Impacts of Fire on a Selectively Logged Rain Forest in
Eastern Amazonia and the Potential for Fire Reduction

Andrew Holdsworth

Approximately 8000 km² of Brazilian Amazon forest are logged each year. Although virgin forest in eastern Amazonia is generally immune to fire, logged forests are transformed into a fire-susceptible mosaic of gaps and forest patches. In eastern Amazonia I studied the impacts of fire on a logged forest, the microclimatic conditions that foster forest fires, and the measures that loggers might take to reduce fire incidence.

After a typical ground fire in a logged forest, 44% of all trees >10 cm died in contrast to the 3% mortality in a control plot. There was a 15 - 32% increase in the Relative Importance of regenerating successional species in three different ground treatments. The density of regenerating timber species decreased by 68% following fire.

The rate of direct Photon Flux Density (PFD), time since logging, and logging techniques influenced the rate of fuel drying over 16 rainless days of measurements. In non-managed forest I found a significant (p = 0.005) negative correlation between the rate of direct PFD and the # of days fuel sticks required to reach the point where fire can spread. In a recently logged forest large gaps (>700 m²) reached fire susceptibility after 6 days and medium-sized gaps (˜200 - 700 m²) reached fire susceptibility after 15 days. Regrowth in large gaps of a forest logged 4 years earlier maintained fuel moisture conditions similar to those found in virgin forest. Careful logging also can reduce the likelihood of fire. Managed-extraction removes the same amount of timber as non-managed extraction but lacks the large gaps that are most fire-susceptible. Considering 5 years of rainless periods, the fire-susceptible area of a managed extraction forest was significantly smaller (p<0.0001) than that of a non-managed extraction forest.