Effects of repeated fire on Florida oak-saw palmetto scrub

Paul Schmalzer and Tammy E. Foster, NASA Environmental and Medical Contract(# 80KSC020D0023), Herndon Solutions Group, Mail Code NEM-022, Kennedy Space Center, FL

Background/Question/Methods
The dominant species of Florida oak-saw palmetto scrub (Quercus spp., Serenoa repens) sprout after burning from belowground or fire-resistant aboveground buds. Sprouting allows a rapid reestablishment of cover of the species present before fire. Responses to multiple fires may differ from that to a single fire. Fire return interval, site differences, and differences among dominant scrub species may influence post-fire responses.
Here we use long-term data from permanent transects in four scrub sites on Kennedy Space Center/Merritt Island National Wildlife Refuge to test whether growth responses differ through multiple fires. Two sites were established in 1983 and sampled 39 times through 2019, burning five times. One site was established in 1994 and sampled 29 times through 2019, burning five times. One site was established in 2002 and sampled 16 times through 2020, burning four times. We use linear mixed models that account for the repeated measures structure of the data to determine if number of fires affects height growth, total cover ≥ 0.5 m, total cover < 0.5 m, bare ground, cover of the dominant oak ≥ 0.5 m, and cover of saw palmetto ≥ 0.5 m. We use nonmetric multidimensional scaling ordination to compare community composition through multiple fires.
Results/Conclusions
Height, total cover ≥ 0.5 m, cover of the dominant oak ≥ 0.5 m, and cover of saw palmetto ≥ 0.5 m increased with time since burn; total cover < 0.5 m and bare ground decreased with time since burn. In most cases a quadratic term in the growth model was significant. The effects of number of fires differed among sites. Number of fires was associated negatively with height, total cover ≥ 0.5 m, and cover of Quercus myrtifolia ≥ 0.5 m but associated positively with total cover < 0.5 m at two sites. At one site, number of fires was associated positively with total cover ≥ 0.5 m and cover of Quercus myrtifolia ≥ 0.5 m. At the fourth site, number of fires was associated positively with height and cover of Serenoa repens ≥ 0.5 m but negatively associated with cover of Quercus chapmanii ≥ 0.5 m. Community level patterns of change after repeated fires were generally similar as indicated by nonmetric multidimensional ordination. Time since burn was correlated to the first or second ordination axis for these sites. There are indications that fires at short fire return intervals may reduce growth rates of scrub species, particularly oaks.