Long-term effects of clearcut and selective cut on seepage chemistry in a N-saturated spruce stand – Case study Höglwald

Abstract

While comprehensive literature is available concerning the effects of clearcutting on N leaching via seepage water little information is available comparing different harvesting intensities. In order to close this gap of knowledge in 1999 an experiment comparing selective cut and clearcut at the Höglwald site was started. The Höglwald is a major Central European ecosystem study site and represents a typical spruce forest ecosystem in Southern Germany, subject to high nitrogen deposition. Bulk deposition, throughfall and seepage water concentrations at 0 and 40 cm depth were measured from 1999 until 2017 at three plots (control, clearcut, selective cut). Elemental fluxes were calculated using measured water fluxes (precipitation, throughfall) or calculated soil water fluxes using a hydrological model. Here we present the final results for the 17-year measurement period comparing different harvesting intensities from initial harvesting until the complete removal of all mature trees.Initial nitrate peaks after clearcutting the nitrogen saturated spruce ecosystems were very high (up to 34 mg nitrate-N l−1) but short-lived (2 years). Afterwards nitrate leaching strongly decreased to values close to zero due to reduced input and the demand of the upcoming vegetation. For the investigated 17-year period cumulative nitrogen losses at the clearcut plot were lower as compared to the uncut control. The selective cut was not able to prevent nitrate leaching in our N-saturated spruce stand. Here cumulative nitrogen losses in the first 17 years are similar compared to the uncut control due to a combination of ongoing high deposition and partially enhanced mineralisation after harvesting events.At our nitrogen saturated study site the selective cut showed no advantages concerning nitrate leaching via seepage water. From a silvicultural and forest ecological point of view, however, big cleared areas with their sudden change to a non-forest climate should be avoided due to several disadvantages like high initial mineralisation with its excessive nutrient release, the risk of grass invasion as well as higher stress and often lower quality of the planted trees.