جستجوی مقالات مرتبط با کلیدواژه « شاخص فاصله ای » در نشریات گروه « آبخیزداری، بیابان، محیط زیست، مرتع »

Knowledge of species distribution patterns in each area is the basis of vegetation measurement. Determining the species distribution pattern helps us select the appropriate methods for measuring quantitative properties such as species density and abundance. In order to study the distribution pattern of three shrub specie, a part of Kurdistan rangelands was selected as the study area. A random systematic sampling method was used along four transects of 300 meters. The first point on each transect was randomly selected and the rest (14 points) were selected along each of the transects with 20-meter intervals from each other. In each vegetation type, criteria such as density and abundance were measured in plots, and the distance from a random point to the nearest plant and to the nearest neighbors was determined along the transects. In addition, the distribution pattern of Acantholimon bracteatum, Astragalus gossypinus and Acanthophyllum mucronatum was determined using distance indices (Eberhardt, Hopkins, Johnson and Zimmer) and the quadrate indices (Green, Morisitas index, Morisitas standard, and Lioyd). The results of analysis showed that the distance indices had more accuracy than quadrate indices with the same performance.

This study aimed to investigate the spatial pattern of two rangeland species; Astragalus verus and Bromus tomentellus in Fereydunshahr-Isfahan. Four range sites (100 × 50 meters) were selected. In each range site, five 100 meters transects were established and the distance of the species from 15 points along the transects were recorded randomly. The number of plants in each species were counted in 2 meters square plots placed in each of the random points along the transects. Spatial patterns of the studied species were determined using distance indices (Hopkines, Pielou, Johnson and Zimer, Eberhart, Holgate, Hines and T square Index); quadratic indices(Green's index, Morisita, Lyoid patchiness, dispersion and standardized Morisita index) and point pattern analysis (nearest neighbor). Because it was not possible to measure all individual of these two plant species coordinates in each site, an area with size of 225 (15 m ×15m) was selected as reference site and spatial coordinates of all A. verus and B. tomentellus were recorded. Results showed that the distribution of both studied species had a random pattern due to relative ecological homogeneous sites and plants behavior. Point pattern analysis had more accuracy than distance and quadratic indices because it considered all perennial species coordination. Among distance indices, Hapkines and Pielou indices offered more appropriate and accurate results. Out of 12 distribution pattern indices, the T square and green indices had the highest precision; and distance indices (except Green's index) had more precision than quadratic indices for detection of spatial pattern of the species.