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1
Moore, T. L., L. E. Valentine, M. D. Craig, G. E. StJ Hardy e P. A. Fleming. "Do woodland birds prefer to forage in healthy Eucalyptus wandoo trees?" Australian Journal of Zoology 61, n. 3 (2013): 187. http://dx.doi.org/10.1071/zo13045.
Testo completoAbstract (sommario):
Globally, many forests and woodlands are in decline. The marked loss of canopy foliage typical of these declines results in reduced foraging resources (e.g. nectar, pollen, and insects) and, subsequently, can reduce habitat quality for woodland birds. In south-west Western Australia, patches of Eucalyptus wandoo woodlands have shown a decline in condition since at least 2002. We investigated how changes in E. wandoo condition affect the woodland bird community. Foraging activities of three bird species were recorded for 20 sites in Dryandra State Forest and Wandoo Conservation Park either by conducting watches on focal trees (‘sitting’ method), or following individuals through the woodland (‘following’ method). Condition assessments of trees used by the birds were compared with those for trees available at the study site. Weebills (Smicrornis brevirostris; canopy insectivore) displayed preference for healthy trees (low amounts of canopy dieback), whereas rufous treecreepers (Climacteris rufa; bark-foraging insectivore) preferred trees with a higher proportion of dead branches. Yellow-plumed honeyeaters (Lichenostomus ornatus; insectivore/nectarivore) foraged in older, larger E. wandoo trees having full canopies with few signs of tree decline. Tree declines, such as that happening in E. wandoo, alter the foraging resources and habitat available to woodland birds.
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Jaikumar, Nikhil S., Samantha S. Stutz, Samuel B. Fernandes, Andrew D. B. Leakey, Carl J. Bernacchi, Patrick J. Brown e Stephen P. Long. "Can improved canopy light transmission ameliorate loss of photosynthetic efficiency in the shade? An investigation of natural variation in Sorghum bicolor". Journal of Experimental Botany 72, n. 13 (29 aprile 2021): 4965–80. http://dx.doi.org/10.1093/jxb/erab176.
Testo completoAbstract (sommario):
Abstract Previous studies have found that maximum quantum yield of CO2 assimilation (Φ CO2,max,app) declines in lower canopies of maize and miscanthus, a maladaptive response to self-shading. These observations were limited to single genotypes, leaving it unclear whether the maladaptive shade response is a general property of this C4 grass tribe, the Andropogoneae. We explored the generality of this maladaptation by testing the hypothesis that erect leaf forms (erectophiles), which allow more light into the lower canopy, suffer less of a decline in photosynthetic efficiency than drooping leaf (planophile) forms. On average, Φ CO2,max,app declined 27% in lower canopy leaves across 35 accessions, but the decline was over twice as great in planophiles than in erectophiles. The loss of photosynthetic efficiency involved a decoupling between electron transport and assimilation. This was not associated with increased bundle sheath leakage, based on 13C measurements. In both planophiles and erectophiles, shaded leaves had greater leaf absorptivity and lower activities of key C4 enzymes than sun leaves. The erectophile form is considered more productive because it allows a more effective distribution of light through the canopy to support photosynthesis. We show that in sorghum, it provides a second benefit, maintenance of higher Φ CO2,max,app to support efficient use of that light resource.
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LeBlanc, David C., e Dudley J. Raynal. "Red spruce decline on Whiteface Mountain, New York. II. Relationships between apical and radial growth decline". Canadian Journal of Forest Research 20, n. 9 (1 settembre 1990): 1415–21. http://dx.doi.org/10.1139/x90-187.
Testo completoAbstract (sommario):
Understanding the relationship between apical and radial growth decline can contribute toward the evaluation of hypotheses regarding causal mechanisms of red spruce decline. The etiology of red spruce decline in montane spruce-fir forests of the northeastern United States includes loss of foliage at branch apices, crown dieback, and unreversed radial growth decline since the 1960s. Demographic analyses of crown damage and radial growth decline for red spruce on Whiteface Mountain, New York, indicate that large, canopy-emergent trees with exposed crowns exhibit greater decline than codominant trees within an intact canopy. In this paper, radial growth decline is shown to have been coincident with decreased apical growth and increased incidence of injury to terminal leaders. Incidence of leader mortality is greatest for canopy-emergent red spruce or trees with exposed crowns, similar to patterns described for radial growth. This relationship suggests that the post-1960 decline of red spruce on Whiteface Mountain is caused, at least in part, by stresses that act directly on the crown.
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Misik, Tamás, Imre Kárász e Béla Tóthmérész. "Understory Development in an Oak Forest in Northern -Hungary: the Subcanopy Layer". Acta Silvatica et Lignaria Hungarica 10, n. 1 (1 settembre 2014): 9–21. http://dx.doi.org/10.2478/aslh-2014-0001.
Testo completoAbstract (sommario):
Abstract Structural changes in the shrub layer were analysed in a Hungarian oak forest after the oak decline pandemics. This paper focuses on the following questions: (1) which of the woody species tolerated better the forest conditions after oak decline? (2) What are the ecological factors that explain the successful response of woody species to changes in light and thermal conditions? In the monitoring plot, the structural condition of specimens only above 8.0 m was observed. After the appearance of oak decline some Acer campestre, Cornus mas and Acer tataricum specimens appeared that reached between 8.0-13.0 m in height. Significant differences were revealed between top canopy density and foliage cover of the subcanopy and between top canopy density and mean cover of field maple. The findings of the study indicate that the forest responded to oak decline with significant structural rearrangement in the shrub layer and that three woody species compensated for the remarkable foliage loss in the top canopy. These species formed a second crown layer directly below the canopy formed by oaks.
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Sands, PJ. "Modelling Canopy Production. I. Optimal Distribution of Photosynthetic Resources". Functional Plant Biology 22, n. 4 (1995): 593. http://dx.doi.org/10.1071/pp9950593.
Testo completoAbstract (sommario):
On the basis of detailed numerical simulations, Field (1983. Oecologia 56, 341-347) stated that total canopy photosynthesis will be a maximum for a fixed total canopy leaf nitrogen provided the derivative δA/δN, where A is photosynthetic rate and N is leaf nitrogen concentration, has the same value throughout the canopy. This paper uses the calculus of variations to formally prove Field's assertion. It shows that if the single-leaf light response is a first-degree homogeneous function of both light-saturated photosynthetic rate Amax and intensity I of photosynthetically active radiation and if Amax is linearly related to N, then the optimal distribution of leaf nitrogen is linearly related to the decline in I with canopy depth, and Amax is proportional to this decline. The nature of photosynthetic gains due to optimisation of canopy nitrogen distribution is illustrated numerically for a simple model canopy. It is found that, for canopies with fixed mean leaf nitrogen, canopy photosynthesis is approximately proportional to canopy leaf area index (LAI), and the gain due to canopy optimisation compared with a uniform canopy is small for shallow canopies but pronounced for deep canopies. It is also found that, for canopies with fixed total leaf nitrogen, there is a canopy LAI which maximises canopy photosynthesis, and that this LAI and the corresponding canopy photosynthesis are approximately proportional to total canopy nitrogen.
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Berdugo, Monica B., e Martin Dovciak. "Bryophytes in fir waves: Forest canopy indicator species and functional diversity decline in canopy gaps". Journal of Vegetation Science 30, n. 2 (marzo 2019): 235–46. http://dx.doi.org/10.1111/jvs.12718.
Testo completo
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O'Grady, A. P., D. Worledge, A. Wilkinson e M. Battaglia. "Photosynthesis and respiration decline with light intensity in dominant and suppressed Eucalyptus globulus canopies". Functional Plant Biology 35, n. 6 (2008): 439. http://dx.doi.org/10.1071/fp08127.
Testo completoAbstract (sommario):
Within canopy gradients in light-saturated photosynthesis (Amax), foliar nitrogen ([N]area) and leaf dark respiration (R15) were studied in the canopies of dominant and suppressed trees within an even-aged (4-year-old) Eucalyptus globulus (Labill) stand in southern Tasmania. Despite being an even-aged stand growing in a relatively uniform environment with respect to nutrient and water availability, the stand exhibited considerable structural complexity. Diameter at 1.3 m ranged between 3 cm and 21 cm, trees average 12 m height and stand leaf area index was ~6 m2 m–2 leading to strong gradients in light availability. We were interested in understanding the processes governing canopy production in trees of contrasting dominance classes. Vertical gradients in photosynthesis and foliar respiration were studied within the canopies of dominant and suppressed trees during 2006 and 2007. Amax varied from ~18 μmol m–2 s–1 in the upper canopy to 3 μmol m–2 s–1 at lower canopy positions. On average, Amax were higher in the dominant trees than in the suppressed trees. However, at any given height, Amax were similar in suppressed and dominant trees and were strongly related to leaf nitrogen content. Dark respiration varied from ~1.4 μmol m–2 s–1 in the upper canopy to 0.2 μmol m–2 s–1 in the lower canopy positions. In contrast to the patterns for Amax, dark respiration rates in the suppressed trees were higher than dominant trees at similar canopy positions. Respiration rates were also strongly related to [N]area and to Amax.
