Wednesday, 3 June 2020

Greater Butterfly Orchid Study - Fourth Year

The lockdown restrictions were eased just in time to allow me to travel down to Christmas Common in the Chilterns to count and measure the greater butterfly orchids there, for the fourth successive year.   The plants are in two enclosures to keep out deer, and in one of those enclosures - the South enclosure, which covers around 200 m2 - all the plants are individually marked once they appear.   So far 330 plants have been marked, of which 253 either flowered or had leaves above ground this year.

Part of the South enclosure
In this enclosure there were 28 flowering plants, 159 had a single leaf, and 66 had 2 leaves.   All the flowering plants were either extant in 2017, the first year of the study or first appeared in 2018.  The number of flowering plants increased by 27% on 2019, but then that was a year when snail damage had a serious impact.   Indeed the numbers are still well down on 2018, and the very dry conditions in late summer 2018 and 2019 also had an impact.   In the North enclosure and outside the enclosure there were a further 38 and 11 flowering plants respectively, bringing the overall total up to 77.

A plant in the North enclosure
 The population structure is changing.   Lots of new plants are emerging, but they are not progressing to robust, flowering plants because of damage by snails and climate factors (which I shall try to quantify).   In the North enclosure orchids are increasingly being crowded out by dog's mercury, cleavers and nettles.

For the first time all the plants outside the South enclosure were marked and measured.   As this area is unfenced, the impact of deer, (muntjac in the main) could be seen.  In addition to the 11 flowering plants the stems of a further 3 were chewed of by deer.  

Several measurements were made on each of the flowering plants in the South enclosure - height, inflorescence, number of flowers and width of lowest leaf.   Photographs of a single flower from each plant were taken so that the flower dimensions and spur length can be calculated, though this is still to be done because it is time consuming.
Plant #205
Plant #205

Plant #205 - Length of spur measurement
With 4 years of data tracking plants individually there is lots of analysis to be done:
  • climate relationships with flowering, new plant generation and plant losses
  • morphology of flowering plants
  • repeat flowering
  • anything else that takes my fancy.
On site there is only one other orchid species, a very few common spotted orchids dotted around.

Common Spotted Orchid

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