Consistent patterns of common species across tropical tree communities

Trees structure the Earth’s most biodiverse ecosystem, tropical forests. The vast number of tree species presents a formidable challenge to understanding these forests, including their response to environmental change, as very little is known about most tropical tree species. A focus on the common species may circumvent this challenge. Here we investigate abundance patterns of common tree species using inventory data on 1,003,805 trees with trunk diameters of at least 10 cm across 1,568 locations1,2,3,4,5,6 in closed-canopy, structurally intact old-growth tropical forests in Africa, Amazonia and Southeast Asia. We estimate that 2.2%, 2.2% and 2.3% of species comprise 50% of the tropical trees in these regions, respectively. Extrapolating across all closed-canopy tropical forests, we estimate that just 1,053 species comprise half of Earth’s 800 billion tropical trees with trunk diameters of at least 10 cm. Despite differing biogeographic, climatic and anthropogenic histories7, we find notably consistent patterns of common species and species abundance distributions across the continents. This suggests that fundamental mechanisms of tree community assembly may apply to all tropical forests. Resampling analyses show that the most common species are likely to belong to a manageable list of known species, enabling targeted efforts to understand their ecology. Although they do not detract from the importance of rare species, our results open new opportunities to understand the world’s most diverse forests, including modelling their response to environmental change, by focusing on the common species that constitute the majority of their trees

SUBGOVERNMENTS AND THE IMPACT OF POLICY FRAGMENTATION AND ACCOMMODATION

For many years political scientists have utilized the subgovernment model of policy-making to explain certain types of policy output. Recently a number of scholars have argued that the traditional conceptualization of subgovernments was simplistic and incomplete. They view subgovernments as a complex and integral part of the larger policy-making environment. This paper examines this "new" subgovernment by analyzing its role in contemporary public policy-making. If subgovernments have lost their autonomy and been exposed to the complex demands of the larger political system, what impact does this have on policy outputs? Relying upon the literature on subgovernments and their principal components, the paper offers an interpretation of how subgovernments have potentially expanded their influence on public policy as a result of two contemporary developments: policy-making fragmentation, and the accommodation of policy outputs. Copyright 1988 by The Policy Studies Organization.