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Citation of this paper

A model for classification of range suitability for sheep grazing in semi-arid regions of Iran

F Amiri

Islamic Azad University, Bushehr Branch. Department of Natural resources, P.O. Box: 751494433 Bushehr-Iran
famiri@na.iut.ac.ir   or   amiri_fazel@yahoo.com

Abstract

Range suitability and its grazing capability are the most important criteria in rangeland analysis and monitoring. Determination and monitoring of factors affecting on range suitability and diagnosis of them are important .All range ecosystem components affect range suitability. Which among them physical and vegetation factors, forage production, water resources and sensitivity to erosion were considered. The objective of this research was to determine range suitability of Ghareh Aghach rangelands to design a model for sheep grazing. Ghareh Aghach watershed with an area of 8,962 hectares located in the northeast of Isfahan province, in semi- arid of Iran, was chosen as a suitable study area for creating a model for classifying rangeland suitability. Simple models of topography, forage production, water resources (quantity, quality and distance), and erosion were integrated within a Geographic Information System so as to create a comprehensive final model for assessing the suitability of specific rangelands for sustainable sheep grazing.

 

The results of the completed overall model of rangeland suitability for sustainable sheep grazing showed that of the 7159 hectares in the study area, 15.73% (1,126 ha) were moderately suitable, 68.67% (4,916 ha) are marginally suitable and 15.6% (1116 ha) were classified as unsuitable for grazing. The most important limiting factors in the area were the abundance of invader plant species, especially around the watering points and villages, low range productivity, erosion, slope classes (relatively flat to steep gradients), access to quality water resources and low temperatures during winter and autumn.

Keywords: GIS, Ghareh Aghach rangeland, grazing, Iran, model, range suitability, sheep grazing capacity


Introduction

Rangeland is an economically and culturally important component of the mountainous region of Iran, as it is elsewhere in the world. People have lived in and exploited these lands in a mostly sustainable fashion over many years. The ecosystems that typically constitute rangelands - grasslands, savannas, shrub lands and woodlands would have shaped early human development. Rangelands were first used by hunter-gatherer societies that relied on the natural environment for most, if not all, of their needs, this lifestyle prevailing for much of human history (Grice and Hodgkinson 2002). By around 11,000 years ago, isolated groups of rangeland people began to domesticate animals and plants to set up subsistence pastoral systems (Diamond 1998).

Managing vegetation and livestock to achieve a sustainable use of grazing lands has been the primary theme of rangeland management. While there is now increasing emphasis on uses and values of rangelands that are not directly dependent on grazing, the fact remains that grazing, be it by domestic animals or herbivorous wildlife, is an integral process in most arid rangelands (Quirk 2002).

 

Grazing will continue to be an important process in all rangelands, regardless of their primary use, and managing grazing will continue to preoccupy landholders and others interested in the sustainable and productive use of rangelands.

 

FAO (1991) reported that extensive grazing is the predominant form of land use on at least a quarter of the world’s land surface. It involves both domesticated animals such as cattle, sheep, goats, camel, horses and a broad range of wild animals kept for meat or game viewing. Giles (1984) describes rangelands as tracts of land used for grazing by domestic livestock or wildlife, where natural vegetation is the main forage resource. They may be used for ranching, as where animals graze on private land, or for three other systems of extensive grazing: nomadic pastoralist, transhumance or sedentary pastoralist.

 

Evaluation of extensive grazing systems, unlike that for cropping or forestry, must take into account both the production of grazing forage, termed primary production, and the livestock that feed on this forage, termed secondary production. Extensive grazing also differs from intensive grazing, in which the animal feed comes mainly from improved exotic pastures and not from unimproved rangeland.   

 

Range suitability assessment is needed to facilitate the sustainable management planning of these renewable resources (Amiri 2008). Range suitability has mostly been considered in terms of the capacity of the land to support extensive grazing (Ibrahim 1975). It may also be defined as the adaptability of an area to grazing by livestock or game. In evaluating the land one must assess the consequences of applying each proposed land use as accurately as possible, so that only those that can be sustained without long-term degradation of the land may be considered for implementation when land suitability is determined (FAO 1991). All major land uses and land utilization types require certain environmental conditions, termed land use requirements, in order to be successfully practiced. Adequate forage in the dry season and access to stock watering points are examples of land use requirements for extensive grazing in the tropics (Arzani et al 2006).

