Impact of Land Use Changes on Soil and Vegetation Characteristics in Fereydan, Iran

Abstract

To understand and manage ecosystem complexity, it is important to determine the relationships between soil characteristics, human activities, and biodiversity. This study analyzes the relationships between vegetation, soil, and man-made damage with regards to land use change in the Fereydan region, Iran. Soil physical properties such as sand and silt content, clay, saturated soil’s moisture content, and gravel percentage as well as chemical properties such as lime content, pH, electro conductivity (EC), and organic matter content were measured. In order to trace these variables, the principle component analysis (PCA) was applied. The study area was divided into three states of conditions; i.e., good condition rangelands, poor condition rangelands, and abandoned rain-fed area. Based on the results there was a significant difference between species diversity in good condition rangelands compared with two other sites. The results further revealed that among soil chemical and physical characteristics, only soil organic matter had a significant difference between different rangeland sites. According to the results, the rangelands with good conditions had the highest amount of organic matter (1.43–1.50%) compared with two other studied rangelands (poor conditions: 1.02–1.09%; abandoned rain-fed: 1.2–1.46%). The most influential factor on the species diversity index was the distance to village parameter that revealed the important role of humans in degrading rangelands and reducing species diversity.

1. Introduction

Plant communities owe their existence to relations between plants and their surrounding environment. A number of environmental factors (e.g., soil nutrients and moisture content) impose a profound effect on the unique characteristics of plants as well as plant and vegetation communities [1,2,3,4,5]. The introduced relations between plant communities and environmental factors underpin a very important debate in ecology [6]. Arid and semi-arid areas are mostly characterized by their scarce vegetation cover which makes its ecosystems fragile and vulnerable to external or internal components such as human activities [7]. The distribution, pattern, and abundance of plant species in arid and semi-arid areas have most often been related to three groups of factors including physical environmental, soil chemistry, and human factors [8]. In order to plan better conservative measures and perform effective well-informed management, one should understand the differences between species of distinct ecological categories within a studied location [9]. The existence of relationships between the environment, humans, and vegetation dictates the progress or regress of a given species within a given area.

The relations between human activities and plant communities have been studied by many researchers. Lavergne et al. (2005) [10] analyzed the implications of environmental and human factors on the presence of rare species, exclusion, and preservation of the species in the Mediterranean region. Comparing the floristic lists of 1886 and 2001 showed that in 2001, rare species tended to migrate to upper elevations. Guo et al. (2007) [11] evaluated that both undisturbed and disturbed communities showed the same changeable bell-shaped trend with an elevation increase. Suzart de Albuquerque et al. (2011) [12] scrutinized human effects on the richness of endemic and exotic plants. Their results showed a strong relationship between the endemic and exotic species. Zhang (2009) [13] also evaluated the influences of grazing intensity, soil, and topography on the status and diversity and found that grazing intensity was an important factor influencing vegetation composition and structure. Soil and topographic variables were also important to vegetation composition, although most soil variables were sensitive to grazing intensity. Similarly, El-khouly (2004) [14] found that overgrazing was the most important activity influencing vegetation diversity and floristic composition. Salinity was also found to be a significant factor that limits the plant species diversity in the location of Siwa Oasis, Egypt. A study by Pueyo et al. (2006) [15] demonstrated that grazing gives rise to the biological diversity in plant species. Mligo (2006) [16] also pointed out that the lightest grazing intensity areas were the main cause of plants reaching a peak in diversity.

Considering the high importance of plants and soils in the lives of humans, and in order to have effective management of a natural system, such as rangeland ecosystem, identifying the relationship between plant and soil has a great importance [17,18,19,20]. Soule and Piper (1992) [21] and Weil (2004) [22] discussed that relationships between soil properties and the dominance of certain plant species in a natural environment may assist in tailoring suitable species for particular soil types within a managed rangeland. In this regard, through field visits and the measuring of various environmental factors in Kamyaran rangelands in Iran, Gholinejad et al. (2012) [23] surveyed environmental determinants including the main soils, and physical and chemical parameters on plant communities’ distribution as one of the most significant structures in semi-arid rangelands. Their findings showed that clay, nitrogen, sand, altitude, and slope have the highest relationships with principal components and are the most important factors affecting the distribution of plant communities in semi-arid rangelands. Accordingly, the first hypothesis of the current study is that there is a significant difference between soils’ physical properties in different rangeland sites. Zare Chahouki et al. (2008) [24] evaluated the relationship between vegetation distribution patterns and soil characteristics in the Poshtkouh rangelands of Yazd Province, Iran. Their results revealed that the vegetation distribution pattern was mainly correlated to soil parameters such assalinity, soluble potassium, texture, gypsum, and lime. Based on the previous studies, the second hypothesis of this study is that there is a significant difference between species diversity in different rangeland sites. In relation to the effects of soil parameters on the diversity of plant species, Munhoz et al. (2008) [25] also worked in the species–environment relationship in the herb-subshrub layer of a moist Savanna site in central Brazil. They found a significant relationship between the soil texture and soil moisture parameters with the plant distribution based on the canonical-correlation analysis. Timsina et al. (2011) [26] found a significant difference between invaded transitional and non-invaded plots in species composition and soil properties in rangelands communities in Nepal. Zhang (2009) [13] also evaluated the influences of soil variables and topographical features on the plant variety and reported that topographical characteristics could alter plant variety while soil variables could permanently alter vegetation varieties and structure. There is sufficient evidence that land use/land cover change is a major driving factor for the balance of SOM (soil organic matter) [27,28,29]. In particular, changes among land use types such as cropland, forestland, and pastureland will result in clear changes in SOM reserves [27]. Houghton (2003) [30] showed that global land use changes since 1850 had caused 156 Pg of soil carbon release into the atmosphere.

