Alexander Olchev. IPEE RAS, Moscow

Transcription

1 Application of a process-based Mixfor-SVAT model to estimate a possible response of net ecosystem CO 2 exchange and evapotranspiration of boreal forest ecosystems to climate changes Alexander Olchev IPEE RAS, Moscow

2 Change of climatic conditions Short-term perspective: Impact on biophysical and biochemical processes in vegetation and soil. Changes of photosynthesis, respiration, transpiration rates, H2O and CO2 exchange. Changes of duration of the growing season Long-term perspective: Changes of forest structure and production, species composition of forests, vegetation and forest zones, etc.

3 Absorption of CO2 from the atmosphere. Carbon storage in vegetation and soil Influence on radiation and energy balances of land surface Influence of forests on climate Influence on land surface evapotranspiration Influence on land surface runoff

4 Key scientific questions: 1. What kind of vegetation changes may be occurring due to modern climatic changes? 2. How sensitive are the main components of CO 2 and H 2 O fluxes of boreal forest ecosystems to changes of climatic conditions and tree species composition? 3. What is potential contribution of the forests to change of balance of greenhouse gases in the atmosphere by the end of the 21 century? 4. How nutrient availability in soil and plants can influence the main components of water and CO 2 balance of forest ecosystems?

5 Main goal of the study is to predict the possible response of H 2 O and CO 2 exchange of forest ecosystems to future climatic changes on the example of spruce forests of the South European taiga by results of numerical experiments with a process based model

6 56 30 N, E Location of experimental area

7 Methods: 1. The paleoenvironmental reconstructions based on pollen, plant macrofossil and radiocarbon data. 2. Long-term meteorological data. 3. Scenarios of projected future climate changes (A1B, ECHAM5, Hamburg). 4. Dendrochronological data 5. Process-based SVAT model (Mixfor-SVAT).

8 The requirement for mathematical models that can be applied to solve such scientific tasks on ecosystem scale Aggregated description of CO2 and H2O exchange in vegetation, soil and the atmosphere. Applicability of model to describe the CO2 and H2O exchange in mixed forest ecosystems taking into account the vertical heterogeneity of forest stand and non-steady-state water transfer in soil-roots-stems-branches-leaves-ambient air system. Time resolution allowing to describe seasonal and daily flux dynamics. The description of CO2 and H2O exchange both in mono-specific and mixed forest stands. Balance between complexity of applied algorithms for description of CO2 and H2O fluxes and availability of model input parameters.

9 One-dimensional process-based multi-layer SVAT model (MixFor-SVAT) The model was developed to describe: total energy, H 2 O, and CO 2 fluxes in mono- and multi-species forests, and partitioning of vertical H 2 O, CO 2 fluxes between different canopy layers and different species. It is based on aggregated description of the physical and biological processes on the different spatial levels of a plant ecosystem (e.g. leaf, tree (plant), entire ecosystem).

10 Energy and matter fluxes described by a MixFor- SVAT model

11 Water fluxes described by a MixFor-SVAT model

12 Mixfor-SVAT assumptions: Forest overstorey is represented as an ensemble of individual trees of different species that are evenly distributed over some homogeneous ground surface area. There are no differences of physical and biological properties between the same tree species. Individual properties for each species: e.g. LAI, LADs, PSAI, heights, BHDs, root depths and distributions, fractions of green leaves

13 The main modules of Mixfor-3D and Mixfor-SVAT: Vegetation and soil structure, radiative and turbulent transfer, thermal and water regime of vegetation and soil, photosynthesis and respiration of vegetation, autotrophic and heterotrophic soil respiration. Input parameters: Biophysical and biochemical properties of vegetation and soil. Meteorological parameters. The main model equations: Heat balance of ecosystem: C T t Rn H EG Balance of СО 2 in ecosystem: NEE GPP RE GPP Water balance of ecosystem: W t почва P Et E i почва max E W почва R a R h Q E i nflow Et s W Radiative transfer in vegetation: C Leaf photosynthesis and respiration: Al min AV, AJ, AP Rl Leaf stomatal conductance: g l I g lmax r, u rgr, I r, L 1 ulr r, ' I r, ' d' 4 Transfer of heat and water in soil: s T t K z T T z Water balance of leaf: W t ; t D z z f1( PAR) f2( Tl ) f3( Da ) f4( l ) f5( Ca) Q r

