Functional ecology of tropical forest recovery

Electronic abstract of the thesis for the library for the acquisitions department of Wageningen UR library (published as a html file so hyperlinks may be included)

In English, one or 2 pages.

Functional ecology of tropical forest recovery

Currently in the tropics, the area of secondary forest exceeds that of mature forest, and the importance of secondary forest will probably continue to increase in the future. Understanding secondary forests’ potential for maintaining biodiversity and critical ecosystem functions is thereby vital. The aim of this study was to mechanistically link tropical forest succession with the recovery of ecosystem functioning after agricultural field abandonment using a trait-based approach. Such an approach makes use of functional traits; components of an organism’s phenotype that are key to assess ecosystem responses to global change drivers, and are at the same time indicators of how organisms drive changes in ecosystem functioning. Trait-based approaches could therefore provide a mechanistic way to scale up from organisms to ecosystems and thereby contribute towards a more predictive biodiversity and ecosystem functioning science. For this study, I made use of secondary forest data from a wet forest region in Chiapas (main study site), that cover the first 3 decades of succession, complemented with data from a dry forest region in Oaxaca, that cover the first 6 decades of succession. Both are tropical regions in Mexico, characterized by high biodiversity levels and rapid forest loss for agricultural expansion. 

In this study I found that functional diversity (the range of different functional traits) increases rapidly and functional composition (the weighted average functional trait value) changes directionally with succession (chapter 2 and 3). These reflect changing habitat filters (changing environmental gradients that underlie succession), and also a gradual shift from habitat filtering towards an increasing effect of competitively driven limiting trait similarity (chapter 4 and 5). Such successional changes in community functional properties suggest strong changes in ecosystem functions, however in situ ecosystem function rates were primarily explained by the total amount of biomass present rather than by biodiversity or functional trait properties of secondary forests (chapter 6). Only the more controlled ex situ decomposition rates were additionally significantly influenced by functional diversity and functional composition. When evaluating the identity of species that drive most of the ecosystem functions I found that different functions were largely driven by the same (dominant) species, implying a limited effect of biodiversity for multifunctionality at a given moment in time. This suggests that biodiversity is mainly important for maintaining multifunctional ecosystems across temporal and spatial scales (chapter 7).

Deforestation is a major threat to natural forests and biodiversity, and I recognize that secondary forests are generally a poor substitute of mature forest. Nevertheless, I show that unassisted recovery through natural succession can be rapid, and contribute considerably to maintenance of biodiversity, functional strategies and ecosystem functions. So while protecting the remaining tracts of mature forests is vital, secondary forests are key components of multifunctional human-modified landscapes where synergies between biodiversity, ecosystem functions and human wellbeing can be optimized.