Interactions among climate, topography, soil structure and rangeland aboveground net primary production

Abstract

Aboveground Net Primary Production (ANPP) of rangeland ecosystems is driven by interactions among multiple environmental factors. This study aimed to model the combined effects of precipitation, elevation, and soil conditions on ANPP variation along an elevation gradient. Ground surveys and vegetation sampling were conducted in 2016 through 26 sampling sites along two elevation profiles in the rangelands of Moghan-Sabalan, Ardabil Province, Iran. At each sampling site, the ANPP of each plant functional type (PFT; grasses, forbs, and shrubs) was measured, and soil samples were taken from 0–15 to 15–30 cm depth. Regression analysis and structural equation modeling (SEM) were used to investigate the factors affecting both total and PFT ANPP. Soil variables were the best predictors of grass (R2 = 0.51), forb (R2 = 0.61), shrub (R2 = 0.71), and total (R2 = 0.76) ANPP. The SEM interpretation suggested that precipitation is the most important direct driver of ANPP with R2 values of 0.20 (Total), 0.30 (Shrubs), 0.26 (Grasses), and 0.10 (Forbs). Whereas soil factors were good predictors in the regression models, the SEM models demonstrated that soil factors were generally unimportant compared with climate, likely owing to the close links between soil-forming factors and climate. The results make it possible to estimate annual ANPP combined with climate forecasts and leads to more accurate estimates of future grazing capacity by policy makers and stakeholders.