 

As the main rangeland enterprise in this study area was sheep grazing, a Geographic Information System (GIS) model was created to determining the suitability of the rangeland for this purpose. Nevertheless, many rangelands are capable of producing more than one product (Stoddart et al 1975) which may form the basis of future studies.
 

 

Material and methods

 

Study area

 

The research was carried out in Ghareh Aghach watershed with an area of 8962.25 hectares. Ghareh Aghach is located between 51 34' 54" to 51 45' 53" east longitude and 31 03' 28" to 31 26' 19" north latitude in the northeast of Semirom province of Iran, a semi-arid area in Zagros Mountain (Figure 1).



Figure 1.  Location of study area within the Ghareh Aghach District


Average annual precipitation is 358 mm (Figure 2).



 Figure 2.  Monthly average rainfall of 2007 and 2008 recorded at Semirom station within the study area


Ghareh Aghach’s rangelands contain 17 vegetation types including 12 shrub communities and 3 grassland communities (Table 1).  


Table 1. Vegetation communities in Ghareh Aghach rangelands

Number

Vegetation type

Yield, kg/ha

Area, ha

1

Agropyron trichophoum

381

123

2

Agropyron trichophoum-Astragalus. sp

34.2

306

3

Agropyron trichophoum-Astragalus. sp-Daphne muacronata

323

898

4

Astragalus adsendence-Agropyron trichophoum-Daphne muacronata

295

386

5

Astragalus. sp-Agropyron trichophoum

312

163

6

Astragalus. sp-Agropyron trichophoum-Daphne muacronata

280

238

7

Astragalus. sp-Bromus tomentellus-Cousinia cylanderica

234

2030

8

Astragalus. sp-Bromus tomentellus-Daphne muacronata

281

116

9

Astragalus. sp-Cousinia cylanderica

257

363

10

Astragalus. sp-Cousinia cylanderica-Daphne muacronata

235

969

11

Astragalus. sp-Ferula ovina

291

106

12

Bromus tomentellus-Astragalus. sp

259

373

13

Cousinia bachtiarica-Astragalus. sp

247

189

14

Cousinia bachtiarica-Scariola orientalis

229

499

15

Festuca ovina-Bromus tomentellus -Astragalus. sp

334

212

16

Hordeum violaceum-Poa bulbosa

646

36..8

17

Bromus tomentellus-Scariola orientalis

293

154

Source: Amiri 2008


Eighteen soil types were classified in 3 groups of Entisols, Inceptisols and Molisols as recognized by Anon (2007). Rangeland users comprise 35 families of Ghasghaei nomads (Amiri 2008). The maps or GIS layers used in this study were of vegetation, soil and land capability, property borders, water resources, location of villages, land use, geology and geomorphology.

 

Field data

 

The vegetation cover data used in this study were collected in frequent field visits at all vegetation type in 2007-08. The data were recorded in May and July 2007 and between May and July 2008. Rainfall in the study area was around average during these years (358.06 mm recorded at Semirom station in 2007 and 2008). Monthly rainfall during and immediately preceding the data collection periods was generally low, with some localised falls during January and May 2007 (Figure. 2).

 

The data field in each vegetation type was collected by stratified random sampling method. In each sampling unit, 10 plots were located randomly on perimeter of a supposed circle with about 20 meter radius and then percentage vegetation cover has been estimated on each plot. Then the average of 10 estimated cover has been considered for each sampling unit.

 

The method introduced by FAO (1993) for range suitability classification used ERDAS version 8.5 as GIS Software. The process included 9 steps (Figure 3);



Figure 3.  The process of land suitability evaluation (Source: FAO 1993


Land evaluation normally requires a comparison between the inputs required and the outputs obtained when each relevant land utilization type is applied to each land unit.

Two orders of range suitability for sheep grazing were considered: suitable (S) and not suitable (N). Three classes of suitability were determined including high suitable (S1), moderately suitable (S2), and marginally suitable (S3) (FAO 1991, 1993).

 

Simple models of forage production, water resources (quantity, quality and distance), and erosion were integrated to create final model of range suitability for sustainable sheep grazing (Figure 4) (Arzani and Yousefi 2006; Arzani et al 2006; Ayoubi 2006, Amiri 2008).


 

Figure 4.  Range suitability sub- model for sustainable sheep grazing


For creating a sub-model of sensitivity to erosion, the Slope map (Figure 5)



Figure 5.  Slope map of Ghareh Aghach Rangeland


and EPM model were used to calculate erosion potential (Figure 6).


