Modeling of Aboveground Net Primary Production Using Topography Factors in Siahpoush and Ganjgah Rangelands of Ardabil Province, Iran

Aboveground Net Primary Production (ANPP) is one of the most important characteristics of rangeland ecosystems that is involved in important issues such as carbon balance. The aim of this study was to model the ANPP of Plant Functional Types (PFTs) and total ANPP with topographic factors in Siahpoush and Ganjgah rangelands of Ardabil province, Iran. Sampling was performed in one square meter plots in three elevation classes, three sloping classes and six geographical directions by clipping and weighing method. ANOVA was used to investigate the relationship between ANPP and topographic factor and ANPP maps were modeled in ArcGIS software using the extracted regression relationships. Results showed that the shrubs ANPP has a significant relationship with elevation. The highest ANPP of grasses and total ANPP which were 1008.27 and 1650.00 kg/ha, respectively were observed in the middle elevation (2107-1877 m). The shrubs ANPP was directly related to the slope and 209.86 kg/ha was estimated at slopes higher than 30%, but the ANPP of grasses and forbs decreased with increasing slope. The highest ANPP of Shrubs (266.25 kg/ha) in the northwest, forbs (458.51 kg/ha) in the eastern direction, grasses (853.44 kg/ha) and total ANPP (1447.00 kg/ha) were observed in the southwest direction. Topographic indices including Topographic Wetness Index (TWI), Stream Power Index (SPI) and Plan Curvature Index (PCI) had no significant effect on variation of ANPP. Assessing the accuracy of the modeled maps was acceptable. These results can provide basic information for estimating ANPP to support rangeland management and balance supply and demand with rangeland products.