Changes in grazing patterns explain post-Soviet fire trends on the Eurasian steppe better than climate

In grassland ecosystems, fire plays an important role in maintaining biodiversity and ecological functioning but also causes substantial greenhouse gas emissions. Both climate and herbivory are key determinants of fire regimes, yet the relative importance of these factors remains debated. We focused on the steppes of Kazakhstan—one of the world’s largest grasslands and a global fire hotspot—to assess the relative importance of climate and grazing patterns on fire regimes. Specifically, we made use of the natural experiment that the post-Soviet collapse of the Kazakh livestock sector provided. We used the MODIS Burned Area Product and calculated annual livestock grazing demand (required forage intake) from 2001 to 2019. We estimated a binomial mixed-effects model to extricate the impact of grazing demand and climate factors on fire occurrence. Our results show that fire regimes changed markedly on the Kazakh steppes, with exceptionally high fire frequencies and extent in the 2000s. We found a clearly negative association between grazing demand and burned area; in other words, more heavily grazed areas burned less frequently. Moreover, annual grazing demand appeared in more of the best-performing models than precipitation, temperature, relative humidity, or growing degree days. Given that livestock herding is declining in many grassland regions, and native grazers have been lost or greatly reduced in the past, our study highlights the increasing risk of fire with less grazing, but also the potential for grazing restoration to mitigate such risks in the world’s grassland regions.