Biodiversity loss from deforestation may be partly offset by the expansion of secondary forests and plantation forestry in the tropics. However, our current knowledge of the value of these habitats for biodiversity conservation is limited to very few taxa, and many studies are severely confounded by methodological shortcomings. We examined the conservation value of tropical primary, secondary, and plantation forests for 15 taxonomic groups using a robust and replicated sample design that minimized edge effects. Different taxa varied markedly in their response to patterns of land use in terms of species richness and the percentage of species restricted to primary forest (varying from 5% to 57%), yet almost all between-forest comparisons showed marked differences in community structure and composition. Cross-taxon congruence in response patterns was very weak when evaluated using abundance or species richness data, but much stronger when using metrics based upon community similarity. Our results show that, whereas the biodiversity indicator group concept may hold some validity for several taxa that are frequently sampled (such as birds and fruit-feeding butterflies), it fails for those exhibiting highly idiosyncratic responses to tropical land-use change (including highly vagile species groups such as bats and orchid bees), highlighting the problems associated with quantifying the biodiversity value of anthropogenic habitats. Finally, although we show that areas of native regeneration and exotic tree plantations can provide complementary conservation services, we also provide clear empirical evidence demonstrating the irreplaceable value of primary forests. biodiversity indicators ͉ congruence ͉ conservation ͉ tropical forests ͉ Amazon

The biodiversity-productivity relationship (BPR) is foundational to our understanding of the global extinction crisis and its impacts on ecosystem functioning. Understanding BPR is critical for the accurate valuation and effective conservation of biodiversity. Using ground-sourced data from 777,126 permanent plots, spanning 44 countries and most terrestrial biomes, we reveal a globally consistent positive concave-down BPR, showing that continued biodiversity loss would result in an accelerating decline in forest productivity worldwide. The value of biodiversity in maintaining commercial forest productivity alone—US$166 billion to 490 billion per year according to our estimation—is more than twice what it would cost to implement effective global conservation. This highlights the need for a worldwide reassessment of biodiversity values, forest management strategies, and conservation priorities. (Résumé d'auteur

The role of the world's forests as a "sink" for atmospheric carbon dioxide is the subject of active debate. Long-term monitoring of plots in mature humid tropical forests concentrated in South America revealed that biomass gain by tree growth exceeded losses from tree death in 38 of 50 Neotropical sites. These forest plots have accumulated 0.71 ton, plus or minus 0.34 ton, of carbon per hectare per year in recent decades. The data suggest that Neotropical forests may be a significant carbon sink, reducing the rate of increase in atmospheric carbon dioxide.

17Drought threatens tropical rainforests over seasonal to decadal timescales [1][2][3][4] , but the drivers 18 of tree mortality following drought remain poorly understood 5,6 . It has been suggested that 19 reduced availability of non-structural carbohydrates (NSC) critically increases mortality risk 20 through insufficient carbon supply to metabolism ('carbon starvation') 7,8 . However little is 21 known about how NSC stores are affected by drought, especially over the long term, and 22 whether they are more important than hydraulic processes in determining drought-induced 23 mortality. Using data from the world's longest-running experimental drought study in tropical 24 rainforest (in the Brazilian Amazon), we test whether carbon starvation or deterioration of the 25 water-conducting pathways from soil to leaf trigger tree mortality. Biomass loss from 26 mortality in the experimentally-droughted forest increased substantially after >10 years of 27 reduced soil moisture availability. The mortality signal was dominated by the death of large 28 trees, which were at a much greater risk of hydraulic deterioration than smaller trees. 29However, we find no evidence that the droughted trees suffered carbon starvation, as their 30 NSC concentrations were similar to those of un-droughted trees, and growth rates did not 31 decline in either living or dying individuals. Our results indicate that hydraulics, rather than 32 carbon starvation, triggers tree death from drought in tropical rainforest. 34Drought-response observations from both field-scale experiments and natural droughts have 35 demonstrated increased mortality over the short-term (1-3 years), with notably higher 36 vulnerability for some taxa, and for larger trees 6,9,10 . After several years of drought, 37 recovering growth rates in smaller trees, dbh (diameter at breast height) <40 cm, and reduced 38 mortality have been recorded at different locations 6,11,12 . However, the long-term (>10 yr) 39 sensitivity of tropical forests to predicted prolonged and repeated water deficit [1][2][3] we synthesise these data to test whether long-term soil moisture deficit alters NSC storage 64 and use in tropical rainforest trees, and if this, or hydraulic processes, are most strongly 65 associated with increased mortality rates. 66By 2014, following 13 years of the TFE treatment, cumulative biomass loss through mortality 67 was 41.0±2.7% relative to pre-treatment values (Fig. 1a), and the rate of loss had increased 68 substantially since the previous reported value of 17.2±0.8%, after 7 years of TFE 6 . 69Accelerating biomass loss and failure to recover substantially, or to reach a new 70 equilibrium 13 , has led to a committed flux to the atmosphere from decomposing necromass of 71 101.9±19.1 Mg C ha -1 (Fig. 1a). This biomass loss has been driven by elevated mortality in 72 the largest trees (Fig. 1b), as previously observed over shorter timescales 6 , and has created a 73 canopy that has had a persistently lower average leaf area index during 2010-2014 74 (12.0±1...

