Iêda Leão do Amaral

Drought sensitivity of the Amazon rainforest

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 × 1015 to 1.6 × 1015 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

*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.

Inventário florístico de floresta ombrófila densa de terra firme, na região do Rio Urucu-Amazonas, Brasil

O presente trabalho teve por objetivo principal caracterizar a vegetacao da area de exploracao de petroleo da PETROBRAS, no rio Urucu, bem como dar subsidios para a utilizacao da floresta de forma organizada e produtiva, baseada em conhecimentos cientificos, de modo nao somente a produzir resultados economicos mas principalmente conservar o ambiente. Os tres hectares de floresta inventariada sustentam 2.241 individuos, abrangendo arvores, palmeiras e cipos com DAP> 10 cm, distribuidos em 577 especies, 225 generos e 60 familias. Tres medidas de importância ecologica — abundância, dominância e frequencia — expressas como tres porcentagens, foram somadas para obter um indice de Valor de Importância (IVI). As duas especies com os maiores IV1E, em toda a area pesquisada, foram Eschweilera coriacea (DC.) S. A. Mori, com 15% no hectare 2 e E. wachenheimii (Benoist) Sandwith, com 14% no hectare 3. As familias que obtiveram os maiores indices de Valor de Importância (IVIF), em media, nos 3 hectares, foram Lecythidaceae (51,6%), Sapotaceae (40,2%) e Chrysobalanaceae (24,6%).

Variation in stem mortality rates determines patterns of above-ground biomass in Amazonian forests: implications for dynamic global vegetation models

Abstract Understanding the processes that determine above‐ground biomass (AGB) in Amazonian forests is important for predicting the sensitivity of these ecosystems to environmental change and for designing and evaluating dynamic global vegetation models (DGVMs). AGB is determined by inputs from woody productivity [woody net primary productivity (NPP)] and the rate at which carbon is lost through tree mortality. Here, we test whether two direct metrics of tree mortality (the absolute rate of woody biomass loss and the rate of stem mortality) and/or woody NPP, control variation in AGB among 167 plots in intact forest across Amazonia. We then compare these relationships and the observed variation in AGB and woody NPP with the predictions of four DGVMs. The observations show that stem mortality rates, rather than absolute rates of woody biomass loss, are the most important predictor of AGB, which is consistent with the importance of stand size structure for determining spatial variation in AGB. The relationship between stem mortality rates and AGB varies among different regions of Amazonia, indicating that variation in wood density and height/diameter relationships also influences AGB. In contrast to previous findings, we find that woody NPP is not correlated with stem mortality rates and is weakly positively correlated with AGB. Across the four models, basin‐wide average AGB is similar to the mean of the observations. However, the models consistently overestimate woody NPP and poorly represent the spatial patterns of both AGB and woody NPP estimated using plot data. In marked contrast to the observations, DGVMs typically show strong positive relationships between woody NPP and AGB. Resolving these differences will require incorporating forest size structure, mechanistic models of stem mortality and variation in functional composition in DGVMs.

Fast demographic traits promote high diversification rates of Amazonian trees

The Amazon rain forest sustains the worlds highest tree diversity, but it remains unclear why some clades of trees are hyperdiverse, whereas others are not. Using dated phylogenies, estimates of current species richness and trait and demographic data from a large network of forest plots, we show that fast demographic traits – short turnover times – are associated with high diversification rates across 51 clades of canopy trees. This relationship is robust to assuming that diversification rates are either constant or decline over time, and occurs in a wide range of Neotropical tree lineages. This finding reveals the crucial role of intrinsic, ecological variation among clades for understanding the origin of the remarkable diversity of Amazonian trees and forests.

Análise ecológica de um hectare em floresta Ombrófila densa de terra-firme, estrada da Várzea, Amazonas, Brasil1

