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Simon L Lewis - One of the best experts on this subject based on the ideXlab platform.
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Aboveground biomass estimation in Tropical Forests at single tree level with ALS data
2016 IEEE International Geoscience and Remote Sensing Symposium (IGARSS), 2016Co-Authors: Michele Dalponte, Simon L Lewis, Tommaso Jucker, David F. R. P. Burslem, Reuben Nilus, Oliver Phillips, David A. CoomesAbstract:In this paper we present a study on the estimation of the aboveground biomass in Tropical Forests at single tree level using airborne laser scanning (ALS) data. Individual tree crowns (ITCs) are firstly detected using a method based on an adaptive window that change its size according to tree height. The diameter at breast height (DBH) and the aboveground biomass (AGB) of each ITC then are predicted using standard allometric models. Lastly, the AGB values are aggregated at plot level, and compared with field measured values. The results show that it is possible to accurately predict the aboveground biomass of Tropical Forests at single tree level using ALS data.
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increasing human dominance of Tropical Forests
Science, 2015Co-Authors: Simon L Lewis, David Edwards, David W GalbraithAbstract:Tropical Forests house over half of Earth’s biodiversity and are an important influence on the climate system. These Forests are experiencing escalating human influence, altering their health and the provision of important ecosystem functions and services. Impacts started with hunting and millennia-old megafaunal extinctions (phase I), continuing via low-intensity shifting cultivation (phase II), to today’s global integration, dominated by intensive permanent agriculture, industrial logging, and attendant fires and fragmentation (phase III). Such ongoing pressures, together with an intensification of global environmental change, may severely degrade Forests in the future (phase IV, global simplification) unless new “development without destruction” pathways are established alongside climate change–resilient landscape designs.
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above ground biomass and structure of 260 african Tropical Forests
Philosophical Transactions of the Royal Society B, 2013Co-Authors: Simon L Lewis, Bonaventure Sonké, Gabriela Lopezgonzalez, Terry Sunderland, Serge K Begne, M F Van Der Heijden, Oliver L. PhillipsAbstract:We report above-ground biomass (AGB), basal area, stem density and wood mass density estimates from 260 sample plots (mean size: 1.2 ha) in intact closed-canopy Tropical Forests across 12 African countries. Mean AGB is 395.7 Mg dry mass ha−1 (95% CI: 14.3), substantially higher than Amazonian values, with the Congo Basin and contiguous forest region attaining AGB values (429 Mg ha−1) similar to those of Bornean Forests, and significantly greater than East or West African Forests. AGB therefore appears generally higher in palaeo- compared with neoTropical Forests. However, mean stem density is low (426 ± 11 stems ha−1 greater than or equal to 100 mm diameter) compared with both Amazonian and Bornean Forests (cf. approx. 600) and is the signature structural feature of African Tropical Forests. While spatial autocorrelation complicates analyses, AGB shows a positive relationship with rainfall in the driest nine months of the year, and an opposite association with the wettest three months of the year; a negative relationship with temperature; positive relationship with clay-rich soils; and negative relationships with C : N ratio (suggesting a positive soil phosphorus–AGB relationship), and soil fertility computed as the sum of base cations. The results indicate that AGB is mediated by both climate and soils, and suggest that the AGB of African closed-canopy Tropical Forests may be particularly sensitive to future precipitation and temperature changes.
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drought mortality relationships for Tropical Forests
New Phytologist, 2010Co-Authors: Oliver L. Phillips, Simon L Lewis, Yadvinder Malhi, Luiz E.o.c. Aragao, Jon Lloyd, Abel Monteagudo, Samuel Almeida, Geertje M F Van Der Heijden, Gabriela Lopezgonzalez, Esteban Alvarez DavilaAbstract:Summary •The rich ecology of Tropical Forests is intimately tied to their moisture status. Multi-site syntheses can provide a macro-scale view of these linkages and their susceptibility to changing climates. Here, we report pan-Tropical and regional-scale analyses of tree vulnerability to drought. •We assembled available data on Tropical forest tree stem mortality before, during, and after recent drought events, from 119 monitoring plots in 10 countries concentrated in Amazonia and Borneo. •In most sites, larger trees are disproportionately at risk. At least within Amazonia, low wood density trees are also at greater risk of drought-associated mortality, independent of size. For comparable drought intensities, trees in Borneo are more vulnerable than trees in the Amazon. There is some evidence for lagged impacts of drought, with mortality rates remaining elevated 2 yr after the meteorological event is over. •These findings indicate that repeated droughts would shift the functional composition of Tropical Forests toward smaller, denser-wooded trees. At very high drought intensities, the linear relationship between tree mortality and moisture stress apparently breaks down, suggesting the existence of moisture stress thresholds beyond which some Tropical Forests would suffer catastrophic tree mortality.
