Fire in the Venezuelan Amazon 1: Fuel biomass and fire chemistry in the evergreen rainforest of Venezuela

The biomass, structure and chemical properties of fuels were measured in seven rainforest communities in the Venezuelan Amazon. Total surface fuel biomass which consisted of the root mat, litter layer, and downed woody materials ranged from 13 t ha-1 in an open canopy, low stature upland forest type (Bana) to 253 t ha-~ in a floodplain forest type (Low Igapo). The majority of the fuel biomass was composed of the root mat and large (> 7.6 cm diam.) woody debris. Chemical contents of vegetation may play an important role in fire behavior. Energy contents of fuels will affect fire severity while compounds in the ash content may act as flame retardants. The energy content, total ash and acid insoluble ash fractions of litter layers and individual plant species varied greatly among communities. Energy content (gross heat of combustion) of the leaf litter layer ranged from - 19,000 to 25,000 kJ kg-~. Forest floor litter ash content varied from 0.8% to 7.7% and acid-insoluble ash varied from 0.4% to 6.2%. In addition to climatic characteristics that affect fuel moisture, it has been suggested that ecosystems with very long fire return intervals (e.g. tropical rainforests) are relatively inflammable because fuel biomass is low, fuel energy contents are low, and flame retardants are high. However, in the Venezuelan Amazon, values of fuel biomass and energy content were often greater and ash contents (flame retardant properties) were often lower than those reported for temperate ecosystems with frequent fire-return intervals.

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