Fire plays a critical role in forests of the Western United States (US), but as wildfire and climate deviate from historical patterns, increasing fire activity may significantly alter forest ecosystems. To understand the impacts of changing climate and wildfire activity on conifer forests, this study examined the impact of wildfire and seasonal post-fire climate on western larch (Larix occidentalis) regeneration. Destructive sampling of 1651 seedlings from 57 sites within 32 fires that burned at moderate or high severity from 2000-2015 in the northwestern US was used to estimate germination years of seedlings and calculate annual recruitment rates. The study results suggest that climate warming has had variable, yet net-neutral, impacts on the climate suitability for post-fire western larch regeneration across its range – with suitability increasing modestly at ‘cooler and wetter’ sites and decreasing modestly at ‘warmer and drier’ sites. Overall, there is and has been broad climate suitability for post-fire regeneration across the distribution of western larch in the US. The strong influence of wildfire-related factors on post-fire regeneration highlights the important impact that management decisions can have in promoting western larch. For instance, facilitating prescribed or managed wildfire with moderate- to high-severity patches will generate conditions most suitable for natural regeneration, provided sufficient seed sources remain nearby. Additionally, our findings support monitoring for natural regeneration or directing outcomes by planting within the first five years after fire, consistent with current management practices.

Northern Rockies Fire Science Network and the Northwest Fire Science Consortium hosted this webinar from Spencer Vieira (ORISE Fellow at the Alaska Climate Adaptation Science Center) presenting his research on larch regeneration.