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UBC Theses and Dissertations

Pre-commercial thinning and repeated fertilization of young lodgepole pine stands : long-term impacts on tree growth, plant diversity, and range Lindgren, Pontus Maurits Fredrik


The 16-year research program studied the impacts of pre-commercial thinning (PCT) and fertilization on tree growth, plant diversity, forage production, and ungulate habitat use. Ecological effects of cattle grazing were also studied. Three study areas were located in south-central British Columbia, Canada. Each study area was comprised of densely stocked stands of young lodgepole pine (Pinus contorta Dougl. ex Loud. var. latifolia Engelm.) thinned to 250, 500, 1000, and 2000 stems/ha. Half of each thinned unit was fertilized five times over 10 years. An unthinned stand completed the experimental design. Fifteen-year increments of crop-tree diameter at breast height (DBH) as well as tree and stand volume were enhanced by fertilization, but not by density level. Non crop trees became abundant, particularly within the heavily thinned stands. Fertilization enhanced herb abundance but decreased herb and shrub diversity, at least temporarily. Plant species richness was unaffected by density levels or fertilization. Structural diversity of the tree layer was greater in the heavily than lightly thinned stands, and overall structural diversity was enhanced by fertilization. Forage yield was enhanced by fertilization, but only within heavily thinned stands. Fertilization also resulted in increased crude protein levels of pinegrass (Calamagrostis rubescens Buckley), an important forage for cattle (Bos taurus L.) for up to six years after the final fertilization. Habitat use by cattle was enhanced by both fertilization and PCT, and this increased use did not appear to have any negative impacts on the native ungulates using these stands. Relative to ungrazed plots, cattle grazing increased both richness and diversity of herbs and shrubs within fertilized stands, whereas grazing decreased shrub richness within unfertilized stands. Results indicated that increased forest and range productivity is possible with treatments of repeated fertilization and, to a lesser extent, PCT. Ecological effects and management implications of these treatments are discussed.

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