Based on the role of plants that bring balance into ecosystems and their products which humans directly as well as indirectly consume, there is an urgent need to understand the relationship between the plants, the surrounding environment as well as human activities to reach stability and sustainability. Given the role of human on ecosystems, the third hypothesis of the current study is that human activities have a significant impact on species diversity. Reasonable management and utilization of rangelands requires recognition of the vegetation per se and the relationship that it has with the environment and humans. It is obvious that soil, climate, and biological characteristics of the region have a direct influence on the diverse plant community [31]. Assessing the mentioned factors is inevitable for finding the reasons of plant distribution and variety and also site capability. Vegetation and diversity conservation, recognition of plant communities, environmental factors, and human effects are fundamental principles for the preservation of natural ecosystems. With respect to the importance of species diversity in managing rangelands, this paper aims to identify and assess the types and potential influences of some influential human and environmental factors regarding plant distribution and diversity in two types of rangelands (degraded and good condition) and abandoned rain-fed regions in the Fereydan district, Isfahan province, Iran.

2. Material and Methods

2.1. Site Description

The study area is located in the South of Karchambouy and Northeast of Boin va Miandasht town, west of the Isfahan province and covers about 9677.5 ha. The geographic coordinates are 49°50′46″ E to 50°00′36″ E and 33° 02′27″ N to 33°11′18″ N. The average annual precipitation exceeds 430 mm and the average annual temperature reaches 9.9 °C (Figure 1). The average land area of the study site is covered by vegetation and in the degraded rangelands, vegetation cover is poor and has an upward trend. Topographically, the area consists of areas that are 2290 m above sea level. Grazing intensity is various in different areas from low to high but generally is high. Astracantha sp., Ferulaovina, Contaurea, and Agropyron sp. are the major plantation cover in study area. The geology of the studied area is mostly alluvial sediments that has been developed from the Quaternary alluvium. According to the WRB system, soil type in this region is Cambisols.

The number of livestock in Fereydan is estimated at 214,810. There are two main types of livestock used to graze grasslands, sheep (197,928) and goats (16,882). The villagers feed their domestic animals partly by fodder, but they also rely heavily on natural pastures which have been diminishing through overgrazing. The intensification of dairy farming has also been found to have a deleterious effect on soil quality, particularly in terms of compaction by trampling, which results in losses of production, pasture quality, and hydraulic conductivity [32]. One of the most important soil properties vulnerable to animal trampling is penetration resistance that is highly sensitive to animal trampling. Grazing effects on soil structural stability were significant only in periods when the soil dried, and it was suggested that stocking rates had to be regulated in those dry periods. However, some workers have reported that animal trampling did not show a significant effect on soil physical properties.

2.2. Methodology

The methodology consisted of the primary recognition and pre-assessment site visits for defining vegetation types. Using random-systematic method, soil and vegetation were sampled in key areas of each vegetation type in 2014. Firstly, the study area was divided into three states of conditions; i.e., good condition rangelands, poor condition rangelands and abandoned rain-fed areas. Rangelands, with 0–26%, 26–50%, 50–75%, and 76–100% vegetation are called respectively poor, fair, good, and excellent condition rangelands [33]. Iran has a total of 90 million ha of rangeland. These rangelands are divided into three parts according to their qualities. These qualities are known as ‘good’, ‘fair’ and ‘poor’. The ‘good’ quality lands comprise 14 million, the ‘fair’ quality lands comprise 60 million and the ‘poor’ quality lands comprise 16 million ha. In this study, rangelands with 51–100% vegetation are called good condition rangelands. Poor condition rangelands consist of those rangelands with 1–50% vegetation. Abandoned rain-fed areas consist of those rangelands with no vegetation cover. Abandoned rain-fed areas are abandoned by their owners because of low potentials for yielding. IWMI (International Water Management Institute) [34] defined abandoned rain-fed as those that cannot be reallocated to irrigate crops or use for other purposes. Given that, they are not included in agricultural land but animal grazing; we considered them as rangeland in this study. The three treatments were not contiguous patches but many mosaic-like patches.

