Response of forage yield and quality to thinning and fertilization of young forests: implications for silvopasture management.

摘要

Integration of trees with forage and livestock production (silvopastoralism) could increase productivity of forest and range resources in western North America. Pre-commercial thinning (PCT) and fertilization are two silvicultural practices that could enhance silvopasture. We tested two hypotheses (H): that yield and quality of forage would be enhanced by (H₁) heavy thinning (PCT) to <=1000 stems.ha-1 and by (H₂) repeated fertilization in lodgepole pine (Pinus contorta Dougl. ex Loud. var. latifolia Engelm.) stands. Study areas were located near Summerland and Kelowna in south-central British Columbia, Canada. Each study area had six treatments: three pairs of stands thinned to densities of 500 (low), 1000 (medium), and 2000 (high) stems.ha-1 with one stand of each pair fertilized five times at 2 year intervals. Forage yield was enhanced by PCT, but only within fertilized stands. Forage quality was generally not affected by PCT, except for crude protein of herbs that was poorer in heavily thinned stands. Fertilization tended to enhance forage yield and quality in the heavily thinned stands. Significantly improved quality of pinegrass (Calamagrostis rubescens Buckley) indicated that repeated fertilization, coupled with heavy thinning, may extend the period when high-quality forage is available, thereby allowing for increased stocking densities of cattle (Bos taurus L.) and perhaps extending the grazing season into the fall.