Population Dynamics of the long-lived terrestrial Orchid, Cypripedium candidum

Background/Question/Methods

Attempts to conserve threatened and endangered populations are often hindered by a lack of available data.  Many long-lived clonal plants, and specifically terrestrial orchids, have faced decades of population decline and habitat loss, yet very little is known about their complete life history.  To examine the demography of a threatened terrestrial orchid, Cypripedium candidum, we began a three year study in 2009 in which we established two-100m transects which were sampled at 5m intervals.  At each interval a 1m x 1m grid was used to select plants for monitoring.  All plants within the grid were marked with numbered metal tags to facilitate recapture in subsequent years.  Demographic characteristics of each plant (number of stems, height, number of flowering stems, presence/absence in years 2 and 3, receipt of pollinia, number of seed capsules,number of seeds produced and capsules preyed upon) were recorded.  Each plant was also classified into a stage, based on size and reproduction,(juvenile, small flowering clump and large flowering clump).  Demographic transitions (seedling emergence, size class, reproductive state, and dormancy) were recorded. Other vegetation within each quadrat as well as distance to the three nearest flowering and non-flowering neighbors was also  measured for each plant in the study.  Vegetation density was sampled by calculating the percent cover in a 1m x 1m plot.

Results/Conclusions

We found reproductive effort to be highly variable from year to year, with an average change of +/- 1.6 flowers year to year.  Approximately 5% of individuals in the study were found to be dead or dormant in the following year.  An average of 56% of flowers have set fruit over the study, however there has been significant variation in yearly capsule set due to weather.  Seedling recruitment has been low as expected, with an average of .1 seedlings per 1m x 1m grid over the study.  

The data collected was used to build a matrix model of the population.  The matrix model was used to determine the important demographic stages and transitions for C. candidum.  In addition to providing an estimate of population survival and risk, this model allows us to model management scenarios in order to determine the best management practices for C. candidum.  This model could also be used for restoration of C. candidum at other sites by providing insight into the important factors that determine population survival.