*2.2.1 Effect of climate change on forest water cycle*

A global (large) water cycle can be defined as a water cycle in which water is transferred between the land and oceans and a local (small) water cycle is defined as a displacement merely over oceans or drainless areas of the land. The water cycle governs all of the natural forest functions. However, forest ecology represents an important aspect of the hydrological cycle at the planetary level, and so these effects impact at a global level. Whereas the global water cycle is related to the adaptation of forests to climate change, the local water cycle interlinks mutual interactions between related forest complexes within the catchment. In general, the impact of forests on global climate change is at its most significant due to cloud formation in the tropics. The formed clouds reflect solar radiation more effectively and, therefore, cool the atmosphere more than does the absorption of greenhouse gases by vegetation [40]. Environmental pollution, deforestation and transformation of the tree species composition reduce the natural ability of forests to adapt to climate change. Monitoring of soil properties focused on water and nutrient cycles in different forest ecosystems offers a tool for assessing the impacts of climate change [41].

Forest functions are the outcome of the interactions between the environmental, soil and vegetation subsystems. Natural functions are based on processes that support self-organization, recovery and development of the ecosystem. The interrelated processes of biodiversity, organic matter formation and nutrient cycles promote production, air circulation, (in-)filtration, evapotranspiration and site differentiation [42]. The water cycle controls the carbon cycle through which forests modify local cycling of all nutrients. The parts of the water and carbon cycles within soils have linked individual forest functions to the self-organized ecosystem [43]. The degree of interconnection is subject to the flow of soil water, but simultaneously also by its scope in the specific cycle.

The global effect of forest functionality consists in the transfer of evaporated water through cloudiness within the catchments from the areas with more significant vapor in the lower parts than the areas in the upper parts, where cloudiness condenses into more frequent precipitation. Precipitation in the upper parts of the catchments flows to the lower parts, where additional water complements the higher evaporation and lower precipitation [44]. As temperatures rise, this phenomenon is intensified: evaporation elevates, and drought deepens in drier areas, while precipitation in wetter areas increases. The consequent accentuation in disparities between drier and wetter areas disrupts the interconnection of forest functions among vegetation zones [45].

Even though the local water cycle defines the hydric functions of forests to catchments, their response to climate change depends on the interconnected monitoring of variability not only within the catchment but also among remote catchments. The link between the effects of global and local water cycles also

exposes mutually unrelated forests to reduced water availability and consequently to reduced service provision [46].

#### *2.2.2 Effects of nutrient cycles on forest hydric functions*

The forest promotes both water and carbon cycles in parallel because they are related to energy flows in the ecosystem. While natural plant-to-plant feedbacks between plants and nutrient cycles underpin ecosystem functionality, forest damage disrupts these processes. If forest damage results in the disruption of the carbon cycle, at the same time the local water cycle is also disrupted, followed by negative impacts on the functioning of related ecosystems [47]. Recognition of forest function damage through the disruption of soil properties is based on the determination of critical values of physical and chemical properties involved in the processes of formation of individual ecosystem functions.

Carbon enters the ecosystem in the form of atmospheric CO2 through photosynthesis of plants, in which solar energy for the synthesis of organic compounds in cells is transformed by the decomposition of water. Plants release carbon by respiration, by being consumed by herbivores or fungi and by exchange reactions with soil biota and litter. The most significant conversions of organically bound carbon occur in the soil. Plants mediate carbon into the soil both by litter to the surface and also by root necrosis, exudation, root cap sloughing or exchange with microorganisms within the soil body (e.g. through mycorrhizal sheaths). Litter is mechanically or biochemically decomposed into residual chains at pH ˃ 4.5, or into stable polyphenol nuclei at lower pH, as a result of the tetravalency of carbon covalent bonds. Soil organisms or enzymes are capable of decomposing chains into organic acids under favorable conditions, but the prevailing unfavorable conditions allow merely incomplete decomposition. Soil carbon accumulates as a consequence of the imperfection of decomposition [48]. However, destruents mineralize organic residues back to CO2 under a range of unfavorable conditions (**Figure 2**).