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Miranda, Eduardo Jacusiel, George L. Vourlitis, Nicolau Priante Filho, Pedro Correto Priante, José Holanda Campelo, George Sanches Suli, Clóvis Lasta Fritzen, Francisco de Almeida Lobo e Shozo Shiraiwa. "Seasonal variation in the leaf gas exchange of tropical forest trees in the rain forest–savanna transition of the southern Amazon Basin". Journal of Tropical Ecology 21, n. 4 (27 giugno 2005): 451–60. http://dx.doi.org/10.1017/s0266467405002427.
Testo completoAbstract (sommario):
The photosynthetic light response of Amazonian semi-deciduous forest trees of the rain forest–savanna transition near Sinop Mato Grosso, Brazil was measured between July 2000 and September 2003 to test the hypothesis that the photosynthetic capacity of trees acclimated to different growth light environments will decline during the dry season. Maximum photosynthesis (Amax) and stomatal conductance (gmax) were significantly higher during the wet season; however, the physiological response to drought was not a clear function of growth light environment. For some species, such as Psychotria sp. growing in the mid-canopy, internal leaf CO2 concentration (Ci) was >30% lower during the dry season suggesting that declines in Amax were caused in part by stomatal limitations to CO2 diffusion. For other species, such as Brosimum lactescens growing at the top of the canopy, Tovomita schomburgkii growing in the mid-canopy, and Dinizia excelsa growing in the understorey, dry season Ci declined by <20% suggesting that factors independent of CO2 diffusion were more important in limiting Amax. Dry-season declines in gmax appeared to be important for maintaining a more consistent leaf water potential for some species (T. schomburgkii and D. excelsa) but not others (Psychotria sp.). These results indicate that while seasonal drought exerts an important limitation on the physiological capacity of semi-deciduous Amazonian forest trees, the mechanism of this limitation may differ between species.
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Strauss, Megan K. L., e Craig Packer. "Did the elephant and giraffe mediate change in the prevalence of palatable species in an East African Acacia woodland?" Journal of Tropical Ecology 31, n. 1 (8 dicembre 2014): 1–12. http://dx.doi.org/10.1017/s0266467414000625.
Testo completoAbstract (sommario):
Abstract:We report on a 2009 survey of Acacia woodlands in the Seronera area of central Serengeti, Tanzania, and compare the results to previous surveys from the 1970s–1980s. We document a substantial change in woodland structure and composition. From 1978 to 2009, woody plant density (mean ± SD) declined from 255 ± 35 trees ha−1 to 147 ± 14 trees ha−1. Canopy cover declined from 15.1 ± 1.9% to 5.7 ± 0.6%. Canopy volume declined from 1810 ± 207 m3 ha−1 to 1410 ± 121 m3 ha−1. A 19% increase in the relative canopy volume of Acacia robusta, a species avoided by the giraffe, represents a sharp decline in the quality of the giraffe's food supply, which was last comprehensively assessed in 1978. We examine these changes in the context of Pellew's 1983 woodland dynamics model describing the impacts of elephant, giraffe and fire on an Acacia tortilis tree population and determine that our data are qualitatively consistent with this model. We hypothesize that selective elephant and giraffe browsing has contributed to an increase in the relative dominance of unpalatable species, consistent with Pellew's predictions.
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Schaberg, Paul G., Paul E. Hennon, David V. D'Amore, Gary J. Hawley e Catherine H. Borer. "Seasonal differences in freezing tolerance of yellow-cedar and western hemlock trees at a site affected by yellow-cedar decline". Canadian Journal of Forest Research 35, n. 8 (1 agosto 2005): 2065–70. http://dx.doi.org/10.1139/x05-131.
Testo completoAbstract (sommario):
To assess whether inadequate cold hardiness could be a contributor to yellow-cedar (Chamaecyparis nootkatensis (D. Don) Spach) decline, we measured the freezing tolerance of foliage from yellow-cedar trees in closed-canopy (nondeclining) and open-canopy (declining at elevations below 130 m) stands at three sites along an elevational gradient in the heart of the decline in southeastern Alaska. Foliar freezing tolerance was also assessed for sympatric nondeclining western hemlock (Tsuga heterophylla (Raf.) Sarg.). Measurements were made in the fall, winter, and spring to evaluate if seasonal differences in cold hardiness help explain species-specific injury. Significant differences in freezing tolerance attributable to site, canopy closure, species, and the interaction of canopy closure and species were each detected for at least one sample period. However, only two results were consistent with field reports of yellow-cedar decline: (1) between winter and spring measurements, yellow-cedar trees dehardened almost 13 °C more than western hemlock trees, so that yellow-cedar trees were more vulnerable to foliar freezing injury in spring than western hemlock; and (2) stands below 130 m appeared more vulnerable to freezing injury than stands above 130 m.
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Reekie, E. G., e P. Wayne. "Leaf canopy display, stomatal conductance, and photosynthesis in seedlings of three tropical pioneer tree species subjected to drought". Canadian Journal of Botany 70, n. 12 (1 dicembre 1992): 2334–38. http://dx.doi.org/10.1139/b92-292.
Testo completoAbstract (sommario):
Seedlings of Piper aurtitum, Cecropia obtusifolia, and Trichospermum mexicanum, pioneer species of lowland tropical rainforests, were subjected to controlled drought cycles, with stomatal conductance and net photosynthesis monitored to determine species response. The affect of soil moisture on canopy display and the response of stomatal conductance to fluctuations in humidity, light, and temperature were also measured. Stomatal conductance and photosynthesis in Piper and Cecropia showed no relationship with soil moisture until it declined to approximately 20%. At higher soil moistures, stomatal conductance in Piper and Cecropia was positively correlated with relative humidity. In contrast, Trichospermum stomatal conductance and photosynthesis showed no relationship with relative humidity and declined gradually as soil moisture decreased. Canopy display in all three species showed a sharp decline at the end of the drought cycle. There were marked differences among species in canopy structure. Piper and Cecropia both have large leaves and a low fibre content in stems, petioles, and leaves, whereas Trichospermum has much smaller leaves and a higher fibre content. In addition, Piper has a higher leaf to stem ratio than Trichospermum. Differences among species in response of stomatal conductance and photosynthesis to environmental factors may reflect the need to maintain a relatively high turgor pressure in Piper and Cecropia for canopy display. Key words: canopy architecture, drought stress, leaf size, Piper auritum, Cecropia obtusifolia, Trichospermum mexicanum.
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Awada, T., M. E. L. Perry e W. H. Schacht. "Photosynthetic and growth responses of the C3 Bromus inermis and the C4 Andropogon gerardii to tree canopy cover". Canadian Journal of Plant Science 83, n. 3 (1 luglio 2003): 533–40. http://dx.doi.org/10.4141/p02-129.
Testo completoAbstract (sommario):
Agroforestry systems are designed to improve the efficiency of use of available resources and to increase potential site productivity. The capability of a plant to acclimate to shade when cultivated beneath trees is important in determining the success of agroforestry projects. The objectives of this study were to determine the morphological, physiological and growth responses of C4big bluestem ( Andropogon gerardii Vitman.) and C3smooth bromegrass ( Bromus inermis Leyss) to various canopy levels of green ash ( Fraxinus pennsylvanica Marsh) in the field, and to examine the impacts of these responses on grass yield. Net photosynthesis (Anet), stomatal conductance (gs), and dark respiration (Rd) declined in response to shade in both species, but the decline was steeper in big bluestem than in smooth bromegrass. Total chlorophyll content (Tchl), specific leaf area (SLA), and N content of the leaves increased with shade in both species. In addition, Tchl, SLA, N, and gs were significantly greater in smooth bromeg r ass than in big bluestem at all canopy levels. Lower gs and N, and higher Anet in big bluestem resulted in a higher water and N use efficiencies in this species than in smooth bromegrass. Yield of big bluestem sharply declined with increased canopy cover, whereas yield of smooth bromegrass was not affected by canopy cover. Our results indicate that while both species were productive under various levels of green ash canopy, and showed similar ecophysiological responses to shade, smooth bromegrass acclimate d better to shade than big bluestem. Key words:
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Rankin, W. T., e Elliot J. Tramer. "Understory succession and the gap regeneration cycle in a Tsuga canadensis forest". Canadian Journal of Forest Research 32, n. 1 (1 gennaio 2002): 16–23. http://dx.doi.org/10.1139/x01-168.
