Decrease of NDVI values in the southern tundra of Yamal in 2001–2018 correlates with the size of domesticated reindeer population

Abstract

This work aimed to establish the direction of the current dynamics of the NDVI index values in the Yamal Peninsula southern subarctic tundra subzone and to assess its possible causes. For this purpose, we recorded NDVI using the VEGA-Science service of the Space Research Institute RAS during the growing seasons in 2001–2018 at 15 polygons. The temperature conditions of the growing seasons and the size of domesticated reindeer population were assumed to be the main factors determining NDVI. We established that the average NDVI (NDVIAVG) values during the growing season in 2001–2018 decreased by 0.036±0.006 NDVIAVG/10 years. Additionally, the average annual air temperature increased by 1.1 °C/10 years. The size of domesticated reindeer population grazing on the peninsula varied from 200 to 330 thousand individuals and increased by 55±12 thousand individuals/10 years on average. The relationship between NDVIAVG and the growing season air temperature is weak and positive; fluctuations in the growing season air temperature explain up to 3 % of the total variability of NDVIAVG. On the contrary, the relationship between NDVI and the reindeer population size is strongly negative; fluctuations in the reindeer population size explain up to 39 % of the NDVIAVG variability. Thus, our data show that a significant factor in the state of vegetation in southern Yamal at the beginning of the 21st century is the heavy pressure of phytophages, namely — domesticated reindeer.