Regional impact assessment on forest structure and functions under climate change—the Brandenburg...

Regional impact assessment on forest structure and functionsunder climate change—the Brandenburg case study

P. Lasch*, M. Lindner, M. Erhard, F. Suckow, A. WenzelPotsdam Institute for Climate Impact Research, P.O. Box 60 12 03, D-14412 Potsdam, Germany

Abstract

A forest simulation model has been applied in a regional impact assessment to investigate impacts of climate change on forest

structure and function in the Federal state of Brandenburg, Germany. The forest model FORSKA-M was linked to a GIS that

included soil, groundwater table and land-use maps. Two climate scenarios (current climate and a climate change of 1.5 K

temperature increase which is combined with a precipitation decrease of 10–20% on average) for 40 meteorological stations in

and around Brandenburg were used to assess the sensitivity of species composition to climate change. Furthermore, the

implications of vegetation changes for other forest functions were analysed by means of several indicators. To evaluate the

impacts of climate change on biodiversity, measures of species diversity (Shannon’s and Simpson’s index) and habitat and

structural diversity (Seibert’s index) were applied. The evaluation of impacts on groundwater recharge of natural and managed

forests was carried out using the soil water balance model of FORSKA-M.

At first, model simulations of the potential natural vegetation (PNV) on the whole area of Brandenburg with different climate

scenarios were analysed. The results indicated that climatic warming would lead to a shift in the natural species composition in

Brandenburg towards more drought tolerant species. The simulated diversity of the forests would be reduced, and groundwater

recharge would be decreased.

The majority of forests in the state of Brandenburg have been managed intensively in the past. At present, large areas of

Brandenburg’s forests are dominated by pure stands of Scots pine, but current forest management practice aims at increasing the

share of deciduous and mixed forests. In order to analyse the possible consequences of climate change on forest management,

forest inventory data were used to initialise FORSKA-M with representative forest stands. Simulation experiments with three

different management scenarios showed that the short to mid-term effects of climatic change in terms of species composition

were not as severe as expected. However, the comparison of different diversity measures indicates a decrease in the species

diversity in contrast to an increase in habitat diversity under climate warming. Furthermore, a decrease in productivity and

groundwater recharge was simulated under the climate change scenario.

The regional impact assessment corroborated the high sensitivity of natural forests in the region to the projected climatic

change and it underlined the importance of adaptive management strategies to help forestry to cope with climatic change.

# 2002 Elsevier Science B.V. All rights reserved.

Keywords: Regional impact analysis; Succession model; FORSKA; Climate change; Forest management; Forest functions

1. Introduction

The temperate forests of Central Europe are man-

aged with multiple objectives, and the rotation periods

are very long—usually between 80 and 200 years.

Forest Ecology and Management 162 (2002) 73–86

* Corresponding author. Tel.: þ49-331-2882662;

fax: þ49-331-2882695.

E-mail address: [email protected] (P. Lasch).

0378-1127/02/$ – see front matter # 2002 Elsevier Science B.V. All rights reserved.

PII: S 0 3 7 8 - 1 1 2 7 ( 0 2 ) 0 0 0 5 1 - 8

Climate models currently project a temperature

increase of approximately 1.5–3.0 K up to the year

2100 (Kattenberg et al., 1996). Thus, the majority of

present day forests will probably live long enough to

experience significant changes in the climatic condi-

tions. In order to ensure the sustainability of the forest

resources including the multitude of forest functions,

there is a clear need to develop adaptive management

strategies to cope with the effects of climate changes

on forests (Lindner, 2000). Since, there are still great

uncertainties about the regional characteristics of the

future climate as well as about the response of our

forests to the changes in the atmospheric and climatic

conditions (Kirschbaum et al., 1996; Korner, 1996;

Solomon et al., 1996; Kellomaki, personal commu-

nication) the development of adaptive management

strategies should be based on sensitivity and risk

analysis.

