Effects of shelterwood management on flower-visiting insects and their floral resources

Abstract

Habitat alteration can affect pollinating-insect community structure, decreasing the efficiency of pollinators on which many agricultural and natural ecosystems rely. Within the Tenderfoot Creek Experimental Forest (TCEF), located in the Little Belt Mountains of Central Montana, two different types of silvicultural techniques, even and group shelterwood, were applied to alter the natural habitats within the lodgepole pine (Pinus contorta) forests. Following logging, surveys of the flower-visiting insects and their floral resources were conducted within four treatments, even and group shelterwood, unlogged and meadow. In addition, individual insects were collected and the pollen removed from their bodies was counted and identified. The density of floral resources and the abundance of flower-visiting insects, as well as several diversity measures of both, were calculated, to examine the response of insects and plants to logging. Spearman rank correlations were used to examine changes over the sample years. Non-metric multi-dimensional scaling (NMS) was used to create ordinations of the treatments while multiple response permutation procedure (MRPP) tested the hypothesis of no difference between treatments with respect to either floral resources or flower-visiting insects. Correlations between the abundances of floral resources and flower-visiting insect taxa were also conducted using Mantel tests. Kruskal-Wallis tests were used to test the hypothesis of no difference between insect taxa with respect to pollen quantity and richness. NMS was used to create ordinations of species within families with respect to types of pollen and quantity carried. Changes in density, abundance, and diversity between years were detected as were differences among treatments. Associations between floral resources and flower-visiting insects were detected. Differences among insect species with respect to pollen type and quantity were detected. Overall, the alteration of the original forest habitats changed the community structure of not only the flower-visiting insects but also their floral resources in the two shelterwood treatments.