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Drought–mortality relationships for Tropical Forests
New Phytologist, 2010Co-Authors: Oliver L. Phillips, Simon L Lewis, Yadvinder Malhi, Geertje Van Der Heijden, Gabriela Lopez-gonzales, Luiz E.o.c. Aragao, Jon Lloyd, Abel Monteagudo, Samuel Almeida, Esteban Alvarez DavilaAbstract:• The rich ecology of Tropical Forests is intimately tied to their moisture status. Multi-site syntheses can provide a macro-scale view of these linkages and their susceptibility to changing climates. Here, we report pan-Tropical and regional-scale analyses of tree vulnerability to drought. • We assembled available data on Tropical forest tree stem mortality before, during, and after recent drought events, from 119 monitoring plots in 10 countries concentrated in Amazonia and Borneo. • In most sites, larger trees are disproportionately at risk. At least within Amazonia, low wood density trees are also at greater risk of drought-associated mortality, independent of size. For comparable drought intensities, trees in Borneo are more vulnerable than trees in the Amazon. There is some evidence for lagged impacts of drought, with mortality rates remaining elevated 2 yr after the meteorological event is over. • These findings indicate that repeated droughts would shift the functional composition of Tropical Forests toward smaller, denser-wooded trees. At very high drought intensities, the linear relationship between tree mortality and moisture stress apparently breaks down, suggesting the existence of moisture stress thresholds beyond which some Tropical Forests would suffer catastrophic tree mortality.
Benjamin L. Turner - One of the best experts on this subject based on the ideXlab platform.
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pervasive phosphorus limitation of tree species but not communities in Tropical Forests
Nature, 2018Co-Authors: Benjamin L. Turner, Tania Brenesarguedas, Richard ConditAbstract:In lowland Tropical Forests in Panama, widespread species-level phosphorus limitation of tree growth is not reflected in community-wide growth or biomass owing to the presence of a few species tolerant of low phosphorus availability. Primary productivity in Tropical Forests is widely assumed to be limited by phosphorus availability, but evidence is equivocal. Benjamin Turner and colleagues examine the growth rates of Tropical tree species along a steep gradient of soil phosphorus availability in Panama, and find that most species grow faster when soil phosphorus availability is higher. No such response is seen at the community level, however, because a subset of species that have adapted to infertile soils grow rapidly despite extremely low phosphorus availability. Phosphorus availability is widely assumed to limit primary productivity in Tropical Forests1,2, but support for this paradigm is equivocal3. Although biogeochemical theory predicts that phosphorus limitation should be prevalent on old, strongly weathered soils4,5, experimental manipulations have failed to detect a consistent response to phosphorus addition in species-rich lowland Tropical Forests6,7,8,9. Here we show, by quantifying the growth of 541 Tropical tree species across a steep natural phosphorus gradient in Panama, that phosphorus limitation is widespread at the level of individual species and strengthens markedly below a threshold of two parts per million exchangeable soil phosphate. However, this pervasive species-specific phosphorus limitation does not translate into a community-wide response, because some species grow rapidly on infertile soils despite extremely low phosphorus availability. These results redefine our understanding of nutrient limitation in diverse plant communities and have important implications for attempts to predict the response of Tropical Forests to environmental change.
