Effects of drought on plant parameters of different rangeland types in Khansar region, Iran

Vegetation changes and drought are among the most important processes affecting the formation of ecosystems. The main objective of this research was to investigate relationships of field-assessed plant parameters with remotely sensed vegetation cover and an index of drought severity. These relationships were assessed across a range of vegetation types and across seasonal and annual scales in the Khansar region of Isfahan Province, Iran. Vegetation cover was measured by the MODIS Normalized Difference Vegetation Index (NDVI) (extracted from the USGS MOD13Q1 image product), and drought severity was estimated by the Standardized Precipitation Index (SPI) (for intervals of 1, 3, 6, 9, and 12 months). Field-based plant parameters (vegetation cover, production rate, and leaf area index (LAI)) were measured for a range of vegetation types covering a range of conditions (315 sites in total, assessed in 2016), using a 4-pixel method. The correlation between NDVI, SPI, and field plant parameters was evaluated using Pearson correlation. The results indicated that the production rate and LAI were higher in rangelands with fair conditions than in those with degraded conditions and varied in each vegetation type during the year. The highest and lowest production rates were observed in Astragalus-Agropyrum (28 g m−2 year−1) and Artemisia sieberi-Scariola (9 g m−2 year−1), respectively. The correlation between NDVI and plant production varied across plant communities, from 0.552 in Artemisia sieberi-Scariola to 0.865 in Astragalus-Agropyrum. The correlation between NDVI and SPI was highest for 1-month intervals and varied by plant community between 0.622 (p = 0.006) for Scariola-Cousinia and 0.840 (p < 0.001) Astragalus-Agropyrum. In general, the observations revealed that vegetation type, vegetation form, rangeland condition, and the stratification of the region have key roles in drought monitoring.