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Atrazine Improves Survival and Growth of Ponderosa Pine Threatened by Vegetative Competition and Pocket Gophers

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Abstract:

Atrazine was applied to 0.1-acre (0.04-ha) plots of planted ponderosa pine (Pinus ponderosa) in south-central Oregon to alleviate competition from herbage and remove the food supply of pocket gophers (Thomomys mazama Merriam) that prey On the trees. Spring treatments were ineffective, but one or two fall applications doubled survival (55 vs. 25 percent) and greatly increased heights (222 vs. 150 cm) of pines after 10 growing seasons. Atrazine reduced grasses and forbs the year after fall application and effects persisted through the 10th year. Fall treatments reduced abundance of gopher mounds eightfold compared with no treatment or application of atrazine in spring. Moreover, few mounds were counted during the years when herbicide effects were greatest. Gophers were responsible for most of the pine mortality, but losses were considerably lower on plots treated in the fall. The chemical also ameliorated adverse impacts on height growth by other animals and insects. The findings show that control of herbage on small plots can effectively lessen competitive impacts of both the plant cover and the gophers dependent on it. Results strongly suggest that treatment may be even more effective on larger tracts where gophers do not have ready access to untreated areas. Forest Sci. 25:99-111.

Keywords: Pinus ponderosa; Thomomys mazama; artificial regeneration; herbicides; plantation release; rodent control

Document Type: Journal Article

Affiliations: Principal Research Wildlife Biologist, Rocky Mountain Forest and Range Experiment Station, Fort Collins, Colorado

Publication date: March 1, 1979

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