Post-fire early successional vegetation buffers surface microclimate and increases survival of planted conifer seedlings in the southwestern United States

Abstract

Climate change and fire-exclusion have increased the flammability of western United States forests, leading to forest cover loss when wildfires occur under severe weather conditions. Increasingly large high-severity burn patches limit natural regeneration because of dispersal distance, increasing the chance of conversion to non-forest. Post-fire planting can overcome dispersal limitations, yet warmer and drier post-fire conditions can still reduce survival. We examined how two shrub species with different structures affect below-shrub microclimate and survival rates of planted tree seedlings (Pinus ponderosa, P. edulis, P. strobiformis, Pseudotsuga menziesii) following a high-severity fire in northern New Mexico. We expected that Gambel oak (Querus gambelii), with its denser canopy, would buffer below-shrub climate causing higher survival rates of planted seedlings more than the lower canopy density New Mexico locust (Robinia neomexicana). Seedlings planted under Gambel oak had survival rates 10% to 35% greater than those planted under New Mexico locust. Higher light availability beneath New Mexico locust corresponded to higher temperatures, lower humidity, and higher vapor pressure deficit, impacting the mortality of planted tree seedlings. These results indicate that by waiting for post-fire shrub establishment, selective use of shrubs can buffer microclimate and increase post-fire planting success in the southwestern United States.

Reduced fire severity offers near-term buffer to climate-driven declines in conifer resilience across the western United States

“…Our work highlights several key drivers of postfire conifer regeneration, but the broadscale nature of our study means that we could not account for local and microsite conditions, fine-scale weather events, intraspecific variation, cone serotiny, or phenotypic plasticity. For example, competition or facilitation from shrubs ( 23 , 61 ), seed dispersal and predation ( 36 , 62 ), interannual variation in seed production ( 63 ), pathogens, herbivory, or edaphic factors not captured in our models may affect conifer establishment and likely vary across our study area. Short-term exposure to extreme conditions [e.g., high soil surface temperatures ( 64 )] can also cause seedling mortality.…”

Novel climate–fire–vegetation interactions and their influence on forest ecosystems in the westernUSA

“…Although fragmented, this live‐tree legacy is superior to complete cover loss because it will facilitate a greater number of species being available during ecosystem reassembly. Local variation in topography or different types of vegetation cover can also cause microclimate to deviate from regional climate sufficient to allow tree seedling establishment (Crockett & Hurteau, 2022; Marsh, Crockett, et al, 2022; Marsh, Krofcheck, et al, 2022). Persistence of mature trees combined with topographic and vegetation mediated microclimate may provide for continued forest cover persistence within landscapes.…”

Experimental warming has limited impacts on post‐fire succession across a burn severity gradient

“…High‐severity fire, as defined in this study, resulted in nearly complete overstorey mortality, which also increased light availability at ground level. Although there are many additional changes to abiotic conditions following high‐severity fire, including altered soil nutrients and microclimatic changes (Muñoz‐Rojas et al., 2016; Pérez‐Valera et al., 2019; Crockett & Hurteau, 2022), the influence of increased light likely played a role in our finding of altered composition in high‐severity areas. The high‐severity areas are dominated by a different community of plants comprised mainly of exotic species with ruderal life histories, suggesting that these species are better able to take advantage of post‐fire light and nutrient resources than native and perennial species.…”