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Ecosystem disruption

A dynamic approach with the CARAIB (Carbon Assimilation in the Biosphere) model is proposed to assess the impacts of climate change on European forest ecosystems. The consequences of change in mean climate and interannual variability on soil water, drought episodes and their impacts on primary productivity and forest fire intensity are studied. Changes in biome distribution are mapped and areas of potential future ecosystem disruption are identified.

Introduction

To study future vegetation evolution under past and future climate dynamic vegetation models are precious tools. We illustrate and analyse with the CARAIB model the potential impacts of climate change on forest productivity and distribution as well as forest fire intensity over Europe.

Background

Significant climatic changes are currently observed and, according to projections, will be strengthened over the 21st century throughout the world with the continuing increase of the atmospheric CO2 concentration. Climate will be generally warmer with notably changes in the seasonality and in the precipitation regime. These changes will have major impacts on the biodiversity and the functioning of natural ecosystems (Fischlin et al. 2007, Morales et al 2007, Schröter et al. 2005). Accurately examining vegetation response and quantifying risks would help to implement sustainable practices and to promote the conservation of the ecological but also the socio-economic function of ecosystems. In the framework of the European ECOCHANGE project, different modelling approaches are used to better understand and evaluate the impacts of the climate change for the European region. In this section projections obtained with the CARAIB dynamic vegetation model are demonstrated (Dury et al. 2011).

The CARAIB model has been driven by various climate scenarios to illustrate and analyse the potential impacts of climate change on European forests. Here are presented CARAIB projections obtained with the ARPEGE, a French climate computer simulation model, (Gibelin & Déqué 2003) forced with the SRES (Special Report on Emission Scenarios) A2 scenario. Within the full range of the IPCC (Intergovernmental Report on Emission Scenarios) emission scenarios (Nakicenovic et al. 2000), the A2 scenario describes the most extreme socio-economic storyline with a rather important increase in atmospheric CO2 concentration (~ 850 ppmv by 2100). We chose to present this pessimistic scenario because it corresponds to very substantial climate change leading to more extreme conditions for plants. Forced with the A2 scenario, ARPEGE/Climate predicts substantial warming over Europe in all seasons (in average 4.3°C increase of the annual mean temperature). Compared with projections of other climate models from the ENSEMBLES European project (van der Linden & Mitchell 2009), ARPEGE/Climate lies among the ones which produce the most significant temperature (warmer) and precipitation (drier) changes. The winter warming in northern Europe is particularly important while the summer temperature increase over southern Europe is in the range of ENSEMBLES projected changes. ARPEGE produces precipitation decreases in winter over southern Europe that are more pronounced and more widespread (by up to 50° N) than those of the other climate models (figure 1a). In summer, the model projects very marked precipitation decrease over western (France, north of Italy) and eastern Europe (Ukraine, Romania, etc.) and almost no change in the Mediterranean region unlike other projections (figure 1b).

Figure 1: Precipitation anomalies (mm) between 2081-2100 and 1981-2000 for (a) winter season and (b) summer season from ARPEGE/Climate model under the SRES A2 scenario.

Figure 1

 

Discussion / interpretation of figures shown

Climate change impacts and potential CO2 fertilization effects on European vegetation under the A2 ARPEGE/climate scenario are illustrated through two CARAIB simulations assuming constant and increasing CO2 concentration in the vegetation model. The two simulations can be expected to bracket the future evolution of the system under an A2 ARPEGE/Climate scenario, the actual path followed depending on the nutrient budget and the efficiency of the CO2 fertilization effects. Without CO2 fertilization, net primary productivity (NPP) might strongly decrease in many European areas except in the northern part (figure 2a). NPP should increase in high latitudes and altitudes (by up to 40 % or even 60-100 %) due to longer growing seasons while it should decrease in temperate (by up to 50 %) and in warmer regions, e.g. Mediterranean area (by up to 80 %), due to summer droughts more recurrent than in the present. When CO2 fertilization is included, such decreases are not observed (figure 2b). However, in both cases, the simulated NPP shows increasing interannual fluctuations associated with more frequent and more severe summer droughts.