 

Figure 6.  EPM Model for Soil Erosion


According to this model;

Z = Y.Xa (Ψ+I 0.5)                              (1) 

where:

Z is the erosion severity index,
Y is the sensitivity of soil and bedrock to erosion,
Xa is the land use index,
Ψ is the erosion index of the watershed, and
I is the average gradient of the slope.

Sensitivity to the erosion sub-model for each vegetation type was created by integrating range condition, land use, slope, erosion potential, soil characteristics, and geology. Sensitivity to erosion was then classified as shown in Table 2.


Table 2.  Classes of sensitivity to erosion (Ahmadi 2004)

Number

Range of Z

Suitability classes

1

< 0.2

S1

2

0.2-0.7

S2

3

0.7-1

S3


In order to create the forage sub-model, relevant information based on equation 2 was integrated for each vegetation type:

DLNN = GP + T + FQ   (2)

Where:

DLNN = Daily Livestock Nutrition Need,
GP = Grazing Period,
T = Topography, and
FQ = Forage Quality (Arzani and Yousefi 2006).

The daily requirement of a 50 kg sheep consuming quality forage was determined as 1.5 kg dry matter. Available forage (AF, kg/day) for livestock was calculated as:

AF = Σ(Y + (P/PUF))   (3)

Where:

Y= yield (kg/ha),
P = palatability, and
PUF = proper use factor (Zheng Gang et al 2006).

PUF was determined by combining information on range condition trend and erosion sensitivity (Badjian et al 2007).

 

Finally, the suitability of forage was classified by integrating the above information (Figure 7).



Figure 7.  Forage suitability sub-model


The quantity and quality of the forage, accessibility of water and livestock information formed the basis of the water resource model (Figure 8).



Figure 8.  Water Resources Model


Layers within the GIS model included accessibility of water and slope, location of water in Samman units and distance to water were integrated. Demand for water was determined from grazing capacity and water requirement per animal (Ibrahimi 1999). Table 3 shows how different suitability classes are influenced by distance to water and classes representing the gradient of the slope. The completed water suitability model was created by combining the above sub-models (Javadi et al 2008). 


Table 3.  Water resource distance (meter) and its suitability classes

>60

30-60

10-30

0-10

                    Slope class, %Suitability class

N

0-1000

0-3000

0-3400

S1

N

1000-3600

3000-4800

3400-5000

S2

N

3600-4100

4800-6000

5000-6400

S3

N

>4100

>6000

>6400

N


Water quality was assessed from laboratory analysis of water in terms of TDS (Total Dissolved Salts), EC and CaCO3 (Table 4) for each water resource.


Table 4.  Water quality for sheep and its suitable classes (Bagley et al 1997).

Suitability class

S1

S2

S3

N

TDS, mil/lit

<3000

3000-6000

6000-10000

>10000

EC, mmohs/lit

<3000

3000-5000

5000-7000

>7000

Caco3,me/lit

<60

61-120

121-180

>180


The completed suitability model was created by combining the sub-models for producing the water suitability map for sheep grazing (Figure 9).



Figure 9.  Model for classification of water resources suitability


The water needs of grazing sheep (w) are calculated by the following equation in this model:

Litres / kg 0.82/ day = w litres/ day  (4)

where:

a= coefficient determined from the local study,
w = water needs of each sheep according to body weight (King 1983).

(The mean weight body for Turkish Ghashghai sheep in this area is about 50 kg).

 

In Iranian rangelands the livestock only can use water in Samman unit.

 

Results

Most parts of the study area were resistant to erosion (Table 5).


Table 5.  Erosion classes of rangelands of Ghareh Aghach

Class of suitability

Erosion index

Vegetation type

Number

N

1.42

Ag.tr

1

N

1.59

A.gtr-As.sp

2

N

1.69

Ag.tr-As.sp-Da.mu

3

S3

0.87

As.ad-Ag.tr-Da.mu

4

N

1.50

As.sp-Ag.tr

5

N

1.87

As.sp-Ag.tr-Da.mu

6

S2

0.59

As.sp-Br.to-Co.cyl

7

S2

0.51

As.sp-Br.to-Da.mu

8

S2

0.60

As.sp-Co.cyl

9

N

1.99

As.sp-Co.cyl-Da.mu

10

S2

0.51

As.sp-Fe.ov

11

S2

0.49

Br.to-As.sp

12

S2

0.47

Co.ba-As.sp

13

S2

0.48

Co.ba-Sc.or

14

S2

0.54

Fe.ov-Br.to-As.sp

15

S2

0.70

Ho.vi-Po.bu

16

S2

0.60

Br.to-Sc.or

17


The results of the erosion sub-model show that from 7,159 hectares of studied rangelands, 4,078 hectares (57.0%) were classified as S2 class (with low limitation), and 386 hectares were (5.4%) classified as S3 class, and 2,696 hectares (37.6%) were classified as unsuitable (N). No studied rangelands were classified as S1.

