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

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

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

$$\text{DP} = \text{IR} + \text{P} - \Delta \text{S} - \text{RO} - \text{ET} \tag{1}$$

where DP: deep percolation; IR: irrigation; P: precipitation; RO: surface run-off; ET: evapotranspiration; ΔS: soil water storage.

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 important environment for the replenishment of groundwater supplies.

**Figure 3.**

*The small water cycle in relation to geological subsoil: Communication of soil water and groundwater.*

The subsurface water can be simply divided into soil water and groundwater. Although it is the same infiltrated surface water, these two divisions differ significantly from one another mainly in the ratio of forces acting on them. Soil water can be divided into three categories, namely adsorption, capillary and gravitational water.

The soil and rock environments can be classified into two zones in terms of saturation of the environment with water. The environment with the presence of air in pores may be termed the aerated unsaturated zone, where adsorption and pellicular water predominate, and gravitational water preponderates only for a limited period. On the contrary, the environment without the presence of air in pores (filled with water) is designated as a saturated aquiferous zone where gravitational water not bound by adsorption and capillary forces prevails. This water may be freely moving or maybe in the form of capillary water, filling small capillary pores.

The zone immediately adjacent to the aquiferous zone itself, that is, groundwater level, is the capillary fringe zone. Capillary water predominates in this zone. Adsorption water and, depending on the circumstances, gravitational water, may also be present. The capillary water completely fills capillary pores and is maintained by a capillary rise from the groundwater level in the zone. Capillary forces create a negative pore water pressure (under pressure). Thus, water cannot be collected from the environment and responds merely to groundwater level fluctuations. From hydrogeology and groundwater hydraulics, the capillary fringe zone can be included in the unsaturated (non-aquiferous) zone. Contrarily, in hydropedology, we work with the capillary fringe zone as with the saturated zone, which significantly affects the physico-chemical properties of the soil and is important in terms of the water supply of the soil environment in agriculture.

In terms of replenishing groundwater reserves by infiltration, gravitational water is the most significant. Gravitational water is used during infiltration, especially for the area of the rock environment above the groundwater level, that is the unsaturated environment. This includes the area between the groundwater level and the subsurface soil-water zone. The capillary fringe zone can also be ranked in this category.

**59**

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

filled with water and when it dries.

groundwater reservoir.

significant reduction in infiltration.

groundwater reserves were continually replenished.

The principle of water infiltration into the rock environment in the unsaturated zone can be expressed by gravitational and water potentials. In particular, infiltration depends on the characteristics of the particular soil or weathered particles (grain size, structure, organic matter content, geological activity, stratigraphy, etc.). Infiltration is determined experimentally for each specific soil type. For this purpose, moisture curves are used, which express the relationship between capillary pressure and moisture. The curves differ (hysteresis of the curves) when the soil is

Vertical flow of infiltrated water through the soil medium is such that during infiltration, pores in the upper soil layer become increasingly saturated with rainwater until saturation of the water-holding capacity is reached, whereupon the saturated zone shifts gravitationally deeper in the soil profile. This occurs because semi-capillary and non-capillary pores are systematically filled with water above the hydrolimit of the water-holding capacity and water moves with gravity in terms of saturated flow according to Darcy's law. As rainwater supply ends, due to termination of the particular rain event, saturation is reduced, and gravitational flow of water slows down and gradually begins to be controlled by the hydraulic conductivity of the particular type of the soil. Water dissipated in the environment and movement is practically stopped. If the rainwater supply is sufficient, infiltrated water may eventually reach the groundwater level, which is progressively raised. Due to gravitational drainage into the body of groundwater, the saturation of the soil environment gradually decreases, and the unsaturated zone is created again. The process of infiltration through the soil environment substantially affects the quality of the infiltrated water, both positively, when it can significantly reduce pollution and thus protect groundwater against chemical or microbial contamination, but also negatively, in the case of contaminated soils (by means of anthropogenic activity, such as the. Enormous doses of industrial fertilizers applied to agricultural soils). Here, the contaminated infiltrated water can lead to the deterioration of the

