KROOF 3 – Legacy effects and limits of drought tolerance of beech/spruce stands Part B: Up to the point of failure–water transport along the soil-plant-atmosphere continuum

• Applicant: Professor Dr. Thorsten Grams
• Subject Area: Forestry
• Term: since 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 541966889

The "Kranzberg Forest Roof Project" (KROOF) has been funded by the DFG since 2013 as a package of three individual proposals. The expertise of the participating groups covers forest growth and yield science, ecophysiology and rhizosphere ecology. The University of Innsbruck is involved through the Weave program. In the first funding period (KROOF 1), a drought experiment with about 100 trees was initiated in a mature beech/spruce forest in southern Germany to study the effects of repeated summer drought on trees and their ectomycorrhiza. In comparison, the adaptation to long-term drought was investigated at five sites along a natural precipitation gradient. In the second funding period (KROOF 2), the focus was on the recovery of trees and stands. We are now applying for a third funding period, during which the drought-treated trees will be exposed to a new, potentially lethal drought. The aim is to clarify whether the stands are acclimated, i.e. less susceptible to renewed drought, or whether they reach the limits of their drought tolerance and suffer lethal damage earlier than trees exposed to severe drought for the first time. Mechanisms of drought tolerance and processes of tree death will be elucidated. The following hypotheses are at the center of the considerations: Mixture hypothesis: Mixed stands benefit from structural heterogeneity and asynchronous resource use under drought. Weakest link hypothesis: Acclimations to water shortage are overridden under extreme drought by breaking of the weakest link in the soil-plant-atmosphere continuum. Legacy hypothesis: Tree-soil systems with a drought legacy cope better with renewed drought than tree-soil systems experiencing severe drought for the first time. The focus is on ecophysiological studies of water transport and use in trees and stands, including water loss via the bark. Mechanisms and vulnerability of water transport at the soil-root interface and within the tree will be investigated in great temporal and spatial detail, with particular emphasis on the effects of past drought ("legacy") and the influence of resource use in pure and mixed stands.

• DFG Programme: Research Grants
• International Connection: Austria
• Partner Organisation: Fonds zur Förderung der wissenschaftlichen Forschung (FWF)
• Cooperation Partner: Dr. Barbara Beikircher