This study is part of ongoing investigations on

impact assessments of climatic change on natural

and anthropogenic systems in the Federal State of

Brandenburg, Germany (Stock and Toth, 1996). For-

ests cover approximately one-third of the territory, i.e.

about 1 million ha. Forestry is an important economic

factor in many remote areas of the state, moreover,

forests are equally important for recreation and tour-

ism, and as a source for high quality drinking water for

the metropolitan area of Berlin. Forests clearly affect

the regional water balance of Brandenburg (Lutzke,

1991). The state of Brandenburg has a large percen-

tage of protected areas in national parks and biosphere

reserves, where the forests are also important for

habitat conservation. However, large forest areas are

currently covered by pure stands of Scots pine (Pinus

sylvestris L.), which are characterised by extraordin-

ary high risks for insect infestations and wildfires.

These stands are a product of more than a century of

intensive forest management aiming at a maximisation

of yield. Under natural conditions broad-leaved spe-

cies (e.g. beech, Fagus sylvatica L., oak, Quercus

robur L. and Q. petraea (Matt.) Liebl., hornbeam,

Carpinus betulus L., lime, Tilia cordata (Mill.)) would

prevail in the majority of these forests.

Brandenburg has a relatively dry temperate climate,

and the water balance is strongly influencing the

growth and vitality of the forests. Therefore, the

projected changes in climate will most likely have

distinct impacts on the forests in this region. In a

previous study (Lindner et al., 1997a), two forest gap

models, FORSKA (Prentice et al., 1993) and ForClim,

(Bugmann, 1996) were applied to simulate the possi-

ble impacts of climate change on the tree species

composition in the potential natural vegetation

(PNV) of Brandenburg. Lasch et al. (1999) improved

the methodology of the regional impact assessment

and extended the analysis to include managed forest

stands. The objective of this study was to combine the

analysis of species composition and forest productiv-

ity with an evaluation of the impacts of simulated

vegetation changes on other forest functions.

2. Methods

2.1. The forest simulation model

In this study a modified version of the forest gap

model FORSKA (Prentice et al., 1993) was used.

FORSKA simulates growth, regeneration and mortal-

ity of individual trees on small forest patches (Botkin

et al., 1972; Shugart, 1984) and was used successfully

to simulate forest dynamics in Scandinavia (Leemans,

1992), Canada (Price and Apps, 1996) and north-east

Germany (Lindner et al., 1997a; Lasch et al., 1998).

The applied version of the model, FORSKA-M,

includes tree-specific response functions for various

climatic factors (Prentice et al., 1993), soil fertility

(Lindner et al., 1997a), and distance to the ground-

water (Lasch et al., 1999). In the current model version

a multi-layer soil percolation model (Grote and

Suckow, 1998) a modified height growth function

(Lindner et al., 1997b), and management subroutines

(Lindner, 2000) are implemented. A more detailed

description of the above mentioned characteristics of

FORSKA-M was given in (Lasch et al., 1999). The

model works with daily time series of mean tempera-

ture, precipitation, and relative sunshine duration as

climatological driving forces.

2.2. Management scenarios

A variety of forest management activities can be

simulated with FORSKA-M using three modes of

regeneration (unrestricted seed availability, natural

regeneration of species with trees, planting of selected

species), different harvesting techniques (clear cut,

74 P. Lasch et al. / Forest Ecology and Management 162 (2002) 73–86

shelter wood harvesting, and selective harvesting), and

a Weibull-distribution based stochastic thinning rou-

tine (Gerold, 1990).

Three different management scenarios were inves-

tigated:

1. Traditional forest management (MS1), favouring

economically important species, which at present

prevail in the stands. No shift of species

composition is considered in the response to

changing climate. Seed availability of other

species was assumed to be 2% of the standard

values for climax species and 10% for pioneer

species.

