AFFORESTATION PRACTICES IN PREVENTING EROSION
IN WATERSHEDS OF TURKEY
Mahmut REİS
Alaaddin YÜKSEL
Orhan ERDAŞ
Fatih TONGUÇ
Abdullah E. AKAY
KSÜ, Faculty of Forestry, Forest Engineering Department,
46060 Kahramanmaraş, Turkey
E-mail: [email protected], [email protected],
[email protected], [email protected], [email protected]
ABSTRACT
Soil erosion is the major source of soil loss in the watersheds of Turkey. The percentage of eroded land in Turkey is approximately 90% in which 63% is severely and
very severely eroded, 20% is moderately eroded, and 7% is lightly eroded. A total of
67 million ha land surface faces to erosion and more than 400 million tons of topsoil
is lost each year. Besides, deposition of erosion and sediment yield in watersheds
dramatically decrease the economical lifetime of dam which are very important for
water resources and power generation. One of the most effective erosion control is
afforestation practices. In this study, the major erosion factors and the importance of
implementing appropriate afforestation methods were presented for watersheds in
Turkey.
Key Words: Erosion, Afforestation, Watershed, Land Use.
1. INTRODUCTION
Natural balances among plant, soil, and water have been deteriorated in the land
of Turkey due to excessive and unplanned usage of these renewable natural resources for centuries. This has resulted in considerable amount of soil loss which is
one of the most important problems in Turkey. Due to soil erosion and runoff, excessive sediment yield reaches to water resources, which leads to dramatic effects on the
soil quality, aquatic life, and the economic lifetime of the dams. Dams are the essential sources for electricity energy, city water, and irrigation in Turkey.
In order to restore the natural balance among the natural resources, sustainable
practices must be immediately applied in managing natural resources. This is also
necessary to retain the efficiency of the dams in generating electricity energy for
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industry. Besides, water itself is the main requirement for industry. For example,
iron-steel manufacturing industry requires 25 m3 water to produce 1 ton steel, 100 m3
water to produce 1 ton paper in cellulose manufacturing industry, and 750 m3 water
to produce 1 ton silk in silk manufacturing industry. Sufficient and clean water resources are crucial to supply city water for increasing population in Turkey. Finally,
enough water should be also reserved for agricultural productions.
In the last decade, hydrological function of forest has regained its importance as
water resources problem increases in Turkey. Forest cover increases the amount of
precipitation reaching the soil by decreasing the amount and intensity of the runoff
on forest surface. Especially forest litter plays an important role in preventing excessive runoff and stabilizes the flow regime, which significant reduces soil erosion.
Kittredge [1955], indicated that forest litter can hold up to 1-5 times more water
than its weight. He also stated that the water holding capacities are 150-350% and
360-460% for fresh needles and broadleaves, respectively. Blow [1955], found that
maximum water holding capacity of litter in mixed forests ranges from 200% to
250%. Furthermore, Curtis [1960], determined that litter under broadleaved trees
held 34.2% of precipitation with 192.3 cm intensity and 3 years duration. Özyuvacı
[1976], found that water holding capacity was 293% and litter weight was 4.55 ton/ha
under pseudomaques, while they were 280.8% and 6.92 ton/ha under coppice forests,
respectively. In this study, firstly, the main erosion factors were indicated, and then,
the necessity of afforestation in erosion control was presented in watersheds of Turkey.
2. EROSION FACTORS
The main erosion factors considered in this study are topographic, climatic,
vegetation cover, and soil erodibility factors. Topographic features that influence
erosion are slope steepness, length, and shape. On steep slopes, runoff can be very
erosive and easily transport detached sediment to downslope. On longer slopes, an
increased accumulation of surface flow results in increased rill erosion. In Turkey,
only 8.5% (6.584.600 ha) of the total land has less than 8% slope steepness. About
12.8% and 16.2% of the land has the slope steepness of 5-10% and % 10-15, respectively, while the rest of the land (62.5%) has more than 15% slope steepness. Besides,
the average altitude from the sea level for Turkey is 1132 m, which is about 800 m
higher than the average altitude in Europe [Erdaş and Yüksel, 1999].
