Executive Summary

Biocontrol of Purple Loosestrife on the Columbia River

Wetland and riparian areas along the lower Columbia River are an important component salmonid habitat. The Lower Columbia River Estuary Partnership (LCREP) is currently developing high-resolution spatial data sets of important estuarine and riparian habitats. The goal of the LCREP study is to produce an estuary-wide map of vegetation and substrate habitats at multiple spatial scales; however, exotic invasive species, such as Purple Loosestrife, will not be mapped as part of the LCREP project. Unfortunately, Purple Loosestrife is well established among the Columbia River Channel Islands. The effect of Purple Loosestrife on salmonid habitat is not well known. Recent observations at other wetlands in Oregon suggest that increasing densities of Purple Loosestrife result in a decrease in species richness of other wetland plants. As the number of plant species decrease, so does insect species richness (S. Schooler, unpublished data). Insects are an important food web link between the primary production of the wetland and salmon.

Insects are also important in current efforts to control Purple Loosestrife. During the past two years, several species of insects have been released at selected sites on the Columbia River. Their effectiveness as biocontrol agents is being evaluated by soon-to-be Dr. Shon Schooler. Shon is evaluating the biocontrol agent’s effectiveness at several spatial scales: at the individual plant scale, he is assessing damage to leaves; at the population scale, he is quantifying the reduction of Purple Loosestrife plant densities. Collecting this type of information is very labor intensive. Consequently, Shon and Dr. Garono are working to use recently collected hyperspectral imagery to evaluate Purple Loosestrife infestation on entire sections of the Columbia River. If successful, remotely sensed imagery can be used to develop a better understanding of the factors that control and regulate the abundance of Purple Loosestrife on the Columbia River and can potentially lead to a powerful tool for natural resource managers.


For our study, we used a combination of fieldwork and image analysis to evaluate past biocontrol agent release sites to determine if control agent augmentation was necessary. We also selected new release sites and six sites at which to evaluate the relationship between Purple Loosestrife and insect communities. In July 2002, a group of Earthwatch students joined us for 10 days on the Columbia River. We used a variety of approaches to characterize our study sites. We measured:

  • Purple Loosestrife stem densities
  • Damage from biocontrol agents
  • Insect diversity in and around the release sites

Earthwatch students sampled insect and plant communities at six Wallace Island sites. We set up our Bug Lab at Sea Resources in Chinook, WA and processed samples.