Human and climate influences on frequent fire in a high‐elevation tropical forest

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Summary Surface fire has increasingly been regarded as a critical threat to tropical forests, but much of the research documenting degradation of tropical forests by fire comes from the low‐elevation humid tropics. Fire in high‐elevation tropical forests has received less research attention, but these forests are of high conservation value because they support unique ecosystems, which are often isolated due to their restriction to widely separated peaks. We investigated the frequency and ecological impact of fire on a high‐elevation tropical forest of Pinus hartwegii in Pico de Orizaba National Park in central Mexico. This forest was previously thought to have been degraded by excessive human‐caused fires. We assessed human‐caused changes to the fire regime as well as the impact of climate on fire occurrence, both previously undocumented in this region. We found no increase in fire frequency or evidence of degradation of the forest. We found that the forest was uneven‐aged and contained many large and old trees (maximum age 483 years). In the twentieth century, the forest experienced a frequent surface fire regime, with fires scarring trees in 90 of 100 years. However, most fires were small and asynchronous among sites. Inter‐annual climatic variability was not an influential driver of fire, and El Niño–Southern Oscillation was not significantly related to the occurrence of widespread fire. Synthesis and applications. Our results show that this high‐elevation tropical forest has not been degraded but has existed with frequent fires for at least a century. A trend in the 21st century towards less‐frequent fire could be cause for concern, as a decrease in fire frequency could lead to an increase in tree density and a loss of resilience in the face of climate change and other future disturbance. We recommend that managers take into account historical fire regimes in their local areas: frequent surface fires in the case of Pico de Orizaba. It is important to recognize that although fire can be detrimental in many low‐elevation tropical forests, it is an integral part of this high‐elevation tropical forest ecosystem, and other high‐elevation forests may show similar patterns.