14 Farquhar approach of photosynthesis (C3 plants) A min A, A R l V J l A min A, A, A R l V J P l A V - Rubisco-limited photosynthesis (the rate of photosynthesis can be predicted by the properties of Rubisco assuming a saturating supply of substrate, RuBP, A J - RuBP-regeneration-limited photosynthesis (light intensity limits the rate of photosynthesis), A P - triose phosphate use (TPU) limitation for Kalvin cycle. The chloroplast reactions have a higher capacity than the capacity of the leaf to use the products of the chloroplasts (Sharkey 1985).

15 Evapotranspiration estimation on ecosystem scale Precipirtation Ecosystem evapotranspiration: E ecosystem = E overstorey + E understorey + E soil Overstorey evapotranspiration: (E overstorey = E species1 + E species2 + + E speciesn ) E species2 Interception, steam flow, canopy drip, througfall Especies3 E вид1 Evapotranspiration of understorey (E understorey ) E species4 E speciesn-1 E speciesn Soil evaporation (E soil ) Precipitation infiltration Olchev et al. 2002, 2008

16 NEE estimation on ecosystem scale Net ecosystem CO 2 exchange: F ecosystem = F overstorey + F understorey + F soil F species2 Net hotosynthesis of understorey (F understorey ) F species1 F species3 Net CO 2 Exchange of overstorey (F overstorey = F species1 + F species2 + + F speciesn ) F species4 F видn F speciesn-1 Autotrophic and heterotrophic respiration (F soil ) Olchev et al. 2002, 2008

17 The main advantages of the developed model Description of H2O and CO2 exchange in mixed forest stands; It takes into account the different biophysical properties of tree species and their different phenology; Aggregated description of leaf stomatal regulation, CO2 and H2O exchange between the forest stand, soil and the atmosphere; Non-steady-state exchange and storage of water in trees; Energy storage by canopy.

18 Scenarios of model experiments to describe the influence of projected climatic and vegetation changes on H2O and CO2 exchange in forest ecosystems of the South-European taiga Change of climatic conditions: temperature and humidity of the air, amount of precipitation, total solar radiation, cloud amount, wind speed. Change of species composition and structure of forest canopy caused by climatic changes: reduction of proportion of spruce in a forest stand, increase of proportion of birch, aspen and broad-leaved tree species. Reduction of amount of available soil nitrogen that is necessary for balanced nutrition of plants under intensive growth of global temperature and CO2 concentration in the air in the 21 century. Possible changes of amount of above and underground biomass of the trees due to changes of environmental conditions in the 21 century. These changes were considered in numerical experiments through changes of Leaf area index (LAI), diameter of tree trunks, thickness of leaves and density of fine roots of trees. In calculations it was assumed that values of the key biophysical parameters characterizing the processes of CO2 and H2O exchange for different tree species (parameters of photosynthesis, respiration, stomatal conductance of leaves and needles) under future climatic conditions will correspond to their modern values.