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soil carbon stocks across Tropical Forests of panama regulated by base cation effects on fine roots
Biogeochemistry, 2018Co-Authors: Daniela F. Cusack, Richard Condit, Lars Markesteijn, Owen T Lewis, Benjamin L. TurnerAbstract:Tropical Forests are the most carbon (C)-rich ecosystems on Earth, containing 25–40% of global terrestrial C stocks. While large-scale quantification of aboveground biomass in Tropical Forests has improved recently, soil C dynamics remain one of the largest sources of uncertainty in Earth system models, which inhibits our ability to predict future climate. Globally, soil texture and climate predict ≤ 30% of the variation in soil C stocks, so ecosystem models often predict soil C using measures of aboveground plant growth. However, this approach can underestimate Tropical soil C stocks, and has proven inaccurate when compared with data for soil C in data-rich northern ecosystems. By quantifying soil organic C stocks to 1 m depth for 48 humid Tropical forest plots across gradients of rainfall and soil fertility in Panama, we show that soil C does not correlate with common predictors used in models, such as plant biomass or litter production. Instead, a structural equation model including base cations, soil clay content, and rainfall as exogenous factors and root biomass as an endogenous factor predicted nearly 50% of the variation in Tropical soil C stocks, indicating a strong indirect effect of base cation availability on Tropical soil C storage. Including soil base cations in C cycle models, and thus emphasizing mechanistic links among nutrients, root biomass, and soil C stocks, will improve prediction of climate-soil feedbacks in Tropical Forests.
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carbon stocks in primary and secondary Tropical Forests in singapore
Forest Ecology and Management, 2013Co-Authors: Benjamin L. Turner, Helene C Mullerlandau, Stuart J Davies, Markku Larjavaara, Nik Faizu Nik HassanAbstract:Tropical Forests contain large reserves of carbon that are vulnerable to perturbation linked to human activities, including deforestation and climate change. Accurate estimates of forest carbon are therefore required urgently to support efforts to conserve Tropical Forests. We quantified carbon stocks in primary and 60-year-old secondary forest plots located on infertile Ultisols in Bukit Timah Nature Reserve, one of the few remaining areas of forest in Singapore. We used tree census data for 24.2 ha of primary forest and 23 ha of secondary forest, together with allometric equations, to estimate aboveground and coarse root biomass. Coarse woody debris stocks were censused along 2.44 km and 2.12 km of transects in primary and secondary forest, respectively. Soil carbon and fine root carbon stocks were assessed from soil samples taken to 3 m depth in a 2-ha secondary forest plot and a 2-ha primary forest plot, combined with bulk density measured in a nearby soil profile pit. Total estimated carbon stock in the primary forest, which was located on the hilltop and upper slopes (80–115 m elevation), was 337 Mg C ha
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long term change in the nitrogen cycle of Tropical Forests
Science, 2011Co-Authors: Peter Hietz, Benjamin L. Turner, Wolfgang Wanek, Andreas Richter, Charles A Nock, Joseph S WrightAbstract:Deposition of reactive nitrogen (N) from human activities has large effects on temperate Forests where low natural N availability limits productivity but is not known to affect Tropical Forests where natural N availability is often much greater. Leaf N and the ratio of N isotopes (δ15N) increased substantially in a moist forest in Panama between ~1968 and 2007, as did tree-ring δ15N in a dry forest in Thailand over the past century. A decade of fertilization of a nearby Panamanian forest with N caused similar increases in leaf N and δ15N. Therefore, our results indicate regional increases in N availability due to anthropogenic N deposition. Atmospheric nitrogen dioxide measurements and increased emissions of anthropogenic reactive N over Tropical land areas suggest that these changes are widespread in Tropical Forests.
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ecology of the podocarpaceae in Tropical Forests
Smithsonian Contributions to Botany, 2011Co-Authors: Benjamin L. Turner, Lucas A. CernusakAbstract:The emergence of angiosperms in Tropical Forests at the expense of the gymnosperms, their ancestral relatives, was one of the most important events in the evolutionary history of terrestrial plants. Gymnosperms were nearly eliminated from the tropics after the evolution of angiosperms in the early Cretaceous, yet conifers of the Podocarpaceae are among the few gymnosperm families that persist in Tropical Forests worldwide. Podocarps are often considered to be restricted to montane sites in the tropics, a feature of their biogeography that is used by paleoecologists to reconstruct past forest communities. However, podocarps also occur in the lowland tropics, where they can be the dominant component of forest canopies. Podocarps have proved to be remarkably adaptable in many cases: members of the family have a semi-aquatic lifestyle, exhibit drought tolerance and resprouting, and include the only known parasitic gymnosperm. Other intriguing aspects of podocarp physiology include the mechanism of water transport in the leaves and the conspicuous root nodules, which are not involved in nitrogen fixation but instead house arbuscular mycorrhizal fungi. Perhaps most surprising, paleobotanical evidence indicates that far from being 'relict' members of Tropical forest communities, podocarps have been dispersing into the tropics since the late Eocene epoch more than 30 million years ago. These and other aspects of the Podocarpaceae explored in this volume have far-reaching implications for understanding the ecology and evolution of Tropical rain Forests.
