Showing papers by "Oliver L. Phillips published in 2006"

Continental-scale patterns of canopy tree composition and function across Amazonia

Abstract: The world's greatest terrestrial stores of biodiversity and carbon are found in the forests of northern South America, where large-scale biogeographic patterns and processes have recently begun to be described. Seven of the nine countries with territory in the Amazon basin and the Guiana shield have carried out large-scale forest inventories, but such massive data sets have been little exploited by tropical plant ecologists. Although forest inventories often lack the species-level identifications favoured by tropical plant ecologists, their consistency of measurement and vast spatial coverage make them ideally suited for numerical analyses at large scales, and a valuable resource to describe the still poorly understood spatial variation of biomass, diversity, community composition and forest functioning across the South American tropics. Here we show, by using the seven forest inventories complemented with trait and inventory data collected elsewhere, two dominant gradients in tree composition and function across the Amazon, one paralleling a major gradient in soil fertility and the other paralleling a gradient in dry season length. The data set also indicates that the dominance of Fabaceae in the Guiana shield is not necessarily the result of root adaptations to poor soils (nodulation or ectomycorrhizal associations) but perhaps also the result of their remarkably high seed mass there as a potential adaptation to low rates of disturbance.

The regional variation of aboveground live biomass in old‐growth Amazonian forests

Abstract: The biomass of tropical forests plays an important role in the global carbon cycle, both as a dynamic reservoir of carbon, and as a source of carbon dioxide to the atmosphere in areas undergoing deforestation. However, the absolute magnitude and environmental determinants of tropical forest biomass are still poorly understood. Here, we present a new synthesis and interpolation of the basal area and aboveground live biomass of old-growth lowland tropical forests across South America, based on data from 227 forest plots, many previously unpublished. Forest biomass was analyzed in terms of two uncorrelated factors: basal area and mean wood density. Basal area is strongly affected by local landscape factors, but is relatively invariant at regional scale in moist tropical forests, and declines significantly at the dry periphery of the forest zone. Mean wood density is inversely correlated with forest dynamics, being lower in the dynamic forests of western Amazonia and high in the slow-growing forests of eastern Amazonia. The combination of these two factors results in biomass being highest in the moderately seasonal, slow growing forests of central Amazonia and the Guyanas (up to 350?Mg?dry weight?ha?1) and declining to 200-250?Mg?dry weight?ha?1 at the western, southern and eastern margins. Overall, we estimate the total aboveground live biomass of intact Amazonian rainforests (area 5.76 × 106?km2 in 2000) to be 93±23?Pg?C, taking into account lianas and small trees. Including dead biomass and belowground biomass would increase this value by approximately 10% and 21%, respectively, but the spatial variation of these additional terms still needs to be quantified

Resilience of southwestern Amazon forests to anthropogenic edge effects.

