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.

Monday, 3 June 2013

The Fields Have Turned Blue

Our croft has turned blue.   Something like a third to a half of the croft has bluebells on it and they are now at their best.  Because every single plant is precious we have to tip-toe round them!

 Normally regarded as a woodland species appearing in glades and rides, on Skye they appear in open fields provided there is some deepish soil, areas also favoured by bracken.    Over the last 5 years we have cleared the bracken (and the brambles) by a combination of strimming, chemicals and hand removal.   My fear was that the use of chemicals might also damage the bluebell population but I don't think it has.

To measure the impact, 3 years ago I staked out 2 plots each a square metre in area and have counted the number of flowering spikes in each plot each year since then.    This table shows the results (flowering spikes per sq metre):
                              Plot 1     Plot 2
               2011        106         107
               2012          88           86
               2013        165           94

In terms of croft maintenance we try to replicate hay meadow conditions which was how it was in the1960's (and a past resident remembers clouds of bluebells then).    We use a powered scythe to cut the grass at the end of July down to about a couple of inches (later and shorter where there are orchids) after the bluebells and grasses have set seed.   Up to 2011 we collected up the mowings into hay ricks, but last you we left the mowings where they were (turning them a little) to add a small amount of nutrient back, except for the area around Plot 2 where the cuttings were removed.

Has this made a difference?   Is the significant increase in Plot 1 a result of the new regime?    Certainly too early to tell, but the seed germinates really easily, if it does not dry out.

 Also in flower at the moment is lousewort, marsh marigold, cuckoo flower, heath milkwort, marsh and dog violets and there are quite a number of common carder bees and white-tailed bumblebees, but only the former seem to pollinate bluebells.

In amongst the bluebells are 3 albino plants, a ratio I calculate of 200,000:1!

We have seen no otters recently.   Gill and Steve at the other end of the village have had a few sightings, one of which last week they thought was a male.  There are a few spraints around.

At the northernmost point of the croft lies a really interesting holt..   Under a rocky bluff  is a holt entrance at the shore, and another entrance at the croft side of the bluff.   There must be a cavernous passage from one to the other.   I have had an infrared trail camera on this for a few days and got pictures of an otter using the holt on 3 days between the hours of 22.00 and 04.00, loosely 'nightime' , remembering that it stays light up almost to midnight at this time of year.