Evaluating immaturity risk in young stands of the serotinous knobcone pine (Pinus attenuata)

As wildfire becomes increasingly frequent, many plant populations risk local extirpation if fire recurs too soon, a problem dubbed “immaturity risk”. We studied the regeneration of a serotinous conifer species, knobcone pine (Pinus attenuata), as a function of the time between high-severity fires (6-79 years). We evaluated age, cone production, and regeneration at two burned sites in northern California, the Ranch Fire (2018) in Mendocino National Forest, and the Carr Fire (2018) in Whiskeytown National Recreation Area. We found an average of 30.5 filled seeds in closed, brown cones (42% viability of filled seeds). The bulk of the older (gray) cones were partially or fully open, and thus available seed in them at the time of fire was approximately halved. Adjusting for survivorship, the estimated minimum age for knobcone pine to produce one recruit per tree (self-replacement) was 8.2 years. Characterizing the probability of burning as a negative exponential model and using an 81-year re..., , , # Evaluating immaturity risk in young stands of the serotinous knobcone pine (Pinus attenuata)

## Abstract

For most statistical analyses, we used a linear regression model approach in R (R Development Core Team 2020) with log transformed variables when necessary to meet assumptions of normality and equal variance. We adopted the cumulative negative exponential model to evaluate immaturity risk in knobcone pine (Equation 1). To calculate the probability of reburning before age (*F*(*t*)), we separately used the modern mean fire cycle and potential historical fire cycle (*RT*), for the entire range of knobcone pine in northern California and southern Oregon.

To estimate the modern fire rotation for knobcone pine, we acquired perimeters of all fires >400 ha occurring between 1984 and 2021 from the Monitoring Trends in Burn Severity (MTBS) program ([www.mtbs.com](http://www.mtbs.com); Eidenshink et al., 2007) and clipped them to the range of knobcone pine as mapped by E.L. Little’s ...