High critical forest habitat thresholds of native bird communities in Afrotropical agroforestry landscapes

Abstract

Our knowledge on the nature of forest species responses to deforestation remains ambiguous. Moreover, most previous research took place in fragmented landscapes or did not take into account the diversity of ecological features among the studied species. Understanding the relationship between forest cover and functional guilds inside a bird community may serve as a valuable tool to assess how much forest is necessary to conserve significant portions of forest species. We sampled birds (198 species, 6 883 encounters) along a full gradient of deforestation across 4 000 km² of forest-dominated landscapes in Southwest Cameroon. We applied multivariate adaptive regression splines to model α-, β-and γ-richness of various bird guilds in relation to forest cover. Overall, β-and γ-richness remained constant above 42% forest cover. However, total α-richness as well as all richness partitions of Guinea-Congo biome-restricted, large-bodied arboreal foliage gleaning, tree nesting, and frugivorous species declined when forest cover was below 74%. Moreover, ant-followers and terrestrial insectivores showed their highest diversity at zero deforestation. In contrast, open-land, granivorous, opportunistic insectivorous and widespread species strongly increased below 42% forest cover. High β-diversity at intermediate deforestation conditions indicate that the sharp decline of original forest bird diversity may only be compensated by habitat and 2 foraging generalists, which benefit from high habitat heterogeneity. Our study implies that Afrotropical forest bird diversity decreases non-linearly with forest loss. Critical habitat thresholds above 70% are much higher than previously reported and highlight the need for conservation measures of large intact forest remnants.

Bird communities in African cocoa agroforestry are diverse but lack specialized insectivores

“…Birds are good indicators of habitat quality (Kupsch et al, 2019), with groups such as insectivores showing high sensitivity to habitat degradation (Karp et al, 2011;Powell et al, 2015;Stratford & Stouffer, 2013;Tchoumbou et al, 2020;Wolfe et al, 2015). In the tropics, many bird species depend strictly on microhabitats often only present in pristine forest (forest specialists; Stratford & Stouffer, 2013).…”

“…Specifically, we know little regarding vertebrate communities, and how they are affected by farm management practices (Schroth & Harvey, 2007;Sekercioglu, 2012). The notable exceptions are Waltert et al (2005) and Kupsch et al (2019), who surveyed birds across a gradient of land-use intensification which included some cocoa plots, and found that although species richness did not decrease with increasing habitat modification, community composition was significantly affected, with a decrease in abundance of largebodied frugivores and terrestrial insectivores.…”

Congo Grey ParrotPsittacus erithacusdensities in oil palm plantation, agroforestry mosaic and protected forest in Southwest Cameroon*

“…This suggests that Grey Parrots are at least to some extent able to adapt to substantial habitat alterations, if large trees are maintained as breeding and roosting sites. Our study highlights the urgent need for a stronger prioritization of Grey Parrots within conservation programmes and the development of multi-facetted conservation strategies containing: (i) effective eco-guard patrolling schemes in the Korup region (Astaras et al 2017), (ii) a consequent inhibition of illegal pet trade routes and markets in the entire region of SW Cameroon/SE Nigeria, and (iii) the promotion of traditional agroforestry practices in preference to monocultural agriculture (Kupsch et al 2019). Such steps along with the implementation of CITES will help prevent further over-exploitation and future declines of wild populations in the region.…”

“…These were Ikondo kondo 1 and Fabe, which are located c.7.5 km and 15 km north-east of Mundemba, respectively (Figure 1). These villages are mainly inhabited by traditional smallholder families, who plant a mixture of subsistence and cash crops in and around their villages within a landscape dominated by remaining primary and secondary forests (Kupsch et al 2019). Fire is often used to clear small areas inside forest, often in the shade of old trees, e.g.…”

“…The rainforests of the Korup region in Southwest Cameroon are still largely unfragmented (Kupsch et al 2019) and should therefore be an important stronghold of the species. Based on survey data from 2008 to 2010, Tamungang et al (2013) provided a population estimate for Southwest Cameroon as well as a more detailed assessment on habitat preferences in three landscape types (Tamungang et al 2016), however, Martin et al (2014b) criticised both their field and analysis methodology as deficient and prone to biases.…”