The influence of climate change on fire regimes and vegetation communities is a current concern. Increased frequency and intensity of fires coupled with drought and heat stress may inhibit or alter recovery of native ecosystems. As a result, plant communities may experience phase shifts, with some forests becoming shrub-steppe, and some shrub-steppe converting to grassland. The Methow Valley in WA experienced record-breaking wildfires in 2014. Fuel buildups from fire exclusion compounded the effects of extreme fire weather. We studied the mortality, survival, recovery, and vegetation dynamics following these fires and abnormal climatic conditions. 75% of the 2014 fire burned non-forested vegetation, while ponderosa pine (Pinus ponderosa) forests comprised the majority of the remaining 25%. Initial analysis indicates these forests experienced ~70% initial mortality.
To understand the resiliency and recovery of ponderosa pine forests to the fire, we are collecting tree regeneration data, in two ways.. The first was a part of a larger, long-term study which began following the 2014 fire, investigating vegetation and wildlife recovery post-fire. Seedling counts were conducted in these long-term plots in 2015 and 2016. The second was from another experiment in 2016, this one focusing solely on regeneration in the northern end of the burn.
Seedling germination and survival during the first year (2015) was poor in long-term plots, most likely due to an extremely hot, dry spring and summer. Only 20% of plots sampled in 2015 had tree seedlings. In 2016, which had a much cooler and wetter summer, 53% of plots had tree seedlings.
To compare 2015 and 2016, plots were grouped into living trees, dead trees, and living-dead trees. In 2015, there was no regeneration in dead plots or living-dead plots, and ~15 seedlings/plot in living plots. In 2016, no regeneration in dead plots, ~15 seedlings/plot in living-dead plots, and ~350 seedlings/plot in living plots.
In the 2016 northern regeneration experiment, there were extremely low rates of regeneration in areas of high-severity burn.
The response of native vegetation post-fire is complex and requires further study. Seedling survival the second year appears much better due to a cool, moist spring and summer, however the proximity of living trees seems to be crucial to any regeneration success. The combination of severe fire and extreme heat and drought may result in range contraction of the ponderosa pine forests. The study reveals the importance of subsequent climatic conditions on post-fire vegetation recovery.