Carbon compounds significantly attract soil water through adhesion to organic molecular chains. That is why carbon storage in the soil irreplaceably increases the WHC of the entire ecosystem. Subsequently, the detection of forest functions using intra-soil processes focuses on common inputs or outputs of substances and energy in the soil subsystem. This can be done by ascertaining the length of the delay of the forest stand response in the aftermath of the alteration of soil property values [49]. The evaluation of conditions of substance inputs or outputs concentrate on assessments of whether or not biochemical and physical properties can regulate the processes of water or carbon cycles. Even though the selected soil properties correlate with one another, the temporal variability of physical properties is incomparably longer than the significant seasonal variability of biochemical properties. Whereas the variability of (bio)chemical properties indicates a threat to the forest after an episode of drought or extreme daily precipitation sum (EDSP), an alteration to correlations of the forest status with poorly variable soil physical properties indicates deviations in development during environmental change [50].

The selection of intra-soil processes affecting forest functions is based on the study of the variability of properties in different parts of the soil body. The functions of circulation, infiltration, evapotranspiration and differentiation are typically regulated by means of one soil process. The indication of individual forest ecosystem functions at the soil level (**Table 1**) can be derived from the generalization of studies focused on the relation between the growth conditions with water balance, biodiversity and the health status of forests [49, 51–53].

**Table 1** shows the soil properties involved in water and carbon cycle processes that increase the efficiency of individual forest functions. The production

**53**

**Figure 2.**

**Table 1.**

indication is centred on the catalase activity, which depends on the intensity of aerobic metabolism. The correlation of the soil catalase activity with the content and character of organic acids reflects the variety of humus forms. It is naturally associated with differentiated forest cover. If the forest disruption does not damage the humus diversity, the catalase activity remains stable. Air circulation is dependent on the atmospheric flow reducing vapor pressure above the partial surface that the soil maintains thanks to minimum aeration capacity. Infiltration is also conditioned by organic matter and clay minerals, which may form organomineral complexes. They significantly retain water by adhesion and capillary rise in capillary pores remaining among their particles [54]. On the contrary, evapotranspiration is the sum of evaporation from the individual types of surfaces in the ecosystem. The rate of evaporation from the soil is directly proportional to the soil water potential [55].

*Connectivity between cycles of water (left) and carbon (right) in forest ecosystem forming hydric functions.*

**Forest function Hydric process Indicative soil property** Production Photochemical water disintegration Catalase activity

Air circulation Vapor pressure decrease Minimum aeration capacity (In-)filtration Physical sorption Organomineral complex content

Evapotranspiration Evaporation Soil water potential Differentiation Debasification Soil water acidity

*Relationships between forest functions and water cycle processes indicated by the selected soil properties.*

*Forest Soil Water in Landscape Context DOI: http://dx.doi.org/10.5772/intechopen.93003* *Forest Soil Water in Landscape Context DOI: http://dx.doi.org/10.5772/intechopen.93003*

#### **Figure 2.**

*Soil Moisture Importance*

to reduced service provision [46].

*2.2.2 Effects of nutrient cycles on forest hydric functions*

formation of individual ecosystem functions.

exposes mutually unrelated forests to reduced water availability and consequently

The forest promotes both water and carbon cycles in parallel because they are related to energy flows in the ecosystem. While natural plant-to-plant feedbacks between plants and nutrient cycles underpin ecosystem functionality, forest damage disrupts these processes. If forest damage results in the disruption of the carbon cycle, at the same time the local water cycle is also disrupted, followed by negative impacts on the functioning of related ecosystems [47]. Recognition of forest function damage through the disruption of soil properties is based on the determination of critical values of physical and chemical properties involved in the processes of

Carbon enters the ecosystem in the form of atmospheric CO2 through photosynthesis of plants, in which solar energy for the synthesis of organic compounds in cells is transformed by the decomposition of water. Plants release carbon by respiration, by being consumed by herbivores or fungi and by exchange reactions with soil biota and litter. The most significant conversions of organically bound carbon occur in the soil. Plants mediate carbon into the soil both by litter to the surface and also by root necrosis, exudation, root cap sloughing or exchange with microorganisms within the soil body (e.g. through mycorrhizal sheaths). Litter is mechanically or biochemically decomposed into residual chains at pH ˃ 4.5, or into stable polyphenol nuclei at lower pH, as a result of the tetravalency of carbon covalent bonds. Soil organisms or enzymes are capable of decomposing chains into organic acids under favorable conditions, but the prevailing unfavorable conditions allow merely incomplete decomposition. Soil carbon accumulates as a consequence of the imperfection of decomposition [48]. However, destruents mineralize organic

residues back to CO2 under a range of unfavorable conditions (**Figure 2**).

indicates deviations in development during environmental change [50].

balance, biodiversity and the health status of forests [49, 51–53].

