Analysis of the relationship between geopedologic characteristics with vegetation. : A case study in the Dagh-Finou catchment,Hormozgan province, IranMohammad Zaremehrjardiri Scientific member of the Agriculture & natural resources research center P.o.box 79145-1577, Bandar-Abbas, Iran zare_mehrjardi@yahoo.com 1. Introduction Vegetation cover and species distribution pattern are two important factors in rangeland management and need accurate mapping and monitoring. Most soil scientists and range managers hypothesize that percentage cover and plant species is function of landform, soil characteristic, and that vegetation cover is a complex object but it is possible to make correlation between them, that is, between vegetation type, landform and kind of soil. For instance, on the basis of landform and soil characteristic correlation, different soil types and landform in the Mediterranean and semiarid condition have been classified. Using this as a tool one can also improve rangeland as well as rehabilitation of rangelands especially in the semiarid and arid area of Iran. A large part of Iran is located in the arid and semi-arid region, where, by any criterion, low and erratic rainfall is the most outstanding characteristic of the land. Most of Iran’s rangeland is in a state of instability mainly due to overgrazing and the lack of appropriate grazing systems, especially with regard to the problem of mixed herds of domestic livestock. These factors in combination with climatic condition and deterrioration of soil condition seem to be some of the main causes for the instability of rangelands condition (Farahpour, 2002). The vegetation is the product of environment (Mannetje, 1978), therefore there is relationship between environmental factors and vegetation properties (Abdollahi, 1997). Under natural condition, the vegetation cover is determined by the interaction of environmental factors such as climate, geology, soil, aspect, slope-steepness, elevation and terrain position (Mohammadi 2000). Considering that relationship between vegetation and environmental factors is very important, this case helps to better monitoring and mapping plant species. Distribution and density of vegetation is affected by biotic factors such as topography, soil, geomorphology and climate. A number of studies have found relationship between canopy vegetation cover and environmental variable. Bayat (1998) studied the relationship between vegetation cover and some environmental variables. According to this study altitude had a significant direct relationship with total vegetation cover and a significant inverse relationship with annual grass cover and perennial forbs and grasses had a significant direct relationship with altitude. All of the forms (Except annul grass which had the highest amount in south aspect) had the maximum amount in north aspect. Slope steepness had an inverse relationship with vegetation cover but this relationship was not significant. Mirakhorlo (1998) studied the influence of several environmental factors on vegetation cover and available forage in rangeland ecosystems. The concluded that slope, aspect, altitude and climate statistically show a significant relationship with vegetation cover and available forage. The highest correlation was found between slope and vegetation. He also found a highly significant correlation between vegetation cover and available forage which allows prediction of available forage based on vegetation cover. Most of the studies show that canopy cover in North aspect was higher than South aspect, because of generally North facing slopes are cooler and more humid than South facing slopes warmer and more arid (Robert, 1975). The amount of both daily extraterrestrial radiation and monthly global radiation in slope areas is the highest on the south aspect and the lowest on the north aspect (Zuviria, 1992). Less solar radiation on the northern aspect causes less evapotranspiration and thereby higher water availability (Frahnak and Movahhed, 1997). Also according to most studies there is significant relationship between altitude and vegetation because of a high correlation between precipitation and elevation has been observed in semiarid landscapes (Smith et al., 1990). Moisture availability is important variable to affect vegetation cover in arid zone. According to Zohary (1973) canopy cover in the cliffs and rock outcrops is more than other stony habitats, because in rock crevices fine soil material is accumulated and most of rain into these clefts is well preserved and protected against evaporation. In this study the relationship between vegetation parameters and environmental factors is determined. Then simple spatial model is developed for the assessment of mapping the vegetation cover. The result will be important for better management in rangelands and consequently for the implementation of soil conservation and prevention of land degradation. 2. Study area Daghfinoo catchment is located in Hormozgan province between latitudes (27?50?_27?57? N) and longitudes (55? 58?_56? 