Showing papers by "Oliver L. Phillips published in 2003"
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TL;DR: In this article, the authors present the first comprehensive spatial model of tree α-diversity and tree density in Amazonian rainforests, based on the largest-yet compilation of forest inventories and bolstered by a spatial interpolation technique that allows them to estimate diversity and density in areas that have never been inventoried.
Abstract: Large-scale patterns of Amazonian biodiversity have until now been obscured by a sparse and scattered inventory record. Here we present the first comprehensive spatial model of tree α-diversity and tree density in Amazonian rainforests, based on the largest-yet compilation of forest inventories and bolstered by a spatial interpolation technique that allows us to estimate diversity and density in areas that have never been inventoried. These data were then compared to continent-wide patterns of rainfall seasonality. We find that dry season length, while only weakly correlated with average tree α-diversity, is a strong predictor of tree density and of maximum tree α-diversity. The most diverse forests for any given DSL are concentrated in a narrow latitudinal band just south of the equator, while the least diverse forests for any given DSL are found in the Guayana Shield and Amazonian Bolivia. Denser forests are more diverse than sparser forests, even when we used a measure of diversity that corrects for sample size. We propose that rainfall seasonality regulates tree α-diversity and tree density by affecting shade tolerance and subsequently the number of different functional types of trees that can persist in an area.
388 citations
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TL;DR: In this article, the authors evaluated the extent and pervasiveness of habitat association of trees within 10, 000 km in south-west Amazonia, using 88 floristic plots and detailed soil analyses, sampling up to 849 tree species.
Abstract: 1: Unravelling which factors affect where tropical trees grow is an important goal for
ecologists and conservationists. At the landscape scale, debate is mostly focused on the
degree to which the distributions of tree species are determined by soil conditions or by
neutral, distance-dependent processes. Problems with spatial autocorrelation, sparse
soil sampling, inclusion of species-poor sites with extreme edaphic conditions, and the
difficulty of obtaining sufficient sample sizes have all complicated assessments for high
diversity tropical forests.
2:
We evaluated the extent and pervasiveness of habitat association of trees within a
10 000 km
2
species-rich lowland landscape of uniform climate in south-west Amazonia.
Forests growing on two non-flooded landscape units were inventoried using 88 floristic
plots and detailed soil analyses, sampling up to 849 tree species. We applied singlespecies
and community-level analytical techniques (frequency-distributions of presence
records, association analysis, indicator species analysis, ordination, Mantel correlations,
and multiple regression of distance matrices) to quantify soil/floristic relationships
while controlling for spatial autocorrelation.
3:
Obligate habitat-restriction is very rare: among 230 tree species recorded in
≥
10
localities only five (2.2%) were always restricted to one landscape unit or the other.
4:
However, many species show a significant tendency to habitat association. For example,
using Monte Carlo randomization tests, of the 34 most dominant species across the
landscape the distributions of 26 (76.5%) are significantly related to habitat. We applied
density-independent and frequency-independent estimates of habitat association and
found that rarer species tend to score higher, suggesting that our full community estimates of
habitat association are still underestimated due to the inadequate sampling of rarer species.
5:
Community-level floristic variation across the whole landscape is related to the
variation in 14 of 16 measured soil variables, and to the geographical distances between
samples.
6:
Multiple regression of distance matrices shows that 10% of the floristic variation can
be attributed to spatial autocorrelation, but even after accounting for this at least 40%
is attributable to measured environmental variation.
7:
Our results suggest that substrate-mediated local processes play a much more
important role than distance-dependent processes in structuring forest composition in
Amazonian landscapes.
342 citations
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TL;DR: In this article, the authors compared the performance of two plots-based sampling methods in terms of the quantity of floristic knowledge and ecological insight gained scaled to the field effort required.
Abstract: The tropical flora remains chronically understudied and the lack of floristic understanding hampers ecological research and its application for large-scale conservation planning. Given scarce resources and the scale of the challenge there is a need to maximize the efficiency of both sampling strategies and sampling units, yet there is little information on the relative efficiency of different approaches to floristic assessment in tropical forests. This paper is the first attempt to address this gap. We repeatedly sampled forests in two regions of Amazonia using the two most widely used plot-based protocols of floristic sampling, and compared their performance in terms of the quantity of floristic knowledge and ecological insight gained scaled to the field effort required. Specifically, the methods are assessed first in terms of the number of person-days required to complete each sample (‘effort’), secondly by the total gain in the quantity of floristic information that each unit of effort provides (‘crude inventory efficiency’), and thirdly in terms of the floristic information gained as a proportion of the target species pool (‘proportional inventory efficiency’). Finally, we compare the methods in terms of their efficiency in identifying different ecological patterns within the data (‘ecological efficiency’) while controlling for effort. There are large and consistent differences in the performance of the two methods. The disparity is maintained even after accounting for regional and site-level variation in forest species richness, tree density and the number of field assistants. We interpret our results in the context of selecting the appropriate method for particular research purposes.
140 citations