Assessing operational silviculture and modeling juvenile growth in Saskatchewan white spruce (Picea glauca (Moench) Voss) plantations Open Access
- Other title
mixedwood growth model
- Type of item
- Degree grantor
University of Alberta
- Author or creator
Johnson, Kirk M
- Supervisor and department
Comeau, Philip (Renewable Resources)
Bokalo, Mike (Renewable Resources)
- Examining committee member and department
Chang, Scott (Renewable Resources)
Thomas, Barbara (Renewable Resources)
Department of Renewable Resources
Forest Biology and Management
- Date accepted
- Graduation date
Master of Science
- Degree level
White spruce (Picea glauca (Moench) Voss) plantations are often established with mechanical site preparation and tending. These silvicultural treatments encourage plantation survival and can influence growth, composition, and yield. To assess operational silviculture and model managed stand growth, 16 white spruce plantations (13-18 years old) and 18 white spruce Permanent Sample Plots (20-29 years old) (PSP’s) were sampled across the Prince Albert Forest Management Agreement in Saskatchewan between 2011 and 2012.
Analysis of Covariance (ANCOVA) with soil moisture regime indicated that white spruce height was not significantly different between Bracke mounding, v-plow scarification, disc trenching, and disc trenching/tended treatments. However, v-plow scarification appeared to increase the DBH of young white spruce relative to Bracke mounding. This DBH difference was linked with a significant change in grass competition but could not be linked with changes in overstory vegetation. Site differences complicated analysis and may have obscured silvicultural effects. In addition, the effectiveness of each silvicultural treatment could not be explored, since a ‘raw planted’ control could not be located.
To estimate subsampled heights, generalized mixed-effects height-diameter models were developed for the PSP dataset. Generalized models containing top height and density often explained the most variation. Small sample sizes prevented validation of the PSP height-diameter models, limiting their use to the fitted PSP data.
Using repeated measurements in the PSP dataset, short-term Mixedwood Growth Model (MGM) projections (1996-2011) were compared to observed growth between 1996 and 2011. Site index assumptions (i.e. height-age site indices or ecosite-based site indices) largely dictated MGM performance. However, given accurate site indices, modeled white spruce height and DBH tracked observed growth in most spruce-aspen mixedwoods. Modeled white spruce height and DBH were overestimated in juvenile stands (<15 years-old) initialized with small trees (<1.3m height) and heavy conifer or deciduous competition. Since many factors influence young white spruce (e.g. browsing, frost damage, leader whip, woody/herbaceous competition), and juvenile site indices (<30 to 35 years breast height age) are difficult to define, initializing MGM with small trees (<1.3m height) or data from young stands (<15 years old) may be problematic.
Finally, long-term growth (120-year rotation) was modeled in MGM using the 16 white spruce plantations and 18 white spruce PSP’s. Juvenile mixedwood stands with a strong white spruce component (~2000 trees/hectare) generally became white spruce-leading mixedwoods (>50% basal area) by age 60 and white spruce dominant (>75% basal area) by age 120. Increasing deciduous competition slowed succession but did not prevent hardwood-leading stands from becoming mixedwoods by age 120. Site index assumptions (i.e. ecosite-based site indices) strongly influenced modeled succession and long-term outcomes.
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