Interactions between insects and plants in a changing world

Sylvicultural practices aim to maximize tree growth but are increasingly required also to mimic natural ecosystem processes. Replanting spruce following harvesting is an essential tool for regenerating mixed and conifer-dominated stands in boreal mixed-wood forests. However, young, planted spruce trees may experience relatively more damage from herbivores than naturally regenerating trees. Intending to reveal general interactions between silviculture practices and herbivory, we examined herbivorous arthropod community and associated damage on white spruce (Picea glauca, Pinaceae) in plantations and in natural regeneration in the northern mixed-wood boreal forest of Quebec. Our research will discover if plantations are experiencing more damage by herbivores due to higher temperatures and better foliage quality, or if the higher diversity of herbivorous insects in under canopy trees leads to more defoliation due to the structural complexity of the habitat.

Climate change is causing the phenology of insect herbivores and plants to advance asynchronously causing a temporal mismatch.  Phenological mismatch can alter both the timing and intensity of herbivory on their host plants. Herbivory negatively affects plants by reducing various floral traits, making the plant less attractive to pollinators. The interactive effects of herbivory intensity and timing on plants and their pollinators have rarely been studied in combination. In this study, I first hypothesize that more foliar damage and an earlier onset of herbivory will reduce floral traits. Second, I hypothesize that reduced floral traits will decrease pollinator visitation frequency. To test these hypotheses, I manipulated the intensity and timing of herbivory on Asclepias incarnata at the University of Michigan Biological Station (UMBS). 90 plants were placed in a full factorial blocked design containing 15 blocks. Each block contained six treatments: 1) low and early herbivory, 2) low and late herbivory, 3) high and early herbivory, 4) high and late herbivory, 5) no herbivory (control), and 6) natural herbivory. For each plant, I measured various floral traits, and the number and identification of pollinator visits. The majority of visits came from vespid wasps and honeybees. I found that nectar volume and sugar concentration were correlated across treatments. Further statistical analyses (in progress) will give us more insight into how climate change will continue to impact insect and plant communities.