Small whorled pogonia, Isotria medeoloides, is a rare terrestrial orchid of temperate forests in eastern North America. It is federally threatened, and 1992 recovery criteria in place for this species need to be evaluated in light of current data. Study of I. medeoloides demography is complicated by the potential for belowground dormancy lasting one to three or more years. From 1986 to 2000, we observed 404 individuals in monitoring plots at four sites in Maine, USA, with up to 241 additional plants followed less intensively outside those plots. We used a life cycle diagram to summarize stage distribution data regarding emergence, recruitment, fruiting, and dormancy. A frequency analysis of the stage dynamics of individuals revealed no consistent patterns. Within plots, 17.9% of individuals bore fruits. Of plants that flowered, mean fruit set overall was 55%. Plant abundance within plots declined over time, possibly due to increasing shade and weather-related effects. In 1993, we removed 33% of the tree basal area over subsections of the populations at two sites while also leaving a portion of both sites untreated. We used mixed-effect regressions to test for increased recruitment and rate of capsule production as a result of the canopy treatment. As of 1993, for 187 plants in the treated zones mean capsule production per flowering plant did not decline, while it did decline in the untreated zones. In a subset of 100 paired plants matched by year and site, 95.8% of those impacted by severe herbivory were dead within 4 years, compared to 58% of counterparts with no herbivory. We used these data to evaluate the recovery criteria and recommend a change from a focus on percent flowering to a minimum of at least two capsules produced per year on average over a ten-year period.
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ACKNOWLEDGMENTS. This research was supported by Section 6 of the Endangered Species Act, through the U.S. Fish and Wildlife Service, and administered by the Maine Natural Areas Program, and by the University of Maine, Orono, ME. Participation by A. C. D. after 2004 was sponsored by Stewards LLC of Brooklin, ME. Reports by the authors were submitted to the Maine State Planning Office and Maine Department of Conservation between 1987-2014. Assistants in field data collection included A. D. Haines, H. C. Smith, and T. F. Vining. H. C. Smith and J. Heppinstall assisted with extracting climatological records. Thank you to W. Persons, formerly at the University of Maine, for consultation in SAS programming, and to M. Docherty and F. C. Smith of the Maine Natural Areas Program for logistic support. We had help with climate data from S. Birkel, R. B. Boone, and W. S. Krohn of the University of Maine, including Climate Re-Analyzer of the Maine Climate Change Institute; A. Lester of the National Weather Service, Gray, ME, and J. Schultz of the North East Regional Climate Center, Cornell University, Ithaca, NY. S. Von Oettingen contributed helpful comments on an earlier version of the manuscript, and the paper was much improved by anonymous reviewers, critique by J. Bellemare, and editing by N. Rajakaruna. Discussions with D. Whigham, Smithsonian Institution, helped in many ways. Communications with other researchers, including S. Cairns and W. Brumback, improved the paper. We thank E. Briggs, P. Bozenhard of the Maine Department of Inland Fisheries and Wildlife, Kent Hill School, and T. Rumpf and B. St. John Vickery of the Maine Chapter, The Nature Conservancy. We are grateful to the landowners who made the study possible.
- habitat manipulation
- mixed-effect regression
- shade environment