Testo completoAbstract (sommario):
We examined understory succession in current and former canopy gaps in mature Tsuga canadensis (L.) Carrière forests in southeastern Ohio. First, we reconstructed understory succession in current gaps by sampling 28 gaps ranging from 0 to 9 years. Second, we reconstructed the gap history of a single Tsuga community by clustering release events evident in the growth rings of 156 trees. The two reconstructions formed an 80-year chronosequence, allowing us to examine both short-term effects of gaps as well as long-term effects of closed-canopy conditions on eight common understory species. Understory cover was highest in canopy gaps. All eight understory species in the study exhibited higher cover in canopy gaps than beneath the closed Tsuga canopy. In addition, one species increased percent biomass allocated towards shoots. Although most species increased cover in gaps, different species reached peak cover at different times during gap succession. Understory species reaching peak cover early in the life of the gap were also present beneath the closed canopy and invested primarily in lateral biomass. Understory species reaching peak cover late in the life of the gap, however, were confined to gaps and invested primarily in vertical biomass. Understory cover declined during gap closure; this decline was most pronounced 20 years following gap formation. Thereafter, total understory cover increased slightly, although never to gap levels.
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Shi, Rongkai, Hao Sun, Wei Qiu, Xiaolan Lv, Fiaz Ahmad, Jiabing Gu, Hongfeng Yu e Zhengwei Zhang. "Analysing Airflow Velocity in the Canopy to Improve Droplet Deposition for Air-Assisted Spraying: A Case Study on Pears". Agronomy 12, n. 10 (6 ottobre 2022): 2424. http://dx.doi.org/10.3390/agronomy12102424.
Testo completoAbstract (sommario):
The suitability of airflow velocity in airborne spraying operations in orchards is mostly evaluated on the basis of inlet and outlet based on the airflow velocity at the canopy. However, the airflow velocity required to penetrate into the inner layer of the canopy, which is prone to pests and diseases, is still unclear due to variation in the geometry of the plant canopies. In this study, pear trees were selected as an example to explore the variations in the law of airflow attenuation in the inner canopy. Furthermore, we examine mist droplet formation in the inner canopy to determine a suitable inner canopy airflow end velocity (ICAEV) for air-assisted application. We also conducted a field validation test. The results showed that the majority of airflow velocity loss occurred in the middle and outer part of the canopy; rapid decline of airflow occurred in the 0–0.3 m section, whereas the slow decline of airflow occurred in the 0.3–0.8 m section. When the ICAEV is in the range of 2.70–3.18 m/s, the spraying effect is better. The droplet deposition variation coefficient was 42.25% compared with 51.25% in the conventional airflow delivery mode. Additionally, the droplet drift was reduced by 12.59 μg/cm2. The results of this study can identify a suitable ICAEV for air-assisted spraying in orchards.
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Pangle, Robert, Kathleen Kavanagh e Remko Duursma. "Decline in canopy gas exchange with increasing tree height, atmospheric evaporative demand, and seasonal drought in co-occurring inland Pacific Northwest conifer species". Canadian Journal of Forest Research 45, n. 8 (agosto 2015): 1086–101. http://dx.doi.org/10.1139/cjfr-2014-0551.
Testo completoAbstract (sommario):
Interspecific variation in stomatal conductance (GS) and transpiration (EL) has been documented in stands of co-occurring species, and this variation has been observed to differ with tree size and canopy height increase. In this study, we present data that examine fluctuations in canopy gas exchange across co-occurring species and varying canopy heights for three montane forest chronosequences located in an inland Pacific Northwest mixed-conifer forest. With the exception of Douglas-fir (Pseudotsuga menziesii var. glauca (Beissn.) Franco), we observed consistent declines in canopy EL and GS with increasing height for the majority of species examined in our 2-year study. Along with declines in canopy GS, we observed decreases in leaf-specific hydraulic conductance (KL) across species as canopy height increased. Seasonally, we observed declines in canopy GS during warmer and dryer summer months of both years. These decreases in GS were significant (up to 50%) and suggest that carbon assimilation in trees was limited during dryer months due to a combination of high evaporative demand and reduced soil H2O availability. Such reductions in GS during periods of increased plant water stress suggest that forest productivity in the inland Pacific Northwest may be impacted negatively if future climate predictions of increasing growing-season water stress are realized.
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Perkins, T. D., R. M. Klein, G. J. Badger e M. J. Easter. "Spruce–fir decline and gap dynamics on Camels Hump, Vermont". Canadian Journal of Forest Research 22, n. 4 (1 aprile 1992): 413–22. http://dx.doi.org/10.1139/x92-054.
Testo completoAbstract (sommario):
Widespread and conspicuous dieback of red spruce (Picearubens Sarg.) accompanied by asymptomatic declines in balsam fir (Abiesbalsamea (L.) Mill.) and white birch (Betulapapyrifera var. cordifolia (Regel.) Fern.) trees on Camels Hump, Vermont, prompted an investigation into the role of spruce–fir decline on gap expansion, tree health, and regeneration dynamics. Forty percent of the study area on Camels Hump was occupied by recent forest gaps in the summer of 1989. Gaps were growing northwesterly (direction 322°) at a rate of 0.8–1.2 m•year−1. Prevailing winds in the study area are from the south-southeast. Gap expansion appears to play a dominant role in continuing forest disturbance. Red spruce vigor was low in all dominance classes (53% foliar retention), while vigor of balsam fir and birch (yellow (Betulaalleghaniensis Britt.) and white) was somewhat higher. Exposure and wind flagging of different tree species within the same crown dominance classes were similar, but apical foliar damage was greater in spruce than in fir or birch. Red spruce and birch trees were older than balsam fir within comparable crown classes. Wind flagging was significantly correlated with crown exposure in red spruce and balsam fir, while diameter was the most important factor related to flagging in birch. All three species tended to die while standing. Dead balsam fir trees were twice as likely as red spruce to have been windthrown or diseased, whereas dead red spruce showed a much higher incidence of past and present insect infestation. Live birch had low levels of biotic damage. Density of red spruce seedlings was low within gaps and adjacent canopy sites. Balsam fir seedling density was significantly higher in the canopied areas, whereas birch density was marginally higher in gap areas. There were no significant differences in ages of spruce or fir seedlings growing in gaps and closed canopy areas. Birch seedlings in gaps were older and taller than those under the canopy, indicating low survivorship of birch under the forest canopy. It is likely that this forest will be predominantly composed of balsam fir and birch in the near future.
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Perkins, T. D., H. W. Vogelmann e R. M. Klein. "Changes in light intensity and soil temperature as a result of forest decline on Camels Hump, Vermont". Canadian Journal of Forest Research 17, n. 6 (1 giugno 1987): 565–68. http://dx.doi.org/10.1139/x87-094.
Testo completoAbstract (sommario):
Light intensity, measured by the anthracene–benzene technique, significantly increased in the montane boreal forest of Camels Hump mountain, Vermont, since the mid- 1960's. The region of increased light corresponds to those elevations where red spruce (Picearubens Sarg.) has declined significantly over the same time period. Soil temperature measured at 15 cm has increased and there is higher week-to-week variability than in the 1960's, especially where canopy decline is most severe.
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Perkins, T. D., R. M. Klein, H. W. Vogelmann e G. J. Badger'. "Betula seedling establishment in response to forest decline induced canopy degeneration". Forest Pathology 18, n. 3-4 (giugno 1988): 250–52. http://dx.doi.org/10.1111/j.1439-0329.1988.tb00924.x.
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Pfeifer, Marion, Michael J. W. Boyle, Stuart Dunning e Pieter I. Olivier. "Forest floor temperature and greenness link significantly to canopy attributes in South Africa’s fragmented coastal forests". PeerJ 7 (10 gennaio 2019): e6190. http://dx.doi.org/10.7717/peerj.6190.
Testo completoAbstract (sommario):
Tropical landscapes are changing rapidly due to changes in land use and land management. Being able to predict and monitor land use change impacts on species for conservation or food security concerns requires the use of habitat quality metrics, that are consistent, can be mapped using above-ground sensor data and are relevant for species performance. Here, we focus on ground surface temperature (Thermalground) and ground vegetation greenness (NDVIdown) as potentially suitable metrics of habitat quality. Both have been linked to species demography and community structure in the literature. We test whether they can be measured consistently from the ground and whether they can be up-scaled indirectly using canopy structure maps (Leaf Area Index, LAI, and Fractional vegetation cover, FCover) developed from Landsat remote sensing data. We measured Thermalground and NDVIdown across habitats differing in tree cover (natural grassland to forest edges to forests and tree plantations) in the human-modified coastal forested landscapes of Kwa-Zulua Natal, South Africa. We show that both metrics decline significantly with increasing canopy closure and leaf area, implying a potential pathway for upscaling both metrics using canopy structure maps derived using earth observation. Specifically, our findings suggest that opening forest canopies by 20% or decreasing forest canopy LAI by one unit would result in increases of Thermalground by 1.2 °C across the range of observations studied. NDVIdown appears to decline by 0.1 in response to an increase in canopy LAI by 1 unit and declines nonlinearly with canopy closure. Accounting for micro-scale variation in temperature and resources is seen as essential to improve biodiversity impact predictions. Our study suggests that mapping ground surface temperature and ground vegetation greenness utilising remotely sensed canopy cover maps could provide a useful tool for mapping habitat quality metrics that matter to species. However, this approach will be constrained by the predictive capacity of models used to map field-derived forest canopy attributes. Furthermore, sampling efforts are needed to capture spatial and temporal variation in Thermalground within and across days and seasons to validate the transferability of our findings. Finally, whilst our approach shows that surface temperature and ground vegetation greenness might be suitable habitat quality metric used in biodiversity monitoring, the next step requires that we map demographic traits of species of different threat status onto maps of these metrics in landscapes differing in disturbance and management histories. The derived understanding could then be exploited for targeted landscape restoration that benefits biodiversity conservation at the landscape scale.
