Biogeomorphology relationships among vegetation, soil, and landform elements (Case study of Hablehroud basin)

Introduction
Biogeomorphology, defined as the two-way interaction between geomorphology and ecology in different scales. Every landform is comprised of several micro-scale landform units such as peak, ridge, shoulder, etc. landform units can create various microhabitats and enhance heterogeneity in ecosystems. This information is obtained by extracting patterns from plants, processes, and landforms in the landscape. Differences in landforms are followed by differences in biological factors (type of cover, plenty, pattern, density) and non-biological factors (form, soil, geological, climatic). One of the important factors is the chemical and physical properties of the soil. Because soil not only provides the environment, water, and minerals for the plant but also affects the pattern and distribution, type, and dynamics of the plant. Soil properties in landforms cause changes in pattern, density, and vegetation composition. So, soil properties are influenced by vegetation at smaller spatial scales. Small-scale landform patterns play a major role in determining the plant distribution pattern and are a good tool for evaluating Macro-scale bio geomorphological relationships.
Materials and Methods
The variables examined in this study include the type of landform element, height, chemical and physical properties of soil, and vegetation characteristics (pattern and density). We tested the hypothesis that landform unit features to determine the spatial distribution of vegetation patterns in the case study. This study was aimed to determine the relationship between vegetation properties (vegetation pattern and density) and landform unit type and soil characterize in Hablehroud. Hablehroud basin, that is located between 35°16' 6"- to 35°57' 22" North latitude and 52°15'43" to 53°-8'-53" East longitude (the area about 3200 square km) Between Semnan and Tehran provinces. Our study is based on remote sensing coupled with field observations and laboratory studies.We prepared geomorphic classification of landform unit, vegetation map, and Eco geomorphology map. Using the Geomorphon method of landforms shows the geomorphon-based maps of landforms. Based on geomorphon technique Classification used DEM 12.5 M resolution in SAGA7.5. Geomorphon map includes most common landform elements. In the next step, the vegetation map of the area was prepared using the vegetation index (SAVI). All calculations were performed in ENVI.5.3 software in the next stage after the matching of these two maps; a new Eco geomorphological map was prepared. Where landform-plant units were identified. A field survey was conducted from Jun to July in 2020. We plotted a total of 40 stands within the four micro-landform units in the study basin According to field surveys, and the percentage of vegetation cover four units were identified. Soil samples were collected from a depth of 20cm for all 40 plots (1×1m) some physio-chemical analyses were conducted on them including (PH, EC, wetness, Organic, Texture). According to google earth, field survey, CAD software four types of vegetation patterns includes (spot-dense, gap-dense, spot-scatter, gap-scatter) were identified for each plot. Statistical analyses were calculated using Minitab18 software. We investigate the significance and correlation, principal component analysis, and stepwise regression.
Results and discussion
Geomorphon map includes the 10 most common landform elements: peak, ridge, shoulder, spur, slope, hollow, foot slope, valley, pit, and flat obtained from 498 patterns. In the geomorphon map, a pattern of various landscapes has been created. The vegetation index (SAVI) of the area was prepared using Landsat8 – July 2020. The map of eco- geomorphological units includes four types of geomorphon: Slope, Hollow, Foot slope, Spur which are extracted with dense to scattered vegetation. Field studies of soil sampling have been done to measure the physical and chemical properties of the soil, plot and photograph the plots to extract plant characteristics (pattern and density). Four patterns were extracted: dense point, dense gap, scattered point, and scattered gap for 40 plots. After data collection, type of landform, height, soil properties (chemical and physical) and vegetation (pattern extraction and density) for statistical analysis and analysis of biogeomorphology in Minitab18 including correlation, factor analysis, and multivariate and stepwise regression has been.
Results showed that there is a significant relationship between the type of landform and density and pattern of vegetation. Among four landform unit which includes (hollow, foot slope, slope, spur). Foot slope and Hallow have the highest density and spot-dense pattern. The correlation between pattern and vegetation density with soil moisture and landform unit type is significant with value (p <0.003) and landform type with value (p <0.007). The value of R2 indicates that the predictor variables explain 72.32% of the variance in the vegetation pattern of the sign. The results of regression equations showed that vegetation pattern as a dependent variable is influenced by the four variables, first landform type, and wetness, organic, sand percentage. Regression model 70.50% of the variations in vegetation pattern was related to these four variables. Because landform units have a direct and indirect role in other factors of plant growth and distribution such as moisture absorption, heat, amount of organic matter, erosion, soil texture, and activity of microorganisms. Each of the landform units, according to its shape and characteristics, plays a role in the pattern and density of vegetation. The domain landform generally has four extraction patterns (spot-dense, gap-dense, spot-scatter, gap-scatter) in the study area. The differences in landform-unit area, climate, and topographic features show different patterns of vegetation distribution. The pattern and density of vegetation in the spur are often scattered and in the hollow and the foot slope are spot dense, which is due to the morphometric and topographic features of the units.
Conclusion
The results showed that changes in plant distribution patterns are well related to landform type and soil properties. In this study, four types of landform elements (hollow, foot slope, slope, spur) along with chemical and physical properties of soil about the pattern and density of vegetation were analyzed. So that the type of vegetation pattern has a positive correlation with the amount of sand, PH, EC and has a negative correlation with the rest of the variables. The results of the factor analysis and regression model showed that approximately 69 to 70% of changes in vegetation patterns could be predicted by the variables mentioned in the study. Among the independent variables of landform unit type, Soil moisture, Organic matter, and Height have a significant relationship with the dependent variable and state that different patterns of vegetation in different parts of the Hablehroud basin are related to landform type, height, and different soil characteristics. The effect of landform elements is quite different depending on how much it is affected by soil properties. About vegetation, the most spot-dense pattern at the foot slope, hollow, the slope, and the least occurred in the spur. The spot-scatter pattern had the biggest portion on the slopes, the spur, the hollow, and the foot slope. Gap-scatter pattern, the portion of slopes was higher than other landform elements, and the spot-scatter pattern had the least repetition on the desired landform elements, which is generally observed in the slopes.
Therefore, the effects of geomorphic processes of vegetation characteristics are inevitable.