Master’s Thesis Abstract by Ella Elman (2001)

Over the past 50 years, an increasing number of timber harvests in national forests of the western United States have occurred in high-elevation ecosystems. The effects of past harvest treatments on these systems were studied to learn more about regeneration conditions 20 years following harvest, and how future forest composition might be affected by past activities. Eighteen sites encompassing three common post-harvest treatments were examined in the Mt. Baker-Snoqualmie National Forest, Washington (USA) at elevations ranging from 830 m to 1460 m. Treatments included: 1) Sites that were broadcast burned and planted with Pacific silver fir (Abies amabilis), 2) unburned sites that were seeded with Pacific silver fir and 3) unburned sites that were planted with Pacific silver fir. Overstory and understory species composition was measured and compared to Forest Service records of mature forest stands in the area.

All sites were dominated by Pacific silver fir and western hemlock, which represented 68 - 100% of all trees present. On burned-planted sites, a smaller proportion of Pacific silver fir was found than on unburned sites. Burned sites also contained significantly less advance regeneration than unburned sites. Understory in clearcut areas was dominated by Epilobium angustifolium, Vaccinium spp. and Rubus spp. The effects of management treatments must be evaluated in the context of how overstory and understory species vary along elevational gradients. Pacific silver fir tree and seedling densities are positively correlated with elevation, and western hemlock (Tsuga heterophylla) is negatively correlated. Two understory vegetation communities are segregated by elevation; an Epilobium angustifolium/Rubus spp. community dominates at lower elevation sites, and a Vaccinium spp. community dominates higher elevation sites. Comparison with Forest Service stand data for the study sites indicates that widespread planting and seeding of Pacific silver fir has not had significant effects on overstory species composition to date, although future stand composition is difficult to predict. Comparison with Forest Service data on understory composition in mature forests in the watershed show a contrast between a shade-tolerant understory community in mature stands and a shade-intolerant pioneer species in clearcut sites. In order to maximize regeneration potential and preserve ecosystem function, management recommendations for high-elevation forests include: 1. Using alternative harvesting techniques that retain stems to provide a favorable microclimate to establishing seedlings, as well as to reduce understory competition by shade-intolerant species. 2. Protecting advance regeneration on sites by minimizing site preparation and mechanical damage of stems during harvest and leaving slash on sites. 3. Avoiding burning when possible to preserve advance regeneration and avoid nutrient depletion from sites.