GIS Assessment of Vegetation and Hydrological Change
in a High Mountain Catchment of the Northern
Limestone Alps
Authors: Dirnböck, Thomas, and Grabherr, Georg
Source: Mountain Research and Development, 20(2) : 172-179
Published By: International Mountain Society
URL: https://doi.org/10.1659/0276-
4741(2000)020[0172:GAOVAH]2.0.CO;2
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Introduction
The headwaters of high mountain systems are impor-
tant water resources in many parts of the world. Water
resources totaling 40,600 km
3
are derived from moun-
tainous areas, and 25% of the global population is sup-
plied largely or entirely by karst water sources (Ford
and Williams 1996). Direct and indirect effects of
human activity include land-use change and climate
change, which can be key issues for water resource
planning and nature conservation (Becker and Bug-
mann 1997; Messerli and Ives 1997). Karst areas are far
more susceptible to a large range of problems due to
environmental impacts than other terrain because
water transmission is accelerated by highly developed
subterranean networks. The poor physical filtration
capacity of shallow karst soils creates additional prob-
lems (Ford and Williams 1996).
The city of Vienna receives about 95% of its water
from karst mountains of the northeasternmost Alps.
The catchment areas for these water resources are
exposed to dynamic land-use change, especially sum-
mer pasturing and forestry. Beyond that, vegetation pat-
terns will probably be affected significantly by climate
change (Grabherr et al 1995) so that hydrological con-
sequences can be expected.
Within the framework of a long-term research ini-
tiative undertaken by the city of Vienna, a research
project was established to guarantee the long-term
availability of Vienna’s water supply. In addition to geo-
logical, hydrological, and geohydrological information,
vegetation mapping was undertaken to obtain spatial
information about the soil–vegetation interface at the
landscape scale. The highly variable topography of
mountainous karst landscapes causes heterogenous
biotic and abiotic patterns. Using modern tools such as
Geographical Information Systems (GIS), large-scale
vegetation mapping is practicable within a reasonable
time, even for extensive areas. To estimate hydrological
properties of homogenous landscape units, physical soil
properties were measured and a survey of the literature
on evapotranspiration data was carried out. Thus, land-
scape functioning was emphasized. It supported the
purely qualitative structural information of vegetation
mapping in order to derive a more comprehensive view
of the main landscape characteristics, including struc-
ture, function, and change (eg, Forman and Godron
1986; Turner and Gardner 1990).
Site description
The catchment areas that supply drinking water to
Vienna are mountainous karst areas with altitudes up
to 2300 m, composed of limestone and dolomite. The
regions are 100–200 km away from Vienna in the
Northern Limestone Alps, from where the karst water
is transported to the city via two conduit systems. The
area under closer investigation focuses on Mount
Schneeberg on the far eastern edge of the Northern
Limestone Alps (Figure 1). Geologically, the moun-
tain system is characterized by mighty Mesozoic limes
and displaced plateau of different altitudes. The slate
base layer represents a more or less impermeable lay-
er forming a confining aquiclude, the so-called Wer-
fener Schichten. For the most part, springs occur at this
level. The catchment is defined mostly by this base
layer and covers an area of 22 km
2
. The soils through-
out are typical calcareous, stony soils, while acid
loamy soil can be found in depressions and flat slope
positions. Historical and recent pasturing as well as
intensive forest utilization have been and continue to
be important factors that influence the present vege-
tation patterns.
172
GIS Assessment of Vegetation and Hydrological Change in a
High Mountain Catchment of the Northern Limestone Alps
Thomas Dirnböck and Georg Grabherr
Large-scale vegetation
mapping (1:10,000)
was applied to obtain
estimates of the hydro-
logical properties and
dynamics in catchment
areas that supply
water to the capital
city of Austria (Vienna).
Vegetation types as
defined by standard
relevé technique, such as alpine grassland, snow bed veg-
etation, and krummholz were related to habitat condi-
tions. A GIS served as the focal exploration tool. The vege-
tation units show specific evapotranspiration rates, which
were derived from literature on experimental research
covering similar vegetation types in the Alps. Additionally,
physical soil properties from field data were used to
derive the specific soil water balance in relation to the
mapped vegetation types. Finally, the hydrological bal-
ances for each landscape unit, as well as for the total
catchment area, were presented by combining the esti-
mates for evapotranspiration and soil water properties.
The consequences of environmental change (forestry, pas-
turing, and climate warming) are a focus of attention for
water management. Predicting general changes in vegeta-
tion patterns reveals contrasting scenarios about the con-
sequences to be expected for the water supply of Vienna.
