Producing Diversity: Agroforests Sustain Avian Richness and Abundance in India's Western Ghats

Abstract

Globally, protected areas have long been the corner stone of biodiversity conservation efforts. In India's Western Ghats, small and isolated protected areas are embedded in a matrix of multiple land-uses, most of which include agroforests. These agroforests are being increasingly recognized for their supplementary role in conserving wildlife. We examined bird species richness and densities in areca (Areca catechu), coffee (Coffea arabica and Coffea canephora) and rubber (Hevea brasiliensis) agroforests in the Western Ghats. We developed a priori hypotheses, predicting that bird species richness and guild density would be highest in coffee, followed by areca and rubber agroforests. We carried out 551 point-count surveys involving 386 hours of sampling in 187 agroforests across a 29,634 km 2 area of the Ghats. We observed 204 bird species, of which 170 were residents. The average estimated richness per agroforest was higher in coffee (60.5) compared to rubber (45.4) and areca (34.1). We modeled species richness as a function of relevant biogeographic and environmental covariates. The most influential factors were tree cover, tree density and rainfall in all agroforests, but the strength of these effects varied. Coffee supported higher densities in all four habitat and three feeding guilds compared to areca and rubber. We integrated extensive field sampling with modeling that accounted for imperfect detection, while assessing bird richness and densities across multiple agroforest types. We establish that coffee agroforests are substantially richer in birds than rubber and areca, but all three agroforests play an important role in providing subsidiary habitats for birds in the Ghats. Policy decisions and markets must incorporate such biodiversity values and services provided by these agroforests to sustain and facilitate long-term biodiversity conservation.

Birds and beans: Comparing avian richness and endemism in arabica and robusta agroforests in India’s Western Ghats

“…There was no evidence of residual spatial autocorrelation for the habitat specialists or foraging guilds (Moran’s I ranged from [−0.06, 0.02] with p ∈ [0.16, 0.41]), consistent with the findings of Karanth et al . 5 .…”

“…Yet on the whole, compared to other major cash crops in the Western Ghats such as areca ( Areca catechu ) and rubber ( Hevea brasiliensis ), Karanth et al . 5 noted that coffee—aggregated across both arabica and robusta —supported higher overall avian richness, endemic richness, and greater densities for the majority of the foraging guilds as well as three out of four vertical structure guilds (low canopy, mid-, and high-canopy guilds).…”

“…Distance to protected area did not exhibit a large effect for forest and endemic bird diversity. Moreover, there was evidence that frugivore and omnivore abundance may still be high far from protected areas, suggesting that coffee agroforests can produce substantial economic and biodiversity benefits as buffers 3 , 5 , 33 , 34 . The pattern we observed is likely not an artifact of the range of distances to protected areas.…”

“…The importance of coffee agroforests as supplementary habitat may be heightened in regions with small protected areas embedded in human-use landscapes 5 , 19 , 20 , 23 . In other parts of tropical Asia where farming practices are more dissimilar to native forest, distance to protected area is often a significant predictor with a large impact on bird diversity 35 , 36 .…”

“…Coffee production systems range from shaded, low-intensity farming where coffee trees are interspersed with native forest, more typical of arabica production, to high-intensity full-sun monoculture characteristic of robusta agroforests. Shade-grown coffee retains biodiversity at higher levels than more intensely farmed, full-sun or monoculture systems 2 – 5 .…”