Every condition; i.e., good condition rangelands, poor condition rangelands and abandoned rain-fed areas was divided into 20 regular blocks. With a random number generator, numbers between 1 and 20 were selected. This provided the location of the blocks. Then, in every condition; i.e., good condition rangelands, poor condition rangelands and abandoned rain-fed areas, four homogenous areas were selected by stratified random sampling method according to similar topography, soil etc. A land unit area (LUA) map was applied as a homogenous field area to guide soil sampling. LUA is a fundamental concept of ecology and is defined as an ecologically homogeneous area of land, considering the scale of the field [35]. A total number of 12 sites were selected and soil and vegetation were sampled. In each of the 12 sites, a sample was drawn at lengths of 300 m transects with 8 plots in the good condition rangelands, 20 plots in the poor condition rangelands, and 7 plots in the abandoned rain-fed rangelands. The sampling plots of 1 m² size were applied for the vegetation type and its distribution. The recorded data in each plot consisted of floristic lists, canopy covers, vegetation density, and the percentage of gravel cover.

In each site with three replications, six soil profiles with an equal distribution were excavated. Soil sampling was conducted in the 0–30 cm depth from the surface topsoil (totally 12 profiles) in order to examine soil characteristics including clay, silt and sand content, soil moisture content, lime content, pH, EC, and organic matter as well as gravel content. Once the soil was dried, it was sieved by a 2 mm mesh size sieve.

Table 1. Slope conditions of the studied region

Rangeland Condition	Repetition	Slope (%)	Slope Direction
Good condition rangeland *	1	8	Southern
	2	9	Southern
	3	7	Southern
	4	8	Southern
Degraded rangeland	1	14	Southern
	2	8	Southern
	3	12	Southern
	4	9	Southern
Abandoned rain-fed lands	1	12	Southern
	2	9	Southern
	3	10	Southern
	4	14	southern

* Good condition rangeland, followed by a description 1:14 million ha.

shows slope conditions for each of the 12 sites.

Distances to roads, villages, and watering points were chosen and considered in order to examine the impacts of human factors. Distances from water or village can be an indicator for grazing intensity; with increased distances, grazing intensity decreases and therefore plant diversity increases. Furthermore, livestock grazing is not the main activity in this study site. In fact, in sites without grazing or with even light grazing, the idea that with increasing distances, grazing intensity decreases and therefore plant diversity increases is not true anymore. Accordingly, in this study the distance to roads, villages and watering points were considered in order to examine the impacts of human factor on the diversity of species. According to the equation of grazing intensity when stocking rate/grazing capacity was >1, it means over grazing and is therefore degraded rangeland and when stocking rate/grazing capacity was ≤1, it is good rangeland.

Soil samples were obtained from three points at each site at a depth of 0–30 cm. The three replicate samples were then homogenized by hand mixing and large live plant material (roots and shoots) and pebbles in each sample were separated by hand and discarded. The soil samples were air-dried and sieved for determination of soil properties. Thus, 70 soil profiles were studied in the site. Soil organic matter (SOM) content was determined by the Walkley–Black method. Soil pH was measured in a saturated paste using a pH electrodes and electrical conductivity (ECe) was determined in the extract using a conductivity meter. Calcium carbonate equivalent (CCE) content was determined by the back-titration method.

The topographic map of the region was geo-referenced in the ArcGIS (geographic information system version 9.3 developed by Environmental Systems Research Institute (ESRI), Redlands, CA, USA), and this led to the measurement of the mentioned parameters of distance to the roads and villages as well as the watering points. The Ecological Methodology software was used in order to identify the species richness in the Fereydan’s rangelands. The Simpson, Shannon, Hill N1 and N2 were used to evaluate the species richness.

2.2.1. Simpson’s Diversity Index

Simpson’s diversity index is a simple mathematical measure that characterizes species diversity in a community. It takes into account the number of present species as well as the abundance of each species. Richness is a measure for the number of different kinds of organisms present in a particular site [36]. This index is calculated according to Equation (1)

Λ = ∑p_i; P_i = n_i/N

(1)

where P_i denotes the number of individuals or the frequency of individuals in proportion to the total vegetation individuals. The Simpson index implies dominancy and varies between 0 to 1; n_i is the abundance of ith species; N shows the total abundance [37].

