مجله بوم شناسی کاربردی
پیاپی 8 (تابستان 1393)

Diversity is one of the most important issues in studies of vegetation ecology. This study was carried out in research forest of Tarbiat Modares University for surveying herbaceous and woody species diversity in relation to topographical factors (altitude، slope and aspect). For this purpose، 48 plots 400 m2 (20×20 m) were established in the region using selective sampling method. Then، the names and canopy cover of all herbaceous and woody species were recorded in the plots. In total، 137 herbaceous and 50 woody species were recognized which belonged to 167 genera and 72 families. In the case of herbaceous species، results showed that elevation factor had a significant effect on species richness، Margalef and Simpson indices. The species richness and Margalef’s index were highest in high altitudes (1450-1700 m a. s. l.)، and Simpson index was highest in high elevations (1200-1450 m a. s. l.). Slope had a significant effect on diversity and richness. Richness and Margalef index were higher in 60-90% slopes، and Simpson’s index was higher in low slopes (0-30%). In the case of woody species، results showed that elevation factor had a strong effect on all diversity indices. The results of correlations showed that indices of species richness، Margalef and Menhenick indices were reduced with an increase in altitude. Higher altitudes (1450-1700 m a. s. l.) showed higher amount of evenness. Also، the effects of slope and aspect were not significant on any woody species diversity indices.

Secondary succession after wildfire usually leads to vegetation types that can differ with the original vegetation in terms of forage productivity and community stability. Plant functional types (PFTs) can be used as ecological indices for assessing effects of disturbances on the natural plant communities. Accordingly، this research was aimed to identify، classify and analyze PFTs in three rangeland sites: burnt in 2004، in 2008، and control (2010)، in Jowzak، Northern Khorasan، Iran. Floristic list، percentage cover and 24 morphological، phonological and reproductive plant traits were recorded within 1m2quadrates. PFT’s were determined by applying hierarchical cluster analyses and discriminant function analysis on the matrices of 45 species24 traits and 45 species3 sites، using SPSS software. Four different PFTs were identified. Leaf wet weight، life forms and Twig dry matter contents were the most important traits for PFT classification. Two functional types identified as adapted to fire، and two groups as functional types sensitive to fire. According to the results of this research، the most important indices for the effect of fire on secondary succession of Jowzak rangelands can be the reduction of hemicryptophytes perennial geophytes and annuals، increase of plant height، seed size، seed weight، specific leaf area and leaf dry matter content، and decrease of stem weight، leaf and twig dry matter content.

The aim of this study was to investigate the status of dust storms in Kermanshah province، Iran، using climatic and remote sensing data. Dusty days recorded at 12 meteorological stations were obtained and analyzed at monthly and yearly scales from 1990 to 2011 and then the relationship of visibility data (<1000m) with other climatic parameters including temperature، relative humidity، rainfall، maximum wind speed and direction were evaluated using multivariable linear regression. Also، two important dust events on 15/9/2008 and 5/7/2009 were selected and then MODIS level 1B satellite data was converted to brightness temperature data with MODIS conversion Toolkit and then three main dust indices including Ackerman، Miller and TDI were used to map dust distribution in the study area. Results showed that the number of dusty days with a visibility less than 1000 m reached 71، 53 and 112 days in Kermanshah، Islamabadgharb and Sarepolezahab stations، respectively. The maximum dusty days (20 days/year) occurred in Somar station in the west of the Kermanshah province، which is the nearest station to Iraq. According to the regression analysis، the visibility data had the highest relationship (R2>0. 77) with rainfall، wind direction and speed parameters. The results of MODIS dust mapping showed that the performance of dust indices differs from one event to another. According to dust classified maps and visibility data، the Ackerman index performed best، followed by TDI and Miller indices.

The most important pollutants that cause water pollution are nitrogen and phosphorus from agricultural runoff called Non-Point Source Pollution (NPS). To solve this problem، management practices known as BMPs or Best Management Practices are applied. One of the common methods for Non-Point Source Pollution prediction is modeling. By modeling، efficiency of many practices can be tested before application. In this study، land use changes were studied from the years 1984 till 2010 that showed an increase in agricultural lands from 516908. 52 to 630737. 19 ha and expansion of cities from 5237. 87 to 15487. 59 ha and roads from 9666. 07 to 11430. 24 ha. Using L-THIA model (from nonpoint source pollution models) for both land use categories، the amount of pollutant and the volume of runoff were calculated that showed high growth. Then، the seventh sub-basin was recognized as a critical zone in terms of pollution among the sub-basins. In the end، land use change was considered as a BMP using Multi-Criteria Evaluation (MCE) based on which a more suitable land use map was produced. After producing the new land use map، L-THIA model was run again and the result of the model was compared to the actual land use to show the effect of this BMP. Runoff volume decreased from 367. 5 to 308. 6 M3/ha and nitrogen in runoff was reduced from 3. 26 to 1. 58 mg/L and water BOD from 3. 61 to 2. 13 mg/L. Other pollutants also showed high reduction. In the end، land use change is confirmed as an effective BMP for Non-Point Source Pollution reduction.

Climatic change can impose physiological constraints on species and can therefore affect species distribution. Bioclimatic predictors، including annual trends، regimes، thresholds and bio-limiting factors are the most important independent variables in species distribution models. Water and temperature are the most limiting factors in arid ecosystem in central Iran. Therefore، mapping of climatic factors in species distribution models seems necessary. In this study، we describe the extraction of 20 important bioclimatic variables from climatic data and compare different interpolation methods including inverse distance weighting، ordinary kriging، kriging with external trend، cokriging، and five radial basis functions. Normal climatic data (1950-2010) in 26 synoptic stations in central Iran were used to extract bioclimatic data. Spatial correlation، heterogeneity and trend in data were evaluated using three models of semivariogram (spherical، exponential and Gaussian) and the best model was selected using cross validation. The optimum model for bioclimatic variables was assessed based on the root mean square error and mean bias error. Exponential model was considered to be the best fit mathematical model to empirical semivariogram. IDW and cokriging were recognised as the best interpolating methods for average annual temperature and annual precipitation، respectively. Use of elevation as an auxiliary variable appeared to be necessary for optimizing interpolation methods of climatic and bioclimatic variables.

With regard to retrogression trend of rangelands in central Zagross، many native plant species are expected to be increasingly on the verge of extinction. Therefore، for proper rangeland management the optimum harvest intensity of important plant species is an essential factor for rehabilitation and recovery of native rangeland species. This research was aimed to study the response of four range species to clipping intensity on yield and regrowth and to determine the appropriate harvesting intensity to increase the stability and survival of four range species. Astragalus caragana، Astragalus cyclophyllon، Astragalus podolobus and Medicago sativa were planted in the college of natural resources greenhouse in Isfahan University of Technology campus، during 2013 growing season. The experiment was conducted in a randomized complete block design with 3 levels: control، 60%، and 80% cuttings of plant stems at harvest times. Production of dry matter and stem heights were measured and evaluated. The results showed significant differences at α=1% among species، harvest intensity and interactions between species and harvest intensities. Based on these results، M. sativa and A. caragana are more tolerant to moderate and heavy grazing than two other species. Consequently، a harvesting intensity of 60% was recommended as the best allowable use of M. sativa and A. caragana. On the other hand، A. cyclophyllon and A. podolobus were more sensitive to harvest intensity. However، A. cyclophyllon and A. podolobus could not tolerate intensive grazing during the first growing season.