Forest-dependent bird communities of West African cocoa agroforests are influenced by landscape context and local habitat management

https://doi.org/10.1016/j.agee.2021.107848Get rights and content

Highlights

  • 140 bird species were recorded in cocoa agroforest, with 60% forest-dependent.

  • Forest-dependent species richness was higher in abandoned than managed cocoa.

  • Denser canopy cocoa had more forest bird species only when there was little forest in the landscape.

  • Landscape context may be important in assessing the conservation value of agro-forest.

Abstract

We undertook nearly 300 point counts of birds in cocoa plantations around Gola Rainforest National Park, eastern Sierra Leone, to assess how their vegetation structure, management and landscape context influence bird communities and the distribution of four globally threatened or forest-restricted species. Forest bird species richness, and the occurrence of Yellow-casqued Hornbill (Ceratogymna elata), were higher in abandoned than in actively managed cocoa farms. Yellow-casqued Hornbill presence was also associated with higher canopy volume and Brown-cheeked Hornbill (Bycanistes cylindricus) was associated with greater forest cover in the surrounding landscape. Overall forest bird species richness was associated with the interaction between canopy volume and proportion of forest in the surrounding landscape. Our results indicate that where forest cover is low in the landscape, low-intensity cocoa agroforestry can provide compensatory habitat for forest bird species, but when forest cover is high, cocoa that is more forest-like in structure may not lead to increased bird species richness, although it may benefit certain species. Most habitat structure variables, other than canopy volume and openness of understorey, were poor predictors of most of the variables analysed, suggesting that within the narrow range of observed production intensity, management has little impact on bird communities once productivity increases above zero by rehabilitating abandoned farms. However, over 60% of the species recorded and over half of all recorded detections were of biome-restricted species, suggesting that low-intensity cocoa plantations hold considerable conservation value. Changes in cocoa management may therefore impact those species.

Introduction

Agroforestry has the potential to meet the twin UN Millennium Development Goals of poverty reduction and environmental sustainability, particularly in tropical rainforest zones where high biodiversity often co-occurs with low income (Waldron et al., 2015). Cocoa has been identified as a commodity whose production may be both profitable and environmentally sustainable (Rice and Greenberg, 2000, Donald, 2004, Perfecto and Vandermeer, 2008, Clough et al., 2011, Abou Rajab et al., 2016), with some studies indicating a positive impact of biodiversity on cocoa yields (Maas et al., 2013, Gras et al., 2016). Most of the world’s cocoa is produced by smallholders who have traditionally cultivated it under the shade of either native forest trees or other crop trees such as fruits, or a mix of both (Oke and Odebiyi, 2007, Sambuichi and Haridasan, 2007). Cocoa agroforests therefore tend to harbour some of the biodiversity of the original forest and are often more biodiverse than alternative land uses such as swidden agriculture (Donald, 2004, Bos et al., 2007, van Bael et al., 2007, Deikumah et al., 2017). Shade trees in cocoa production systems can lead to increased yields and profitability (Waldron et al., 2015, Jezeer et al., 2017, Niether et al., 2020), improve soil fertility (Sauvadet et al., 2020), and reduce the incidence of pest species and cocoa tree disease (Bisseleua et al., 2013, Andres et al., 2018), thus buffering farmers from environmental uncertainty. They also sequester carbon (Jadan et al., 2015, Abou Rajab et al., 2016, Schroth et al., 2016) and provide a range of other ecosystem services (Vaast and Somarriba, 2014). Shade cocoa can therefore be effective in reducing the environmental impacts of forest fragmentation while offering growers the opportunity to charge a premium from the expanding market for environmentally sustainable and certified products (Asare et al., 2014, Tayleur et al., 2018).

However, the sustainability of cocoa production is threatened by a drive towards reduced shade or monoculture cocoa in an attempt to meet increasing demand (Vaast and Somarriba, 2014). Since almost all global cocoa production occurs within biodiversity hotspots, its management may have profound consequences for biodiversity (Donald, 2004). Over 70% of the world’s cocoa is grown in sub-Saharan Africa, where it is the fastest expanding export-oriented crop (Wessel and Quist-Wessel, 2015, Ordway et al., 2017). Despite the increase in proportion of monoculture cocoa globally, this has not resulted in increased yield per ha (FAO, 2020), meaning that a rise in demand has not so far been met through intensifying production methods on the same area of land.

