Browsing by Autor "Yadvinder Malhi"

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Allocation trade‐offs dominate the response of tropical forest growth to seasonal and interannual drought
(Wiley, 2014) Christopher E. Doughty; Yadvinder Malhi; Alejandro Araujo‐Murakami; Daniel B. Metcalfe; Javier E. Silva‐Espejo; Luzmila Arroyo; Juan P. Heredia; Erwin Pardo-Toledo; Luz M. Mendizabal; Victor D. Rojas-Landivar
What determines the seasonal and interannual variation of growth rates in trees in a tropical forest? We explore this question with a novel four-year high-temporal-resolution data set of carbon allocation from two forest plots in the Bolivian Amazon. The forests show strong seasonal variation in tree wood growth rates, which are largely explained by shifts in carbon allocation, and not by shifts in total productivity. At the deeper soil plot, there was a clear seasonal trade-off between wood and canopy NPP, while the shallower soils plot showed a contrasting seasonal trade-off between wood and fine roots. Although a strong 2010 drought reduced photosynthesis, NPP remained constant and increased in the six-month period following the drought, which indicates usage of significant nonstructural carbohydrate stores. Following the drought, carbon allocation increased initially towards the canopy, and then in the following year, allocation increased towards fine-root production. Had we only measured woody growth at these sites and inferred total NPP, we would have misinterpreted both the seasonal and interannual responses. In many tropical forest ecosystems, we propose that changing tree growth rates are more likely to reflect shifts in allocation rather than changes in overall productivity. Only a whole NPP allocation perspective can correctly interpret the relationship between changes in growth and changes in productivity.
Amazon forest response to repeated droughts
(Wiley, 2016) Ted R. Feldpausch; Oliver L. Phillips; Roel Brienen; Emanuel Gloor; Jon Lloyd; Gabriela López‐González; Abel Monteagudo‐Mendoza; Yadvinder Malhi; Alejandro Alarcón; Esteban Álvarez‐Dávila
Abstract The Amazon Basin has experienced more variable climate over the last decade, with a severe and widespread drought in 2005 causing large basin‐wide losses of biomass. A drought of similar climatological magnitude occurred again in 2010; however, there has been no basin‐wide ground‐based evaluation of effects on vegetation. We examine to what extent the 2010 drought affected forest dynamics using ground‐based observations of mortality and growth from an extensive forest plot network. We find that during the 2010 drought interval, forests did not gain biomass (net change: −0.43 Mg ha −1 , confidence interval (CI): −1.11, 0.19, n = 97), regardless of whether forests experienced precipitation deficit anomalies. This contrasted with a long‐term biomass sink during the baseline pre‐2010 drought period (1998 to pre‐2010) of 1.33 Mg ha −1 yr −1 (CI: 0.90, 1.74, p < 0.01). The resulting net impact of the 2010 drought (i.e., reversal of the baseline net sink) was −1.95 Mg ha −1 yr −1 (CI:−2.77, −1.18; p < 0.001). This net biomass impact was driven by an increase in biomass mortality (1.45 Mg ha −1 yr −1 CI: 0.66, 2.25, p < 0.001) and a decline in biomass productivity (−0.50 Mg ha −1 yr −1 , CI:−0.78, −0.31; p < 0.001). Surprisingly, the magnitude of the losses through tree mortality was unrelated to estimated local precipitation anomalies and was independent of estimated local pre‐2010 drought history. Thus, there was no evidence that pre‐2010 droughts compounded the effects of the 2010 drought. We detected a systematic basin‐wide impact of the 2010 drought on tree growth rates across Amazonia, which was related to the strength of the moisture deficit. This impact differed from the drought event in 2005 which did not affect productivity. Based on these ground data, live biomass in trees and corresponding estimates of live biomass in lianas and roots, we estimate that intact forests in Amazonia were carbon neutral in 2010 (−0.07 Pg C yr −1 CI:−0.42, 0.23), consistent with results from an independent analysis of airborne estimates of land‐atmospheric fluxes during 2010. Relative to the long‐term mean, the 2010 drought resulted in a reduction in biomass carbon uptake of 1.1 Pg C, compared to 1.6 Pg C for the 2005 event.