2. Adaptive forest management (MS2), favouring the

climatically best-adapted species. Climatic adap-

tation was estimated using the climate response

functions of the FORSKA model (Prentice et al.,

1993). Two tolerance thresholds to identify

species with high and low drought risk under the

typical climate at a site were introduced: a lower

threshold below which a species is considered to

be sensitive to drought stress, and an upper

threshold, above which a species is considered to

be well-adapted for this climate. When stand

regeneration occurred the three best-adapted

species were planted with 1333 saplings per ha.

3. Maximisation of tree species diversity (MS3),

regenerating all climatically well-adapted species.

Climatic adaptation was estimated as described

above. All well-adapted species were planted with

a density of 4000/Nspec saplings per ha, where

Nspec was the number of well-adapted species at

the site.

2.3. Climate scenarios

The climate data necessary to drive the model

include time series of daily temperature (8C), preci-

pitation (mm) and relative sunshine duration (%) for

40 meteorological stations in or around the state of

Brandenburg.

Time series of current climate and a climatic change

have been produced using a multivariate statistical

analysis of long-term meteorological observations

from several meteorological stations in the state of

Brandenburg (Werner and Gerstengarbe, 1997). The

basic scenario S0 represents climate of the period

1951–1990 and serves as reference scenario. The

climate change scenario was calculated for a time

period of 55 years after an instantaneous increase of

temperature by 1.5 K (S2). A description of the sce-

nario production and an analysis of the scenarios was

carried out in Lasch et al. (1999) and showed that the

temperature increase was well reproduced by the

climate change scenarios. For annual precipitation

most scenarios indicated a clear decrease between

40 and 140 mm (Gerstengarbe et al., 1999).

2.4. Data

FORSKA-M requires soil and groundwater infor-

mation, which were derived from the map ground-

water table produced by the WASY Gmbh

(Gesellschaft fur wasserwirtschaftliche Planung und

Systemforschung mbH) and the digital soil map of

Germany (Bodenubersichtskarte der Bundesrepublik

Deutschland 1:1,000,000, BUK 1000) generated by

the Federal Institute for Geosciences and Natural

Resources (BGR), Hannover (cf. Lasch et al.,

1999). It was assumed that soil conditions and depth

of water table remain unchanged under climate

change. Furthermore, the CORINE land use map of

Germany (Statistisches Bundesamt Wiesbaden) was

used.

The simulation of managed forests is based on the

inventory data of the ‘‘Okologische Waldzustandskon-

trolle’’, a forest health monitoring program of former

East Germany. The 488 data sets were selected which

included stand data as number of tree strata, number,

age, mean height and diameter of trees, basal area of

strata for 1990. The selected sites are representative

for the forests of Brandenburg. Most of them are pure

Scots pine stands (74%) with some mixed pine broad-

leaved stands (17%) and few beech and oak stands

(Fig. 1).

2.5. Evaluation of forest functions

The effects of vegetation changes and management

under current climate and climate change on different

forest functions (biodiversity, habitat value, and

groundwater recharge) were evaluated. The evaluation

of the impacts on forest functions was based on the

simulated vegetation responses of unmanaged and

managed forest ecosystems.

P. Lasch et al. / Forest Ecology and Management 162 (2002) 73–86 75

Fig. 1. Map of the selected 488 sites from the inventory database of the Federal state of Brandenburg.

76

P.

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orest

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2.5.1. Biodiversity and habitat value

Species diversity and structural diversity were used

as indicators of the biodiversity and habitat values of

the forest stands. Two measures of species diversity

were applied. Both indices were derived from relative

biomass frequencies of tree species pi as independent

variables. The relative biomass frequencies were cho-

sen according to Kohl and Zingg (1996) and Swindel

et al. (1991). For the evaluation of model simulations

the proportion of biomass of a species gives a more

realistic view for the occurrence of the species in the

stand than the number of individuals because the

model is able to regenerate a lot of small trees every

year which do not live very long. The first index was

calculated using Shannon’s index H (Shannon, 1948),

a measure for the entropy of a finite probability field:

H ¼ �Xn

i¼1

pi ln pi where pi ¼Bi

Bi ¼ 1; . . . ; n

(1)

n is the number of species; Bi the share of biomass of

species i in total biomass; B the total biomass of stand.

