Showing papers by "Carlos A. Quesada published in 2016"

Amazon forest response to repeated droughts

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.

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.

Storm-triggered landslides in the Peruvian Andes and implications for topography, carbon cycles, and biodiversity

Abstract: . In this study, we assess the geomorphic role of a rare, large-magnitude landslide-triggering event and consider its effect on mountain forest ecosystems and the erosion of organic carbon in an Andean river catchment. Proximal triggers such as large rain storms are known to cause large numbers of landslides, but the relative effects of such low-frequency, high-magnitude events are not well known in the context of more regular, smaller events. We develop a 25-year duration, annual-resolution landslide inventory by mapping landslide occurrence in the Kosnipata Valley, Peru, from 1988 to 2012 using Landsat, QuickBird, and WorldView satellite images. Catchment-wide landslide rates were high, averaging 0.076 % yr−1 by area. As a result, landslides on average completely turn over hillslopes every ∼ 1320 years, although our data suggest that landslide occurrence varies spatially and temporally, such that turnover times are likely to be non-uniform. In total, landslides stripped 26 ± 4 tC km−2 yr−1 of organic carbon from soil (80 %) and vegetation (20 %) during the study period. A single rain storm in March 2010 accounted for 27 % of all landslide area observed during the 25-year study and accounted for 26 % of the landslide-associated organic carbon flux. An approximately linear magnitude–frequency relationship for annual landslide areas suggests that large storms contribute an equivalent landslide failure area to the sum of lower-frequency landslide events occurring over the same period. However, the spatial distribution of landslides associated with the 2010 storm is distinct. On the basis of precipitation statistics and landscape morphology, we hypothesise that focusing of storm-triggered landslide erosion at lower elevations in the Kosnipata catchment may be characteristic of longer-term patterns. These patterns may have implications for the source and composition of sediments and organic material supplied to river systems of the Amazon Basin, and, through focusing of regular ecological disturbance, for the species composition of forested ecosystems in the region.

Evolutionary heritage influences Amazon tree ecology.

Abstract: Lineages tend to retain ecological characteristics of their ancestors through time. However, for some traits, selection during evolutionary history may have also played a role in determining trait values. To address the relative importance of these processes requires large-scale quantification of traits and evolutionary relationships among species. The Amazonian tree flora comprises a high diversity of angiosperm lineages and species with widely differing life-history characteristics, providing an excellent system to investigate the combined influences of evolutionary heritage and selection in determining trait variation. We used trait data related to the major axes of life-history variation among tropical trees (e.g. growth and mortality rates) from 577 inventory plots in closed-canopy forest, mapped onto a phylogenetic hypothesis spanning more than 300 genera including all major angiosperm clades to test for evolutionary constraints on traits. We found significant phylogenetic signal (PS) for all traits, consistent with evolutionarily related genera having more similar characteristics than expected by chance. Although there is also evidence for repeated evolution of pioneer and shade tolerant life-history strategies within independent lineages, the existence of significant PS allows clearer predictions of the links between evolutionary diversity, ecosystem function and the response of tropical forests to global change.

Forest structure along a 600 km transect of natural disturbances and seasonality gradients in central‐southern Amazonia

Abstract: A negative relationship between stand biomass and the density of stems is expected to develop during the self-thinning process in resource-limited forests; this leads to a large proportion of the total biomass occurring in large trees. Nevertheless, frequent disturbance regimes can reduce self-thinning and the accumulation of large trees. We investigated size-density relationships and the contribution of large trees (dbh ≥ 70 cm) to stand biomass in 55 1-ha plots along a 600 km transect in central-southern Amazonia. The effects of natural-disturbance gradients (frequency of storms and soil characteristics) and seasonality on forest-structure components (density of stems and mean individual mass) and stand biomass were examined. Contrary to self-thinning predictions, stand biomass increased in forests with higher stem densities. Large trees contained only an average of 5% of stand biomass, and half of the stand biomass was represented by small trees with diameters

Soil–Vegetation Interactions in Amazonia

Abstract: Edaphic properties are an important environmental factor modulating the structure and function of tropical forests. Here we discuss more than a century of literature regarding the interactions between soils and forests in the Amazon basin. Soil properties are first discussed in the perspective of the sequence of geological events leading to the diverse edaphic mosaic found in the present day with the importance of soil properties in influencing nutrient cycling characteristics of mature tropical forests discussed. An examination of the relationship between nutrient concentrations in leaves versus soils is then used to show that diverse conditions of nutrient limitation and abundance exist across the basin. The interacting influences of soil physical and chemical properties in determining basin-wide patterns of forest floristic composition, above-ground biomass, growth, and tree residence time are also considered with a new conceptual model integrating the role of different soil properties as key effectors of variations in forest structure and function discussed.