Amazonian and Andean tree communities are not tracking current climate warming
(National Academy of Sciences, 2025) William Farfán-Ríos; Kenneth J. Feeley; Jonathan A. Myers; J. Sebastián Tello; Jhonatan Sallo‐Bravo; Yadvinder Malhi; Oliver L. Phillips; Timothy R. Baker; Alex Nina; Karina García‐Cabrera
Climate change is shifting species distributions, leading to changes in community composition and novel species assemblages worldwide. However, the responses of tropical forests to climate change across large-scale environmental gradients remain largely unexplored. Using long-term data over 66,000 trees of more than 2,500 species occurring over 3,500 m elevation along the hyperdiverse Amazon-to-Andes elevational gradients in Peru and Bolivia, we assessed community-level shifts in species composition over a 40+ y time span. We tested the thermophilization hypothesis, which predicts an increase in the relative abundances of species from warmer climates through time. Additionally, we examined the relative contributions of tree mortality, recruitment, and growth to the observed compositional changes. Mean thermophilization rates (TR) across the Amazon-to-Andes gradient were slow relative to regional temperature change. TR were positive and more variable among Andean forest plots compared to Amazonian plots but were highest at midelevations around the cloud base. Across all elevations, TR were driven primarily by tree mortality and decreased growth of highland (cool-adapted) species rather than an influx of lowland species with higher thermal optima. Given the high variability of community-level responses to warming along the elevational gradients, the high tree mortality, and the slower-than-warming rates of compositional change, we conclude that most tropical tree species, and especially lowland Amazonian tree species, will not be able to escape current or future climate change through upward range shifts, causing fundamental changes to composition and function in Earth's highest diversity forests.
An international network to monitor the structure, composition and dynamics of Amazonian forests (RAINFOR)
(Wiley, 2002) Yadvinder Malhi; Oliver L. Phillips; Jon Lloyd; Timothy R. Baker; Jim Wright; S. Almeida; Luzmila Arroyo; T. Frederiksen; J. Grace; Níro Higuchi
Abstract. The Amazon basin is likely to be increasingly affected by environmental changes: higher temperatures, changes in precipitation, CO 2 fertilization and habitat fragmentation. To examine the important ecological and biogeochemical consequences of these changes, we are developing an international network, RAINFOR, which aims to monitor forest biomass and dynamics across Amazonia in a co‐ordinated fashion in order to understand their relationship to soil and climate. The network will focus on sample plots established by independent researchers, some providing data extending back several decades. We will also conduct rapid transect studies of poorly monitored regions. Field expeditions analysed local soil and plant properties in the first phase (2001–2002). Initial results suggest that the network has the potential to reveal much information on the continental‐scale relations between forest and environment. The network will also serve as a forum for discussion between researchers, with the aim of standardising sampling techniques and methodologies that will enable Amazonian forests to be monitored in a coherent manner in the coming decades.
An international network to monitor the structure, composition and dynamics of Amazonian forests (RAINFOR)
(Wiley, 2002) Yadvinder Malhi; Oliver L. Phillips; Jon Lloyd; Timothy R. Baker; Jennifer Wright; S. Almeida; Luzmila Arroyo; T. Frederiksen; J. Grace; Níro Higuchi
Abstract. The Amazon basin is likely to be increasingly affected by environmental changes: higher temperatures, changes in precipitation, CO2 fertilization and habitat fragmentation. To examine the important ecological and biogeochemical consequences of these changes, we are developing an international network, RAINFOR, which aims to monitor forest biomass and dynamics across Amazonia in a co-ordinated fashion in order to understand their relationship to soil and climate. The network will focus on sample plots established by independent researchers, some providing data extending back several decades. We will also conduct rapid transect studies of poorly monitored regions. Field expeditions analysed local soil and plant properties in the first phase (2001–2002). Initial results suggest that the network has the potential to reveal much information on the continental-scale relations between forest and environment. The network will also serve as a forum for discussion between researchers, with the aim of standardising sampling techniques and methodologies that will enable Amazonian forests to be monitored in a coherent manner in the coming decades.
