Afforestation has been used as a way to make a dry land greener so as to prevent desert to migrate, the so-called Three North Afforestation Project (TNAP) in China is a good example. It has been found that this measure is not always effective as trees consume more water from the soil than bare soil or grassland, so recharge to the aquifer is reduced. Our study shows that, at climate zones with 300 mm of annual precipitation, it is not sustainable because soil water is reduced by 30-90% off original water content. What do you know about this change in other climate zones? Please share with us.
Please take a look at these useful RG links.
Article Impacts of afforestation on groundwater resources and quality
Article Effects of afforestation on groundwater recharge and water b...
There are many water yield studies due to deforestation and afforestation summarized by Hibbart about 1962. Most of these studies were not in or at desert interface. I heard a presentation by Moshe Cohen about 1995 where past deforestation of cedars had led to dry creeks, excess sediment and bare soil and conversion to desert. His work summarized scalping efforts to dig small holes or pits where individual cedars were replanted, and some temporary efforts to provide water to stave off mortality until their roots developed may have been necessary. Each scalped pit encouraged rain water to be contained for that tree. Eventually the cedar forest was reestablished, streams flowed again and there was no longer desert. Granted vegetation uses water, and some species more than others. It would be difficult to assume that afforestation would necessarily recharge groundwater. But trees and other vegetation help soils develop so water can be absorbed and erosion reduced. In one of Luna Leopoldo papers in SW USA, he found that erosion in dry lands was actually greater during droughts than during wet periods due to the difference in vegetation cover. The retention and release of water would be delayed and reduce runoff and flash flooding that can be a problem in dry areas. Exceeding dry soils seem to be unable or difficult to absorb intense rainfall, like a forest or grassland soil could. In our area of SE USA, pine has been shown to use substantially more water than hardwoods or grasslands, so selection of forest or other cover species can be critical, and often native species will be better adapted to the regional extremes in rainfall, weather, disease, etc.
Luna Leopold- my tablet has its own mind sometimes. Luna Leopold, geomorphologist, had a major position with USGS before he became a professor at USC. His father, Aldo Leopold, was a famous conservationist. Both were well published. Some of Luna’s papers in SW USA would be interesting relative to your subject.
The positive impact of forests on groundwater nutrition is usually not in doubt. This is due to the transfer of a significant part of the surface water flow to the underground. Groundwater, in turn, feeds rivers, providing a higher water level in them in winter and summer (the period of autumn). In the spring and summer rains, more water enters the rivers from treeless areas due to surface runoff. The latter is inevitably associated with water pollution by products of soil erosion and other agents, as well as with the likelihood of floods and their destructive power. The great floods in the yellow river basin, the disastrous floods of the Mississippi, don, Vistula, and many other rivers are largely related to deforestation in their basins.
The main reason for increasing ground and reducing surface runoff by forests is to maintain good soil permeability under them (protected by forest floor, loosened by roots, etc.), as well as more uniform moisture flow to its surface (slow snow melting intensity, dampening of rain force by the forest canopy, etc.). During the rain, elastic water jets fall with force on the branches and gently flow down from them to the forest floor, consisting of fallen leaves and forest grasses. Through the litter, water slowly goes into the soil and flows down its deep layers into rivers. Thus, the forest protects the soil from erosion, river banks from washouts. In winter, no more than 3-5% of precipitation is delayed on the foliage crowns, but the snow that falls on the forest lies there as a strong soft blanket. In coniferous forests, especially spruce forests, up to 60% of winter precipitation is delayed by crowns.
Snowmelt and rain water in the forest is intensively replenish the groundwater reserves. Groundwater resources under forest because in the forest there is an accumulation of moisture. In winter, the thickness of snow in the forest is greater than in the fields, so the soil freezes less. In the spring, it thaws faster and begins to absorb meltwater. Loose forest floor, mosses have a high water capacity. 1 m of this peculiar sponge can absorb up to 6 kg of rainwater in the southern taiga. In the forest, there is less wind speed and, consequently, evaporation. In summer, the litter reduces the heating of the soil and thus helps to preserve moisture in it. Under the protection of the forest, the land is slowly saturated with life-giving moisture.
