The effect of exotic tree plantations on the biodiversity of leaflitter arthropods in tropical islands

Replacing native forests by plantations of exotic tree species causes a reduction in the local biodiversity because plantations are commonly simplified systems. This practice would have greater impacts on islands, where the biota is especially vulnerable to environmental changes. I studied leaflitter arthropod diversity associated with native forests and abandoned (45 years) exotic wood plantations of mahogany, Casuarina and Caribbean pine in tropical islands. My general hypotheses were: (1) native forests harbor higher species richness than abandoned exotic wood plantations; (2) leaflitter structural complexity influences positively the arthropod species richness, and (3) endemic and native arthropods will be more diverse in native forests than in the plantations. I found a general tendency of higher species richness in the native forests than in the plantations. Nevertheless, the arthropod species richness was higher in one of the mahogany plantation study sites. Consequently, I seek to identify a mechanism behind these patterns. Since the complexity of the leaflitter habitat is related to the diversity of the surrounding forest, one would expect that a natural, diverse forest would exhibit more complexity in the leaflitter habitat than a timber plantation. I tested this hypothesis using leaflitter interstitial space as a surrogate for leaflitter complexity. Although the native forest exhibited higher leaflitter habitat complexity, it was not correlated with higher arthropod species richness. Then, I conducted a translocation experiment using native forest, mahogany and Casuarina leaflitter, and found that the arthropod species composition was influenced by the leaflitter type more than by the surrounding forest. For my third hypothesis, I used leaflitter ants as the target group. I found that endemic, native and exotic ants were diverse in native forest and exotic plantations, and concluded that this change did not have a differential impact on endemic, native, or exotic ant species. In general, this study found native forests had higher species richness of leaflitter arthropods than Casuarina and pine plantations, even after the plantations were abandon for 45 years. It also indicates that for wood plantations, certain tree species harbor higher biological diversity than others. Hence, forest management decisions need to incorporate ecological knowledge of the systems to conserve their biodiversity.