Microbial decomposition is predicted to increase following
boreal forest fires in part because wildfires are assumed to create
abiotic conditions that are favorable for decomposition. Cold temperatures
and water-saturated soils in late successional boreal
forests typically constrain the activity of decomposer microbes and
lead to slow rates of decomposition (Van Cleve et al., 1983). Boreal
forest fires of North America increase the amount of solar radiation
that reaches the soil surface, because fires reduce canopy thickness
and remove the insulating moss groundcover. As a consequence,
growing season soil temperatures in the top 10 cm of soil in
recently burned stands are typically 510 C higher than in late
successional stands (Treseder et al., 2004; Liu et al., 2005). Post-fire
increases in soil temperature can also be accompanied by decreases
in soil moisture (Holden et al., 2013). Microbial decomposition is
often highest at intermediate moisture levels, when soils are dry
enough that oxygen availability is not limited but not so dry that
microbes have insufficient access to water (Chapin et al., 2011a).
Thus, post-fire changes in microbial decomposition may depend on
the degree of soil drying following the fire.