The University of West Florida Campus Ecosystem Study: Age-Diameter and Growth Relationships of Longleaf Pine Using Hurricane-Induced Windthrows

Abstract

The campus of the University of West Florida 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 that 65% of these pines are 75 to 125 years old, with estimates based on a model from old-growth longleaf in southern Georgia. To obtain more accurate age data, one can use an increment corer to collect samples from live trees on site; more accurately, disks can be collected from recently fallen trees. On 16 September 2020, Hurricane Sally impacted UWF as a Category 2 storm, with winds reaching 125 kph. Our study took advantage of longleaf pines blowdowns by Sally to obtain cross-sections for age determinations. Two on-campus natural areas 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 of annual rings were recorded. Based on a total of 50 sampled trees, linear regression revealed a highly significant (P<0.00001; r2 =0.84) relationship between DBH and age. Applying this to DBH measures 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 wide-spread 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 represented sites of contrasting land-use history. Direction of stem windthrows did not vary between natural areas and was consistent with characteristics of the eyewall of Hurricane Sally with strongest wind gusts moving from a southeast to northwest direction.