Biotic interactions in organic farm systems

Abstract

Fire, drought, and grazing were primary ecological drivers of the historical Great Plains' prairie ecosystem. The suppression of fire, a shift in grazing and cropping systems, and the introduction of windbreaks and other woody vegetation altered the landscape. The abundance, vertical diversity, and composition of woody species have noticeably increased. A subsequent shift has been documented in relative abundance of bird species in the state, with shrubland and edge species filling the ecological niche created with the conversion of many cropland acres to woodland. Shrubland and edge birds may fill an important functional role in agroecosystems. Organic farms frequently have greater habitat heterogeneity then other farm types. Agroforesty is an important component of this habitat diversity. To quantify the effect of woody land-use and land-cover on biodiversity and to assess the functionality of avian species as predators in organic farm systems, avian and insect diversity were sampled on 23 organic farms in eastern Nebraska and Kansas in 2007 and 2008. Species response to the presence and arrangement of woodland cover on farms is of great interest. An N-mixture model was used to estimate abundance and detectability of farmland bird species. Results from these analyses will be used to assess the functional role of birds and explore relationships between insect and bird communities to determine whether woodland edge bird species have the potential to effectively suppress crop pests on organic farms.