Sponsored by the California Fire Science Consortium
Presented by Derek Young, Ph.D. Candidate at the University of California, Davis.
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Presentation info: In many California forests, the post-fire regeneration period represents an important opportunity for forest communities to respond to changing environmental conditions, including changes in climate. We examined how post-fire weather and climate can influence tree recruitment by surveying regenerating vegetation 4-8 years after 14 different wildfires that burned between 2004 and 2012, a period that captured a wide range of post-fire weather conditions. We found a consistent but weak effect of post-fire drought in reducing regeneration of conifers, especially shade-tolerant species, supporting model-based projections that shrub and hardwood species will increase in dominance as drought becomes more common. However, post-fire recruitment patterns were also strongly related to long-term climate and adult tree species abundance, suggesting that “biological legacies” may constrain post-disturbance recovery outcomes and may limit the ability of forests to naturally track changes in climate.
When natural post-fire tree regeneration is expected to be poor, managers often seek to speed forest recovery by planting trees. Managers generally prioritize planting seedlings grown from locally-collected seed, but little is known about how the seedlings that are adapted to a given site today will perform as the climate changes. Some have suggested planting seedlings from lower-elevation populations that may be better adapted to the more arid conditions expected in the future. To evaluate this strategy, managers on four National Forests in California conducted post-fire restoration plantings using seedlings from populations near the planting sites and from up to 3500 feet below the planting sites. We monitored these seedlings over four years following planting, a window that included three years of extreme drought. We found that in general, seedlings from populations below the planting site performed as well as or better than local seedlings. However, we also observed a wide range of performance both within and among source populations, likely due in part to the limited geographic specificity of seed collection efforts and records. If relocation of genotypes is to be applied more widely, managers should seek to be as specific as possible about seed source and destination environments and consider other potential consequences of manipulating natural genetic patterns across the landscape.