Are compound leaves an adaptation to seasonal drought or to rapid growth? Evidence from the Amazon rain forest
(Wiley, 2010) Ana C. M. Malhado; Robert J. Whittaker; Yadvinder Malhi; Richard J. Ladle; Hans ter Steege; Oliver L. Phillips; Luiz E. O. C. Aragão; Timothy R. Baker; Luzmilla Arroyo; Samuel Almeida
ABSTRACT Aim To assess the hypotheses that compound leaves of trees in the Amazon forest are an adaptation to drought and/or rapid growth. Location Amazon rain forest, South America. Methods Genera from 137 permanent forest plots spread across Amazonia were classified into those with compound leaves and those with simple leaves. Metrics of compound leaf prevalence were then calculated for each plot and regression models that accounted for spatial autocorrelation were used to identify associations between climate variables and compound leaf structure. We also tested for associations between compound leaf structure and a variety of ecological variables related to life history and growth strategies, including wood density, annual increase in diameter and maximum height. Results One plant family, Fabaceae, accounts for 53% of compound‐leaved individuals in the dataset, and has a geographical distribution strongly centred on north‐east Amazonia. On exclusion of Fabaceae from the analysis we found no significant support for the seasonal drought hypothesis. However, we found evidence supporting the rapid growth hypothesis, with possession of compound leaves being associated with faster diameter growth rates and lower wood densities. Main conclusion This study provides evidence that possession of compound leaves constitutes one of a suite of traits and life‐history strategies that promote rapid growth in rain forest trees. Our findings highlight the importance of carefully considering the geographical distribution of dominant taxa and spatial clustering of data points when inferring ecological causation from environment–trait associations.
Does the disturbance hypothesis explain the biomass increase in basin‐wide Amazon forest plot data?
(Wiley, 2009) Manuel Gloor; Oliver L. Phillips; Jon Lloyd; Simon L. Lewis; Yadvinder Malhi; Timothy R. Baker; Gabriela López‐González; J. Peacock; S. Almeida; A. C. ALVES De OLIVEIRA
Abstract Positive aboveground biomass trends have been reported from old‐growth forests across the Amazon basin and hypothesized to reflect a large‐scale response to exterior forcing. The result could, however, be an artefact due to a sampling bias induced by the nature of forest growth dynamics. Here, we characterize statistically the disturbance process in Amazon old‐growth forests as recorded in 135 forest plots of the RAINFOR network up to 2006, and other independent research programmes, and explore the consequences of sampling artefacts using a data‐based stochastic simulator. Over the observed range of annual aboveground biomass losses, standard statistical tests show that the distribution of biomass losses through mortality follow an exponential or near‐identical Weibull probability distribution and not a power law as assumed by others. The simulator was parameterized using both an exponential disturbance probability distribution as well as a mixed exponential–power law distribution to account for potential large‐scale blowdown events. In both cases, sampling biases turn out to be too small to explain the gains detected by the extended RAINFOR plot network. This result lends further support to the notion that currently observed biomass gains for intact forests across the Amazon are actually occurring over large scales at the current time, presumably as a response to climate change.
Drought Sensitivity of the Amazon Rainforest
(American Association for the Advancement of Science, 2009) Oliver L. Phillips; Luiz E. O. C. Aragão; Simon L. Lewis; Joshua B. Fisher; Jon Lloyd; Gabriela López‐González; Yadvinder Malhi; Abel Monteagudo; Julie Peacock; Carlos Alberto Quesada
Amazon forests are a key but poorly understood component of the global carbon cycle. If, as anticipated, they dry this century, they might accelerate climate change through carbon losses and changed surface energy balances. We used records from multiple long-term monitoring plots across Amazonia to assess forest responses to the intense 2005 drought, a possible analog of future events. Affected forest lost biomass, reversing a large long-term carbon sink, with the greatest impacts observed where the dry season was unusually intense. Relative to pre-2005 conditions, forest subjected to a 100-millimeter increase in water deficit lost 5.3 megagrams of aboveground biomass of carbon per hectare. The drought had a total biomass carbon impact of 1.2 to 1.6 petagrams (1.2 x 10(15) to 1.6 x 10(15) grams). Amazon forests therefore appear vulnerable to increasing moisture stress, with the potential for large carbon losses to exert feedback on climate change.
