Changes in Bark Properties and Hydrology Under Different Fire Regimes in Temperate Forests
To answer these questions, bark samples were collected from mature pine (Pinus taeda) and oak (Quercus montana) trees from sites across the Bankhead National Forest in Alabama, USA under three different burn regimes: 3-year cycle, 9-year cycle, and no fire. Samples were analyzed in the laboratory for bulk density, porosity, water storage capacity, and hygroscopicity (the amount of atmospheric water vapor absorbed by bark during non-rainfall conditions). Drying rates of saturated samples under simulated wetting conditions were also assessed. Bark bulk density was +2 times greater in oak compared to pine (p<0.001) and was 23 and 13% lower in both species in stands that were burned every 3 years (p<0.001). Bulk porosity was 32% greater in pine than in oak (p<0.001) and was 9 and 5% greater in stands burned every three years compared to stands that were not burned or burned less frequently (p<0.001). This translated into a 6 to 19% increase in bark water storage capacity as burn frequency increased (p<0.001). Hygroscopicity was 62 to 78% smaller in pine compared to oak (p<0.001). Hygroscopicity also decreased 20% in pine bark at sites burned most frequently (p=0.005). Unburned pine dried nearly 2-times slower than all other bark samples (p<0.001). Preliminary findings suggest that bark structure does indeed change with repeated exposure to fire leading to increases in water storage capacity and slower evaporation.