Rainfall partitioning varies across a forest age chronosequence in the southern Appalachian Mountains

Evaporation of precipitation from plant surfaces, or interception, is a major component of the global water budget. Interception has been measured and/or modelled across a wide variety of forest types; however, most studies have focused on mature, second-growth forests, and few studies have examined interception processes across forest age classes. We present data on two components of interception, total canopy interception (E-i) and litter interception-that is, O-i+O-e horizon layers-(E-ff), across a forest age chronosequence, from 2years since harvest to old growth. We used precipitation, throughfall, and stemflow collectors to measure total rainfall (P) and estimate E-i; and collected litter biomass and modelled litter wetting and drying to estimate evaporative loss from litter. Canopy E-i, P minus throughfall, increased rapidly with forest age and then levelled off to a maximum of 21% of P in an old-growth site. Stemflow also varied across stands, with the highest stemflow (similar to 8% of P) observed in a 12-year-old stand with high stem density. Modelled E-ff was 4-6% of P and did not vary across sites. Total stand-level interception losses (E-i+E-ff) were best predicted by stand age (R-2=0.77) rather than structural parameters such as basal area (R-2=0.49) or leaf area (R-2<0.01). Forest age appears to be an important driver of interception losses from forested mountain watersheds even when stand-level structural variables are similar. These results will contribute to our understanding of water budgets across the broader matrix of forest ages that characterize the modern forest landscape.