The application of this index is based on the hypoth-

esis that a community of species is maximally diverse if

the species are equally distributed. In this case Shan-

non’s index has a maximum, which depends only on n.

The second measure of species diversity is Simp-

son’s index D (Simpson, 1949):

D ¼ 1 �Xn

i¼1

p2i (2)

This index varies from 0 to (1 � 1=n). D can simply be

interpreted as the probability that two randomly cho-

sen individual trees will be found to belong to the same

species type (Simpson, 1949). In contrast to Shannon’s

index H the maximum value of Simpson’s index D is

limited by 1, whereas, Shannon’s index increases with

the total number of species. D is mainly determined by

the frequency of the dominating species (Kohl and

Zingg, 1996).

To include an additional facet of diversity a struc-

tural diversity index of a forest stand, Ds was adopted

from expert knowledge of vegetation scientists (Seibert,

1980):

Ds ¼Dlay þ Dspec

2(3)

Dlay is a rating, which evaluates the occurrence of tree

and shrub layers and the height of ground vegetation.

It is calculated as a total sum of points corresponding

to the different existing layers of a forest according

to Table 1. The maximum number of Dlay is 5. Dspec is

defined as a rating calculated by the total number

of species of the stand according to Table 2. The

structural index varies for the considered forest types

between 1.5 (for example, pure beech stand) and 4.5

(hardwood/floodplain forest). All 27 forest types of

Brandenburg simulated by the model FORSKA-M

were characterised by the structural diversity index

using descriptions of forest ecosystems by vegetation

scientists (Seibert, 1980; Hofmann, 1997).

2.5.2. Groundwater recharge

Different methods of quantitative evaluation of the

groundwater recharge of forest ecosystems are possi-

ble. We used the annual percolation at 1 m soil depth

calculated by FORSKA-M. We assume that this value

approximates the annual groundwater recharge below

a forest stand.

2.6. Model application—natural and managed forests

The PNV was simulated for the whole area of

Brandenburg. The overlay of soil and groundwater

Table 1

Ratings of Dlay, which evaluates the layer structure of a forest stand

Occurrence of structure Rating (points)

First tree layer 1

Second tree layer 1

First shrub layer 1

Second shrub layer 0.5

Ground vegetation with height >30 cm 1

Ground vegetation with height <30 cm 0.5

Table 2

Ratings of Dspec, which evaluates number of species in the

structural index according to (Seibert, 1980)

Species number Rating (points)

1–10 1

11–20 2

21–30 3

31–40 4

>40 5


data with the land use map using a geographic infor-

mation system (GIS) resulted in 648 polygons with

different site conditions. Climate data were assigned

to the polygons from the nearest of the 40 climatolo-

gical stations. The model simulated 600 years of forest

growth starting from bare patches without trees. For

each polygon a steady-state species composition was

calculated as aggregated value of the simulation runs

by averaging the model output of the years 400–600 on

50 replicated patches. The species composition was

classified by the dominant species with respect to

standing biomass into 27 forest types similar to those

of the German forest inventory.

In order to analyse the impact of climate change and

management strategies on managed forests FORSKA-

M was applied at 488 sites of the forest inventory data

set. The model was initialised with the inventory

data by means of a structure generator, which supplies

the model specific stand data input (Lindner, 2000).

The simulations were carried out for 110 years (1990–

2100) with two climate scenarios (Section 2.3) com-

bined with three management scenarios (Section 2.2).

In this experiment, the simulated output variables like

biomass and groundwater recharge were averaged

over the last 20 years and analogously classified as

in the case of PNV simulations.

The simulation tool SPRINT-S (Flechsig, 1998)

was used to execute the model runs on a parallel

computer system (SP2) and to supply data sets for

the visualisation of the results in the GIS. A more

detailed description of the methodology of these

simulations can be found in Lasch et al. (1999).