Rain forest fragments in central Amazonia were found to experience a dramatic loss of above-ground tree biomass that is not offset by recruitment of new trees. These losses were largest within 100 meters of fragment edges, where tree mortality is sharply increased by microclimatic changes and elevated wind turbulence. Permanent study plots within 100 meters of edges lost up to 36 percent of their biomass in the first 10 to 17 years after fragmentation. Lianas (climbing woody vines) increased near edges but usually compensated for only a small fraction of the biomass lost as a result of increased tree mortality.

The extent to which pre-Columbian societies altered Amazonian landscapes is hotly debated. We performed a basin-wide analysis of pre-Columbian impacts on Amazonian forests by overlaying known archaeological sites in Amazonia with the distributions and abundances of 85 woody species domesticated by pre-Columbian peoples. Domesticated species are five times more likely than nondomesticated species to be hyperdominant. Across the basin, the relative abundance and richness of domesticated species increase in forests on and around archaeological sites. In southwestern and eastern Amazonia, distance to archaeological sites strongly influences the relative abundance and richness of domesticated species. Our analyses indicate that modern tree communities in Amazonia are structured to an important extent by a long history of plant domestication by Amazonian peoples

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Aim Large trees (d.b.h.≥70 cm) store large amounts of biomass. Several studies suggest that large trees may be vulnerable to changing climate, potentially leading to declining forest biomass storage. Here we determine the importance of large trees for tropical forest biomass storage and explore which intrinsic (species trait) and extrinsic (environment) variables are associated with the density of large trees and forest biomass at continental and pan-tropical scales. Location Pan-tropical. Methods Aboveground biomass (AGB) was calculated for 120 intact lowland moist forest locations. Linear regression was used to calculate variation in AGB explained by the density of large trees. Akaike information criterion weights (AICc-wi) were used to calculate averaged correlation coefficients for all possible multiple regression models between AGB/density of large trees and environmental and species trait variables correcting for spatial autocorrelation. Results Density of large trees explained c. 70% of the variation in pan-tropical AGB and was also responsible for significantly lower AGB in Neotropical [287.8 (mean)±105.0 (SD) Mg ha -1 versus Palaeotropical forests (Africa 418.3±91.8 Mg ha-1; Asia 393.3±109.3 Mg ha-1). Pan-tropical variation in density of large trees and AGB was associated with soil coarseness (negative), soil fertility (positive), community wood density (positive) and dominance of wind dispersed species (positive), temperature in the coldest month (negative), temperature in the warmest month (negative) and rainfall in the wettest month (positive), but results were not always consistent among continents. Main conclusions Density of large trees and AGB were significantly associated with climatic variables, indicating that climate change will affect tropical forest biomass storage. Species trait composition will interact with these future biomass changes as they are also affected by a warmer climate. Given the importance of large trees for variation in AGB across the tropics, and their sensitivity to climate change, we emphasize the need for in-depth analyses of the community dynamics of large trees. (Résumé d'auteur