Abstract
Abstract. Many currently forested areas in the southern Appalachians were harvested in the early 1900s and cleared for agriculture or pasture, but have since been abandoned and reverted to forest (old-field succession). Land-use and land-cover changes such as these may have altered the timing and quantity of water yield (Q). We examined 80 years of streamflow and vegetation data in an experimental watershed that underwent forest–grass–forest conversion (i.e., old-field succession treatment). We hypothesized that changes in forest species composition and water use would largely explain long-term changes in Q. Aboveground biomass was comparable among watersheds before the treatment (208.3 Mg ha−1), and again after 45 years of forest regeneration (217.9 Mg ha−1). However, management practices in the treatment watershed altered resulting species composition compared to the reference watershed. Evapotranspiration (ET) and Q in the treatment watershed recovered to pretreatment levels after 9 years of abandonment, then Q became less (averaging 5.4 % less) and ET more (averaging 4.5 % more) than expected after the 10th year up to the present day. We demonstrate that the decline in Q and corresponding increase in ET could be explained by the shift in major forest species from predominantly Quercus and Carya before treatment to predominantly Liriodendron and Acer through old-field succession. The annual change in Q can be attributed to changes in seasonal Q. The greatest management effect on monthly Q occurred during the wettest (i.e., above median Q) growing-season months, when Q was significantly lower than expected. In the dormant season, monthly Q was higher than expected during the wettest months.
Highlights
Forests play a critical role in regulating hydrological processes in headwater catchments by moderating the timing and magnitude of streamflow (Burt and Swank, 2002; Chang, 2003; Ice and Stednick, 2004; Ford et al, 2011b; Vose et al, 2011)
After the grass was treated with herbicide, and the forest was allowed to reestablish, the forest shifted to dominance by Liriodendron tulipifera and Robinia pseudoacacia
Our results demonstrate that species changes largely explain the decreasing trend in Q following old-field abandonment based on modeled growing-season daily water use (DWU) over time, and enable us to assess the effects of forest structure and species composition on Q
Summary
Forests play a critical role in regulating hydrological processes in headwater catchments by moderating the timing and magnitude of streamflow (Burt and Swank, 2002; Chang, 2003; Ice and Stednick, 2004; Ford et al, 2011b; Vose et al, 2011). Hydrological processes in forests are sensitive to disturbances that reduce tree vigor or leaf area and decrease evapotranspiration (ET) (Aranda et al, 2012; Edburg et al, 2012; Brantley et al, 2013). Most efforts at studying the effects of disturbance on watershed hydrology have focused on quantifying the effects of forest harvesting practices on water yield (Q) (Bosch and Hewlett, 1982; Stednick, 1996; Burton, 1997; Brown et al, 2005; Wei and Zhang, 2010; Ford et al, 2011a; Zhang and Wei, 2012; Liu et al, 2015). Brantley et al (2013, 2015) showed that lasting changes in annual Q (lower) and persistent changes in peak flow (> 20 %, after the most intense storms) were observed with only about a 5 % basal area loss of eastern hemlock (Tsuga canadensis (L.) Carrière). Brantley et al (2013) suggested that a change in forest composition with less evergreen hemlock relative to deciduous trees could result in an increase in Q in winter months
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