3. Results

3.1. Impacts on natural forests

3.1.1. Impacts on forest composition and productivity

Fig. 2 presents maps of simulated forest types under

current climate and the climate change scenario. Under

current climate, FORSKA-M simulated beech and

beech–oak forests in the north-west of Brandenburg

as well as in few scattered sub-regions in the south

of the state. Pine forests occurred only on the sites

poorest in nutrients. Mixed forests dominated

mainly by oak covered the rest of the area. With

increasing temperature (>1.5 K) the abundance of

beech decreased significantly. Most forests were com-

posed of drought tolerant species such as pine, oak,

hornbeam and lime, the latter two on fertile sites.

3.1.2. Impacts on other forest functions

The species diversity as evaluated with Shannon’s

index (Fig. 3) of most simulated plots decreased

strongly. Under current climate Shannon’s index var-

ied from 0. to 1.74 (corresponding to seven species)

but under climate change the upper limit decreased to

1.59. The mean value over all forest areas decreased

from 0.93 to 0.64. Rather uniform stands of lime on

fertile sites and oak and pine on pure sites caused this

decrease in simulated diversity.

A comparison of groundwater recharge under both

climate scenarios is given in Fig. 4. Regional differ-

ences were large under current climate with annual

averages varying from 0 to 148 mm. The temperature

increase and the precipitation decrease of the climate

change scenario caused a distinct decrease in the

average annual groundwater recharge in comparison

with the current climate simulation on almost all

plots. The overall average of groundwater recharge

decreased from 39 to 9 mm and the maximum value

from 148 to 60 mm. The share of areas without any

groundwater recharge increased.

3.2. Impacts on managed forests

3.2.1. Forest composition and productivity

Aggregated results regarding the productivity of the

488 investigated forest stands after 110 years simula-

tion time are given by Table 3. Under the climate

change scenario the average productivity of all stands

decreased with all management strategies. Most simu-

lated stands were less productive under climate change

compared with the current climate and had lower

standing biomass. The reduction of average standing

biomass varied from 53% (MS2) to 67% (MS1). For

each climate scenario there were only slight differ-

ences in biomass comparing the three management

scenarios. Adaptive management (MS2) produced

greater standing biomass at the end of the simulation

period under current climate than the other manage-

ment strategies (14% gain in comparison with MS1,

5% gain in comparison with MS3). Under climate

change forests generated by MS1 had more average

biomass at the end of the simulation period than


Fig. 2. Maps of the GIS-based simulated PNV under current climate (left) and climate change (right).

P.

La

schet

al./F

orest

Eco

log

ya

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–8

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9

forests generated by the adaptive and the maximising

management strategies (MS2, MS3).

Table 4 presents a comparison of biomass losses

and gains for the 488 stands. Relative biomass per

stand at the end of the simulation period was calcu-

lated by dividing biomass under climate change by

biomass per stand under current climate. Regardless

Fig. 3. Maps of the Shannon index calculated from the GIS-based simulations of PNV under current climate (left) and climate change (right).

Fig. 4. Maps of groundwater recharge (mm) calculated from the GIS-based simulations of PNV under current climate (left) and climate

change (right).

Table 3

Average biomass (t/ha) of all 488 inventory stands under two

climate scenarios S0 and S2 and three management scenarios

MS1 MS2 MS3

S0 146.91 167.50 160.03

S2 98.09 89.41 90.32


of management, in about 80% of all stands biomass

was reduced under climate change. Some stands with

low productivity showed higher biomass at the end of

the simulation period (relative biomass >1). This may

be caused by a delayed harvesting of the stands under

temperature increase and low precipitation.

