Assessment of beetle and bug diversity in low input cattle farms of varying cattle density and surrounding land use

Background/Question/Methods

Insects and the services they provide are significant to agroecosystems. Low input farms depend on high biodiversity for ecosystem services, yet little is known about how livestock grazing systems affect diversity.  Intensive high-input farming systems have been linked with decreased biodiversity, soil erosion, and habitat degradation.  However, all farms are vulnerable to degradation and alteration of the surrounding landscape, which may affect biodiversity even if a farm uses sustainable practices. Insects are common on farms and effective biodiversity indicators and are informative in determining how farming practices may benefit biodiversity.  We monitored insects during one field season to determine the effects of farming practices, cattle densities and land use patterns on biodiversity. We measured family-level diversity and abundance of beetles and bugs on five grass-fed cattle farms near Davidson, North Carolina using pitfall trapping and sweep-netting.  For each farm, we determined the acreage, cattle density, average grass height, and the surrounding landscape as percentages of forest, pasture, and developed land. We predicted that farms with lower cattle densities and cattle rotational frequencies would support greater diversity and abundance.  We hypothesized that a greater percentage of less developed land would positively correlate with diversity and abundance.

Results/Conclusions

There were differences among farms in density of several beetle families and beetle diversity, but beetle diversity and abundance were unrelated to cattle density.  Activity density of most families tested and family-level diversity were positively correlated with grass height near pitfall traps, which may help explain between farm differences.  Total hemipteran abundance also increased with increases in grass height. Family-level beetle diversity declined with increases in utility right-of-ways, weevil abundance declined with increases in roads, and scarab abundance increased with increases in percent developed land. Hemipteran diversity increased with increases in size of the study pasture, and abundance of Alydidae increased with total pasture surrounding farms.  Agricultural practices on grass-fed cattle farms, at least the practices on these five farms, appear to have moderate effects on beetle and bug diversity, especially the positive effects associated with grass height.  However, analysis of land use patterns surrounding farms suggests that maintenance of diversity on farms is not solely related to agricultural practices on farms.