15? E). The study area has an area of 18360 ha and is situated in mountain and hill area having elevation ranging from 860 m to 3081 m (Fig. 1). The climatic condition of study area is influenced by medium elevation (1500 m) above sea level, with temperatures never below zero. In addition, the study area is affected by the air mass systems mentioned above, whereas the first and third portions have a more influence on precipitation. Annual rainfall is 214 mm, mean temperature 24.33, average maximum temperature 31.25 and average minimum is 17.35 c?. The soils of the study area are mostly shallow. The soils in outcrop of mountain are very shallow and rocky. In mountains without outcrop there is coarse debris of material so the soil is still shallow and stony. The mountains have only suitability as rangeland for herd grazing. In hills depth of soil is more than mountain but the soil is still shallow and stony  Figure 1:Location of the study area 3. Methods At the first prepared of terrain map unit (TMU).A TMU map was created by stratification the study area into relatively homogenous areas that are Terrain Units. In this study black and white aerial photographs from August 1957 were available. The aerial photo interpretation was based on geomorphology and geology. This was done by stereoscope before the fieldwork. The boundaries of interpretation are then corrected during the fieldwork. At the first the study area was divided to tree main units base on geomorphology. Then each main unit subdivided into sub units based on lithology and morhpology. The final TMU shows the distribution of 15, land unit in the study area. The summarized data for each land unit are shown in table 1  In this study the quadrate plots were used for measuring vegetation parameters. For each TMU unit 4 to 19 plots were taken. According to present subject and situation of study area, the stratified sampling method was selected. The observation sites were established by the help of topography, TMU and vegetation type map. In this study size of sample were chosen based on minimal area method which is100 m2 (10*10) and in each plot (10*10) were taken 3 plots 1m2 (1*1). Totally 104 plot with 100 m2 size were taken. At each plot (10*10m) a relevee data sheet was filled in. At the first, a visual estimate of browsing damage, %grass cover, %forbs cover and %shrub cover was made in plots of 100sqm. Then three plots (1m*1m) were randomly taken inside the main plots (100m2). Percentage cover of each species of vegetation type was measured in each plot (1m*1m). Parameters of slope such as slope length, slope shape, slope percent and aspect were measured by compass and altimeter in plots of 100m2. One soil sample was taken for measurement of EC, pH, texture of soil. Field data from relevee sheet were entered into Microsoft Excel and SPSS. Exploratory data analysis was analysed using box plot and confirmatory data analysis through correlation, regression, and Kruskal-Wallis test for finding the relationship between environmental variables and vegetation. 4. Result 4.1. Relationship between geopedologic map unit and vegetation cover There are differences in vegetation cover in different geopedologic map units (Figure 3). The highest vegetation cover occur in Hill with glacis relief-type, moderate slope percent, dominate class altitude is 1200-1400 and deep soil. Lowest cover percentage of vegetation occur in Valley. There is a significant difference in canopy cover percentage of vegetation between glacis (Hi211) and other landform except some part of mountain with soil cover(Mo221). Also it was found significant differences in vegetation cover of Valley with Moutain and Hill.  Fig. 3 Box plot of canopy cover % of vegetation in geopedologic map units 4.2. The relationship between altitude and vegetation There was a low positive correlation between altitude and vegetation cover (r=0.22, p=0.026). When increase altitude increase vegetation cover. There is significant difference in canopy cover percentage of vegetation between altitude <1200and 1200-1400 (Kruskal-Wallis test P<0.01). Also figure 4 shows difference in vegetation cover between different altitude.  Fig. 4 Box plot of canopy cover % of vegetation versus class altitude 4.3. Relationship between slope and vegetation There is a positive correlation between vegetation cover and slope (r=0.373, p<0.01). When increase slope increase vegetation cover and there is difference in vegetation cover between different slope class (figure 5) and some of this difference is significant. There is a significant difference in vegetation cover between slope >65 and slope 0-10, 10-35.  Fig 5 Box and Whisker plots of average cover percentage against slope classes. 4.4. Relationship between aspect and vegetation There is difference in vegetation cover between different aspect (figure 6) but this difference is not significant. High temperature, low soil depth on the hillsides has caused low topsoil moisture. There is no considerable impact of different aspect on increasing the soil moisture and consequently vegetation cover.  