At present (i.e. in this current episode of anthropogenically driven climate change), it is of utmost importance to maintain the soil environment in as favorable as possible a condition in terms of enabling infiltration of rainwater into the soil environment or, more precisely, into the groundwater collector. The principal negative factors include soil compaction, the loss of soil structure and the reduction of organic matter content in the soil. These three factors significantly reduce the water-holding capacity of the soil, that is, the ability to retain and gradually release water, either in the form of evapotranspiration or infiltration into the groundwater reservoir. Vast impermeable anthropogenic surfaces (asphalt, concrete, roofs, etc.) also inflict a

Nowadays, it is highly desirable to ensure infiltration of rainwater from these areas by appropriate technical and biotechnical measures, thus preventing their rapid surface or sub-surface run-off. Groundwater recharge in the Central European region historically took place in the colder half of the year, mainly from snowmelt. In this region this represented 3–4 months a year, when the zone between soil water and groundwater level was saturated and thus the regional

In the last 20 years, probably due to climate change, but also relevant alterations in landscape utilization, the saturation period of this zone has been significantly shortened and, consequently, there has been limited replenishment of groundwater supplies. A key role is played by noticeably lower snow reserves in the winter months, the overall temperature elevation during the year (i.e. increased evapotranspiration), and changes in rainfall distribution (accumulation of rainfall and decreased soil absorption capacity). Groundwater recharge is thus

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

*Soil Moisture Importance*

gravitational water.

**Figure 3.**

The subsurface water can be simply divided into soil water and groundwater. Although it is the same infiltrated surface water, these two divisions differ significantly from one another mainly in the ratio of forces acting on them. Soil water can be divided into three categories, namely adsorption, capillary and

*The small water cycle in relation to geological subsoil: Communication of soil water and groundwater.*

The soil and rock environments can be classified into two zones in terms of saturation of the environment with water. The environment with the presence of air in pores may be termed the aerated unsaturated zone, where adsorption and pellicular water predominate, and gravitational water preponderates only for a limited period. On the contrary, the environment without the presence of air in pores (filled with water) is designated as a saturated aquiferous zone where gravitational water not bound by adsorption and capillary forces prevails. This water may be freely moving

The zone immediately adjacent to the aquiferous zone itself, that is, groundwater level, is the capillary fringe zone. Capillary water predominates in this zone. Adsorption water and, depending on the circumstances, gravitational water, may also be present. The capillary water completely fills capillary pores and is maintained by a capillary rise from the groundwater level in the zone. Capillary forces create a negative pore water pressure (under pressure). Thus, water cannot be collected from the environment and responds merely to groundwater level fluctuations. From hydrogeology and groundwater hydraulics, the capillary fringe zone can be included in the unsaturated (non-aquiferous) zone. Contrarily, in hydropedology, we work with the capillary fringe zone as with the saturated zone, which significantly affects the physico-chemical properties of the soil and is important in

In terms of replenishing groundwater reserves by infiltration, gravitational water is the most significant. Gravitational water is used during infiltration, especially for the area of the rock environment above the groundwater level, that is the unsaturated environment. This includes the area between the groundwater level and the subsurface soil-water zone. The capillary fringe zone can also be ranked in this category.

or maybe in the form of capillary water, filling small capillary pores.

terms of the water supply of the soil environment in agriculture.

**58**

The principle of water infiltration into the rock environment in the unsaturated zone can be expressed by gravitational and water potentials. In particular, infiltration depends on the characteristics of the particular soil or weathered particles (grain size, structure, organic matter content, geological activity, stratigraphy, etc.). Infiltration is determined experimentally for each specific soil type. For this purpose, moisture curves are used, which express the relationship between capillary pressure and moisture. The curves differ (hysteresis of the curves) when the soil is filled with water and when it dries.

Vertical flow of infiltrated water through the soil medium is such that during infiltration, pores in the upper soil layer become increasingly saturated with rainwater until saturation of the water-holding capacity is reached, whereupon the saturated zone shifts gravitationally deeper in the soil profile. This occurs because semi-capillary and non-capillary pores are systematically filled with water above the hydrolimit of the water-holding capacity and water moves with gravity in terms of saturated flow according to Darcy's law. As rainwater supply ends, due to termination of the particular rain event, saturation is reduced, and gravitational flow of water slows down and gradually begins to be controlled by the hydraulic conductivity of the particular type of the soil. Water dissipated in the environment and movement is practically stopped. If the rainwater supply is sufficient, infiltrated water may eventually reach the groundwater level, which is progressively raised. Due to gravitational drainage into the body of groundwater, the saturation of the soil environment gradually decreases, and the unsaturated zone is created again.

