The University of West Florida Campus Ecosystem Study: age-diameter and growth relationships of longleaf pine using hurricane-induced windthrows.

The campus of the University of West Florida (UWF) was constructed among second-growth longleaf pine (Pinus palustris) stands that survived extensive logging in the Florida Panhandle. Previous studies on longleaf pine on the main UWF campus have estimated, based on a model from old-growth longleaf in southern Georgia, that oldest stems were just under 200 yr old and that > 80% of stems on the main UWF are between 50 and 125 years old. More accurate age data can be obtained from disks collected locally from recently fallen trees. On 16 September 2020, Hurricane Sally impacted UWF as a Category 2 storm, with winds reaching 49 m/sec. Our study took advantage of longleaf pine blowdowns by Sally to obtain cross-sections for age determinations. Two natural areas of the UWF campus were chosen for sampling: the Edward Ball Nature Trail and the Baars-Firestone Wildlife Sanctuary. For each sampled section, diameter at breast height (DBH) and number and width of annual rings were recorded. Based on a total of 50 sampled trees, linear regression revealed a statistically significant (P < 0.00001; R² = 0.82) relationship between DBH and age. Applying this to DBH measurements of 2,165 stems on the main campus indicates that the oldest longleaf pines are ~ 130 years old (mean age = 63.9 ± 0.4 yr), consistent with cessation of historically widespread harvesting in the region. Mean age for the Trails site (55.7 ± 1.6 yr) was significantly lower than that of the Sanctuary (66.7 ± 2.0 yr), suggesting that they represent sites of contrasting land-use history. Annual growth rates of older pines were mostly negatively correlated with temperature. Directions of stem windthrows did not vary between natural areas and were consistent with characteristics of the eyewall of Hurricane Sally with strongest wind gusts moving from a southeast to northwest direction. This study confirms that college/university campuses can be used as a units of ecological study in a way that takes advantage of stochastic events such as tropical cyclones. [ABSTRACT FROM AUTHOR]