring plots in forest ecosystems of Tuscany. <em>Forest Ecology and</em>&nbsp;&nbsp; <em>Management</em>.141:201-210. Colwell, R.K., Rahbek, C. And Gotelli, N.J. (2004). The mid-domain effect and species richness patterns: What have we learned so far? <em>American Naturalist</em>. 163:E1-E23. Colwell, R.K. and Hurtt, G.C. (1994). Nonbiological gradients in species richness and a spurious Rapoport effect. <em>The American Naturalist</em>. 144:570-595. Curtis, J.T. (1959). <em>The vegetation of Wisconsin university</em>. Wisconsin University.&nbsp; Wisconsin Press, Madison. Curtis, J.T. and Cotton, G. (1956). <em>Plant Ecology Workbook, Laboratory Field</em> <em>Manual</em>. Burgess publishing, Minnesota.pp.193 Dallmeier, F. and Comiskey, J.A. (1998). Forest biodiversity assessment, monitoring and evaluation for adaptive management. In <em>Forest biodiversity research, Monitoring and Modelling: Conceptual Background and Old World Case Studies</em> (eds Dallmeier, F. and Comiskey, J.A.), Partheon Publishing, Paris. pp. 529-540. Eltih, J., Graham, C.H., Anderson, R.P., Dudik, M., Ferrier, S., Guisan, A., Hijmans, R.J., Huettmann, F., Leathwick, J.R., Lehmann, a., Li, J., Lohmann, L.G., Loizelle, B.A., Manion, G., Moritz, C., Nakamura, M., Nakazawa, Y., Overton, J., townsend Peterson, A., Phillips, S.J., Richardson, K., Scachetti-Pereira, R., Schapire, R.E., Soberon, J., Williams, S., Wisz, M.S. and Zimmermann, N.E. (2006). Novel methods improve prediction of species&rsquo; distributions from occurrence data. <em>Ecography</em>. 29:129-51. Good, N.F. and Good, R.E. (1972). Population dynamics of tree seedlings and saplings in mature Eastern hardwood forest. <em>Bull Torrey Bot. Club</em>. 99 Greig-Smith, P. (1957). Quantitative Plant Ecology, 2^ndedition. Butterworth, London. Grubb, P.J. (1977). The maintenance of species-richness in plant communities: the importance of the regeneration niche. <em>Biological Reviews</em>. 52: 107&ndash;145. Grytness, J.A. (2003a). Species richness patterns of vascular plants along seven altitudinal transects in Norway. <em>Ecography</em>. 26:291-300. Grytness, J.A. (2003b). Ecological interpretations of the mid-domain effect. Ecological Letter. 6:883-888. Grytness, J.A. and Vetaas, O.R. (2002). Species richness and altitude, a comparision between simulation models and interpolated plant species richness along the Himalayas altitudinal gradient, Nepal. <em>The American Naturalist</em>. 159:294-304. Guisan, A. and Thuiller, W. (2005). Predicting species distribution: offering more than simple habitat models. <em>Ecology Letters</em>. 8:993-1009. Haines, H.H. (1921-25). <em>The botany of Bihar and Orissa</em>, 6 parts. Adlard &amp; Son and West New man Ltd. London. Heaney, L.R. (2001). Small mammal diversity along elevational gradients in the Philippines: an assessment of patterns and hypotheses. <em>Global Ecology and Biogeography</em>.10:15-39. Hooker, J.D. (1872-97). <em>The flora of British India</em>. London. Huang, W., Pohjonenen, V., Johansson, S., Nashanda, M., Katigula, M.I.L. and Luukkanen, O. (2003). Species diversity, forest structure and species composition in Tanzanian tropical forests. <em>Forest Ecology and Management</em>. 173:11-24. Huston, M.A. (1994). Biological diversity: the coexistence of species on changing landscape, Cambridge University Press, Cambridge. Kelly, C.K. and Bowler, M.G. (2002). Coexistence and relative abundance in forest trees. <em>Nature</em>. 417:437&ndash; 440. Kershw, K.K. (1973). Quantitative and Dynamic Plant Ecology. 2^ndedition, FLBS and Edwards Arnold (Publ.) London, pp.308. Koellner, T., Hersperger, A.M. and Wohlgemuth, T. (2004).&nbsp; Rerefraction method for assessing plant species diversity on a regional scale. <em>Ecography</em>. 27:532-544. Kumar, A., Bruce, G.M. and Ajai, S. (2006). Tree species diversity and distribution patterns in tropical forests of Garo hills. <em>Current Science</em>. 91:1370-1381. Kumar, M. and Bhatt V.P. (2006). Plant biodiversity and conservation of forests in foot hills of Garhwal Himalaya. <em>Journal of Ecology and Application</em>. 11(2):43-59. Lomolino, M.V. (2001). Elevation gradients of species-richness, historical and prospective views. <em>Global Ecology and Biogeography</em>. 10:3-13. Lovett, J.C., Rudd, S., Taplin, J. and Frimont-Moller, C. (2000). Patterns of plant diversity in African south of the Sahara and their implications for conservation management.<em> Biodiversity and Conservation</em>. 9:37-46. Mac Arthur, R.H. (1972). Geographical ecology: Patterns in the distribution of species. Harper &amp; Row, New York. Md. Nor, S. (2001). Elevational diversity patterns of small mammals on Mount Kinabalu, Sabah, Malaysia. <em>Global ecology and Biogeography</em>. Mahajan, D.M. and Kale, V.S. (2006). Spatial characteristics of vegetation cover based on remote sensing and geographical information system (GIS). <em>Tropical Ecology</em>. 47(1): 71-79. Marimon, B.S., Felfili, J.M. and Lima, E.S. (2002). Floristics and phytosociology of the gallery forest of the Bacaba stream, Nova Xavantina, Mato Grosso, Brazil.<em> Edinberg Journal of Botany</em>. 59(2): 303- 318. Mishra, B.P., Tripathi, O.P. and Laloo, R.C. (2005). Community characteristics of a climax subtropical humid forest of Meghalaya and population structure of ten important tree species. <em>Tropical Ecology. </em>&nbsp;46(2):241-251. Mishra, R. (1968). <em>Ecology Work Book</em>. Oxford and IBH Publications, Co. New&nbsp;&nbsp; Delhi. Misra, R.C., and Das, P. (2004). Vegetation stratification of Gandhamardan Hill ranges, Orissa using remote sensing technique. <em>Journal of Economic and Taxonomic Botany</em>. 28(2):429- 438. Misra, R.C. and Das, P. (1998a). Phytogeographical affinities of Plants of Gandhamardan Hill range of Orissa with major Indian mountains. <em>Journal of Economic and Taxonomic.&nbsp; Botany</em>. 22 (1):207-210. Misra, R.C., and Das, P. (1998b). Vegetation Status of Nrusinghanath-Harishankar complex, Orissa. <em>Journal of Economic and Taxonomic Botany</em>. 22(3):547-554. Misra, R.C. and Das, P. (1998c). Inventory of Rare and endangered vascular plants of Gandhamardan Hill ranges in western Orissa. <em>Journal of Economic and Taxonomic .Botany</em>. 22 (2):353-357. Misra, R.C. (1990). Ethnobotanical studies on some plants of Nrusinghanath- Harishankar complex, Orissa<em>. Journal of Environmental Sciences.</em> 3(2): 36-42. Mooney, H. (1950). <em>Supplement to the Botany of Bihar and Orissa, International Book</em> <em>Distributors</em>, Dehradun. Nebel, G., Kvist, L.P. and Vanclay, J.K. (2001). Structure and floristic composition of flood plain forests in the Peruvian Amazon, I. Overstorey.<em> Forest Ecology and</em> <em>Management</em>.150:27- 57. Odum, E.P. (1971). Fundamentals of Ecology. III ed. W.B. Saunders Co., Philadelphia. USA. Pacala, S.W. and Roughgarden, J. (1982). Spatial heterogeneity and interspecific competition. <em>Theoretical Population Biology</em>. 31:92 &ndash;113. Panigrahi, G., Chowdhury, S., Raju, D.C.S. and Deka, G.K. (1964). A contribution to the botany of Orissa. <em>Bulletin of Botanical Survey of India</em>. 6(2-4):237-266. Parthasarathy, N. (2001). Changes in forest composition and structure in three sites of tropical evergreen forest around Sengaltheri, Western Ghats. <em>Current </em>Science. 80:389-393. Pearson, R.G., Dawson, T.P. and Liu, C. (2004). Modelling species distribution in Britain: a hierarchical integration of climate and land cover data. <em>Ecography</em>. 27:285-98. Pianka, E.R. (1966). Latitudinal gradients in species diversity: a review of concepts. <em>American Naturalist.</em> 100:33-46. Rahbek, C. (1997). The relationship among area, elevation and regional species richness in neotropical birds. <em>The American Naturalist</em>.149: 875-902. .<strong>Rahbek, C. (1995).</strong> The elevational gradient of species richness, a uniform pattern? <em>Ecography.</em> 18:200-205. .<strong>Rapoport, E.H. (1982).</strong> Areogrphy: geographical strategies of species. Trans. B. Drausal, Vol.1. Pergamon, New York. Rapoport, E.H. (1975). Areografia: estrategias geograficas des las species. <em>Fondo de Cultura Economica</em>, Mexico City. .Reddy, C.S. and Ugle, P. (2008).Tree species diversity and distribution pattern in tropical forest of Eastern Ghats, India: a case study. <em>Life science Journal</em>. 5(4):87-93. .Rennolls, K. and Laumonier, Y. (2000). Species diversity structure analysis at two sites in the tropical rainforest of Sumatra. <em>Journal of Tropical Ecology</em>.16:253-270. Richards, P.W. (1996). The tropical Rain Forest: an Ecological study.<em>2^nd edition,</em> <em>Cambridge University Press</em>, London. Ruijven, J.V. and Berendse, F. (2007).&nbsp; Contrasting effects of diversity on the temporal stability of plant populations. <em>Oikos</em>.116:1323-1330. . Saxena, H.O. and Brahmam, M. (1996). <em>The flora of Orissa. Vol. I-IV, </em>Orissa&nbsp;&nbsp; Forest&nbsp; Development Corporation, Bhubaneswar, Orissa. Singh, J.S and Yadav P.S. (1974). Seasonal variation in composition, plant biomass and net primary productivity of tropical grassland of Kurukshetra, India. <em>Ecology Monograph</em>. 44:351-375. . Stevens, G.C. (1989).The latitudinal gradient in geographical range: How so many species coexist in the tropics? <em>American&nbsp; Naturalist.</em> 1333:240-256. Stevens, G.C. (1992). The elevational gradient in altitudinal range: An extension of Rapoport&rsquo;s latitudinal rule to altitude. <em>American Naturalist</em>. 140:893-911. Terborgh, J. (1977). Bird species diversity on an Andean elevational gradient. <em>Ecology</em>. 58:1007-1019. . Whittaker, R.J., Willis, K.J. and Field, R. (2001). Scale and species richness; towards a general, hierarchical theory of species diversity. <em>Journal of Biogeography</em>. 28:453-470. &nbsp;

