Do sapflow and soil parameters shape tree growth in a near-natural beech forest?

Climate change is leading to rising temperatures and erratic rainfall patterns. Higher temperatures in combination with changes in frequency and intensity of precipitation have a strong effect on physiological processes in trees. For central european forest ecosystems higher frequency of droughts is predicted, which could lead to increased forest decline and tree mortality rates particularly for drought-sensitive species such as european beech (Fagus sylvatica L.; Dolschak et al., 2019). To assess the factors affecting beech tree growth in a changing climate, a better understanding of the coping mechanisms of beech forest under drought conditions is needed. How the relationship between tree growth and the site water balance is altered due to changing climatic conditions remains unclear. To improve the knowledge on this relationship is particularly important as tree growth can contribute significantly to the site’s carbon balance.

In our research we aim at: 1) quantify tree growth along a natural gradient of dry, intermediate, and wet soil conditions in a near-natural beech forest on sandy-textured soils, and 2) determine the influence of meteorological and soil parameters and sapflow dynamics on stem growth of beech trees. The overall research question is: to what extent do sapflow, soil variables, and meteorological parameters explain the differences in stem growth along a soil moisture gradient from wet to dry conditions? Under the same climatic and stand management conditions we hypothesize: 1) there is a stronger correlation among weather variables, sapflow, and growth under wet soil moisture conditions, and 2) the correlation between soil matric potential, sapflow, and growth is more pronounced under dry soil moisture conditions.

The research is carried out under the framework of the Beneath Project, which focuses on understanding how soil moisture and water balance influence carbon dynamics in beech forests. For this purpose, three sites along a soil moisture gradient have been selected for the installation of three intensive monitoring plots (IMPs). The IMPs are located at a dominant beech tree of the respective site; the monitored trees present similar characteristics. At each IMP, the monitoring of different elements of the hydrological and C cycles is carried out.  Soil moisture and matric potential, sap flow, stem growth, leaf area index (LAI) and meteorological variables were measured for two growing seasons (June-October 2022 and 2023) in the Dübener Heide Nature Park in Saxony, Germany. The expected differences in growth among sites would suggest that the consideration of interdisciplinary approaches i.e. including soil-plant factors is necessary to improve the knowledge of growth dynamics in beech forests under a changing climate.

Reference:

Dolschak et al., 2019 The impact of rising temperatures on water balance and phenology of European beech (Fagus sylvatica L.) stands. https://doi.org/10.1007/s40808-019-00602-1