The selection of intra-soil processes affecting forest functions is based on the study of the variability of properties in different parts of the soil body. The functions of circulation, infiltration, evapotranspiration and differentiation are typically regulated by means of one soil process. The indication of individual forest ecosystem functions at the soil level (**Table 1**) can be derived from the generalization of studies focused on the relation between the growth conditions with water

**Table 1** shows the soil properties involved in water and carbon cycle processes that increase the efficiency of individual forest functions. The production

Carbon compounds significantly attract soil water through adhesion to organic molecular chains. That is why carbon storage in the soil irreplaceably increases the WHC of the entire ecosystem. Subsequently, the detection of forest functions using intra-soil processes focuses on common inputs or outputs of substances and energy in the soil subsystem. This can be done by ascertaining the length of the delay of the forest stand response in the aftermath of the alteration of soil property values [49]. The evaluation of conditions of substance inputs or outputs concentrate on assessments of whether or not biochemical and physical properties can regulate the processes of water or carbon cycles. Even though the selected soil properties correlate with one another, the temporal variability of physical properties is incomparably longer than the significant seasonal variability of biochemical properties. Whereas the variability of (bio)chemical properties indicates a threat to the forest after an episode of drought or extreme daily precipitation sum (EDSP), an alteration to correlations of the forest status with poorly variable soil physical properties

**52**

*Connectivity between cycles of water (left) and carbon (right) in forest ecosystem forming hydric functions.*


#### **Table 1.**

*Relationships between forest functions and water cycle processes indicated by the selected soil properties.*

indication is centred on the catalase activity, which depends on the intensity of aerobic metabolism. The correlation of the soil catalase activity with the content and character of organic acids reflects the variety of humus forms. It is naturally associated with differentiated forest cover. If the forest disruption does not damage the humus diversity, the catalase activity remains stable. Air circulation is dependent on the atmospheric flow reducing vapor pressure above the partial surface that the soil maintains thanks to minimum aeration capacity. Infiltration is also conditioned by organic matter and clay minerals, which may form organomineral complexes. They significantly retain water by adhesion and capillary rise in capillary pores remaining among their particles [54]. On the contrary, evapotranspiration is the sum of evaporation from the individual types of surfaces in the ecosystem. The rate of evaporation from the soil is directly proportional to the soil water potential [55].

In contrast, the capability of ecosystem differentiation is estimated by the chemical composition of the soil solution. It grows when soil run-off contains a minimum of base cations. Increased concentrations of bases in run-off water indicate soil acidification, which reduces the ecological diversity of the catchment [56].

## *2.2.3 Hydrographical division of forests*

The soil indicators relating to forest functionality are naturally subdivided into a total of eight biomes relating to differences in water availability due to variations in evapotranspiration and the water-holding capacity (**Table 2**) [57]. Despite the differences between forest biomes, large catchments possess similar zonality of hydric functions internally. Nonetheless, the WHC affects the variances in forest hydric functions of forests between individual habitats within the catchment as its value is directly proportional to the soil types present. The largest overlaps in the WHC values occur in the catchments of Mediterranean, temperate and tropical coniferous forests with more similar soil development at medium temperature intervals relative to boreal, mangrove or tropical broadleaved rainforests [58]. For example, the values of the WHC in **Table 2** were found to be related to the macroclimatic properties of forest biomes. This can be further related to the weighted means of the soil types as found in the Harmonized World Soil Database (HWSD) [59].