Canopy shape and depth may influence crop uniformity of peach trees at harvest. To test this hypothesis we examined yield distribution and fruit quality changes at different canopy levels of peach trees trained to delayed vase (DV) and perpendicular Y (Y). Trees of both training forms were divided vertically into six or seven 50-cm-deep layers and fruit was harvested at commercial ripening from each layer separately. Regardless of training form, number of fruit and yield per layer were highest in the central part of the canopy, but more evenly distributed among canopy layers in Y trees. In DV trees, fruit weight decreased linearly from top to bottom, whereas it remained constant along the top and middle portion of Y canopies to decrease rapidly at the bottom. In DV trees, 83% of the fruit fell into AAA, AA and A size categories, whereas fruit of Y trees was more evenly distributed among all size categories. Hue of fruit peel color increased linearly with distance from canopy top in both training forms, but more sharply in DV trees. Fruit soluble solid content decreased linearly from canopy top to bottom, regardless of training form. A more uniform crop load distribution within the canopy in combination with a light penetration gradient resulted in greater variability of quality parameters for Y than DV trees.

<b>Background and aims</b> – Based on data across tropical forests, a leading hypothesis posits that lianas are better competitors than trees under water shortage. Evaluating this hypothesis at a local scale may provide insights into its generality. We tested whether the abundance of lianas –relative to trees– decreases with soil moisture in a Neotropical dry forest. We also evaluated the influence of water availability on liana diversity.<b>Methods</b> – Lianas (≥ 1 cm diameter) and trees (≥ 1.5 m height) were counted and identified, and soil moisture was measured, in twenty 10 × 10 m plots at different distances to water sources. Linear regressions assessed the relationships between water availability and relative abundance and diversity of lianas.<b>Key Results</b> – We found a significant an d positive relationship between the relative abundance of lianas and water availability. Liana density ranged from 21 to 77 individuals per plot. Soil moisture did not influence liana species richness (S) or Fisher's α. Eighteen liana species were recorded , from ten families.<b>Conclusions</b> – Our results show that, in contrast with geographic and regional patterns, relative abundance and diversity of lianas at a local scale are not favoured by water shortage. This suggests that different mechanisms may prevail in the liana-tree interaction across water availability gradients.

