Trends in Ecology & Evolution
OpinionOn the hope for biodiversity-friendly tropical landscapes
Section snippets
Conservation out of the wild
To date, conservation strategies for tropical biodiversity have often been based on safeguarding large ‘intact’ tropical forest reserves. Although recommended [1], this conservation target is proving to be increasingly challenging [2]. Creation of new mega-reserves will soon be severely constrained because most tropical regions already lack large blocks of pristine forest available for conversion into conservation areas [3]. Therefore, the management of HMLs (see Figure I in Box 1) has emerged
Forest transition questioned
Economic growth, rural exodus, and urbanization are often correlated and represent a widespread and historical phenomenon that results in the abandonment of agricultural lands, particularly those considered marginally productive [29]. In this context, a huge amount of land has been predicted to be available for natural forest regeneration in many tropical countries as long as their economies become increasingly industrialized [30]. This phenomenon, known as ‘forest transition’ (i.e., the
Context matters
HMLs typically contain patches of regenerating or secondary forests [49], which globally account for more than 50% of remaining tropical moist forest 50, 51. This figure, plus the assumption of ongoing forest transition, has led scientists to ask whether regeneration or secondary forest patches are able to guarantee long-term biodiversity persistence as regrowth forests expand their coverage across HMLs [52]. Whereas some studies have recorded significant portions of the original biota in
Disturbance and conservation thresholds
Ecosystem services, such as carbon storage, soil protection, water cycling, and provision of forest products, are positively correlated with forest aboveground biomass [62]. As disturbance proceeds and harvest of forest products intensifies, forest biomass in a landscape will cross a threshold, thus greatly reducing the services and products provided by that forest [64]. This connection between human disturbance, forest biomass, and provision of ecosystem services implies that a maximum level
Multiple pathways for HMLs
Based on the evidence discussed so far, we propose a conceptual model describing potential trajectories for tropical forest landscapes (Figure 1). Initially, deforestation converts ‘natural landscapes’ into ‘conservation landscapes’ (Figure 1; flow 1), which retain a high old-growth:secondary forest ratio and low coverage of edge-affected habitats. Following further forest loss and fragmentation, conservation landscapes move towards ‘functional landscapes’, with intermediate
Theoretical and applied implications
Although our trajectory model represents a simplification of the real world, it makes at least two important contributions. First, it identifies, classifies, and establishes causal connections between the major forces determining shifts among tropical HMLs. Here, it is important to mention that global climatic change can also affect HML trajectories, because current models of climate change predict a reduction in precipitation in many tropical forests over the next few decades [69]. This could
Acknowledgments
We thank Bill Laurance and John Vandermeer for helpful comments on early versions of this manuscript. Thanks to CI-Brasil, Cepan, CNPq, Capes, CONACyT, Universidade Federal de Pernambuco, Universidad Nacional Autónoma de México, and Carleton University for funding this study.
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