Transitions of forest hydric functions in the catchment are the basis for the derivation of hydrographic zonality. Large forest catchments include montane, submontane and floodplain forest ecosystems [50]. These zones emerge thanks to the local water cycle from wetter mountains to drier floodplains. Undisturbed forests are capable of water supply to all the parts of the catchment continuously even though most water supplies on the mainlands are unavailable to plants. Over 62.4% of mainland water supplies are concentrated in glaciers, 36.2% in underground reservoirs and 0.42% in lakes or ground level reservoirs. Only 0.29% of water is found in the soil and 0.09% in rivers [60, 61]. Atmospheric precipitation over the dry land brings merely 0.008% of the global water balance, but over 50% of precipitation occurs in montane areas. Continuous water management in the catchment is ensured by forests by means of modifications of evapotranspiration and run-off. Forests cover 39.7% of the dry land


*AP, area proportion (%); T, average temperature (°C); P, annual precipitation (mm); AET, actual evapotranspiration; PET, potential evapotranspiration; WHC, water-holding capacity (%). Data according to [57].*

**55**

*Forest Soil Water in Landscape Context DOI: http://dx.doi.org/10.5772/intechopen.93003*

22% WHC and dampening 67–75% of EDSP [63].

radiation directly impacting on the soil surface [64].

slope that subsequently does not cause erosion.

and tree species composition.

but account for 67.6% of evapotranspiration. Simultaneously, only the structure of the forest can return the evaporated water sufficiently by cloud/fog water or seasonal

Deceleration of run-off by the forest ecosystem is irreplaceable in reducing seasonal variations in water availability between winter and the growing season and in dampening of EDSP. EDSP typically exceeds the average soil WHC either in above-average climatic episodes of precipitation or during the most intense precipitation season. Overcoming WHC prefigures a temporary increase in the flow of soil water and subsequently also river water. It is precise because the values of WHC naturally alter within soil development regardless of the tree species composition or altitude, that (sub)montane forests can dampen run-off after extraordinary rainfall with similar efficiency [62]. The actual water-holding capacity of forest soils due to the constant presence of natural moisture is approximately only 30 mm, providing

Alterations in the tree species composition of forests have had the greatest impact on the forest hydric functions during transitions of the seasons of the year. Coniferous trees may be characterized by average higher interception and evapotranspiration. At the same time, coniferous forests capture more snow and significantly slow down melting, reducing the surface run-off in early spring when most of the vegetation is inactive. In deciduous broadleaved forests, this deceleration of run-off does not occur due to defoliation of trees in winter and thus increased solar

Hydrographic forest zonality indicates differentiated forest efficiency in the modification of the local water cycle. The differentiation of the effective influence of forests is determined by the relief of the landscape as well as soil development

Montane forests are located in the upper parts of catchments with the highest amount of precipitation. Their structure is adapted to the application of more frequent horizontal precipitation. Soils are permeable due to the prevailing mechanical weathering. The erosion on steep slopes and the nature of the soil-forming substrate cause rockiness and shallowness of soils. The water-holding capacity of montane soils is maintained by means of accumulation and the slower degradation of humus. Montane drainless depressions with accumulating humus are habitats of ombrogenic bogs in the presence of excessive rainfall. At transitions of the mantle rock with the outcrop of impermeable subsoil, there are water springs at the points of concentrated groundwater run-off. Montane forests not only increase the total amount of precipitation but at the same time, they are crucial for stable surface water run-off. The total amount of precipitation increases not only by collecting horizontal precipitation but also by lower evaporation due to lower temperatures than in the lower parts of the catchment. Humus accumulations reduce run-off on a

Submontane forests form the zonal vegetation between montane and floodplain

ecosystems. They occur mostly on slopes with harmonious water balance. Soils are generally moderately permeable due to a balanced proportion of stoniness and fine-grained weathered particles. The formation of bogs is excluded on dominant, slanting slopes and more favorable temperatures that intensify soil respiration prevent excessive accumulation of surface humus. Higher clay content and lower humus accumulation distinguish water retention properties of submontane soils from montane soils. Submontane forests inhibit atmospheric precipitation only up to an amount corresponding with potential evapotranspiration, while continuous run-off along the surface as well as from the soil body occurs when WHC is exceeded. Floodplain forests occur in a flat relief formed by floods. On the one hand, floods lay terraces; on the other hand, they tear down banks. The activity of rivers

pollen release, which can create a condensation nucleus to form cloudiness.