Purpose - In this study, we propose an empirical model for predicting seasoned equity offering (SEO here after) using machine learning methods. Design/methodology/approach - The models utilize the random forest method based on decision trees that considers non-linear relationships, as well as the gradient boosting tree model. SEOs incur significant direct and indirect costs. Therefore, CEOs’ decisions of seasoned equity issuances are made only when the benefits outweigh the costs, which leads to a non-linear relationship between SEOs and a determinant of them. Particularly, a variable related to market timing effectively exhibit such non-linear relations. Findings - To account for these non-linear relationships, we hypothesize that decision tree-based random forest and gradient boosting tree models are more suitable than the linear methodologies due to the non-linear relations. The results of this study support this hypothesis. Research implications or Originality - We expect that our findings can provide meaningful information to investors and policy makers by classifying companies to undergo SEOs.

Current theory on plant–animal interactions predicts that the outcome of herbivory on plant performance will be dependent on plant productivity. Thus, slow-growing plants should be less able to compensate for biomass losses than fast-growing plants, and therefore be more susceptible to herbivory if attacked. We simulated winter browsing by moose (Alcesalces (L.)) on Scots pine (Pinussylvestris L.) along a gradient of plant productivity and addressed the following questions: (1) Does herbivory affect growth independently of plant productivity? (2) Is herbivory a more important mortality factor for slow-growing than for fast-growing plants? (3) Is there any effect of herbivory on fecundity, and is it related to plant productivity? Two clipping regimes simulated different intensities of moose winter browsing. Mortality was followed annually, and after 4 years we measured tree growth and fecundity on control as well as on treatment pines. The effect of clipping on growth was related with both clipping intensity and plant productivity. In the light-clipping treatment mortality was restricted to the slow-growing pines, in contrast with the severe treatment, where it occurred across the whole range of plant growth. Moreover, in the light-clipping treatment most mortality occurred within 1 year after treatment, whereas tree death occurred over 2 or more years in the severe treatment. We found no effect of age on mortality within growth-rate classes. The proportion of trees with cones increased with growth rate for control trees but not for treated trees, indicating that herbivory more strongly affects fecundity on fast-growing than on slow-growing trees. Our results confirm the hypothesis that herbivory affects plant performance differently across a gradient of plant productivity. We suggest that mammalian herbivores can increase mortality of plant genets after the seedling stage primarily in stands on low-productivity sites, especially in combination with a high density of the herbivore.

Abstract. The relative complexity of the mechanisms underlying savanna ecosystem dynamics, in comparison to other biomes such as temperate and tropical forests, challenges the representation of such dynamics in ecosystem and Earth system models. A realistic representation of processes governing carbon allocation and phenology for the two defining elements of savanna vegetation (namely trees and grasses) may be a key to understanding variations in tree–grass partitioning in time and space across the savanna biome worldwide. Here we present a new approach for modelling coupled phenology and carbon allocation, applied to competing tree and grass plant functional types. The approach accounts for a temporal shift between assimilation and growth, mediated by a labile carbohydrate store. This is combined with a method to maximize long-term net primary production (NPP) by optimally partitioning plant growth between fine roots and (leaves + stem). The computational efficiency of the analytic method used here allows it to be uniquely and readily applied at regional scale, as required, for example, within the framework of a global biogeochemical model.We demonstrate the approach by encoding it in a new simple carbon–water cycle model that we call HAVANA (Hydrology and Vegetation-dynamics Algorithm for Northern Australia), coupled to the existing POP (Population Orders Physiology) model for tree demography and disturbance-mediated heterogeneity. HAVANA-POP is calibrated using monthly remotely sensed fraction of absorbed photosynthetically active radiation (fPAR) and eddy-covariance-based estimates of carbon and water fluxes at five tower sites along the North Australian Tropical Transect (NATT), which is characterized by large gradients in rainfall and wildfire disturbance. The calibrated model replicates observed gradients of fPAR, tree leaf area index, basal area, and foliage projective cover along the NATT. The model behaviour emerges from complex feedbacks between the plant physiology and vegetation dynamics, mediated by shifting above- versus below-ground resources, and not from imposed hypotheses about the controls on tree–grass co-existence. Results support the hypothesis that resource limitation is a stronger determinant of tree cover than disturbance in Australian savannas.

Abstract. The relative complexity of the mechanisms underlying savanna ecosystem dynamics, in comparison to other biomes such as temperate and tropical forests, challenges the representation of such dynamics in ecosystem and Earth system models. A realistic representation of processes governing carbon allocation and phenology for the two defining elements of savanna vegetation (namely trees and grasses) may be a key to understanding variations in tree/grass partitioning in time and space across the savanna biome worldwide. Here we present a new approach for modelling coupled phenology and carbon allocation, applied to competing tree and grass plant functional types. The approach accounts for a temporal shift between assimilation and growth, mediated by a labile carbohydrate store. This is combined with a method to maximise long-term net primary production (NPP) by optimally partitioning plant growth between fine roots and (leaves + stem). The computational efficiency of the analytic method used here allows it to be uniquely and readily applied at regional scale, as required, for example, within the framework of a global biogeochemical model. We demonstrate the approach by encoding it in a new simple carbon/water cycle model that we call HAVANA (Hydrology and Vegetation-dynamics Algorithm for Northern Australia), coupled to the existing POP (Population Orders Physiology) model for tree demography and disturbance-mediated heterogeneity. HAVANA-POP is calibrated using monthly remotely-sensed fraction of absorbed photosynthetically active radiation (fPAR) and eddy-covariance-based estimates of carbon and water fluxes at 5 tower sites along the Northern Australian Tropical Transect (NATT), which is characterized by large gradients in rainfall and wildfire disturbance. The calibrated model replicates observed gradients of fPAR, tree leaf area index, basal area and foliage projective cover along the NATT. The model behaviour emerges from complex feed-backs between the plant physiology and vegetation dynamics, mediated by shifting above- vs. below-ground resources, and not from imposed hypotheses about the controls on tree/grass co-existence. Results support the hypothesis that resource limitation is a stronger determinant of tree cover than disturbance in Australian savannas.

The distribution of epiphytic lichens on Quercus pubescens in Tuscany, central Italy, was studied by means of multivariate techniques along an altitudinal gradient from 0 to 900 m. Great differences in community structure were found and the altitude of 500 m was identified as an ecotone. Epiphytic lichen vegetation on trees below the ecotone varied significantly in relation to bark pH. Climatic parameters (temperature and rainfall) were probably related to altitude. Dust was probably responsible for the rise in bark pH. The distribution of lichen species in the sampling belts fitted the core-satellite hypothesis. The use of core and satellite species as biomonitors of air pollution and bioindicators of environmental conditions is discussed.