2.2.2. Shannon–Weiner Diversity Index

Two basic assumptions are taken into account in this index. Firstly, the number of individuals is randomly sampled. Secondly, all species present in the society are included. This index is estimated according to Equation (2)

$$H^{\prime }=-{\displaystyle \sum }_{i=1}^S(p_{i}ln{p}_i)H^{\prime }=-{\displaystyle \sum }_{i=1}^S(p_{i}ln{p}_i)$$

(2)

where P_i shows the number of individuals or the frequency of individuals in proportion to the total vegetation individuals; S shows the total species and varies from 0 to 4.5 [38].

2.2.3. Hill N1 Diversity Index

Hill N1 is the index of diversity influenced by species richness which is shown in Equation (3).

$$H{D}_1=N_1=e^{H^{\prime }}=\exp \left(H^{\prime }\right)$$

(3)

where e shows the natural logarithm’s exponent with the quantity of 2.71828, $H^{\prime }$ is the Shannon–Weiner equation and N1 is the variety index [39].

2.2.4. Hill N2 Diversity Index

Hill N2 is an index that is predominantly influenced by the abundance of the dominant species as estimated in Equation (4)

$$H{D}_2=\frac{1}{\sum P_i^2}=\frac{1}{P_1^2+P_2^2+\dots +P_n^2}$$

(4)

where 1/D is the reversed Simpson index.

Neher and Darby (2009) [40] regarded this as N2 (P1 symbolizes the frequency of the first studied species in proportion to the total number of individuals by n samples). The Simpson index or Jenney—Simpson (1-D) index ranges from 0 (low diversity) to maximally 1 (1-1/s) while the reverse Simpson index (1/D) ranges from 1 to S (Simpson’s index) (the number of species in the sample).

The stepwise regression was applied for anticipation species diversity and edaphic and human activities. The best model was selected and reported based on AIC (Akaike information criterion). A model with low AIC is better which are shown in the results. In the regression analysis, species diversity index was applied as dependent and soil, as well as anthropogenic activities were used as independent variables. Soil physical properties such as sand and silt content, clay, saturated soil’s moisture content and gravel percentage and also chemical properties such as lime content, pH, electro conductivity (EC), and organic matter content were measured. Moreover, human activities including distance from roads, villages, and watering point were considered.

3. Results

Table 2. Soil properties of the studied sites at the depth of 0–30 cm

Soil Properties	Rangeland Condition	Min	Max	Mean	Std. Deviation
Gravel content (%)	Good condition rangeland	39	49	43	18
	Degraded rangeland	39	51	45	9
	Abandoned rain-fed lands	40	52	45	13
pH	Good condition rangeland	17.7	22.2	20.3	0.26
	Degraded rangeland	17.7	23.3	20.4	0.12
	Abandoned rain-fed lands	15.3	24.6	20.0	0.05
Electrical Conductivity (EC) dS/m	Good condition rangeland	32.5	38.1	36.2	0.10
	Degraded rangeland	29.8	37.5	34.0	0.11
	Abandoned rain-fed lands	32.7	35.9	34.4	0.11
SP (saturation percentage) (%)	Good condition rangeland	16	27	20	2
	Degraded rangeland	14	21	17	1
	Abandoned rain-fed lands	13	14	14	3
Organic matter content (%) *	Good condition rangeland	1.4b	1.5	1.4	0.03
	Degraded rangeland	1.0a	1.0	1.0	0.03
	Abandoned rain-fed lands	1.2c	1.4	1.3	0.12
Lime content	Good condition rangeland	34.7	40.3	37.8	5.26
	Degraded rangeland	33.7	37.4	35.3	2.76
	Abandoned rain-fed lands	33.2	41.5	37.2	0.55
Clay (%)	Good condition rangeland	0.5	0.7	0.6	2.5
	Degraded rangeland	0.5	0.8	0.7	3.2
	Abandoned rain-fed lands	0.5	0.7	0.6	1.4
Silt (%)	Good condition rangeland	7.51	8.1	7.8	2.2
	Degraded rangeland	7.7	8.0	7.9	2.5
	Abandoned rain-fed lands	7.6	7.8	7.7	4.9
Sand (%)	Good condition rangeland	20.1	60.4	33.4	4.5
	Degraded rangeland	21.4	42.0	33.8	5.2
	Abandoned rain-fed lands	13.2	42.3	23.7	6.3
Soil texture	Good condition rangeland	CL/SCL
	Degraded rangeland	CL/SCL
	Abandoned rain-fed lands	CL/SCL

SP: soil’s moisture percentage. CL: clay loam, SCL: sandy clay loam. * Signs (a, b, c) on the numbers indicate significant differences (p < 0.05) in the study sites (obtained from Tukey test).

shows the physicochemical properties of soils in different land management situations in this study. The results of the ten experimented physicochemical properties of the soil indicated that only the amount of organic matter has a significant difference between the studied rangeland sites. The rangeland in good conditions had the highest amount of organic matter compared to the other two studied rangelands. When water logging occurs in the soil, it will result in the accumulation of organic matter. The higher densities of the dominant species can also cause more organic matter in the soil.

