Western Red Cedar die-off in Pacific Spirit Park

In the last few years, I have observed a significant die-off of Western red cedar in several high traffic and peripheral areas of Pacific Spirit Regional Park (PSRP) in Vancouver, BC. I noticed a higher concentration of this extensive, seemingly non-random disease and mortality occurring near the eastern edge of the park, possibly associated with disturbance in the form of residential construction or localized sites of soil disturbance, such as near the Sasamat reservoir (Fisher et al., 2020). The majority of the cedar trees I saw were noticeably consumed by browning, small, and young, with most likely more shallow root systems. This is consistent with vegetative stress to which young trees have not developed resilience, but older trees may be less impacted (Fisher et al., 2020). The landscape of PSRP has been significantly altered by historical logging, potentially degrading habitat for understory species (Fang et al., 2019). Clearing of forest continues to occur in multiple locations around the university campus, primarily for residential development (Hernandez, 2017; Chan, 2017). The resulting habitat fragmentation and loss of biodiversity can lower forest resilience to climate change impacts and the introduction of invasive species (UNEP, 2019). Furthermore, the regeneration failure of species like Western Red Cedar in urban plant communities could be a result of increased trampling and soil compaction (Pickett et al., 2001). Another anthropogenic factor potentially modifying urban ecosystems could be the increased spread of invasive species and modified successional trajectories due to urban-related drivers that impact these ecosystems (Pickett et al., 2001). It is possible that water pooling in certain areas is restricting airflow to tree roots, potentially drowning the trees, or that changing moisture levels in the soil have resulted in this lagged response. The east side of the park neighbours a more dense residential area than on the west and the areas of concentrated cedar death also exhibit very visible human development and environmental alteration, such as the dumping of trail building material (Fisher et al., 2020). It is possible that plants on the edge of the park are more affected by these human activities.

Expert consult with Julie Nielsen, a SFU PhD candidate working with the Conservation and Policy Research Group and the Forest Ecology and Management Lab: Although most of the mortality and dieback caused by the 2017 and 2018 droughts seems to have worked its way through stands, Nielsen has continued to observe crown dieback of younger red cedar trees along the coast of BC. It is possible that the area in which I observed dieback is continually flooded, essentially drowning their roots, or that their soil moisture supply has been disturbed or cut off. Although there is less documentation of the conditions associated with physiological stress responses in older red cedar trees, the phenomenon of apical crown dieback in areas of coastal BC may reveal more about this relationship. Evidence suggests that warmer drier conditions are responsible for crown dieback in red cedar with the primary cause of the dieback being climatically induced recent summer droughts, or in other words, soil moisture stress in warmer drier zones during the primary growing season (Klinka and Brisco, 2009; Seebacher, 2007). Nielsen explained that knowing the local environment is key to assessing potential contributing factors and from there we could connect this occurrence to other regions experiencing die-off, which most likely means that landscape factors like climate change are at work.

References Chan, Kenneth. (2017, September 28). Construction begins on 1,250-unit condo project at UBC Pacific Spirit Park. Daily Hive. Retrieved from: www.dailyhive.com Fang, P., Hester, O., Milne, E., & Wang, K. (2019). A spatial analysis of terrestrial salamander distributions and disturbance levels in Pacific Spirit Regional Park. Fisher, B., Kim, J., Campbell, M., & Tudor, H. (2020). Tracking Salal (Gaultheria shallon) and Western Red Cedar (Thuja plicata) Dieoff in Pacific Spirit Regional Park. Hernandez, Jon. (2017, October 19). More UBC trees get axed to make way for market housing. CBC News. Retrieved from: www.cbc.ca Klinka, K., & Brisco, D. (2009). Silvics and silviculture of coastal western redcedar: a literature review. Special Report Series-Ministry of Forests and Range, British Columbia, (11). Pickett, S.T.A., Cadenasso, M.L, Grove, J.M., Nilon, C.H., Pouyat R.V., Zipperer W.C., and Costanza, R. 2001. Urban ecological systems: linking terrestrial ecological, physical, and socioeconomic components of metropolitan areas. Annual Review of Ecology and Systematics 32, 127–157. Seebacher, T. (2007). Western redcedar dieback: possible links to climate change and implication for forest management on Vancouver Island, BC. (MSc thesis). Fac. Graduate Stud., Univ. British Columbia, Vancouver, B.C.