Vegetation survey of knapweed on the Yakima Training Center - 1992
This report summarizes and discusses the results of a vegetation survey conducted in 1992 on a portion of the Yakima Training Center (YTC). Pacific Northwest Laboratory (PNL) conducted this survey and a similar survey in 1991 for the U.S. Department of the Army. The objectives of the survey were to evaluate the impact of the herbicide picloram on forbs where aerial applications of picloram were made in 1988, 1989, and 1991 to control knapweed infestations. Forbs are of special interest because they are an important part of the spring and summer diet of the western sage grouse, which is a U.S. Fish and Wildlife Service candidate species for the threatened and endangered list. We also conducted a limited evaluation of the effectiveness of the spray program in controlling the spread of knapweed. Percent plant canopy cover and number of forbs were measured on 120 transacts on the herbicide-treated and untreated control areas. Herbicide treatment in 1991 resulted in a significant reduction in knapweed based on percent cover and density. The treatment areas also all had lower percent canopy cover of perennial forbs and fewer perennial forbs compared to control areas. Canopy cover of shrubs and annual, biennial, and perennial forbs measured on the YTC increased between the 1991 and 1992 survey, which may indicate a recovery of these vegetation types after disturbance. These increases also could reflect the mild 1992 winter and superior growing conditions in the spring of 1992. We recommend that these vegetation transacts continue to be monitored for an additional growing season to evaluate (1) whether knapweed increases to its previous abundance in the 1991 herbicide-treated area, (2) the efficacy of herbicide application on transacts along roadways, and (3) the increase in invasive annuals in herbicide-treated areas and the possible effects on community vegetation structure and sage grouse habitat.
- Research Organization:
- Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
- Sponsoring Organization:
- Department of Defense, Washington, DC (United States)
- DOE Contract Number:
- AC06-76RL01830
- OSTI ID:
- 10149785
- Report Number(s):
- PNL-9448; ON: DE94011435; TRN: 94:005457
- Resource Relation:
- Other Information: PBD: Apr 1994
- Country of Publication:
- United States
- Language:
- English
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