MODEST TRADE-OFFS BETWEEN TIMBER MANAGEMENT AND FIRE SUSCEPTIBILITY OF A BOLIVIAN SEMI-DECIDUOUS FOREST

Fire threatens to undermine the conservation potential of tropical production forests. Expecting seasonally deciduous forests that require intensive silviculture to secure sustained yields of commercial species to be especially fire prone, I assessed fire susceptibility in a Bolivian semi-deciduous forest subjected to four management intensities: no logging control; selective harvest only; and two harvest treatments with additional silviculture. I quantified treatment effects on fuel loads, vegetative cover, dry-down rates of 10-h fuels, and fire spread in 4-m2 test plots. With these data and daily rainfall records, I estimated the number of fire-prone days per month associated with each treatment. Fuel loads increased with management intensity, but principally in the 1000-h size class. Treatment impacts on vegetative cover were modest, in part because only 30% of the control forest comprised mature stands with closed canopies >16 m high. Fuels dried enough to ignite in 3–5 days in sites with sparse cover, but within 11 days in sites with dense cover. Given that rainless periods of 20 days are common throughout the dry season, fuels are dry enough to burn for long periods in this forest. In the late dry season in forest logged 2–4 months previously, total cover had little effect on whether test plots burned. Plots in recently logged forest burned more readily than those in forest logged one and three years previously. The model developed for calculating fire-prone days indicated that, unlike intact evergreen Amazon forests that typically remain fire resistant, this forest is very fire prone during most dry seasons. The similar number of fire-prone days among treatments suggests that forest managers need not worry about elevating fire susceptibility with their silviculture. These results suggest that timber management and fire susceptibility trade-offs are modest in this forest because it is already fire prone and because the intensity of silvicultural treatments applied was low compared to other tropical production forests. Fire severity, however, would likely increase with management intensity due to increases in 1000-h fuels. Fire prevention efforts must complement silviculture treatments to achieve sustained yields if these and similar forests are to serve both production and conservation goals.