Drought–mortality relationships for tropical forests
(Wiley, 2010) Oliver L. Phillips; Geertje van der Heijden; Simon L. Lewis; Gabriela López‐González; Luiz E. O. C. Aragão; Jon Lloyd; Yadvinder Malhi; Abel Monteagudo; Samuel Almeida; Esteban Álvarez Dávila
*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.
Hyperdominance in Amazonian forest carbon cycling
(Nature Portfolio, 2015) Sophie Fauset; Michelle Johnson; Manuel Gloor; Timothy R. Baker; Abel Monteagudo M.; Roel Brienen; Ted R. Feldpausch; Gabriela López‐González; Yadvinder Malhi; Hans ter Steege
Increasing biomass in Amazonian forest plots
(Royal Society, 2004) Timothy R. Baker; Oliver L. Phillips; Yadvinder Malhi; Samuel Almeida; Luzmila Arroyo; Anthony Di Fiore; Terry L. Erwin; Níro Higuchi; Timothy J. Killeen; Susan G. W. Laurance
A previous study by Phillips et al. of changes in the biomass of permanent sample plots in Amazonian forests was used to infer the presence of a regional carbon sink. However, these results generated a vigorous debate about sampling and methodological issues. Therefore we present a new analysis of biomass change in old-growth Amazonian forest plots using updated inventory data. We find that across 59 sites, the above-ground dry biomass in trees that are more than 10 cm in diameter (AGB) has increased since plot establishment by 1.22 +/- 0.43 Mg per hectare per year (ha(-1) yr(-1), where 1 ha = 10(4) m2), or 0.98 +/- 0.38 Mg ha(-1) yr(-1) if individual plot values are weighted by the number of hectare years of monitoring. This significant increase is neither confounded by spatial or temporal variation in wood specific gravity, nor dependent on the allometric equation used to estimate AGB. The conclusion is also robust to uncertainty about diameter measurements for problematic trees: for 34 plots in western Amazon forests a significant increase in AGB is found even with a conservative assumption of zero growth for all trees where diameter measurements were made using optical methods and/or growth rates needed to be estimated following fieldwork. Overall, our results suggest a slightly greater rate of net stand-level change than was reported by Phillips et al. Considering the spatial and temporal scale of sampling and associated studies showing increases in forest growth and stem turnover, the results presented here suggest that the total biomass of these plots has on average increased and that there has been a regional-scale carbon sink in old-growth Amazonian forests during the previous two decades.
Late twentieth-century trends in the biomass of Amazonian forest plots
(2005) Timothy R. Baker; Oliver L. Phillips; Yadvinder Malhi; Samuel Almeida; Luzmila Arroyo; Anthony Di Fiore; Terry L. Erwin; Níro Higuchi; Timothy J. Killeen; Susan G. W. Laurance
Abstract This chapter discusses a previous study by Phillips et al. (1998) on biomass changes in Amazonian permanent sample plots which has been used to infer the presence of a regional carbon sink, generating vigorous debate about sampling and methodological issues. A new analysis of biomass change in old-growth Amazonian forest plots is presented here using new inventory data. It has been found that across fifty-nine sites, the above-ground dry biomass in trees of more than 10 cm in diameter has increased since plot establishment by about 1.22 Mg per hectare per year, or about 0.98 Mg per hectare per year if individual plot values are weighted by the number of hectare years of monitoring. This significant increase is not confounded by spatial or temporal variation in wood specific gravity, nor does it depend on the allometric equation used to estimate biomass. Overall, these results suggest a slightly greater rate of net stand-level change than reported in 1998, and indicate the presence of a significant regional-scale carbon sink in old-growth Amazonian forests during the past two decades.
