In this post Michelle Harrison and Cristina Banks-Leite discuss a recent paper by Luc Barbaro and colleagues ‘Avian pest control in vineyards is driven by interactions between bird functional diversity and landscape heterogeneity‘.
The global wine industry currently contributes roughly US$303 billion to the world’s economy (Plant and Food Research, 2013). Wine is a key export for many European countries such as Italy, France and Spain and is a growing industry in countries like China and in the Middle East. As such it provides hundreds of thousands of jobs and services a global demand for wine that continues to grow with each passing decade. Thus it is important to understand the mechanisms that influence grape production and yield.
Vineyard establishment has major implications for local ecosystems, with the vast majority of native vegetation being removed. Soil is unearthed for plowing and often sterilised with chemicals and vines are treated with fertilisers and fungicide (Turner et al., 2010; Couloma et al., 2006). As monocultures, the vineyards provide little habitat value for native mammals, birds and reptiles, attracting higher numbers of non-native species (Hilty et al., 2006; Hilty and Merenlender, 2004). It is well documented that birds provide important ecosystem services for agricultural systems (Wenny et al., 2011; Maas et al., 2015), particularly with regards to pest management. However, the relationship between the functional composition of bird communities and the degree of top-down control on arthropod populations is not as well understood.
This recent study by Luc Barbaro and colleagues determined the effect of habitat complexity on bird functional diversity and its associated control of arthropod populations. In southern France, Barbaro sampled the bird communities of 20 vineyards and measured the level of insectivorous activity by quantifying predation marks left on plasticine ‘caterpillars’. The vineyards varied at the local scale in terms of sward heterogeneity and the surrounding landscape matrix composition.
Surprisingly, the researchers found that bird functional diversity (a proxy for the number of ecosystem functions birds may perform in the ecosystem) decreased as the complexity of surrounding landscape increased. However, when focusing on avian insectivores the opposite trend was found, with abundance increasing with the percentage of semi natural habitat in the surrounding matrix. On a local scale, sward heterogeneity was associated with an increase in bird functional diversity. These trends were reflected in the level of avian predation on the plasticine models. Avian functional evenness was the metric with the greatest power in determining levels of insectivorous activity in more heterogeneous environments.
Top-down control of folivorous arthropods by bird predators has been documented in agro-forests such as cocoa and coffee plantations. In such agricultural systems, where heterogeneous forest structure and high plant diversity promote and maintain a diverse insectivorous bird population, ecosystem services can be preserved (Van Bael et al., 2008). Even in these plantations, connectivity to surrounding native forest habitat was important in sustaining bird diversity (Raman, 2006). Similarly, avian communities have been shown to be important in controlling arthropod numbers in monocultures such as palm oil (Koh, 2008). Across all climatic zones, from tropical to boreal regions, plants generally perform better in the presence of birds (Mäntylä et al., 2011), due to pest control.
What are the implications of this study for vineyard management and agro-ecology in general? Agriculture, by its nature, promotes the dominance of monocultures and the homogenization of habitats often to the point where ecosystem services are no longer provided by local animal communities. Without these natural ecosystem functions, farmers increasingly rely on chemical control of pests, which is both detrimental to the environment and has cumulative effects up the food chain. Clearly, it is important to the industry to maintain a viable population of insectivorous species in situ. This study suggests that local matrix composition is key in achieving this and should be included in any management plans and policy decisions going forward. Surrounding grasslands and woodlands provide vital habitat for birds that enter vineyards to forage for insects. The effect of local sward heterogeneity within the vineyards also needs to be taken into account to provide sufficient cover for insectivorous species. Proper management could decrease plant damage, increase yield and reduce the need for frequent pesticide application.