|Alberta-Pacific Forest Industries Inc.
Object & Deliverables
The primary focus of this study was to further understand the factors affecting the growth and survivorship of white spruce growing under deciduous canopies. The three objectives to this study are: to quantify the relationship between understory spruce height and overstory variables such as crown closure, light transmittance, tree spacing factor, and density (trees/ha); to use this information to produce a predictive growth equation that can be incorporated into the Mixedwood Growth Model (MGM); and to make a preliminary assessment of the understory spruce mortality experienced in the sample stands. These objectives were met by: analyzing the field data from the Central Mixedwood Natural Sub-region and the Lower Foothills Natural Sub-region; and by establishing additional plots in stands with an overstory dominated by trembling aspen (Populus tremuloides Michx.) and an understory with white spruce (Picea glauca (Moench) Voss).
The project data utilized came from two sources: available existing data sets; and field data collected during the sampling program. Data gathering was done using three methods: interviews with knowledgeable professionals; review of current data sets where white spruce is regenerating (either naturally or planted) under a deciduous overstory; and field sampling. Non-linear regression analysis was utilized to examine the relationship between understory white spruce growth and potential individual explanatory factors. Relative crown length, breast height age, and overstory tree spacing were the explanatory factors that showed the strongest correlation to understory white spruce growth. The importance of relative crown length (RCL) for predicting height increment resulted in the need for a model to predict RCL. The final RCL model included breast height age, overstory coniferous spacing factors, and deciduous spacing factor as explanatory variables. The height increment and RCL models were then jointly incorporated for use in the Mixedwood Growth Model (MGM).
The results quantify the regeneration growth of white spruce under different deciduous overstories factors. This information can be used when performing silvicultural applications, and will assist in predicting future growth and survivorship of understory white spruce. In addition, the growth trends of understory spruce will be incorporated into the MGM as a means of projecting white spruce growth. These growth projections can then be used to estimate future stand volumes which could potentially be used in a timber supply analysis.
The field work associated with this Study was carried out over the summer seasons of 2000 and 2001. The project results are contained within a Master’s Thesis completed in the winter of 2003 by Glenn Buckmaster, and an updated Mixedwood Growth Model which can be accessed through the University of Alberta website http://mgm.ales.ualberta.ca/.