2023, Siegert, Courtney, Ilek, Anna, Wade, Adam, Schweitzer, Callie

AbstractIn the eastern United States, the use of prescribed fire as a silvicultural technique to manage for desirable upland tree species is increasing in popularity. Bark physical properties such as thickness, density, and porosity have known associations with fire tolerance among species. These physical properties simultaneously influence rainfall interception and canopy storage and thus are of interest across a range of disciplines. Furthermore, while these characteristics are innate to a species, it is unknown whether repeated exposure to fire facilitates physical change in bark structure and whether these changes are consistent among species. To answer these questions, bark samples were collected from mature pine (Pinus taeda L.) and oak (Quercus montana Willd.) 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 analysed in the laboratory for bulk density, porosity, water storage capacity, and hygroscopicity (the amount of atmospheric water vapour absorbed by bark during non‐rainfall conditions). Drying rates of saturated samples under simulated wetting conditions were also assessed. Oak bark had higher bulk density, lower porosity, and dried slower than pine bark. Interestingly, bark from both species had lower bulk density, higher porosity, greater water storage capacity, and dried faster in stands that were burned every 3 years compared to other fire regimes (p < 0.001). In summary, this study demonstrates that prescribed fire regimes in an eastern US forest alter bark structure and thus influence individual tree control on hydrological processes. The increase in bark water storage capacity, coupled with faster bark evaporation times may lead to less water inputs to the forest floor and drier overall conditions. Further investigation of this fire‐bark‐water feedback loop is necessary to understand the extent of these mechanisms controlling landscape‐scale conditions.

2025, Ilek, Anna, Tonello, Kelly Cristina

Tree bark plays a crucial role in the distribution of rainfall within forest ecosystems, particularly through its impact on stemflow. To gain a comprehensive understanding of how bark controls stemflow, it is essential to identify all factors affecting bark water storage capacity, as this determines the onset of stemflow during rainfall events. Our study analyzed how the position of bark on the stem and the altitude above sea level impact bulk density, water storage capacity, and the time required for bark saturation. We conducted research on Norway spruce bark collected at four altitudes: 400, 550, 700, and 1150 m asl. Our findings revealed that bark from the 400 m altitude had a bulk density that was approximately 24.5% greater than that from higher altitudes. Additionally, the water absorption time for bark from 1150 m was over 68% longer than that for bark from other altitudes. The longest absorption time (about 6.4 days) was observed in the bottom part of the trees, while the shortest (about 4.4 days) was in the top part of the trees. We also observed that the bark water storage capacity increased from the base to the top of the trees and with increasing altitudes. Specifically, the water storage capacity of bark taken from 400 m was approximately 33% lower than that from 1150 m. These findings highlight the significance of stem height position and altitude as key determinants of bark water storage capacity.