The process of infiltration through the soil environment substantially affects the quality of the infiltrated water, both positively, when it can significantly reduce pollution and thus protect groundwater against chemical or microbial contamination, but also negatively, in the case of contaminated soils (by means of anthropogenic activity, such as the. Enormous doses of industrial fertilizers applied to agricultural soils). Here, the contaminated infiltrated water can lead to the deterioration of the groundwater reservoir.

At present (i.e. in this current episode of anthropogenically driven climate change), it is of utmost importance to maintain the soil environment in as favorable as possible a condition in terms of enabling infiltration of rainwater into the soil environment or, more precisely, into the groundwater collector. The principal negative factors include soil compaction, the loss of soil structure and the reduction of organic matter content in the soil. These three factors significantly reduce the water-holding capacity of the soil, that is, the ability to retain and gradually release water, either in the form of evapotranspiration or infiltration into the groundwater reservoir. Vast impermeable anthropogenic surfaces (asphalt, concrete, roofs, etc.) also inflict a significant reduction in infiltration.

Nowadays, it is highly desirable to ensure infiltration of rainwater from these areas by appropriate technical and biotechnical measures, thus preventing their rapid surface or sub-surface run-off. Groundwater recharge in the Central European region historically took place in the colder half of the year, mainly from snowmelt. In this region this represented 3–4 months a year, when the zone between soil water and groundwater level was saturated and thus the regional groundwater reserves were continually replenished.

In the last 20 years, probably due to climate change, but also relevant alterations in landscape utilization, the saturation period of this zone has been significantly shortened and, consequently, there has been limited replenishment of groundwater supplies. A key role is played by noticeably lower snow reserves in the winter months, the overall temperature elevation during the year (i.e. increased evapotranspiration), and changes in rainfall distribution (accumulation of rainfall and decreased soil absorption capacity). Groundwater recharge is thus

#### *Soil Moisture Importance*

usually carried out during longer term, higher rainfall events. In the case of torrential rain, the surface zone is rapidly saturated and hence minimum infiltration, and erosive strong surface run-off occurs. Contrarily, during long-term moderate rain, the entire transitional zone gradually saturates to the groundwater level, and thus its reserves are replenished.

Groundwater reservoirs are also replenished at tectonic faults (fractures). The entire soil body need not be saturated within the process of infiltration, but gravitational water can flow because of fissure permeability, replenishing the groundwater reserves.

#### **2.4 The soil-forest-water-civilization nexus**

#### *2.4.1 The elements of life*

The soil-forest-water-civilization nexus has never been more important than at present. The Ancient Greeks recognized four basic elements of life: fire, water, air and soil. Yet throughout history, perturbation of the hydrosphere, atmosphere and geosphere has created huge issues for humanity and the rest of the Biosphere.

Trees are an essential component of most ecosystems on our planet, and the forests of the world play key roles in the hydrological cycle, nutrient cycles and the carbon cycle. Deforestation undermines ecosystem function upon which we rely for our very survival. Forests are major contributors to rainfall, with the Amazon rainforest producing some 70% of precipitation in the Rio de Plata river basin [72]. Forests also play a crucial role in temperature regulation, not only as repositories for carbon, but in terms of evapotranspiration and the production of microbial flora and biogenic volatile organic compounds which act as condensation nuclei for cloud formation and rain events. It is estimated that deforestation may account for as much as 18% of current global warming [73]. Forests purify surface and ground water [74]. Deforestation also reduces soil structure and organic carbon content, negatively impacting the water-holding capacity [75]. Environmental degradation leads to economic collapse and social instability [76]. Healthy forests and healthy soils are inextricably linked. Deforestation has three significant impacts: soil erosion, soil salinization and eutrophication.

