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Efficacy and Consequences of Aspen Treatments: The USU/Deseret Land & Livestock Manipulation Project
A.J. Leffler, H.V. Miegroet, T.A. Monaco, J.N. Long, and R.J. Ryel, Utah State University, Logan, UT
Utah State University, in cooperation with landowners in northern Utah, is conducting a forest manipulation study to examine the efficacy and consequences of various forestry treatments to regenerate aspen stands encroached by conifers. Treatments include control, selective harvest of merchantable timber, clear-felling, chaining, and burning, arranged in a split-plot design replicated four times on three north-facing hillslopes. Each block consists of eight 1-ha treatment units. Pre-treatment data were collected in summer 2007. Sampling was designed to 1) assess stand composition, 2) quantify understory biomass and species composition, and 3) determine soil bulk density and C and N status. Blocks differed considerably in canopy species composition, ranging from nearly uniform cover by aspen to virtually no aspen detected. Soils of aspen units had lower bulk density than soils from conifer and mixed units, while mixed units had lower soil C and N, and a higher C:N ratio. For understory biomass, there was a trend toward decreasing woody cover and increasing non-woody cover with increasing basal area of aspen. Over 70 species were observed in the understory and only eight of these were non-native. Blocks differed in species composition but species diversity was similar among blocks. Ordination analysis (DCA) suggests four distinct understory communities associated with each study block. Ordination axes are correlated with aspen basal area and basal area of sub-alpine fir, suggesting canopy species composition strongly influences the understory. Currently, mechanical treatments are taking place. Burning treatment is scheduled for fall 2009. Changes in these variables will be monitored for several years following all manipulations.