Dr. Frank S Gilliam

Fire is important for the sustainability of longleaf pine ecosystems, preventing establishment of competing species, maintaining spatial heterogeneity and light availability, and enhancing soil nutrient availability. Although longleaf stands within the UWF natural areas exhibit characteristics of chronic fire exclusion, many of these occur along the permanent openings created by powerline rights of way (ROW), altering solar radiation within these stands. Solar radiation not only affects plant growth, but also drives soil weathering, which can be assessed by the three primary particles that determine soil texture: sand, silt, and clay. Sand weathers to silt, and then silt to clay.
The UWF Campus Ecosystem Study (CES) has studied fire-excluded pine stands of the main campus and natural areas since 2019 (Gilliam et al. 2020, 2021, 2022, 2023, 2024). Our study addressed the following questions: (1) how does light in the forest understory vary with respect to permanent openings? (2) how does the forest community vary among three sites relative to the ROW? (3) how does soil texture vary among plots and between sites?

The importance of soil cannot be understated for forest ecosystems, as it comprises the foundation that supports plants by providing nutrients and water necessary for growth and reproduction. Soil texture influences all of these.
Three primary particles determine soil texture: sand, silt, and clay. These arise as products of weathering from both abiotic processes (e.g., water, solar radiation) and biotic factors (e.g., microbes, plants).
A relevant abiotic factor when comparing forest types is solar radiation. Higher solar radiation can increase weathering and alter soil texture (Gilliam et al. 2014). Thus, contrasting canopy types may have different levels of solar radiation leading to different soil texture.
The UWF Campus Ecosystem Study (CES) has to date studied pine- and hardwood-dominated stands of the main campus and natural areas (Gilliam et al. 2020, 2021, 2022, 2023). Our study addressed the following questions: (1) how does light vary with forest type? (2) how does soil texture vary with stand type? (3) is there a soil seed bank?

The longleaf pine (Pinus palustris) ecosystem is among the more diverse in North America, being home to a unique assemblage of species. Over the last century, these forests have been at risk of disappearing due to logging, urbanization, and fire exclusion (Gilliam et al. 2020). Longleaf pine (hereafter, pine)-dominated stands contrast sharply with hardwood stands, both by tree species affecting soil and soil fertility affecting tree species. This ecological feedback has been referred to as circulus vitiosus (Jenny et al. 1969).

The UWF Campus Ecosystem Study (CES) has to date studied pine-dominated stands of the main campus and natural areas (Gilliam et al. 2020, 2021, 2022). Our research extends this to include a hardwood stand (Fig. 1). Our study examined differences between these two forest types, addressing the following questions: (1) how does species composition vary with forest type? (2) how does soil fertility vary with stand type? (3) how does soil microbiome vary with stand type (to be answered later)?

The campus of the University of West Florida was designed in 1963 by John Jarvis to maintain numerous ecological habitats, removing a minimum number of trees during construction. Previous work has examined the campus as a unique urban interface (Gilliam et al. 2020).
Among these ecological features are extensive stands of longleaf pine (Pinus palustris) in natural areas that represent an ecological paradox-longleaf pine is a fire-maintained species (Gilliam and Platt 2006), but urban interfaces typically exclude fire. Images above depicts the following (1-r): a longleaf stand with frequent fire, an on-campus stand without fire, and an open matrix representing what much of the campus was like prior to construction.
The purpose of our research was to address the following questions: (1) what is the composition and structure of unburned longleaf stands of the two areas? (2) how does soil fertility vary between natural areas and change under fire exclusion? (3) what is the age structure of longleaf pine in each natural area and how does that compare to that of the main UWF campus?

The University of West Florida was constructed among second growth longleaf pine (Pinus palustris Mill.) stands that had survived extensive logging in the Florida Panhandle. Previous work on the UWF campus based on tree core data from southern Georgia estimated that 65% of longleaf pines are between 75 and 125 years old (Gilliam et al. 2020). To better estimate age, a more accurate model was developed locally and based on counts of annual rings from whole cross-sections of trees.
Hurricane Sally impacted UWF as a Category 2 storm, with wind speeds ~165 kph (Gilliam 2021),that created numerous longleaf windthrows (i.e., blow downs). Our study took advantage of the longleaf windthrows from Sally to obtain cross-sections for accurate age determinations. Images on the banner above depict (l-r): a windthrow-created opening in a longleaf pine canopy, satellite imagery of Hurricane Sally, and a windthrow longleaf pine after sampling.
Our research addressed the following questions: (1) what is the relationship between stem age and diameter? (2) how does stem growth vary between UWF natural areas? (3) What is the age structure of longleaf pine on UWF campus? (2) how does stem growth vary between UWF natural areas? (3) What is the age structure of longleaf pine on UWF campus?

The long-term reference watershed (WS4), at Fernow Experimental Forest, West Virginia, displays symptoms of N saturation despite considerable spatial heterogeneity in soil properties, such as texture, N pools, and cycling rates. We identified a weathering gradient of three sites within WS4 by assessing differences in clay content across a common geologic substrate. Across these sites (LN, MN, and HN), NO3 production rates vary significantly (low, medium, and high nitrification, respectively) and are negatively related to clay content. It is unknown whether microbial communities vary across these sites and contribute to variability in NO3 production. This study characterized soil microbial communities along this gradient and assessed factors potentially important in explaining microbial composition. We sampled mineral soil from each of the sites, analyzing for moisture, pH, organic matter, extractable N, and microbial biomass and community composition via phospholipid fatty acid (PLFA) analysis. Analysis of variance and canonical correspondence analysis indicated that microbial community composition varied among sites, with a predominance of fungal markers (18:2n6 and 18:1n9c) at the most weathered LN site and Gram negative bacteria (18:1n7c) at the less weathered MN and HN sites. Accordingly, the fungi/bacteria ratio increased in the direction of LN plots in ordination space. Correlations between measured environmental parameters and PLFA data suggest that acidic conditions and low NO3 abundance at the LN site have selected for fungal dominance, although other important factors known to exert an influence on soil microbial communities, such as differences in plant community and clay and organic matter content, may also be playing a role in determining the observed patterns.

The importance of soil cannot be understated for forest ecosystems, as it comprises the foundation supporting plants by providing nutrients and water necessary for growth and reproduction. Soil texture influences all of these.
Three primary particles determine texture: sand, silt, and clay. These arise as products of weathering from both abiotic processes (e.g., water, solar radiation) and biotic factors (e.g., microbes, plants).
A relevant abiotic factor when comparing forest types is solar radiation. Higher solar radiation can increase weathering and alter soil texture (Gilliam et al. 2014). Thus, contrasting canopy types may have different levels of solar radiation leading to different soil texture.
The UWF Campus Ecosystem Study (CES) has to date studied pine-dominated stands of the main campus and natural areas (Gilliam et al. 2020, 2021, 2022, 2023). Our study addressed the following questions: (1) how does light vary with forest type? (2) how does soil texture vary with stand type? (3) is there a soil seed bank?