Fruit Set in the Greater Butterfly Orchids at Christmas Common

Back in March I thought that the coronavirus restrictions might impede or worse, lead to the cancellation of the greater butterfly orchid study I am undertaking at Christmas Common, but in the last week I was able to count the number of fruits on the plants that flowered in early June.   This was the final act of the year, so this year's data has been collected without interruption.

Fruit set this year was higher than in any of the previous 3 years at an average of 47%, the number of individual flowers that were pollinated.   Night-flying moths are the pollinators, though in 10 years I have never managed to see a moth actually pollinating a plant.  A typical flower spike has 10 to 15 flowers, opening up first from the bottom of the spike.   Flowers in the middle of the spike are more likely to be pollinated than those at the bottom, and especially those late opening flowers at the top.

A few of the plants simply wither away after flowering but I have no idea why and there are no obvious differences to the majority.

I am all set now to analyse the data during the winter, though my next trio to the site will be in November to cut back bramble, and check the plant labels.   Of particular interest will be to see what inferences can be made about the impact the very dry conditions in July and August last year and in May this year had on plant numbers, and flowering behaviour.

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

Short term extremes of weather and the impact on plants

Covid-19 must be serious; lack of rain for at least a month has not even been mentioned in the newspapers, and this in a country obsessed by the weather.  This month we have had just over 1 mm of rain so far; its a drought!

I went to my nearby meadow at the beginning of the week, and where a couple of weeks ago there were 4 butterfly orchids in bud out of a total of around 25 plants, the dry weather has had a significant impact, shrivelling up the buds and the leaves.   There won't be any flowers this year, and given the state of the leaves they are unlikely to produce sizeable enough tubers for next year's plants to thrive.   I fear that this relatively short spell of continuous dry weather might well have seriously impaired this little population of orchids for two to three years.

On Skye I looked at correlations between orchid populations and climate parameters.  Now, in a more comprehensive study that is now in its fourth year, the landowner and I are undertaking a study of the population dynamics of butterfly orchids in a farm in the Chilterns.   I have carried out some climate comparisons, taking monthly data, but in the analysis I might in the past have missed the importance of some short term extremes such as the current drought.  Were it to rain heavily for a couple of days later this month the dry conditions day after day will be masked in the monthly total figure,  so in future analyses I am going to incorporate the number of days when no appreciable rain fell.  Heavy rain on a few days, with the ground drying out between bursts, is much less helpful than regular rainfall.

Meanwhile our study greater butterfly orchids in the Chilterns are just beginning to flower and I shall undertake a comprehensive count early next week, now that travel is less restricted.

I have been regularly moth trapping, and after a very slow start at the beginning of May, 2 nights ago I had 42 species (59 species year to date) several of which I had not seen before.   

Miller

There is a blackbird nesting in the honeysuckle along my fence in the garden.

Enjoying the Lockdown

I think I have adapted well to confinement.   Staying close to home therefore (no more than 2 to 3 km away), the flowering plant count is now up to around 100 for April, and now includes Adder's-tongue fern, (Ophioglossum vulgatum) in a calcareous field at Coldharbour, which is I think a first for the Hook Norton hectad, but even more excitement came from finding 2 plants of Herb-Paris (Paris quadrifolium) for which there are a scattering of old records, but super to see, and one of my favourites.   I would not have been any near where I found it in any normal year, and there are still a few more corners nearby that I plan to explore, so there might be further delights to find

Herb Paris

Adder's-tongue Fern

I did stretch the rules a bit on Friday, but don't think I transgressed.  I drove 8 km to Wolford Wood, but then spent several hours there.  Lots of Early purple orchids (Orchis mascula) and of course bluebells, bluebells and yet more bluebells.

Early Purple Orchid

Early Purple Orchid

Meanwhile moths seem to have gone into lockdown.  The dry weather allowed me to put the trap out on 4 occasions in April but the counts have been derisory.  So far only 12 species year-to-date compared to 16 in 2019.

House Arrest

Instead of Andalucia, the Chilterns and Dorset, the lockdown has meant Manor Farm, Coldharbour Farm, Belle Isle Farm and Court Farm at points east, west, north and south out of the village along footpaths no more than a couple of miles from home.  As I went, I counted flowering plants, just under 40 in each direction, but in aggregate over 70 in the last 10 days.   All of course common, and in another year I would have ignored them, but in these strange times....

In addition five butterflies (Orange-tip, Brimstone, Peacock, Small Tortoiseshell and Small White) four mammals (Roe Deer, Grey Squirrel, Rabbit, Hare), and at least 20 birds including a flock of maybe a hundred or more fieldfare, getting ready to fly north.

I found leaves of three orchids (Common twayblade, Common spotted, and Pyramidal) - I could be studying them quite intensively this year, being only a couple of kilometers away and within walking distance, whilst my normal study areas are out of bounds.

Early Spring at Foxholes

A couple of days of sunshine gave an opportunity to venture out along oozing mud, once recognised as footpaths.   I went to Foxholes yesterday, a BBOWT reserve near Bledington and Kingham, and mercifully was only hassled by one uncontrolled dog charging along despite the vain and pitiful cries of its owner to heel.  There are several signs asking for dogs to be kept on a short leash.  

Despite  the dog, I saw two muntjac deer, a hare and a short-tailed vole; primroses were in flower and the rosettes of early purple orchids were showing.   These were on bare ground except for a moss, which I think was Rhytidelphus loreus.  There were a few scarlet elf caps nearby.   One of the things I want to do this summer is identify plants and mosses in close association with orchids to get a feel for the extent of plant competition, aggressive or otherwise/  

Primrose

Early purple orchid rosette

Moss, Rhytidelphus loreus (I think)

Scarlet elf cap

The previous day I went to Harvest Hill, a Warwickshre Wildlife Trust reserve near Coventry.   This is a small meadow, which at this time of year has flowering wild daffodils (Narcissus pseudonarcissus) which have none of the coarse, brashness of daffodil cultivars.  