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Navarro-Cerrillo, Rafael M., Jesus Beira, Juan Suarez, Georgios Xenakis, Raúl Sánchez-Salguero e Rocío Hernández-Clemente. "Growth decline assessment in Pinus sylvestris L. and Pinus nigra Arnold. forest by using 3-PG model." Forest Systems 25, n. 3 (2 dicembre 2016): e068. http://dx.doi.org/10.5424/fs/2016253-08610.
Testo completoAbstract (sommario):
Aim of the study: We assessed the ability of the 3-PG process-based model to accurately predict growth of Pinus sylvestris and P. nigra plantations across a range of sites, showing declining growth trends, in southern Spain.Area of study: The study area is located in “Sierra de Los Filabres” (Almería).Material and methods: The model was modified in fifteen parameters to predict diameter (DBH, cm), basal area increment (BAI, cm2 yr-1) and leaf area index (LAI, m2 m-2) in healthy trees and trees showing declining growth. We assumed that a set of specific physiological parameters (stem partitioning ratio-pFS20, maximum litterfall rate-γFx, maximum canopy conductance-gCx, specific leaf area for mature aged stands-σ1, age at which specific leaf area = ½ (σ0 + σ1), age at full canopy cover-tc, and canopy boundary layer conductance-gB) included in 3-PG would be suitable for predicting growth decline related to climate conditions. The calibrated model was evaluated using dendrochronological and LAI data obtained from plots.Main results: Observed and simulated DBH showed a high correlation (R2 > 0.99) between modelled and measured values for both species. In contrast, modelled and observed BAI showed lower correlation (R2 < 0.68). Sensitivity analysis on 3-PG outputs showed that the foliage parameters - maximum litterfall rate, maximum canopy conductance, specific leaf area for mature aged stands, age at which specific leaf area, and age at full canopy cover - were important for DBH and BAI predictions under drought stress.Research highlights: Our overall results indicated that the 3-PG model could predict growth response of pine plantations to climatic stress with desirable accuracy in southern Spain by using readily available soil and climatic data with physiological parameters derived from experiments.Keywords: Hybrid process model; forest management models; growth prediction; Pinus spp, Parameterization; forest decline.
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Jain, Theresa B., Russell T. Graham e Penelope Morgan. "Western white pine growth relative to forest openings". Canadian Journal of Forest Research 34, n. 11 (1 novembre 2004): 2187–98. http://dx.doi.org/10.1139/x04-094.
Testo completoAbstract (sommario):
In northern Rocky Mountains moist forests, timber harvesting, fire exclusion, and an introduced stem disease have contributed to the decline in western white pine (Pinus monticola Dougl. ex D. Don) abundance (from 90% to 10% of the area). Relations between canopy openings (0.1–15 ha) and western white pine growth within different physical settings are identified. Objectives include relating western white pine seedling and sapling growth to canopy opening attributes (defined by fisheye photography), identifying western white pine competitive thresholds (occupancy, competitive advantage, free-to-grow status) in relation to opening size, and relating canopy opening attributes to overstory density descriptors. We sampled 620 western white pine plus competing trees, canopy opening characteristics, landscape position, and overstory density descriptors. Analysis included log-linear and polynomial regression. Visible sky (canopy opening) and tree age were significantly related to growth of selected pines. Radiation explained less variation in growth than canopy opening. Thresholds for western white pine to occupy a site (>23% canopy opening), gain a competitive advantage (>50% canopy opening), and achieve free-to-grow status (>92% canopy opening) over western hemlock were developed. There was a significant although weak (R2 < 0.12) relation between canopy opening and overstory density descriptors.
22
Bliss, Aimee, Lynda D. Prior e David M. J. S. Bowman. "Lack of reliable post-fire recovery mechanisms makes the iconic Tasmanian conifer Athrotaxis cupressoides susceptible to population decline". Australian Journal of Botany 69, n. 3 (2021): 162. http://dx.doi.org/10.1071/bt20117.
Testo completoAbstract (sommario):
Athrotaxis cupressoides is an iconic Tasmanian palaeoendemic conifer that is vulnerable to fire. A survey of three populations burnt by severe fire in 2016, conducted 1year post-fire, found 33% of stems were still alive, with many surviving stems suffering some canopy scorch. We re-surveyed these populations to quantify delayed mortality, resprouting, and presence of juveniles, and to determine whether fire impacts can be reliably assessed after 1year. We applied three measures of fire severity: canopy scorched, canopy consumed, and the minimum burnt twig diameter of neighbouring shrubs. We found overall stem survival in 2020 was 31%, and that 97% of stems that were dead 4years post-fire had died within the first year. Our best predictor of stem mortality was percentage canopy scorched. Overall, 1.8% of burnt stems resprouted, but severely burnt stems did not resprout. Juveniles were present ~9.9% of burnt trees in 2017, and only 1.8% in 2020. We conclude that A. cupressoides stems are not unusually fire sensitive, but rather, that the species’ vulnerability to severe fire results from its lack of reliable recovery mechanisms. This study shows that fire-caused mortality can be reliably assessed 1year post-fire, and possibly earlier. Interventions such as sowing seed or transplanting seedlings could be necessary to re-establish fire-killed populations.
23
Battles, John J., e Timothy J. Fahey. "Spruce decline as a disturbance event in the subalpine forests of the northeastern United States". Canadian Journal of Forest Research 26, n. 3 (1 marzo 1996): 408–21. http://dx.doi.org/10.1139/x26-046.
Testo completoAbstract (sommario):
During the last 2 decades red spruce (Picearubens Sarg.) trees have died at high rates in the mountains of New York and New England. Given the importance of disturbance in organizing plant communities, the impact of the decline was evaluated in terms of its effect on disturbance processes. The first step was to describe the current disturbance regime in subalpine forests across the region. Canopy gaps were the predominant mode of disturbance. Estimates of gap-phase disturbance in four old-growth sites ranged from 15% to 42% of the total forested area. Gap abundance varied between 19 and 49 gaps/ha. A constant among the sites was that dead spruce trees accounted for more of the gap area than expected considering their abundance in the canopy. In the spruce–fir forest, most gaps were small (<100 m2). Gaps were not shaped like simple geometric figures but rather like irregular polygons. Forty percent of the canopy gaps were created by the death of a single tree; the rest were multitree gaps. Standing dead trees were the most common damage type. It seems that decline of spruce effected a quantitative but not qualitative shift in the disturbance regime.
24
Uddin, Jasim, Rod Smith, Nigel Hancock e Joseph Foley. "Evaluation of Sap Flow Sensors to Measure the Transpiration Rate of Plants during Canopy Wetting and Drying". Journal of Agricultural Studies 2, n. 2 (14 agosto 2014): 105. http://dx.doi.org/10.5296/jas.v2i2.6134.
Testo completoAbstract (sommario):
Accurate measurement of transpiration is required to estimate the various components of evaporation losses during sprinkler irrigation. Among the methods, sap flow measurements have widely used for direct measurements of transpiration rate in plant. To evaluate the applicability of this method to field experiments involving canopy wetting (by sprinkler irrigation), stem flow measurements were compared with transpiration values estimated from successive mass measurements of small potted plants using pre-calibrated mini-lysimeters in a glasshouse at the University of Southern Queensland, during the period August–October 2010. From this study it was found that when the canopy was dry, the sap flow measurements mirrored the transpiration rate of plants with reasonable accuracy, overestimating the transpiration rate by about 11%. The measurements showed no evidence of time lag between sap flow and transpiration. Following wetting of the plant canopy the sap flow declined rapidly reflecting a decline in the transpiration rate transpiration and sap flow. Location of the sap flow gage on the stem was seen to be a factor with gages at different heights giving different sap flow rates again due to the buffering capacity of the stem.
25
Ferretti, Marco, Giovanni Bacaro, Giorgio Brunialti, Marco Calderisi, Luc Croisé, Luisa Frati e Manuel Nicolas. "Tree canopy defoliation can reveal growth decline in mid-latitude temperate forests". Ecological Indicators 127 (agosto 2021): 107749. http://dx.doi.org/10.1016/j.ecolind.2021.107749.
Testo completo
26
Taylor, Anthony R., Meelis Seedre, Brian W. Brassard e Han Y. H. Chen. "Decline in Net Ecosystem Productivity Following Canopy Transition to Late-Succession Forests". Ecosystems 17, n. 5 (5 marzo 2014): 778–91. http://dx.doi.org/10.1007/s10021-014-9759-3.
