Document Details
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Title |
Effects of the variable retention silvicultural systems on microclimate, establishment and growth of trees in west coast forests | ||||||||
Author |
Nick | ||||||||
Date |
2008 | ||||||||
Abstract |
The original study site was moved to a mixed group/dispersed retention site located off the Malahat (MH) Highway on Vancouver Island from the Stillwater dispersed VR site (near Powell River) at the beginning of May, 2005. Our proposed plan to move fixed sensor transects between several retention types within the same growing season became logistically and financially impractical due to the complexity of the new fixed transects (many more sensors and longer sensor leads) that were built to capture the variability in microclimate surrounding the larger dimensions of the MH group retention site. At the start of the 2006 field season our intention was to preserve the continuity of the data record and improve the robustness of our forest growth model validation by leaving the fixed transects in place for a full growing season in both the group and dispersed VR plots. For the final year of the project, however, we have chosen to maintain the focus of our study on the group retention patch that has been the subject of the first two years of the project. Our decision to remain in the group retention plot rather than move the equipment to the dispersed retention plot is based on two factors. First, an enhanced seedling growth response 15-m from the retention patch edge has been observed in measurements of seedling height and diameter and corroborated by the seedling CO2 uptake data from 2005. Initially, the 2006 data did not show the same pattern; however, once these data had been recalculated after correcting for leaf area index, seedlings growing 15 m from the patch edge on the east and west transects showed the same enhanced CO2 uptake observed in 2005 (see Fig. 1). Another growing season of transect measurements of soil moisture in the mineral soil layer may help to explain this spatial variation in growth response. Second, the fall/winter of 2006-7 have seen particularly severe windstorms move through the MH site area. During a recent site visit, project collaborator N. Smith estimated that the storms have blown down up to 30% of the trees originally retained in the 50 m x 50 m patch, damaging some of our transect sensors and communications equipment. At the time of writing our site access is restricted until the area around the patch can be cleaned up by an experienced crew of fallers. This logistical challenge presents us with a research opportunity for our final field season, however, as the canopy gap structure of the retained patch of trees is now dramatically different from that present in the first year of the study. The light, moisture and temperature regimes experienced by the seedlings growing around the patch are likely to be much different, thus leaving the fixed transects in place and performing additional seedling photosynthesis measurements will allow us to characterize the changes in microclimate and to detect any changes in seedling growth response associated with anticipated changes in microclimate resulting from the loss of so many trees in the patch. | ||||||||
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