PARENT SESSION
Oral Session # 65: Herbivory V: Deer, Geese, and Chemistry.
Presiding: K Bjorndal
Thursday, August 7. 8:00 AM to 11:30 AM, SITCC Meeting Room 103.
Effects of Key Deer herbivory after fire in pine rockland understory.
Koptur, Suzanne1, Snyder, James2, Ross, Michael3, Liu, Hong1, Borg, Christopher3, 1 Department of Biological Sciences, Miami, FL, USA2 USGS Biological Resources Division, Ochopee, FL3 Southeast Environmental Research Center, Miami, FL, 33199
ABSTRACT- We conducted a two-year experiment to detect and measure effects of Key Deer grazing after fire (as part of a larger study investigating fire effects on vegetation in Lower Keys pine rockland). Pine rockland is a fire-dependent successional habitat, with the diverse understory flora giving way to hardwoods if the habitat is protected from fire for many years. Fire kills all aboveground plant parts, stimulating resprouting in most species and seed germination and establishment in some. New growth is more palatable than surrounding vegetation, and Key Deer eat a variety of plants. We hypothesized that selective herbivory by the deer has the potential to shape the plant community. We built small exclosures (4 ft high field fence) around circular 1 m2 plots in a blocked array in summer burn, winter burn, and control units (exclosures were put up within several weeks of the burns). Deer herbivory in open (non-exclosure) plots was substantially greater in burned than control units, so differences between exclosure and open plots were most dramatic in the burned units. Many plant species attain greater heights inside exclosures, especially in burned units. There was a significant interaction between exclosure treatment and season of burn. Some herbaceous species were able to flower prolifically after fire inside exclosures, whereas they were less abundant and flowered less when deer had access to them. However, we detected no significant differences in overall plant density with either exclosure treatment or season of burn. Cover was estimated with a quantitative scale, and no significant differences were detected with exclosure treatment; however, season of burn did affect cover of plants in the unit one year post-burn. Herbaceous plant species richness was greatest inside exclosures in burned units, followed by open plots in burned units, and lowest in unburned units (no significant difference between exclosures and open plots). Normal interactions may be exaggerated since Key Deer numbers are at an all-time high and much of the pine rockland in the Key Deer Refuge has been long unburned, but there is evidence from our study that selective herbivory after fire affects plant morphology, reproduction, and species richness of the plant community.
Key words: vegetation, herbivory, diversity, fire