Ponderosa pine (Pinus ponderosa) ecosystems of the western United States have been drastically altered by stand replacing wildfires over the last decade. Reestablishment of ponderosa pine forests after wildfires depends on ponderosa pine regeneration, which is governed by various factors, including the amount of viable seeds, nutrient availability, and the soil microbial community. Restoration treatments were implemented at the Rogers Research Site (RRS) in the Northern Laramie Mountains of Wyoming three years after the high-severity Arapaho Fire. Ponderosa pine was introduced through handplanting seedlings and broad cast seeding, but two years after introduction the average seedling survival was extremely low and regeneration from broad cast seeding was almost nonexistent. To better understand the factors influencing ponderosa pine regeneration after wildfire, we established a growth experiment. Ponderosa pine seeds collected from the Laramie Mountains prior to the fire were seeded in pots filled with soil collected at RRS from the high and low-severity burn plots, and monitored for seedling emergence and growth. In addition, soil nutrient availability and microbial enzyme activity, as well as root mycorrhizal colonization were measured after ~7 and 14 months of growth.
Results/Conclusions
After seven month of growth, both above- and belowground seedling biomass was significantly reduced in soils from the high severity compared to the low-severity burn control plots. Soil nitrogen availability followed the same trend as seedling growth, with lower amounts in the high-severity plots. Preliminary data show that the reduced seedling growth is accompanied by lower mycorrhizal root colonization. Further work will determine the specific mycorrhizal species associated with the seedlings, and if presence of specific taxa may give additional benefits to seedling growth and vigor. Results from this study may be used for improving seedling restoration success after high-severity wildfires, specifically for ecosystems with limited precipitation.