Hydric functions of forests belong to the best known and most important functions. It means the influence of forest on the water
in its widest meaning of the word. Interactions among forest, water and other components of the environment vary widely
variable. Forest is only one factor of water cycle in the landscape, so its impact on the water regime is different in different
conditions.
More than 100 years of research, it was confirmed that the forests provide:
 extraordinary ability to retain rainfall water in runoff (retention function)
 accumulate rainfall water over large surface of trees, in litter and in soil (accumulation function)
 slowing down outflow of water by transformation of surface runoff to underground drainage (retardation function)
 The ability to control the amount of run-off water in surface streams (regulatory function)
 Ability to influence the quality and hygiene of available water, cleanness of streams and rivers and silting of water reservoirs
 Ability to influence the quality, quantity, movement and speed of snow melting
Specified sorting of forestfunction forms an essential information base for the use of a function of trees and their communities in
the landscape by human society. Due to the market mechanism is therefore necessary to create the widest range of
possibilities for using the functions of trees and their communities and gradually create the legislative proposals for solving the
financial consideration for the use of forest functions in the economic and social spheres.
Water balance in forest ecosystems illustrate the correlation between income component of water (atmospheric precipitation)
and out come components of water (evapotranspiration, runoff into surface and ground water).
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Evapotranspiration of forest ecosystems depends on:
 except for climatic conditions also on habitat of vegetation cover and its properties, as evaporation from vegetation
(transpiration) is determined not only by physical laws, as well as anatomical, morphological and physiological properties of
plants.
 size of surface, which could be damped
 the intensity of rainfall, temperature, humidity and air movement
 the total rainfall
 the occurrence of horizontal precipitation
 the species, age and spatial structure of vegetation, the degree of impairment, disability tree species and entire forest stand
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Sprinkle losses - water retention by wetting the surface of tree species depends on:
 size of surface, which could be damped
 intensity of precipitation
 total rainfall
 occurrence of horizontal precipitation
 species, age and spatial structure of vegetation
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Infiltration of rainwater in the soil is closely related to the state of the overlying layer of humus. If forest management disrupt this
layer, immediately it rapidly increase surface runoff and erosion, what caused fluctuating of flow rate in catchment.
The process of infiltration is influenced by the intensity and the duration of rainfall and the character of the soil, especially partcle
size composition and initial soil moisture condition of the soil. The wetter the soil, the less water permeability.
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Impact of forest on runoff during melting of the snow
In areas with large snowfalls forests have an important function in reducing peaks of spring flood outflow rate and extending the
outflow for a longer period of time.
Forest prevents the rapid melting of snow. While from the meadows flew in one day from 5.8 to 11.8 mm - owing to the
exposure slope, from spruce forest flew 5.0 mm and from beech forest 4.3 mm of water from melting snow, regardless of
exposure slope.
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Impact of forest cover on runoff water during flood waves
Forests, although not completely prevent flood waves, but can significantly mitigate their progress.
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Total retention = retention capacity of forest stands for short-term heavy rainfall may reach up to 70 mm. This value applies to
state of the 100% forest cover in the landscape and the stand density of 1.0 (or 100% canopy). However the part of forest
includes treeless areas ( the deforested area) which decrease the retention capacity of the landscape. At first slowly, up to 50-
60% forest cover , then - below this threshold, is a decrease of retention more significant.
Retention capacity of forest ecosystems
Canopy of forest stand
Herbal cover and litter layer
Forest soil
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 If the soil is completely saturated , rainfall´s water outflows and it creates the most dangerous flow for creating floods .
 Soil as a water reservoir has amazing potential and can retain up to 400 mm of water . In our natural conditions , the forest
soil is always partially saturated.
 In extreme rainfall in a short period of time with intensity of 100 mm retained forests 68 mm water and grassland only 46 mm
of water, or about 67 % of the amount of water retained by forest. Significantly poorer retention capacity of water has arable land
in the period without vegetation cover .
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Determinants of resulting runof and its temporal changes include:
 geomorphological characteristics of topography ( slope, embossed topography , etc. . )
 hydrogeological structure of catchment (nature of permeability rocks , the presence of aquifers , etc. . )
 meteorological conditions ( duration and intensity of rainfall , interaction of horizontal precipitation , etc. . )
 water balance of forest stands ( interception, reserve of soil water , the state of forest road network in relation to surface runoff , etc. . )
 total catchment forest cover and structure of non-forest landscape of catchment
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In terms of water management, it is important to realize that hydric forest functions can satisfactorily and longly fulfill only healtly
forest, corresponding to a given site conditions , thus ecologically stable forest
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A separate chapter is :
 Impact on water quality and hygiene
 Impact on quantity of water in flows
 The influence of the source of drinking water
 Impact on protection of mineral water sources
 The impact on flows, water areas and life in them
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 forest complexes reduced rainfall Extremities - reduce the size of big water runoff and increase the size of small water runoff .
 In our conditions , forest cover can cause a reduction in the maximum runoff by up to 50 %
 In the driest months, the runoff from the forest is 1.43 times higher than runoff from fields and 1.58 times higher than the
outflow of permanent grassland
 Very important is information that in forestless areas occurs about 47 % higher culmination of big waters compared to
forested land. By afforestation of forestless landscape was reduced the culmination of big waters approximately in 1.5 times .
 Extreme water level in forested catchment, what occurs likely once every 100 years ( " hundred water" ), it is possible in
compareble deforested catchment expected every 16 years .
 Forest ecosystems reduce the extremity of weather, but fulfill also an important role in terms of quality and quantity of drinking
water