This has resulted in an expansion in the area of production (Gockowski and Sonwa, 2011, Wessel and Quist-Wessel, 2015). Such expansion is most likely in countries in the Congo Basin and Guinea forest zones as they have the highest forest cover and smallest area of potentially available cropland outside forested areas (Ordway et al., 2017), with the two largest cocoa producing countries experiencing the fastest increases in primary forest loss (Weisse and Goldman, 2019). Agroforest cocoa, which can produce yields equivalent to monoculture (Blaser et al., 2018), may ameliorate the impact of forest loss on biodiversity. Understanding the impact of cocoa agroforest structure and landscape context on biodiversity in cocoa is vital in order to understand how agroforests could effectively support such species.

Around Gola Rainforest National Park (GRNP) in eastern Sierra Leone, West Africa, cocoa agroforests are being promoted as a way of generating local livelihoods while enhancing connectivity between the two main blocks of forest in GRNP and between GRNP and Gola Forest National Park (GFNP) in neighbouring Liberia, as part of a REDD+ project (Hulme et al., 2018). Understanding the impact of cocoa management and landscape context on biodiversity in this area is therefore of fundamental importance to inform effective biodiversity conservation policies. Little research has been undertaken on the predictors of bird communities within cocoa agroforests, none in the area around GRNP, and very little in Africa, although there is some evidence that greater retention of large native shade trees and reduced distance to forest edge lead to increased bird abundance and diversity (van Bael et al., 2007, Clough et al., 2011, Deikumah et al., 2017). The interaction between canopy cover and forest in the landscape in determining biodiversity on cocoa farms is also not well understood. In temperate landscapes, the impact of forest-like habitat remnants on farmed land on avian diversity has been found to depend on landscape context, with avian diversity only increasing with farmland structural complexity when natural habitats were scarce in the landscape (Batáry et al., 2010). Such relationships have rarely been explored in tropical smallholder systems where they might also exist (but see Clough et al., 2009). In this paper, we therefore aim to quantify: (i) the influence of agroforest structure and management on bird communities in cocoa agroforests around GRNP; (ii) the influence of forest cover in the local landscape on bird communities; and (iii) the extent to which these two factors interact to determine bird diversity and presence.

Section snippets

Study area

We collected data in cocoa (cacao) agroforests in the Upper Guinea Forest zone of Sierra Leone, West Africa in the area surrounding Gola Rainforest National Park (GRNP), which runs along the boundary with Liberia in the east of the country (Fig. 1). This region is tropical forest in the tropical and sub-tropical forest biome (Olson et al., 2001), with native vegetation dominated by lowland moist evergreen high forest and an annual rainfall of c. 3000 mm, primarily occurring between May to

Bird communities in cocoa agroforests

Point counts in cocoa agroforests recorded a total of 140 species, of which three are listed as Globally Threatened, 17 (12.1%) classed as forest restricted, 84 (60%) as forest-dependent and 90 (63.8%) as biome-restricted (Table S1). Bird communities were dominated by a relatively small number of species. The 13 most frequently recorded species (9.2% of all species), which included six biome-restricted species and 12 forest-dependent species, accounted for 50% of all occurrence records, and the

Discussion

Our results indicate that cocoa agroforestry in eastern Sierra Leone supports an important bird community, with the great majority of records being of forest-dependent species, and over half being of biome-restricted species. Indeed, many plantations contained more than the threshold number of biome-restricted species required for sites to qualify as IBAs, emphasising the global conservation importance of this area.

Most habitat structure variables, other than canopy volume and understorey

Funding

This work was supported by the UK government's Darwin Initiative (project number), IDH: the Sustainable Trade Initiative (Netherlands) and Divine Chocolate, UK. None of the funders were involved in study design, data collection, analysis, interpretation, manuscript writing or any other aspect of this study.

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements

We are grateful to all the staff of Gola Rainforest Conservation and to the forest edge communities and cocoa farmers for their warm welcome, for permission to work on their land and for all their assistance during fieldwork. We are also indebted to the editor and two anonymous reviewers for their helpful comments which improved an earlier version of this manuscript.

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  • Cited by (0)

    1

    Present address: Department of Zoology, University of Cambridge, Downing St, Cambridge CB2 3EJ, UK.

    2

    Present address: Conservation Society of Sierra Leone, 86 Main Road, Congo Town, Freetown, Sierra Leone.

    3

    Present address: University of the West Indies, St Augustine, Trinidad and Tobago.

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