Growth of understory spruce following mountain pine beetle attack and recalibration and validation of the Mixedwood Growth Model for black spruce

Felix Oboite
Effective forest management requires reliable growth and yield models and adequate information on changes in the forest resulting from climate change, insect outbreak and competition from neighboring trees. Growth responses of white spruce (Picea glauca (Moench) Voss) and black spruce (Picea mariana (Mill.) B.S.P) were examined in mountain pine beetle affected stands in the lower foothills of western Alberta, Canada. Diameter and height growth increased after release with white spruce
more » ... te spruce responding a year earlier as well as having a higher mean growth than black spruce. Post-release diameter and height growth were also affected by initial sizes of trees (positive effect), and age (negative effects). High spruce/fir densities resulted in increased height growth and reduction in diameter growth of both spruces. Spruce/fir tree density assessed with a plot radius of 5.64m and their spatial distribution was more adequate for estimating understory light than 3.99m plot radius. While both spruces have the potential to replace dead pine trees, thinning may be needed in areas where high spruce/fir densities might result in competitive suppression of growth. In the second component of this study, long term measurement data collected across western Canada and Alaska were used for this study to characterize the effects of deciduous and coniferous competition and climate on growth and mortality of black spruce. A non-linear mixed model and a generalized logistic function were used to develop growth and mortality functions, respectively. Results showed that climate was a very important predictor in growth and mortality models. Temperature related variables (mean annual temperature and frost free period) increased diameter and height growth while moisture related variables (climate moisture index and mean annual precipitation) had negative effects. Coniferous competition (pine and spruce/fir) negatively affected growth while iii deciduous competition showed a positive influence suggesting that deciduous trees may be compatible with black spruce because they utilize different niches and/or due to facilitative effects of deciduous. The positive effect of deciduous on black spruce growth might be due to smaller mean densities (tree per hectare) of deciduous competition (369) compared to pine (1263) and spruce (4355) competition that affected growth negatively. Pine competition had stronger effects on black spruce mortality than did deciduous and spruce/fir competition. Black spruce trees allocated more growth to diameter than height or volume when they are larger in size and in wetter sites (higher moisture index and precipitation) with less spruce/fir competition. Finally, models developed in this study were incorporated into the Mixedwood Growth Model (MGM) and results of validation for Alberta and Saskatchewan suggest that the recalibrated version of MGM works better than the earlier version with only a slight bias for stand volume and basal area. This clearly shows that predictions from this new version of MGM can reliably simulate black spruce growth across a range of stand conditions in western Canada. iv Preface This thesis is my original work. My supervisor (Dr Phil Comeau) contributed by providing comments and suggestions for revisions of the drafts of all chapters of this thesis. I collected measurement data for Chapter 2 while PSP data were made available for Chapter 3, 4 and 5. I was responsible for the statistical analysis, methodology, write-up and organization of all of Chapters of this thesis.
doi:10.7939/r36q1sz9r fatcat:ldkf3gf3jvhrpab4vzgsaxeytm