Modest Trade-Offs Between Timber Management and Fire Susceptibility of a Bolivian Semi-Deciduous Forest

Abstract

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.

Reduced-impact logging: Challenges and opportunities

“…Such mismatches are common because, although it is generally recognized that substantial canopy openings and sometimes even soil disturbances are required to secure regeneration of light-demanding and small-seeded species (e.g., Dickinson et al, 2000;Snook, 1996;Pariona et al, 2003;Putz and Fredericksen, 2004; but see Sist and Brown, 2004), environmentalists and even ecologists (e.g., Foley et al, 2007) often equate the maintenance of pre-logging forest structure with good management. Admittedly, canopy disturbances cause forest understories to be drier and more fire prone (e.g., Holdsworth and Uhl, 1997, but see Blate, 2005), but if yields of commercially important light-demanding species are to be sustained (e.g., Swietenia macrophylla, Cedrela spp., Entandrophragma spp., and Shorea leprosula), then minimizing changes in canopy cover is not a logical silvicultural goal. One cause of this common misunderstanding is the assumption that tropical forests and tree populations are generally at equilibrium before the first modern logging intervention whereas many are still recovering from severe but unrecorded natural or anthropogenic disturbances (e.g., Denevan, 1992).…”

Determining the annual periodicity of growth rings in seven tree species of a tropical moist forest in Santa Cruz, Bolivia

“…Most of them have been caused by uncontrolled fires from agricultural areas adjacent to the forest concession. There have been two recent fire events, in 1995 and 2004, when about 30% of the concession was burned (Blate, 2005). In the area burned in 1995, it was found that although trees were affected by fire, many of them survived and presented fire scars.…”

Leafcutter Ant Nests Inhibit Low-Intensity Fire Spread in the Understory of Transitional Forests at the Amazon's Forest-Savanna Boundary

“…Although this study primarily demonstrates a correlation, the shortage of leaf litter and small-medium woody debris (combustible material), provoked by leaf-cutter ant bioperturbation, likely provides a mechanism whereby fire spread of low-intensity fires is diminished. In this transitional forest, fuel quantity can be more important in determining fire intensity and spread than relative humidity and other microclimate variables, which control fire behavior during the dry season of a typical humid Amazon forest [38][39][40][41]. In fact, fuel mass determined fire behavior in this transitional forest at the AmazonCerrado boundary, where a slight decline in fuels after two annual burns limited fire intensity and spread rates [35].…”