Degradation of the Oyamel-Pine Forests in Michoacan

Chip Taylor chip at
Fri Oct 10 18:33:25 EDT 2003

The following is a review of the Brower, et al paper on degradation 
of the forests in the vicinity of the monarch overwinterings sites in 

>>From page 57 of the 2001 Monarch Watch Season Summary:
>Degradation of the Oyamel-Pine Forests in Michoacan
>Those of us who have visited the monarch overwintering sites in
>Mexico over many years have seen an erosion of the forests near and
>within the Monarch Reserve. The stream of lumber trucks coming off
>the mountains in the dry (winter) season and the abundance of lumber
>mills in the area have been clear signs of the increasing
>encroachment on the forests. Although the forests within the Reserve
>are managed, with a certain degree of selective cutting allowed,
>whether these harvests could be sustained by natural regeneration and
>growth is in doubt. Indeed, if deforestation continues unchecked, the
>oyamel-pine forests that host the overwintering monarch population
>could become so degraded as to be unable to sustain this population,
>particularly during winter storms that can devastate the population.
>We live on a changing planet and most of us are aware of the rapid
>changes in land use in the areas surrounding our cities. Yet, even
>though change is apparent to some, others, particularly decision
>makers, are blind to it or consider it beneficial, irrespective of
>the secondary consequences. The problem for those of us who are
>interested in controlling change, or minimizing its secondary
>effects, is that we have to convince the doubters that change is
>underway and that the consequences are potentially negative. To make
>the case that change is occurring, particularly for the politicians
>and organizations that support conservation efforts, we need evidence
>(quantitative data) showing the impact of particular practices, such
>as deforestation, and the future impact on the area if these trends
>Fortunately, we now have quantitative data that defines the rate of
>deforestation. Lincoln Brower (Sweet Briar College), working with
>Guillermo Castilleja of the World Wildlife Fund and a team of
>colleagues from the National University of Mexico (UNAM) recently
>published a quantitative analysis of the changes in forest cover from
>1971 until 1999 (Brower, et al. 2002). The analysis is based on the
>careful study of aerial photographs of the forested areas in and
>adjacent to the Monarch Reserves. The baseline forest was considered
>to be one in which at least 80% of an area was covered by forests.
>(There are natural gaps in most forests and 80% cover was considered
>to be an intact forest in this study). The first question addressed
>was how much of this intact forest, as of 1971, had changed in the
>subsequent 28 years. The authors found that 44% of the forest with
>80% cover had been degraded in this period. Further, the rate of
>deforestation for the general region had increased over the last 15
>years to 2.41% per year. Surprisingly, the loss of forest was even
>higher for the areas protected by the presidential decree of 1986 -
>3% per year - suggesting that this decree had not been as effective
>as hoped at protecting the monarch overwintering habitat. To verify
>and refine the interpretations from the aerial photographs,
>qualitative ground checks of the tree cover were made in both 1985
>and 1999. This is a necessary part of these studies and lends support
>to the veracity of the data.
>The original article contains color photographs, samples of aerial
>photographs that show both loss and recovery of forest cover, as well
>as three color maps showing the overall loss of forest in the study
>area. The locations of known wintering monarch colonies is shown on
>these maps and it is clear that forests in Chivatí-Huacal, which
>supported colonies in the past are gone (or nearly so) and that
>colonies at El Rosario are precariously close the edge of the forest.
>Two aspects of deforestation, modifications of local and regional
>climates and watershed protection, are not dealt with in the paper
>due to its focus on the specifics of change, yet these are important
>factors that have an impact, usually negative, on both the human and
>monarch populations.
>This paper is valuable in many respects. It provides the quantitative
>data needed to establish the extent to which the forest has been
>degraded in the last 28 years. In the future, it will serve as a
>basis for measuring changes in land use and forest quality. And, it
>will be used as the basis for management decisions by conservation
>organizations, foresters, and governments. Hopefully, this paper will
>influence policy and land use in a way that will protect the forests,
>watersheds, soil quality, and the monarchs.
>Brower, L. P., G. Castilleja,  A Peralta,  J. Lopez-Garcia, L.
>Bojorquez-Tapia,  S. Diaz,  D Melgarejo, and M. Missrie. 2002.
>Quantitative Changes in Forest Quality in a Principal Overwintering
>Area of the Monarch Butterfly in Mexico. 1971-199. Conserv. Biol.

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