Wednesday, 5 July 2017

Greater Butterfly Orchids in the Chilterns - Fruiting

Down in the Chilterns, a farmer with a strong interest in wildlife has turned over some of his less productive arable fields to wild flower hay meadows.   He is quite passionate about orchids, and in an adjoining woodland there is a thriving population of Greater butterfly orchids (Platanthera chlorantha), which he found a few years ago.   The numbers have increased over those years with a modest degree of management.

I have been fortunate to be allowed free rein on starting a study of the plants, which hopefully will lead to a long term demographic study. The plants are in two patches around 75 yards apart, separated by a forest track, and the farmer has enclosed each group with a four foot fence to keep out deer (conveniently the North and South enclosures)  The canopy, of hazel and beech, shades the plants to quite a degree and we made some measures of the light levels.  Bramble and Dog's mercury surround the orchids.
Plant #89

Plant #89 in Fruit

Plant #84

Plant #84 in Fruit
So far we have marked just about all the plants - flowering and non-flowering - with a total of 343 plants.   We measured the leaf width of the non-flowering plants, and for those that flowered we measured the height, leaf width, spur length, and number of flowers.   Last week we went back to count the number of fruits on  the plants that flowered.  The fruiting success was 31.7% in the Southern enclosure and 28.0% in the Northern enclosure, though I don't think the difference is statistically significant, because the fruiting success of individual plants ranged from zero to in one case, 100%.    By comparison the 5-year average on Skye was 28.6%, plants out in the open in a quite different environment.

Analysis will follow, but an early observation is that the fruiting success of the earliest flowering plants was much the same as those that flowered a couple of weeks later.

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