Dormancy of some terrestrial orchids

Philip Roetman, who is also interested in citizen science, directed me to a paper by Nancy Sather summarising 25 years of monitoring of a species of terrestrial orchids in Minnesota, in central North America next to Lake Superior.  I have picked out some points of interest that could be relevant to understanding terrestrial orchids in Australia.

Link for image

The plant monitored was the Platanthera praeclara (Western Prairie Fringed Orchid).  This is a species with up to 24 showy, white flowers on a spike reaching 1.2 metres tall.  It grows in remnant prairies and sedge meadows and sometimes emerges while areas are covered with water.

The paper was published at a conference in August 2012.  It summarises results from 1985-2010.  The number of plants counted peaked at over 10,000 with high counts in the years between 1993 and 1996.  Average counts in 2006 to 2009 were at 15% of those in the high years.

Dormancy is a fascinating feature of these orchids.  In one study, up to 12% of plants were dormant each year and 30% experiencing dormancy of one to three years.  At two sites the average life spans were 4-8 years with individual plants surviving 22-26 years with episodes of dormancy.

I have heard that individual plants of Calochilus cupreus (Copper Beard-orchid) in South Australia do not come up every year.  The remaining population is monitored once every year.

Figure

The Minnesota Department of Natural Resources uses the nested orchid monitoring protocol depicted in Figure 1 (above), with decreasing numbers of sites as intensity of monitoring becomes greater.  These Levels show the possibilities for monitoring for Australian terrestrial orchids.  Those interested in studying orchids will find want to read the detail about these levels and how the data were collected.

A study by Quintana-Ascencio et al. (2004) is cited in which dormancy is reported lasting “as long as eight years, with more than half of all dormancy episodes as short as one year. Rates of dormancy can be quite high. Across the full 25 years of the study at Burnham WMA, 57% of plants that ever flowered and 70% of plants that lived more than three years but never flowered exhibited at least one episode of dormancy.”

Sather (2012) reports that it was possible to observe plants enter and emerge from multiple periods of dormancy.

“Periods of extended dormancy may also help explain the well-recognized tendency for the locus of flowering plants to shift geographically within populations from time to time and the resurgence of orchid populations after near-disappearance or periods of low numbers. Variations in demographic characteristics of populations between sites and years exhibited in preliminary analyses of our data (Quintana-Ascencio et al. 2004) suggest that it is unwise to draw conclusions from short-term studies or to extrapolate between sites. Studies of 3-5 years are insufficient to frame development of recruits to flowering plants and periods of dormancy that last for three or more years.”

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5 thoughts on “Dormancy of some terrestrial orchids

  1. peonyden

    Such studies obviously require long term observation.
    How long must one wait to declare a particular locality has lost its Orchids (of Species X)?
    I know of several cases where certain Orchids have been seen once and not again.
    But lack of data is not necessarily data of a the loss of the Orchid.
    How long does one have to wait to declare an Orchid deceased (in the field).
    Cheers
    Denis

    Reply
  2. Robert Lawrence

    Hi Denis,

    I recall the figure of 50 years being used in South Australia. Still, if all of the potential habitat of a particular species is destroyed or highly modified, then one could be justified in expecting it to be extinct. With individual plants possibly being dormant or simply not flowering for year, 50 years is probably needed.

    Robert

    Reply
    1. peonyden

      My goodness, Robert.
      I don’t have that long.
      It gives a whole new meaning to “longitudinal studies”.
      Oh dear!
      Thanks
      Denis

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