Contrasting trends in biodiversity of birds and trees during succession following cacao agroforest abandonment

Haley Arnold,Mark F. Hulme,Amy E. Deacon,Dan Jaggernauth,Alex Sansom,Anne E. Magurran

doi:10.1111/1365-2664.13869

Abstract

Abstract Understanding how transformed habitats act as reservoirs of biodiversity is a key challenge at a time when ecosystems are under unprecedented pressure. Here we compare tree and bird biodiversity in actively cultivated and abandoned cacao agroforests, and use a space for time approach to ask how this diversity has changed over 100 years of succession. Tree and bird communities were surveyed in cacao agroforests, secondary forests at different stages of succession and primary forests in the Northern Range of Trinidad, West Indies, to test the prediction that there are consistent temporal trends in alpha and beta‐diversity across taxa. Temporal alpha‐diversity was taxon dependent. We found that tree alpha‐diversity increased with forest age. In contrast, there was no temporal trend in bird alpha‐diversity. Tree and bird species richness were negatively correlated. Tree and bird composition varied with forest age and environmental distance. A greater proportion of native trees, and of highly forest‐dependent and insectivorous birds were found in older forests. Our analyses show that actively cultivated and young abandoned cacao agroforests can sustain high bird alpha‐diversity, despite lower levels of tree alpha‐diversity. Old secondary and primary forests have unique species compositions including more sensitive and specialist species. Compositional shifts with successional stage for both trees and birds produce a patchwork of habitats that contribute to regional gamma‐diversity. Synthesis and applications. Our research highlights the value of actively cultivated cacao agroforests and secondary forest alongside primary forests as reservoirs of biodiversity. By supporting both biodiversity and livelihoods, traditionally grown shade‐cacao agroforests fall within a people and nature framework. Taken together, these results emphasise the contributions of secondary forests, which are often overlooked, to conservation.

Highlights

Growing anthropogenic pressures on ecosystems mean that global biodiversity is being threatened in ways that have no precedent in historical times (Blowes et al, 2019; Isbell et al, 2017; Magurran & Dornelas, 2010)
Tree and bird communities were surveyed in cacao agroforests, secondary forests at different stages of succession and primary forests in the Northern Range of Trinidad, West Indies, to test the prediction that there are consistent temporal trends in alpha and beta-diversity across taxa
We found that tree alpha- diversity increased with forest age

Summary

| INTRODUCTION

Growing anthropogenic pressures on ecosystems mean that global biodiversity is being threatened in ways that have no precedent in historical times (Blowes et al, 2019; Isbell et al, 2017; Magurran & Dornelas, 2010). To better understand whether this form of habitat transformation could support biodiversity conservation within the ‘people and nature’ framework, we investigate abandoned and active cacao agroforests in Trinidad's. Cacao farming has transformed parts of the Northern Range as many of the old agroforests were periodically abandoned and new ones started over time (Bekele, 2004; NATT, 2017). This pattern of transformation provides an informative case study for understanding how Trinidad's history of cacao farming shapes patterns of biodiversity, and the potential contribution of actively managed and abandoned cacao agroforests to biodiversity conservation. We ask how compositional change (species turnover as measured by a Jaccard index) in both taxa (trees and birds) is linked to site age and environmental differences between sites

| MATERIALS AND METHODS

Findings

| DISCUSSION