Effects of winged burning bush (Euonymus alatus), management strategy, and white-tailed deer (Odocoileus virginianus) on spider assemblages
Invasive shrubs can have major impacts on forest ecosystems through the alteration of biotic structure and abiotic parameters. Spiders are sensitive to changes in the forest environment (habitat structure, temperature, humidity, light, soil moisture). Burning bush (Euonymus alatus) is a growing invasive concern in Ohio. Because it shares many traits with established invasive shrubs, burning bush has the potential to alter forest and spider communities. Similar to invasive plant species, deer alter forest communities through alterations in vegetation. This reengineering of forest plant communities alters microclimates and spider assemblages. Management of invasive plant species and deer are key to many restoration strategies, but different management strategies may have different effects on associated spider assemblages. In this study we sought to identify how burning bush is affecting associated spiders, identify which management strategy maximizes spider diversity, and determine if the presence of deer alters these interactions. We constructed deer exclosures with adjacent controls in burning bush- and native-dominated areas. Within each exclosure, we applied three management treatments to the existing woody plants (none, complete removal, and a basal herbicide treatment that left aboveground dead biomass standing). Ground-dwelling spiders were sampled using pitfall-traps, and shrub-dwelling spiders were sampled using a pesticide application.
Total spider abundance and family richness were approximately two times higher in native plots (5.5±1.2, 2.7±0.3) than in burning bush plots (2.8±0.5, 1.8±0.2; p = 0.05; p = 0.02); and native plots were more diverse (13 families among 221 sampled individuals compared to 11 among 85). In plots where burning bush was present, the herbicide treatment that left dead biomass standing supported the highest overall abundance (5.6±0.8) and richness (3.2±0.3), and the highest diversity (8 families among 46 individuals) of the management strategies. Changes in the shrub-dwelling and ground-dwelling spider assemblages (two times higher abundance and richness in native plots) were not significant, likely due to the short sampling time and small sample sizes. Deer exclosure also had no significant effects on spider abundance, richness, or diversity, likely because plots were sampled relatively soon after deer were excluded. Although this study has only been for a short time, the negative effects of burning bush on the total spider assemblages are immediately apparent. Overall, native plots support a greater abundance and diversity of total spiders; and in areas where burning bush is already established, a basal spray management regime would appear to benefit spider abundance and diversity.