Distribution of western hemlock dwarf mistletoe (Arceuthobium tsugense [Rosendahl] G.N. Jones Subsp. tsugense) in mature and old-growth Douglas-fir (Pseudotsuga menziesii [Mirb.] Franco) forests
| Authors: | Mark E. Swanson, David C. Shaw, Tisha K. Marosi |
| Year: | 2006 |
| Type: | Scientific Journal |
| Station: | Pacific Northwest Research Station |
| Source: | Northwest Science |
Abstract
We investigated the landscape distribution and spatial patterns of western hemlock dwarf mistletoe in old-growth and mature Douglas-fir forests of the Wind River Experimental Forest. The study was conducted in two settings: the old-growth forest (500 year) of the 478-ha T.T. Munger Research Natural Area (T.T. Munger RNA) and the higher elevation, predominantly 157-year-old stand of the 1400-ha Panther Creek Division of the Wind River Experimental Forest. Existing transects and tagged trees were used in the T.T. Munger RNA to survey for dwarf mistletoe infection. Eighty-three percent of the transect segments within the T.T. Munger RNA had some level of dwarf mistletoe infection. Dwarf mistletoe was found only in legacy old-growth patches in the Panther Creek Division, and these composed only 2.4 percent of the division area. The three legacy old-growth patches containing dwarf mistletoe were restricted to drainage bottoms and well-watered benches. Spatial analysis of transect segments (using Moran's I) in both T.T. Munger RNA and Panther Creek Divisions showed that within both old-growth and legacy patches in mature forest, western hemlock dwarf mistletoe infection is spatially aggregated. Dwarf mistletoe is maintained on this landscape by survival in refugia, most often in riparian areas, or, in the case of the T. T. Munger RNA, in low-density, low-productivity areas that do not burn completely during wildfire events. Dwarf mistletoe must persist in these refugia until host trees recover in burned areas, a process that may take many decades in intensely burned watersheds.