3C.5
New fire regimes as spatial agents of land cover change in tropical landscapes: Lessons from the Amazon for natural resource management, conservation and sustainable development
Mark Cochrane, Center for Global Change and Earth Observations, East Lansing, MI
Landscapes are dynamic. Everything from geomorphology to the vegetative land cover changes, albeit on different time cycles. Human activity is dramatically accelerating the pace of change in the tropics. The massive waves of deforestation that have already swept across the World’s temperate forests are now proceeding at even faster rates in the tropics. These landscapes are sometimes being denuded of trees (e.g. Haiti), but more frequently, the once contiguous forests are being chopped into ever smaller pieces. These remnant forest fragments now exist as islands within, or highly irregular borders of, anthropogenic-dominated lands that are undergoing a variety of land uses and fire management schemes. However, even if these forest fragments are protected from intentional deforestation, they still face disturbance regime changes that will alter their character, composition and potentially jeopardize their survival.
One of the main threats to tropical forest remnants is fire. Due to the frequent use of fire and the flammable vegetation surrounding forest fragments, escaped fires are inevitable. Although fire is not a new disturbance in tropical forests, the current fire frequency being experienced by many of these forests is outside of their ecologically tolerable bounds. Individual trees in some of these forests (e.g. deciduous dry forests) are able to survive the fires, but fire threatens their continued regeneration due to the high frequency of burning. In evergreen tropical forests the situation may be even more dire. In these forests, fire propagation is normally impossible due to the characteristically humid environments that are maintained by evapotranspiration from lush foliage that is sealed in by closed canopies. However, damage from desiccating winds along forest edges and the collateral damage of many logging operations reduce their fire resistance. Even in the absence of such damage, the near continual presence of fire across the landscape makes forest fires a question of when they will occur, not if. Once a drought of sufficient length exists, these sensitive forests become susceptible to surface fires that cause damage out of all proportion with their intensity. Previous forest fires can also completely change the fire dynamic of recurrent fires.
At a landscape level, fires create coherent, not random patterns. While there are many modulating factors, from human land use to local microclimates, the resultant fire regimes in these forests can most clearly be described as gradients of decreasing fire-return-intervals that are directly, but nonlinearly, related to proximity of forest edges. The results of such spatially variant fire regimes are degradation and erosion of forest fragments. Most people view the landscape as a static entity but ecosystems are dynamically linked to their disturbance regimes. Even where deforestation frontiers have stabilized, forests will continue to change and be progressively deforested by fire unless current fire return intervals can be substantially lengthened. Conservation of these ecosystems will not be achieved through deforestation legislation or establishment of parks alone. Unless landscape level fire occurrence can be managed much better, many of these remnant forests will not be sustainable. The challenge faced is spatial, social and ecological.
.Session 3C, Changing Fire Regimes in Tropical Environments (Track III)
Tuesday, 18 November 2003, 10:30 AM-6:30 PM
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