Woody vegetation patches in South Indian rice landscapes support tree-affiliated birds but reduce food production, with complex non-linear effects

Context

Managing agricultural landscapes for sustainability while maintaining high yields is a pressing challenge. Protecting and restoring native or semi-natural vegetation patches is often a core strategy, but its impacts are seldom measured at scales appropriate to understanding yield-biodiversity relationships.

Objectives

In a predominantly rice-growing area of South India, we examined how increasing woody vegetation patch cover impacts (1) harvest- and landscape-level (25 ha) crop yield, (2) densities of birds of different trophic guilds and forest dependencies, and (3) bird community similarity to natural forests.

Methods

We sampled landscapes spanning a continuum of embedded vegetation patch cover. We used statistical weighting to account for confounders and fitted generalised linear and hierarchical Bayesian models, using g-computation to assess the effects of these patches on yield and bird biodiversity.

Results

Vegetation patches reduced harvest-level yield at low cover levels, with landscape-level yield declining more sharply than expected based on patch-occupied area alone. Above ~ 10% cover, harvest-level yield slightly increased, while landscape-level yield remained constant. Pest control-contributing guild densities rose with vegetation cover, above a ~ 10% area threshold. Forest-dependent species responded positively to increasing vegetation cover, while non-forest species showed mixed responses. Similarity to forest bird communities increased with vegetation cover but remained low.

Conclusions

Vegetation patch-free landscapes maximise yield but are of low bird conservation value, and patch covers < 10% entail a yield penalty rather than providing ecosystem-service-related yield benefits, as theory predicts. Increasing vegetation cover from 10 to 20% improves biodiversity with no further yield penalties, suggesting that at least ~ 10% cover may be needed for multifunctional management in this South Indian context.