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

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 (three oaks (Quercus chapmanii, Q. inopina, Q.
geminata), three ericaceous species (Lyonia fruticosa, L. lucida,
Vaccinium myrsinites), and two palmettos (Sabal etonia, Serenoa
repens)) in Florida scrub 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, two, 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 414-698 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
vs. burned treatments showed comparable effects of DRI and similar
trajectories over time. Numbers of stems were affected by DRI,
disturbance type, and species. Stems increased after disturbances,
especially with less frequent disturbances and mowing, and
subsequently declined over time. NSC concentrations varied among
species and over time and was 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 effectively used in restorations.