A fitossociological survey was carried out in a terra firme dense tropical rainforest on a stretch of Estrada da Varzea (Foodplain road) linking Manaus to the counties of Silves and Itapiranga in Amazonas state. The work was aimed at analysing floristic composition fitossociological parameters necessary for determining species ecological importance value index (IVI), as well as, the vegetation structure. Sample distribution was carried out through sattelite image analysis. Sampling was done in a 10 x 1.000m transect, divided into 20 subplots, each measuring 10 x 50m. All arboreal individuals with a circumference at breast height (CBH) ≥ 30cm, such as, palm trees, vines and terrestrial herbs were included from which samples were taken for later identification; according to the Cronquist system. As a result, 527 individuals distributed into 47 families, 118 genera and 196 species, were recorded. Families presenting the highest diversity were Lecythidaceae (20), Lauraceae (19), Sapotaceae (17), Chrysobalanaceae, Burscraceae (12) and Annonaceae (9), representing 47% of the family diversity, showing local diversity to be concentrated within few families. Species with highest importance value index (IVI), Goupia glabra Aubl. (9.34), Ocotea rubra(Meiss.) Allen (8.71), because of their large diameter represented in the relative dominance. Nevertheless, when comparing local density with the one obtained from other works using the same sampling criteria it was concluded that the locality is less abundant in number of individuals per ha., but the diversity of families and species docs not differ from results reached for terra-firme forests within other areas in Amazonia.

Aspectos florísticos de 13 hectares da área de Cachoeira Porteira-PA

ABSTRACT This work describes the floristic composition in the future Cachoeira Porteira UHE-PA water reservoir area (located onthe left margin of the Trombetas river), and the characterization of the vegetation. Data on abundance, dominance,frequency, Species Importance Value Indexes (IVIE), Family Importance Value Index (IVIF), and forest horizontal structureanalysis, are presented in the present study. The studies developed in this work show the area‘s most important speciesand families, according to their influence on the forest structural profile definition, in addition to the identification ofvegetation different types. The 13 surveyed forest hectares support 4.583 individuals, comprising trees, palms andlianas with DAP > 10cm, distributed in 359 species, 217 genera and 55 families (Three measures of ecological importancewere totaled to give an Importance Value Index (IVIE) of the species). The two species with the highest IVIE, in allsurveyed area, were Eschweilera coriacea

Soil-induced impacts on forest structure drive coarse woody debris stocks across central Amazonia

Background: Coarse woody debris (CWD) is an essential component in tropical forest ecosystems and its quantity varies widely with forest types. Aims: Relationships among CWD, soil, forest structure and other environmental factors were analysed to understand the drivers of variation in CWD in forests on different soil types across central Amazonia. Methods: To estimate CWD stocks and density of dead wood debris, 75 permanent forest plots of 0.5 ha in size were assessed along a transect that spanned ca. 700 km in undisturbed forests from north of the Rio Negro to south of the Rio Amazonas. Soil physical properties were evaluated by digging 2-m-deep pits and by taking auger samples. Results: Soil physical properties were the best predictors of CWD stocks; 37% of its variation was explained by effective soil depth. CWD stocks had a two-fold variation across a gradient of physical soil constraints (i.e. effective soil depth, anoxia and soil structure). Average biomass per tree was related to physical soil constraints, which, in turn, had a strong relationship with local CWD stocks. Conclusions: Soil physical properties appear to control average biomass per tree (and through this affect forest structure and dynamics), which, in turn, is correlated with CWD production and stocks.

Low Phylogenetic Beta Diversity and Geographic Neo-endemism in Amazonian White-sand Forests

Over the past three decades, many small-scale floristic studies of white-sand forests across the Amazon basin have been published. Nonetheless, a basin-wide description of both taxonomic and phylogenetic alpha and beta diversity at regional scales has never been achieved. We present a complete floristic analysis of white-sand forests across the Amazon basin including both taxonomic and phylogenetic diversity. We found strong regional differences in the signal of phylogenetic community structure with both overall and regional Net Relatedness Index and Nearest Taxon Index values found to be significantly positive leading to a pattern of phylogenetic clustering. Additionally, we found high taxonomic dissimilarity but low phylogenetic dissimilarity in pairwise community comparisons. These results suggest that recent diversification has played an important role in the assembly of white-sand forests causing geographic neo-endemism patterns at the regional scale.

Salicilatos isolados de folhas e talos de Salix martiana Leyb. (Salicaceae)

Salix martiana Leyb. is an endemic species from the Amazon river floodplain areas (varzeas), of the State of Amazonas. Stems and leaves were extracted with dichloromethane, methanol and hydro-alcohol and these extracts were fractionated by using conventional chromatographic techniques. The major substances isolated, salicin and trichocarposide (6-0-p-coumaroyl salicin), were determined through analyses of NMR 1D (1H and 13C) and NMR 2D (gHSQC and gHMBC). These compounds were isolated for the first time in Salix martiana Leyb. (Salicaceae). The percentage of these compounds in S. martiana is very high. The extracts were analyzed for their DPPH antioxidant capacity and the methanolic from the leaves and the hydro-alcoholic from the stems were the more active.