Climate change and fire-exclusion have increased the flammability of western US forests, leading to forest cover loss when wildfires occur under severe weather conditions. Increasingly large high-severity burn patches are a limitation to natural regeneration because of dispersal distance, increasing the chance that these areas are converted to non-forest. Post-fire planting can overcome dispersal limitations, yet warmer and drier post-fire conditions can still limit survival. Early successional vegetation can alter surface microclimate; however, it is unclear whether this is enough to increase planted seedling survival in southwestern US forests. Here we examined how two shrub species of different canopy density would affect survival rates of planted tree seedlings following a high-severity fire in northern New Mexico. We expected that shrubs with a higher density canopy (Gambel oak) would have a greater effect on buffering below-shrub climate than shrubs with a lower density canopy (New Mexico locust) and seedlings planted under Gambel oak would have higher survival rates. We found that seedlings planted under Gambel oak had survival rates approximately 10% to 35% greater than those planted under New Mexico locust.  The higher light availability beneath New Mexico locust corresponded to higher temperatures, lower humidity, and higher VPD, which impacted the mortality of planted tree seedlings. These results suggest that by waiting for post-fire shrub establishment, shrubs can be leveraged to buffer microclimate and increase post-fire planting success in the southwestern US.

These data are from an experiment to quantify the effects of two common post-fire shrub species (Quercus gambelii and Robinia neomexicana) alter survival rates of planted conifer seedlings by modifying microclimate.  We planted 64 individuals each of four tree species (Douglas-fir, ponderosa pine, southwestern white pine, and piñon pine) in a 2km long zone between 2400m and 2750m asl in the footprint of the 2011 Las Conchas Fire in the Jemez Mountains of northern New Mexico. Seedlings were planted under Q. gambelii and R. neomexicana during winter 2018. We instrumented five Gambel oak and five New Mexico locust planting locations with upward facing game cameras (Moultrie D-80) and iButton® temperature/humidity logger (Model number DS1923; Temperature accuracy ±0.5°C; humidity resolution 0.6%; https://www.maximintegrated.com/en/products/ibutton-one-wire/data-loggers/DS1923.html). Camera and microclimate data were used to quantify the relationship between shrub canopy gap fraction and microclimate variables.  Planted seedlings were surveyed throughout the 2018 growing season.