Timber harvest and Cypripedium montanum: Results of a long-term study on the Medford District BLM

This report summarizes results from a long-term study of mountain lady’s slipper (Cypripedium montanum) on the Medford District, Bureau of Land Management (BLM). This orchid is currently a Survey and Manage vascular plant species with the BLM and the U.S. Forest Service. Populations of this orchid were monitored from 1984 through 1998 in the Foots Creek and Galls Creek watersheds of the Ashland Resource Area.

Goals and Objectives

The overall goal of this project was to evaluate the effects of intensive forest management and document basic life-history traits of this poorly known species. Specific objectives included:

• Compare populations of mountain lady’s slipper with differing management histories for differences in characteristics such as number of stems, stem height, percentage of stems flowering, percentage of flowers setting fruit, and dormancy and mortality rates. Forest management included these four categories:
  • clearcut
  • shelterwood cut
  • second growth (1966 clearcut)
  • unmanaged forest (control)
• Document and describe life-history process such as mortality, dormancy, and growth. Specific questions to address included, are plants more likely to go dormant if they flower or not? If they fruit or not? Are flowering plants likely to flower every year, or are they prone to becoming vegetative after blooming?

Strengths and limitations

This is the first long-term study of mountain lady’s slipper and represents the only carefully collected information on its response to forest management. It also represents the only demographic study of this rare orchid to date.

Results of this study must be interpreted carefully. Forest management treatments were not properly replicated for standard statistical tests, and the clearcut population was located 6 miles from the other populations. Therefore, the following conclusions are best stated as comparisons of populations rather than management actions.

Conclusions

• All measures of mountain lady’s slipper abundance, size and reproduction varied substantially over the course of this long-term study. In fact, year to year variability was the most prominent pattern.

• The population in the clearcut performed poorly compared to most of the other populations in most years. This population lost over 85% of its stems between 1985 and 1998, had relatively short stems, few flowers and low fruit set. Also, mortality was greatest in this population for the years 1991-94 (the period with demographic data), with 38% of the plants dying compared to about 10% in all other locations.

• One of two control populations in an uncut forest stand also did not perform well, at least in some years. By 1998, it had lost 70% of its stems compared to 1985 and generally ranked low in stem height and percentage flowering.

• The population in the shelterwood cuts, in contrast, out-paced the others in many regards. It generally increased or held steady its stem numbers, always was among the top two populations in terms of percentage of stems flowering, and ranked top in fruit set in several years and overall. The other populations generally were intermediate between these extremes.

• Dormancy, the phenomenon of plants not appearing in some years, was the most notable life-history trait of mountain lady’s slipper. Up to 30% of a population was observed to be dormant in any given year, suggesting that long- term studies of tagged individuals are necessary to document population trends in this species.

Summary

The population of mountain lady’s slipper in a clearcut declined dramatically and performed poorly compared to other populations in this study, especially seven years after forest harvest. One control population that was not harvested also declined. Plants in shelterwood habitat did well. Dormancy is a common state in this orchid species. The relatively poor growth, reproduction, and survival of Cypripedium montanum in a single clearcut does not provide conclusive evidence that forest harvest is detrimental to this species. Further studies will be necessary to resolve this with certainty. However, it may give land managers reason to be cautious and favor habitat protection or alternative forest harvest methods such as shelterwood cuts.