Date of Award:


Document Type:


Degree Name:

Doctor of Philosophy (PhD)


Wildland Resources

Committee Chair(s)

John C Malechek


John C Malechek


Dale L. Bartos


David L. Coppock


Ronald J. Ryel


James N. Long


Heavy and repeated ungulate browsing on reproductive suckers has limited trembling aspen (Populus tremuloides Michx.) regeneration on many Western landscapes. However, little is known about the specific effects of season and intensity of browsing. My objectives were to determine the effects of season and intensity of clipping (simulated browsing) on suckers’ (1) density and growth characteristics, and (2) nutritional quality and quantity. Three randomly selected stands were clear-felled in mid-July, 2005, and fenced. Simulated browsing treatments of 0%, 20%, 40%, and 60% removal of current year’s growth were randomly applied in early, mid-, and late summers of 2006 and 2007. Sucker density, height, leader length, twig numbers, bud numbers, basal area, and biomass harvested were monitored in each quadrat. Harvested material was analyzed for crude protein and in vitro true dry matter digestibility. Early summer clipped suckers suffered no winter mortality compared to mortalities of 41% and 42% for mid- and late summer clipped suckers, respectively. However, even at the highest mortality, there were still ample numbers of suckers for stand regeneration. Sucker height was restricted by all early summer treatments. Clipping at 20% and 40% in mid- and late summer, respectively, did not reduce sucker height, but suckers clipped 60% were ≤ 40 cm shorter than controls. Twig and bud density both declined with increasing intensity of clipping. By the study’s end, basal area of early summer clipped suckers was higher than for those clipped in late summer. Crude protein of clipped biomass decreased with season’s advance and clipping intensity. Levels ranged from 12.8% to 22.9% and 10.6% to 16.5% in 2006 and 2007, respectively. Digestibility ranged from 80.1% to 93.4% and 75.2% to 90.7% in 2006 and 2007, respectively. Biomass (260 vs. 181 kg/ha) and total digestible dry matter (197 vs. 142 kg/ha) harvested were higher in mid-summer clipped plots in 2007 than in 2006, respectively. Apart from early summer, total nitrogen harvested was not affected differently by season of clipping. Clear-felling programs that allow browsing of ≤ 40% in mid- and late summer would ensure sustained aspen stand density and growth. (184 pages)