Trembling aspen has the potential to be a long-term competitor with conifers for light in some ecosystems and for soil resources in others, and the importance and intensity of these interactions appear to vary across ecosystems and climatic regions. Due to the lengthy interaction between conifers and broadleaf trees in juvenile stands, however, there has been a lack of long-term data across a range of ecosystems and regional climates to characterize these effects. This knowledge gap has resulted in considerable controversy regarding levels of broadleaf retention that are biologically acceptable in stands where conifer growth is the primary regeneration objective. Recent work by Newsome et al. [2008, in revision] describes interactions between aspen and pine on an ecosysem-specific basis in the Cariboo-Chilcotin region of British Columbia, but information is also required for more southerly regions of the province.
The PROBE (PRotocol for Operational Brushing Evaluations) project has studied brushing effects on conifer seedlings and vegetation since 1991 (Simard et al. 2001), and includes 96 trial sites across the climatically variable southern interior of BC. In recent years, this project has focused strongly on broadleaf-dominated communities to help address the provincial need to define thresholds for broadleaf retention that facilitate both conifer growth and ecosystem health over the long-term. Acquiring this information across a range of climatic regions is increasingly critical for informing new directions for managing ecosystem health and resilience under changing future climates (Future Forests Ecosystem Initiative 2006).
We are now in the process of collecting long-term data for the Aspen complex across a range of ecosystems (submesic to subhygric) and climatic regions (IDF, MS, and ICH zones). All sites were measured in years 0, 1, 3, and 5 post-treatment, and we currently have 10-15 year post-brushing data for 7 of the sites. With FSP funding already acquired (Y091093), we are collecting similar data at 4 additional sites, and alternate funding is being sought for a 12th site. We will then have an extensive set of long-term data that will allow us to examine conifer and vegetation responses across a range of climatic, ecosystem, site, and treatment characteristics, in stands that are now 15-20 years old.
Past analyses for the PROBE project used ANOVA to examine brushing effects for groups of sites with similar ecosystem, conifer species, vegetation community, and brushing method. In the proposed work, we will use multivariate, logistic regression and maximum likelihood analyses to investigate responses across a wider range of conditions. For the multivariate approach, we will use Non-metric Multidimensional Scaling (NMS), a technique particularly well-suited to the analysis of ecological data (McCune and Mefford 1999), to test for differences among climatic regions, sites and treatments in the Aspen complex using data collected from 12 individual sites. More specifically, the importance of climate variables (temperature, precipitation and growing degree days, based on the biogeoclimatic classification), site characteristics (e.g., soil moisture regime, slope, aspect, elevation), and treatment factors (e.g., brushing method and severity, stand age at brushing) to growth and health of lodgepole pine, Douglas-fir and aspen will be compared using NMS. Significance differences will be detected using Multi-Response Permutation Procedures. We will use the same approach to examine effects on vascular plant community measures such as composition, richness and diversity. Canonical Correspondence Analyses will be used to test for correlations between climate or site gradients and conifer growth and survivorship as well as aspen competitive intensity. In addition to multivariate analysis, we will use logistic regression to analyze conifer mortality data, and maximum likelihood analysis to test a variety of growt ...
Forest Investment Account (FIA). 2009. Responses of conifers and trembling aspen-dominated vegetation a decade after manual and chemical brushing in southern interior of BC: examining the role of climate, ecosystem, site, and vegetation characteristics. Forest Investment Account (FIA) - Forest Science Program. Forest Investment Account Report. FIA2009MR042
Topic: FLNRORD Research Program
Keywords: Forest, Investment, Account, (FIA), British, Columbia
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