Oliver L. Phillips - One of the best experts on this subject based on the ideXlab platform.
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above ground biomass and structure of 260 african Tropical Forests
Philosophical Transactions of the Royal Society B, 2013Co-Authors: Simon L Lewis, Bonaventure Sonké, Gabriela Lopezgonzalez, Terry Sunderland, Serge K Begne, M F Van Der Heijden, Oliver L. PhillipsAbstract:We report above-ground biomass (AGB), basal area, stem density and wood mass density estimates from 260 sample plots (mean size: 1.2 ha) in intact closed-canopy Tropical Forests across 12 African countries. Mean AGB is 395.7 Mg dry mass ha−1 (95% CI: 14.3), substantially higher than Amazonian values, with the Congo Basin and contiguous forest region attaining AGB values (429 Mg ha−1) similar to those of Bornean Forests, and significantly greater than East or West African Forests. AGB therefore appears generally higher in palaeo- compared with neoTropical Forests. However, mean stem density is low (426 ± 11 stems ha−1 greater than or equal to 100 mm diameter) compared with both Amazonian and Bornean Forests (cf. approx. 600) and is the signature structural feature of African Tropical Forests. While spatial autocorrelation complicates analyses, AGB shows a positive relationship with rainfall in the driest nine months of the year, and an opposite association with the wettest three months of the year; a negative relationship with temperature; positive relationship with clay-rich soils; and negative relationships with C : N ratio (suggesting a positive soil phosphorus–AGB relationship), and soil fertility computed as the sum of base cations. The results indicate that AGB is mediated by both climate and soils, and suggest that the AGB of African closed-canopy Tropical Forests may be particularly sensitive to future precipitation and temperature changes.
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drought mortality relationships for Tropical Forests
New Phytologist, 2010Co-Authors: Oliver L. Phillips, Simon L Lewis, Yadvinder Malhi, Luiz E.o.c. Aragao, Jon Lloyd, Abel Monteagudo, Samuel Almeida, Geertje M F Van Der Heijden, Gabriela Lopezgonzalez, Esteban Alvarez DavilaAbstract:Summary •The rich ecology of Tropical Forests is intimately tied to their moisture status. Multi-site syntheses can provide a macro-scale view of these linkages and their susceptibility to changing climates. Here, we report pan-Tropical and regional-scale analyses of tree vulnerability to drought. •We assembled available data on Tropical forest tree stem mortality before, during, and after recent drought events, from 119 monitoring plots in 10 countries concentrated in Amazonia and Borneo. •In most sites, larger trees are disproportionately at risk. At least within Amazonia, low wood density trees are also at greater risk of drought-associated mortality, independent of size. For comparable drought intensities, trees in Borneo are more vulnerable than trees in the Amazon. There is some evidence for lagged impacts of drought, with mortality rates remaining elevated 2 yr after the meteorological event is over. •These findings indicate that repeated droughts would shift the functional composition of Tropical Forests toward smaller, denser-wooded trees. At very high drought intensities, the linear relationship between tree mortality and moisture stress apparently breaks down, suggesting the existence of moisture stress thresholds beyond which some Tropical Forests would suffer catastrophic tree mortality.
