DOI: 10.5061/dryad.x3ffbg7k8
title: Evaluating immaturity risk in young stands of the serotinous knobcone pine (Pinus attenuata)

description: 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 return time, we found the likelihood of reburn before 8.2 years
 was 0.09. Our study demonstrated the importance of understanding the size
 and time to reproductive maturity in serotinous tree species to adequately
 quantify immaturity risk. Based on our results and current estimates of
 return time, we suggested that immaturity risk is very low for knobcone
 pine. Our approach could be broadly applied to better quantify immaturity
 risk in other conifer species.
description: # 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 &gt;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 “Atlas of
 United States Trees” (USGS 1999). We used the fire perimeter data to
 calculate the fire rotation for the 25-year period preceding each year
 from 2009 to 2021 following Reilly et al. (2019). Fire rotation was
 calculated as the 25-year time period divided by the proportion of the
 total range of knobcone pine that burned during that time period. We then
 used the inverse of the fire rotation as the single parameter in the
 negative exponential fire cycle (Johnson 1996). ## Usage notes These
 datasets were collected in Whiskeytown National Recreation Area and
 Mendocino National Forest 2019-2021. Details for each dataset are provided
 in the README file. ## Datasets included: 1. Knobcone * Data collected on
 trees and cones from Whiskeytown and Mendocino * Fire = Whiskeytown or
 Mendocino * Age = average age of trees within 5-15 square meters radius *
 DBH = average DBH in millimeters * DBHcm = DBH in centimeters * rgn =
 number of recruits within 5-15 square meters radius * rpm = number of
 recruits per 5-15 square meters radius * rrpm = number of recruits per
 5-15 square meters radius, adjusted for survivorship * lrpm = log of rrpm
 * rpt = number of recruits within 5-15 square meters radius per number of
 trees within 15 square meters radius * gcones = number of cones on the
 ground within 5-15 square meters radius for Whiskeytown, with no values
 for Mendocino (cones in trees and on ground were not differentiated at
 this location). Therefore these cells are filled with n/a. * rrpt = number
 of recruits within 5-15 square meters radius per number of trees within 15
 square meters radius, adjusted for survivorship * tcon = cones in trees
 within 5-15 square meters radius for Whiskeytown, or all cones within 15
 square meters for Mendocino * cpm = total cones per 5-15 square meters
 radius for Whiskeytown and Mendocino * lcpm = log total cones per 5-15
 square meters radius * rpc = number of recruits per number of cones within
 5-15 square meters radius * cpt = total number of cones per number of
 trees within 5-15 square meters radius * lcpt = log total number of cones
 per number of trees within 5-15 square meters radius * trees = number of
 trees within 5-15 square meters radius * dens = number of trees per 5-15
 square meters radius * tall = average height of trees within 5-15 square
 meters radius 1. PIAT 25 Yr Fire Rotation * Year, sum of burn area (ha),
 and percent (the 25-year time period divided by the proportion of the
 total range of knobcone pine that burned during that time period) ##
 Sharing/Access information This data is not uploaded or sourced from any
 other location.