Possible developments of northern forest ecosystems in a changing climate

Transcription

1 Possible developments of northern forest ecosystems in a changing climate Bjarni D. Sigurdsson Prof. of Forest Science, AUI bjarni@lbhi.is Talk given at the NordGen conference: Northern Forests in a Changing Climate Hallormsstad, Iceland, Sept, 2013

2 Why Bjarni? Ecophysiologist focusing on environmental x growth interactions in forest ecosystems. Iceland / Sweden Impact studies: Effects of elevated CO 2, temperature and nutrient status Natural gradients Ecosystem structure and function 45 primary publications in peerreviewed journals/books, most dealing with these issues. Halldór Björnsson (chairman), Árný Erla Sveinbjörnsdóttir, Anna K. Daníelsdóttir, Árni Snorrason, Bjarni D. Sigurdsson, Gísli Viggóson, Jóhann Sigurjónsson, Snorri Baldursson, Sólveig Þorvaldsdóttir, Trausti Jónsson og Einar Sveinbjörnsson Scientific panel appointed to review facts and predictions related to climate change

3 Northern forests... = boreal and subarctic forests Short growing seasons Low MAT Mainly coniferous trees (and birch) Water generally not limiting Nutrients mostly found in SOM slow turnover!

4 Many studies have been conducted! Source: European Forest Institute factsheets_en.pdf

5 What is climate change? NOT only increase in MAT => CO 2, T, P, N-dep., seasonality, disturbance, etc.! Annual volume increment m3/ha,a Spruce Pine What is the strongest driver in the boreal forest dynamics? MAT? Max air temperature? Winter frosts? Growing season length and timing? Annual rainfall? Summer water balance? Nutrient cycle feedbacks Created by Ola Langvall 2006 Soil temperature and nutrient turnover? Soil humidity and nutrient turnover? Other CC-Biotic interactions?

6 Recent review for boral forests New Phytologist (2007) 173:

7 Main message: you can not predict changes in forest growth with single environmental factors! Forest trees are long-living Initial responses for seedlings may be very misleading for the net-effect! Nutrient-feedbacks are VERY important in the Boral forest!

8 Nordic research project (Sune Linder): Effects of CO 2, T and N on tree growth Denmark: beech Finland: Scots pine Norway: Scots pine Sweden: Norway spruce Iceland: black cottonwood

9 Main findings of the Nordic project The main limiting factors for tree growth in Iceland were: 1. Nutrient availablity (N) 2. Growing season s length 3. Temperature 4. CO 2 Interactions between those factors are complex!

10 Increased growing season T in Iceland by 1.1 C increased tree growth by 45%. T + miniralization effects The length of the growing season was not affected. (Sigurdsson PhD thesis) Leaves, branches and stem Roots

11 Elevated CO 2 only increased growth where nutrients were added. The slow N and P cycles are generally limiting plant growth in the cool climate of Iceland! Reduced LAI and changed phenology Leaves, branches and stem Roots

12 Changes in air temperature and [CO 2 ] are not enough!

13 Elevating air temperature 4 C without increasing soil temperature did not increase aboveground growth of Norway spruce at (natural) low N-availability Flakaliden WTCs Increasing soil temperatue by 4 C did however increase 3-year growth by +115% (Strömgren & Linder 2002)

14 FORHOT 13 researchers and 11 students (Natural soil warming in natural grasslands and a Sitka spruce forest in Iceland) See

15 +4-5 C is optimum for spruce BEFORE X AFTER 2012 Lenz and Sigurdsson (unpubl. data)

16 Ecosystem approach 14 different modules Effects of soil warming (0-15 C) on... x, y, z Temp x ecosystem type Temp x duration of warming

17 Effects of climate warming on regional forest growth Integrated growth of all tree species under the current climate, and the change in growth under climate change: (a) total current growth (m 3 ha 1 yr 1 ); percentage of total growth change for (b) , (c) and (d) NOW Whole tree chambers on mature Sotch pine forest in E-Finland Kellomäki S et al. Phil. Trans. R. Soc. B 2008;363: Univ. of Eastern Finland / Joensuu 2008 by The Royal Society

18 But even if forests grow better, they might change! Water may become an issue in more southern locations! Shift towards more Scots pine and birch? Kellomäki S et al. Phil. Trans. R. Soc. B 2008;363: Univ. of Eastern Finland / Joensuu

19 Regional studies II Due to climate change, total biomass growth increases between 20% and 25% over large areas of Finland and Sweden. An even larger increase of up to 35% was seen in maritime conditions. The increase was smaller under continental conditions because of more frequent drought episodes. This pattern was similar for the Baltic countries. The total biomass available for forest and energy industries in the Nordic and Baltic countries may increase to 760 million Mg during this century. Assuming that the management systems and the use of timber are the same as for today, an increase of 20% in biomass growth would mean that. In terms of annual stem volume growth, the increase is roughly 50 million m 3 /yr One extra Fennoscandian country Seppo Kellomäki Biofuels. In: Fenger J (ed.) Impacts of Climate Change on Renewable Energy Sources: Their role in the Nordic energy system. Nordic Council of Ministers, Copenhagen, pp

20 Future changes other issues!? 2010: t/files/documents/borealforestregional.pdf Increasing atmospheric CO 2 concentration Climate warming Higher (soil) temperatures Longer growing seasons Changes in precipitation Generally predicted to increase N of 50 N Large oceanic effects + regional differences Nitrogen deposition Human influence (management) Biotic interactions

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22 27 new pest spp during past 110 years Range shifts expected...

23 Relative crown damages in birch (B. pubescens) Epinotia solandriana mediated deforestation in SE-Iceland

24 Take-home messages: In the Boreal forest it is nutrient feedbacks and soil processes which govern the response to CC Forest growth in Fennosandia expected to increase by 20-30% - or ca. 50 million m 3 Even if precip increases in Fennoscandia, water limitation may become more important => Effect on Norway spruce!? Disturbances and biotic interactions may become more important! But very difficult to predict.

25 Thank you! Photo: Leena Finér