Long-term decline of the Amazon carbon sink
(Nature Portfolio, 2015) Roel Brienen; Oliver L. Phillips; Ted R. Feldpausch; Emanuel Gloor; Timothy R. Baker; Jon Lloyd; Gabriela López‐González; Abel Monteagudo‐Mendoza; Yadvinder Malhi; Simon L. Lewis
Mapping landscape scale variations of forest structure, biomass, and productivity in Amazonia
(2009) Sassan Saatchi; Yadvinder Malhi; Brian R. Zutta; Wolfgang Buermann; Liana O. Anderson; Alejandro Araújo; Oliver L. Phillips; J. Peacock; Hans ter Steege; G. Lopez Gonzalez
Abstract. Landscape and environmental variables such as topography, geomorphology, soil types, and climate are important factors affecting forest composition, structure, productivity, and biomass. Here, we combine a network of forest inventories with recently developed global data products from satellite observations in modeling the potential distributions of forest structure and productivity in Amazonia and examine how geomorphology, soil, and precipitation control these distributions. We use the RAINFOR network of forest plots distributed in lowland forests across Amazonia, and satellite observations of tree cover, leaf area index, phenology, moisture, and topographical variations. A maximum entropy estimation (Maxent) model is employed to predict the spatial distribution of several key forest structure parameters: basal area, fraction of large trees, fraction of palms, wood density, productivity, and above-ground biomass at 5 km spatial resolution. A series of statistical tests at selected thresholds as well as across all thresholds and jackknife analysis are used to examine the accuracy of distribution maps and the relative contributions of environmental variables. The final maps were interpreted using soil, precipitation, and geomorphological features of Amazonia and it was found that the length of dry season played a key role in impacting the distribution of all forest variables except the wood density. Soil type had a significant impact on the wood productivity. Most high productivity forests were distributed either on less infertile soils of western Amazonia and Andean foothills, on crystalline shields, and younger alluvial deposits. Areas of low elevation and high density of small rivers of Central Amazonia showed distinct features, hosting mainly forests with low productivity and smaller trees.
Methods to estimate aboveground wood productivity from long-term forest inventory plots
(Elsevier BV, 2014) Joey Talbot; Simon L. Lewis; Gabriela López‐González; Roel Brienen; Abel Monteagudo; Timothy R. Baker; Ted R. Feldpausch; Yadvinder Malhi; Mark C. Vanderwel; Alejandro Araujo Murakami
Pattern and process in Amazon tree turnover, 1976–2001
(Royal Society, 2004) Oliver L. Phillips; Timothy R. Baker; Luzmila Arroyo; Níro Higuchi; Timothy J. Killeen; William F. Laurance; Simon L. Lewis; Jon Lloyd; Yadvinder Malhi; Abel Monteagudo
Previous work has shown that tree turnover, tree biomass and large liana densities have increased in mature tropical forest plots in the late twentieth century. These results point to a concerted shift in forest ecological processes that may already be having significant impacts on terrestrial carbon stocks, fluxes and biodiversity. However, the findings have proved controversial, partly because a rather limited number of permanent plots have been monitored for rather short periods. The aim of this paper is to characterize regional-scale patterns of 'tree turnover' (the rate with which trees die and recruit into a population) by using improved datasets now available for Amazonia that span the past 25 years. Specifically, we assess whether concerted changes in turnover are occurring, and if so whether they are general throughout the Amazon or restricted to one region or environmental zone. In addition, we ask whether they are driven by changes in recruitment, mortality or both. We find that: (i) trees 10 cm or more in diameter recruit and die twice as fast on the richer soils of southern and western Amazonia than on the poorer soils of eastern and central Amazonia; (ii) turnover rates have increased throughout Amazonia over the past two decades; (iii) mortality and recruitment rates have both increased significantly in every region and environmental zone, with the exception of mortality in eastern Amazonia; (iv) recruitment rates have consistently exceeded mortality rates; (v) absolute increases in recruitment and mortality rates are greatest in western Amazonian sites; and (vi) mortality appears to be lagging recruitment at regional scales. These spatial patterns and temporal trends are not caused by obvious artefacts in the data or the analyses. The trends cannot be directly driven by a mortality driver (such as increased drought or fragmentation-related death) because the biomass in these forests has simultaneously increased. Our findings therefore indicate that long-acting and widespread environmental changes are stimulating the growth and productivity of Amazon forests.