Keywords: Alps; vegetation dynamics; water supply; evap-
otranspiration; soil water; Austria.
Peer reviewed: May 1999. Accepted: December 1999.
Mountain Research and Development Vol 20 No 2 May 2000: 172–179
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Regional climate conditions
The geographical position of the study area on the east-
ern edge of the Alps and the proximity of the dry and
warm pannonian continental climate have a strong
influence on the regional climate. In comparison to the
Northern Limestone Alps, precipitation is low. Further-
more, there is a significant decrease of precipitation
from north to south and northwest to southeast. The
altitudinal intensification of precipitation is 18 mm/100
m (during the summer). The altitudinal decrease in
temperature is 0.6°C/100 m. Moreover, it is evident that
micro- and mesoscale topographic conditions such as
slopes versus plateau, large rocks, and the omnipresent
dolines can produce considerable microscale contrasts,
a common feature of mountain climate. Temperature
inversion, with high summit temperatures and low val-
ley temperatures, is important primarily in autumn and
early winter.
Methodology
The methodological procedure was divided into the fol-
lowing:
1. Vegetation mapping.
2. Soil field survey, including calculation and estima-
tion of physical soil properties.
3. A survey of the literature to examine evapotranspira-
tion.
4. Spatial modeling of the water balance properties.
The large-scale vegetation map was produced in the
classical way. The mapping units are based on phytoso-
ciologically defined plant communities according to
Grabherr and Mucina (1993), Mucina et al (1993), and
Zukrigl (1973). The position of the sample plots was
chosen subjectively, with 92 altogether in the subalpine
and alpine regions and another 81 in the forested area.
The floristic description was done according to Braun-
Blanquet (1964). Furthermore, canopy characteristics
such as height and coverage of vegetation layers were
recorded. Thirty-three mapping units were derived in
the subalpine-alpine area. Data from the forest invento-
ry and the forest site mapping were used and aggregat-
ed to derive 13 forest mapping units. In some regions
where no data existed, they were interpreted from
infrared aerial photographs (scale 1:6000). Overall
management of the spatial data was supported by GIS.
The ecotope concept, very common in geoecology
and landscape ecology (eg, Forman and Godron 1986),
was employed to describe functional landscape aspects.
According to this concept, an ecotope, better known as
a hydrotope when hydrological properties are taken
into account, can be identified by its range of lateral
(eg, interflow) and vertical processes and the homo-
geneity of vertical processes (eg, soil moisture, infiltra-
tion, and evapotranspiration). The congruent develop-
ment of soil and vegetation and their close correlation,
especially in little-utilized landscapes such as the alpine
zone, are well known and have often been verified (eg,
Grabherr 1997). Consequently, soil properties of the
173
Research
FIGURE 1 The catchment
areas for Vienna’s drinking
water resources. Investigations
were carried out on the
easternmost mountain called
Schneeberg.
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Mountain Research and Development Vol 20 No 2 May 2000
upper subalpine and alpine zone were assumed to be
homogenous for each vegetation unit. In contrast, soils
in forested areas were mapped in the field in the course
of the forest inventory.
Table 1 summarizes the parameters, procedures,
and measuring units used to derive physical soil proper-
ties. While field capacity (FC) represents an equilibri-
um water capacity 2 to 3 days after rain, the maximum
water capacity (WC
max
) corresponds to the quantity of
water that the soil, fully saturated, can absorb. Due to
high precipitation, especially in the alpine and sub-
alpine regions, soil moisture remains predominantly
above field capacity (Körner et al 1989) except in
extremely dry periods. Thus, the maximum water hold-
ing or retention capacity (RC
max
) is defined as the dif-
ference between WC
max
and FC and, accordingly, repre-
sents the quantity of water a soil can absorb after rain-
fall without substantial surface runoff.
In order to estimate the actual evapotranspiration
(ET) of the hydrotopes, a comprehensive survey of the
literature was carried out. A deductive data model was
generated (see also Köppel and Pfadenhauer 1994). The
literature survey showed that the data investigated were
usually from small plot studies. Only data on identical
and comparable vegetation types were examined. Papers
on the ET of specific plant species were also analyzed.
The data used showed climatically comparable overall
conditions, a further limitation. Fifteen interception, 19
transpiration, and 90 ET measurements were evaluated
for alpine and subalpine plant communities. Reviews of
studies concerned with forests were consulted (eg,
McNaughton and Jarvis 1983; Larcher 1984; Waring and
Schlesinger 1985; Baumgartner and Liebscher 1996).