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Drought–mortality relationships for Tropical Forests
New Phytologist, 2010Co-Authors: Oliver L. Phillips, Simon L Lewis, Yadvinder Malhi, Geertje Van Der Heijden, Gabriela Lopez-gonzales, Luiz E.o.c. Aragao, Jon Lloyd, Abel Monteagudo, Samuel Almeida, Esteban Alvarez DavilaAbstract:• The rich ecology of Tropical Forests is intimately tied to their moisture status. Multi-site syntheses can provide a macro-scale view of these linkages and their susceptibility to changing climates. Here, we report pan-Tropical and regional-scale analyses of tree vulnerability to drought. • We assembled available data on Tropical forest tree stem mortality before, during, and after recent drought events, from 119 monitoring plots in 10 countries concentrated in Amazonia and Borneo. • In most sites, larger trees are disproportionately at risk. At least within Amazonia, low wood density trees are also at greater risk of drought-associated mortality, independent of size. For comparable drought intensities, trees in Borneo are more vulnerable than trees in the Amazon. There is some evidence for lagged impacts of drought, with mortality rates remaining elevated 2 yr after the meteorological event is over. • These findings indicate that repeated droughts would shift the functional composition of Tropical Forests toward smaller, denser-wooded trees. At very high drought intensities, the linear relationship between tree mortality and moisture stress apparently breaks down, suggesting the existence of moisture stress thresholds beyond which some Tropical Forests would suffer catastrophic tree mortality.
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increasing carbon storage in intact african Tropical Forests
Nature, 2009Co-Authors: Simon L Lewis, James A. Comiskey, Bonaventure Sonké, Timothy R Baker, Justin M Reitsma, Lee White, Oliver L. Phillips, Gabriela Lopezgonzalez, Kofi AffumbaffoeAbstract:Tropical Forests store and process large amounts of carbon, affecting the amount of CO2 in the atmosphere, and hence the rate and magnitude of climate change. The extent of the contribution of Tropical Forests in this role is uncertain, largely because of a lack of monitoring. An international collaboration has now collected and analysed data from a ten-country network of 79 long-term monitoring plots across the largest Tropical continent - Africa. Their findings reveal that above-ground carbon storage in live trees increased by 0.63 tonnes of carbon per hectare per year between 1968 and 2007. Extrapolation to unmeasured forest components and scaling to the continent implies a total increase in carbon storage in African Tropical forest trees of 340 million tonnes a year. These results provide evidence that increasing carbon storage in old-growth Forests is a pan-Tropical phenomenon. This study reports data from a network of long-term monitoring plots across African Tropical Forests, which finds that above-ground carbon storage in live trees increased by 0.63 Mg C ha−1 yr−1 between 1968 and 2007. The data is extrapolated to unmeasured forest components, and by scaling to the continent, a total increase in carbon storage in African Tropical forest trees of 0.34 Pg C yr−1 is estimated. These results provide evidence that increasing carbon storage in old-growth Forests is a pan-Tropical phenomenon. The response of terrestrial vegetation to a globally changing environment is central to predictions of future levels of atmospheric carbon dioxide1,2. The role of Tropical Forests is critical because they are carbon-dense and highly productive3,4. Inventory plots across Amazonia show that old-growth Forests have increased in carbon storage over recent decades5,6,7, but the response of one-third of the world’s Tropical Forests in Africa8 is largely unknown owing to an absence of spatially extensive observation networks9,10. Here we report data from a ten-country network of long-term monitoring plots in African Tropical Forests. We find that across 79 plots (163 ha) above-ground carbon storage in live trees increased by 0.63 Mg C ha-1 yr-1 between 1968 and 2007 (95% confidence interval (CI), 0.22–0.94; mean interval, 1987–96). Extrapolation to unmeasured forest components (live roots, small trees, necromass) and scaling to the continent implies a total increase in carbon storage in African Tropical forest trees of 0.34 Pg C yr-1 (CI, 0.15–0.43). These reported changes in carbon storage are similar to those reported for Amazonian Forests per unit area6,7, providing evidence that increasing carbon storage in old-growth Forests is a pan-Tropical phenomenon. Indeed, combining all standardized inventory data from this study and from Tropical America and Asia5,6,11 together yields a comparable figure of 0.49 Mg C ha-1 yr-1 (n = 156; 562 ha; CI, 0.29–0.66; mean interval, 1987–97). This indicates a carbon sink of 1.3 Pg C yr-1 (CI, 0.8–1.6) across all Tropical Forests during recent decades. Taxon-specific analyses of African inventory and other data12 suggest that widespread changes in resource availability, such as increasing atmospheric carbon dioxide concentrations, may be the cause of the increase in carbon stocks13, as some theory14 and models2,10,15 predict.
