This project builds on an ongoing research program examining biotic and environmental factors affecting stand establishment in complex stands (Simard and Vyse 2006). Predicting seedling recruitment under a variety of residual stand structures in a range of climatic regions, and therefore the design of silvicultural systems across forests and landscapes under changing climatic conditions requires a basic understanding of the competitive and facilitative processes underlying residual tree effects on seedling recruitment and growth. Our earlier work established that competition for light and soil water, mediation of resource availability through soil organisms (particularly mycorrhizas), and carbon acquisition through established common mycorrhizal networks (CMNs), were important determinants of seedling growth in Douglas-fir forests, but that these relationships changed as stands developed, and varied across ecosystems (Simard et al. 1997; Simard and Sachs 2004; Simard et al. 2005). Proximity, density, composition and age of neighbors, presence of an established CMN, as well as forest productivity (as determined by climate and site), were important factors in the performance of establishing seedlings. CMNs appeared to facilitate seedling establishment through rapid fungal inoculation as well as transfer of carbon, nutrients or water from neighboring residual trees (Simard and Durall 2004).
With the recent summer drought occurrences in southern interior BC, and the predicted increase in average annual temperature for all of BC with rising atmospheric CO2 concentrations (Hamann and Wang 2006), concerns are increasing about forest recruitment following harvest or natural disturbance. Ensuring forests regenerate and remain healthy under increasing climatic stress, particularly those in the most vulnerable ecosystems (e.g., Douglas-fir forest near its climatic limits; Hamann and Wang 2006), requires that we design silvicultural systems using a sound understanding of the climatic, site and biotic factors regulating recruitment.
To that end, we are conducting field and growth chamber experiments examining Douglas-fir seedling establishment as a function of BGC subzone, proximity to residual trees, links into CMNs with residual trees, seedling origin (seed or seedling) and provenance, and atmospheric CO2 concentrations. To predict climatic change effects on seedling recruitment, we are assessing the interaction of these factors at field locations in different interior BGC subzones, using spatial climatic variability as a proxy for climate change. We predict that partial retention and linkage into a CMN will be of increasing importance to seedling recruitment in BGC zones with greater summer drought stress, and hence in regions that will experience greater drought stress with climate change. The experimental design, which includes replication at the stand and climatic region levels, will provide basic information for designing silvicultural systems across multiple scales. Additionally, ambient CO2 levels are predicted to nearly double by the year 2100, so inferences made about stand dynamic changes in response to climate change will be inaccurate without accounting for atmospheric CO2 changes, given that ambient CO2 levels affect basic plant physiology and therefore competitiveness with neighbors. Manipulating CO2 levels, along with climatic variables, will be accomplished in a growth chamber experiment.
The field study is being conducted in three interior BGC subzones that include forests with a major component of Douglas-fir. Three interior subzones were selected to represent a climatic moisture gradient, and include interior sites in the IDFxh2, IDFdk and ICHwm3. Three replicate sites are distributed across a broad area in each BGC unit to capture within-BGC unit variability.
Additional factors tested in each BGC unit are presence of a CMN (three levels using different sized mesh barriers that exclude roots and hyp
Simard, Suzanne W.. 2009. Effects of partial retention and common mycorrhizal networks on seedling recruitment in Douglas-fir forests across British Columbia. Forest Investment Account (FIA) - Forest Science Program. Forest Investment Account Report
Topic: FLNRORD Research Program
Keywords: Forest, Investment, Account, (FIA), British, Columbia
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