Edaphic Drivers Influencing Forage Grasslands in Bujagh National Park, Iran

The edaphic and environmental changes in Bujagh grasslands have led to a gradual decline in the wintering waterbird populations in the associated national park. This has particularly affected forage habitats for birds, especially migratory geese. Our aim was to identify the reasons for the loss of habitat quality by examining the structure of the plant community and the edaphic factors that have been instrumental in shifting the grass community pattern to a Rush–Rubus type along the succession route. Bujagh National Park is surrounded by marine, riverine fresh water, and lagoon habitats, and the seasonal floodings of the Sefidrud and Ushmak rivers impact the grassland area along the deltaic pathway to the Caspian Sea. We used the TWINSPAN classification function to extract plant groups and their dominant species. Subsequently, we analyzed land cover changes in the study area over two times (2010 and 2020) to identify alterations in the coverage of main plants and land uses. Following the evaluation of unconstrained ordination methods and the selection of NMDS ordination, we compared the dominant species of groups to the main edaphic predictors. The results indicated that the chemicals and heavy metals in the soil did not play a direct role in the shift from grassland to Rush–Rubus plant type. However, these elements could have a significant impact on the evolution of the structure and the competitive capability among the main dominant species of the grass group. In conclusion, the dominance of the Rush–Rubus type is likely related to other unmeasured environmental and anthropogenic factors that support and enhance their reproductive attributes and herbal proliferation in the grassland territory.