Deforestation dramatically changes the flow pattern and hydrological regime of rivers, causing rapid spring floods and sharp shallowing of rivers in the summer. In order for the water-regulating value of forests to be displayed with maximum efficiency, they must be located evenly throughout the river's catchment area.
In the scientific literature, the term "desertification "is often used together with the term" degradation":" degradation and desertification","degradation or desertification". In the first case, the meaning should be understood that these are two different phenomena, in the second – they are synonyms. Thus, there is no clear division between the concepts of "degradation" and"desertification". Some scientists have tried to clarify these concepts and have obtained the equality of degradation and desertification, that is, land degradation of different degrees of manifestation and is itself desertification in arid areas. But this is not true for all possible degradation. For example, water erosion in conditions of rugged relief increases with increasing Guidetti climate. One thing is clear: anthropogenic desertification occurs as a result of various degradation processes. At the same time, the ecological state of the natural environment changes, degraded soils appear to varying degrees, their productivity decreases, that is, there is an environmental destabilization of the natural-soil environment. In this regard, it is possible to separate the phenomena of degradation and desertification: degradation is proposed to be considered as processes, and desertification – not so much as processes, but as the ecological state of soils and the environment. Thus, we can say that the complex of degradation processes leads to desertification of the territory.
Most often, soil degradation occurs under the combined influence of natural and anthropogenic factors, and anthropogenic influence creates prerequisites for a sharp activation of natural impacts. This can be seen in the South of the Volga upland, where the reduction of natural woody vegetation and high ploughing of the territory accelerated the rate of natural erosion, turning it into an anthropogenic one. Another example is the Volgograd Zavolzhye, where the involvement of naturally saline soils in irrigation over two or three decades has led to the emergence of huge tracts of second-saline land.
Until recently, the problems of desertification and land degradation were considered relevant mainly for arid territories, in particular for Central Asia and Kazakhstan. The scale and rate of land degradation in Russia seemed less significant and did not attract much attention. However, on the territory of the Russian Federation, there have long been and are expanding areas of high environmental tension that originated 30-50 years ago: deflated arable land of the Altai virgin land, anthropogenic desert in the Black lands region in Kalmykia, as well as territories in 27 subjects of the Russian Federation that are subject to intensive processes of land degradation. In our country, desertification manifests itself in the loss of fertile land resources, as well as in economic and social instability in the affected regions. Over the past few decades, the area of degraded land in Russia has grown by more than 1.6 times to more than 100 million hectares of desolate and desertification-prone farmland. It is home to about half of the country's population and produces more than 70% of agricultural products. The combination of low forest cover, flat terrain, high wind conditions and low precipitation with a high ploughed area has led to the fact that for the steppe zone of our country, the main types of degradation that lead to land desertification are water erosion and deflation.
It is known that in the steppe zone, an optimal proportionate ratio of arable land, forests and forage land contributes to increasing the stability and productivity of agricultural landscapes and hindering the development of desertification processes. However, recently there has been a heated discussion in the press between proponents of protective afforestation and proponents of restoring and preserving steppes. Nature conservation activities in Russia have traditionally been associated with tree planting and reforestation; on the contrary, the virgin steppe has traditionally been perceived as a "wild field", an empty place to be filled and improved. However, the idea of total afforestation of fallow lands has its opponents. Briefly consider both points of view.