It's definitely spring.

Wild daffodil

Wild daffodil

Changes in the Distribution of Orchids in Oxfordshire Over Time

Last Friday I went to the farm near Christmas Common to check on the greater butterfly orchids there.  4 out of the 10 plants I checked were appearing above ground; one had reached 2 cm high.  They are roughly at the same stage as they were 12 months ago, and before snails created havoc.

Plant #214

Plant #111

Plant #89 

The Christmas Common population is probably the largest in Oxfordshire, but greater butterfly orchid is probably declining in Oxfordshire and indeed more widely. 

The study there is to look at population dynamics but more generally  I am trying to better understand whether orchids are becoming rarer, as seems to be the case, and if so why.  For example, BBOWT has long term datasets  at its Warburg reserve, and for several species the numbers have fallen in recent years.  Two species are no longer found there.

To look at whether orchid species are disappearing in the county I analysed BSBI's records for Oxfordshire (or rather more precisely that bit of the administrative county covered by BSBI's Vice County 23) to determine if orchids are less common than they were 50 years ago.  A limitation is that BSBI's data gives localities but not abundance (a locality with 1 plant has the same weight as another with hundreds), but nevertheless I thought the crude analysis of occurrence would be still be meaningful.

I split the records into decades, from which I then determined how many species were present in each decade and in how many monads i.e.1 km squares (botanists would not be top of the list at Plain English awards), each species was present to give some idea of how rare or otherwise a species might be.  I took the data that was there without any amendment or refinement. 

The number of records per decade and the number of recorders who provided those records were:

• 1970-9     954 records 186 recorders
• 1980-9     833 records 74 recorders
• 1990-9     494 records 167 recorders
• 2000-9     936 records 170 recorders
• 2010-9   1597 records 239 recorders

The rise in activity in the last decade is due to the increased BSBI effort to underpin its Atlas 2020 which will be published in a couple of years or so.

The number of species found in the county has fallen:

• 1970-9 31 species
• 1980-9 29 species
• 1990-9 28 species
• 2000-9 28 species
• 2010-9 26 species

We have lost ghost orchid (not seen anywhere in the UK since 2009, and declining in Europe), musk and burnt orchids, (plants that are associated with short unimproved grassland, and struggle against more aggressive grasses), military orchid (a bit of a special case I suspect) and sword-leaved helleborine (in this part of the world, a lightly shaded woodland plant, but another that does not cope well with aggressive competition).  

Another 3 species are declining and are represented in less than half the monads where they were in the 1970's: greater and lesser butterfly orchids and narrow-lipped helleborine.   The reasons for decline might be:

• loss of habitat
• changes in climate, and one aspect I am looking at is whether warmer winters have led to larger populations of snails, and hence increased predator pressure
• changes in the levels of ammonia, nitrogen oxides, and ozone in the atmosphere, leading to nitrification and enhanced plant competition, and maybe impairment of soil mycorrhiza on which orchids depend to a greater or lesser extent.
• declines in pollinator availability.

But it is not all bad news.   3 species seem to be spreading: bee Orchid, common spotted orchid, and pyramidal orchid.   Of course this may only be due to the increased recording effort in the last two decades - recorder bias (and the number of monads in which they are found correlates well with the number of records collected in each decade), but I think the increase is a genuine one.   These three are early colonisers and seem to germinate easily, often turning up in gardens, and road verges which have been disturbed, or mown regularly at the right time.  Bee orchids in Britain are self pollinated so there are no pollinator availability constraints.

The other 20 species have not seen any real trend in their distributions through the county, though as pointed out earlier, my analysis says nothing about abundance.

Mosses and Liverworts South of Swerford

As winter diversion, the Oxfordshire vice county recorder for plants, David Morris, has teamed up with his counterpart for bryophytes (mosses and liverworts), Oli Pescott, to run field meetings to record mosses and liverworts in potentially interesting parts of the county.   There was one yesterday, starting from a farm on the A361 (the Banbury to Chipping Norton road), just south of Swerford.   Because it was local I joined, despite knowing virtually nothing about these flowerless plants. Bryophytes are daunting; there are almost 1000 species in the UK, nearly all green, and whilst I have the field guide published by the British Brological Society (plus the rather weighty Moss Flora of Britain and Ireland - Smith), I have found it challenging to get even a foothold.   Scientific names are used almost universally; there are common names but they are not in general use, and my knowledge of Latin is confined to a scratchy GCE 'O' level obtained after a resit.  I hated it.   

We spent quite a few hours in a wooded, wet valley where there were springs coming off the limestone cap.   In places tufa was forming.   The total number of species found was almost 50.  David Morris will provide a comprehensive review  of what was found on his blog Oxfordshire Botany, in the coming days

Weatherwise it was awful, with storm Ciara passing through, and it was much too wet to take satisfactory in-situ pictures.   So I brought home fragments of a few for which I could remember the names to see if I could work through identification keys to get to a match.  Here are a handful which look really neat under the microscope.

Palustriella commutata growing as a tuft on tufa

Palustriella commutata

Liverwort - Plagiochila asplenoides on a wet bank

Liverwort - Plagiochila asplenioides

Liverwort - Plagiochila asplenioides

Liverwort - Conocephalum conicum

Fissidens taxifolius var taxifolius found on rotting branch

Fissidens taxifolius var taxifolius 

Fissidens taxifolius var taxifolius found on rotting branch

Zygodon viridissimus

Zygodon viridissimus