Reproductive vigor and environmental factors in populations of an endangered North American orchid, Isotria medeoloides (Pursh) rafinesque

Isotria medeoloides is an endangered orchid found in the eastern deciduous forests of North America. Most sites have acidic soils and are characterized as second-growth deciduous or deciduous-coniferous forest with an open herb layer, low to moderate amounts of shrubs, and a relatively open canopy. Sites are frequently located near breaks in the canopy such as old logging roads or streams. Reproductive output and survivorship were measured in eleven small populations of Isotria medeoloides. Sites were also evaluated in terms of associated vegetation, topography, soil nutrients, and land use history. Data from these sites were contrasted with data from three sites at which I. medeoloides formerly occurred but had recently become extinct. Specific reasons for declines in population size and reproductive output are not known, but may be related to an increase in the amount of associated vegetation surrounding individual I. medeoloides plants. Populations with flowering individuals were generally found in situations with low to moderate amounts of ground, shrub, and canopy cover. Populations without flowering plants had greater amounts of vegetative cover. Sites at which I. medeoloides populations had become extinct had the highest vegetative cover values. Survivorship and flowering of individual plants was positively correlated with estimates of available light.