Climate variability may delay post-fire recovery of boreal forest in southern Siberia, Russia

Abstract

Prolonged dry periods and increased temperatures that result from anthropogenic cli-22 mate change have been shown to increase the frequency and severity of wildfires in the boreal 23 region. There is growing evidence that such changes in fire regime can reduce forest resilience 24 and drive shifts in post-fire plant successional trajectories. The response of post-fire vegetation 25 communities to climate variability is under-studied, despite being a critical phase determining 26 the ultimate successional conclusion. This study investigated the responses of post-fire recruited 27 species to climate change and inter-annual variability at 16 study sites that experienced high se-28 verity fire events, mostly in early 2000, within the Scots pine forest – steppe zone of south-eastern 29 Siberia, Russia. These sites were originally dominated by Scots pine; by 2018 they were recruited 30 by different successional species. Additionally, three mature Scots pine stands were included for 31 comparison. A Bayesian Additive Regression Trees (BART) approach was used to model the re-32 lationship between Landsat-derived Normalized Difference Vegetation Index (NDVI) time se-33 ries, temperature and precipitation in the 15 years after a stand replacing fire. Using the resulting 34 BART models, together with six projected climate scenarios with increased temperature and en-35 hanced inner-annual precipitation variability, we simulated NDVI at five-year intervals for 15 36 years post-fire. Our results show that the BART models performed well, with in-sample Pseudo-37 R2 varying from 0.49 to 0.95 for fire-disturbed sites. Increased temperature enhanced greenness 38 across all sites and across all three time periods since fire, exhibiting a positive feedback in a 39 warming environment. Repeatedly dry spring periods reduced NDVI at all the sites and wetter 40 summer periods following such dry springs could not compensate for this, indicating that a pro-41 longed dry spring has a strong impact consistently over the entire early developmental stages 42 from the initial five years to 15 years post-fire. Further, young forests showed higher climate 43 sensitivity compared to the mature forest, irrespective of species and projected climatic condi-44 tions. Our findings suggest that a dry spring not only increases fire risk, but also delays recovery 45 of boreal forests in southern Siberia. It also highlights the importance of changing rainfall sea-46 sonality as well as total rainfall in a changing climate for post-fire recovery of forest.