Fast Regrowth of Montane Forest Understory Vegetation and Associated Recovery of Ecosystem Carbon, Water and Energy Fluxes during the First Two Years after Severe Wildfire in Waterton National Park, Canada
Abstract
Wildfires affect ecosystem-atmosphere interactions and climate feedbacks in two major ways: (i) net release of CO2 during combustion and initial ecosystem recovery; and (ii) changing plant species composition during post-fire succession alters albedo, energy exchange, carbon and water cycling with subsequent feedbacks to the atmosphere and climate system. However, the magnitudes and consequences of these feedbacks are not well understood because they are complex, non-linear and occur over vast areas of the forested landscape that are in post-fire successional stages. The Kenow wildfire burned approximately 39% of Waterton National Park in September 2017. We studied a site that was previously a mature forest, dominated by lodgepole pine, subalpine fir and Engelmann spruce. The site was severely burned, incurred large loss of soil organic matter, and all the trees were killed. Repeat photographs and plant height measurements were used to record regrowth of the understory vegetation in permanent plots. There was rapid regrowth of native forbs and small shrubs, with significant ground coverage starting in July 2018 and continuing until the end of September when canopy height reached 17 cm, and plant greenness (green chromatic coordinate (gcc) calculated from photographs) averaged 0.40. The impressive vegetation regrowth continued in 2019 when it began in May and peaked in mid-July with canopy height at 50 cm and ggc values at 0.44. We measured ecosystem flux processes using the eddy covariance technique. Average net ecosystem CO2 exchange measurements during the first two weeks in July 2018 indicated there was little diurnal pattern, with continuous daily net loss of CO2 from the ecosystem (source). By contrast, in the last two weeks of August 2018, and more intensely in the 2019 growing season, the ecosystem showed a strong diurnal pattern with respiratory loss of CO2 at night and net CO2 uptake (sink) during the day (see figure). The ecosystem was a daily net sink for CO2 during much of the 2019 growing season. Comparison of average midday values for early July between 2018 and 2019 showed that Bowen ratio decreased from 1.81 to 0.43, while albedo increased from 0.09 to 0.15. The fast recovery of ecosystem flux processes was supported by the mesic site conditions and minimal decomposition rates of the standing dead trees.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFM.B53H2483F
- Keywords:
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- 0414 Biogeochemical cycles;
- processes;
- and modeling;
- BIOGEOSCIENCES;
- 0426 Biosphere/atmosphere interactions;
- BIOGEOSCIENCES;
- 0428 Carbon cycling;
- BIOGEOSCIENCES;
- 0439 Ecosystems;
- structure and dynamics;
- BIOGEOSCIENCES