Manage perennial bioenergy crops to benefit butterflies and moths
Overall effectiveness category Awaiting assessment
Number of studies: 1
Background information and definitions
Bioenergy crops are grown to produce oil, which is used as fuel in place of traditional fossil fuel derivatives. Perennial bioenergy crops, such as grasses, can be sown once and harvested for multiple years, which creates opportunities to establish grassland ecosystems, unlike annual cropping systems. Management of perennial bioenergy crops to benefit butterflies and moths may include changing the mix of seeds planted, altering the timing or frequency of harvest, or limiting the application of chemicals to the crop.
Studies on annual bioenergy crops are included within actions for annual crops, for example “Increase crop diversity across a farm or farmed landscape”, “Plant more than one crop per field (intercropping)”, “Leave uncropped, cultivated margins or plots” and “Leave unharvested crop headlands within arable fields”. For studies which test reductions in chemical application alone, see “Threat: Pollution”.
Supporting evidence from individual studies
A replicated, controlled study in 2009–2010 on an arable farm in Iowa, USA (Myers et al. 2012) found that plots planted with a diverse mix of bioenergy crops had a higher abundance and species richness of butterflies than plots with a restricted range of grass species. On plots sown with 16 or 32 plant species, both the abundance (4–8 individuals/50 m) and species richness (3–5 species/month) of butterflies were higher than on plots sown with one or five plant species (abundance: 1–3 individuals/50 m; richness: 1–3 species/month). The difference was consistent across sandy loam, loam and clay loam soils. See paper for individual species results. In May 2009, forty-eight 0.30–0.56 ha plots were established across seven fields (3.7–6.1 ha) previously sown with soybean on a 40-ha farm. In each plot, one of four native seed mixes was sown: switchgrass Panicum virgatum monoculture, “warm-season mix” (five grasses), “biomass mix” (16 grasses, legumes and non-woody, broadleaved plants “forbs”), or “prairie mix” (32 grasses, legumes, forbs and sedges). There were four replicates of each mix on each of three soil types: sandy loam, loam and clay loam. All plots were mown to 10 cm height in July 2009. From June–September 2010, butterflies were surveyed along one 50-m transect/plot twice during each of five survey periods.Study and other actions tested