Testo completo
27
MacInnis, Gail, David Greene, Jason Straka e Peter Kevan. "Filtração de partículas através do dossel de uma floresta tropical úmida". Boletim do Museu Paraense Emílio Goeldi - Ciências Naturais 9, n. 3 (11 febbraio 2021): 455–63. http://dx.doi.org/10.46357/bcnaturais.v9i3.502.
Testo completoAbstract (sommario):
Understanding the dinamics of filtration of pollen and spores by plant canopies is crucial to the in the modelling of their dispersal, yet few studies have quantified filtration. Here, we examine the decline in the density of flour particles descending through a 40 m-tall tropical canopy on a windless day at Caxiuanã National Forest, Pará, Brazil. Using these data and estimates of canopy leaf density, we also tested one of the few existing models for the effect of impaction. The Bache model, which incorporates particle and vegetation structure, probability of particle transmission and the probability of impaction, explained approximately 93% of the variation in flour granules captured on passive samplers placed throughout the canopy. The canopy filtered 99.65% of the flour released, but a significant amount of small particles were captured at the forest floor. These findings suggest that the rarity of anemophily seen in the tropics may be more a result of high species richness than high canopy density.
28
Jones-Held, Susan, Michael Held, Joe Winstead e William Bryant. "Immediate and Delayed Effects of Severe Winds on an Old-Growth Forest in Kentucky: A Forty-Year Retrospective". Forests 10, n. 3 (19 marzo 2019): 271. http://dx.doi.org/10.3390/f10030271.
Testo completoAbstract (sommario):
Wind disturbance is an important factor that can affect the development of the forests of the Central Hardwood Region of the United States. However, there have been few long-term studies of the recovery of these systems following wind damage. Long-term studies of protected forest systems, such as Dinsmore Woods in Northern Kentucky, within the fragmented forest of this region are valuable as they provide a resource to document and understand the effect of both abiotic and biotic challenges to forest systems. This study is a 40-year analysis of both overstory and understory changes in the forest system at Dinsmore Woods as the result of damage caused by severe winds in the spring of 1974. The forest was surveyed before and immediately following the windstorm and then at 10-year intervals. Although the windstorm had an immediate effect on the forest, the pattern of damage was complex. The forest canopy (diameter at breast height (DBH) ≥ 30 cm) experienced an irregular pattern of damage while in the subcanopy (DBH ≤ 30 cm) there was a 25% reduction in total basal area. However, the major effects of the windstorm were delayed and subsequently have altered forest recovery. Ten years following the disturbance declines were seen in total density and basal area in the canopy and subcanopy of the forest as a consequence of windstorm damage. In the past 20 years the total basal area of the canopy has increased and exceeds the pre-disturbance total basal area. In contrast, the subcanopy total basal area continued to decline 20 years post-disturbance and has not recovered. Further openings in the canopy and subcanopy due to the delayed windstorm effects helped to establish a dense understory of native shrubs and sugar maple which have affected tree regeneration and is reflected in the continual decline in species diversity in the subcanopy and sapling strata over the 40-year period.
29
Salgadoe, Arachchige Surantha Ashan, Andrew James Robson, David William Lamb e Elizabeth Kathryn Dann. "Assessment of Canopy Porosity in Avocado Trees as a Surrogate for Restricted Transpiration Emanating from Phytophthora Root Rot". Remote Sensing 11, n. 24 (11 dicembre 2019): 2972. http://dx.doi.org/10.3390/rs11242972.
Testo completoAbstract (sommario):
Phytophthora root rot (PRR) disease is a major threat in avocado orchards, causing extensive production loss and tree death if left unmanaged. Regular assessment of tree health is required to enable implementation of the best agronomic management practices. Visual canopy appraisal methods such as the scoring of defoliation are subjective and subject to human error and inconsistency. Quantifying canopy porosity using red, green and blue (RGB) colour imagery offers an objective alternative. However, canopy defoliation, and porosity is considered a ‘lag indicator’ of PRR disease, which, through root damage, incurs water stress. Restricted transpiration is considered a ‘lead indicator’, and this study sought to compare measured canopy porosity with the restricted transpiration resulting from PRR disease, as indicated by canopy temperature. Canopy porosity was calculated from RGB imagery acquired by a smartphone and the restricted transpiration was estimated using thermal imagery acquired by a FLIR B250 hand-held thermal camera. A sample of 85 randomly selected trees were used to obtain RGB imagery from the shaded side of the canopy and thermal imagery from both shaded and sunlit segments of the canopy; the latter were used to derive the differential values of mean canopy temperature (Δ Tmean), crop water stress index (Δ CWSI), and stomatal conductance index (Δ Ig). Canopy porosity was observed to be exponentially, inversely correlated with Δ CWSI and Δ Ig (R2 > 90%). The nature of the relationship also points to the use of canopy porosity at early stages of canopy decline, where defoliation has only just commenced and detection is often beyond the capability of subjective human assessment.
30
Airi, Subodh, e Ranbeer S. Rawal. "Patterns of vegetation composition across levels of canopy disturbance in temperate forests of west Himalaya, India". Biodiversity Research and Conservation 45, n. 1 (26 gennaio 2017): 27–33. http://dx.doi.org/10.1515/biorc-2017-0004.
Testo completoAbstract (sommario):
AbstractThis study analyses the impacts of canopy disturbance on vegetation compositional attributes of two characteristic temperate forests (i.e., mixed broad-leaf and banj-oak forests) in west Himalayan part of India. Following the standard approaches, quantitative information on compositional attributes of forest vegetation was generated and analyzed. Considerable changes in these attributes were revealed across different levels of canopy disturbance in both forests. In particular, tree density and total basal area (TBA) exhibited significant decline from undegraded to degraded stands. Among others, seedling and sapling density of mixed broad-leaf forest was affected adversely by increased level of canopy disturbance. However, herb density in this forest increased significantly with increasing levels of disturbance; the same was not true for banj-oak forest. A significant decline in relative frequency and density of native herbaceous species was apparent towards degraded stands, implying that the disturbed sites in both forests created an opportunity for the establishment and proliferation of non-natives. However, with significant increase in relative density of non-native herbs, the degraded stands of banj-oak forest emerged as critically vulnerable to non-native proliferation. The patterns of tree size class distribution in both forests also exhibited certain trends across canopy disturbance, which suggested possible future changes in composition. In particular, the patterns of common tree associates (i.e., Myrica esculenta and Rhododendron arboreum) in banj-oak forest and Pinus roxburghii in mixed broad-leaf forest were indicative of likely compositional changes in near future. The study concludes that: (i) compositional attributes of both mixed broad-leaf and banj-oak forests were sensitive to increasing levels of canopy disturbance, (ii) mixed broad-leaf forest exhibited greater sensitivity to canopy disturbance at recruitment levels, (iii) increased canopy disturbance led to establishment and proliferation of non-native species in the herbaceous layer of both forests, and (iv) banj-oak forest exhibited high vulnerability to non-native proliferation at degraded stage.
31
Fallahi, Esmaeil, D. Ross Rodney e Zahra Mousavi. "Growth, Yield, and Fruit Quality of Eight Lemon Cultivars in Arizona". Journal of the American Society for Horticultural Science 115, n. 1 (gennaio 1990): 6–8. http://dx.doi.org/10.21273/jashs.115.1.6.
Testo completoAbstract (sommario):
Tree growth, yield, and fruit quality of eight lemon cultivars [Citrus limon (L.) Burro. f.] on macrophylla (Alemow) (C. macrophylla Wester) rootstock were compared when grown in sandy soil in the arid climate of south-western Arizona. `Foothill Lisbon' had higher cumulative yield and titratable acids than `Monroe Lisbon', `Prior Lisbon', `Eureka', and `Villafranca', and had larger fruit than other `Lisbon' cultivars. `Prior Lisbon' produced a larger tree canopy with lower yield efficiency than all other cultivars and did not show any decline due to sieve tube necrosis 12 years after planting. Overall, `Eureka' cultivars and `Villafranca' had lower relative cumulative yields, canopy volumes, total soluble solids content, titratable acids, and seed content, but higher tree decline than `Lisbon' cultivars. Overall, `Foothill Lisbon', in spite of carrying exocortis viroid, produced good yields and fruit quality and `Prior Lisbon' had a satisfactory growth-performance.
32
Caspari, Horst W., M. Hossein Behhoudian, David J. Chalmers e A. Richard Renquist. "Pattern of Seasonal Water Use of Asian Pears Determined by Lysimeters and the Heat-pulse Technique". Journal of the American Society for Horticultural Science 118, n. 5 (settembre 1993): 562–69. http://dx.doi.org/10.21273/jashs.118.5.562.