#### **Table 2.**

*Characteristics of water balance in forest biomes.*

#### *Forest Soil Water in Landscape Context DOI: http://dx.doi.org/10.5772/intechopen.93003*

*Soil Moisture Importance*

*2.2.3 Hydrographical division of forests*

In contrast, the capability of ecosystem differentiation is estimated by the chemical composition of the soil solution. It grows when soil run-off contains a minimum of base cations. Increased concentrations of bases in run-off water indicate soil acidification, which reduces the ecological diversity of the catchment [56].

The soil indicators relating to forest functionality are naturally subdivided into a total of eight biomes relating to differences in water availability due to variations in evapotranspiration and the water-holding capacity (**Table 2**) [57]. Despite the differences between forest biomes, large catchments possess similar zonality of hydric functions internally. Nonetheless, the WHC affects the variances in forest hydric functions of forests between individual habitats within the catchment as its value is directly proportional to the soil types present. The largest overlaps in the WHC values occur in the catchments of Mediterranean, temperate and tropical coniferous forests with more similar soil development at medium temperature intervals relative to boreal, mangrove or tropical broadleaved rainforests [58]. For example, the values of the WHC in **Table 2** were found to be related to the macroclimatic properties of forest biomes. This can be further related to the weighted means of the

soil types as found in the Harmonized World Soil Database (HWSD) [59].

Transitions of forest hydric functions in the catchment are the basis for the derivation of hydrographic zonality. Large forest catchments include montane, submontane and floodplain forest ecosystems [50]. These zones emerge thanks to the local water cycle from wetter mountains to drier floodplains. Undisturbed forests are capable of water supply to all the parts of the catchment continuously even though most water supplies on the mainlands are unavailable to plants. Over 62.4% of mainland water supplies are concentrated in glaciers, 36.2% in underground reservoirs and 0.42% in lakes or ground level reservoirs. Only 0.29% of water is found in the soil and 0.09% in rivers [60, 61]. Atmospheric precipitation over the dry land brings merely 0.008% of the global water balance, but over 50% of precipitation occurs in montane areas. Continuous water management in the catchment is ensured by forests by means of modifications of evapotranspiration and run-off. Forests cover 39.7% of the dry land

**Forest biome AP** *T P* **AET PET WHC**

Boreal 25.59 −2.54 ± 12.37 642 ± 19 256 ± 75 298 ± 64 49.11 ± 9.15 Mediterranean 5.45 15.05 ± 5.34 586 ± 26 316 ± 121 962 ± 225 32.39 ± 9.44 Mangroves 0.59 26.07 ± 1.70 1900 ± 94 502 ± 476 1303 ± 492 69.18 ± 3.89

*evapotranspiration; PET, potential evapotranspiration; WHC, water-holding capacity (%). Data according to [57].*

*AP, area proportion (%); T, average temperature (°C); P, annual precipitation (mm); AET, actual* 

33.46 21.82 ± 1.35 1988 ± 83 892 ± 200 1270 ± 172 24.96 ± 3.38

5.09 24.16 ± 1.93 1263 ± 79 717 ± 180 1203 ± 174 26.34 ± 5.09

1.20 19.40 ± 2.31 1438 ± 83 716 ± 97 1218 ± 74 33.71 ± 6.97

21.71 9.73 ± 7.39 1072 ± 30 508 ± 127 688 ± 112 31.13 ± 9.80

6.91 6.39 ± 7.82 918 ± 36 428 ± 88 700 ± 100 29.63 ± 8.31

**54**

**Table 2.**

*Characteristics of water balance in forest biomes.*

Tropical rain broadleaved

Tropical dry broadleaved

Tropical coniferous

Temperate mixed

Temperate coniferous

but account for 67.6% of evapotranspiration. Simultaneously, only the structure of the forest can return the evaporated water sufficiently by cloud/fog water or seasonal pollen release, which can create a condensation nucleus to form cloudiness.

