Variations in canopy and litter interception across a forest chronosequence in the southern Appalachian Mountains

Tuesday, 16 December 2014: 1:40 PM
Steven Terry Brantley1, Paul Bolstad2, Christine Sobek3, Stephanie Laseter3, Kimberly A Novick4, James M Vose5 and Chelcy Ford Miniat6, (1)Joseph W. Jones Ecological Research Center, Newton, GA, United States, (2)University of Minnesota Twin Cities, Department of Forest Resources, Minneapolis, MN, United States, (3)Coweeta Hydrologic Laboratory, USDA Forest Service, Otto, NC, United States, (4)Indiana University - Bloomington, Bloomington, IN, United States, (5)USDA Forest Service, Southern Research Station, Center for Integrated Forest Science, Raleigh, NC, United States, (6)USDA Forest Service, Southern Research Station, Coweeta Hydrologic Laboratory, Otto, NC, United States
Variations in evapotranspiration (ET) have been well documented across a variety of forest types and climates in recent decades; however, most of these data have focused on mature, second-growth stands. Here we present data on two important fluxes of water, canopy interception (Ic) and forest floor litter interception (Iff), across a chronosequence of forest age classes in the southern Appalachian Mountains. We used climate stations and throughfall collectors to measure gross rainfall and estimate Ic at each site and used a non-linear mixed model to determine the effects of forest age and precipitation on stand Ic. We also collected forest floor biomass monthly at each site and used these data in a model of litter wetting and drying to determine the quantity of water lost to Iff. Precipitation varied from 1690 to 2002 mm yr-1 across sites and across years (2011–2013). Canopy interception increased rapidly as forests aged to a maximum of 190 mm yr-1 in an 85 yr old forest. Despite higher leaf area in older stands, forest floor biomass did not vary significantly among sites (p = 0.47), suggesting lower decomposition rates in younger sites or effects of residual material from logging activity. At all sites, Iff accounted for 88-104 mm year-1 of total ET. Unlike Ic, modeled estimates of interannual variation in Iff were insensitive to annual rainfall amount and were dependent primarily on forest floor biomass. Additional measurements are currently underway to validate the litter interception model using litter moisture probes and forest floor wet and dry weights. Improved estimates of interception will contribute to our understanding of how forest structure and climate variability affect forest water use and help improve models of rainfall partitioning across the broader matrix of forest age classes.