Seed Sources and Safe Sites As Drivers of Larix Cajanderi Regeneration Following Wildfire in the Siberian Arctic

Larix cajanderi forests, which occupy vast regions of Siberia, grow atop and protect carbon-rich permafrost. Regeneration of these forests has important implications for long-term feedbacks into the climate system and their regeneration is strongest following stand-replacing fires. The goal of this project was to assess sources of regeneration limitation in L. cajanderi forests in northeastern Siberia. We focused on (1) regeneration potential of stands varying in tree density and (2) analyzing seedling establishment patterns in relationship to microsite conditions (safe sites) in the landscape. Seed sources were assessed through cone counts and stand surveys in the summers of 2017 and 2018 in 17 mature L. cajanderi stands. L. cajanderi recruitment patterns in relationship to safe site availability were assessed in 15 areas, spanning approximately 800 km2 along the northern portion of the Kolyma River (69.5477 degrees N, 161.3641 degrees E). Density of trees in a stand was negatively related to the number of cones that the average tree produced and stands of moderate density produced more cones per area than either high-or low-density stands. L. cajanderi seedling establishment was facilitated by safe sites in the landscape. We discovered strong evidence that safe sites are considerably more important for seedling establishment in lowland sites than upland areas. The biological explanation for this pattern is presently unknown; however, we hypothesize this pattern is driven by persistently wet (marshy) soils in some lowland sites as a limiter of seedling establishment. Overall, these data suggest the potential for complex linkages between forest density, propagule availability, fire, safe sight colonization, and seedling establishment that may regulate long-term dynamics in the understudied L. cajanderi forests of the Siberian Arctic.