The mechanisms under which shrubs outcompete grasses to cause shrub encroachment in the African savannas a contentious issue. The popular model, Walter’s two-layer hypothesis is still inconclusive. It suggests that trees and shrubs in the savannas develop deeper roots to avoid competition with grasses. This study was designed to test this hypothesis by investigating the root system of T. sericea, one of the common encroaching species in the Kalahari Basin. Using direct excavation methods, 39 shrubs were randomly excavated across the Kalahari Basin. Results revealed contrasting rooting strategies by T. sericea under varying climatic conditions, with drier areas exhibiting largely lateral roots, whereas moist sites were dominated by dual root systems. These findings are not consistent with the existing framework which argues that savanna shrubs are essentially deeper rooted. Instead, results support an emerging hypothesis that certain savanna shrubs opportunistically adapt their root systems in response to the prevailing environmental stimuli such as moisture. A shrub such as T. sericea with lateral roots abundantly deployed in shallow soil depth points to a direct niche competition with grasses in the Kalahari Basin. It is probable that the occurrence of shrub encroachment by T. sericea is a manifestation of this competitive interaction.

Bacterial communities associated with roots influence the health and nutrition of the host plant. However, the microbiome discrepancy are not well understood under different healthy conditions. Here, we tested the hypothesis that rhizosphere soil microbial diversity and function varies along a degeneration gradient of poplar, with a focus on plant growth promoting bacteria (PGPB) and antibiotic resistance genes. Comprehensive metagenomic analysis including taxonomic investigation, functional detection, and ARG (antibiotics resistance genes) annotation revealed that available potassium (AK) was correlated with microbial diversity and function. We proposed several microbes, Bradyrhizobium, Sphingomonas, Mesorhizobium, Nocardioides, Variovorax, Gemmatimonadetes, Rhizobacter, Pedosphaera, Candidatus Solibacter, Acidobacterium, and Phenylobacterium, as candidates to reflect the soil fertility and the plant health. The highest abundance of multidrug resistance genes and the four mainly microbial resistance mechanisms (antibiotic efflux, antibiotic target protection, antibiotic target alteration, and antibiotic target replacement) in healthy poplar rhizosphere, corroborated the relationship between soil fertility and microbial activity. This result suggested that healthy rhizosphere soil harbored microbes with a higher capacity and had more complex microbial interaction network to promote plant growing and reduce intracellular levels of antibiotics. Our findings suggested a correlation between the plant degeneration gradient and bacterial communities, and provided insight into the role of high-turnover microbial communities as well as potential PGPB as real-time indicators of forestry soil quality, and demonstrated the inner interaction contributed by the bacterial communities.

Tree crowns and growth rings are physiologically and functionally connected through supporting and resource sharing. Management interventions may strongly influence tree growth by altering this linkage. However, conventional approaches have limited ability to characterize crown shape precisely, thus hindering our understanding of the relationship between crown shape and tree ring patterns. We, thus, aimed to test three hypotheses: (HI) Crown shape (regularity vs. irregularity) and ring patterns (regularity or irregularity) are significantly correlated and (HII) vary across density gradients; if so, (HIII) internal ring patterns could be predicted from external crown shape metrics. We, therefore, employed terrestrial laser scan-based crown shape and coring-based TRP metrics for Norway spruce (Picea abies (L.) H. Karst.) trees covering a range of density gradients to assess temporal changes of crown shape and tree ring patterns. We found a significant and positive influence of crown shape quantifying metrics on ring patterns, indicating crown regularity or irregularity strongly reflects tree ring regularity or irregularity (p &lt; 0.05). Crown shape and ring patterns always showed comparable patterns across density gradients (e.g., trees from lower-density stands produced transgressive crown and ring growth) and significantly varied across competition level. Trees grown in lower-density stands are more likely to produce upper-reaching crowns (maximum crown radius expansion shifted to the mid- to upper-crown) than trees grown in competitive conditions, which result in lower-reaching crowns (maximum crown radius shifted to the crown base) with reduced crown shape and ring pattern parameters. Crown irregularities increased as density decreased through competition reduction, resulting in more regular ring patterns (stable growth). Since both crown shape and ring patterns are simultaneously impacted by stand density or competition, the relationship between crown shape and ring patterns is competition-neutral. When viewed separately, both patterns had a strong relationship with the competition index. Finally, our comparative model predictions showed that approaches ranging from simple linear models to complex machine learning techniques (e.g., random forest, neural network, support vector machine, etc.) were effective in predicting ring patterns using external TLidar-crown shape, indicating a potential method to evaluate the crown shape and ring pattern link. The relationship between the crown and growth ring and their synchronous patterns across competition gradients suggests that internal growth can be assessed from the external appearances of trees and recommends further consideration in forest modeling.

Abstract. Solitary trees are natural land surface elements found in almost all climates, yet their influence on the surrounding airflow is poorly known. Here we use state-of-the-art, laser-based, remote sensing instruments to study the turbulent wind field in the near-wake region of a mature, open-grown oak tree. Our measurements provide for the first time a full picture of the mixing layer of high turbulence that surrounds the mean wind speed deficit. In this layer, we investigate the validity of a two-dimensional vectorial relation derived from the eddy-viscosity hypothesis, a hypothesis commonly used in modelling the turbulence transport of momentum and scalars in the atmosphere. We find that the momentum fluxes of the streamwise wind component can be adequately predicted by the transverse gradient of the mean flow. Using the mixing-length hypothesis we find that for this tree the corresponding turbulence length scale in the mixing layer can be approximated by one height-independent value. Further, the laser-based scanning technology used here was able to accurately reveal three-dimensional turbulent and spatially varying atmospheric flows over a large plane without seeding or intruding the atmospheric flow. This capability points to a new and more exact way of exploring the complex earth–atmosphere interactions.

We studied the habitat selection and thermal biology of two sympatric Chinese skinks ( Eumeces elegans Boulenger, 1887 and Sphenomorphus indicus (Schmidt, 1928)) to test the effect of thermal preference on habitat partitioning. We measured thermal and structural attributes of the microhabitats occupied by these two skink species, as well as their field body temperatures and activity patterns. We then quantified the preferred body temperatures of these species in a thermal gradient. Compared with S. indicus, E. elegans occupied microhabitats with fewer trees, more rocks, and higher ambient temperatures. Active S. indicus were mainly found in the morning, whereas active E. elegans were found at noon. The thermal environment of the microhabitats at these two periods correlated with the skinks’ thermal preferences. Preferred temperatures of E. elegans were significantly higher than those of S. indicus. These results support (i) the hypothesis that habitat partitioning between ectotherms is related to interspecific differences in thermal requirements; (ii) the labile hypothesis that describes the adaptability of thermal physiology, because the two sympatric skinks, which select different thermal environments, differed in thermal physiology; and (iii) the cold-climate hypothesis that explains the evolution of viviparity, because viviparous S. indicus occupy colder habitats than do oviparous E. elegans.

