Owen Hargrove wrote:
I have recently observed several dead or dying cedar trees on Salt Spring Island, particularly on the north end of the island. While I have only lived on the island for two years, the number of dying cedar trees (as observed by a change in bough colouration and a loss of leaf cover) has seemed more prevalent after last summer and through the winter, as well as more frequent than I have noticed while living in areas such as Vancouver Island and the central coast of BC. I believe this perceived increase in mortality is due to an increase in summer temperatures and a decrease in summer rainfall over the last two years.
In viewing historic weather data, there appears to be a trend towards hotter and drier summers, with temperatures taken during the summer months at the nearby Victoria International Airport weather station averaging more than half a degree celsius higher in the period of 1981-2010 compared to the averages from 1961-1990, with a small decrease (~2%) in the average number of days with rainfall during those same periods (Environment and Climate Change Canada, 2018). Data from July and August of 2016 and 2017 showed further increases in average temperature and fewer days of precipitation. Many of the impacted trees I have observed are in rocky areas with shallow soil or along roadsides where water retention may be lower, which I suspect impacts a tree’s ability to withstand stress from a changing climate.
Tree mortality caused by drought and heat is discussed in detail by Allen et al. (2010).
References
Allen, C.D., Macalady, A.K., Chenchouni, H., Bachelet, D., McDowell, N., Vennetier, M., Kitzberger, T., Rigling, A., Breshears, D.D., Hogg, E.T. and Gonzalez, P., 2010. A global overview of drought and heat-induced tree mortality reveals emerging climate change risks for forests. Forest ecology and management, 259(4), pp.660-684.
.