Table 3. Distance from roads, villages, and watering place in the studied sites

Studied Areas	Distance from Road (m)	Distance to Villages (m)	Distance from Watering Place (m)
Good condition rangeland	100	2116	2090
Degraded rangeland	170	478	476
Abandoned rain-fed land	112	424	423

presents the results for investigating the effects of human activities on plant communities showing the distance from a few man-made facilities in the study site. As the table shows, the good condition rangeland sites are located more than 1 km away from human infrastructure (such as road, watering place etc.) and rural sites whereas abandoned rain-fed and poor condition rangelands are located in the vicinity of the human infrastructures. Accordingly, these two categories of rangelands have less than 200 and 500 m distance from the roads and water holes, respectively.

In order to identify the most important environmental factors influencing the vegetation diversity, the PCA (principle component analysis) was applied which supports the importance of the variables devised in each factor [41]. This method is concerned with establishing which linear components exist within the data and how a particular variable might contribute to that component [42]. In accordance with eigenvalues of the PCA axis, which are useful for selecting the axis, the most important axis was selected. According to the results, the first and second axis justify the most significant changes of the eigenvalues, respectively 0.402 and 0.234. Therefore, the most important factors correspond to the first and then second axis. Thus, according to the eigenvalues, the most effective factors evaluated in the study are located in the first and second axis including CaCO₃, watering place, village distance, and roads.

Figure 2 and Figure 3 show the result of the PCA method for distribution of plant species in the study site and the effective environmental and anthropogenic disturbance in the coordinate axis. Accordingly, SP (saturation percentage) percentage and OM (organic matter) axis are in the same direction and the low angle is a sign of high correlation between these two factors. Shannon and Hill diversity indices in good condition rangelands in the second quarter of the coordinate axis show high plant diversity. Poor condition rangeland is located in the third quarter of the coordinate axis and soil factors including silt, pH, and gravel content are effective in the distribution of poor quality plant species while the abandoned rain-fed site is located in the first and fourth quarters of the coordinate axis. Floristic list in the designated site is shown in the

Table 4. Floristic list of the studied region (grasses (A), shrub (B), and forbs(C))

