Date of Award

5-2003

Level of Access Assigned by Author

Open-Access Thesis

Degree Name

Master of Science (MS)

Department

Ecology and Environmental Sciences

Advisor

Francis Drummond

Second Committee Member

Stephen Woods

Third Committee Member

Constance Stubbs

Abstract

The short and long-term effects of glyphosate application on the diversity and abundance of ants in Maine clearcuts was assessed in a two-year study. Glyphosate is applied to release coniferous trees from suppression by competition with deciduous vegetation after a forest is clearcut. Previous research indicates glyphosate has limited immediate and long-term effects on non-target fauna, though specific species can be affected. Limited research on the effects of herbicides on insects indicates some initial decrease in insect populations. Beneficial insects, such as pollinators and predators, positively influence the forest ecosystem, but little research has examined the effects of herbicide application on those insects. Ants are predators of a variety of insects, including those considered pest insects. The presence of ants in the forest may influence pest population abundance and thus indirectly affect the abundance and diversity of vegetation. Therefore, land managers need to understand the effects of herbicide application on ants to determine the impacts of their land management strategies. To observe the effects of herbicide application, eighteen to twenty study sites located in western Maine including young (3-5 years since harvest) glyphosate treated, young non-treated, old (10-15 years since harvest) glyphosate treated, old non-treated, plantations (old glyphosate treated then planted), and mature sites (not harvested) were utilized. In 2000 and 2001, pitfall traps were used to assess the diversity and abundance of ants. Soil pH, soil percent organic matter, soil moisture, and the density of herbaceous and woody vegetation were measured in each site to quantify the effects of these factors on ant communities. In 2000, a total of 2168 ants and in 2001, a total of 2045 ants were collected. Six genera and 13 species were found in both years. In 2000, significantly more ants were found in young herbicide sites than young non-herbicide and in old herbicide than in non-herbicide sites, but there was no difference in ant diversity. Similarly in 2001, there were significant age*herbicide interactions, indicating an herbicide effect. Ant populations in old herbicide sites and plantations were significantly more abundant than those in young herbicide and young non-herbicide sites in both years. There were also significantly more ants in young herbicide than non-herbicide in both years. The total ant captures in old sites was significantly higher than in young sites indicating the age since harvest affects ant abundance. In 2001, ant diversity was higher in old herbicide than in young herbicide sites. Soil pH, percent organic matter, soil moisture, hardwood density and floral density did not affect the diversity or abundance of ants in either year. Softwood density was positively correlated to total ant abundance in both years as well as to the abundance of specific ant species. Softwood density may explain the pattern of both glyphosate and age effects.

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