59 - Historical ¹⁴C evidence of fire in tropical montane cloud forests in the Chimalapas region of Oaxaca, southern Mexico

Summary

ABSTRACT

Tropical montane cloud forests (TMCF) in the Chimalapas region of Oaxaca, Southern Mexico were subjected to large-scale fires during the El Niño events of 1997/98. This raised the question as to whether fire occurrence in this type of forest is cyclic. Charcoal fragments were collected for ¹⁴C dating throughout mineral soil profiles down to 50 cm depth at two sites with contrasting geology. Three distinct clusters of fires were found, the first dating from 2350–1900 yr BP, the second from 960–670 yr BP, and the third from 670–470 yr BP. These new data suggest that there have been fires in these TMCF in the past, but at very long time intervals. The identified clusters of enhanced fire activity in the Chimalapas correlate with other paleo-climatic data from Central America and the Caribbean, suggesting periods when the climate was distinctly drier throughout the region. The clustering of fire occurrence at certain times indicates an enhanced risk of repeated fires in secondary TMCF, as has been found for other humid tropical forests.

INTRODUCTION

Sanford et al. (1985) suggested that the fire ecology of tropical rain forests should be considered in both historic and present-day contexts. During the last decades a number of severe large-scale fires have occurred throughout the humid tropical forest domain – usually related to changes in vegetation (fuel and moisture preservation) – and these fires have rendered also shorter droughts critical (Goldammer, 2007). Major El Niño/Southern Oscillation (ENSO) events accompanied by extreme droughts, e.g. in 1982/83 in South-East Asia (Leighton and Wirawan, 1986) and in 1997/98 also in Amazonia and Central America (Malhi and Wright, 2005), have exercerbated fire activity.