19 Reconstructed canopy species composition and temperatures in the Holocene Optimum of the Ноlосеnе is paleoanalogue for an increase of global temperature by 1ºC Reconstruction by transfer function suggested by Klimanov (1984)

20 Changes of climatic conditions for period up to for А1В scenario in central part of European Russia (ECHAM5) Air temperature (+3.4ºС) Precipitation (+26%) Months Months Water vapor pressure (-5%) Solar radiation (-14%) Months Months

21 Modeled (Mixfor-SVAT) ET, Tran, GPP, NPP, NEE, RE of spruce forests of the South-European taiga under present climatic conditions Forest types GPP NPP NEE RE ET Tran Mono-specific spruce forests of the southern taiga on well drained soils Mixed spruce forest with 50% admixture of birch, aspen and linden on well drained soils Secondary birch - aspen linden forest on well drained soils in the area of the south-european taiga forests Fluxes of Н 2 О in mm year -1 Fluxes of СО 2 in gc m -2 year -1

22 Sensitivity of CO 2 and H 2 O fluxes to changes of species composition NEE Net Ecosystem Exchange of CO 2 GPP Gross Primary Productivity NPP Net Primary Productivity RE Ecosystem Respiration

23 Modelled patterns of evapotranspiration (E), and transpiration (TR) for present and future (A1B) climatic conditions with/without changes of vegetation biomass. Projected changes of LAI in future LAI future NPP NPP future present LAI present

24 Modelled patterns of Net Primary Productivity (NPP) and Net Ecosystem Exchange (NEE) for present and future (A1B) climatic conditions with/without changes of vegetation biomass.

25 Influence of projected climate changes on evaporation of boreal forest ecosystems Temperature increase +3.4 С Precipitation increase +26% Increase of CO 2 concentration 2 Solar radiation decrease -14% Decrease of water vapor deficit -5% Scenario A1B (ECHAM5) Evaporation: +3% Transpiration: -10% Evaporation: +9% Transpiration: -1% Precipitation increase on 180 mm year -1 Evaporation increase on 20 mm year -1 Increase of runoff And soil water content on 160 mm year -1 Increase of ground water level, increase of drought intensity

26 Influence of projected climate changes on CO2 fluxes of boreal forest ecosystems Temperature increase +3.4 С Precipitation increase +26% Increase of CO 2 concentration 2 Solar radiation decrease -14% Decrease of water vapor deficit -5% Scenario A1B (ECHAM5) GPP: +22% Ecosystem respiration: +14% GPP: +26% Ecosystem respiration : +19% Net ecosystem exchange of СО 2 (NEE) -90 gс m -2 year -1 NEE of СО gс m -2 year -1 Olchev et al. 2009

27 Change of ET, NEE and NPP of coniferous forests of the southern taiga under climatic changes (the scenario A1B IPCC) at various scenarios of specific composition changes of a forest stand (a ratio of spruce and deciduous species in a forest stand), and also percentage changes of amount of available nitrogen (N) in tree leaves. LAI future NPP NPP future present LAI present

28 Dendrochronological studies

29 Dynamics of climatic conditions and spruce and pine increment during the 20 century in the study area Spruce Pine Meteorological measurements at station Vishniy Volochek Dendrochronological data obtained by M. Hughes within NASA-LCLUC NEESPI (NNX09AK58G) project

30 The main results: 1. Predicted changes of climatic conditions and structure of vegetation cover can lead to significant changes of CO2 and H2O exchange in forest ecosystems at south- European Taiga. 2. Predicted relatively small increase in ET (about 10%) of spruce forest ecosystems growing in well drained soils of the South-European taiga in comparison with projected growth of precipitation amount (about 20%) can lead to some increase in soil moisture and surface runoff, and also to reduce the risks of emergence of soil droughts in the area to the end of 21 century. 3. According to provided model experiments it was obtained that exhaustion of available nitrogen in soil and plant leaves due to increase of consumption of mineral substances by plants for maintenance of a normal rate of biochemical reactions under growth of atmospheric CO2 can lead to reduction of photosynthesis rate and respiration of trees in considered modeled forest stands, to decrease of stomatal conductance of leaves, and as a result, to reduction of NEE and ET of forest ecosystems. Decrease of amount of available nitrogen spruce needles down to 50-60% can quite completely neutralize an effect of increase of photosynthesis due to projected double increase of CO2 in the air and growth of the air temperature on NEE by the end of the 21 century.

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