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 (Ei) and litter interception—i.e. Oi + Oe horizon layers—(Eff), across a forest age chronosequence, from 2 years since harvest to old-growth. We used precipitation, throughfall, and stemflow collectors to measure total rainfall (P) and estimate Ei; and collected litter biomass and modelled litter wetting and drying to estimate evaporative loss from litter. Canopy Ei, P minus throughfall, increased rapidly with forest age and then leveled off to a maximum of 21% of P in an old-growth site. Stemflow also varied across stands, with the highest stemflow (~8% of P) observed in a 12 year-old stand with high stem density. Modelled Eff was 4–6% of P, and did not vary across sites. Total stand-level interception losses (Ei + Eff) were best predicted by stand age (R2 = 0.77) rather than structural parameters such as basal area (R2 = 0.49) or leaf area (R2 < 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.