Deceleration of run-off by the forest ecosystem is irreplaceable in reducing seasonal variations in water availability between winter and the growing season and in dampening of EDSP. EDSP typically exceeds the average soil WHC either in above-average climatic episodes of precipitation or during the most intense precipitation season. Overcoming WHC prefigures a temporary increase in the flow of soil water and subsequently also river water. It is precise because the values of WHC naturally alter within soil development regardless of the tree species composition or altitude, that (sub)montane forests can dampen run-off after extraordinary rainfall with similar efficiency [62]. The actual water-holding capacity of forest soils due to the constant presence of natural moisture is approximately only 30 mm, providing 22% WHC and dampening 67–75% of EDSP [63].

Alterations in the tree species composition of forests have had the greatest impact on the forest hydric functions during transitions of the seasons of the year. Coniferous trees may be characterized by average higher interception and evapotranspiration. At the same time, coniferous forests capture more snow and significantly slow down melting, reducing the surface run-off in early spring when most of the vegetation is inactive. In deciduous broadleaved forests, this deceleration of run-off does not occur due to defoliation of trees in winter and thus increased solar radiation directly impacting on the soil surface [64].

Hydrographic forest zonality indicates differentiated forest efficiency in the modification of the local water cycle. The differentiation of the effective influence of forests is determined by the relief of the landscape as well as soil development and tree species composition.

Montane forests are located in the upper parts of catchments with the highest amount of precipitation. Their structure is adapted to the application of more frequent horizontal precipitation. Soils are permeable due to the prevailing mechanical weathering. The erosion on steep slopes and the nature of the soil-forming substrate cause rockiness and shallowness of soils. The water-holding capacity of montane soils is maintained by means of accumulation and the slower degradation of humus. Montane drainless depressions with accumulating humus are habitats of ombrogenic bogs in the presence of excessive rainfall. At transitions of the mantle rock with the outcrop of impermeable subsoil, there are water springs at the points of concentrated groundwater run-off. Montane forests not only increase the total amount of precipitation but at the same time, they are crucial for stable surface water run-off. The total amount of precipitation increases not only by collecting horizontal precipitation but also by lower evaporation due to lower temperatures than in the lower parts of the catchment. Humus accumulations reduce run-off on a slope that subsequently does not cause erosion.

Submontane forests form the zonal vegetation between montane and floodplain ecosystems. They occur mostly on slopes with harmonious water balance. Soils are generally moderately permeable due to a balanced proportion of stoniness and fine-grained weathered particles. The formation of bogs is excluded on dominant, slanting slopes and more favorable temperatures that intensify soil respiration prevent excessive accumulation of surface humus. Higher clay content and lower humus accumulation distinguish water retention properties of submontane soils from montane soils. Submontane forests inhibit atmospheric precipitation only up to an amount corresponding with potential evapotranspiration, while continuous run-off along the surface as well as from the soil body occurs when WHC is exceeded.

Floodplain forests occur in a flat relief formed by floods. On the one hand, floods lay terraces; on the other hand, they tear down banks. The activity of rivers increases the diversity of soil properties, mostly at interfaces with zonal sites. The functionality of floodplain forests is determined by river water and waterlogging. The duration of the flood, the variability in the height of the river level and the fluctuation of the groundwater level induce differentiation of floodplain ecosystems. Extraordinary floods most significantly alter the dynamics of their development. The function of floodplain forests varies due to the lack of precipitation for evapotranspiration, which they are able to replace thanks to floods or high groundwater levels. The long-term decline of the soil water level at high evaporation can result in the replacement of the floodplain forest with the forest-steppe [65]. Floodplain forests with optimal soil moisture and high evaporation transpire almost 80% of potential evapotranspiration. This amount contains up to 70% of groundwater and 30% of precipitation. However, the transpiration of trees is not merely inhibited by the lack of soil water, but also by the lack of air during a prolonged flood [66].

#### *2.2.4 Vulnerability of forest hydric functions*

In Central Europe, the current health status of forest stands is closely linked to the climatic situation, particularly the availability of water for woody plants. Water in forest soils is a key part of the feedback relations, both in the soil–plant direction, currently mainly as a limiting eco-factor, and in the soil-landscape direction, in terms of the landscape water regime, water retention in the landscape and prevention of flood events.