#### *2.4.2 Soil erosion*

The incredible diversity of the biosphere in its many forms speaks to a complex foundation upon which such a magnificent edifice is built. Yet terrestrial ecosystems are almost entirely dependent upon a thin, living skin, stretching across some fifty million square kilometers, but with a mean depth of only 15 cm: the soil. Most plants need soil, and plants form the basis of most terrestrial food chains. Yet in the last 150 years, we have lost 50% of the planet's topsoil through soil erosion. Lester W. Brown, the President of the Earth Policy Institute, has written that civilization can survive the loss of its oil reserves, but it cannot survive the loss of its soil reserves [77].

Soil erosion is not a new problem. Plato bemoaned the fact that the soil of Greece was, by his own time, eroding, observing that 'what now remains compared with what then existed is like the skeleton of a sick man, all the fat and soft earth having wasted away, and only the bare framework of the land being left' (in Glacken [78]). Around 60 BC, Lucretius, the philosopher and poet, recognized the seriousness of soil exhaustion in Italy. He thought that the Earth itself was dying [79]. A comprehensive review of the historical significance of soil erosion and the contribution of deforestation to this can be found in Dotterweich [80].

**61**

reverse.

*2.4.3 Eutrophication*

*2.4.4 Soil salinization*

around 2 billion dollars each year [88].

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

lower soil moisture through evapotranspiration [85].

42 billion dollars per year, impacting 170 million people [86].

logical cycle, shifting water from the soil back to the atmosphere.

Accelerated erosion has been occurring in Britain since the first clearances of primeval forest 5000–6000 years ago [81]. While early human agriculturalists used hand-held tools, maintaining a rough surface, allowing infiltration, later iron tools smoothed the surface, leading to run-off and erosion. By medieval times, many European villages had been abandoned as a result of soil erosion, elevating food prices due to crop failure and leading to social instability [82]. Today, 751 million ha of the planet's soil has been severely eroded [83]. Overgrazing by livestock and intensive agricultural practice has led to huge swathes of erosion. But deforestation has been one of the most significant contributors to the erosion crisis facing the planet. One and a half million square kilometers of dense tree cover were lost between 2000 and 2012 [84]. Shallow tree roots bind soil aggregates, increasing soil cohesion, while protecting against surface wash erosion. Deeper roots anchor the regolith to the bedrock, preventing landslides, debris flows and mudflows. Trees also reduce the load from

Soil production takes many years, and today losses far exceed formation. In China, the soil is being lost 54 times faster than it is being formed, leading to huge economic and social insecurity. In the case of China, soil loss accounts for the loss of

It is thought that the Babylonian and Sumerian kingdoms collapsed due to soil erosion, blocking irrigation systems [87]. Once the soil is gone, the risk of flooding after heavy rain increases dramatically. The trees form a crucial link in the hydro-

Wind erosion is an equally serious threat to humanity. The Dust Bowl in the USA stands as a striking example, where a 10-year collapse in agriculture was due to soil erosion driven by agricultural mismanagement in the 1930s. On Black Sunday, 14 April 1935, the sunlight was blocked out by the dust, when three million tonnes of topsoil from the Midwest was blown into the atmosphere. The Dust Bowl forced around two and a half million people to flee from their mid-west farms and head to California.

Soil erosion contributes to another major threat to our planet, eutrophication. Eutrophication is caused by nutrients being washed into the hydrosphere from the soil. Soil itself is a nutrient bomb, and so erosion delivers huge amounts of nutrients into streams, rivers, lakes and the oceans, leading to hypoxia, cyanobacterial blooms, toxic red tides and fish death. In Europe, Asia and North America, 50% of freshwater bodies are now eutrophic, while dead zones are a regular occurrence in the oceans, devastating fish populations. In the US alone, eutrophication costs

Deforestation also leads to soil salinization. Currently, 25% of the world's cropland is affected, while in Africa, this figure is 50% [89]. By 2050 it is estimated that some 50% of cropland will have productivity halved due to build-up of salt in the surface soil [90]. Nagendran [91] observes that salinization is the most striking effect of agriculture in all parts of the world. Soil salinization is very difficult to

Salinization is a particular threat to Australian agriculture, given that most of the country is desert. In the Murray Darling Basin, 63% of the forested area has been converted to cropland in the last 200 years [92]. This has led to increased downward water fluxes below the root zone by one to two orders of magnitude [93] because the trees are no longer performing their role as water shifters from

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

*Soil Moisture Importance*

groundwater reserves.