Table 5 summarises simulated forest types for all

scenario simulations (three management scenarios

combined with two climate scenarios). All simulated

forest types were aggregated into nine types of forest

stands. Most forest stands of the inventory plots were

pine or pine dominated stands. The management

scenario 1 generated only little changes in simulated

forest types under climatic change compared to cur-

rent climate. Under both climate scenarios, the domi-

nant role of pine forests was preserved. Additionally, a

slight share of hardwood forests including lime, horn-

beam and oak forests was present. Under both climate

scenarios, the adaptation management scenario (MS2)

generated mainly oak forests and a smaller share of

birch forests. In the case of the species maximising

scenario (MS3) mainly hardwood forests developed

with hornbeam, lime, elm, ash, and oak forests. It is

remarkable that beech disappeared completely under

the climate change scenario and the management

scenarios MS2 and MS3 increased the share of decid-

uous species.

Generally, every management scenario simulated

similar forest types for current climate and the climate

change scenario.

3.2.2. Impacts on other forest functions

Three diversity indices were calculated for the

scenario experiment. They were averaged over all

488 stands (Table 6). All indices showed an increasing

average species diversity of simulated stands in com-

parison with the average species diversity of the stand

initialisation. Both Shannon’s and Simpson’s index

declined in the case of climate change, whereas,

Seibert’s index increased. The decrease was caused

by the change of simulated forest type towards rather

uniform stands with lime on fertile sites (MS3) or

birch on less fertile sites. Because the lime forest is

rich in shrubs and herbaceous species, Seibert’s index

increased for those stands. Fig. 5 exemplifies cumu-

lative frequencies of Shannon’s index, which demon-

strate the increasing share of stands with lower species

diversity under climate change for all management

scenarios. The model simulations with management

scenario MS2 under current climate indicated that

<30% of the stands had a Shannon index �0.1 but

Table 4

Frequencies of relative biomass (biomass under climate change

(S2) divided by biomass under current climate (S0) per stand) for

three management scenarios

Relative biomass MS1 MS2 MS3

0.5 184 219 211

1 174 173 194

1.5 72 48 50

2 23 27 15

2.5 9 9 4

3 10 4 2

3.5 3 3 4

4 4 3 2

>4 9 2 6

Table 5

Occurrence of forest types at all 488 inventory sites after 110 years for current climate (S0) and climate change (S2) and the management

scenarios MS1, MS2, MS3, the column initialisation shows the forest types of initialisation

Forest type Current climate (S0) Climate scenario (S2) (>1.5 K)

Initialisation MS1 MS2 MS3 MS1 MS2 MS3

Pure Scots pine 360 154 0 1 237 0 4

Mixed pine–broadleaf 83 189 9 184 132 20 131

Beech forests 13 29 15 50 0 2 0

Oak forests 7 30 234 86 29 286 145

Mixed oak–pine 3 3 55 34 12 90 40

Birch forests 0 32 147 1 35 65 0

Hardwoods 0 30 20 118 23 16 151

Other forests 19 14 0 5 10 0 0

Bare patches 3 7 8 9 10 9 17


under climate change the share increased to >40%.

The other management scenarios produced similar

shifts between current climate and climate change

but differed in the frequency distribution of species

diversity.

The average annual groundwater recharge over 488

inventory plots after 110 years of simulation was

significantly reduced under climate change (Table 7).

The reduction varied from 33% (MS1) to 37% (MS2)

with similar trends under all management scenarios.

The number of plots with a very low annual ground-

Table 6

Shannon, Simpson and Seibert’s index averaged for the 488

inventory sites after 110 years for current climate (S0) and climate

change (S2) and the management scenarios MS1, MS2, MS3

Shannon Simpson Seibert

Initialisation 0.17 0.10 2.39

MS1/S0 0.54 0.28 2.50

MS1/S2 0.5 0.30 2.70

MS2/S0 0.68 0.35 2.40

MS2/S2 0.48 0.27 2.40

MS3/S0 1.23 0.63 3.10

MS3/S2 0.93 0.53 3.20

Fig. 5. Cumulative frequencies of Shannon’s index calculated for the three management scenarios MS1, MS2, MS3 under current climate (S0)

and climate change (S2).