Forest functions are threatened by dieback, fragmentation and transformation of tree species composition. The loss of forests leads to a decrease in evaporation, with cloud formation also declining. The decrease in cloud formation affects the whole catchment. Although the evaporation reduction should prevent soil moisture diminution, unlike evapotranspiration, it is not regulated by means of the vegetation cover, but merely by temperature alteration. A denuded land is easier to warm up, increasing biological activity and mineralization intensity. This occurs provided that removal of the stand component does not result in (frequent) waterlogging of a site, which would be limiting to the aerobic organisms at least until the lost functionality of the subsequent stand is restored. Soil without organic matter loses both water retention capacity and fertility. The decrease in forests is most distinctive in the lower parts of the catchment, which are more accessible, mostly non-waterlogged and more hydrologically suited for agriculture. Since the occurrence of precipitation also lowers in the spring-dependent parts of catchments as the cloud formation diminishes, the subsequent decline in river levels causes a decline in water supply to tributary-dependent parts of the catchment [67].

The greatest differences in the soil water-holding capacity are found between forested and treeless catchments. Flooding in forested catchment areas occurs in the aftermath of exceeding EDSP. Conversely, treeless catchments are affected by flash floods even after precipitation ˂30 mm. The protection of the water retention capacity of the catchment consists primarily in the prevalence of unbroken stretches of forests. Young open forest stands resemble treeless zones in terms of the water balance. Only closed stands over 20 years of age reach a water balance comparable to that of adults. Even though homogeneous forest stands provide hydric functionality similar to richly structured mixed forests, richly structured forests appear more resilient to climate change. Protecting the hydric functions of forests during climate change can be achieved in the following ways:

• Promotion of the transformation of tree species composition in favor of the natural state, with a natural proportion of trees within each stand type exceeding 50%

**57**

*Forest Soil Water in Landscape Context DOI: http://dx.doi.org/10.5772/intechopen.93003*

compact the upper soil horizons

soil solution, and at the same time, K+

spatial diversity

vegetation

• Favoring understorey or small-scale differentiated farming to increase age and

• Construction of a sufficiently dense transport network to minimize machinery driving through stands, giving priority to mining technologies that do not

Drought stress in forest stands has been shown to reduce both transpiration and the water content in plants [68, 69]. This occurs because of the loss of assimilation apparatus, thus reducing leaf area available for transpiration, but also because of the reduced availability of nutrients, which convert to a dehydrated state in a differentiated way [70]. At higher humidity, there is more Ca2+ and Mg2+ present in the

This is due to the size of the hydration envelope of the ions, which conditions their hydration energy for various nutrients in a differentiated way. This is necessary for the nutrient to be taken up by the plant. To hydrate diverse ions, different amounts of water molecules are needed, so potassium is absorbed at lower soil moisture than magnesium or calcium—two elements that frequently prove nutritionally deficient

In the contemporary cultural landscape, the natural water cycle is, to a large extent, influenced (in other words, 'shortened') by vertical water movement within terrestrial systems. Consequently, communication within soil hydrological systems and the rock

The amount of water is distributed very unevenly in space and time on Earth. That is why there are problems with its lack in many regions. Redistribution of water in the landscape can be expressed by the fundamental elementary redistribution

where DP: deep percolation; IR: irrigation; P: precipitation; RO: surface run-off;

On the basis of this balance equation, two basic hydrological cycles are identified: the large and small water cycles. In the water cycle (**Figure 3**), the main sources are precipitation and the surface, lateral and underground inflow in the hydrogeological collector. Water that falls on the soil surface immediately infiltrates the soil or, under conditions of insufficient infiltration capability and hydraulic conductivity, it drains or accumulates in micro-depressions of the relief (detention). Infiltrated water is redistributed in the soil body and remains below the soil surface, suspended in a capillary manner. Gravitational water then flows out of the area laterally (hypodermically) and migrates to the capillary fringe (see below), through which it percolates into an aquiferous hydrogeological collector. In relation to the vegetation, the water cycle is influenced by evapotranspiration and interception. Soil, or more exactly the soil environment, is the main location of infiltration of water into the rocky underground environment. In general, this is the most impor-

DP = IR + P − ΔS − RO–ET (1)

even though they may be at an optimal concentration in the soil.

subsoil is impaired. The reasons will be explained in the following section.

equation of water (this is also referred to as the balance equation [71]):

tant environment for the replenishment of groundwater supplies.

