Browning Crowns in Tombstone Territorial Park

Observation by Amanda Bell:

Trees in the Tombstone Territorial Park (TTP), Yukon appear to have damage to the upper portion of the crown that is exposed above the snowpack in winter. According to local knowledge, the growing season is longer in the area, and temperatures are warmer, leading to trees growing taller (Personal communication, Tombstone Territorial Park Interpretive Centre, August 12, 2024). Come winter, these taller trees are more vulnerable to extreme elements (Personal communication, Tombstone Territorial Park Interpretive Centre, August 12, 2024). Eliot McIntire of the Pacific Forestry Centre and National Forest Inventory says this is an emergence from snow effect, when damage occurs to plants that are exposed to the harsh winter conditions. McIntire states that snow provides protection for trees against winter extremes; it behaves as an insulator of heat radiated from the ground. When snow is absent from parts of the tree, the emergence from snow effect acts as a catalyst for browning.

The local reporting of trees growing taller in the TTP is consistent with tree growth patterns recorded in the Northwest Canadian Arctic by Roxanne Frappier, a Research Affiliate at the Centre for Remote Sensing in Canada. The reported longer growing season is consistent with data collected on Canada’s overall shorter winter season (Derksen et al., 2019). Conversely, the reported increase in temperature by TTP locals is not scientifically supported due to lack of local data, though Frappier et al. (2023) observed a 2.6°C increase in average January temperatures from data collected at the nearby weather station in Dawson City.

Frappier says that statistical analysis of snow accumulation is inconsistent and unreliable as demonstrated by the conflicting data recorded in artic areas. The WWF (n.d.) declared an increase in arctic winter precipitation, while Derksen et al. (2019) reported a 5-10% decrease in snowfall across Canada since 1981. The discrepancy supports Frappier’s conclusion that snowfall data can be unreliable in these instances as it is difficult to monitor due to missing data and unique local factors. Meaning that reported changes in snowfall in the TTP currently relies on local knowledge and observations.

Multiple variables could be contributing to the browning observed in the TTP. This behaviour could be a result of the changes to the growing season/temperatures reported by TTP locals, shifting precipitation patterns or as Frappier suggests, an isolated incident. The TTP tree browning observation requires further investigation over time to be certain.

References Derksen, C., Burgess, D., Duguay, C., Howell, S., Mudryk, L., Smith, S., Thackeray, C. and Kirchmeier-Young, M. (2019). Changes in snow, ice, and permafrost across Canada; Chapter 5 in Canada’s Changing Climate Report, (ed.) E. Bush and D.S. Lemmen; Government of Canada, Ottawa, Ontario, p.194–260.

Frappier, R., Lacelle, D., & Fraser, R. H. (2023). Landscape changes in the Tombstone Territorial Park region (central Yukon, Canada) from multilevel remote sensing analysis. Arctic Science, 9(4), 838–855. https://doi.org/10.1139/as-2022-0037 Tombstone Territorial Park Interpretive Centre. (August 12, 2024). Interpretive Walk.

WWF. (n.d.). The importance of snow. https://www.arcticwwf.org/the-circle/stories/the-importance-of-snow/

Comment from Gemini:

The related 'See Also 'posts provide context, with stories and observations about the health of northern conifers. Several of the observations detail similar instances of tree damage and die-off, particularly among spruce and cedar. A recurring theme in these observations is the role of drought and extreme weather conditions, potentially exacerbated by climate change, in weakening trees and making them susceptible to diseases and pests. For example, observations from British Columbia document widespread cedar die-off attributed to recurring summer droughts (Cedar die off impacts many on Vancouver Island, Western red cedars die off as extended dry spells continue, Western red cedars are dying of drought and scientists say it's one more portent of climate change). Observations from Alaska highlight the impact of spruce bark beetles and other diseases, often linked to warmer and drier conditions (Anchorage spruce trees are dying. We need to talk about what happens next., Discolored Spruce (Picea sitchensis) Trees).

While the observation mentions the "emergence from snow effect," the related observations suggest that other factors, such as drought stress, insect infestations, or diseases, could be playing a significant role, either independently or in combination with the snow exposure. The warmer temperatures noted in the observation, supported by data from Dawson City (Frappier et al., 2023), could be contributing to these factors. The observation also points to the unreliability of snowfall data in the region, further highlighting the need for continued monitoring and investigation to determine the precise cause of the browning crowns. It would be beneficial to investigate whether there have been similar observations of browning crowns in other boreal or arctic regions experiencing warming temperatures and changing snow patterns. It would also be valuable to conduct on-the-ground assessments to examine the affected trees for signs of disease, insect damage, or other stresses.