Testo completoAbstract (sommario):
Seasonal water use data are presented for 4-year-old Pyrus serotina Rehder cv. Hosui growing in drainage lysimeters and trained onto a Tatura trellis. Weekly water use (WU) was calculated using the mass balance approach. For 8 consecutive weeks during late summer, instantaneous WU was also measured by the compensation heat-pulse technique for measuring sap flow. Although good agreement was found between the two methods for 4 weeks after probe installation, discrepancies increased after this time. Water use was highest in early to mid-January in New Zealand, averaging ≈8 liters/tree per day, or 2 liters·m-2 canopy surface area/day. Total water use over the growing season was 1070 liters/tree, or 245 liters·m-2 canopy surface area. The correlation coefficient between weekly WU and evaporation from a nearby Class A pan was 0.81 for the season. Weekly crop coefficients thus calculated for the well-watered trees ranged from 0.15 to 0.55 and 0.20 to 0.83 when calculated using canopy surface area and projected ground area, respectively. Low values were due to low values of canopy leaf area early in the season. Withholding irrigation during three periods resulted in a gradual decline in water use. Water-stressed trees had a lower predawn water potential than fully irrigated trees. This pattern was followed by a more-rapid decline during the morning, and a slower recovery during late afternoon and early evening. Midday leaf water potential never fell below -2.5 MPa.
33
Turner, Edgar C., e William A. Foster. "The impact of forest conversion to oil palm on arthropod abundance and biomass in Sabah, Malaysia". Journal of Tropical Ecology 25, n. 1 (gennaio 2009): 23–30. http://dx.doi.org/10.1017/s0266467408005658.
Testo completoAbstract (sommario):
Abstract:Deforestation rates in South-East Asia are among the highest of any tropical region, with expansion of oil palm being one important factor. Despite this, few studies have investigated the impact of oil palm expansion on the arthropod fauna. We report here the first study on the impact of forest conversion to oil palm on overall arthropod abundance, biomass and composition. We compared arthropod abundance and biomass, collected from epiphytic bird's nest ferns, the canopy, and leaf litter between primary forest, logged forest and oil palm plantation. Epiphytes, canopy and litter all contained a lower abundance (epiphytes: 67.2%, canopy: 2.3% and litter: 77.1% reduction) and biomass (epiphytes: 87.5%, canopy: 37.9% and litter: 72.4% reduction) of arthropods in oil palm compared with primary forest. However, not all orders of arthropods showed the same level of decline, with some groups having higher abundance and biomass in oil palm, resulting in an altered community composition in the epiphytes and canopy in oil palm compared with forest. Our results show that forest conversion to oil palm impacts detrimentally on invertebrates in all compartments of the forest ecosystem.
34
Sridhara, S., e T. G. Prasad. "RADIATION USE EFFICIENCY, ABOVE GROUND BIOMASS ACCUMULATION, CANOPY DEVELOPMENT, LEAF AREA-LIGHT INTERCEPTION PROFILES AND RADIATION INTERCEPTION OF SUNFLOWER (Helianthus annuus L.) AS INFLUENCED BY IRRIGATION REGIMEN / INFLUENCIA DEL RÉGIMEN DE IRRIGACIÓN SOBRE LA EFICACIA DEL USO DE LA RADIACIÓN, LA ACUMULACIÓN DE BIOMASA, EL DESAROROLLO DEL CANOPEO, EL ÁREA DE LA HOJA Y LOS PERFILES DE INTERCEPCIÓN DE LUZ Y DE RADIACIÓN EN GIRASOL (Helianthus annuus L.) / EFFICACITÉ DE L’UTILISATION DES RADIATIONS SOLAIRES, ACCUMULATION DE LA BIOMASSE DANS LA PARTIE AÉRIENNE, DÉVELOPPEMENT DE L’OMBRELLE, PROFILS D’INTERCEPTION DE LA LUMIÈRE PAR LA FEUILLE ET INTERCEPTION DES RADIATIONS SOLAIRES CHEZ LE TOURNESOL (Helianthus annuus L.) SOUS L’INFLUENCE D’UN RÉGIME D’IRRIGATION". HELIA 24, n. 35 (dicembre 2001): 101–10. http://dx.doi.org/10.1515/helia.2001.24.35.101.
Testo completoAbstract (sommario):
SUMMARYA field experiment was conducted at Gandhi Krishi Vignana Kendra, University of Agricultural Sciences, Bangalore to study the effect of irrigation regimens on the biomass accumulation, canopy development, light interception and radiation use efficiency of sunflower. The treatments includes irrigating the plants at 0.4, 0.6, 0.8 and 1.0 cumulative pan evaporation. The results indicated that the aboveground biomass, canopy development, radiation interception and radiation use efficiency were influenced favorably by the irrigation regimens. Irrespective of the irrigation regimen, the radiation use efficiency of sunflower increased from 15 DAS to 75 DAS and then tended to decline. The decrease in RUE after anthesis is coupled with decrease in leaf nitrogen content. In general the RUE of sunflower ranged from 0.49 g MJ-1 to 1.84 g MJ-1 at different growth stages. The light transmission within the canopy increased exponentially with plant height and the canopy extension coefficient is found to be 0.8.
35
Gavin, Daniel G., Brian Beckage e Benjamin Osborne. "Forest dynamics and the growth decline of red spruce and sugar maple on Bolton Mountain, Vermont: a comparison of modeling methods". Canadian Journal of Forest Research 38, n. 10 (ottobre 2008): 2635–49. http://dx.doi.org/10.1139/x08-106.
Testo completoAbstract (sommario):
Montane forests in the northeastern United States have experienced symptoms of declining vigor, such as branch dieback and increased mortality, over the last half-century. These declines have been attributed to the cumulative impacts of acid deposition, but reconstructing these declines from tree-ring records has proved difficult because of confounding factors that affect low-frequency growth patterns, including climate and natural growth trajectories following disturbance. We obtained tree-ring records of red spruce ( Picea rubens Sarg.) and sugar maple ( Acer saccharum L.) from three elevations on Bolton Mountain, Vermont, and applied traditional dendroclimatological analyses that revealed a profound declining growth–climate correlation since ca. 1970 for sugar maple but much less so for red spruce. We then applied a new multifaceted statistical approach that conservatively detrends tree-ring records by minimizing the influences of tree size, age, and canopy disturbances on radial growth. In contrast with the traditional analysis, this approach yielded chronologies that were consistently correlated with climate but with important exceptions. Low-elevation sugar maple suffered distinct episodes of slow growth, likely because of insect defoliators, and also a progressive decline since ca. 1988. Red spruce experienced subdecadal episodes of decline that may be related to freeze–thaw events known to injure foliage but showed no evidence of a progressive decline. This analysis was supported by a forest plot resurvey that indicated major declines in these species.
36
Fallon, Beth, Anna Yang, Cathleen Lapadat, Isabella Armour, Jennifer Juzwik, Rebecca A. Montgomery e Jeannine Cavender-Bares. "Spectral differentiation of oak wilt from foliar fungal disease and drought is correlated with physiological changes". Tree Physiology 40, n. 3 (6 febbraio 2020): 377–90. http://dx.doi.org/10.1093/treephys/tpaa005.
Testo completoAbstract (sommario):
Abstract Hyperspectral reflectance tools have been used to detect multiple pathogens in agricultural settings and single sources of infection or broad declines in forest stands. However, differentiation of any one disease from other sources of tree stress is integral for stand and landscape-level applications in mixed species systems. We tested the ability of spectral models to differentiate oak wilt, a fatal disease in oaks caused by Bretziella fagacearum ``Bretz'', from among other mechanisms of decline. We subjected greenhouse-grown oak seedlings (Quercus ellipsoidalis ``E.J. Hill'' and Quercus macrocarpa ``Michx.'') to chronic drought or inoculation with the oak wilt fungus or bur oak blight fungus (Tubakia iowensis ``T.C. Harr. & D. McNew''). We measured leaf and canopy spectroscopic reflectance (400–2400 nm) and instantaneous photosynthetic and stomatal conductance rates, then used partial least-squares discriminant analysis to predict treatment from hyperspectral data. We detected oak wilt before symptom appearance, and classified the disease with high accuracy in symptomatic leaves. Classification accuracy from spectra increased with declines in photosynthetic function in oak wilt-inoculated plants. Wavelengths diagnostic of oak wilt were only found in non-visible spectral regions and are associated with water status, non-structural carbohydrates and photosynthetic mechanisms. We show that hyperspectral models can differentiate oak wilt from other causes of tree decline and that detection is correlated with biological mechanisms of oak wilt infection and disease progression. We also show that within the canopy, symptom heterogeneity can reduce detection, but that symptomatic leaves and tree canopies are suitable for highly accurate diagnosis. Remote application of hyperspectral tools can be used for specific detection of disease across a multi-species forest stand exhibiting multiple stress symptoms.
37
Butler, CL, VL Lucieer, SJ Wotherspoon e CR Johnson. "Multi-decadal decline in cover of giant kelp Macrocystis pyrifera at the southern limit of its Australian range". Marine Ecology Progress Series 653 (29 ottobre 2020): 1–18. http://dx.doi.org/10.3354/meps13510.