Table 7

Average annual groundwater recharge of all inventory plots

Current climate Climate scenario (1.5 K)

Mean Minimum Maximum Mean Minimum Maximum

MS1 52.6 0 186.4 17.6 0 138.2

MS2 55.3 0 188.6 21.1 0 115.1

MS3 51.8 0 197.2 17.8 0 126.6

Mean: mean value of annual groundwater recharge of 488 plots (mm); minimum: minimum value of groundwater recharge of 488 plots (mm);

maximum: maximum value of groundwater recharge of 488 plots (mm).


water recharge, below 0.5 mm, increased from 13 to

104 plots averaging over all management scenarios.

4. Discussion

Forest management in central Europe is facing

difficult decisions. It is currently not possible to make

reliable forecasts of the regional climate for the next

century. Nevertheless, the forests, which are regener-

ated today, will most probably grow under changing

environmental conditions. The presented simulation

study suggests that a temperature increase of 1.5 K

may have strong impacts on forest productivity and the

competitive relationships between different tree spe-

cies in Brandenburg. The impacts of climate warming

on forest growth are mainly negative in this region,

because changes in the water balance will lead to

increased drought stress. Other simulation studies

have shown that, for example, in northern Europe

where water limitations are less important, climate

warming may enhance forest productivity (Kellomaki

and Kolstrom, 1993; Kellomaki et al., 1993). Simula-

tion studies with a variety of climate change scenarios

have indicated that positive growth responses could

also occur in temperate forests if increasing precipita-

tion balances the increased evaporative demand under

elevated temperatures (Bugmann, 1997; Lindner et al.,

1997a).

Climatic change will not only affect the composi-

tion and growth of the forests; it will also influence

other forest functions. We enhanced the analysis of

impacts on forest functions which was based on the

simulations of potential natural forest conditions

(Lindner et al., 2000) by an analysis of impacts on

forest functions based on simulations of managed

forest stands. The results indicate that the simulated

shifts in the species composition would be associated

with a reduction in species diversity and habitat value.

Furthermore, groundwater recharge decreased in the

case of the climate change scenario. Hence, the total

impact of climatic change may imply more than

vegetation changes alone.

Most of the methods to evaluate the impacts of

climate change on other forest functions were origin-

ally designed for other purposes. They have typically

been applied to stand scale investigations under cur-

rent climatic conditions and, therefore, there are clear

limitations, which should be kept in mind when

interpreting the results of the regional impact assess-

ment. The used soil water model is only applicable at

sites with low groundwater table because capillary rise

of water was ignored. The rooting depth was consid-

ered to extent down to 1 m soil depth.

The habitat diversity, for example, was evaluated

using indicator species and empirical data from

detailed forest ecosystem analysis. It is unknown,

however, if the rich flora and fauna of mixed hardwood

forests could re-establish in impoverished Scots pine

forests.

The soil water model implemented in FORSKA-M

calculates the soil water percolation out of the given

soil layers on sites with low groundwater table. It was

validated and tested as a part of the FORSANA pine

model (Grote and Suckow, 1998). The application

of the model to calculate groundwater recharge allows

the consideration of climate change scenarios, because

the model calculates the water budget depending on

temperature and precipitation conditions including the

calculation of evapotranspiration rates, which respond

to the changing climate.

At present, the forests of Brandenburg are still

dominated by managed Scots pine stands and natural

forests are rare. However, with an increasing impor-

tance of tourism and a high percentage of national

parks and other protected landscapes in the state,

forest reserves as well as the biological diversity

and amenity values of forests receive more attention

than in the past.

