Title: Precommercial thinning: implications of early results from the Tongass-Wide Young-Growth Studies experiments for deer habitat in southeast Alaska
Author: Hanley, Thomas A.; McClellan, Michael H.; Barnard, Jeffrey C.; Friberg, Mary A.
Source: Res. Pap. PNW-RP-593. Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific Northwest Research Station. 64 p.
Description: This report documents the results from the first “5-year” round of understory responses to the Tongass-Wide Young-Growth Studies (TWYGS) treatments, especially in relation to their effects on food resources for black-tailed deer (Odocoileus hemionus sitkensis). Responses of understory vegetation to precommercial silviculture experiments after their first 4 to 8 years posttreatment were analyzed with the Forage Resource Evaluation System for Habitat (FRESH)-Deer model. The studies were conducted in western hemlock (Tsuga heterophylla)-Sitka spruce (Picea sitchensis) young-growth forests in southeast Alaska. All four TWYGS experiments were studied: (I) planting of red alder (Alnus rubra) within 1- to 5-year-old stands; (II) precommercial thinning at narrow and wide spacings (549 and 331 trees per hectare, respectively) in 15- to 25-year-old stands; (III) precommercial thinning at medium spacing (420 trees per hectare) with and without pruning in 25- to 35-yearold stands; and (IV) precommercial thinning at wide spacing (203 trees per hectare) with and without slash treatment versus thinning by girdling in >35-year-old stands. All experiments also included untreated control stands of identical age. FRESHDeer was used to evaluate the implications for deer habitat in terms of forage resources (species-specific biomass, digestible protein, and digestible dry matter) relative to deer metabolic requirements in summer (at two levels of requirements—maintenance only vs. lactation) and in winter (at six levels of snow depth). Analyses for both summer and winter indicated that in all cases except for Experiment I (red alder planting in 1- to 5-year-old stands), habitat values of all treatments exceeded untreated controls (P < 0.05), and earlier treatments yielded greater benefits than did later treatments (i.e., treating at 15 to 25 years of age was more effective than at 25 to 35 years, and at >35 years was least effective). When compared to a wide range of old-growth stands from throughout the region, it was apparent that in summer and winter with low snow depths (<20 cm) early treatments (15- to 25-year-old stands) yielded better food resources than did old-growth forest, while later treatments (25- to 35-, and 35+ year-old stands) yielded poorer habitat than old growth. These results, however, are from only the first 4 to 8 years posttreatment. The next study of TWYGS responses is scheduled to occur at 9 to 13 years posttreatment.
Keywords: Silviculture, adaptive management, Odocoileus hemionus, habitat model, nutrition, understory vegetation, snow.
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Hanley, Thomas A.; McClellan, Michael H.; Barnard, Jeffrey C.; Friberg, Mary A. 2013. Precommercial thinning: implications of early results from the Tongass-Wide Young-Growth Studies experiments for deer habitat in southeast Alaska. Res. Pap. PNW-RP-593. Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific Northwest Research Station. 64 p.
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