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fingerprinting the impacts of global change on Tropical Forests
Philosophical Transactions of the Royal Society B, 2004Co-Authors: Simon L Lewis, Yadvinder Malhi, Oliver L. PhillipsAbstract:Recent observations of widespread changes in mature Tropical Forests such as increasing tree growth, recruitment and mortality rates and increasing above-ground biomass suggest that ‘global change’ agents may be causing predictable changes in Tropical Forests. However, consensus over both the robustness of these changes and the environmental drivers that may be causing them is yet to emerge. This paper focuses on the second part of this debate. We review (i) the evidence that the physical, chemical and biological environment that Tropical trees grow in has been altered over recent decades across large areas of the tropics, and (ii) the theoretical, experimental and observational evidence regarding the most likely effects of each of these changes on Tropical Forests. Ten potential widespread drivers of environmental
Yadvinder Malhi - One of the best experts on this subject based on the ideXlab platform.
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photosynthetic seasonality of global Tropical Forests constrained by hydroclimate
Nature Geoscience, 2015Co-Authors: Kaiyu Guan, Haibin Li, Adam Wolf, Jin Wu, David Medvigy, Kelly K Caylor, Justin Sheffield, Eric F Wood, Yadvinder MalhiAbstract:Droughts can cause dry-season productivity to decline in Tropical Forests. This decline occurs when precipitation is below 2,000 mm yr−1, resulting in insufficient subsurface water storage to maintain constant production through the dry season.
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Tropical Forests in the anthropocene
Annual Review of Environment and Resources, 2014Co-Authors: Yadvinder Malhi, Toby A Gardner, Gregory R Goldsmith, Miles R Silman, Przemyslaw ZelazowskiAbstract:The Anthropocene is characterized as an epoch when human influence has begun to fundamentally alter many aspects of the Earth system and many of the planet’s biomes. Here, we review and synthesize our understanding of Anthropocene changes in Tropical Forests. Key facets include deforestation driven by agricultural expansion, timber and wood extraction, the loss of fauna that maintain critical ecological connections, the spread of fire, landscape fragmentation, the spread of second-growth Forests, new species invasion and pathogen spread, increasing CO2, and climate change. The patterns of change are spatially heterogeneous, are often characterized by strong interactions among different drivers, can have both large-scale and remote effects, and can play out through ecological cascades over long timescales. As a consequence, most Tropical Forests are on a trajectory to becoming altered ecosystems, with the degree of alteration dependent on the intensity and duration of the current bottleneck of human-induced pressures. We highlight the importance of this understanding to develop the strategies necessary for shaping the transition of Tropical Forests through the early Anthropocene, as well as highlight the opportunities and challenges for the Tropical forest science community in the coming decades.
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drought mortality relationships for Tropical Forests
New Phytologist, 2010Co-Authors: Oliver L. Phillips, Simon L Lewis, Yadvinder Malhi, Luiz E.o.c. Aragao, Jon Lloyd, Abel Monteagudo, Samuel Almeida, Geertje M F Van Der Heijden, Gabriela Lopezgonzalez, Esteban Alvarez DavilaAbstract:Summary •The rich ecology of Tropical Forests is intimately tied to their moisture status. Multi-site syntheses can provide a macro-scale view of these linkages and their susceptibility to changing climates. Here, we report pan-Tropical and regional-scale analyses of tree vulnerability to drought. •We assembled available data on Tropical forest tree stem mortality before, during, and after recent drought events, from 119 monitoring plots in 10 countries concentrated in Amazonia and Borneo. •In most sites, larger trees are disproportionately at risk. At least within Amazonia, low wood density trees are also at greater risk of drought-associated mortality, independent of size. For comparable drought intensities, trees in Borneo are more vulnerable than trees in the Amazon. There is some evidence for lagged impacts of drought, with mortality rates remaining elevated 2 yr after the meteorological event is over. •These findings indicate that repeated droughts would shift the functional composition of Tropical Forests toward smaller, denser-wooded trees. At very high drought intensities, the linear relationship between tree mortality and moisture stress apparently breaks down, suggesting the existence of moisture stress thresholds beyond which some Tropical Forests would suffer catastrophic tree mortality.