There is evidence to suggest that vascular epiphytes experience low competition for resources (light, water, and nutrients) compared to terrestrial plants. We tested the hypothesis that low resource competition may lead to higher nestedness among vascular epiphyte assemblages compared to trees. We studied the species composition and biomass of epiphytes and trees along an elevation gradient in a tropical dry forest in SW Ecuador. Both life-forms were inventoried on 25 plots of 400 m2 across five elevation levels (550–1250 m). Tree species density and total species richness increased with elevation, whereas basal area and biomass did not show significant trends. Epiphyte species density and richness both increased strongly with elevation, in parallel to biomass. Plot-level compositional changes were similarly strong for both life-forms. We attribute elevational increases in the species richness of trees and epiphytes to increasing humidity, i.e., more mesic growth conditions. We attribute the more pronounced elevational increase in epiphyte biomass, species density, and richness—the latter coupled with a higher degree of nestedness—to the greater moisture dependency of epiphytes and relatively low direct competition for resources. Our study provides a first comparison of elevational trends in epiphyte and tree diversity and biomass for a tropical dry forest.

Abstract - The goal of this study is to advance early detection of heart disease through a data-oriented strategy that employs machine-learning algorithms and various data classification techniques. There is a greater awareness globally around managing cardiovascular disease as we strive to achieve accurate and precise diagnosis within the parameters of time in clinical practice. In this study we explore a number of supervised learning methods such as Logistic Regression, Decision Trees, Random Forest, Support Vector Machines (SVM), K-Nearest Neighbors (KNN), and Gradient Boosting for prediction of heart disease with clinical and demographic data. The Cleveland Heart Disease dataset was used for much of the study. There was an extensive preprocessing phase including data normalization, handling missing values, and selection of features. Each model was evaluated on standard metrics that included accuracy, precision, recall, F1 score, and ROC AUC. The results reveal that Random Forest and Gradient Boosting ensemble models outperform all individual classifiers, but data also supports the hypothesis that ensemble techniques elevate performance across all metrics examined . Key Words: Heart Disease Prediction, Machine Learning, Data Classification, Ensemble Methods, Random Forest

Resource and nutrient availability varies spatially and influences animal foraging patterns. Under the compensation hypothesis, animals should preferentially forage for the most limiting nutrient in the environment. Animal nutrient preferences have been well studied in the tropics, where terrestrial and arboreal fauna are clearly differentiated and limited by different nutrients. In temperate forests, vertical stratification of the fauna may be less pronounced and its role in foraging ecology is poorly understood. Here, we examine nutrient preference patterns over a vertical gradient in temperate forests and nearby urban centers in North Carolina, USA. Using a bait-choice experiment and novel bait design, we measured ant community nutrient preferences in the canopy and on the ground of 83 trees across 14 sites and assessed ant diversity and community composition. Ant diversity did not differ across the vertical strata or habitat types, but species turnover altered community composition to create four distinct assemblages. In temperate forests, ants did not prefer a particular nutrient in either stratum, likely due to extensive foraging across strata. In urban habitats, however, ant nutrient preferences matched patterns well known from tropical systems: arboreal animals preferred protein, while terrestrial animals preferred carbohydrates. Rather than stratum-specific nutrient limitations, however, we attribute the differences in urban preference patterns to changes in native species’ foraging intensity and the addition of uniquely urban species with specific nutrient preferences. These results underscore the necessity of testing ecological hypotheses across biomes and suggest that urbanization may produce established ecological patterns via novel mechanisms.

Research Highlights: We detected the longitudinal gradients of genetic diversity parameters, such as the number of alleles, effective number of alleles, heterozygosity, and inbreeding coefficient, and found that these might be attributable to climatic conditions, such as temperature and snow depth. Background and Objectives: Genetic diversity among local populations of a plant species at its distributional margin has long been of interest in ecological genetics. Populations at the distribution center grow well in favorable conditions, but those at the range margins are exposed to unfavorable environments, and the environmental conditions at establishment sites might reflect the genetic diversity of local populations. This is known as the central-marginal hypothesis in which marginal populations show lower genetic variation and higher differentiation than in central populations. In addition, genetic variation in a local population is influenced by phylogenetic constraints and the population history of selection under environmental constraints. In this study, we investigated this hypothesis in relation to Abies sachalinensis, a major conifer species in Hokkaido. Materials and Methods: A total of 1189 trees from 25 natural populations were analyzed using 19 EST-SSR loci. Results: The eastern populations, namely, those in the species distribution center, showed greater genetic diversity than did the western peripheral populations. Another important finding is that the southwestern marginal populations were genetically differentiated from the other populations. Conclusions: These differences might be due to genetic drift in the small and isolated populations at the range margin. Therefore, our results indicated that the central-marginal hypothesis held true for the southernmost A. sachalinensis populations in Hokkaido.

Understanding the mechanisms of biological invasions (e.g., competitive exclusion) is a key conservation challenge, especially on islands. Many mechanisms have been tested by comparing the characteristics of native and alien species, but few studies have considered ecological strategies. Here we aim at comparing the competitive ability, stress tolerance, and ruderalism (CSR) of native and alien trees in the tropical rainforests of Réunion Island. A total of sixteen 100 m2 plots (eight ‘near-trail’ and eight ‘off-trail’, at less disturbed sites) were established over a 2100 m elevational gradient. Three traits were measured in 1093 leaves from 237 trees: leaf area, leaf dry matter content and specific leaf area. They were converted into a CSR score assigned to each of the 80 surveyed tree species (70 native and 10 alien) using the ‘Stratefy’ ordination approach. C scores increased with basal area and S scores with elevation, but R scores were not higher along the trail, thus only partially validating Stratefy. Native and alien trees had similar CS strategies, thus challenging invasion hypotheses predicting a difference in ecological strategies and rather demonstrating the importance of environmental filtering. However, other differences falling outside the CSR theory may also explain the success of alien species on Réunion.

Abstract Storms are among the greatest natural disturbances in temperate forests, and increased nitrogen (N) availability is thought to increase storm damage. However, the extent to which N availability increases damage from snowfall is less clear. To test how N availability might affect the susceptibility of trees to snow damage in a temperate forest, we took advantage of an opportunistic storm and surveyed damage in fertilized and unfertilized stands, and across a native N availability gradient. In response to a severe, early season snow storm—a consequence of Superstorm Sandy—the percentages of both basal area and stems damaged were lower in a fertilized watershed than in an unfertilized watershed. Across the native N availability gradient, the percentage of basal area damaged by snow decreased with higher soil N. The effects of N availability on damage were also affected by tree species. Our results suggest that N availability decreases damage from snow storms, contrary to our hypotheses drawn from broader studies. Understanding the relation between storm damage and N availability is important, considering the global increase in N deposition, and since severe storms are likely to become more prevalent with climate change.

