Evaluating Shade Bias in Insect Trap Catch and Assessing the Short- and Long-term Impacts of Herbicide Application in Regenerating Clearcuts on Flowering Plant Communities

Kathryn M. Georgitis


Regenerating clearcuts are commonly sprayed with a broad-spectrum herbicide, Glyphosate, to suppress regenerating hardwoods that outcompete the more desirable softwood species. Although the direct effects of herbicide application are minimal, the resulting changes in vegetation have raised concern over its indirect effects on wildlife. On the other hand, clearcuts are high in plant diversity, which may provide beneficial resources for Hymenoptera in the clearcut area and the adjacent forest stands. To assess the short- and long-term impacts of herbicide application on insect communities, comparisons between stands of various ages and treatments are necessary. Insect traps provide one efficient method for assessing differences in insect communities with minimal effort. However, legitimate comparisons can only be obtained if traps are not biased by the environmental conditions within the stand. One condition that differs between stands with and without herbicide application, as well as between stands of different ages, is the amount of sunlight. Thus, an insect trap that collects equivalent amounts of insects regardless of differing light conditions would be a benefit to researchers. The first study examined the potential influence of shade on insect catch in malaise and flight-intercept traps. Six malaise trap types were investigated over a five year period. The traps differed in the color and type of material used in the lower and upper panels. Trap catch was compared between traps in artificial shade and full sunlight. Also, the trap efficiency of various malaise traps was reported where comparisons were appropriate. Overall there was a consistent shade bias detected in the malaise and flight-intercept traps. Thus, researchers should use caution when using these traps to make comparisons of insect communities from forest stands with differing light levels. The second study investigated the short- and long-term impacts of herbicide application in regenerating clearcuts on flowering plant communities. Many of the Hymenopteran insect groups require floral resources in order to persist in an environment. Thus, an evaluation of habitat suitability for the beneficial Hymenoptera must contain some measure of available floral resources. The flowering plant communities in twenty forest stands located in western Maine were sampled with the line intercept method. Six treatment groups were investigated: recent clearcuts that were sprayed with herbicide or un-sprayed, older clearcuts that were sprayed with herbicide or un-sprayed, plantations, and mature stands. Overall there were few differences in flowering plant richness, abundance, and floral density between sprayed and non-sprayed sites within the recent and older age groups. However, there was a general trend of sites sprayed with herbicide having greater numbers of flowering plants. The age of the stand influenced the flowering plant abundance and floral density. The younger sites consistently had more compared to the older sites. The plantations had a greater abundance of flowering plants than did the older sites, possibly related to the uniform spacing between trees. However, the flowering species within the clearcuts and plantations were primarily non-native species or plants found in disturbed areas. Thus, their suitability as floral resources for native pollinators and parasitoids should be investigated.