(A)
Number	Species	Family	Palatability Class	Life Form	Life Time	Relative Frequency (%)
						Good Condition Rangelands	Poor Condition Rangelands	Abandoned Rain-fed
1	Bromus tomentellus	Gramineae	I	Grasses	perennial	25.6	0.1	0.4
2	Bromus danthoniae	Gramineae	II	Grasses	annual	8	5.7	11.6
3	Taeniatherum crinitum	Gramineae	III	Grasses	annual	5.4	11.8	0.2
4	Bromus tecturum	Gramineae	II	Grasses	annual	5.7	10.4	1.4
5	Eremo songarica	Gramineae	I	Grasses	annual	8.2	4.3	12
6	Boissera squarrosa	Gramineae	III	Grasses	annual	2.8	4	19.5
7	Poa bulbosa	Gramineae	II	Grasses	perennial	4.2	2.6	1.1
8	Eremopoa songarica	Gramineae	II	Grasses	annual	1.3	0	0
9	Agropyron trichophorum	Gramineae	II	Grasses	perennial	0.4	0	0.4
10	Phalaris arundinaceae	Gramineae	I	Grasses	perennial	0	0.3	0
11	Stipa barbata	Gramineae	II	Grasses	perennial	0.1	0	0
12	Agropyron intermedium	Gramineae	I	Grasses	perennial	0	0.5	0
13	Festuca ovina	Gramineae	I	Grasses	perennial	<0.1	0	0
(B)
Number	Species	Family	Palatability Class	Life Form	Life Time	Relative Frequency (%)
						Good Condition Rangelands	Poor Condition Rangelands	Abandoned Rain-fed
1	Astragalus verus	Papilionaceae	III	Shrub	perennial	12	48.4	0.9
2	Scariola orientalis	Compositae	III	Shrub	perennial	1.7	1	3.4
3	Acanthophyllum heterophyllum	Caryophyllaceae	III	Shrub	perennial	1.3	0.6	0
4	Astragalus microcephalus	Papilionaceae	III	Shrub	perennial	0	4.1	0
5	Noaea mucronata	Chenopodiaceae	II	Shrub	perennial	0	1.6	0
6	Acanthophyllum microcephalum	Caryophyllaceae	III	Shrub	perennial	0	1.2	0.1
(C)
Number	Species	Family	Palatability Class	Life Form	Life Time	Relative Frequency (%)
						Good Condition Rangelands	Poor Condition Rangelands	Abandoned Rain-fed
1	Cousinia bachtiarica	Compositae	III	forbs	perennial	4.8	0	0
2	Phlomis persica	Labiatae	III	forbs	perennial	4.2	0	0
3	Eryngium billardieri	Umbelliferae	III	forbs	perennial	3.3	2. 4	44
4	Ferula ovina	Umbelliferae	I	forbs	perennial	0	0.3	0
5	Alyssum inflatum	Cruciferae	III	forbs	annual	3.6	0.4	2.5
6	Minuartia meyeri	Caryophyllaceae	III	forbs	annual	3.5	13	0
7	Phlomis olivieri	Labiatae	III	forbs	perennial	4.4	0.3	0
8	Arabis nova	Cruciferae	II	forbs	annual	2	0.4	0
9	Phlomis anisodonta	Labiatae	III	forbs	perennial	1.4	0	0
10	Ziziphora capitata	Labiatae	II	forbs	annual	1.2	0	0
11	Gypsophila virgata	Caryophyllaceae	III	forbs	perennial	1	0	0
12	Euphorbia descipiens	Euphorbiaceae	III	forbs	perennial	0.7	1.4	0.1
13	Rochelia disperma	Boraginaceae	III	forbs	annual	0.8	1.7	0
14	Centaurea luristanica	Compositae	III	forbs	perennial	1	0	0.5
15	Crepis sancta	Compositae	III	forbs	annual	0.8	0	0
16	Ziziphora tenuior	Labiatae	II	forbs	annual	0.7	0	0
17	Cardaria draba	Cruciferae	III	forbs	annual	0.4	0	0
18	Echinops robustus	Compositae	III	forbs	perennial	0.4	0	0
19	Galium verum	Rubiaceae	III	forbs	perennial	0.3	0	0
20	Silene arbuscula Fenzl ex Boiss	Caryophyllaceae	II	forbs	perennial	0.2	0	0
21	Taraxacum officinale	Compositae	I	forbs	perennial	0.2	0	0
22	Cirsium bracteosum	Compositae	III	forbs	perennial	0	6.1	3.1
23	Ceratocephalus falcatus	Compositae	II	forbs	annual	0	1.1	0
24	Malcolmia taraxacifolia	Cruciferae	II	forbs	annual	0	0.9	0
25	Medicago sativa	Papilionaceae	I	forbs	annual	0	0.3	0
26	Senecio glaucus	Compositae	III	forbs	annual	0	0.2	0.8
27	Bonium cylindricum	Umbelliferae	I	forbs	annual	0	0.3	0
28	Achillea vermicularis	Compositae	III	forbs	perennial	0	0	3.8
29	Veronica orientalis	Scrophulariaceae	III	forbs	perennial	0	0	1.2
30	Euphorbia cheiradenia	Euphorbiaceae	III	forbs	perennial	0	0	1.2
31	Geranium tuberosum	Geraniaceae	III	forbs	perennial	0.1	0	1.8
32	Tragopogon graminifolius	Compositae	I	forbs	perennial	0	0	1.6
33	Asperula arvensis	Rubiaceae	II	forbs	annual	0	0	0.7
34	Centaurea virgata	Compositae	III	forbs	perennial	0	0	1
35	Nepeta laxiflora	Labiatae	III	forbs	perennial	0	0	0.6
36	Scutellaria multicaulis	Labiatae	III	forbs	perennial	0	0	0.4
37	Sedum hispanicum	Crassulaceae	III	forbs	annual	0.1	0	0
38	Scabiosa olivieri	Dipsacacea	III	forbs	annual	0	0	0.1
39	Orobanch alba	Scrophulariaceae	III	forbs	annual	<0.1	0	0
40	Polygonum polycnemoides	Polygonaceae	III	forbs	perennial	0	0	<0.1
41	Consolida tomentosa	Ranunculaceae	III	forbs	annual	0	<0.1	0
42	Turgenia latifolia	Umbelliferae	III	forbs	annual	0	0	<0.1
43	Valerianella oxyrrhyncha	Valerianaceae	III	forbs	annual	<0.1	0	0
44	Heteranthelium piliferum	Gramineae	III	forbs	annual	0	0	<0.1

with the percentage of the relative frequency. Major vegetation of abandoned rain-fed areas has low or non-palatability and the vegetation of abandoned rain-fed includes invasive species. Main species is Eryngium billardieri and accompanying species are Boissiera squarrosa and Euphorbia descipiens. In the good condition rangelands, the dominant species is Bromus tomentellus and other accompanying species are: Astragalus verus, Ferula ovina, and Eremo songarica. Annual species and non-palatable ones such as Bromus tectorum and Astragalus verus are the main plant cover of poor condition rangelands.

