Using light to predict fuels-reduction and group-selection effects on succession in Sierran mixed-conifer forest
Bigelow, Seth W.; North, Malcolm P.; Salk, Carl F.
Many semi-arid coniferous forests in western North America have reached historically unprecedented densities over the past 150 years and are dominated by shade-tolerant trees. Silvicultural treatments generally open the canopy but may not restore shade-intolerant species. We determined crossover-point irradiance (CPI) (light at which the height growth rank of pairs of species changes) for seedlings in Sierra Nevada mixed-conifer forest and used these to interpret light environments produced by fuels-reduction thinning and group selection with reserved large trees. Nine of 21 species pairs had well-defined CPIs. The CPI of the most common shade-tolerant and intolerant species (white fir (Abies concolor (Gordon & Glendl.) Lindl. ex Hildebr.) and ponderosa pine (Pinus ponderosa Douglas ex P. Lawson & C. Lawson)) was 22.5 mol.m(-2).day(-1) or 41% of full sun. Median understory irradiance increased from 9.2 mol.m(-2)day(-1) (17% full sun) in pretreatment forest to 13 mol.m(-2).day(-1) (24% full sun) in lightly and 15.5 mol.m(-2).day(-1) (28% full sun) in moderately thinned stands and 37 mol.m(-2).day(-1) (67% full sun) in group-selection openings. We estimate that 5%-20% of ground area in lightly to moderately thinned stands would have enough light to favor shade-intolerant over shade-tolerant growth compared with 89% of ground area in group-selection openings. The CPI provides a tool to assess regeneration implications of treatment modification such as increasing heterogeneity of thinning to enhance regeneration or reserving large trees in group-selection openings to maintain wildlife habitat.
Canadian Journal of Forest Research
2011, Volume: 41, number: 10, pages: 2051-2063
Publisher: CANADIAN SCIENCE PUBLISHING, NRC RESEARCH PRESS
UKÄ Subject classification
Permanent link to this page (URI)