Fire Regimes of Forested Kipukas, New Mexico

Funded by the JFSP, Project 01-3-3-29

ABSTRACT

Currently, ecosystem processes that maintain the forests of the American Southwest are operating outside the historical range of variation that existed prior to Euro-American settlement.  Areas that have been minimally disturbed by humans should be targeted for research because they contain valuable information about past ecological processes. In El Malpais National Monument, islands of older substrate material are surrounded by younger lava flows. These areas, known as kipukas, likely preserve pre-settlement forest structure and contain trees old enough to provide information on past ecological processes. The purpose of this study is to reconstruct fire history on minimally disturbed kipukas in El Malpais National Monument, New Mexico. Eight sites were sampled and 105 fire-scarred samples were collected.  Increment cores were taken from living ponderosa pine (Pinus ponderosa Douglas ex. Lawson) trees on two kipukas to examine the age structure of the kipuka forests and to determine whether fire suppression away from the kipukas may be allowing ponderosa pines to encroach onto areas not in their local distribution in the monument. Weibull Modal Fire Intervals ranged from 2.8 years to 42.8 years. The MOI was used because it has been shown to be a superior measure of central tendency, and more effective at identifying Southwestern fire structure independent of variables such as environmental gradient and habitat type. The age structure analyses indicated large numbers of ponderosa pine seedlings as well as a large age cohort <100 years old.  The combined analyses indicate that 20^th century changes in fire frequency on the lava flows due to fire suppression may be indirectly affecting the forest composition on the kipukas.