MAERC at Buck Island Ranch
300 Buck Island Ranch Road Lake Placid, Florida 33852 USA
Phone: 863-699-0242 FAX: 863-699-2217 
Email: maerc@archbold-station.org

MacArthur Agro-ecology Research Center (MAERC)

Experimental Design | Plot sampling scheme | Research Project Home

Rationale

The primary limits of productivity in grasslands are the availability of water, nutrients and light.  There have been many excellent long-term studies of how the major ecological drivers in grassland systems, such as fire and grazing, influence productivity by altering the relative availability of these different resources.  There have been few studies in subtropical grasslands to examine basic controls on productivity and nutrient cycling, inter-annual variability in productivity, and the interactive effects of fire and nutrients on productivity, community structure and soil processes.  This experiment examines these interactions in a subtropical wet prairie at MAERC.  We will examine the effect of fire frequency, season of fire and nutrient addition on annual productivity, and species composition of dominant vegetation and over time will also examine the interactive effects of these treatments on belowground nutrient cycling processes and microbial functioning.  Season of fire is particularly applicable to these subtropical prairies because the management burns used by cattle ranches occur in the winter; whereas the "natural" fires in these systems occurred primarily in summer.  These systems are likely limited by the availability of N and we expect N additions to increase productivity and alter species composition of the dominant vegetation.  Phosphorus may also be limiting in these nutrient poor ecosystems and P addition is an additional component of this experiment.

Experimental Design

The experiment is based on a completely randomized split-plot design in which fire is the the main plot treatment and nutrient addition is the split-plot treatment.  The three fire treatments are: 1) annual winter fires  2) annual summer fires and  3) unburned control plots applied to 20 x 20 m plots.  Winter fires will set in January and summer fires in June of each year pending on burn conditions.  Unburned control plots may be burned at a longer interval (e.g. 5 years), which has yet to be determined.  The four nutrient treatments, applied to 10 x 10 m subplots are: 1) annual fertilization with N (50 kg/ha)  2) annual fertilization with P (20 kg/ha)  3) annual fertilization with N and P and 4) unfertilized control.  The nutrients will be added to the plots in March of each year.  The entire experimental areas is surrounded with a wire fence to keep out cattle.  To account for the effects of grazing, four set-aside plots with the winter burn treatment only have been set up just to the south of the fenced area to allow grazing in treatment plots.  These plots can be used for rigorous replicated comparison to ungrazed winter burned plots in the main experimental area.

Minimum annual sampling in the plots includes net primary productivity (peak standing biomass, litter) and species composition (see below).  Additional measurements, such as soil nutrient cycling, will be made on a project-by-project basis, and the plots are available for student projects and cross site studies.  Meteorological conditions at the site are monitored by a nearby meteorological station.

Plot Figure Legend

WB = plots burned annually in winter (January) 

SB = plots burned annually in summer (June)

CB = plots not burned (burn control)

N = nitrogen applied once annually at a rate of 40 kg N ha (NH₄NO₃) 

P = phosphorus applied once annually at a rate of 20 kg ha P₂O₅

NP = nitrogen and phosphorus applied annually at the above rates

C = no nutrients added

I, II, III, IV = Blocks 1, 2, 3 and 4, respectively

Photos of plots during and after first winter burn treatment on January 21, 2003.

Individual plot layout

Regular annual measurements in plots include plant biomass sampling at three areas (50 x 50 cm) per plot at peak biomass (October), and plant species composition in spring and fall at permanent 10 m² areas within the plots.  An example of the annual sampling regime is given below for a winter burned plot.

Funding Sources

Home | Top | Index