The major climatic factors affecting erosion include temperature, humidity, solar
radiation, and wind. The effects of these factors become more evident on evaporation
and transpiration processes. These processes reduce soil water content and subsequently decrease runoff and surface erosion. Topographical structure over the land
of Turkey varies in different geographical regions. For example, mountains lie parallel to the sea shores in Blacksea and Mediterranean Regions, while they are perpen-
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dicular to the sea shores in Aegean Region. Therefore, the precipitation intensity also
varies in these regions. For example, Konya in Central Anatolia Region receives the
average annual precipitation of 278 mm, while Rize in Blacksea Region receives the
average annual precipitation of 2696 mm.
Erosion effects are more clearly seen on the coastal regions of Turkey, due to
high precipitation amounts in these regions. Erosion indexes change between 15.2
and 481.3 on yearly basis. These indexes also change between seasons. For example,
erosion indexes are 20.21, 21.97, 29.66 and 27.67 for spring, summer, autumn, and
winter, respectively [Doğan, 1995].
Vegetation cover plays a major role in reducing erosion. If the trees are removed,
open areas become vulnerable for dramatic soil erosion. During the last 30-40 years, a
significant portion of the world’s forest cover was removed by human activities. In
Turkey, deforestation due to human activities is even more catastrophic. Today, only
27% of the country is covered by forest (21.18 million/ha) and about half of this area
is subject to afforestation and erosion control studies [Anonymous, 2006].
About 34% of the land is used for agricultural production in Turkey. Agricultural lands are mostly susceptible to erosion since they are generally located in steep
sloped, infertile, and shallow lands. Besides, the rangeland areas, which are important for soil conservation, are converted into agricultural lands in last 5 decades.
Today, about 27% of the land is covered by rangelands. In Turkey, rangeland vegetation has been degraded because of heavy and unsuitable grazing. Having lack of
effective rangeland areas directed grazing activities into the forest lands. Therefore,
improper land use is also one of the main erosion factors in Turkey (Table 1).
Soil erodibility characterizes erosion tendency, depending on varied properties
of soil. Although active erosion is not observed on soils under dense and protective
vegetation cover, the erodibility indexes might be high in those kinds of soils due to
geological structure. Especially, neogen, plio-quarterner, volcanic sand,
Table 1. The area of land use classes in Turkey.
Land Use
I
Area (Ha)
5 012 537
Percent (%)
6.5
II
III
IV
V
VI
VII
VIII
6 738 702
7 574 330
7 201 016
165 547
10 238 533
36 288 553
3 455 513
8.8
9.9
9.4
0.2
13.4
47.3
4.5
cretase and eosene structure, and tufa, which cover large areas in Turkey, are susceptible to the erosion. Removing protective cover of such soils may cause even more
erosion if topographic and precipitation conditions are suitable.
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3. AFFORESTATION
Desertification is a land degradation problem of major importance in the semiarid regions of the Turkey. According to the Global Desertification Vulnerability
Map, mid-Anatolia has severe and very severe desertification problem. Deterioration
in soil and plant cover has adversely affected nearly 50 percent of the land areas as
the result of human mismanagement of cultivated lands and range lands.
In GAP (Southern Anatolia Project) region, soil erosion rates for Fırat river
reaches to 45 million ton in which large dams of Atatürk and Karakaya were established. Unfortunately, this rate reaches 21.4 million ton for Kızılırmak River, 14.1
million ton for Sakarya River and 12.6 million ton for Dicle River.
Table 2 indicates the sediment yield for some of the primary rivers in Turkey.
According to the previous studies, it was necessary to establish 18.5 million ha of
new forests (24% of the land) in Turkey. Afforestation studies reached up to 250 000
ha per year in the mid 1980’s and continued until 1987. However, the afforested areas
were decreased to 130 000 ha per year till 1991. Totaly 3.2 million ha was afforestated
by the end of 1991. After the year of 1991, about 130 000 ha per year should have
been afforestated for 142 years to complete rest of the required new forests (15.3
million ha).
