Abstract Detail

The North American Coastal Plain: a Global Biodiversity Hotspot

Ellair, Darin [1], Crandall, Raelene [2], Huffman, Jean [1], Platt, William [1].

Fire, hurricanes, and biodiversity: dynamic processes drive local small-scale biodiversity and heterogeneity across pine savannas.

Pine savannas are major contributors to the North American Coastal Plain Biodiversity Hotspot. Physiognomically a single overstory pine species and a grass-dominated ground layer, these savannas often appear homogenous across flat landscapes. Nonetheless, the considerable small-scale groundcover plant biodiversity changes in composition across local landscapes, in association with small-scale changes in environmental conditions (e.g., elevation, moisture, soils, light levels). We propose that two natural disturbances, fires and tropical cyclones, produce environmental conditions enhancing small-scale biodiversity and accentuating environmental heterogeneity. Predictable aspects of lightning-ignited fires, based on fire scars in pines, include high frequency (1-3 years) and seasonal timing (transition from dry springs to wet summers). Characteristics of individual fires, however, are highly variable within landscapes, and interact with local site conditions (e.g., soil moisture) to influence distributions of species. For example, even with small changes in elevation (<50 cm), fire-tolerant resprouting shrubs are more common in drier uplands where fire return intervals are short, while fire-sensitive reseeding species are restricted to wetter lowlands where fires are patchier and less frequent. Local fire characteristics are influenced by the presence of pyrogenic pine fuels (shed resinous needles). Abundant pine fuels near overstory pines increase fire intensity (burn hotter and for longer durations), removing litter and top-killing groundcover plants. Resilient herbs, such as those with underground storage organs, appear most likely to colonize opened space. Fires are less intense wherever needles are absent (e.g., away from pines). In patches without pines, hardwoods may escape the "fire-trap" and grasses are less likely to burn out in fires. Thus local small-scale biodiversity and spatial heterogeneity result from fires. Hurricanes also increase fuel loads. Local accumulations of pine needles may be doubled; resulting elevated fire intensities may negatively affect groundcover plants across landscapes, opening space. Felled overstory pines generate boles and crowns that burn at very high-intensity, especially if increased pine fuels are combined with long-burning woody fuels. Resulting patches, often with fewer survivors, tend to be colonized by pine seedlings and plant species that immigrate from elsewhere or survive as buried seeds. Disturbances common to pine savannas, such as fires and hurricanes, frequently open the groundcover to varying degrees across landscapes and over time. In addition, these disturbances generate a range of microsite conditions that likely vary in suitability for colonization. This heterogeneity should contribute to the high plant species biodiversity observed in North American Coastal Plain savannas.

Broader Impacts:

1 - Louisiana State University, Department of Biological Sciences, 202 Life Science Building, Baton Rouge, LA, 70803, USA
2 - Washington University - St. Louis, Department of Biology And Tyson Research Center, Box 1137, St. Louis, MO, 63130, USA

Keywords:
fire
hurricane
pine savanna
environmental gradient
heterogeneity
biodiversity.

Presentation Type: Symposium or Colloquium Presentation
Session: SY08
Location: Elmwood/Riverside Hilton
Date: Tuesday, July 30th, 2013
Time: 3:45 PM
Number: SY08006
Abstract ID:391
Candidate for Awards:None