Abstract
Network analysis is an important tool to analyze the structure of complex systems such as tropical forests. Here, we infer spatial proximity networks in tropical forests by using network science. First, we focus on tree neighborhoods to derive spatial tree networks from forest inventory data. In a second step, we construct species networks to describe the potential for interactions between species. We find remarkably similar tree and species networks among tropical forests in Panama, Sri Lanka and Taiwan. Across these sites only 32 to 51% of all possible connections between species pairs were realized in the species networks. The species networks show the common small-world property and constant node degree distributions not yet described and explained by network science. Our application of network analysis to forest ecology provides a new approach in biodiversity research to quantify spatial neighborhood structures for better understanding interactions between tree species. Our analyses show that details of tree positions and sizes have no important influence on the detected network structures. This suggests existence of simple principles underlying the complex interactions in tropical forests.
Highlights
Network analysis is an important tool to analyze the structure of complex systems such as tropical forests
Tree networks were about factor 50 to 250 larger than their corresponding species network (Table 1, Fig. 1d–e)
The main component of the tree network at the 50-ha plot of Barro Colorado Island (BCI) in Panama included 20,730 out of 20,735 trees which means that almost all trees of the forest were connected
Summary
Network analysis is an important tool to analyze the structure of complex systems such as tropical forests. We apply network analysis for the first time to CTFS‒ForestGEO mega plots (25–50 ha), using all trees with diameter at breast height (dbh) larger than 10 cm for the analysis of the spatial proximity networks of trees and tree species to assess the potential for species interactions. Our focus here is on the non-spatial species networks that are constructed on top of the marked tree networks (with the mark “species”) by combining trees (nodes) of the same species. With this approach a species pair is connected if the interaction zones of at least one pair (or a larger number of pairs) of trees overlap. The tree and species networks should capture essential features of the interaction structure in tropical forests, given that competition for space and light are main driving forces of forest structure and dynamics[36,37,38,39]
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