Changes in tree growth synchrony and resilience in Siberian Pinus sylvestris forests are modulated by fire dynamics and ecohydrological conditions

Abstract

Wildfires are the main disturbance of boreal ecosystems, one of the largest reservoirs of terrestrial carbon. Two-thirds of boreal forests are in Siberia, where peatlands commonly appear mixed with mineral soils. Siberian forests are currently facing a dual shift in environmental conditions regarding climate change and increased fire activity. Therefore, assessing growth patterns of trees subjected to different disturbance regimes is essential to understand the impact of ongoing environmental changes on forest functioning. Following a dendroecological approach, we aimed at analyzing spatial synchrony (âC) patterns of trees subjected to different ecohydrological and fire disturbance conditions in forests of Pinus sylvestris of south-western Siberia. Furthermore, we assessed growth suppression as a proxy for fire occurrence based on tree-ring width chronologies after removing climate signals. Our results endorsed climate as the main driver of âC, which showed different trends depending on substrate type. A release of temperature constraints in the more temperature-limited peat soils led to decreasing âC from mid-1960s onwards, while the opposite pattern was found in mineral soils where stronger reliance on summer precipitation progressively increased âC. However, frequently burned stands suffered a sharp reduction in âC since 1980s likely due to the decoupling of growth from climate as a result of an increase in fire activity. Strong replication of growth suppressions supported by historical and palaeoecological records pointed to 1915, 1952, 1977, 1983, 2003 and 2012 as potential fire years. Post-fire legacies on tree growth after such fire events lasted from one to five years, although differences were modulated by soil type, fire event, growth rate prior fire and tree age. This study highlights the usefulness of addressing spatial synchrony in tree growth and past growth suppressions to disentangle the impacts of climate change and increased fire occurrence on boreal forests.