Effects of frequent fire and mowing on resprouting shrubs of Florida scrub, USA

Abstract

Background: Resprouting is an effective strategy for persistence of perennial plants after disturbances such as fire. However, can disturbances be so frequent that they limit resprouting? We examined the effects of fire and mowing frequency on eight species of resprouting shrubs in Florida scrub, USA, using a factorial field experiment. We burned or mowed plots at four disturbance return intervals (DRI): either annually, biennially, every three years, or once in six years (with all plots being treated in the sixth year to control for time since disturbance). We analyzed plant growth responses (height, aboveground biomass, number of stems) based on sampling pre treatment, and six months, one year, two years, and four years post-treatment. We also measured non-structural carbohydrates (NSC) and soil properties to evaluate these factors as potential drivers of resprouting responses. Results: Fire temperatures were hot (mean maxima 414 to 698 °C among burn days), typical of larger fires in Florida scrub. Plant biomass and heights were affected by DRI (being suppressed by frequent disturbance, especially initially) and varied among species with palmettos recovering biomass faster, and species within the same genus generally showing similar responses. Biomass recovery in mown versus burned treatments showed comparable effects of DRI and similar trajectories over time. Numbers of stems were affected by DRI, disturbance type, and species, and increased after disturbances, especially with less frequent disturbances and mowing, and subsequently declined over time. NSC concentrations varied among species and over time and were positively related to biomass. One year post disturbance, soil moisture and organic matter content were higher in mown plots, while pH was higher in burned plots. Given the slightly lower elevation of the mown plots, we interpreted these differences as site effects. Soil properties were not affected by DRI and did not affect biomass responses. Conclusions: Although very frequent disturbances reduced shrub growth responses, the magnitude of plant responses was modest and the effects temporary. Because resprouting shrubs in Florida scrub appear resilient to a range of disturbance return intervals, frequent fire or mowing can be used effectively in restorations.