In spring 2014, an experimentally controlled study will be conducted under full sun conditions to evaluate the effects of different depths of simulatedlogging debris on broom establishment and on soil surface and light environment factors. Germinating broom seedlings will be counted at 2-5 day intervals. To determine fifth-year treatment effects on broom seed-bank demographics,soil coreswill be collected from each treatment plot in fall 2017, composited and mixed, and kept moist for 90 days in a controlled environment growth chamber. Soil temperature and water content will be measured continuously. At Dry Bed Creek, the researchincludes a five-year evaluation (2014-2018) of the efficacy of Scotch broom control and associated regeneration performance of planted Douglas-fir following combinations of logging debrisand herbicide treatments.Three components of broom establishment will be monitored annually: seedling density,survival, andgrowth. Project Methods Methods for Objective 1: Soil and light conditions contributing to broom establishment We willexpand on the recently-installedproject at Dry Bed Creek, as well asconduct laboratory studies, to quantify the effects of different levels of soil disturbance and logging debris after forest harvesting on establishment of Scotch broom. The proposed research assesses a broad variety of ecological processes related to integrated pest management of Scotch broom and then uses links between forestry practices and broom invasion to design strategies to prevent future invasions, control existing infestations, and mitigate the impacts of broom. For Objective (3), areas will be established at one site in which broom was removed 4 and 10 years previously to evaluate potential soil P depletion, altered soil physical properties, and allelopathic effects. For Objective (2), soil properties and plant community characteristics will be compared between broom-invaded and non-invaded areas at two sites. For Objective (1), we will compare five-year development of Scotch broom and planted Douglas-fir among combinations of logging debris, soil disturbance, and herbicide treatments. A combination of manipulative and observational studies will be conducted at three existing research sites that differ in soil texture and nutrient pools. Specific objectives are to: (1) identify relative contributions of soil disturbance, altered soil and light environments, and seed bank dynamics to broom invasion, (2) determine effects of broom on soil chemical and physical properties, resource supply, and plant community structure, and (3) assess potential recovery of soil properties and native plant communities after broom removal. Relatively little is known about links between management practices and invasion, effects on soil properties, and whether these impacts can be reversed. Non Technical Summary Scotch broom (Cytisus scoparius) is a non-native, invasive plant species of major concern in Douglas-fir forests of the Pacific Northwest capable of causing long-term changes in soil ecological processes, resource supply, and forest community structure.
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