3C.2
Tropical Fire Regimes of the Past
Kenneth H. Orvis, University of Tennessee, Knoxville, TN; and S. P. Horn, H. D. Grissino-Mayer, L. M. Kennedy, B. L. League, and J. H. Speer
One of the central challenges in managing wildlands is defining the goal: what exactly are the natural conditions we hope to maintain? One of the most scientifically and politically difficult pieces of that challenge is the question of fire: its presence or absence, intensity, and frequency. This paper will look at what we know about fire history in tropical ecosystems, and how we know it, and how much it is possible to know.
Old World and New World tropical ecologies differ fundamentally in the role of humans. In tropical Old World environments, fire-wielding hominids have been part of the ecology for hundreds of thousands of years. In the New World tropics and parts of Oceania humans appear to have been present for a far shorter timespan: long enough to affect vegetation patterns and associations, but perhaps not the plants themselves. In other words, human-set fire is a natural part of Ethiopian ecologies, but might reasonably be considered unnatural disturbance in Panama. When we look back in time at a particular place, we must also decide during which time periods in the past it experienced “natural” fire frequencies, and why.
One insight into fire history is the degree of fire adaptation of the present vegetation taken as a whole. Plant attributes such as prolific post-fire sprouting, seeding strategies adapted to colonize fresh burns, or thickened, insulating basal bark may indicate fire adaptation of individual taxa over evolutionary timespans, but the presence of many fire-adapted species within a particular vegetation community suggests strong fire pressure during recent history. Charcoal in soils and sediments offers another window into the past. Soils are usually not stratigraphic and may be dynamic but charcoal is long-lived within them and can be dated. Sediment sinks such as lakes and bogs preserve records of both regional and local fires that may be separable. Fire scars on living and dead woody stems of trees and large shrubs document fires in recent decades and sometimes over several centuries. Where the scarred plants form annual rings, detailed fire histories can be developed. All of these methods have been employed by the authors variously in the Caribbean and Central and South America, and our studies will serve as examples to illustrate what is possible.
The greatest challenge in interpreting fire history is understanding the range of climatic variation over time, and where the present local climate fits within that history. Patterns and cycles of human occupation and resource use superimpose themselves on climatic changes. The history of human activity in part reflects human response to climate and climate change. Conversely, human activities alter climate both at local scales (opening of canopy, alteration of hydrology, drying of soils and fuels) and at regional scales (decrease in boundary-layer moisture, cloud cover, and precipitation). Modern anthropogenic climate change, both regional and global, may lead to climate regimes unlike historic and prehistoric ones, that will affect future wildfire regimes in ways that may be wholly incompatible with wildland-management needs.
.Session 3C, Changing Fire Regimes in Tropical Environments (Track III)
Tuesday, 18 November 2003, 10:30 AM-6:30 PM
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