Fruit of sweet cherry (Prunus avium L.) crack during or after rain due, in part, to absorption of water through the fruit surface driven by the water potential gradient. In 1972, J. Vittrup-Christensen suggested that overhead misting of calcium salts during precipitation may be an effective way to prevent cherry cracking by reducing the water potential gradient. We tested this hypothesis by designing a computer-controlled irrigation system to intermittently spray a 10% CaCl2 solution on trees during rain events. Spray emitters were placed in the middle and at the top of the canopy. The program turned the system on for 90 s at each 0.3 mm of rain and monitored daily rainfall and accumulated mist times. Two `Emperor Francis' and two `Ulster' were treated with equal number of controls. Intact and cracked cherries were counted on four branches per tree at three times when cherries were susceptible to cracking. Overall, cracking was reduced from 33% to 11% by the CaCl2 spray at the end of the experiment. Treated `Ulster' had 9% cracked fruit, while control had 43% cracked fruit. Differences for `Emperor Francis' were not significant. Phytotoxicity was estimated at about 15 % of leaf area. This system will be reevaluated in 1995 with the added objective of quantifying and reducing phytotoxicity.

Fruit of sweet cherry (Prunus avium L.) crack during or after rain due, in part, to absorption of water through the fruit surface driven by the water potential gradient. In 1972, J. Vittrup-Christensen suggested that overhead misting of calcium salts during precipitation may be an effective way to prevent cherry cracking by reducing the water potential gradient. We tested this hypothesis by designing a computer-controlled irrigation system to intermittently spray a 10% CaCl2 solution on trees during rain events. Spray emitters were placed in the middle and at the top of the canopy. The program turned the system on for 90 s at each 0.3 mm of rain and monitored daily rainfall and accumulated mist times. Two `Emperor Francis' and two `Ulster' were treated with equal number of controls. Intact and cracked cherries were counted on four branches per tree at three times when cherries were susceptible to cracking. Overall, cracking was reduced from 33% to 11% by the CaCl2 spray at the end of the experiment. Treated `Ulster' had 9% cracked fruit, while control had 43% cracked fruit. Differences for `Emperor Francis' were not significant. Phytotoxicity was estimated at about 15 % of leaf area. This system will be reevaluated in 1995 with the added objective of quantifying and reducing phytotoxicity.

Abstract Tree roots penetrate the soil to several meters depth, but the role of subsoils for the supply of nutrient elements such as phosphorus (P) to the trees is poorly understood. Here, we tested the hypothesis that increased P deficiency in the topsoil results in an increased microbial recycling of P from the forest subsoil. We sampled soils from four German temperate forest sites representing a gradient in total P stocks. We analyzed the oxygen isotopic composition of HCl-extractable phosphate (δ18OP) and identified differences in P speciation with increasing soil depth using X-ray absorption near-edge structure (XANES) spectroscopy. We further determined microbial oxygen demand with and without nutrient supply at different soil depths to analyse nutrient limitation of microbial growth and used nanoscale secondary ion mass spectrometry (NanoSIMS) to visualize spatial P gradients in the rhizosphere. We found that δ18OP values in the topsoil of all sites were close to the isotopic signal imparted by biological cycling when oxygen isotopes in phosphate are exchanged by enzymatic activity. However, with increasing soil depth and increasing HCl-P concentrations, δ18Ο values continuously decreased towards values expected for primary minerals in parent material at depths below 60 cm at sites with high subsoil P stocks and below more than 2 m at sites with low subsoil P stocks, respectively. For these depths, XANES spectra also indicated the presence of apatite. NanoSIMS images showed an enrichment of P in the rhizosphere in the topsoil of a site with high P stocks, while this P enrichment was absent at a site with low P stocks and in both subsoils. Addition of C, N and P alone or in combination revealed that microbial activity in subsoils of sites with low P stocks was mostly P limited, whereas sites with high P stocks indicated N limitation or N and P co-limitation. We conclude that subsoil P resources are recycled by trees and soil microorganisms. With continued weathering of the bedrock and mobilisation of P from the weathered rocks, P cycling will proceed to greater depths, especially at sites characterised by P limitation.

Quantitative knowledge of xylem physical tolerance limits to dehydration is essential to understanding plant drought tolerance but is lacking in many long-vessel angiosperms. We examine the hypothesis that a fundamental association between sustained xylem water transport and downstream tissue function should select for xylem that avoids embolism in long-vessel trees by quantifying xylem capacity to withstand air entry of western North American oaks (Quercus spp.). Optical visualization showed that 50% of embolism occurs at water potentials below −2.7 MPa in all 19 species, and −6.6 MPa in the most resistant species. By mapping the evolution of xylem vulnerability to embolism onto a fossil-dated phylogeny of the western North American oaks, we found large differences between clades (sections) while closely related species within each clade vary little in their capacity to withstand air entry. Phylogenetic conservatism in xylem physical tolerance, together with a significant correlation between species distributions along rainfall gradients and their dehydration tolerance, suggests that closely related species occupy similar climatic niches and that species' geographic ranges may have shifted along aridity gradients in accordance with their physical tolerance. Such trends, coupled with evolutionary associations between capacity to withstand xylem embolism and other hydraulic-related traits, yield wide margins of safety against embolism in oaks from diverse habitats. Evolved responses of the vascular system to aridity support the embolism avoidance hypothesis and reveal the importance of quantifying plant capacity to withstand xylem embolism for understanding function and biogeography of some of the Northern Hemisphere’s most ecologically and economically important plants.

In arid regions many tree species develop broad crowns. A number of hypotheses involve trade-offs between growth in height and horizontal spreading, but there is no explanation for the switch from vertical to horizontal growth during development. Using Acacia papyrocarpa Benth as a model, we measured tree height and crown shape across different sites and topographic positions. We also measured δ13C of phyllodes from crown tops and lateral spreading branches. Trees were significantly taller at the base of a hill, where water availability is typically greater, than on the adjacent steep hillslope. In contrast, δ13C from the treetops was not significantly different across this topographic gradient, despite variation in tree height. In addition, δ13C was higher at treetops than in lower, lateral branches. These observations are consistent with hydraulic limitation to tree height. The shape of mature and young crowns in open environments was not symmetrical. At all sites, branches were shortest, but tree crowns tallest, on south-facing (i.e. shadiest) aspect of crowns. This suggests that light limitation may also affect crown development. If upper branches become water-limited and lower branches light-limited, then middle lateral branches become the less-stressed part of the crown and may grow more, producing a broad crown.

Canonical correspondence analysis and linear regressions were used to relate height, diameter, and dispersion measurements of 36,380 stems from 197 species recorded in 2,341 plots against both climatic and landscape variables. Above ground biomass increased in wetter and cooler locations that ameliorate the seasonal rainfall deficits. Taller and greater diameter trees with lower wood densities occur at higher altitudes. Differences between locations are based on a change in the composition of species rather than a change in the allometric properties within a species. The results support the hydraulic limitation and species packing hypotheses. These interrelationships may be affected by the interactions of fire frequency and drought which are a common feature of much of the study area. Under current climate change scenarios it is likely that there will be a reduction in above ground biomass, the number of stems per hectare, average height, average diameter, and basal area due to increasing seasonality of rainfall, temperatures, and the intensity and frequency of fires. The largest of trees are likely to be removed early due to their inability to cope with increased drought stress. The results suggest a marked reduction in carbon storage will occur across the study region in eastern Australia.

