Sunday, 8 March 2020

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/  


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

Thursday, 27 February 2020

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.

      Monday, 10 February 2020

      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

      Friday, 8 November 2019

      Collecting Butterfly Orchid Measurements Together

      The weather has not been inviting for a wander across the fields in recent days so instead I have been trying to find patterns in data that I have collected over the years.   In addition to the study Anne and I made of the butterfly orchids on Skye, and the ongoing work on a population of greater butterfly orchids in the Chilterns, whenever I find either of the two butterfly orchids I make measurements, as far as possible trying to get a random sample.  I used to restrict these to height, bottom leaf width, and the number of flowers, but I now take a flower photo - chosen at random - to measure the labellum length and width, the subtended angle between the pollinia,  the distance between the viscidia, the length of the lateral sepal and the angle of that sepal to the horizontal.

      Greater Butterfly Orchid, Bald Hill 5.6.19

      Lesser Butterfly Orchid, Cae Blaen Dyffryn 15.6.19

      Hybrid, Warburg 16.6.19

      I put all the data together, from 22 locations together with summaries from Skye and the Chilterns.
      It includes some hybrids, mainly from Gloucestershire, but there is one from Warburg.  Altogether there are 224 observations for lesser and greater and 16 for the hybrid, (excluding Skye and the Chilterns studies) though not necessarily including all parameters for each observation

      The data is very variable, but as might be expected there are clear differences between lesser and greater butterfly orchids, and indeed the hybrid.  A few examples of the averages (the differences have not been subjected to any statistical tests)

      Ratio of  number of flowers to height
         LBO      0.70
         GBO     0.35 to 0.53
         Hybrid  0.69

      Subtended angle between the pollinia
         LBO       4 degrees
         GBO     37 degrees
         Hybrid  15 degrees

      Labellum width to height
         LBO       0.30
         GBO      0.24
         Hybrid   0.26

      Spur length
         LBO      20.8mm
         GBO     27.1 to 33.8mm
         Hybrid  25.3mm

      Spur length is dependent on latitude, but not to the extent I expected; the further north the shorter the spur, but shading also seems to have an  impact - shaded plants have longer spurs.  Plant height is affected by shading, but also by environment and latitude.   The Chilterns woodland greater butterfly orchids are taller than average, but have fewer flowers than would be expected for their heights.   Bald Hill, an open site, part of the Aston Rowant NNR, has stunted greater butterfly orchids yet is only a few miles from the Chilterns woodland site.   

      The plant with the longest spur though was a hybrid from Warburg at 40mm (pictured above), reminiscent of long spurred orchids found in Holland, but as there was only 1 plant and it did not re-emerge this year, then all I can assume that it is simply a natural variation

      Monday, 16 September 2019

      Helleborines (Epipactis) in Fruit

      Over the last few days I made a couple of trips to the Chilterns and one to a wood near Solihull to look for helleborines in fruit.  I found four species, dune, broad-leaved, green-flowered and violet.

      I measured the fruit set success by counting the number of seed pods compared to the number of bracts in the inflorescence.  

      Fruit set Fruit set
      Sample size
      Dune 89% 9
      Broad-leaved 89% 3
      Violet 37% 1
      Green-flowered 72% 2

      Both dune and especially green-flowered, are self-fertilising.   Green flowered did not open out at flowering time, but nevertheless set fruit.  High rates of fruit set are therefore to be expected.  With green-flowered some of the flowers simply blackened and withered.

      The fruit set % for violet helleborine is again to be expected; it is pollinated by bees and wasps, but it grows in deep shade, where wasps are not commonplace.  Higher fruit set rates are commonplace in mainland Europe though.   By contrast broad-leaved helleborine seems to attract every wasp from a distance around and that leads to a high fruit set.

      Tree Wasp Pollinating Broad-leaved Helleborine in early August
      These though were not random samples - I was attracted to the biggest and boldest in the case of broad-leaved helleborines, and later I did find a few plants where spikes had no seed pods.

      Dune Helleborine
      Green-flowered Helleborine

      Broad-leaved Helleborine
      Violet Helleborine

      I then took averages of the seed pod width and length for each species and the angle that the seed pods are held from the vertical (facing up then less than 90°, facing down greater than 90°.   I finally brought a few seeds of each home and got an average for length and width.

