Water yield following forest–grass–forest transitions

Katherine J. Elliott, Peter V. Caldwell, Steven T. Brantley, Chelcy F. Miniat, James M. Vose, Wayne T. Swank
2017 Hydrology and Earth System Sciences  
<p><strong>Abstract.</strong> 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 (<i>Q</i>). We examined 80 years of streamflow and vegetation data in an experimental watershed that underwent forest&amp;ndash;grass&amp;ndash;forest
more » ... ndash;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 <i>Q</i>. Aboveground biomass was comparable among watersheds before the treatment (208.3<span class="thinspace"></span>Mg<span class="thinspace"></span>ha<sup>−1</sup>), and again after 45 years of forest regeneration (217.9<span class="thinspace"></span>Mg<span class="thinspace"></span>ha<sup>−1</sup>). However, management practices in the treatment watershed altered resulting species composition compared to the reference watershed. Evapotranspiration (ET) and <i>Q</i> in the treatment watershed recovered to pretreatment levels after 9 years of abandonment, then <i>Q</i> became less (averaging 5.4<span class="thinspace"></span>% less) and ET more (averaging 4.5<span class="thinspace"></span>% more) than expected after the 10th year up to the present day. We demonstrate that the decline in <i>Q</i> and corresponding increase in ET could be explained by the shift in major forest species from predominantly <i>Quercus</i> and <i>Carya</i> before treatment to predominantly <i>Liriodendron</i> and <i>Acer</i> through old-field succession. The annual change in <i>Q</i> can be attributed to changes in seasonal <i>Q</i>. The greatest management effect on monthly <i>Q</i> occurred during the wettest (i.e., above median <i>Q</i>) growing-season months, when <i>Q</i> was significantly lower than expected. In the dormant season, monthly <i>Q</i> was higher than expected during the wettest months.</p>
doi:10.5194/hess-21-981-2017 fatcat:jaaca4zehvh7xeplndhdavzalm