Image: Representation of the ‘intermediate landscape-complexity hypothesis’ from Tscharntke et al. (2012).
With agricultural intensification pushing to provide more food, bioenergy, and other products for a growing human population, there is also a great need for concurrent intensification of ecological services like biological control of pest insects.
There have been many strategies tried over the years to increase ecosystem services on farms, for example planting flower strips with the intent of providing extra resources for biological control agents. The thought is that these flower strips could increase biological control agents which would then reduce pests in nearby crops. Sometimes planting floral resource strips works and increases biological control and sometimes it doesn’t.
One hypothesis explaining this variation in efficacy is that farm scale diversification activities will only increase services measurably when the farm is located in a landscape of intermediate diversity. The figure above provides a visual description of this ‘intermediate landscape-complexity hypothesis.’ Determining the veracity of this hypothesis is important if we are to optimize our productivity and conserve biodiversity in agroecological systems.
A new paper by Jonsson et al. (2015) in the Journal of Applied Ecology provides empirical support for the intermediate landscape complexity hypothesis.
Image: Figure 2 from Jonson et al. (2015).
The authors planted floral strips in kale crops across a range of landscape complexity. The effect of these strips on parasitism of aphids and the diamond back moth were higher in areas of intermediate landscape complexity and lower in areas with very high landscape complexity.