EAGER: Contribution of outbreak insect herbivore ecological subsidies to stream food webs

Central Washington University, Ellensburg WA

Investigators

Abstract

Spruce budworms are the most important defoliators of conifer forests in the United States Pacific Northwest, injuring or killing hundreds of thousands of acres of trees each year. Budworm infestations can decrease forest growth and as a result affect streams that drain from those forests. But the actual connections between infestations and the functioning of streams remain unknown. Budworms could increase the amount of organic material entering streams directly as they feed, or they could increase the amount of nutrients that runoff the landscape indirectly as a result of reduced forest growth and nutrient demand. In either case, the growth of algae and bacteria in streams, both key components of stream food webs, could be stimulated with consequences for fish or other stream organisms. Since so little is currently known about these possible connections, it is difficult to predict how streams will respond to budworm attacks, especially as budworms are expected to become more active in the future under a warming climate. This project will enable better predictions of how streams in the forests of central Washington state will change as a result of increased spruce budworm feeding and how they would likely respond under a warmer climate. There are clear implications of project results for the regional economy, which has a large base in timber production, recreation, and water supply for hydropower, fisheries and irrigation. Researchers will engage natural resource managers in the region to assist in the development of better adaptive management plans for Federal, State, and Tribal forests and streams. The project will support the education and training of two undergraduate students and will provide new activities for local fifth grade classes who already are learning about ecosystems in their science curriculum. Finally, the researchers will collaborate on the curation of a display about the management of Pacific Northwest forests and streams at a public museum at Central Washington University. The focus of this project is on the sensitivity of streams to increased organic matter and nutrient inputs. There are three main approaches to be employed. First, whole-stream experiments will be used to simulate increased nutrient runoff for measurements of how algae and bacteria respond to nutrient additions under light and dark conditions. Second, observations will be made of how budworms affect stream food webs by tracing how stable isotopes of important nutrients derived from budworm material become incorporated into stream insects. Third, historical data about spruce budworm feeding intensity will be gathered to gain insights about where spruce budworms will most likely affect forests in the future. The exploratory nature of the project, which takes advantage of current regional budworm infestations to generate important background data and experimental infrastructure for future studies, justifies this project as an EAGER.