The main purpose of protective forest stands is to prevent dust storms, reduce droughts and dry spells. Meliorative plantings reduce wind speed by 30-50%, improve the microclimate in the protected area, reduce evaporation from the water surface by 25-30%, and increase crop yields by 24-31%. In addition, HLS have a great environmental and social significance and a positive integrated impact on the environment, production activities and human health. Forested agro-territories expand food and feed bases for humans, domestic and wild animals, lengthen trophic links in the natural cycle and thereby increase the resistance of the agro-sphere to negative natural and anthropogenic impacts, reduce the intensity of meteorological factors in ecologically disadvantaged areas. Reclamation forests form the framework of a protective complex, and they occupy a key position in the design of agricultural landscapes. Having pronounced landscape-stabilizing properties, SLN significantly change the appearance of the territory, form the spatial division of land, to some extent regulating land use.
However, the current rate and quality of forest reclamation and forestry work in protective afforestation are low and often have a non-complex, fragmentary nature. Forest planting works are often carried out in gross violation of the current legislation. The selection of sites for afforestation is often carried out without the participation of specialists-agroforest reclaimers. The current state of protective forest stands is generally unsatisfactory, they are in a neglected state, often contaminated with industrial and household waste, damaged by fires, unauthorized logging, diseases and pests. More than half of the area occupied by plantations requires urgent forest management measures: generational change, reconstruction, improvement of sanitary conditions and improvement of reclamation efficiency of stands. Thus, artificial plantings are not long-term stable and exist depending on the investment of financial resources for their maintenance.
The geographical position of the arid steppes has determined their important ecological role as a barrier to aridization of the Northern territories. Multi-tiered closed herbage, which is dominated by cereals-xerophytes, delays surface runoff, preventing the development of water erosion, and protects the soil surface from direct sunlight, reducing the evaporation of soil moisture, and it is the predominance of evaporation over the arrival of moisture with precipitation that is the main feature of arid ecosystems. In addition, preserved steppe ecosystems and fallow lands are the habitat of a number of rare and endangered species of steppe animals and plants.
However, unfortunately, there is nothing to oppose to steppe grassy vegetation against dust storms in conditions of high ploughing of agricultural land. The most severe and destructive dust storms in the southern Russian steppes occur in late winter and early spring, when a large stationary anticyclone is located over the South-East of the European territory of Russia and Western Kazakhstan, blocking the Western transfer of air masses and maintaining its position in some years up to 1-1. 5 months. Take for example the North-East of the Krasnodar territory, which is considered to be the agricultural breadbasket of the South of Russia. Here, on average, about 75-85 dry days are observed during the summer period. During dust storms, the wind speed can reach more than 20-25 m/s. What kind of crop could we remove from agricultural fields on this territory, if they were outlined not by forest strips, but by areas of untouched steppe vegetation?
In addition, spontaneous self-restoration of fallow lands, as a passive method of preserving steppes, is an unreasonably long process that lasts for tens and hundreds of years. As an active way to restore steppes, a very promising method of creating so-called "agrosteps" is proposed. However, it also involves certain financial and labor costs for mechanized harvesting of steppe seed mixture, preparing the soil for sowing a mixture of seeds of steppe plants, fighting secondary weeds, and caring for agricultural crops in the first and subsequent years of life to eliminate the factor of inhibition of regenerative succession. Otherwise, the spread of certain invasive species that occupy a dominant position in the early stages of succession may block it and lead to the formation of long-existing weeds. The issue of restoration of steppe fauna, including ungulates, remains urgent, since poor grazing is necessary to maintain the balance of the steppe community. Not without reason, under the ecological restoration of steppe ecosystems, A. A. Tishkov understands a whole range of measures aimed at restoring ecosystems to a close to the natural state, including topography, microclimate conditions, hydrological regime, soil and vegetation cover and animal population. Taking into account all of the above factors, we would not argue that the cost of restoring grass ecosystems is lower than the cost of forest plantations. In our opinion, separate scientific research is needed to resolve this issue.
Thus, we see that both concepts – protective afforestation and steppe restoration-have both positive and not always manageable and predictable aspects. The latter are partly related to the human factor, as always happens with human intervention in natural processes, but in fact, protective afforestation and restoration of the steppes are also anthropogenic effects on nature.