Testo completoAbstract (sommario):
Knowledge of long-term and multi-scale trends in ecological systems is a vital component in understanding their dynamics. We used Landsat satellite imagery to develop the first long-term (1986-2015) data set describing the cover of dense surface canopies of giant kelp Macrocystis pyrifera around the entire coastline of Tasmania, Australia, and assessed the extent to which potential environmental drivers explain the dynamics of surface canopies at multiple spatial and temporal scales. Broad-scale temporal patterns in canopy cover are correlated with El Niño-Southern Oscillation events, while regional patterns are related to sea surface temperature and nutrient regimes are associated with the East Australian Current. Regression models developed to predict the presence or absence of giant kelp canopy emphasise the importance of sea surface temperature in these systems. Long-term decline in canopy cover is clearly evident in most regions, and in light of increasing thermal stress associated with a changing ocean climate, this raises concern for the future of this species as a major habitat-forming kelp in Australia and some other regions worldwide. Given that Tasmania represents the stronghold of the range of this species in Australia, but is a geographic trap in that there is no suitable habitat for M. pyrifera to the south, our findings support the Federal listing of giant kelp communities in Australia as an endangered marine community type.
38
Hickey, Laura J., Jeff Atkins, Robert T. Fahey, Mark T. Kreider, Shea B. Wales e Christopher M. Gough. "Contrasting Development of Canopy Structure and Primary Production in Planted and Naturally Regenerated Red Pine Forests". Forests 10, n. 7 (8 luglio 2019): 566. http://dx.doi.org/10.3390/f10070566.
Testo completoAbstract (sommario):
Globally, planted forests are rapidly replacing naturally regenerated stands but the implications for canopy structure, carbon (C) storage, and the linkages between the two are unclear. We investigated the successional dynamics, interlinkages and mechanistic relationships between wood net primary production (NPPw) and canopy structure in planted and naturally regenerated red pine (Pinus resinosa Sol. ex Aiton) stands spanning ≥ 45 years of development. We focused our canopy structural analysis on leaf area index (LAI) and a spatially integrative, terrestrial LiDAR-based complexity measure, canopy rugosity, which is positively correlated with NPPw in several naturally regenerated forests, but which has not been investigated in planted stands. We estimated stand NPPw using a dendrochronological approach and examined whether canopy rugosity relates to light absorption and light–use efficiency. We found that canopy rugosity increased similarly with age in planted and naturally regenerated stands, despite differences in other structural features including LAI and stem density. However, the relationship between canopy rugosity and NPPw was negative in planted and not significant in naturally regenerated stands, indicating structural complexity is not a globally positive driver of NPPw. Underlying the negative NPPw-canopy rugosity relationship in planted stands was a corresponding decline in light-use efficiency, which peaked in the youngest, densely stocked stand with high LAI and low structural complexity. Even with significant differences in the developmental trajectories of canopy structure, NPPw, and light use, planted and naturally regenerated stands stored similar amounts of C in wood over a 45-year period. We conclude that widespread increases in planted forests are likely to affect age-related patterns in canopy structure and NPPw, but planted and naturally regenerated forests may function as comparable long-term C sinks via different structural and mechanistic pathways.
39
PARASHURAM, DEVATHI, STEFFEN OPPEL, CALVIN FENTON, GLENFORD JAMES, JAMES DALEY, GERARD GRAY, NIGEL J. COLLAR e PAUL M. DOLMAN. "The Forest Thrush Turdus lherminieri prefers mature mesic forest with dense canopy". Bird Conservation International 25, n. 4 (2 febbraio 2015): 503–13. http://dx.doi.org/10.1017/s0959270914000495.
Testo completoAbstract (sommario):
SummaryHabitat loss, the primary driver for loss of biodiversity worldwide, is of special concern for species that have a small area of occurrence, such as those restricted to islands. The Forest Thrush Turdus lherminieri is a ‘Vulnerable’ (VU) species endemic to four islands in the Caribbean, and its population has declined dramatically over the past 15 years. Because this decline is poorly understood, we studied its habitat associations on Montserrat. We conducted three repeat point count surveys and measured forest structure and habitat at each of 88 randomly placed locations in the largest forest area remaining on the island. We related Forest Thrush abundance to habitat using binomial mixture models that account for imperfect detection. Detection probability was a function of survey time, survey date, location of the survey point, and wind. Local habitat structure had the greatest influence on Forest Thrush abundance, with birds being more abundant at mid-elevations under closed canopies. We conclude that the Forest Thrush prefers mature mesic and wet forests on Montserrat. Assuming similar habitat selection in the rest of its range, the species’s long-term future depends on good protection of these natural forests on all four islands where it occurs.
40
LeBlanc, David C. "Red spruce decline on Whiteface Mountain, New York. I. Relationships with elevation, tree age, and competition". Canadian Journal of Forest Research 20, n. 9 (1 settembre 1990): 1408–14. http://dx.doi.org/10.1139/x90-186.
Testo completoAbstract (sommario):
Detailed stem analysis and stand structure and history analyses are used to evaluate relationships between growth decline in populations of red spruce (Picearubens Sarg.) on Whiteface Mountain and elevation, tree age and size, and stand dynamics. The study sites are virgin, uneven-aged spruce-fir forests at 900 and 1100 m elevation. Most red spruce sampled exhibited substantial decreases in annual stem wood volume increment from 1964 to 1984, particularly large trees and trees from higher elevation. While larger trees exhibited more severe growth decline, there is no evidence of a direct causal link between tree age and decline. Inverse relationships between growth and competition indices are evident for periods prior to the onset of decline, but these relationships degrade during the period of growth decline; competition is not causally linked to decline. There is some indication that the decline-inciting stress was particularly severe for canopy-emergent and exposed red spruce, suggesting the action of an atmospheric stress.
41
Nagel, Thomas A., Jurij Diaci, Klemen Jerina, Milan Kobal e Dusan Rozenbergar. "Simultaneous influence of canopy decline and deer herbivory on regeneration in a conifer–broadleaf forest". Canadian Journal of Forest Research 45, n. 3 (marzo 2015): 266–75. http://dx.doi.org/10.1139/cjfr-2014-0249.
Testo completoAbstract (sommario):
Understanding how forests respond to multiple disturbances is becoming increasingly important under global change. We examined the simultaneous influence of canopy decline and deer browsing on regeneration in an old-growth reserve and surrounding managed forest dominated by Fagus sylvatica L. and Abies alba Mill. in Slovenia. We quantified both disturbance processes by measuring characteristics of canopy gaps and reconstructing historical deer densities. Forest response was assessed with repeated measurements of tree regeneration and regeneration patterns within deer exclosures. Most gaps were formed by mortality of A. alba (71%), and gapmaker characteristics suggest that gaps formed slowly and often expanded, resulting in a mosaic of openings covering 17% of the old-growth reserve. Fagus sylvatica dominated the regeneration layer throughout the reserve and recruited to taller height classes over the past 26 years. The recruitment failure of preferred browse species (A. alba and Acer pseudoplatanus L.) in the reserve and the successful recruitment of these species within exclosures indicate that selective browsing by deer has altered the successional response to A. alba decline, facilitating the dominance of F. sylvatica. Given that global change may increase forest decline worldwide and the ubiquitous nature of deer browsing in many temperate forests, understanding their combined effects on forests will become increasingly important.
42
West, P. W. "Do increasing respiratory costs explain the decline with age of forest growth rate?" Journal of Forestry Research 31, n. 3 (28 settembre 2019): 693–712. http://dx.doi.org/10.1007/s11676-019-01020-w.
Testo completoAbstract (sommario):
Abstract Once forests have achieved a full canopy, their growth rate declines progressively with age. This work used a global data set with estimates from a wide range of forest types, aged 20‒795 years, of their annual photosynthetic production (gross primary production, GPP) and subsequent above- plus below-ground biomass production (net primary production, NPP). Both GPP and NPP increased with increasing mean annual temperature and precipitation. GPP was then unrelated to forest age whilst NPP declined progressively with increasing age. These results implied that autotrophic respiration increases with age. It has been proposed that GPP should decline in response to increasing water stress in leaves as water is raised to greater heights as trees grow taller with age. However, trees may make substantial plastic adjustment in morphology and anatomy of newly developing leaves, xylem and fine roots to compensate for this stress and maintain GPP with age. This work reviews the possibilities that NPP declines with age as respiratory costs increase progressively in, any or all of, the construction and maintenance of more complex tissues, the maintenance of increasing amounts of live tissue within the sapwood of stems and coarse roots, the conversion of sapwood to heartwood, the increasing distance of phloem transport, increased turnover rates of fine roots, cost of supporting very tall trees that are unable to compensate fully for increased water stress in their canopies or maintaining alive competitively unsuccessful small trees.
