Deep ground fires cause massive above- and below-ground biomass losses in tropical montane cloud forests in Oaxaca, Mexico

Abstract

Although fire is occurring at greater frequencies and spatial scales in the moist tropics, few studies have examined the ecological impacts of fire in tropical montane cloud forest (TMCF). This study, conducted in the Chimalapas region of Oaxaca, Mexico, documents changes in live tree biomass, live fine-root biomass, and fallen and standing dead wood 4 y following deep ground fires occurring in TMCF during the 1997–98 El Niño Southern Oscillation event. Forests growing on two different substrates (metamorphic and sedimentary) and having three different statures (mean canopy heights: 20–30 m, 15–20 m and 4–6 m) were assessed within six paired plots established on adjacent burned and unburned forest sites. Total live tree biomass was 82% and 88% lower for burned TMCF growing on metamorphic and sedimentary substrates, respectively, compared with unburned TMCF. Nearly 100% of the living biomass was killed in elfin TMCF located on exposed sedimentary limestone at the highest elevations. Live fine-root biomass in the upper organic soil horizon of burned TMCF sites was 49% lower on metamorphic substrates and 77% lower on sedimentary substrates compared with unburned sites. The amount of total dead wood was 3- to 14-fold greater in burned forests compared with unburned forests. These results suggest that first-time fires in relatively undisturbed TMCF can cause dramatic changes in live above- and below-ground biomass at levels greatly exceeding values reported for most lowland tropical rain forests. These patterns may be attributed to the slower decomposition rates and thick organic soils typical of TMCF, combined with the relatively fast drainage associated with steep topography and, in some locations, sedimentary limestone-derived substrates.