Abstract: : Anthropogenic edge effects can compromise the conservation value of mature tropical forests. To date most edge-effect research in Amazonia has concentrated on forests in relatively seasonal locations or with poor soils in the east of the basin. We present the first evaluation from the relatively richer soils of far western Amazonia on the extent to which mature forest biomass, diversity, and composition are affected by edges. In a southwestern Amazonian landscape we surveyed woody plant diversity, species composition, and biomass in 88 × 0.1 ha samples of unflooded forest that spanned a wide range in soil properties and included samples as close as 50 m and as distant as >10 km from anthropogenic edges. We applied Mantel tests, multiple regression on distance matrices, and other multivariate techniques to identify anthropogenic effects before and after accounting for soil factors and spatial autocorrelation. The distance to the nearest edge, access point, and the geographical center of the nearest community (“anthropogenic-distance effects”) all had no detectable effect on tree biomass or species diversity. Anthropogenic-distance effects on tree species composition were also below the limits of detection and were negligible in comparison with natural environmental and spatial factors. Analysis of the data set's capacity to detect anthropogenic effects confirmed that the forests were not severely affected by edges, although because our study had few plots within 100 m of forest edges, our confidence in patterns in the immediate vicinity of edges is limited. It therefore appears that the conservation value of most “edge” forests in this region has not yet been compromised substantially. We caution that because this is one case study it should not be overinterpreted, but one explanation for our findings may be that western Amazonian tree species are naturally faster growing and more disturbance adapted than those farther east. Resumen: Los cambios antropogenicos pueden comprometer el valor de conservacion de bosques tropicales maduros. A la fecha, la mayor parte de la investigacion del efecto de borde en la Amazonia se ha concentrado en bosques en localidades relativamente temporales o con suelos pobres en el este de la cuenca. Presentamos la primera evaluacion del grado en que la biomasa, diversidad y composicion de bosques maduros son afectadas por los bordes en los suelos relativamente mas ricos en el lejano oeste de la Amazonia. Muestreamos la diversidad, composicion de especies y biomasa de plantas lenosas en 88 parcelas de 0.1 ha en bosques no inundables en un paisaje del suroeste de la Amazonia con una amplia gama de caracteristicas edaficas y que incluian muestras tan cercanas como 50 m y tan distantes como >10 km de los bordes antropogenicos. Aplicamos pruebas de Mantel, regresion multiple en matrices de distancia y otras tecnicas multivariadas para identificar los efectos antropogenicos antes y despues de considerar los factores edaficos y la autocorrelacion espacial. La distancia al borde, punto de acceso y centro geografico de la comunidad mas cercana (efectos antropogenicos-distancia) no tuvieron efecto detectable sobre la biomasa o diversidad de especies de arboles. Los efectos antropogenicos-distancia sobre la composicion de especies de arboles tambien estuvieron debajo de los limites de deteccion y fueron insignificantes en comparacion con los factores ambientales y espaciales. El analisis de la capacidad del conjunto de datos para detectar efectos antropogenicos confirmo que los bosques no fueron afectados por los bordes severamente, aunque nuestra confianza en los patrones de la vecindad inmediata del borde es limitada, porque nuestro estudio tenia pocas parcelas a menos de 100 m del borde. Por lo tanto, parece que el valor de conservacion de la mayoria de los bosques “borde” en esta region aun no ha sido comprometido sustancialmente. Prevenimos que este es un estudio no debe ser sobre interpretado porque solo es un caso, pero una explicacion para nuestros resultados puede ser que las especies de arboles de la Amazonia occidental estan naturalmente mas adaptadas a perturbaciones y tienen crecimiento mas rapido que las del oriente.

Impacts of global atmospheric change on tropical forests.

Abstract: In a recent TREE review, Wright [1] concluded that the structure and dynamics of tropical forests are changing, caused by large-scale alterations in the abiotic environment. However, his assertions that the evidence for such a response comes ‘almost exclusively from censuses of tree plots and is controversial’ requires further clarification. We suggest that a more complete review of recent forest-plot research and the inclusion of studies from fields outside community ecology considerably reduces the controversy and exclusivity of the plot-based results.

Tropical forests and atmospheric carbon dioxide: current conditions and future scenarios

Abstract: This volume, first published in 2006, presents findings on climate change from leading international scientists, for researchers, policy-makers and engineers.

Tropical forests and atmospheric carbon dioxide: current knowledge and potential future scenarios

Abstract: Tropical forests affect atmospheric carbon dioxide concentrations, and hence modulate the rate of climate change - by being a source of carbon, from land-use change (deforestation), and as a sink or source of carbon in remaining intact forest. These fluxes are among the least understood and most uncertain major fluxes within the global carbon cycle. We synthesise recent research on the tropical forest biome carbon balance, suggesting that intact forests presently function as a carbon sink of approx. 1.2 Pg C a ^-1, and that deforestation emissions at the higher end of the reported 1 - 3 Pg C a^ -1 spectrum are likely. Scenarios suggest that the source from deforestation will remain high, whereas the sink in intact forest is unlikely to continue, and remaining tropical forests may become a major carbon source via one or more of (i) changing photosynthesis/respiration rates, (ii) functional/biodiversity changes within intact forest, or widespread forest collapse via (iii) drought, or (iv) fire. Each scenario risks possible positive feedbacks with the climate system suggesting that current estimates of the possible rate, magnitude and effects of global climate change over the coming decades may be conservative.

Impacts of global change on the structure, dynamics and function of South American tropical forests

Abstract: In addition to documenting the vulnerability of tropical rainforests, the volume focuses on strategies for mitigating and combating emerging threats.