*2.4.1 The elements of life*

thus its reserves are replenished.

**2.4 The soil-forest-water-civilization nexus**

sion, soil salinization and eutrophication.

deforestation to this can be found in Dotterweich [80].

*2.4.2 Soil erosion*

reserves [77].

usually carried out during longer term, higher rainfall events. In the case of torrential rain, the surface zone is rapidly saturated and hence minimum infiltration, and erosive strong surface run-off occurs. Contrarily, during long-term moderate rain, the entire transitional zone gradually saturates to the groundwater level, and

Groundwater reservoirs are also replenished at tectonic faults (fractures). The entire soil body need not be saturated within the process of infiltration, but gravitational water can flow because of fissure permeability, replenishing the

The soil-forest-water-civilization nexus has never been more important than at present. The Ancient Greeks recognized four basic elements of life: fire, water, air and soil. Yet throughout history, perturbation of the hydrosphere, atmosphere and geosphere has created huge issues for humanity and the rest of the Biosphere. Trees are an essential component of most ecosystems on our planet, and the forests of the world play key roles in the hydrological cycle, nutrient cycles and the carbon cycle. Deforestation undermines ecosystem function upon which we rely for our very survival. Forests are major contributors to rainfall, with the Amazon rainforest producing some 70% of precipitation in the Rio de Plata river basin [72]. Forests also play a crucial role in temperature regulation, not only as repositories for carbon, but in terms of evapotranspiration and the production of microbial flora and biogenic volatile organic compounds which act as condensation nuclei for cloud formation and rain events. It is estimated that deforestation may account for as much as 18% of current global warming [73]. Forests purify surface and ground water [74]. Deforestation also reduces soil structure and organic carbon content, negatively impacting the water-holding capacity [75]. Environmental degradation leads to economic collapse and social instability [76]. Healthy forests and healthy soils are inextricably linked. Deforestation has three significant impacts: soil ero-

The incredible diversity of the biosphere in its many forms speaks to a complex foundation upon which such a magnificent edifice is built. Yet terrestrial ecosystems are almost entirely dependent upon a thin, living skin, stretching across some fifty million square kilometers, but with a mean depth of only 15 cm: the soil. Most plants need soil, and plants form the basis of most terrestrial food chains. Yet in the last 150 years, we have lost 50% of the planet's topsoil through soil erosion. Lester W. Brown, the President of the Earth Policy Institute, has written that civilization can survive the loss of its oil reserves, but it cannot survive the loss of its soil

Soil erosion is not a new problem. Plato bemoaned the fact that the soil of Greece was, by his own time, eroding, observing that 'what now remains compared with what then existed is like the skeleton of a sick man, all the fat and soft earth having wasted away, and only the bare framework of the land being left' (in Glacken [78]). Around 60 BC, Lucretius, the philosopher and poet, recognized the seriousness of soil exhaustion in Italy. He thought that the Earth itself was dying [79]. A comprehensive review of the historical significance of soil erosion and the contribution of

**60**

Accelerated erosion has been occurring in Britain since the first clearances of primeval forest 5000–6000 years ago [81]. While early human agriculturalists used hand-held tools, maintaining a rough surface, allowing infiltration, later iron tools smoothed the surface, leading to run-off and erosion. By medieval times, many European villages had been abandoned as a result of soil erosion, elevating food prices due to crop failure and leading to social instability [82]. Today, 751 million ha of the planet's soil has been severely eroded [83]. Overgrazing by livestock and intensive agricultural practice has led to huge swathes of erosion. But deforestation has been one of the most significant contributors to the erosion crisis facing the planet. One and a half million square kilometers of dense tree cover were lost between 2000 and 2012 [84].

Shallow tree roots bind soil aggregates, increasing soil cohesion, while protecting against surface wash erosion. Deeper roots anchor the regolith to the bedrock, preventing landslides, debris flows and mudflows. Trees also reduce the load from lower soil moisture through evapotranspiration [85].

Soil production takes many years, and today losses far exceed formation. In China, the soil is being lost 54 times faster than it is being formed, leading to huge economic and social insecurity. In the case of China, soil loss accounts for the loss of 42 billion dollars per year, impacting 170 million people [86].