Current hypotheses on conifer tree stem degradation at treeline indicate the influence of frost desiccation caused by dehydration of wind-exposed needles above the snowpack because of frozen soil or wind abrasion. Here, we examine, in an exploratory study, the potential of detailed stem analysis to identify other causal factors at a subarctic treeline site using black spruce (Picea mariana (Mill.) BSP.) trees distributed along a wind-exposure gradient and showing various degrees of stem damage, from the normal, conical growth form to the mat growth form. Temporal patterns of stem development revealed a relatively integrated growth system within the tree as long as the normal arborescent form was maintained. With the gradual loss of the normal form owing to defoliation, the growth system of the damaged trees became fragmented into a wind-exposed (west–ast), horizontal component and a vertical (below–bove snowpack) component outlined by the asymmetric development of stem and foliage. Although cool growing seasons reduce tree-ring growth, frost events in July appear also influential, possibly when killing frosts occur during bud break. The impact of such abrupt events may have a long-enduring influence on radial growth, a factor much neglected in dendroclimatological studies of boreal and subarctic environments. Stem degradation may be initiated by the changing position of the snowpack line associated with variable snow precipitation during several consecutive years, thus inducing a shifting erosional zone along the stem most effective when temperatures are below average, i.e., likely the result of mechanical defoliation caused by the synergistic influence of snow and ice abrasion during blizzards and severe windchill conditions on the brittle, cold-exposed needles. Our results suggest that sustained winter defoliation at treeline has an overwhelming influence on subsequent radial growth. More dendroecological studies and experimental field work are needed to test our conclusions. Keywords: stem analysis, treeline, black spruce, winter defoliation, tree rings, subarctic.

The basic wood density influences the carbon stock, playing a crucial role in climate-changing global mitigation through carbon sequestration. Understanding wood carbon release depends on the Nitrogen assessment and CN ratio. Therefore, our research aimed to: (i) Compare basic density, organic carbon, nitrogen, and C/N ratio among the Khaya grandifoliola, K. ivorensis, and K. senegalensis; (2) Analyze the gradient along positions and diameter of the commercial stem; (3) Recommend the most representative sampling position for each species based on the diameter. The experimental area is located in Southeastern Brazil. Twelve average-diameter trees per species were cut down, and wood disc samples were collected at 0, 25, 50, 75, and 100% commercial height. Our results show statistical differences in wood basic density among the species, and K. senegalensis has the highest basic density, 592 kg m3. There was no statistical difference in organic carbon between species and along the stem. Stem diameter instead of commercial height improved the variable studied, confirming the research hypothesis. Sampling at 17% of the commercial height, ranging to 18–22 cm stem diameters, is recommended for greater representativeness.

Oesophago-gastric cancer is difficult to diagnose in the early stages given its typical non-specific initial manifestation. We hypothesise that machine learning can improve upon the diagnostic performance of current primary care risk-assessment tools by using advanced analytical techniques to exploit the wealth of evidence available in the electronic health record. We used a primary care electronic health record dataset derived from the UK General Practice Research Database (7471 cases; 32,877 controls) and developed five probabilistic machine learning classifiers: Support Vector Machine, Random Forest, Logistic Regression, Naïve Bayes, and Extreme Gradient Boosted Decision Trees. Features included basic demographics, symptoms, and lab test results. The Logistic Regression, Support Vector Machine, and Extreme Gradient Boosted Decision Tree models achieved the highest performance in terms of accuracy and AUROC (0.89 accuracy, 0.87 AUROC), outperforming a current UK oesophago-gastric cancer risk-assessment tool (ogRAT). Machine learning also identified more cancer patients than the ogRAT: 11.0% more with little to no effect on false positives, or up to 25.0% more with a slight increase in false positives (for Logistic Regression, results threshold-dependent). Feature contribution estimates and individual prediction explanations indicated clinical relevance. We conclude that machine learning could improve primary care cancer risk-assessment tools, potentially helping clinicians to identify additional cancer cases earlier. This could, in turn, improve survival outcomes.

To assess the coupling between a particular hemidiaphragm and the individual lungs, the left and right phrenic nerves were separately stimulated in anesthetized dogs, and the mean changes in pleural pressure over the two lungs were evaluated by measuring the changes in airway opening pressure (ΔPao) in the two bronchial trees. Stimulation induced a fall in Pao in both lungs. However, ΔPao in the contralateral lung was only 65% of that in the ipsilateral lung. Thus, although the canine ventral mediastinum is a delicate structure, it sustained a significant pressure gradient. The hypothesis was then considered that this gradient was allowed to develop through the stretching and stiffening of the mediastinum caused by the descent of the diaphragm, and it was tested by measuring ΔPao in the two lungs during isolated, unilateral contraction of the inspiratory intercostal muscles. In this condition, ΔPao in the contralateral lung was 92% of that in the ipsilateral lung. A model analysis of the respiratory system led to the estimate that mediastinal elastance was ∼25 times greater during hemidiaphragmatic contraction than during unilateral intercostal contraction. These observations indicate that 1) a particular hemidiaphragm has an expanding action on both lungs and 2) during contraction, however, it makes the mediastinum stiffer so that the pressure transmission from the ipsilateral to the contralateral pleural cavity is reduced. These observations imply that the mediastinum may play a significant role in determining the pressure-generating ability of the diaphragm.

Decline of yellow-cedar ( Chamaecyparis nootkatensis ((D. Don) Spach) has occurred on 200 000 ha of temperate rainforests across southeastern Alaska. Because declining forests appeared soon after the Little Ice Age and are limited mostly to low elevations (whereas higher elevation forests remain healthy), recent studies have hypothesized a climatic mechanism involving early dehardening, reduced snowpack, and freezing injury. This hypothesis assumes that a specific suite of microclimatic conditions occurs during late winter and declining cedar populations across the region have responded similarly to these conditions. Based on the first geographically extensive tree ring chronologies constructed for southeastern Alaska, we tested these assumptions by investigating regional climatic trends and the growth responses of declining cedar populations to this climatic variation. Warming winter trends were observed for southeastern Alaska, resulting in potentially injurious conditions for yellow-cedar due to reduced snowfall and frequent occurrence of severe thaw–freeze events. Declining cedar forests shared a common regional chronology for which late-winter weather was the best predictor of annual growth of surviving trees. Overall, our findings verify the influence of elevational gradients of temperature and snow cover on exposure to climatic stressors, support the climatic hypothesis across large spatial and temporal scales, and suggest cedar decline may expand with continued warming.