 

An assessment of the water resources showed that the most limiting factor of potable water in the mountainous areas is the gradient of land slope. However, according to the water resources (quantity, quality and distance) models the results show that water distance and accessibility to water are the most important factors for determining suitability. Quality and quantity were limiting factors in parts, but not all, of the study area. The results show that from 7,159 hectares of studied rangelands, 5,519 hectares (77.1%) classified as S1 class (with no limitation), 859 hectares (12.0%) classified as S2 class (with low limitation), and 478 hectares (6.7%) classified as N class (unsuitable) (Figure 10).



Figure 10.  Suitability of water resources in Samman unit of Ghareh Aghach Rangeland


The results of the forage production sub-model showed that, from 7,159 hectares of studied rangelands, 979 hectares (13.7%) classified as S2 class (with low limitation) the condition of the area has fair to good, with permanent and upward trend (vegetation types 1, 4, 8, 9, 16 , 17), and 5,211 hectares (72.8%) classified as S3 class, the area has fair to poor condition with permanent and downward trend (vegetation types 2, 3, 5, 6, 7, 10, 12, 13,14, 15), and 969 hectares (13.5%) classified as N class, the area has poor condition with downward trend, and no studied rangelands were classified as S1 class (Table 6 and Figure 11).


Table 6.  Suitability based on forage production and available forage in Ghareh Aghach

Available forage suitability Available forage, kg/ha  x100  
            
     Yield, Kg/ha
Available forage, kg/ha Yield, kg/ha

Vegetation type

Number

S2

33.3

124.4

373.4

Ag.tr

1

S3

29.7

91.96

310

A.gtr-As.sp

2

S3

29.6

85.73

289.3

Ag.tr-As.sp-Da.mu

3

S2

33.5

87.86

262

As.ad-Ag.tr-Da.mu

4

S3

29.2

76.1

260.1

As.sp-Ag.tr

5

S3

29.1

74.29

255.3

As.sp-Ag.tr-Da.mu

6

S3

28.8

54.95

190.8

As.sp-Br.to-Co.cyl

7

S2

33.2

89.7

264.6

As.sp-Br.to-Da.mu

8

S3

28.1

57.87

206.2

As.sp-Co.cyl

9

N

19.9

37.6

188.4

As.sp-Co.cyl-Da.mu

10

S2

32.2

91.52

283.8

As.sp-Fe.ov

11

S3

29.2

72.1

248.8

Br.to-As.sp

12

S3

28.6

58.53

204.2

Co.ba-As.sp

13

S3

25

50.87

203.4

Co.ba-Sc.or

14

S2

37.1

116.4

313.4

Fe.ov-Br.to-As.sp

15

S2

34.4

209.05

607.5

Ho.vi-Po.bu

16

S3

28.3

81.2

286.8

Br.to-Sc.or

17




Figure 11.  Suitability of forage production at Ghareh Aghach Rangelands


Integrating the three sub-models that were used to assess the relative importance of erosion, water resources and forage as determinants of land suitability showed that 15.7% (1,126 ha) of Ghareh Aghach rangelands are in S2 suitability class and 68.7 and 15.6 percentages are in S3, N order respectively and no studied rangelands were classified as S1 class (Figure 12).



Figure 12.  Final range suitability map of Ghareh Aghach Rangelands


The S1 class is level rangelands with no limitation from slope for sheep grazing. S2 and S3 are undulating and mountainous areas. The result of the Model-based categorization of land area (ha; %) into suitability classes. shows in table 7.


