Soil moisture variation and dynamics across a wildfire burn boundary in a loblolly pine (Pinus taeda) forest

- Soil moisture is monitored across a burn boundary.
- Several techniques are used including electrical resistivity.
- Burned end has higher soil moisture content.
- Differences in soil moisture can be explained burning of vegetation.

SummaryA year after the most destructive wildfire in Texas (USA) history which occurred in and around Bastrop State Park, we established a 165 m-long study transect, bridging burned and unburned areas, to study post-wildfire soil moisture dynamics. Soil moisture content (θ) was monitored indirectly approximately monthly for half a year using a variety of methods with different measurement scales including: 2D electrical resistivity (ER) imaging and surface and vertical profiles using probes which measure soil dielectric properties. The burned section, where the majority of loblolly pine trees were killed, had higher θ and lower ER whereas the unburned end which is still populated by live pine trees had lower θ and higher ER. This pattern persisted from the ground surface and down to ∼2 m and through the study period even after a rainfall event which made the whole transect generally wetter but with the burned end showing a much stronger wetting response to the storm. The differences in θ cannot be explained by differences in soil texture with the burned end with sand soil and the unburned end with less permeable loamy sand. The differing results may be explained by loss of canopy cover and by reduced transpiration at the burned end where the dead roots may also potentially serve as macropores. Thus, after fires and until new vegetation cover has grown, the burned areas will store and transmit more water which could lead to increased groundwater recharge and promote the recovery or invasion of certain types of vegetation.