Seasonal trends of Amazonian rainforest phenology, net primary productivity, and carbon allocation
(Wiley, 2016) Cécile Girardin; Yadvinder Malhi; Christopher E. Doughty; Daniel B. Metcalfe; Patrick Meir; Jhon del Águila Pasquel; Alejandro Araujo‐Murakami; Antônio C. L. da Costa; Javier E. Silva‐Espejo; Filio Farfán Amézquita
Abstract The seasonality of solar irradiance and precipitation may regulate seasonal variations in tropical forests carbon cycling. Controversy remains over their importance as drivers of seasonal dynamics of net primary productivity in tropical forests. We use ground data from nine lowland Amazonian forest plots collected over 3 years to quantify the monthly primary productivity ( NPP ) of leaves, reproductive material, woody material, and fine roots over an annual cycle. We distinguish between forests that do not experience substantial seasonal moisture stress (“humid sites”) and forests that experience a stronger dry season (“dry sites”). We find that forests from both precipitation regimes maximize leaf NPP over the drier season, with a peak in production in August at both humid (mean 0.39 ± 0.03 Mg C ha −1 month −1 in July, n = 4) and dry sites (mean 0.49 ± 0.03 Mg C ha −1 month −1 in September, n = 8). We identify two distinct seasonal carbon allocation patterns (the allocation of NPP to a specific organ such as wood leaves or fine roots divided by total NPP ). The forests monitored in the present study show evidence of either (i) constant allocation to roots and a seasonal trade‐off between leaf and woody material or (ii) constant allocation to wood and a seasonal trade‐off between roots and leaves. Finally, we find strong evidence of synchronized flowering at the end of the dry season in both precipitation regimes. Flower production reaches a maximum of 0.047 ± 0.013 and 0.031 ± 0.004 Mg C ha −1 month −1 in November, in humid and dry sites, respectively. Fruitfall production was staggered throughout the year, probably reflecting the high variation in varying times to development and loss of fruit among species.
Spatial distribution and functional significance of leaf lamina shape in Amazonian forest trees
(Copernicus Publications, 2009) Ana C. M. Malhado; Robert J. Whittaker; Yadvinder Malhi; Richard J. Ladle; Hans ter Steege; Nathalie Butt; Luiz E. O. C. Aragão; C. A. Quesada; A. Murakami-Araujo; Oliver L. Phillips
Abstract. Leaves in tropical forests come in an enormous variety of sizes and shapes, each of which can be ultimately viewed as an adaptation to the complex problem of optimising the capture of light for photosynthesis. However, the fact that many different shape "strategies" coexist within a habitat demonstrate that there are many other intrinsic and extrinsic factors involved, such as the differential investment in support tissues required for different leaf lamina shapes. Here, we take a macrogeographic approach to understanding the function of different lamina shape categories. Specifically, we use 106 permanent plots spread across the Amazon rainforest basin to: 1) describe the geographic distribution of some simple metrics of lamina shape in plots from across Amazonia, and; 2) identify and quantify relationships between key environmental parameters and lamina shape in tropical forests. Because the plots are not randomly distributed across the study area, achieving this latter objective requires the use of statistics that can account for spatial auto-correlation. We found that between 60–70% of the 2791 species and 83 908 individual trees in the dataset could be classified as having elliptic leaves (= the widest part of the leaf is on an axis in the middle fifth of the long axis of the leaf). Furthermore, the average Amazonian tree leaf is 2.5 times longer than it is wide and has an entire margin. Contrary to theoretical expectations we found little support for the hypothesis that narrow leaves are an adaptation to dry conditions. However, we did find strong regional patterns in leaf lamina length-width ratios and several significant correlations with precipitation variables suggesting that water availability may be exerting an as yet unrecognised selective pressure on leaf shape of rainforest trees. Some support was found for the hypothesis that narrow leaves are an adaptation to low nutrient soils. Furthermore, we found a strong correlation between the proportion of trees with non-entire laminas (dissected, toothed, etc.) and mean annual temperature once again supporting the well documented association that provides a basis for reconstructing past temperature regimes.