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Pryor, S. C., K. E. Hornsby e K. A. Novick. "Forest canopy interactions with nucleation mode particles". Atmospheric Chemistry and Physics 14, n. 21 (14 novembre 2014): 11985–96. http://dx.doi.org/10.5194/acp-14-11985-2014.
Testo completoAbstract (sommario):
Abstract. Ultrafine particle size distributions through a deciduous forest canopy indicate that nucleation mode particle concentrations decline with depth into the canopy, such that number concentrations at the bottom of the canopy are an average of 16% lower than those at the top. However, growth rates of nucleation mode particles (diameters 6–30 nm) are invariant with height within the canopy, which implies that the semi-volatile gases contributing to their growth are comparatively well-mixed through the canopy. Growth rates of nucleation mode particles during a meteorological drought year (2012) were substantially lower than during a meteorologically normal year with high soil water potential (2013). This may reflect suppression of actual biogenic volatile organic compound (BVOC) emissions by drought and thus a reduction in the production of condensable products during the drought-affected vegetation season. This hypothesis is supported by evidence that growth rates during the normal year exhibit a positive correlation with emissions of BVOC modeled on observed forest composition, leaf area index, temperature and photosynthetically active radiation (PAR), but particle growth rates during the drought-affected vegetation season are not correlated with modeled BVOC emissions. These data thus provide indirect evidence that drought stress in forests may reduce BVOC emissions and limit growth of nucleation mode particles to climate-relevant sizes.
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Mandre, Malle, Hardi Tullus e Jaan Klõšeiko. "Partitioning Of Carbohydrates And Biomass Of Needles In Scots Pine Canopy". Zeitschrift für Naturforschung C 57, n. 3-4 (1 aprile 2002): 296–302. http://dx.doi.org/10.1515/znc-2002-3-417.
Testo completoAbstract (sommario):
The study was aimed at the quantitative evaluation of the temporal and spatial partitioning of non-structural carbohydrates and needle biomass in a canopy of Scots pine (Pinus sylvestris L.) growing in a Myrtillus site type forest stand (predominant in Estonia). The tree canopy was divided into ten equal layers and the material for the spatial partitioning of the investigated characteristics was sampled from all layers. Our findings revealed a significant variation in morphology and in the partitioning of carbohydrates in needles in different layers of the canopy. The study of the temporal dynamics of carbohydrates showed that starch content in needles started to increase in early spring before budbreak, which was accompanied by a decline in soluble carbohydrates. In October, the starch content of needles was low, but the concentration of soluble sugars started to increase attaining a maximum in winter. Regression analysis indicated that before budbreak, the partitioning of soluble sugars in different canopy layers was relatively weakly correlated with the height of the layer; however, a strong correlation was observed for starch. In autumn, when the growth of trees stopped and daily temperatures decreased, the allocation of soluble sugars was correlated with the height of the canopy layer
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Wright, GC, e GL Hammer. "Distribution of nitrogen and radiation use efficiency in peanut canopies". Australian Journal of Agricultural Research 45, n. 3 (1994): 565. http://dx.doi.org/10.1071/ar9940565.
Testo completoAbstract (sommario):
The allocation pattern of leaf nitrogen throughout a crop canopy can theoretically affect crop photosynthetic performance and radiation use efficiency (RUE). No information is available on the existence of leaf nitrogen gradients in peanut (Arachis hypogaea L.) canopies, nor on how these gradients might impact on RUE. Peanut crops (cv. Tifton-8) were grown in warm and cool environments, and the canopy profiles of leaf area index, light interception, specific leaf weight (SLW), leaf nitrogen concentration (LNC) and specific leaf nitrogen (SLN) were examined at 73 and 112 days after planting. Crop RUE was also measured during this period. There was a marked decline in SLN from the top to the base of the canopy in both environments. The gradient in SLN occurred due to changes in SLW and LNC in the warm environment, but only due to changes in SLW in the cool environment. The gradient appeared to be largely controlled by the light environment within the canopy, as evidenced by the commonality (across environments) of the relationship between SLN and cumulative light interception throughout the canopy. Radiation use efficiency was 33% higher in the crop grown in the warm compared to the cool environment, suggesting that cool temperatures can limit RUE in peanut. For the crop at the warm site, RUE was 32% higher than the theoretical RUE assuming a uniform SLN distribution in the canopy. It is suggested that the existence of non-uniform SLN distribution in the canopy may allow enhanced RUE compared to canopies with uniform SLN distribution.
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Eschtruth, Anne K., e John J. Battles. "DEER HERBIVORY ALTERS FOREST RESPONSE TO CANOPY DECLINE CAUSED BY AN EXOTIC INSECT PEST". Ecological Applications 18, n. 2 (marzo 2008): 360–76. http://dx.doi.org/10.1890/07-0446.1.
Testo completo
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Guo, Tingdong, Justin Morgenroth, Tenley Conway e Cong Xu. "City-wide canopy cover decline due to residential property redevelopment in Christchurch, New Zealand". Science of The Total Environment 681 (settembre 2019): 202–10. http://dx.doi.org/10.1016/j.scitotenv.2019.05.122.
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Chagnon, Catherine, e Stéphane Boudreau. "Shrub canopy induces a decline in lichen abundance and diversity in Nunavik (Québec, Canada)". Arctic, Antarctic, and Alpine Research 51, n. 1 (1 gennaio 2019): 521–32. http://dx.doi.org/10.1080/15230430.2019.1688751.
Testo completo
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Pote, John, Zhaolong Wang e Bingru Huang. "Timing and Temperature of Physiological Decline for Creeping Bentgrass". Journal of the American Society for Horticultural Science 131, n. 5 (settembre 2006): 608–15. http://dx.doi.org/10.21273/jashs.131.5.608.
Testo completoAbstract (sommario):
Knowledge of the level of soil temperatures that is detrimental for shoot and root growth for cool-season grasses may help develop heat-tolerant plants and effective management practices to improve summer performance. The objectives of this study were to determine the level and duration of high temperatures in the root zone that will induce decline for various growth and physiological parameters and to compare the responses of different physiological parameters and cultivars to high root-zone temperatures. Nine creeping bentgrass [Agrostis stolonifera L. var. palustris (Huds.) Farw.] cultivars were subjected to eight root-zone temperatures (20, 21, 22, 23, 25, 27, 31, 35 °C) in water baths while exposed to a constant air temperature of 20 °C for 54 days. Root number, dry weight, and depth, active root biomass, turf quality, leaf cytokinin content, and canopy net photosynthetic rate (Pn), decreased in all nine cultivars as root-zone temperature increased from 20 to 35 °C, but the time and temperature at which the decline occurred varied for each parameter measured. Pn, cytokinin content, root number, and turf quality declined at 23, 27, 27, and 35 °C, respectively, after 28 days of exposure. Active root biomass, root number, root dry weight, turf quality, and rooting depth declined at 23, 25, 25, 25, and 35 °C, respectively, at 54 days. At a 31 °C root-zone temperature the decline in root number, cytokinin content, and turf quality occurred at 19, 37, and 47 days, respectively. The results suggest that root-zone temperatures of 23 °C or above this level were detrimental to root activities, Pn, and overall turf growth. Root and Pn decline at lower temperatures and earlier in the study than turf quality suggest that the disturbance of physiological activities of roots and leaves could lead to turfgrass quality decline at high root-zone temperatures.
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Houle, Gilles. "Growth patterns of sugar maple seedlings and mature trees in healthy and in declining hardwood stands". Canadian Journal of Forest Research 20, n. 7 (1 luglio 1990): 894–901. http://dx.doi.org/10.1139/x90-120.
Testo completoAbstract (sommario):
Openings created in the forest canopy as a result of the decline of sugar maple (Acersaccharum Marsh.) may increase microsite heterogeneity and favor the growth of tree seedlings on the forest floor and possibly neighboring healthy trees because of resource release. To corroborate these hypotheses, I studied the growth of sugar maple seedlings and mature trees, and some microsite characteristics, in healthy and in declining hardwood stands. Sampling was carried out in 400-m2 quadrats in four stands of similar composition. In two of the stands, the trees showed no apparent symptoms of decline (healthy stands), but in the other two (declining stands), dieback had caused tree cover to be reduced by ≈25 to 30%. Photosynthetically active radiation below the canopy was significantly lower and less variable in the healthy than in the declining stands, under both cloudy and sunny conditions. In one of the declining stands, soil pH was higher and soil organic matter content was lower than in both healthy stands. Stem elongation of sugar maple seedlings did not differ among the stands prior to 1984, but following that date it was significantly higher and more variable among seedlings in the declining stands. Ring width of apparently healthy trees decreased markedly in the early 1980s and increased somewhat during the 1985–1987 period on the declining sites. Microsite heterogeneity and growth of tree seedlings on the forest floor were thus greater in the declining than in the healthy stands. Neighboring healthy trees did not necessarily respond to the opening of the canopy (as a result of dieback) by increased ring width; this possibly resulted from the hierarchical position within the canopy, the differential time of reaction, and the age and (or) the health status of each individual.