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Abstract Detail

Conservation Biology

Finch, Jessamine [1], Brumback, William [1], Piantedosi, Michael [1].

Emergence and reproductive trends of a globally rare orchid, small whorled pogonia (Isotria medeoloides), over 30 years of monitoring.

Small whorled pogonia (Isotria medeoloides) is a globally rare orchid native to the eastern U.S. with the majority of the world’s populations found in Maine and New Hampshire. Populations are generally found in deciduous or evergreen-deciduous forests with an open understory. Demographic monitoring of a New Hampshire site with several subpopulations began in the 1980s to better understand population dynamics, identify threats, and inform conservation. Monitoring efforts are complicated by long periods of dormancy in the species, with an average length of 6.48±0.08 years. Emergence rates vary from year to year, with 54% of individuals emerging, on average. Plant size is significantly related to reproduction (p < 0.001), with every additional millimeter in leaf whorl width increasing likelihood of fruit production by 12.6±0.5%. Individuals ≥127mm have ≥90% chance of fruiting. The vast majority of reproductive individuals produce a single flower, with 8% producing two blooms. Double blooming plants (135±2mm) are significantly larger than single blooming plants (120±1mm, p < 0.001). However, maximum plant size was greater for single blooming plants, with the largest double blooming plant 35mm (17%) smaller than the largest single blooming individual. Double blooming individuals have a significantly higher rate of capsule production (36%) compared to single bloomers (28%; p < 0.001). Field observations suggested that decreasing light availability in maturing forests is a limiting factor in population growth and reproduction. In 1998, an experimental thinning experiment removing 25% of tree basal area was initiated, doubling light transmission. In the thinned treatment, the number of emerged individuals increased by >600% over the subsequent 15 years while the control remained relatively unchanged. Reproduction also increased under thinning, averaging 17x the number of individuals producing capsules under the control. Future work will evaluate optimal frequency of canopy thinning, as well as the impact of hemlock wooly-adelgid on forest light levels and performance of I. medeoloides. These data provide a unique, long-term view of woodland orchid population behavior and critical insights for continued monitoring and site management.

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Related Links:
Native Plant Trust, Saving Imperiled Plants, A Matter of Sunlight-but How Much?
Center for Plant Conservation, Plant Profile, Isotria medeoloides

1 - Native Plant Trust, Conservation, 180 Hemenway Road, Framingham, MA, 01701, USA

rare species
temperate forest
canopy thinning
population dynamics.

Presentation Type: Oral Paper
Session: TBA
Location: /
Date: Thursday, January 1st, 1970
Time: TBA
Abstract ID:89
Candidate for Awards:None

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