Canopy and litter interception vary with forest age in the southern Appalachian Mountains

Printer-friendly version

Southern Appalachian forests are comprised of a mix of species, ages and management regimes and as such, are expected to exhibit differences in hydrologic budgets. However, much of our current understanding of water budgets is based upon studies of mid-successional forests. At the Coweeta Hydrologic Laboratory LTER site, we are quantifying differences in the individual components of the hydrologic budget for a range of age classes, from early successional (<5 years after harvesting) to mature forests (dominated by trees>200 years old), using a chronosequence approach. We estimate net canopy and litter interception, the evaporation of rainfall captured by forest surface areas, and subsequently unavailable for plant uptake or streamflow. These sub-components of evapotranspiration (ET) were estimated using measurements of throughfall, stemflow, forest floor mass and moisture content, and gross precipitation. The proportion of precipitation that was intercepted by the canopy increased with forest age, rapidly increasing during early regeneration and leveling off at ~21% of gross precipitation in the oldest stand. Litter interception varied significantly across the stands due to differences in precipitation patterns with the oldest stand losing ~6% of gross precipitation to interception of litter. Our ongoing research will incorporate these values with transpiration estimates from sap flux sensors, canopy and subcanopy ET from eddy covariance systems, and runoff from flumes and weirs to quantify the remaining components of the forest water budget. Quantifying how components of the hydrologic cycle vary with forest structure will increase our understanding of how these ecosystems will respond to future climate variability and management.