Factors affecting survival dynamics in balsam fir in New Brunswick, Canada
University of New Brunswick
Interaction of factors influencing individual-tree survival remains one of the least understood elements of forest growth and yield. An approach to the environment that addresses a combination of environmental variables is indispensable to the study of tree mortality. This thesis is based on an evaluation of mortality caused by unknown factors as well as eight documented factors, including insect damage, tree suppression, broken top, stem breakage, windthrow, over mature, stem wound, and cut. Data from 939 permanent sample plots (PSP’s) in New Brunswick containing balsam fir are sampled to determine mortality over consecutive measurement periods. Tree data in PSP’s are analyzed with environmental surface data accounting for water, energy, and light requirements of the trees. Spruce budworm [SBW; Choristoneura fumiferana (Clem.)] is the most important of all insects causing mortality in balsam fir. The impact of SBW during and after infestation is evaluated. Mortality as a “legacy effect” of the latest SBW infestation (1972-1993) is manifested in the form of windthrow (33.3%), stem breakage (33.3%), and broken tops (16.7%), mainly in the Highland ecoregion of the province where winds are frequently strong. Anthropogenic causes of mortality account for another 12.4% of observed mortality, i.e., 6.7% and 5.7% from likely cut and stem wound damage, respectively. Hot spot analysis of unexplained mortality suggests that greatest mortality occurs in the Grand Lake ecoregion, mostly in high soil water content and high growing degree-day areas of the province. Unexplained mortality may be largely ascribed to the process of self-thinning, while documented causes are more catastrophic in nature. This study fosters an improved understanding of regional survival dynamics in balsam fir.