11
Patterns of Tree Species Diversity
Among Tropical Rain Forests
PETER S. ASHTON l AND J.V. LAFRANKlE2
I Arnold Arboretum and Organismic and Evolutionary Biology, Harvard University, 22
Divinity Avenue, Cambridge, MA 02138, USA
2 Center for Tropical F'orest Science, Nanyang Technical University, National Institute of
Education, 469 Bukit Timah Road, Singapore 1025, Republic of Singapore
Abstract
In this early report of a global program of tropical rain forest research, the causes of
tree species diversity are examined through comparisons at global, regional and
local scales. Species diversity in communities of sessile organisms has been attributed to many factors. Hypotheses which address two of these, Connell's on intermediate levels of disturbance and Tilman's on competition for heterogeneous soil
resources, are reviewed and clarified in context of exceptionally rich communities.
Our evidence suggests that many factors are important, but at varying scales in
space and time. Thcse differing scales will be discussed with reference to our new
data. Unresolved impediments to thc community drift hypothesis will be presented.
In the summary, lessons for conservation will be identified.
1 Introduction
The rapidly increasing research 011 plant biodiversity has come to focus on two
kinds of questions: Where and why is biodiversity concentrated geographically;
and what are the relative roles of selection (i.e., ecological deterministic forces)
versus historical (i.e., stochastic) forces including catastrophe and dispersal opportunities, in determining patterns of biodiversity? Biodiversity encompasses not only
the numbers of different entities, but also the diversity in their levels of abundance.
Fundamentally, biodiversity refers to the genetic diversity of ecosystems, but the
Key words. correlates of species richness, tropical lowland evergreen forest, tropical Asia,
long-term tree demography research plots
161
Patterns of Tree Species Diversity
Among Tropical Rain Forests
PETER S. ASHTON l AND J.V. LAFRANKlE2
I Arnold Arboretum and Organismic and Evolutionary Biology, Harvard University, 22
Divinity Avenue, Cambridge, MA 02138, USA
2 Center for Tropical F'orest Science, Nanyang Technical University, National Institute of
Education, 469 Bukit Timah Road, Singapore 1025, Republic of Singapore
Abstract
In this early report of a global program of tropical rain forest research, the causes of
tree species diversity are examined through comparisons at global, regional and
local scales. Species diversity in communities of sessile organisms has been attributed to many factors. Hypotheses which address two of these, Connell's on intermediate levels of disturbance and Tilman's on competition for heterogeneous soil
resources, are reviewed and clarified in context of exceptionally rich communities.
Our evidence suggests that many factors are important, but at varying scales in
space and time. Thcse differing scales will be discussed with reference to our new
data. Unresolved impediments to thc community drift hypothesis will be presented.
In the summary, lessons for conservation will be identified.
1 Introduction
The rapidly increasing research 011 plant biodiversity has come to focus on two
kinds of questions: Where and why is biodiversity concentrated geographically;
and what are the relative roles of selection (i.e., ecological deterministic forces)
versus historical (i.e., stochastic) forces including catastrophe and dispersal opportunities, in determining patterns of biodiversity? Biodiversity encompasses not only
the numbers of different entities, but also the diversity in their levels of abundance.
Fundamentally, biodiversity refers to the genetic diversity of ecosystems, but the
Key words. correlates of species richness, tropical lowland evergreen forest, tropical Asia,
long-term tree demography research plots
161