Furthermore, the indices of plants richness and diversity were analyzed. In doing so, the Hill N1 and Shannon–Weiner were applied as appropriate indices to approximate species diversity.

The results of the Simpson, Shannon, Hill N1, and Hill N2 are presented in

Table 5. Mean values of plant diversity indices in the study rangeland area based on the canopy cover of all species

Rangeland Area	Simpson	Shannon	Hill N1	Hill N2
Good rangeland	0.82 a	3.3a	10.13 a	6.44 a
Degraded rangeland	0.8 a	3 b	8.17 b	5.95 a
Abandoned dry land farming	0.74 a	2.52 b	5.81 b	3.87 a

Marks (a and b) presented for showing difference between mean values and similarity in marks indicate not significant deference (obtained results from Tukey test).

and

Table 6. Mean values of plant diversity indices in the study rangeland area based on the canopy cover of perennial plant species

Rangeland Area	Simpson	Shannon	Hill N1	Hill N2
Good condition rangeland	0.70 a	2.37 a	5.18 a	3.46 a
Degraded rangeland	0.62 b	1.90 b	3.78 b	2.85 b
Abandoned rain-fed land	0.51 b	1.58 b	3.05 b	2.10 b

illustrating that the maximum and minimum values belong to the Hill N1 and Simpson diversity indices, respectively. The estimated Shannon and Hill N1 indices show significant difference between the good rangeland site and abandoned rain-fed or poor condition rangeland based on all species (p ≤ 0.05). Also, the calculated diversity indices based on perennial species coverage show significant difference between the good condition rangeland site and abandoned rain-fed or poor condition rangeland (p ≤ 0.05). In the multivariate regression analysis, the Shannon–Weiner and Hill N1 species diversity index is applied as dependent, and soil and anthropogenic activities used as independent variables.

4. Discussion

According to the results of this study, among all the tested physicochemical properties of soil, the amount of organic matter indicated a significant difference between the three types of rangeland sites (i.e.,1.4, 1, and 1.3 percent for good rangeland, degraded rangeland, and abandoned dry land farming, respectively). Accordingly, the first hypothesis is rejected as only organic matter indicated a significant difference between the rangeland sites. Similarly, using the same methodology, Zare et al. (2011) [43] found that salinity, soil texture, effective soil depth, potassium, organic matter, available nitrogen, lime, and soil moisture criteria were the main soil parameters responsible for diversity in vegetation pattern in Shahriyar rangelands, Iran. If water logging occurs in the soil, it will cause the accumulation of organic matter [44]. The higher densities of dominant species can also be the cause for more organic matter in the soil. While the proper utilization of the natural ecosystems is leading to the preservation of biological diversity, exclusive conservation will not bring about biological diversity at its most appropriate condition [45]. In this study, organic matter is projected to be the most influential soil component in the plant species to establish their diversity (i.e., 1.4, 1, and 1.3 percent for good rangeland, degraded rangeland, and abandoned dry land farming, respectively). Hersak (2004) [46] also suggested that soil organic matter and nitrogen content should be considered as the most important factors to define plant succession series over the sand dunes of the northern parts of Croatia.

Examining different rangelands in the Fereydan district showed the existence of a significant difference of species diversity between good condition rangelands compared with the other sites. Accordingly, the second hypothesis of the study is accepted as plant diversity is different between rangeland sites. This study showed that among soil chemical and physical characteristics, only soil organic matter has a direct relationship with the vegetation cover. According to the fact that in the studied rangelands, geological and physiographic features show slight differences, it could be concluded that species diversity has no effect on the edaphic factors and any change made in the soil organic matter is the overall outcome of the interactions of soil and vegetation which itself is under the influence of the utilization level.

With regard to the effects of human-related factors, this study showed that the rangeland areas are in good condition when they are located at a far distance from rural areas and constructed facilities (such as road, watering place) by human in the study site whereas abandoned rain-fed and degraded rangelands are located much closer to these three human infrastructures. Accordingly, the third hypothesis of the study is also accepted as human activities have influential impacts on species diversity. Perhaps, in farther distances, grazing intensity decreases, thus species diversity increases. One of the factors that is effective in plant communities is grazing due to livestock density around the watering places. Findings of Zhao (2007) [47] and Todd and Hoffman (2009) [48] suggest that grazing has significant influence on vegetation to the extent that the number of the palatable species decreases and coverage of ephemerals increases considerably. Similarly, decreased local species diversity is confirmed as a widespread impact of human activity [49,50]. De Bello (2006) [51] observed the highest number of rare species in abandoned areas, while abandoned areas correspond to the lowest species diversity in this study. Mitchell et al. (2002) [32] reported that the reduction in species diversity is preceded by destructive human operations and this could result in a loss of primary production. Also, communities that lost the species dominant at high diversity had higher pathogen loads, presumably because relaxed competition allowed greater in-creases in host abundances. In total, their results support the hypothesis that decreased species richness will increase foliar pathogen load if this increases the host abundance and, therefore, disease transmission. Bornman et al. (2008) [52] provided the evidence that distance to water acts as one of the most critical variables determining the distribution of plant types in Southern Africa that is consistent with our findings. According to the previous study, there are environmental variables that had the greatest influence on the distribution of the dominant salt marsh species. These environmental variables included soil moisture, distance from the estuary, elevation above mean sea level, and depth to the water table. The most important ecological driver for salt marsh vegetation, especially along the arid west coast of southern Africa, is moisture. Woldewahid et al. (2007) [53] also reported that access to water and land-use conditions are the main human factors affecting the distribution of plant types along the coasts of the Red Sea, Sudan that is also in line with the current study findings.