Fig 6 Box and Whisker plots of average cover percentage against aspects 4.5. Relationship between soil map units and vegetation There is difference in vegetation cover percentage in different soil map units (figure 7) and some of this difference in significant. Lowest canopy cover occur in B soil map unit that consist Tyipic Xerofluvents, Loamy Skeletal and Tyipic Xerorthents, Loamy Skeletal. There is significant difference in canopy cover between soil map unit B and A, D, E, (?=0.01, p<0.003) and between soil map unit C and A, D, E, (?=0.05, p<0.03).  Fig. 7 Box-Whisker plot of cover % of vegetation again soil map unit A= Typic Xerorthents, Loamy Skeletal over Fine loamy B= Typic Xerofluvents, Loamy Skeletal & Typic Xerorthents Loamy Skeletal C= Typic Xerorthents, Fine loamy over Loamy Skeletal D= Rock & Lithic Xerorthents, Loamy Skeletal E= Lithic Xerorthents, Loamy Skeletal & Typic Xerorthents F= Lithic Xerorthents, Loamy Skeletal & Rock & Typic Xerorthents 4.6. Relationship between vegetation with EC and soil texture There is a negative relationship between EC and cover percentage of vegetation, when increase amount of EC decrease cover percentage of vegetation (figure8) but this relationship is not significant (Kruskal-Whallis taste ?=0.05, p>0.05). There is not difference in cover percentage of vegetation between different soil texture (figure 9)  Fig. 8 Box-Whisker plot of vegetation cover % again EC  Fig. 9 Box-Whisker plot of canopy cover % in various soil texture 4.7. Relationship between browsing damage and vegetation Browsing damage influence cover percentage of vegetation therefore relationship between browsing damage and cover percentage of vegetation was assessed in different geopologic map units, slope classes, altitude. There is an negative relationship between cover percentage and browsing damage in landscapes Hill , Piedmont and Valley (figure 10). Lowest vegetation cover occur in valley whereas has highest browsing damage. There is not clear relationship between cover percentage of vegetation and browsing damage in different altitude classes. There is a negative relationship between browsing and cover in different slope, it means when slope steepness increases vegetation cover increase and browsing damage decrease (figure 11)  Fig10 Average cover %and browsing damage in different geopdologic map units  Fig. 11 Average cover % and browsing damage in different slope 5. Discussion and Conclusion There is significant difference in canopy cover in different geopedological map unit. Highest canopy cover percentage of vegetation occur in hill with glacis relief-type. In this unit natural condition for vegetation is good, soil is deep, and slope percent is low, with moderate elevation. Lowest vegetation cover percentage occurs in the valley. Although this unit has good natural condition for vegetation growth the cover is scarse probably because of high human activity such as over grazing and cutting vegetation cover. Due to the impacts of human the ecology balance is disturbed in such a way that unpalatable species such as Acantholimon spp. become dominant. Generally, canopy cover percentage in the landscape mountain is higher than other landscapes because the study area is located in arid zone, where the important factor influencing vegetation is moisture. In the “Mountain” with calcareous lithology, moisture is available more than other landscapes. The result is the same as under desert conditions, where cliffs and rocky outcrops often enjoy conditions more favorable to plant life than other stony habitats (Zohary, 1973). This is because in rock crevices fine soil material is accumulated and most of rain water that runs into these clefts is well preserved and protected against evaporation. In addition, rocks are favourable habitat for a number of shade demanding plants. Rocks are also inhabited by true lithophytes, whose roots are able to break the solid rock into pieces. There is low positive correlation between altitude and canopy cover percentage(r=0.221, p=0.024). Vegetation cover percentage in the high elevation is significantly more than low elevation (Kruskal-Wallis test). Many studies confirm this result that there is significant relationship between altitude and vegetation because of high correlation between precipitation and elevation has been observed in semiarid landscapes (Smith et al., 1990) There is low positive correlation between slope and vegetation cover percentage(r=0.347, p=0.00) and based on the Kruskal-Wallis test there is a significant difference in vegetation cover between high and low slopes. With increasing slope increase vegetation cover percentage, because human activity such as cutting and browsing damage in low slope is more than high slope and there is inverse relationship between vegetation cover and browsing in the low and high slopes. Generally, north facing slopes are cooler and more humid whereas south facing slopes are warmer and more arid (Robert H. Whittler, 1975). But in the study area because of high temperature, low rainfall, and shallow soil depth on the hillsides there is no considerable impact of different aspects on increasing the soil moisture and consequently vegetation cover. Therefore although box plot shows difference in vegetation cover between different aspects, this difference is not significant. 7. Reference
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