Vegetation survey of knapweed on the Yakima Training Center - 1992

Abstract

This report summarizes and discusses the results of a vegetation survey conducted in 1992 on a portion of the YakimaTrainingCenter (YI"C). PacificNorthwestLaboratory(PNL) conductedthis surveyand a similarsurveyin 1991 for the U.S. Departmentof the Army. The objectivesof the surveywereto evaluatethe impactof the herbicidepicloramon forbs where aerial applicationsof picloramweremade in 1988, 1989, and i991 to controlknapweed (Centaureaspp.) infestations.Forbsare of specialinterestbecausethey are an importantpart of the springand summerdiet of the westernsage grouse(Centrocercus urophasianus phaios), whichis a U.S. Fish and WildlifeServicecandidatespeciesfor the threatenedand endangered list. We also conducteda limitedevaluationof the effectiveness ofthe spray programin controllingthe spreadof knapweed. This documentisa companiondocumentto the report detailingresultsof the vegetationsurveysconductedin 1991 (Eberhardtet al. 1992). Percentplantcanopycoverand numberof forbs were measuredon 120 transectson the herbicide-treated(78 transects)and untreatedcontrol(42 transects)areas. The 1992 survey showedthat areastreatedwithpicloramin 1988, 1989, and 1991 continuedto showevidence of knapweedsuppressioncomparedto controlareas. Herbicidetreatmentin 1991 resultedin a significantreductionin knapweedbased on percentcoverand density. The treatmentareas also all had lowerpercentcanopycoverof perennialforbsand fewer perennialforbs compared to controlareas. Canopy cover of shrubs and annual, biennial, and perennial forbs measuredon the YTC increased between the 1991 and 1992 survey,which may indicate a recovery of these vegetation types after disturbance. These increasesalso could reflect the mild 1992 winter and superior growing conditions in the spring of 1992. We recommendthat these vegetation transects continueto be monitored for an additional growing season to evaluate 1) whether knapweed increasesto its previous abundance in the 1991 herbicide-treated area, 2) the efficacy of herbicide application on transects 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.

Sage grouse on the Yakima Training Center: A summary of studies conducted during 1991 and 1992

“…Hoping to gain additional insight into the reasons that sage grouse may prefer or avoid spray areas, we examined data collected by Downs et al (1994) relative to forb cover in several spray areas. They found that the 1991 spray area had less knapwced and fewer perennial forbs than the control area in 1991.…”