High‐Severity Burning Increases Jack Pine Seedling Biomass Relative to Low‐Severity Prescribed Fires

CORE IDEAS: Prescribed fire did not affect jack pine seed germination or seedling establishment. Severely burned soil had 10‐fold the available P and significantly lower organic matter and higher pH. Jack pine seedlings produced about twice as much biomass in severely burned soil. Regional genetic differences in jack pine may alter seedling establishment. Within the state of Wisconsin, there is a gradient of serotiny in Pinus banksiana Lamb. (jack pine). With prescribed burning becoming more common in Wisconsin, understanding the dynamic and variable effects of burning on soil properties and their interactions with post‐fire plant communities is critical. Our objective was to isolate and examine how fire effects on soil properties affect P. banksiana seed germination and seedling growth and establishment. We investigated these effects in two pot experiments and an intact paired core experiment, maintained in a greenhouse for 19 to 24 wk. Soils from the O and A horizons were collected from Coon Fork Barrens, Eau Claire County, WI, before and after a prescribed fire, and O horizon soil was burned in the laboratory to mimic a high‐severity wildfire. In the intact core experiment, seed germination and seedling aboveground mass were not affected by prescribed burning. In the pot experiments, jack pine seedlings produced more biomass in laboratory‐burned soils than prescribed‐burned soils, and seedlings from northwest seed lots consistently had a higher frequency of establishment compared to those from central seed lots. For the low‐severity prescribed fire considered in this study, effects on measured soil properties were minimal, and did not result in any improvement to seedling establishment. For soil properties to play an important role in promoting jack pine seedling growth, hotter fires may be required, while lower‐severity fires will require other effects‐ such as seed release, changes to moisture dynamics, or competition‐ to affect jack pine germination and establishment.