Figure 2: Net primary productivity relative anomalies (%) between 2081-2100 and 1981-2000 with (a) constant and (b) increasing atmospheric CO2 concentration conditions under the A2 ARPEGE/Climate scenario.

Figure 2

Fire risk will most likely increase in the Mediterranean region but also in other parts of Europe (animation 1). The projected increase in air temperature and reduction in summer rainfall lead to more severe droughts after 2050. The large interannual variability in soil water might induce large fluctuations in the burned area. Wet years lead to burned area values which are comparable or lower than those calculated for the present while very dry years, occurring typically every 10-15 years, can increase burned area by a factor of 3-5 with respect to present most severe fires. In mid-latitude Europe, up to 60°N and especially in western France, Poland, Romania, central Russia and Ukraine, fire frequency and intensity also increase significantly in the simulation. Thus, fire risks might increase almost everywhere in Europe and most countries might have to deal with likely increasing fire damages. Only Scandinavia and northern Russia might not have to face this increasing fire risk.

Animation 1: Annual area burned (ha) in Europe over the 1961-2100 period computed by CARAIB under the A2 ARPEGE/Climate scenario.

Climate change might strongly modify the vegetation distribution in Europe (figure 3). Around 60 % of the European vegetation might be affected by a cover change. In southern Europe, around the Mediterranean Basin and the Black Sea, future landscape is characterized by more open vegetation. The warm temperate open woodland expands to the detriment of temperate broadleaved deciduous forests. The Mediterranean vegetation shifts northwards, in western and Central Europe. Temperate and boreal forests shift northwards and eastwards as well as upwards in the mountainous regions. As a consequence of this tree-line displacement, European tundras might disappear almost completely and might be replaced by boreal forests. The shift from mixed forest (deciduous and conifers trees) to deciduous forest is favoured under rising CO2 conditions. The CO2 fertilization effect also limits the extension of desert areas in Central Asia by stimulating grassland development.

Figure 3: Biome difference map between 2081-2100 and 1981-2000 periods computed by CARAIB under the A2 ARPEGE/Climate scenario.

Figure 3

 

 

Further reading / Bibliography

Dury M., Hambuckers A., Warnant P., Henrot A., Favre E., Ouberdous M., François L. (2011). Responses of European forest ecosystems to 21st century climate: assessing changes in interannual variability and fire intensity. iForest 4, 82-99.

Fischlin, A., Midgley, G.F., Price, J.T. et al (2007). Ecosystems, their properties, goods and services. Climate Change 2007: Impacts, Adaptation and Vulnerability. Contribution of Working Group II to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change (ed. by M.L. Parry & O.F. Canziani & J.P. Palutikof & P.J. Van Der Linden & C.E. Hanson). Cambridge University Press, Cambridge.

Gibelin AL, Déqué M (2003). Anthropogenic climate change over the Mediterranean region simulated by a global variable resolution model. Climate Dynamics 20: 327-339.

Morales P, Hickler T, Rowell DP, Smith B, Sykes MT (2007). Changes in European ecosystem productivity and carbon balance driven by regional climate model output. Global Change Biology 13: 108-122.

Nakicenovic N, Alcamo J, Davis G et al. (2000). Special Report on Emissions Scenarios: A Special Report of Working Group III of the Intergovernmental Panel on Climate change. Cambridge University Press, Cambridge.

Schröter, D., Cramer, W., Leemans, R. et al. (2005) Ecosystem Service Supply and Vulnerability to Global Change in Europe. Science, 310, 1333-1337.

Van der Linden P, Mitchell JFB (eds.) (2009). ENSEMBLES: Climate Change and its Impacts: Summary of research and results from the ENSEMBLES project. Met Office Hadley Centre, FitzRoy Road, Exeter EX1 3PB, UK. 160 pp.

 

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