Three adjustment tools were applied to adapt the
estimates of ET to the specific climatic situation of the
examined area and to include the abiotic features of the
evaporation process: (1) a potential ET model, (2) data
from experimental sites with similar climatic conditions,
and (3) total catchment ET to compare it with values
from Baumgartner et al (1983). The potential ET was
modeled according to Turc-Wendling (DVWK 1996) as
ET
pot
= (Equation 1)
where R
G
= global radiation (J/cm
2
), T = temperature
(°C), and L = latent heat of vaporization (J/cm
2
)
(DVWK 1996). The temperature was calculated from
monthly mean values applying linear regressions with
the independent variable altitude (r
2
= 0.74–0.99). Pre-
cipitation distribution was calculated to transform rela-
tive ET values to absolute values. The precipitation pat-
tern (for the vegetation period) follows a multiple lin-
ear regression (r
2
= 0.86) with the variables altitude,
longitude, and latitude. In addition, a plausibility test
of the hydrological model was made by comparing the
catchment water budget with the pan-Alpine hydrologi-
cal survey by Baumgartner et al (1983).
Results and discussion
Vegetation and soil properties
The basin of Mount Schneeberg ranges from 500 to
2075 m above sea level. Forests grow up to 1600–1800
m, while a forest-like Pinus mugo belt (krummholz)
reaches approximately 1900 m. Above this level, the
landscape is characterized by alpine grassland. Beech
forest and Pinus nigra forest are the two most common
forest stand types from 500 to 1000 m. Spruce-beech-fir
forests predominate in the upper montane zone from
1000 to 1500 m. On edaphically extreme sites on very
steep slopes between 1200 and 1700 m, natural spruce
forests are found. In addition, spruce forests, specifical-
ly spruce-larch forests, also occur naturally in the sub-
alpine belt from 1400 m upward (Figure 2).
Calcareous soils are typical of almost all forest sites.
Soil depth (subsoil as well as organic soil layer) can vary
considerably. For example, the mollic A-Horizon of the
krummholz can be as deep as 1 m, whereas Pinus nigra
174
Thomas Dirnböck and Georg Grabherr
2.3 (T + 22)
(T + 123)(0.71R
G
/L + 0.72)
Parameter Procedure Measuring unit
Soil horizon depth Field measurement cm
Coarse earth Field estimation % by volume
fragment
Textural class Textural triangle % by mass of
(Schlichting et al 1995) fine earth
fraction
Bulk density Drying at 105°C g/cm
3
(Schlichting et al 1995)
Organic matter Glowing at 430°C % by mass of
(Schlichting et al 1995) fine earth
fraction
Field capacity Estimation using % by volume
(FC) texture, bulk density,
coarse fragment, and
organic matter according
to AG Boden (1996)
Maximum water Estimation using % by volume
absorption texture, bulk density,
capacity (WC
max
) coarse fragment, and
organic matter according
to AG Boden (1996)
Maximum RC
max
= WC
max
- FC % by volume
retention
capacity (RC
max
)
TABLE 1 Parameters,
procedures and measuring
units used to derive physical
soil properties.
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forest soils are very shallow. Dystric Cambisols were also
found on some sites where acidic rock occurs.
The natural forests have been changed considerably
by intense utilization over several centuries. The main
impacts of this utilization are (1) a diminished propor-
tion of deciduous trees, (2) unification of tree ages with-
in the stands, and (3) clear cutting of the uppermost
krummholz area in order to gain pasture (Figure 3).
In the alpine zone, grassland extends up to the
summit area (2075 m). Carex firma grassland is the pre-
dominant plant community on wind-swept ridges as well
as on slopes facing west. Their soils consist almost
exclusively of organic material and a noticeable depth
of 30–40 cm. In flat areas, the accumulation of clay and
silt results in soils of the Humic Cambisol type. These
sites are characterized by Festuca pumila-Agrostis alpina
grassland and Deschampsia cespitosa grassland. Slopes fac-
ing south are dominated by Carex sempervirens-Sesleria
albicans grassland on a shallow heterogeneous Rendzic
Leptosol. Pasture grassland with soils similar to those in
the above-mentioned Festuca-Agrostis grassland predomi-
nates on the plateau itself within the krummholz belt.
Only initial soils and vegetation are found in depres-
sions and ditches with long-lasting snow cover. Scree
and rock vegetation cover huge areas.
Literature survey of evapotranspiration—
facts and problems
The ET of a site is determined to a great degree by
plants. Leaf diffusive conductance, leaf area index
175
Research
FIGURE 2 Vegetation map of the investigation area.
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