Soil texture and porosity influence time to mortality for Pinus ponderosa seedlings

The interaction of land use and climate change in the southwestern US has increased the frequency of large, high-severity burn patches. Post-fire reforestation in large, high-severity burn patches can be limited by the hotter and drier environment that typically follows forest overstory mortality. Higher seedling survival often occurs in cooler, wetter microsites. Tree seedling survival could also be moderated or enhanced by plant-soil interactions, a relationship that is less well understood in post-fire landscapes of the southwestern US. We sought to investigate the influence of soil, as a moderator of water availability, on ponderosa pine ( Pinus ponderosa ) seedlings, a commonly planted species in the Southwest US. We used a greenhouse experiment with soil columns from four high-severity burn areas in northern New Mexico, USA to test the hypothesis that fine-textured, high porosity soil would provide the most plant-available water to seedlings. We planted seedlings in soil columns that were filled to field capacity and let them dry. We found that median time to mortality was significantly influenced by soil type, ranging from 87 to 110 days. Higher porosity and clay content increased the time to mortality and explained 46% of the variability. Given that the hottest and driest period occurs prior to the onset of the North American Monsoon and onset delay is projected with additional climate warming, our results suggest that post-fire planting into favorable soil types could increase the probability of survival.