Apr. 10, 2002 Despite decades of legal protection, the billion or so monarch butterflies that overwinter in Mexico are losing the cloudbelt forests they depend on. New research shows that logging in these forests has actually increased and, if unchecked, will destroy most of the monarch's overwintering habitat within decades.
Up to a billion monarch butterflies overwinter in Mexico's cloudbelt forests, and the government has legally protected them for decades. But new research shows that timber harvest in and around these reserves has actually increased and that, at the current rate, logging will destroy most of the monarch's overwintering habitat within decades.
"Our findings reflect the limitations of government-mandated protection decrees as deterrents to habitat degradation," say the researchers. "The grandeur of the monarch butterfly overwintering phenomenon in this tiny area of Mexico is too great a cultural and biological treasure for this rampantly destructive process to continue."
This work is presented in the April issue of Conservation Biology by Lincoln Brower, who was then at the University of Florida at Gainesville and is now at Sweet Briar College in Sweet Briar, Virginia, and seven Mexican co-authors.
Every fall, the eastern North American monarch butterflies migrate to mountain forests in central Mexico, where they overwinter in dense clusters on the boughs and trunks of oyamel firs. The 30 or so overwintering sites are in a cloudbelt that protects the butterflies from freezing on cold nights and from dessicating during the winter dry season. Since these overwintering sites were discovered in 1975, there have been three presidential decrees protecting them (in 1980, 1986 and 2000). But logging has still continued in and around the monarch butterfly reserves.
To assess the effects of this logging, Brower and his colleagues compared aerial images of a major overwintering area that were taken over a 28-year period (in 1971, 1984 and 1999). The 100,000-acre area includes three monarch overwintering reserves (Chincua, Campanario and Chivati Huacal). The researchers gauged forest quality in the area based on the extent of continuous cover: conserved forest had 80% continuous cover, semialtered forest had 30-80% continuous cover and altered forest had less than 30% continuous cover.
Brower and his colleagues found that in 1971, the three reserves were surrounded and connected by extensive areas of conserved forest. But by 1999, more than 40% of the conserved forest had been degraded to semialtered or altered forest. Moreover, the remaining conserved forest was far more fragmented: the number of fragments more than quadrupled (from 13 to 60) and the average size dropped nearly 90% (from about 5,000 to 600 acres).
The researchers also found that degradation of conserved forest actually increased after the 1986 presidential decree protecting the monarch overwintering sites. Degradation around the reserves increased from about 1.7% to 2.4% per year; and, even worse, degradation in the reserves more than tripled, rising from about 1% to 3% per year.
Since then, the rate of forest degradation has continued to accelerate "ominously", says Brower. "A recent visit in March 2002 indicates severe illegal logging around the decreed areas as well as within them, in direct violation of the 2000 presidential decree," he says.
Even so, there is hope. The 2000 decree established a new ecosystem-based monarch butterfly reserve system. Besides tripling the area protected to nearly 140,000 acres, this decree approved use of a multimillion-dollar trust fund to compensate local people for their wood rights and to help them shift to conservation-based economies.
However, Brower and his colleagues caution that the new decree will help the butterflies only if it has teeth: wood harvest must be limited and the limit must be enforced. In addition, local communities must be compensated fairly. If these conditions are met, field observations suggest that this habitat could restore itself naturally within a few decades, say the researchers.
Brower's co-authors are: Guillermo Castilleja of the World Wildlife Fund's Endangered Species Program in Washington, DC; Armando Peralta and Jose Lopez-Garcia of the Universidad Nacional Autonoma de Mexico's Instituto de Geografia in Mexico City; Luis Bojorquez-Tapia, Salomon Diaz and Daniela Melgarejo of the Universidad Nacional Autonoma de Mexico's Instituto de Ecologia in Mexico City; and Monica Missrie of the University of Minnesota in St. Paul.
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