Furthermore, the results of PCA in this study showed that the most effective factors affecting the plant diversity index are CaCO₃, watering place, village distance and roads (i.e., the most significant changes of the eigenvalues are respectively 0.402 and 0.234). Similarly, Qian (2008), by applying a cluster analysis and PCA in China, considered soil chemical and physical characteristics such as nutrients, moisture, salinity, and pH as the main determinants of ecosystem’s homogeneity and the spatial distribution of plant societies in that area.

There are different studies that investigate the relations between various edaphic, environmental and human activities and their impact on plant diversity and distribution, such as Zare et al. (2011) [43] in Iran and Wang et al. (2012) [7] in Qinghai-Tibet Plateau of China. Similarly, Gholinejad et al. (2012) [23] showed that major factors influencing the plant communities’ distribution in rangelands of Kamyaran rangelands, Iran are physical soil properties and physiographic parameters amongst which soil texture is one of the most effective determinants in the distribution of plant communities in the studied region. With regard to the distribution of plant species in the study area and effective environmental and anthropogenic disturbance, SP percentage, and OM showed a significant difference between the study sites. Moreover, Shannon and Hill diversity indices in good condition rangeland show high plant diversity. Whittaker (1977) [54] observed that the highest diversity of plants is seen in good condition rangelands. Distance from village, clay percentage and lime content are effective in high diversity and the distribution of plant species such as Bromus tomentellus, Festuca ovina, and other desirable species for livestock. In contrast, soil factors such as silt, pH, and gravel content are effective in the distribution of poor quality plant species in poor condition rangelands. Rutherford and Powrie (2010) [55] studied to quantify and understand the impact of severe land degradation on plant diversity in Succulent Karoo in South Africa and found that although the total number of species declined due to heavy grazing, greater equality resulted in an increase in species diversity.

According to this study, the Hill N1 index is the best for recognition the difference between different rangelands. This is in the line with Peet’s (1974) [56] results about the Hill index. However, Magurran (1988) [57] determined that the Shannon diversity and Simpson diversity indices are the best for recognition of species diversity. The estimated Shannon and Hill N1 indices in this study showed significant differences between the good rangeland area and abandoned rain-fed or poor condition rangelands based on all species as well as on perennial species coverage. Panitsa et al. (2010) [58], applied stepwise regressions to test the effects of similar factors on the species richness of native and especially of endemic plants, at local scales. They concluded that a strong correlation exists between intercept values arising from species–area relationships at the family level and total richness of these families in their studied area (South Aegean, Greece).

5. Conclusions

The study showed that distance to roads, villages, and watering points can affect rangeland sites. Poor condition rangelands and good condition rangelands have the closest and the farthest distances to the human made facilities, respectively. Good condition rangelands have the highest level of species diversity and richness among all the mentioned sites. According to the multivariate regression analysis, the most influential factor on the species diversity index is the distance to village parameter; which signifies the important role of humans in degrading rangelands and reducing species diversity. Accordingly, this study concludes that the best way to conserve natural ecosystems, especially rangeland ecosystems is rangelands management in terms of extending and reserving plant species diversity. This study addressed some dimensions of interactions between human and environmental factors and plant vegetation in native rangelands within semi-arid areas of Iran. It was forecasted that the result of this study could be utilized as a basis for anticipating of the probability of the plant species in rangeland within similar ecosystems and recommend the suitable guidance for management and development of rangelands for similar regions.

The current study had some limitations in selecting soil properties. This study just focused on soil physical properties such as sand and silt content, clay, saturated soil’s moisture content, and gravel percentage as well as chemical properties such as lime content, pH, electro conductivity, and organic matter content. So, we recommend that future studies focus on determining biological and physical properties of soil quality assessment after land sue change, such as soil respiration, carbon biomass, hydraulic conductivity, soil aggregation, and mean weight diameter. It is also recommended that future studies focus on determining the degree of protection of the species and identify vulnerable, endangered, and critically endangered species.