An ecological assessment of insect diversity at organic Central Coast vegetable farms on two spatial scales

Background/Question/Methods

Modern industrial agriculture is the principle cause of anthropogenic land use changes on terrestrial ecosystems.  Approximately 40% of the planet’s land surface, or around half of the habitable area, is comprised of agricultural landscapes.  The industrialization of agriculture and the increasing amount of landscape devoted to its production are two of the biggest drivers of biodiversity loss. The Central Coast of California epitomizes the industrialization and specialization of agriculture, and exemplifies the trend of agricultural intensification in the United States.  Diversified organic agriculture, however, may offer some refuge for non-crop species. This study analyzed insect and plant biodiversity on and adjacent to organic vegetable farms on the Central Coast of California at two spatial scales; the landscape-scale and a smaller within-farm scale. Specifically I asked the following research questions: do farms with greater levels of vegetation in the surrounding landscapes harbor greater levels of parasitoid biodiversity? My second question was, within a smaller area, is biodiversity of insects greater in areas of greater on-farm biodiversity?

At the landscape-scale, insect data were collected using malaise traps across 35 organic farms in 2005 and 2006, and vegetation diversity was assessed using 0.5 km radius circular plots. At the smaller farm-scale insect biodiversity was assessed using 4.5 cm radius pan traps to collect insects in a single heterogeneous organic farm in 2012, and vegetation was assessed in 1.5m radius circular plots.

Results/Conclusions

Non-crop vegetation biodiversity was associated with insect biodiversity at both scales, but landscape-scale results showed greater temporal and spatial variation than farm-scale results.  The results highlight the importance as well as the complexities of the “landscape matrix” in understanding the multifaceted but essential role that plant vegetation and insect diversity play in maintaining the functional balance and structure of managed agroecosystems.  Overall, the diverse farm systems enhanced the biological diversity and productivity of the agricultural landscape