Drought Stress Resilience of European Beech and Norway Spruce – Effects of Facilitation, Re-watering and Mixture

Scientist: Benjamin Hesse
PI: Prof. Dr. Thorsten Grams
Funding: Deutsche Bundesstiftung Umwelt

Drought stress, as a consequence of the ongoing climate change, has emerged globally to one of the biggest threats for ecosystem. Especially, long-living ecosystems, such as forests in Central Europe, are strongly affected, as the extreme warm and dry summers of 2003, 2015 and 2018 revealed. Mixed-species forests, however, tended to have a higher resistance against stress than monocultures. Strikingly, many forest ecosystems did not die during the drought period, but in the following (relatively humid) years. The question now is, why some forests regenerated while others succumbed. A lot of research has been done on the effects of drought stress and its effects on plants, but comparatively very few studies were done on the effects of re-watering and recovery.
In this project the effects of drought stress and especially of re-watering on the water- and carbon household of isohydric Norway spruce (Picea abies (L) Karst.) and anisohydric European beech (Fagus sylvatica L) will be investigated. In three experiments, the difference in resilience of mixed- and monocultures will be analyzed and compared. In this context, also facilitative effects (positive interactions between individuals), such as exchange of water or carbon between trees, will be one focus.

1.    Climate chamber experiment about facilitation and resilience in mixed and pure combinations

a. Abiotic stress amplifies facilitative effects more in mixed than in mono combinations
b. Climate change (e.g. rise in temperature and atmospheric CO2) will amplify facilitation
c. Re-watering intensity influences facilitation and resilience

Mechanisms behind facilitation and resilience

2.    Field experiment about NSC reserve pools during and after drought in the KROOF-Experiment (http://kroof.wzw.tum.de)

a. Beech is less affected by “Carbon Starvation” than spruce
b. NSC-pools of sink organs are more affected by drought than of source organs
c.  Spruce benefits from the mixture with beech

Facilitation during and after drought stress in NSC-reserve pools

3.    Field experiment about re-watering after longterm, re-occurring summer-drought in the KROOF-Experiment (http://kroof.wzw.tum.de)

a. Anisohydric beech recovers faster after drought than isohydric spruce
b. Mixed stands recover faster than monocultures

Resilience after drought and relevance in the forest

Publication list

Grams TEE, Hesse BD, Gebhardt T, Weikl F, Rötzer T, Kovacs B, Hikino K, Hafner BD, Brunn M, Bauerle TL, Häberle K-H, Pretzsch H, Pritsch K (2020) The Kroof experiment – realization and efficacy of a recurrent drought experiment plus recovery in a beech/spruce forest. Ecosphere in press

Hafner BD, Hesse BD, Bauerle TL, Grams TEE (2020) Water potential gradient, root conduit size and root xylem hydraulic conductivity determine the extent of hydraulic redistribution in temperate trees. Funct Ecol:1–14.

Hafner BD, Hesse BD, Grams TEE (2020) Friendly neighbours: Hydraulic redistribution accounts for one quarter of water used by neighbouring drought stressed tree saplings. Plant Cell Environ:1–14.
Hesse BD, Hafner BD, Grams TEE (2019) Reverse conductivity for water transport and related anatomy in fine roots of six temperate tree species – a potential limitation for hydraulic redistribution. J Plant Hydraul 6

Manuela BAUMGARTEN, Benjamin D. HESSE, Ingrida AUGUSTAITIENĖ, Vitas MAROZAS, Gintautas MOZGERIS, Steigvilė BYČENKIENĖ, Genrik MORDAS, Ainis PIVORAS, Gintaras PIVORAS, Diana JUONYTĖ, Vidmantas ULEVIČIUS, Algirdas AUGUSTAITIS, Rainer MATYSSEK (2019) Responses of species-specific sap flux, transpiration and water use efficiency of pine, spruce and birch trees to temporarily moderate dry periods in mixed forests at a dry and wet forest site in the hemi-boreal zone. J Agric Meteorol 75:13–29.

Hesse BD, Goisser M, Hartmann H, Grams TEE (2019) Repeated summer drought delays sugar export from the leaf and impairs phloem transport in mature beech. Tree Physiol 39:192–200.

Tomasella M, Nardini A, Hesse BD, Machlet A, Matyssek R, Häberle K-H (2018) Close to the edge: effects of repeated severe drought on stem hydraulics and non-structural carbohydrates in European beech saplings. Tree Physiol:1–12.

Tomasella M, Häberle K-H, Nardini A, Hesse B, Machlet A, Matyssek R (2017) Post-drought hydraulic recovery is accompanied by non-structural carbohydrate depletion in the stem wood of Norway spruce saplings. Sci Rep 7:14308.

Tomasella M, Beikircher B, Häberle K-H, Hesse B, Kallenbach C, Matyssek R, Mayr S (2017) Acclimation of branch and leaf hydraulics in adult Fagus sylvatica and Picea abies in a forest through-fall exclusion experiment. Tree Physiol:1–14.