The Biogeochemistry of the Main Forest Vegetation Types in Amazonia

Abstract: The structure and functioning of natural ecosystems reflect spatial and temporal characteristics of the atmosphere, physiography (geology, topo-hydro-pedo sequences), and biodiversity (vegetation type and associated fauna). Exchanges of gases, water, and organic and inorganic compounds between atmosphere and biosphere (vegetation, soil) strongly contribute to biogeochemical phenomena in Amazonia and to atmospheric phenomena within and outside of Amazonia. Some of these exchanges have importance for cloud formation and rainfall, while others (carbonic and trace gases) contribute to carbon sequestration/greenhouse effects. The Amazon basin encompasses diverse combinations of climate, soil, and hydrology that result in a variety of vegetation types. The current state of knowledge on Amazonian regional biochemistry is mainly based on studies carried out in terra firme type ‘lowland evergreen rainforest’, with a focus on the carbon cycle. For a better understanding of the biogeochemical functioning of the Amazon basin, attention to physiography and its relationship, including feedback mechanism, with vegetation diversity at the landscape scale is needed. This chapter synthesises patterns in biogeochemistry of the main vegetation formations of the Amazon basin. The objective is to demonstrate differences in elemental cycles (stock and fluxes) among the main vegetation formations. The patterns of fixation, storage, and use of nutrients for biomass production, the patterns of internal (re)cycling (leaching of crown nutrients, litterfall, root growth and death) within the main forest types, and the patterns of litter decomposition and soil processes (nutrient availability, nitrogen mineralisation vs. immobilisation) and gas emissions from soil are discussed.

Riqueza e seletividade de palmeiras ao longo de gradientes ambientais na região do interflúvio purus-madeira em porto velho, ro

Abstract: This study aimed to evaluate environmental gradients influence on richness and selectivity of Palm (Arecaceae) species in a section of Purus-Madeira interfluvial region, Cunia Ecological Station, in Porto Velho – Rondonia, Brazil. It has been used RAPELD sampling method. 48 plots were studied in a 25km 2 area, being 30 plots in Terra Firme and 18 riparians. It was identified a comunity composed of 49 species distributed in 11 genres. Cluster similarity analysis (Twinspan ordenation method) were used to verify preferential species according to local conditions. Sorensen and Twinspan similarity analysis indicates response from species to soil type variation and water distance, some species occuring only at hidromorphic soils. Results show that site Palms richness and selectivity are determined in part by soil inclination, type and humidity, existing selectivity internal gradients inside and between sampling plots which evidence its strong influence on site palms richness. Keywords: Arecaceae; palms; environmental factors; Amazon; vegetation distribution.

Trait data from: "Evolutionary heritage influences Amazon tree ecology"

Abstract: Lineages tend to retain ecological characteristics of their ancestors through time. However, for some traits, selection during evolutionary history may have also played a role in determining trait values. To address the relative importance of these processes requires large-scale quantification of traits and evolutionary relationships amongst species. The Amazonian tree flora comprises a high diversity of angiosperm lineages and species with widely differing life history characteristics, providing an excellent system to investigate the combined influences of evolutionary heritage and selection in determining trait variation. We used trait data related to the major axes of life history variation among tropical trees (e.g. growth and mortality rates) from 577 inventory plots in closed-canopy forest, mapped onto a phylogenetic hypothesis spanning >300 genera including all major angiosperm clades to test for evolutionary constraints on traits. We found significant phylogenetic signal for all traits, consistent with evolutionarily related genera having more similar characteristics than expected by chance. Although there is also evidence for repeated evolution of similar, pioneer and shade tolerant life history strategies within independent lineages, the existence of significant phylogenetic signal allowsLineages tend to retain ecological characteristics of their ancestors through time. However, for some traits, selection during evolutionary history may have also played a role in determining trait values. To address the relative importance of these processes requires large-scale quantification of traits and evolutionary relationships amongst species. The Amazonian tree flora comprises a high diversity of angiosperm lineages and species with widely differing life history characteristics, providing an excellent system to investigate the combined influences of evolutionary heritage and selection in determining trait variation. We used trait data related to the major axes of life history variation among tropical trees (e.g. growth and mortality rates) from 577 inventory plots in closed-canopy forest, mapped onto a phylogenetic hypothesis spanning >300 genera including all major angiosperm clades to test for evolutionary constraints on traits. We found significant phylogenetic signal for all traits, consistent with evolutionarily related genera having more similar characteristics than expected by chance. Although there is also evidence for repeated evolution of similar, pioneer and shade tolerant life history strategies within independent lineages, the existence of significant phylogenetic signal allows clearer predictions of the links between evolutionary diversity, ecosystem function and the response of tropical forests to global change. clearer predictions of the links between evolutionary diversity, ecosystem function and the response of tropical forests to global change.