It is thought that the Babylonian and Sumerian kingdoms collapsed due to soil erosion, blocking irrigation systems [87]. Once the soil is gone, the risk of flooding after heavy rain increases dramatically. The trees form a crucial link in the hydrological cycle, shifting water from the soil back to the atmosphere.

Wind erosion is an equally serious threat to humanity. The Dust Bowl in the USA stands as a striking example, where a 10-year collapse in agriculture was due to soil erosion driven by agricultural mismanagement in the 1930s. On Black Sunday, 14 April 1935, the sunlight was blocked out by the dust, when three million tonnes of topsoil from the Midwest was blown into the atmosphere. The Dust Bowl forced around two and a half million people to flee from their mid-west farms and head to California.

### *2.4.3 Eutrophication*

Soil erosion contributes to another major threat to our planet, eutrophication. Eutrophication is caused by nutrients being washed into the hydrosphere from the soil. Soil itself is a nutrient bomb, and so erosion delivers huge amounts of nutrients into streams, rivers, lakes and the oceans, leading to hypoxia, cyanobacterial blooms, toxic red tides and fish death. In Europe, Asia and North America, 50% of freshwater bodies are now eutrophic, while dead zones are a regular occurrence in the oceans, devastating fish populations. In the US alone, eutrophication costs around 2 billion dollars each year [88].

#### *2.4.4 Soil salinization*

Deforestation also leads to soil salinization. Currently, 25% of the world's cropland is affected, while in Africa, this figure is 50% [89]. By 2050 it is estimated that some 50% of cropland will have productivity halved due to build-up of salt in the surface soil [90]. Nagendran [91] observes that salinization is the most striking effect of agriculture in all parts of the world. Soil salinization is very difficult to reverse.

Salinization is a particular threat to Australian agriculture, given that most of the country is desert. In the Murray Darling Basin, 63% of the forested area has been converted to cropland in the last 200 years [92]. This has led to increased downward water fluxes below the root zone by one to two orders of magnitude [93] because the trees are no longer performing their role as water shifters from

soil to atmosphere. This has resulted in a rapid rise in the groundwater table at a rate of∼1 m year<sup>−</sup><sup>1</sup> , leading to the salinization of some 5.7 million ha of farmland, devastating harvests [94].

Similar large-scale salinization events have been recorded in California, north-west India and much further back in time, in Ancient Mesopotamia [95–97].

#### *2.4.5 The biotic pump*

Finally, deforestation leads to huge changes in the rainfall distribution patterns on our planet. The biotic pump theory [98] proposes that evapotranspiration creates lower pressure above forest canopies, drawing in moist air from the oceans, and supplying precipitation far inland. The reduction in evapotranspiration as a result of deforestation leads to an increase in the height of the convective boundary layer because of the stronger sensible heat flux over pastures. This is less conducive to rainfall formation. Deforestation is thought to have contributed 60% to the drought conditions that led to the collapse of the Mayan empire [99].

Much like climate destabilization, the biotic pump acts across national boundaries, requiring international collaboration. If inland nations carry out significant deforestation, the impacts are not only felt within that nation, in terms disruption to the local hydrological cycle, exacerbating flood risks, landslides, soil erosion and water purity, but also in nations that lie between the oceans and the deforested region, as the pressure gradient is no longer as strong, reducing the strength of the pump.

Critics of the biotic pump theory have argued that air movements as a result of condensation are multi-directional, representing an isotropic (uniform in all directions) process and this means that there will not be any uni-directional, net flow from ocean to continental landscapes [100]. In this orthodox approach, mass air movements alone drive the hydrological cycle across latitudinal cells set up by temperature gradients due to the uneven heating from the sun as a result of the axial tilt and curvature of the Earth.

However, it has been demonstrated experimentally that condensation can trigger anisotropic, uni-directional flow, supporting the biological pump theory [101, 102]. Sheil [103] points out that disruption of the biological pump through deforestation can lead to dramatic, non-linear transitions in local climate, from wet to dry regimes. Interestingly, reforestation can lead to a similarly dramatic transition in the opposite direction, from a dry to a wet local climate regime [103]. However, there is no guarantee that reforestation will return the region to an identical ecological state as that prior to deforestation, as species may have suffered extinction, and recolonization routes may no longer exist.