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Drought–mortality relationships for Tropical Forests
New Phytologist, 2010Co-Authors: Oliver L. Phillips, Simon L Lewis, Yadvinder Malhi, Geertje Van Der Heijden, Gabriela Lopez-gonzales, Luiz E.o.c. Aragao, Jon Lloyd, Abel Monteagudo, Samuel Almeida, Esteban Alvarez DavilaAbstract:• The rich ecology of Tropical Forests is intimately tied to their moisture status. Multi-site syntheses can provide a macro-scale view of these linkages and their susceptibility to changing climates. Here, we report pan-Tropical and regional-scale analyses of tree vulnerability to drought. • We assembled available data on Tropical forest tree stem mortality before, during, and after recent drought events, from 119 monitoring plots in 10 countries concentrated in Amazonia and Borneo. • In most sites, larger trees are disproportionately at risk. At least within Amazonia, low wood density trees are also at greater risk of drought-associated mortality, independent of size. For comparable drought intensities, trees in Borneo are more vulnerable than trees in the Amazon. There is some evidence for lagged impacts of drought, with mortality rates remaining elevated 2 yr after the meteorological event is over. • These findings indicate that repeated droughts would shift the functional composition of Tropical Forests toward smaller, denser-wooded trees. At very high drought intensities, the linear relationship between tree mortality and moisture stress apparently breaks down, suggesting the existence of moisture stress thresholds beyond which some Tropical Forests would suffer catastrophic tree mortality.
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fingerprinting the impacts of global change on Tropical Forests
Philosophical Transactions of the Royal Society B, 2004Co-Authors: Simon L Lewis, Yadvinder Malhi, Oliver L. PhillipsAbstract:Recent observations of widespread changes in mature Tropical Forests such as increasing tree growth, recruitment and mortality rates and increasing above-ground biomass suggest that ‘global change’ agents may be causing predictable changes in Tropical Forests. However, consensus over both the robustness of these changes and the environmental drivers that may be causing them is yet to emerge. This paper focuses on the second part of this debate. We review (i) the evidence that the physical, chemical and biological environment that Tropical trees grow in has been altered over recent decades across large areas of the tropics, and (ii) the theoretical, experimental and observational evidence regarding the most likely effects of each of these changes on Tropical Forests. Ten potential widespread drivers of environmental
Stefano Tebaldini - One of the best experts on this subject based on the ideXlab platform.
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Digital Terrain Model Retrieval in Tropical Forests Through P-Band SAR Tomography
IEEE Transactions on Geoscience and Remote Sensing, 2019Co-Authors: Mauro Mariotti D’alessandro, Stefano TebaldiniAbstract:This paper focuses on the retrieval of terrain topography below dense Tropical Forests by means of synthetic aperture radar (SAR) systems. Low-frequency signals are needed to penetrate such a thick vegetation layer; however, this expedient alone does not guarantee proper retrieval. It is, here, demonstrated that the phase center of P-band backscatter may lie several meters above the ground, depending on the slope and incidence angle. SAR tomography is shown to overcome this problem and retrieves the actual topography even in the presence of dense trees up to 50 m tall. Digital terrain models returned by SAR tomography are, here, put in comparison with light detection and ranging (LiDAR) terrain models: the accuracy of radar-derived maps is found to be at least comparable with the one offered by LiDAR systems. Moreover, the discrepancy between tomography and LiDAR is larger if large-footprint LiDAR is considered thus suggesting that, in this case, tomographic maps should be considered the reference height. Analyses are carried out by processing three data sets gathered over different Tropical Forests in western Africa. The robustness of the radar estimates is assessed with respect to both ground slope and treetop height.
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Retrieval of Terrain Topography in Tropical Forests Using P-Band Sar Tomography
IGARSS 2018 - 2018 IEEE International Geoscience and Remote Sensing Symposium, 2018Co-Authors: Mauro Mariotti D'alessandro, Stefano TebaldiniAbstract:This paper presents the results achieved by SAR tomography in estimating digital terrain models under Tropical Forests. Several airborne data stacks have been processed, they have been gathered on dense Forests in central Africa in the framework of the AfriSAR campaign and in South America. The joint exploitation of polarimetry and multi baseline interferometry enabled to separate ground from vegetation above and to analyze it alone. Also, airborne LIDAR measurements were available and provided a reliable comparison. Results indicate that terrain topography in Tropical Forests can be retrieved by P-Band SAR Tomography to within an accuracy at least comparable to that of LIDAR systems. Furthermore, few meaningful details visible in SAR derived DTMs are missing in LIDAR maps probably due to the high density of the vegetation layer.