It is clear that there can be no single solution to the question of the priority of an approach in combating desertification. Here we fully share the opinion of A. A. Chibilev and co-authors that the priority of certain types of phytomelioration should be determined by both the soil and landscape potential of the territory and the specific features of specific land users. It is necessary to choose the "Golden mean" and start, first of all, from the specifics of using a specific territory. For areas with different natural conditions and economic development necessary to apply different methods of environmental optimization: whether the ecological restoration of disturbed lands in the strictly protected and special protected areas, or agroforestry arrangement of agricultural landscape, which, however, does not exclude the preservation and restoration of steppe ecosystems as elements of cocarcea site. Historically, the steppes have always been the main suppliers of agricultural products for our country and will remain so in the future, despite possible downturns in agriculture, for example, as it happened in the 90s of the last century. This is a given that supporters of the "steppe" approach will have to accept. Protective afforestation has a longer history of development, during which, through trial and error, theoretical and technological techniques and methods of adaptive landshift arrangement of agricultural land were developed. The fact that currently the development of agroforestry science is not used at all, or is used with the grossest mistakes – is a consequence of the General socio-economic decline in all sectors of the national economy of our country. Let's hope that over time, protective afforestation and the" steppe " approach will co-exist peacefully within the framework of a single concept of the ecological framework of the territory of the South of the Russian Federation.
The main thing to note is that only a comprehensive programme of activities can bring tangible results in the fight against desertification, since desertification itself is a complex problem. In different territories, the focus should be on specific measures to combat the prevailing type of degradation, but the approach to the problem should still be comprehensive, since preventing the threat or elimination of one type of degradation does not guarantee against the emergence of another.
In my research on the subject I have found that:
Actual evaporation especially during and immediately after rainfall occurrences is difficult to quantify. Appreciation of the hydrographs on a seasonal or even monthly basis often masked any recharge prediction, even when daily evaporation data had been taken into account.
The occurrence of high conductivity porous or karst associated with bold relief and forest cover, restrict significantly the runoff volume in favour of recharge.
Prevailing recharge mechanism is important. When identified as direct recharge on the ground surface and transmission losses along a significant length attained by the stream network - in analogy to the size of the catchment – forest cover enhanced recharge no matter what the state of the surface water network (from wet for a few days after rainfall events to all year long).
In numerous cases studies of various annual P from ~400 mm to 1.000 mm Conifer (Pinophyta) forest cover favors recharge compared to the same geology and relief but no forest. In most cases examined forests were made of Pine-trees the leaves of which show low storage capacity.
Most of the case studies concerned various island environments in the Mediterranean and to a lesser degree mainland Greece. All island cases were classified as: 5 hyper-arid months with the rest of the months moving gradually to at least a month classified as humid in the middle of the wet season (according to Lang and De Martonne indeces).
In the whole of the bibliography I ve seen, the role of the forest cover, although controversial, in numerous cases proved to enfavour rain-water infiltration. Although the increased losses to traspiration must be acknowledged, vegetation restricts run-off volumes, and affects the microclimatic conditions by maintaining low temperature and high vapour pressure. Such conditions have proven to affect the rate of infiltration in the karst (Mangin, 1988). Field studies on limestone-dolomite watersheds that underwent changes of land use to reforestation, have shown surface runoff retardation in favour of ground water infiltration, with no measurable change in the total quantity of evapotranspiration or other losses (Sodemann et al. 1965; Snyder, 1963).
in our research we found we found a huge cost and effect of (vegetation change) on mobile sand movement, dust deposition rates, the rainfall\precipitation rates, surface temperature and surface wind rather than effect on economy.
Article Cost and effect of native vegetation change on aeolian sand,...
ِThe afforestations cause the decrease in reflection of sun rays by the ground (the albedo phenomena). If the albedo increases, it cause disperssion of the clouds and decrease of the rainfall. The lower the albedo (via afforstation) causes increase in rainfall and groundwater recharge.
- Badges
- Science topic
- Similar topics
- Computer Communications (Networks)
- Simulators