High versus coppice forests: comparison of sap flow and stem growth of Quercus petraea Matt. during two growing seasons with different precipitation patterns

This work is focused on a comparison of sap flow and tree growth in adult high and overaged coppice oak forests. The main hypothesis is that the older root system of coppice provides better access to soil water, and thus coppice is able to withstand drought stress better than high forest. During two growing seasons (2014–2015), two adult Quercus petraea (Matt.) stands (high and coppice forest) were continuously measured for sap flow (SF), stem diameter variation (SDV) and microclimatic conditions. The SF reaction and SDV of high forest and coppice to different amounts of precipitation after drought as well as the recovery rate were similar for both stands. In 2014, although long-term average SF values were higher for high forest than for coppice, the stem increment of coppice was significantly higher. The reason for this was long-term spring drought. The threshold for positive SF response was low precipitation of 5 mm in both stands. This indicates that a larger portion of the root biomass should be concentrated closer to the soil surface in both forest types. Nevertheless, the higher long-term average SF values for high forest indicate that its root system is able to explore soil better than does old coppice forest. An explanation for this could be that the older root systems of coppice have reached the senescence phase of tree ontogeny. The higher SF values, but similar tree growths of high forest compared to coppice show lower water use efficiency on the part of high forest. In the context of ongoing climate change, coppice appears to be a good alternative to high forest, especially in areas where the frequency and duration of drought stress are expected to increase. Nevertheless, overaged coppice should be replaced by new generations grown from seed since old root systems are not able to regenerate constantly.