Forest-dependent bird communities of West African cocoa agroforests are influenced by landscape context and local habitat management
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.
References (60)
- et al.
Agroforestry systems can mitigate the severity of cocoa swollen shoot virus disease
Agric. Ecosyst. Envrion.
(2018) - et al.
Landscape-moderated importance of hedges in conserving farmland bird diversity of organic vs. conventional croplands and grasslands
Biol. Conserv.
(2010) - et al.
Local and landscape factors determine functional bird diversity in Indonesian cacao agroforestry
Biol. Conserv.
(2009) Frugivory and seed dispersal by vertebrates in tropical and subtropical Asia: an update
Glob. Ecol. Conserv.
(2017)- et al.
Improving cocoa harvest can mitigate for crop damage by wildlife in a forest-agriculture matrix
Agric. Ecosyst. Envrion.
(2018) - et al.
Shaded coffee and cocoa - double dividend for biodiversity and small-scale farmers
Ecol. Econ.
(2017) Frugivory and seed dispersal by hornbills (Bucerotidae) in tropical forests
Acta Oecol.
(2011)- et al.
Traditional cocoa-based agroforestry and forest species conservation in Ondo State, Nigeria
Agric. Ecosyst. Envrion.
(2007) - et al.
Spider species richness in cocoa agroforestry systems, comparing vertical strata, local management and distance to forest
Agric. Ecosyst. Envrion.
(2012) - et al.
Where are commodity crops certified, and what does it mean for conservation and poverty alleviation?
Biol. Conserv.
(2018)
Cocoa production in West Africa, a review and analysis of recent developments
NJAS-Wagening. J. Life Sci.
Cacao cultivation under diverse shade tree cover allows high carbon storage and sequestration without yield losses
PLoS One
The effect of land use systems on tree diversity: farmer preference and species composition of cocoa-based agroecosystems in Ghana
Agrofor. Syst.
Cocoa agroforestry for increasing forest connectivity in a fragmented landscape in Ghana
Agrofor. Syst.
Fitting linear mixed-effects models using lme4
J. Stat. Softw.
Shade Tree Diversity, Cocoa Pest Damage, Yield Compensating Inputs and Farmers’ Net Returns in West Africa
PLoS One
Climate-smart sustainable agriculture in low-to-intermediate shade agroforests
Nat. Sustain.
Birds of Western Africa
The contribution of cacao agroforests to the conservation of lower canopy ant and beetle diversity in Indonesia
Biodivers. Conserv.
Global restoration opportunities in tropical rainforest landscapes
Sci. Adv.
Model averaging and muddled multimodel inferences
Ecology
Combining high biodiversity with high yields in tropical agroforests
Proc. Natl. Acad. Sci. USA
Land use types influenced avian assemblage structure in a forest-agriculture landscape in Ghana
Ecol. Evol.
Biodiversity impacts of some agricultural commodity production systems
Conserv. Biol.
Lizard diversity and agricultural disturbance in a Caribbean forest landscape
Biodivers. Conserv.
Cocoa intensification scenarios and their predicted impact on CO2 emissions, biodiversity conservation, and rural livelihoods in the guinea rain forest of West Africa
Environ. Manag.
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.