Frequent, controlled burns are a widely-used, efficient, and effective land management tool across much of the Southeastern U.S. Frequent, low-severity fire (1–5 year return intervals) supports numerous land management objectives, including reducing fuel loads, maintaining biodiversity, creating habitat for rare species, and promoting game species. Frequent fire also has the potential to minimize the quantity of water lost through evapotranspiration. Frequently-burned woodlands are characterized by relatively low basal area, minimal woody midstory, reduced accumulation of dead vegetation, and dominance of fire-adapted species. These characteristics are thought to minimize transpiration and rainfall interception. Dominant fire-adapted species such as longleaf pine and wiregrass also tend to be more water conservative than fire-intolerant species that replace them in the absence of fire. Here, we present the results of a five-year study comparing several components of the water budget for burned and unburned longleaf pine woodlands. Burned sites were burned every 2 years. Unburned sites have had fire excluded for > 15 years. We measured canopy and sub-canopy sap-flux, canopy interception, and litter interception in two sites across a soil moisture gradient. Our objective was to understand how fire suppression changes each component of woodland water use and the overall water budget.
Results/Conclusions
Our results indicate some of the greatest differences between burned and unburned sites are found in evaporative losses due to canopy and litter interception, and transpiration losses due to increased leaf area in the midstory. Unburned sites had 2.0–4.4 times more midstory basal area relative to burned sites. This resulted in an 11–23% increase in total stand basal area, and a 25–34% increase in total stand leaf area. As a result, canopy and midstory interception in the unburned sites was 42%–58% higher than interception at frequently burned sites, depending on soil type. Changes were generally greater at sites with wetter soils. We also found higher litter interception in unburned sites, particularly for small rain events. In rain events < 5 mm, unburned sites intercepted 3-4 times more throughfall than frequently burned sites. While additional data and analyses are needed to account for changes in transpiration and groundcover, our results indicate that the suppression of frequent controlled burns substantially increases interception and suggests increases in transpiration. These results can inform management in forested watersheds throughout areas where controlled burning of fire-prone ecosystems has declined.