      Seed pod Angle   Ratio Seed Pod L;W ratio
      L mm W mm to Stem ° L:W L mm W mm over Seed L
      Dune 10.3 6.8 94 1.41 1.11           0.24 1.26
      Broad-leaved 12.4 7.6 126 1.63 1.08           0.26 1.51
      Violet 11.3 6.8 118 1.67 1.29           0.20 1.28
      Green-flowered 10.2 6.7 157 1.54 1.06           0.19 1.46

      The angle held to the stem is interesting, and is helpful in discriminating, as too is that final calculation - the pod length:width ratio divided by seed length.   This together with the angle to the stem, and leaf colour and dimensions should enable a helleborine to be identified to species level.  Of course though my sample size was far from statistically sound.

      For the broad-leaved helleborines I also  worked out pod dimensions by the position on the inflorescence.
      Average Average  Average L:W
      Angle Length mm Width mm
      Bottom Quartile   137            14.1             8.1           1.73
      Lower Middle Quartile  123           13.0             7.7           1.69
      Upper Middle Quartile  134           12.2             7.7           1.58
      Top Quartile 113           10.6             6.9           1.55

      The seed pods became smaller and less narrow moving up the stem, and were kept nearer to 90°.   I did not have enough measurements from the other three species but violet did not seem to behave in the same way.

      I then ran out of things to measure! 

      Monday, 9 September 2019

      Orchids in Fruit at Yeosden Bank

      Yesterday we joined the ANHSO field trip to Yeosden Bank in Buckinghamshire near Chinnor, one of the newer BBOWT reserves.    It was led by BBOWT's warden.  It is an area of chalk grassland with a small area of woodland - ash and beech.   In the grassland were lots of  Chiltern gentians (Gentianella germanica)  and Small scabious (Scabiosa columbaria).   At the woodland edge there were dense patches of Devil's-bit scabious (Succisa pratensis).   To some the latter is quite a novelty, but from my time on Skye I remember it as one of the commonest plants, found in almost every tetrad on the island. Whereas to me, Chiltern gentian is worth getting excited about!

      Chiltern Gentian
      Small Scabious
      Devil's-bit Scabious

      Yeosden Bank has several orchids and I thought I would try to identify spikes based on appearance, leaves if extant, seed pod dimensions and the angle of attachment of seed pods to the stem.   I think I found examples of three orchids, Common spotted, (Dactylorhiza fuchsii), Pyramidal  (Anacamptis pyramidalis) and Chalk fragrant (Gymnadenia conopsea):

      Probably common spotted:

      Seed pod length 9.5 mm width 4.2 mm
      Angle of attachment 29 degrees

      Probably common spotted:

      Seed pod length 7.7 mm width 2.7 mm
      Angle of attachment 37 degrees

      Probably chalk fragrant:

      Seed pod length 7.4 mm width 2.6 mm
      Angle of attachment 11 degrees
      It is getting a bit late in the year for butterflies, but were numerous butterflies still to be seen though many were worn.  Amongst the fairly battered Common Blues, I am pretty sure this is a fairly battered Adonis Blue. 

      A mammal stole the show however  - a hare running up the bank.   As ever only a fleeting glance - and much too fast for a  photo opportunity.  They are such a treat to see.

      Monday, 2 September 2019

      Autumn Lady's-tresses close to home

      North Oxfordshire, sitting on ironstone and clay, is not rich in orchids.  The nearest reliable sites from Hook Norton are more than 15 miles away.

      Well that has all changed - ok, just a bit.  Last year the joint vice county recorders for Northamptonshire, found a single plant (?) of Autumn Lady's-tresses in Banbury (it's in the administrative county of Oxfordshire but the botanical vice-county of Northamptonshire, so they weren't trespassing).   A  mere 11 miles from Hooky, I went to the site yesterday to see for myself.  Its on an industrial estate to the east of the town centre which was part of the expansion of Banbury alongside the M40. 

      There were 6 flowering spikes in all, though one was damaged, on a landscaped road verge, which fortunately had not been mowed for two or three weeks.   Only in the one place though possibly because other verges are kept mown rather more regularly.   My priority now is to try to convince the owners and maintenance contractors to restrict mowing until after tha plants have fruited.