Table 7.  Model-based categorization of land area (ha; %) into suitability classes

Sub-model

S1

S2

S3

N

Erosion

0

4,078 (57.0%)

386 (5.4%)

2,696 (37.6%)

Water Resources

0

4,519 (77.1%)

859 (12.0%)

478 (6.7%)

Forage production

0

979 (13.7%)

5,211 (72.8%)

969 (13.5%)

Integrated model

0

1,126 (15.7%)

4,918 (68.7%)

1,116 (15.6%)

Total land area in study = 7,159 ha


The most important limiting factors in the area were the abundance of invader species especially around the watering points and villages, steep slope gradient classes, water resources and low temperature during winter and autumn. The GIS facilitated integration of the information layers within and between the models.

 

Discussion

Although Iran is the second largest country in the Middle East, it has limited natural resources such as fertile soil and water, resulting in limited opportunities to expand and/or intensify arable farming (Sheidaei and Nemati 1978). Extensive animal husbandry, on the other hand, including nomadic, transhumant and sedentary forms, is widespread over the rangelands of the country.

 

Rangelands and animal husbandry have been of great importance in Iran for a very long time, as witnessed by the teachings of Zoroaster (Bavari 1980; Seraj 1970). More recently, many people have died in defence of their rangelands, even after land nationalization, when only the right of use was at stake (Farahpour and van Keulen 2004). The degree of importance attached to a specific rangeland area reflects its productivity, land scarcity and the availability of alternative sources of income. In Iran, as in other parts of the world, animal husbandry is the most productive use of the semi-arid zones bordering the desert (Reed and Bert 1995; Breman and De Wit 1983). As Niknam and Kyne (cited by Sheidaei and Nemati 1970) have calculated, 80 to 90 % of the livestock production of Iran, equal to 168,000 to 180,000 ton y -1 of meat (M.P.B 2006), is associated with the rangelands. Annual dry matter production of rangelands is estimated at more than ten million tons per hectare. In addition to forage production, mining, fuel wood collection, industrial use of rangeland by-production, e.g. medicinal plants and recreation are other rural enterprises in the rangelands of Iran (Farahpour 2002).

 

There are some limiting factors in each of the sub-models of erosion, water resources and forage production that affected rangeland suitability. Only a small area of the rangelands is unsuitable for forage production so that essentially all rangelands are suitable for grazing. The reasons are suitable climatic condition and utilization by those nomads that are in the area for part of the year. The only limitation to forage productivity was the presence of unpalatable and toxic plant species around the watering points and villages, in agreement with Jankjue (1996).

 

There was no limitation in terms of water quantity and quality in the area. All 24 water resources were in S1 classes. The only limitations for water were its accessibility to steep sloping areas, and sometimes the quantity of water in the highlands under drought conditions. Similar problems were reported by Jankjue (1996), Fashami (2002), and Arzani et al (2006) for the central area of Alborz in Iran.

 

Chemical and physical erosion were observed in some parts of the highlands in Ghareh Aghach. But most parts of the area were insensitive to erosion because of the underlying geology.

 

In the completed model the agricultural lands and urban areas were recognized as unsuitable for grazing. Most of these areas were classified as S2. So limited access to grazing land is not serious in the region. Poisonous plants were recognized as a limiting factor for sheep grazing by Curran and Grice (1992) who suggested that their impact could be reduced by grazing management. Rangeland managers should apply appropriate grazing systems to reduce the number of undesirable species within plant communities. This current study was focused on the suitability of rangeland for sheep, but as Holechek et al. (2003) has stated, significant income from rangelands can only be derived by selling products other than livestock. Further investigation therefore needs to be done to address the multiple use of rangelands in the study area.

 

Grazing is recognized as a valid use of rangeland ecosystems, and if undertaken in a planned and attentive manner based on range suitability, it can occur without range degradation.

 

Humans are now and have always been part of the ecosystem and are an instrument of ecological change. Healthy natural ecosystems reflect and create healthy human systems; we are only as healthy as the lands that sustain us. Healthy range condition is desirable from an environmental and economic-societal point of view. As Arzani et al (2001) reported, most land degradation has been observed in small properties that are not economically viable. So in addition to considering rangeland suitability, an assessment of economic viability requires that the ecological and social condition of each area should also be determined.

 

A GIS can provide better information and easier integration of various information layers to support a model for assessing rangeland suitability. We found a GIS to be particularly useful for providing greater flexibility and accuracy in assessing rangeland suitability (Banai 1989).

 

Acknowledgements

The authors are grateful to Dr David White of ASIT Consulting, Australia, for his suggestions and advice in the preparation of this paper.

 

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Received 8 November 2008; Accepted 16 December 2008; Published 1 May 2009

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