Spatial distribution and functional significance of leaf lamina shape in Amazonian forest trees
(2009) Ana C. M. Malhado; Robert J. Whittaker; Yadvinder Malhi; Richard J. Ladle; Hans ter Steege; Luiz E. O. C. Aragão; C. A. Quesada; Alejandro Araújo; Oliver L. Phillips; Julie Peacock
Abstract. Leaves in tropical forests come in an enormous variety of sizes and shapes, each of which can be ultimately viewed as an adaptation to the complex problem of optimising the capture of light for photosynthesis. However, the fact that many different shape "strategies" coexist within a habitat demonstrate that there are many other intrinsic and extrinsic factors involved, such as the differential investment in support tissues required for different leaf lamina shapes. Here, we take a macrogeographic approach to understanding the function of different lamina shape categories. Specifically, we use 106 permanent plots spread across the Amazon rainforest basin to: (1) describe the geographic distribution of some simple metrics of lamina shape in plots from across Amazonia, and; (2) identify and quantify relationships between key environmental parameters and lamina shape in tropical forests. Because the plots are not randomly distributed across the study area, achieving this latter objective requires the use of statistics that can account for spatial auto-correlation. We found that between 60–70% of the 2791 species and 83 908 individual trees in the dataset could be classified as elliptic (=the widest part of a leaf is on an axis in the middle fifth of the long axis of the leaf). Furthermore, the average Amazonian tree leaf is 2.5 times longer than it is wide and has an entire margin. Contrary to theoretical expectations we found little support for the hypothesis that narrow leaves are an adaptation to dry conditions and low nutrient soils. However, we did find strong regional patterns in leaf lamina length-width ratios and several significant correlations with precipitation variables suggesting that water availability may be exerting an as yet unrecognised selective pressure on leaf shape of rainforest trees. Furthermore, we found a strong correlation between the proportion of trees with non-entire laminas (dissected, toothed, etc.) and mean annual temperature once again supporting the well documented association that provides a basis for reconstructing past temperature regimes.
Spatial trends in leaf size of Amazonian rainforest trees
(2009) Ana C. M. Malhado; Yadvinder Malhi; Robert J. Whittaker; Richard J. Ladle; Hans ter Steege; Luiz E. O. C. Aragão; C. A. Quesada; Alejandro Araujo‐Murakami; Oliver L. Phillips; J. Peacock
Abstract. Leaf size influences many aspects of tree function such as rates of transpiration and photosynthesis and, consequently, often varies in a predictable way in response to environmental gradients. The recent development of pan-Amazonian databases based on permanent botanical plots (e.g. RAINFOR, ATDN) has now made it possible to assess trends in leaf size across environmental gradients in Amazonia. Previous plot-based studies have shown that the community structure of Amazonian trees breaks down into at least two major ecological gradients corresponding with variations in soil fertility (decreasing south to northeast) and length of the dry season (increasing from northwest to south and east). Here we describe the results of the geographic distribution of leaf size categories based on 121 plots distributed across eight South American countries. We find that, as predicted, the Amazon forest is predominantly populated by tree species and individuals in the mesophyll size class (20.25–182.25 cm2). The geographic distribution of species and individuals with large leaves (>20.25 cm2) is complex but is generally characterized by a higher proportion of such trees in the north-west of the region. Spatially corrected regressions reveal weak correlations between the proportion of large-leaved species and metrics of water availability. We also find a significant negative relationship between leaf size and wood density.