Crop, Native Vegetation, and Biofuels: Response of White- Tailed Deer to Changing Management Priorities

The expansion of the cellulosic biofuels industry throughout the United States has broad-scale implications for wildlife management on public and private lands. Knowledge is limited on the effects of reverting agriculture to native grass, and vice versa, on size of home range and habitat use of white-tailed deer (Odocoileus virginianus). We followed 68 radio-collared female deer from 1991 through 2004 that were residents of DeSoto National Wildlife Refuge (DNWR) in eastern Nebraska, USA. The refuge was undergoing conversion of vegetation out of row-crop agriculture and into native grass, forest, and emergent aquatic vegetation. Habitat in DNWR consisted of 30% crop in 1991 but removing crops to establish native grass and wetland habitat at DNWR resulted in a 44% reduction in crops by 2004. A decrease in the amount of crops on DNWR contributed to a decline in mean size of annual home range from 400 ha in 1991 to 200 ha in 2005 but percentage of crops in home ranges increased from 21% to 29%. Mean overlap for individuals was 77% between consecutive annual home ranges across 8 years, regardless of crop availability. Conversion of crop to native habitat will not likely result in home range abandonment but may impact disease transmission by increasing rates of contact between deer social groups that occupy adjacent areas. Future research on condition indices or changes in population parameters (e.g., recruitment) could be incorporated into the study design to assess impacts of habitat conversion for biofuel production.

Impacts of Plant Size, Density, Herbivory, and Desease on Native Platte Thistle (Cirsium Canescens)

Abstract. Based on prior field observations, we hypothesized that individual and interacting effects of plant size, density, insect herbivory, and especially fungal disease, influenced seedling and juvenile plant growth in native Platte thistle populations (Cirsium canescens Nutt.). We worked at Arapaho Prairie in the Nebraska Sandhills (May - August 2007), monitoring plant growth, insect damage, and fungal infection within different density thistle patches. In the main experiment, we sprayed half of test plants in different density patches with fungicide (Fungonil© Bonide, containing chlorothalonil) and half with a water control. Fungal infection rates were very low, so we found no difference in fungal attack between these treatments. However, plants that received the fungicide treatment had significantly faster growth over the season than did the control plants. At the same time, plants in the fungicide treatment had significantly reduced insect herbivory. These results strongly suggest that the fungicide had insecticidal effects and that insect herbivory significantly decreases juvenile Platte thistle growth. Further, damage by insect herbivores tended to be higher for larger plants, and herbivory was variable among different patches. However, plant density did not appear to have a large effect on the amount of insect herbivory that individual juvenile Platte thistle plants received. In the second experiment, we examined germination and survival success in relationship to seed density, and found that germination success was higher in areas of lower seed density. In the third experiment, we tested germination for filled seeds categorized primarily by color variation and size, and found no difference in germination related to either color or seed weight. We conclude that seed density, but not seed quality as estimated by color or size, affects germination success. Further, although herbivory was not significantly affected by plant density at any of the scales examined, insect herbivory significantly reduces the growth and success of juveniles of this characteristic native sand prairie plant.