WP2 Near real-time measurements of tree growth and transpiration (PI Christian Ammer)

Objective: Transpiration, i.e. releasing water through opened stomata while acquiring CO2, is one of the most fundamental processes of plant metabolism. It is directly related to productivity and the water status of a plant (Larcher 1994). Drought reduces transpiration and can lead to starvation and embolism (Hartman et al. 2018). However, trees differ in their response to limited soil water availability depending on intra- and interspecific competition by neighbouring trees (Metz et al. 2016). We hypothesize that lower tree-to-tree competition and higher neighbourhood diversity buffers negative impacts of climate change on transpiration and stem growth. By upscaling the tree responses in high time resolution we can relate tree performance with CO2 and H2O fluxes (WP1), structural changes (WP3), and remote sensing signals (WP4).

Approach: Transpiration will be assessed by the heat dissipation method (Granier, 1987) at 60 trees of different tree sizes and species. At every second tree, a self-measuring fully automatized dendrometer will be installed measuring half-hourly stem girth (Metz et al. 2020). The dendrometers measure stem girth microvariations half-hourly by continuously recording tree circumference and show how the current environmental conditions feed into diameter growth and hence biomass production (Metz et al. 2020; Vospernik et al. 2020). The analysis of data on stem growth and transpiration under drought in near real-time and its relation to fluxes and structures will unravel how climate extremes affect forest ecosystem functioning and stand structures (Gebhardt et al. 2014). Hence, it will be possible to observe in near real-time the impact of summer drought on growth and transpiration across neighbourhood identity and density.