Climate changes bring a new era in which hot dry areas become even hotter and drier. This leads to state shifts and specifically desertification processes. Desertification includes the state shifts from non-desert to deserts and within deserts reduction of primary productivity. Studying shifts in ecosystem states and desertification requires long term ecosystem research and monitoring (LTERM). This can take decades and because temporal variability of precipitation in deserts is very high, it is difficult to distinguish between noise and trends. Space for time substitution is a tool aiding LTER research. Specifically hyper-arid ecosystems (HAE), the driest deserts on earth, are a good tool to study possible scenarios of climate changes. Understanding structure and function of HAE allows us to imagine possible dynamics that can occur in wetter ecosystems.Our new assertion is that if extreme climate change drives arid lands to function under alternate extreme conditions, then arid land ecosystems will function like an HAE as an alternative state, rather than progress to desertification. To support our assertion, we developed a conceptual framework of HAEs that includes a geo-hydrological "abiotic engine" that drives HAE function by soil moisture diversity and plant functional groups. Based on this conceptual framework, we suggest incorporating two new hypotheses in climate change studies to advance our understanding of responses of large-scale, water-limited ecosystems:Hydro-climatic extremes in water-limited ecosystems will reduce the degree of resource conservation by slope ecosystems due to reduction in plant cover and soil. The decreased ecosystem function on the slope will be compensated for by increasing the effect of the abiotic engine on the ephemeral stream, thus enhancing meta-ecosystem functioning in the ephemeral stream.In water-limited ecosystems, climate change toward hydro-climatic extremes will rescale the dominant hydro-ecological processes of pulse–reserve, source–sink, and connectivity along the semiarid, arid, and HA gradients in two ways:shrinking of both spatial and temporal dimensions; and shrinking in the temporal dimension and expanding in the spatial dimensions.The first rescaling trajectory is related to biodiversity–ecosystem function and the second to the abiotic engine processes.The forecasted increased frequency and intensity of extreme climatic events may strongly affect ecosystem structure and function in the future. It is unclear how ecosystems will function in the long run over a large spatial scale under a new extreme water cycle. This open question calls for a conceptual framework as a fundamental basis for theoretical and experimental exploration of ecosystem function on a large scale driven by an extreme climate envelope. We investigated hyper-arid ecosystems (HAEs) as natural tangible models that already function under an extreme climatic envelope. The results indicate that unique geological settings can retain runoff water from a single significant flash flood that is sufficient to sustain perennials even during drought years. We calculated a water balance for a large rain event and found that 38% of the rain water infiltrated to the main riverbed which supports local trees, 46% exited the watershed to a larger river and only 19% were lost to either evaporation or the bare slopes. We propose a modified pulse–reserve mechanism that provides water to large acacia trees during the hot dry summer in hyperarid areas.

To correct for a large number of hypothesis tests, most researchers rely on simple multiple testing corrections. Yet, new methodologies of selective inference could potentially improve power while retaining statistical guarantees, especially those that enable exploration of test statistics using auxiliary information (covariates) to weight hypothesis tests for association. We explore one such method, adaptiveP-value thresholding (AdaPT), in the framework of genome-wide association studies (GWAS) and gene expression/coexpression studies, with particular emphasis on schizophrenia (SCZ). Selected SCZ GWAS associationPvalues play the role of the primary data for AdaPT; single-nucleotide polymorphisms (SNPs) are selected because they are gene expression quantitative trait loci (eQTLs). This natural pairing of SNPs and genes allow us to map the following covariate values to these pairs: GWAS statistics from genetically correlated bipolar disorder, the effect size of SNP genotypes on gene expression, and gene–gene coexpression, captured by subnetwork (module) membership. In all, 24 covariates per SNP/gene pair were included in the AdaPT analysis using flexible gradient boosted trees. We demonstrate a substantial increase in power to detect SCZ associations using gene expression information from the developing human prefrontal cortex. We interpret these results in light of recent theories about the polygenic nature of SCZ. Importantly, our entire process for identifying enrichment and creating features with independent complementary data sources can be implemented in many different high-throughput settings to ultimately improve power.

Abstract. Understanding the relationships between plant traits and ecosystem properties at large spatial scales is important for predicting how compositional change will affect carbon cycling in tropical forests. In this study, we examine the relationships between species wood density, maximum height and above-ground, coarse wood production of trees ≥10 cm diameter (CWP) for 60 Amazonian forest plots. Average species maximum height and wood density are lower in Western than Eastern Amazonia and are negatively correlated with CWP. To test the hypothesis that variation in these traits causes the variation in CWP, we generate plot-level estimates of CWP by resampling the full distribution of tree biomass growth rates whilst maintaining the appropriate tree-diameter and functional-trait distributions for each plot. These estimates are then compared with the observed values. Overall, the estimates do not predict the observed, regional-scale pattern of CWP, suggesting that the variation in community-level trait values does not determine variation in coarse wood productivity in Amazonian forests. Instead, the regional gradient in CWP is caused by higher biomass growth rates across all tree types in Western Amazonia. Therefore, the regional gradient in CWP is driven primarily by environmental factors, rather than the particular functional composition of each stand. These results contrast with previous findings for forest biomass, where variation in wood density, associated with variation in species composition, is an important driver of regional-scale patterns in above-ground biomass. Therefore, in tropical forests, above-ground wood productivity may be less sensitive than biomass to compositional change that alters community-level averages of these plant traits.

Artificial Intelligence (AI) is the human-like intelligence imbued in machines so that they can perform tasks that normally require human intelligence. Machine learning is an AI technique which carries on the concepts of predictive analytics with one important distinction: the AI system can make assumptions, test hypotheses, and learn independently. XGBoost, Extreme gradient boosting, is a popular machine-learning library for regression tasks. It implements the gradient-boosting decision tree algorithm, which combines several feeble decision trees to produce a robust predictive model. In Boosted Trees, boosting is the process of transforming poor learners into strong learners. It is an ensemble method; a weak learner is a classifier with a low correlation with classification, whereas a strong learner has a high correlation. Maize is a staple food in Kenya and having it in sufficient amounts in the country assures the farmers' food security and economic stability. Crop yield measures the seeds or grains produced by a particular plot of land. Typically, it is expressed in kilograms per hectare, bushels per acre, or sacks per acre. This study predicted maize yield in Uasin Gishu, a county in Kenya, using XGBOOST regression algorithm of machine learning. The regression model used the mixed-methods research design, the survey employed well-structured questionnaires comprising of quantitative and qualitative variables, directly administered to selected representative farmers from 30 clustered wards. The questionnaire comprised 30 variables related to maize production from 900 randomly selected maize farmers distributed across 30 wards. XGBOOST machine learning regression model was fitted, and it could predict maize yield and identify the top features or variables that affect maize yield. The model was evaluated using regression metrics Root Mean Squared Error (RMSE), Mean Squared Error (MSE), Mean Absolute Percentage Error (MAPE) and Mean Absolute Error (MAE), which values were 0.4563, 0.2082, 25.2700 and 0.3532, respectively. This algorithm was recommended for maize yield prediction.