**2.3 Soil water and its relationship with groundwater**

ET: evapotranspiration; ΔS: soil water storage.

is better released by mineralization processes.

• Maintaining a closed canopy to protect the soil surface, where understorey can be mined at the restoration stage without affecting the species diversity of *Soil Moisture Importance*

tion of flood events.

*2.2.4 Vulnerability of forest hydric functions*

change can be achieved in the following ways:

exceeding 50%

increases the diversity of soil properties, mostly at interfaces with zonal sites. The functionality of floodplain forests is determined by river water and waterlogging. The duration of the flood, the variability in the height of the river level and the fluctuation of the groundwater level induce differentiation of floodplain ecosystems. Extraordinary floods most significantly alter the dynamics of their development. The function of floodplain forests varies due to the lack of precipitation for evapotranspiration, which they are able to replace thanks to floods or high groundwater levels. The long-term decline of the soil water level at high evaporation can result in the replacement of the floodplain forest with the forest-steppe [65]. Floodplain forests with optimal soil moisture and high evaporation transpire almost 80% of potential evapotranspiration. This amount contains up to 70% of groundwater and 30% of precipitation. However, the transpiration of trees is not merely inhibited by the lack of soil water, but also by the lack of air during a prolonged flood [66].

In Central Europe, the current health status of forest stands is closely linked to the climatic situation, particularly the availability of water for woody plants. Water in forest soils is a key part of the feedback relations, both in the soil–plant direction, currently mainly as a limiting eco-factor, and in the soil-landscape direction, in terms of the landscape water regime, water retention in the landscape and preven-

Forest functions are threatened by dieback, fragmentation and transformation of tree species composition. The loss of forests leads to a decrease in evaporation, with cloud formation also declining. The decrease in cloud formation affects the whole catchment. Although the evaporation reduction should prevent soil moisture diminution, unlike evapotranspiration, it is not regulated by means of the vegetation cover, but merely by temperature alteration. A denuded land is easier to warm up, increasing biological activity and mineralization intensity. This occurs provided that removal of the stand component does not result in (frequent) waterlogging of a site, which would be limiting to the aerobic organisms at least until the lost functionality of the subsequent stand is restored. Soil without organic matter loses both water retention capacity and fertility. The decrease in forests is most distinctive in the lower parts of the catchment, which are more accessible, mostly non-waterlogged and more hydrologically suited for agriculture. Since the occurrence of precipitation also lowers in the spring-dependent parts of catchments as the cloud formation diminishes, the subsequent decline in river levels causes a decline in water supply to tributary-dependent parts of the catchment [67].

The greatest differences in the soil water-holding capacity are found between forested and treeless catchments. Flooding in forested catchment areas occurs in the aftermath of exceeding EDSP. Conversely, treeless catchments are affected by flash floods even after precipitation ˂30 mm. The protection of the water retention capacity of the catchment consists primarily in the prevalence of unbroken stretches of forests. Young open forest stands resemble treeless zones in terms of the water balance. Only closed stands over 20 years of age reach a water balance comparable to that of adults. Even though homogeneous forest stands provide hydric functionality similar to richly structured mixed forests, richly structured forests appear more resilient to climate change. Protecting the hydric functions of forests during climate

• Promotion of the transformation of tree species composition in favor of the natural state, with a natural proportion of trees within each stand type

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Drought stress in forest stands has been shown to reduce both transpiration and the water content in plants [68, 69]. This occurs because of the loss of assimilation apparatus, thus reducing leaf area available for transpiration, but also because of the reduced availability of nutrients, which convert to a dehydrated state in a differentiated way [70]. At higher humidity, there is more Ca2+ and Mg2+ present in the soil solution, and at the same time, K+ is better released by mineralization processes. This is due to the size of the hydration envelope of the ions, which conditions their hydration energy for various nutrients in a differentiated way. This is necessary for the nutrient to be taken up by the plant. To hydrate diverse ions, different amounts of water molecules are needed, so potassium is absorbed at lower soil moisture than magnesium or calcium—two elements that frequently prove nutritionally deficient even though they may be at an optimal concentration in the soil.
