FRIENDS OF EDGEWOOD NATURAL PRESERVE
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FRIENDS OF EDGEWOOD NATURAL PRESERVE
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YST WEEDING YIELDS RESULTS By Ken Himes
Monitoring can be defined as repeated observations or measurements in an area to evaluate change in conditions or progress toward achieving management goals. A major management goal at Edgewood has been to control the spread and reduce the densities of the highly invasive plant, yellow star-thistle (YST, Centaurea solstitialis) in Edgewood’s grasslands. During the period 2001 to 2004, we have monitored by two methods: 1) photo documentation done yearly to observe change over time, and 2) vegetative sampling along transects in treatment areas to measure change. At Edgewood, we want to determine if well-timed mowing can reduce densities of YST and avoid negative impacts to native species. The graph below shows several encouraging trends in treatment areas as a result of monitoring during this period. Percent cover of a plant is determined by the area occupied by that plant in a sampling frame at pre-determined intervals along a transect. Since 2001, the cover of YST has decreased by 6.5 percentage points in treatment areas compared to control areas. This trend is to be expected, since well-timed mowing is known to prevent seed production. Native purple needlegrass (Nasella pulchra) growing in treatment areas has increased in cover by 4 percentage points over control areas. This positive trend is unexpected, since mowing can damage plants. The trend may be attributed more to a decline in cover of purple needlegrass in control areas than an increase in cover in treatment areas. YST plants, being annuals, build up large amounts of thatch over time and the thatch results in purple needlegrass plants being affected by shading. Mowing breaks up thatch in treatment areas and prevents a build-up of thatch. Lastly, the annual summer-to-fall-flowering hayfield tarweed (Hemizonia congesta ssp. luzulifolia), also a native, shows a 5.9 percentage point increase in cover in treatment areas compared to control areas. This is also expected since the tarweed is in direct competition with YST for space, light, water, minerals, and other resources. This increase results from decreasing YST densities (or percent cover) in treatment areas. These encouraging trends show well-timed mowing is an effective management method to control YST. But the key is to continue monitoring and adapt our methods to control YST as needed. |
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