User: | Open Learning Faculty Member:
My chosen area of study is a Garry oak and Douglas-fir ecosystem, typical of south-facing exposures on southern Vancouver Island and the Gulf islands. It is located on the north side of Cowichan Bay near the city of Duncan, on a ~45%, SSW aspect and ~90 meters above sea level. Ample groundwater flow during the rainy season tapers to drought conditions with only a few weeks of no rain. Bedrock is exposed in areas, and average soil thickness likely between 0.5 and 1 meter. This area does not have any specific designation (it is private property) though there is an ecological preserve to the west. Note that due to this site being below my house, one could say that my visitation of this site is ongoing!
Figure 1: Study site.
Figure 2: section of Garry oak forest with Douglas-fir. Though not visible, this fir is gradually losing its needles from the top down.
Across southern Vancouver Island, Garry oak ecosystems are declining in area as the more vigorous (but less drought and fire resistant) Douglas-fir outcompetes the oaks and as non-native grasses, shrubs and vines overtake meadows. There are also exceedingly few Gary oak seedlings or young trees anywhere. Two questions arise from these observation:
- Why have I observed so few Garry oak seedlings?
- What is the impact of non-native vs. native grasses and shrubs on Garry oak propagation and competition?
However, I’ve also noticed in recent years a pattern of Douglas-fir trees dying for unknown reasons, in areas which had historically likely been Gary oak ecosystems (due to lack of water, aspect, and ease of fire progression). This is evident in the immediate study area outline above, as well as throughout the broader hillside. Provided that my observation is indeed correct (and not incidental) and that there is an increase in Douglas-fir mortality on dry, south aspects, my final question is:
- What is/are the causes of this increase in Douglas-fir mortality? (Some possible causes: Increased summer temperatures, changes in timing and amount of precipitation, pathogen, etc)
