The Percentage of Trees Bearing Cones as a Predictor for Annual Longleaf Pine Cone Production

Thomas Patterson

doi:10.3389/ffgc.2021.718218

Abstract

The U.S. Forest Service has monitored longleaf pine cone production at sites throughout the southeastern United States for over 60 years. Data from the multi-decadal surveys have supported our understanding of the variability of stand-level cone production as it relates to environmental and ecological processes, and more broadly, how longleaf pine operates as a masting species. Cones from longleaf pine are counted each spring using visual surveys that follow a standard protocol. Rapid mast assessments have been proposed in the literature as an alternative to traditional methods, yet these approaches have not been examined for longleaf pine. In this study, I compared average cone production (using the traditional method) to the percentage of trees bearing cones (rapid assessment) to understand the relationship between these two mast measurements. I examined 29 years of data from 18 cone-monitoring sites containing 234 trees. Using simple linear models, I discovered the percentage of trees bearing cones explained 58–94% of the variance in log-average cone production across all sites. One-way ANOVA analysis revealed cone crops required for successful regeneration (25 + cones per tree) occurred when the percentage of trees bearing cones exceeded 90%, and the results from this study underscore the utility of a simple 90% threshold when determining a successful cone crop. While traditional cone-count methods should not be abandoned, I advocate for the use of rapid cone-crop assessments when a proxy approach is suitable.

Highlights

The southeastern United States once supported a variety of longleaf pine ecosystems prior to European settlement, and during the last three centuries the spatial extent of longleaf pine has contracted from over 37 million hectares to less than 2 million hectares due to land-use changes coupled with fire suppression (Frost, 2006)
Longleaf pine cone crops have entered their seventh decade of observation, beginning in Escambia County, Alabama in 1958 (Connor et al, 2014) and currently monitored by the United States Forest Service and collaborators at 11 locations throughout the species’ range (Brockway, 2019)
The percent of trees bearing cones was a strong predictor for log-average cone production at all sites (Table 2)

Summary

Introduction

The southeastern United States once supported a variety of longleaf pine ecosystems prior to European settlement, and during the last three centuries the spatial extent of longleaf pine has contracted from over 37 million hectares to less than 2 million hectares due to land-use changes coupled with fire suppression (Frost, 2006). Longleaf pine cone crops have entered their seventh decade of observation, beginning in Escambia County, Alabama in 1958 (Connor et al, 2014) and currently monitored by the United States Forest Service (hereafter USFS) and collaborators at 11 locations throughout the species’ range (Brockway, 2019) Data from these stands have supported numerous studies that have examined annual cone production as it relates to climate (Pederson et al, 1999; Guo et al, 2016; Leduc et al, 2016), fire (Haymes and Fox, 2012), stand dynamics (Loudermilk et al, 2016), basal ring growth (Patterson and Knapp, 2016, 2018), and its inherit complexity as a masting species (Chen et al, 2016, 2017, 2018, 2020). The robustness of the multi-decadal dataset lies in the repeated measures of cone counts, which are outlined each year in the annual USFS cone report (e.g., Brockway, 2019)

Methods

Results

Discussion

Conclusion