Afforestation methods used in erosion control activities differ from the methods
used in general afforestation activities due to removal of topsoil in eroded lands.
Besides, there is insufficient organic matter, biological activities are reduced in these
lands, and parent material is exposed in some places due to shallow soils (Figure 1).
There are usually not enough water content and nutrition for the seedlings in
semi-arid eroded lands [Ürgenç, 1998]. In humid eroded lands, excessive runoff
occurs due to insufficient soil depth. Therefore, in afforestation studies, mechanical
erosion control structures (i.e. terraces) should be installed to hold water in arid and
semi-arid lands and to discharge water in humid land (Figure 2).
Table 2. Sediment amounts for primary rivers.
River Basin
Karasu, Keban
Tortum
Fırat, Dutluca
Dicle, Diyarbakır
Kızılırmak, İnönü
Yeşilırmak, Çarşamba
Kelkit
Ceyhan, Yeniköprü
Seyhan, Uçtepe
Göksu, Karahacık
B.Menderes, Söke
Gediz, Mania Köprüsü
Sakarya, Botbaşı
Filyos, Devecikıran
Dalaman, Suçatı
İyidere, Şimşirli
Average
Mean average
sediment (ton/km2)
525
2500
1167
1085
923
1521
1977
922
563
648
519
582
651
610
266
219
600
Total Sediment
(million/ton)
33,5
2,5
108,2
6,8
44,9
54,9
10,8
19,6
7,8
6,8
12,4
5,8
8,5
8,1
0,9
0,5
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Figure 1. The view of a land with active surface erosion.
Figure 2. Afforestation application on terraces in semi-arid lands.
In semi-arid lands, first, soil erosion should be reduced by applying physical (i.e.
cultivation) and biological (i.e. planting herbaceous) techniques. The coniferous species with deep root system should be selected such as Pinus nigra, Pinus brutia, Cedrus
libani, and Juniperus sp. Broadleaved trees (i.e. Quercus sp., Robinia pseudoacacia, Ailanthus sp., and Juglans sp.) should be also planted along with coniferous species to improve the nitrogen amount of the soil.
Converting the degraded forests to productive forests in Turkey would have
some advantages such as; protecting soil from erosion, preventing dams from the
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excessive sediment yield, supplying adequate and high quality water, supplying
recreational activities, providing work opportunities to villagers, and preventing air
pollution in urban settlement.
4. CONCLUSIONS
Without implementing sustainable management practices, the increasing demands on the natural resources can cause long term environmental impacts on plant,
soil, and water resources in Turkey. Especially, unplanned usage of forests results in
excessive amount of soil loss, which is the most important natural problem in Turkey. This problem also leads to dramatic effects on the soil quality, aquatic life, and
the economic lifetime of the dams. Thus, necessary soil conservation precautions
should be taken to prevent soil erosion and sediment yield in watersheds of Turkey.
Afforestation practices are the most effective erosion control methods that include
direct-seeding, planting seedlings, and natural and/or artificial regeneration activities. Along with afforestation, some precautions need to be taken such as rehabilitating grazing lands and rangelands, applying appropriate land use types according to
land cover classification, and preventing illegal cuttings. Besides, mechanical measures such as terracing watersheds of dams and installing barriers and fences in plantations.
5. REFERENCES
Kittredge, J, 1955, “Litter and Forest Floor of The Chaparral in Parts of The San Dimas Experimental Forest”, California, Hilgardia, Vol. 23. No.13.
Blow, F.E., 1955, “Quantity and Hydrologic Characteristics of Litter Under Upland Oak Forest
in Eastern Tennessee”, Journal of Forestry, Vol. 53: 190-195.
Curtis, W.R., 1960, Moisture Storage by Leaf Litter, US Forest Ser. Lake States Forest Experiment Station Technical Notes No. 577.
Özyuvacı, N., 1976, “Arnavutköy Dresi Yağış Havasında Hidrolojik Durumu Etkileyen Bazı
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