USA: The impact of wildfire on vegetation phenology appears to be stronger than that of periods of extreme weather or climate events. That’s according to researchers in the US who used data from the Hayman Fire in Colorado during June and July 2002, which burned an area of 526 square km.
The Hayman site provided an opportunity to investigate post-fire recovery, which is a function of burn severity and vegetation types. The data also highlight how land disturbances caused by wildfire complicate the assessment of climate change.
Derived from satellite images, the “start of season” describes the timing of seasonal increase in vegetation greenness over a plant community during a growing period. For land with the same vegetation community, the variation of the start of season from year to year can serve as a useful indicator of potential changes in climate. However, as researchers observed for the Hayman burn area, wildfire alters the vegetation community and this results in different responses relative to pre-fire conditions.
Jianmin Wang and Xiaoyang Zhang at South Dakota State University found that the Hayman Fire advanced the area-integrated start of season by 15.2 days. What’s more, the event converted start of season from a delaying trend of 3.9 days per decade to an advancing trend of –1.9 days per decade, as determined by assessing the period 2001–2014.
The researchers caution that this wildfire influence needs to be factored into climate analysis to improve our understanding of the bigger picture.
“It’s important to note that post-fire recovery takes longer than a decade and variations that you may see in the start of season do not simply reflect the long-term changes in climate,” Zhang told environmentalresearchweb. “Instead, for these areas the trend in the start of season should be viewed as a combination of the impact of land disturbance and changes in climate.”
In the case of the Hayman Fire, evergreen forests, which were dominant beforehand, were converted into shrub- and grasslands. Both these vegetation types tend to unfold their leaves earlier than mature trees.
The team reported their study in Environmental Research Letters (ERL)