Articles | Volume 21, issue 2
Research article
16 Feb 2017
Research article |  | 16 Feb 2017

Water yield following forest–grass–forest transitions

Katherine J. Elliott, Peter V. Caldwell, Steven T. Brantley, Chelcy F. Miniat, James M. Vose, and Wayne T. Swank

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.

Short summary
Our long-term results are relevant to land areas that are in pasture and those that have reverted back to forests. We found that within a deciduous forest, species identity matters in terms of how much precipitation leaves the watershed as evapotranspiration versus water yield. We demonstrate that a shift in tree species composition from species with ring-porous xylem to species with diffuse-porous xylem can increase water use, and in turn, produce a long-term reduction in water yield.