#### *2.4.6 Regime shifts*

Of greater concern yet is the fact that such widescale changes resulting from deforestation and the destabilization of the soil-water relationship may lead to regime shifts. Lees et al. [104] define regime changes as abrupt changes on several trophic levels, leading to rapid ecosystem reconfiguration between alternative states. Both structures and processes are transformed and such changes, in turn, result in significant alterations in ecosystem services [105, 106]. Complex non-linear systems, such as ecosystems, become vulnerable to phase shifts, where relatively small changes in an already stressed system can result in the irreversible collapse of the system, switching, for example, from a wet forested state to a dry savanna, and creating an alternative equilibrium, with devastating consequences [107–109]. Such shifts are more likely to occur as anthropogenic perturbation increases [110].

**63**

**Acknowledgements**

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

**3. Conclusion**

the spread of regime shifts across the biosphere [113].

relationship between human needs and natural resources.

way ahead and a place for our own sub-species within the biosphere.

Of additional concern is the reality that ecosystems are interconnected to other ecosystems, to such an extent that a regime change in one part of the biosphere can catalyze changes in other ecosystems. One example relates to regime changes in the Arctic, wherein sea-ice changes lead to reorganization of tropical convection that in turn triggers an anticyclonic response over the North Pacific, resulting in significant drying over California [111], potentially leading to regime change. Ecosystems are sub-systems, not isolated systems. Thus, changes run throughout the biosphere, impacting on all levels of organization, in non-linear ways. We would expect this in any self-organizing system, where feedback dictates context and change. One such conduit is the soundscape, wherein ecological simplification can lead to radical transitions at the ecosystem level facilitated by the absence of audible cues [112]. Another feedback conduit is the hydrological cycle, and forests play a central role here. Interfering with water relations can have huge impacts on regime stability and

Forest soil water balance plays an essential, central role in ecosystem functionality. The modification of water balance within forests can enhance self-regulation of all ecosystems in a landscape, but intensive, anthropogenic landscape transformation can negatively impact it. Human activities, such as deforestation, have had damaging impacts on evaporation, precipitation and run-off. The protection of forest water balance has been highlighted as a priority through coordinated research based on analysis of soil properties and ecosystem function restoration. Underpinning any hope of achieving this lies the urgency of attaining a sustainable

Thus, we see that forests are essential components in both the hydrological cycle and in soil functionality, while also playing a crucial role in the carbon cycle. Forests, much like soil and water, are currently under-appreciated by the human race, yet our futures rely on their restoration and respect. Kravčík [114] have called for a new paradigm in order to rescue humanity from a crisis beyond our imagining: regime shifts and the functional collapse of the terrestrial and aquatic ecosystems. Such a paradigm no longer views water as an isolated entity, a fixed renewable resource and having little to do with the suite of environmental crises facing us, along with the coming economic and societal collapse undoubtedly awaiting us on our current trajectory. Instead, they call for a prioritization of the restoration of the water balance at all levels, but particularly at the level of the small water cycle. Intrinsic to this is healthy soils and healthy forests. The soil-forest-water-civilization nexus must urgently be understood as a synergy, connected and united within the Earth system if we are to find a constructive

This chapter was supported with the institutional support of Mendel University in Brno financed from the institutional support of the development of the research organization provided by the Ministry of Education, Youth and Sports, Czech Republic.

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

Of additional concern is the reality that ecosystems are interconnected to other ecosystems, to such an extent that a regime change in one part of the biosphere can catalyze changes in other ecosystems. One example relates to regime changes in the Arctic, wherein sea-ice changes lead to reorganization of tropical convection that in turn triggers an anticyclonic response over the North Pacific, resulting in significant drying over California [111], potentially leading to regime change. Ecosystems are sub-systems, not isolated systems. Thus, changes run throughout the biosphere, impacting on all levels of organization, in non-linear ways. We would expect this in any self-organizing system, where feedback dictates context and change. One such conduit is the soundscape, wherein ecological simplification can lead to radical transitions at the ecosystem level facilitated by the absence of audible cues [112]. Another feedback conduit is the hydrological cycle, and forests play a central role here. Interfering with water relations can have huge impacts on regime stability and the spread of regime shifts across the biosphere [113].
