Comparison of vegetation, production and species diversity in different range condition classes (Case study: Darmian-Sarabisheh Protected Area)

It seems that there is a mutual relationship between the classes of rangeland conditions and the characteristics of vegetation and biodiversity. However, there is relatively little and contradictory information in this regard. This research was conducted to compare the percentage of cover, litter, density, production, and numerical indicators of biodiversity among 11 types of plants in the Darmian-Sarabisheh protected area. 

After the field survey and identification of plant types, 11 plant types could be identified in the entire area. Sampling was done by the random-systematic method. For this purpose, three key areas were selected for each plant type, three transects were established in each key area, and 20 plots of 4 square meters were sampled in each transect. In each plot, the percentage of vegetation cover, litter, density, and production was measured. Canopy cover and litter percentage were determined visually. Plant density was calculated by counting plants per unit area. Production was estimated through cover vegetation by double sampling. The Adelaide method was used to estimate shrub production. The range condition was evaluated by the modified four-factor method. Species diversity components, including species richness, evenness, and dominance, were calculated by numerical indices. Also, species abundance distribution models (broken-stick, log-normal, log series, and geometric series) were applied to evaluate plant diversity graphically. The chi-square goodness-of-fit test was used to determine the most accurate fit of species distribution to each statistical model. To compare vegetation characteristics and species diversity components among the 11 studied plant types, one-way analysis of variance (ANOVA) and Duncan's multiple range tests were conducted.  

The results of the analysis of variance showed that between the 11 plant types studied in terms of vegetation characteristics, including the percentage of vegetation cover, litter, plant density, and production, and numerical indices related to species diversity, including species richness, evenness, and dominance, there is a significant difference at the p≤0.01. The mean comparison results showed that the highest vegetation cover percentage belongs to Artemisia aucheri - Stipa barbata (51.23%) in good condition. Acantholimon scorpinus - Cousinia eryngioides and Eryngium bungei- Cousinia eryngioides (46.27% and 40.44%, respectively) in poor condition are in the next. The highest plant density belongs to Artemisia aucheri - Stipa barbata (157 individuals) in good condition, followed by Eryngium bungei- Lactuca orientalis (126 individuals) in poor condition. Astragalus verus- Artemisia aucheri in good condition and Acantholimon scorpinus - Cousinia eryngioides in poor condition have higher species diversity (H¢=2.51 and 2.48, respectively). The species abundance of Eryngium bungei- Cousinia eryngioides and Eryngium bungei- Lactuca orientalis types (in poor condition) follows the log-normal series, which represents stable communities. Also, Astragalus verus- Artemisia aucheri and Artemisia aucheri- Stipa barbata, which are in good condition, follow the log series and the geometric series, which represent unstable and fragile communities. 

Range condition was independent of vegetation cover, production, density, species richness, diversity, evenness, and dominance. Some vegetation types are in poor condition despite high vegetation cover, density, and production. The present study also showed that high species diversity is observed even in the poor-condition class of vegetation types and does not necessarily indicate rangeland stability. Determining ecosystem stability and biodiversity based on species abundance distributions (SADs) is also impossible.