INFLUENCE OF TREE TRANSPIRATION ON MASS WATER BALANCE OF MIXED MOUNTAIN FORESTS
OF THE WEST CARPATHIANS
J. Minďáš1, K. Střelcová2, J. Škvarenina2
National Research Centre - Forest Research Institute, T.G. Masaryka 24, 960 01 Zvolen, Slovakia
mindas@nlcsk.org
Technical University in Zvolen, Forestry Faculty, T.G.Masaryka 24, 960 53 Zvolen, Slovakia
strelcov@vsld.tuzvo.sk, jarosk@vsld.tuzvo.sk
Mixed beech-fir stands are the most productive forest communities in the West Carpathians.
Forest trees (beech, fir and spruce) are growing in optimal ecological conditions, that are mainly
temperature regime and balanced water regime. In forest hydrology, tree transpiration can be a major
component of the mass water balance of watersheds and may influence water yield from catchments.
Analysis of precipitation-runoff processes in mixed forest in relation to tree transpiration have shown
that forests may play a crucial role in a runoff regime especially in maximum runoff coarse because of
high transpiration and evapotranspiration. From the above mentioned reasons it is necessary to take
into account the active water management function of forest ecosystems in the landscape and forest
management mainly in the flood sensitive catchments.
The mass water balance of a site, stand or watershed can be simply described with equation:
P  W  ET  O
where ΔW is the change in fytomass and root volumetric water content during the time period P, ET
and O are average precipitation, evapotranspiration and runoff over the time period (mm. time -1).
When the time period is one year, than ΔW can be assumed to be negligible and an annual estimate
of ET (mm.year-1) is estimated simply as the difference between precipitation and runoff.
Brief information about water balance of the Carpathian temperate forest ecosystem are
presented in the paper. Experimental research was done in a mature mixed fir-spruce-beech stand in
the research plot “PoľanaHukavský grúň” (850 m a.s.l.) in the south-eastern part of Poľana Mts. in
the Biosphere Reserve UNECSO in the Central Slovakia. Individual parameters of water budget have
been continously monitored. The water consumption of the model beech trees, as well as approximate
model beech stand transpiration were estimated on the basis of sap flow measurements and upscaling through dendrometrical approach. Sap flow of model beech trees was estimated by direct,
non-destructive and continuous measurements by tree-trunk heat balance method (THB) with internal
heating and sensing of temperature. These values were compared with potential evapotranspiration
according Türc. Precipitation parameters have been measured through the various collectors at
several levels: above the canopy (vertical and horizontal precipitation – percepted collectors area of
500 cm2), under the canopy (throughfall precipitation - Hellman’s rain gauges, stemflow – sillicon
collars). Fog precipitation – cloud water was measured through fog collectors (according Grunow).
Inflow water through the soil profile have been collected by the lysimeters at several levels (0, 12 and
33 cm) of the mineral topsoil.
The fig.1 presents the results of the water budget and the portion of the tree transpiration
within the individual water flows. Amount of transpirated water differ according to surface
characteristics, meteorological conditions and soil water regime. Approximately 40-90% of
precipitation total is lost by evapotranspiration in the Central Europe. Evapotranspiration of forest
ecosystem in the middle mountain region (850 m a.s.l.) includes: transpiration (35% of precipitation
total), interception (21%), evaporation (8%), resp. (figure 1). There are differences between tree
species in mass of transpirated water. Transpiration of spruce and fir reaches two-thirds of beech
transpiration. Fog precipitation contribution to the water balance of beech-fir stand is 5%. Concurrently
fog precipitation lower the interception losses of vertical precipitation.
P = 100
ET = 64
PV = 95
IP = 20
T = 35
PH = 5
EP = 8
ΔW R
+0.5
ΔW
+1
PK =
72,5
IB = 1
PS = 7
OP ≤ 1
LEGEND
––
---.....
ΔW P
+0.5
PZ = 77,5
water
vapour
O = 35
water
storage
Figure 1 Mass water balance of the mature mixed Carpathian forest at the Poľana – Hukavský grúň
site at 850 a.s.l, where in %: P - precipitation in the open area, PV - vertical precipitation (rain,
snow…), PH – horizontal precipitation (from fog, hard rime...), P K – throughfall precipitation, PS stemflow, PZ – infiltration into the mould and soil, OP – above ground runoff, O – underground runoff,
IB – interception of the herb layer, IP – interception of the tree layer, EP – evaporation from the soil, T –
transpiration of the tree layer, ET – evapotranspiration, ΔW R – the change of water content in the
fytomass, ΔW P – the change of water content in the soil and mould, ΔW – the change in the fytomass
and root volumetric water content during the time period
Key words
Biosphere Reserve Poľana, spruce-beech-fir stand, evapotranspiration, sap flow, interception,
precipitation, fogwater, infiltration, runoff