Thomas Dirnböck, Environment Agency Austria

Round Table Session “Arctic and Alpine ecosystems in face of climate change”

Increased disturbances in mountain forests under climate change

EUROPE‘S FOREST CARBON SINK

© zhu difeng – Fotolia.com

Bellassen, V. & Luyssaert, S. (2014), Nature 506,153–155

Legacy

~ 10%

FOREST DISTURBANCES ARE ON THE RISE

3

Tomiczek et al. (2011)

Forest Damage between 1944-2010• Wind throw / snow

• Spruce bark beetle

© Uweltbundesamt

REDUCTION IN CARBON SINK STRENGTH

4

Kobler et al. (2015, European

Journal of Forest Research)

C – Pools [ha-1]

So

il134 t

Ro

ots

33 t

Ste

m153 t

Bra

nc

hN

eed

le30 t

C – Fluxes [ha-1y-1]

Litter 2.7 t

Litter >1.6 t

Photosyntheses

Respiration

Heterotrophic soil-

respiration 6.5 t

Root-respiration

∑ = Growth 2.9 t

∑ total 7.2 t - ∑ total 6.5 t = 0.7 t (NEP)

Leaching ?

C – Pools [ha-1]

So

il115 t

Ro

ots

22 t

Ste

m109 t

Bra

nc

hN

eed

le26 t

C -Fluxes [ha-1y-1]

Litter 2.2 t

Litter >1 t

Photosyntheses

Respiration

Heterotrophic soil-

respiration 5.9 t

Root-respiration

∑ = Growth 2.8 t

∑ total 6.0 t - ∑ total 5.9 t = 0.1 t (NEP)

Leaching ?

POST-DISTURBANCE EFFECT OF THE HERB LAYER

age 25

C-s

ink

age 6

C-s

ou

rce

age 3

C-s

ou

rce

Mature (age 115)

C-s

ink

Mic

rob

ialC

resp

irati

on

DOC-C < 0.05t

Zehetgruber et al. (2017, Plant and Soil)

FOREST UNDERSTORY CONTRIBUTES TO MAINTAIN

THE C SINK IN DISTURBED FORESTS

NATIONAL PARK KALKALPEN, AUSTRIA

7© Erich Mayrhofer

© Roland Mayr

© Roland Mayr

© Franz Sieghartsleitner

© Robert Maybach

REGIONAL CARBON SINK IN THE NATIONAL PARK KALKALPEN

Understory effectCarbon sink between 2000

and 2015

Dirnböck et al. (2020, Landscape Ecology)

UNDERSTORY CONTRIBUTED 16-37% TO NET ECOSYSTEM

PRODUCTION AND UP TO 65% IN DISTURBED AREAS

NN – no understory

R – tree regeneration

H – herb/grass layer

HR – tree regeneration +

herb/grass layer

Dirnböck et al. (2020, Landscape Ecology)

WHILE DISTURBANCE WILL INCREASE C LOSS, TREE COMPOSITION

CHANGES MAY MITIGATE FURTHER CLIMATE CHANGE

Thom, Seidl et al. (2017, Ecological Monographs)

1

1

CONCLUSIONS

Climate change will accelerate forest disturbances causing a drop

in forest C sink strength in the future

Vital tree regeneration is crucial in reducing C loss after forest stand

replacement

The grass and herb layer developing in disturbance patches

substantially reduces ecosystem C loss

Long-term monitoring in combination with modelling and remote

sensing is an ideal setting to study such complex ecosystem

processes

© a

wpix

el.com

–F

oto

lia.c

om

© Stefan Smidt