Thursday, 27 June 2013

Orchid Invasion

Northern Marsh Orchid
The fields of blue are just a memory as the bluebells have faded and are setting seed.   There is lots of pignut where they flowered but nothing like as spectacular, not helped by some pretty average weather.  

The botanical interest has shifted to other areas of the croft where the soils are poorer (not that any part can be said to be anything other than marginal) and we now have six species of orchid in flower: early marsh, northern marsh, heath fragrant, heath spotted and both greater and lesser butterfly orchids.   There may be a seventh, common spotted orchid, because a few plants have the characteristic long middle lobe on the labellum but I am not sure whether it is not just variability in the heath spotted orchids.   I need to take a closer look.

Over a 3 to 4 week period, the early marsh appear first, followed by northern marsh and lesser butterfly together with a few heath fragrant and heath spotted but the majority of these last species come later along with greater butterfly orchids.   This year the orchids started flowering a couple of weeks later than usual. 

Heath Fragrant Orchid
I have done a count of the orchids in each of the last 5 years to monitor the impact of our maintenance regime.   The croft is not grazed.   The orchid areas are strimmed close to the soil in September after seed set and dispersal, with the trimmings raked off and removed.   Last year there were just under a thousand orchids in total, with hundreds of heath spotted and heath fragrant orchids, though the number of every species has increased year on year.  This year's count is under-way interrupted frequently by rain and midges - clouds of them everywhere.

Heath Spotted Orchid
Early Marsh Orchid

Each orchid species seems to have a preferred niche.   Early march orchids are in the wet, marshy areas where bog asphodel and eared willow are common, and whilst there is some overlap with lesser butterfly orchids the latter seem to prefer slightly drier, low nutrient areas.   Heath spotted are found in both environments but also where there is some heather.   There are differences related to where they grow; in the heathery, moorland-like areas they are paler and have the classic broad labellum but in the wetter areas they are tinged pink and do not have quite the same broad labellum.    There is some overlap between greater and lesser butterfly orchids other than in the marshy areas where there are no greater, but characteristically greater are found in the areas with a deeper sward, often where bracken was previously dominant.   Fragrants are the most catholic as to where they appear.   

I have casually looked at the associated plants and plan to make a more ordered and structured survey this year.   I have also tried to get some indication of soil quality but the commercial garden tests available provide no useful information so I am a bit stuck there.

Lesser Butterfly Orchid
Whilst genetically the two butterfly orchid species are very similar they look different.   Greater are slightly creamier than the paler lesser butterflies, and are physically more robust.   Of course the positioning of the pollinia is regarded as the best differentiator; lesser have two parallel pollinia over a small opening to the nectar-filled spur, whereas the pollinia in greater butterflies are angled widely apart and the opening to the spur is large.   

Greater Butterfly Orchid
I have made a particular study of the butterfly orchids measuring a number of physical attributes for comparative purposes.   All the greater and lesser that have flowered in the previous two years are marked so as well as comparative data I have some interesting stuff on what happens to plants year on year.   Some of the data goes back 5 years.   At the end of this year's count I will summarise the results.  

Hybrid probably Northern x Heath Spotted
There are also some interesting hybrids which can be challenging to assign to parent species.   

I have seen no otters lately and there are no signs anywhere either.   I am hoping Steve and Gill are still seeing them at the other end of the village.   At the start of the month the trail camera was still picking up an otter visiting the 'cliff holt' regularly between 10pm and 4am but I have had to remove the camera because bracken has grown too tall over the otter run triggering the camera in every slight breeze.

White-tailed Bumblebee
Small Heath Butterfly
I was quite surprised to find a white-tailed bumblebee apparently pollinating an early marsh orchid; it is pretty unusual to find any insects on them in the day time.   Elsewhere there were lots of small heath butterflies, suffering like me in the rain.

1 comment:

  1. Hi Terry,
    Steve and I have been away on holiday, so no otter watching between 20th and 30th June. But today (8th July) at 10.15pm we have still water at the end of a hot day, and three otters just offshore from us (south end of Ard Dorch). These are mother and two cubs, but they seem to me to be smaller animals than the ones we've been watching this spring. I could be completely wrong but I wonder if they are a different family.