The application of the model FORSKA-M for

simulation of PNV and of managed forests supplied

information about the competitiveness of different tree

species. Results of both simulation experiments

stressed the hazard of beech under the assumed cli-

mate change and suggested that other deciduous tree

species may benefit from this change. The evaluation

of forest functions from results of both the experi-

ments supplied similar results. Analysing Shannon’s

index it has to be stated that the climate change

scenario led to a decrease in species diversity due

to the fact that the simulated forest types of PNV or

managed forests are rather uniform with a lower

number of species and one dominating tree species.

The evaluation of biodiversity by the used indices was

limited to the evaluation of tree species and structural

diversity.


The analysis of effects of climate change on ground-

water recharge indicated that the decreasing precipita-

tion and increasing temperatures will lead to a

reduction of percolation rates and finally of ground-

water recharge in consequence of increasing transpira-

tion demand. Furthermore, the percolation calculation

under both PNV and managed forests indicated that

the share in forest areas without groundwater recharge

will increase under climate change. All this may have

unfavourable consequences for the regional water

balance in Brandenburg which is already critical

today.

Forest management needs to respond to climatic

change because projected shifts in the natural species

composition (as indicated by the simulated PNV) will

restrict the choice of suitable species that can be

cultivated at a specific location in the future. Further-

more, the productivity of existing and future forest

stands will also be influenced by changes in the

climate. While most species in the investigated forest

stands tolerate the projected scenarios of climate

change, there are clear responses in terms of simulated

biomass production. The average simulated biomass

on all stands of the inventory data sets decreased under

the climate change. Previous analyses of the transient

behaviour of biomass development indicated that on

fertile soils an adaptive management might be able to

more than compensate for the reduced productivity of

drought sensitive species (Lindner, 1999). Moreover,

increased biomass production on some sites led to a

shortage of thinning period that induced an additional

thinning at the end of the simulation period. In this

case, the average biomass of the last 20 years of

simulation period is very low. On poor sandy soils

even the stress tolerant pine responded to the climate

change scenario with reduced biomass production.

The productivity related results under different cli-

mate and management scenarios were not always

conclusive. We used standing biomass as an indicator

of productivity and, in most sites, we observed a clear

response of the simulated biomass to the climate

change scenario. However, when different manage-

ment scenarios were compared, it became obvious that

decreased growth sometimes will lead to delayed

thinning and harvesting schedules. Because we com-

pared the average biomass over the last 20 simulation

years, the standing biomass during this period may be

higher in a low productivity scenario if this postpones

stand harvesting long enough. More direct measures

of productivity like NPP or mean annual stand growth

would, therefore, produce more meaningful results

under such circumstances. While FORSKA-M could

be used to generate growth related information, there

has been only very limited evaluation of forest gap

models in this respect. For more detailed analyses of

productivity effects of climate change it is recom-

mended to apply process-based models (Friend et al.,

1997; Makela et al., 2000; Thornley and Cannell,

2000).

Nevertheless, forest management retains a consid-

erable choice of management options under climate

change and different management strategies are fea-

sible. Each strategy implies different consequences for

the forests and their functions considered above.

Therefore, not only impacts on biomass production

but also on water balance and species diversity need to

be considered in the decision making process of the

forest management. The regional application of three

management scenarios demonstrates the possibilities

of analysing alternative strategies with regard to

impacts on different forest functions under the climate

change.

5. Conclusions

The extended model FORSKA-M allows an assess-

ment of forest dynamics and functioning under chan-

ging climatic conditions and management. While

simulated long-term impacts of climate change on

the potential natural forest composition show drastic

changes in species composition in Brandenburg as

well as in groundwater recharge and species diversity,

the analysis of impacts on managed forests indicates

that the future development (until the year 2100) may

depend strongly on stand composition and site char-

acteristics as well as management strategies. The

results underline the gain of information by evaluation

of management strategies regarding impacts on pro-

duction in connection with impacts on secondary

values of forests.

A regional assessment taking into account the con-

sequences of both climate change and management on

the productivity of forests and their functions consider-

ing species diversity and groundwater recharge seems

to be necessary as first step towards recommendations


and implications for the forest planning authorities

that helps them cope with climate change.

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