Llanelli Naturalists Newsletter - March 2003 - No 69
In late June 2002, I visited Cae Blaen Dyffryn SSSI, a nine acre nature reserve owned by Plantlife, the Plant Conservation Charity. The reserve is located south of Lampeter in North Carmarthenshire. I was met by the Plantlife Wales Officer, Dr.Trevor Dines, and the Honorary Wardens, Llanelli Naturalists’ members, Mary and James Iliff, together with more than a dozen Plantlife members. The tenant who grazes his cattle at this site also joined us, which was encouraging to see.
Cae Blaen Dyffryn is of importance for its semi-improved neutral grass-land (NVC MG5a and MG5c sub-communities: Cynosurus cristatus - Centaurea nigra - Lotus corniculatus grassland) and its population of Platanthera bifolia (Lesser Butterfly Orchid). P. chlorantha (Greater Butterfly Orchid) also occurs on the site and Botrichium lunaria (Moonwort) has been recorded here in the past.
Trevor gave an informative talk about the site, the grassland and many of the species present. Of particular interest to the group was his demonstration of the differences between P. bifolia and P. chlorantha. The diagnostic character is the position of the pollinia (the pollen-bearing sacs positioned in the tops of the flowers): they are parallel in P. bifolia and they diverge downwards in P. chlorantha. Other useful characteristics that can be used to confirm identification are the size differences between the two plants: not only does P. bifolia tend to be a smaller plant but it also tends to have fewer flowers on the spike. Furthermore, the spur on P. bifolia tends to be less than 2cm whereas in P. chlorantha it tends to be longer than 2cm. Similarly, the labellum (the lower petal) is less than 1cm in P. bifolia and more than 1cm in P. chlorantha.
The quality of the grassland was assessed by recording presence/absence of key species within 1m quadrats. Also recorded, was the percentage cover of plants that can indicate when the sward is becoming rank (for example Holcus lanatus (Yorkshire fog )). It was difficult not to tread on the orchids whilst we were doing this, as there were so many of them. Fortunately, before we set about counting the butterfly orchids the party’s numbers were boosted to around thirty by members of the Wildlife Trust for South and West Wales. We spread out across the top of the field and then progressed down-slope in the style of a police forensic team looking for evidence (minus the white suits)! We soon had to abandon counting in fives (| | | |) as it was often possible to count over thirty butterfly orchids from one position. After about half an hour, we reached the bottom of the field and totted up figures for both species. The most arithmetically adept in the group added-up our figures and we eagerly awaited their results. We had counted 3480 P. bifolia and 2440 P. chlorantha! I had called at the site a week earlier and counted over 800 butterfly orchids in the space of 20 minutes so knew to expect large numbers but this exceeded all of our expectations. Previously, the highest counts (since records for this site began, in 1993) were 300 P. bifolia and 76 P. chlorantha in 1998. Between 1998 and 2002 total numbers have only been in double figures, for example, in 2001 there were 28 P. bifolia and 24 P. chlorantha recorded. The figures for 2002 show that this is by far the largest P. bifolia population in Carmarthenshire.
There could be several factors influencing the butterfly orchid population at Cae Blaen Dyffryn including those of climate and grazing. Anecdotal evidence suggests that numbers of P. chlorantha at several other Carmarthenshire sites were far greater in 2002 than in previous years. I would be interested to hear if anyone else has noticed if this was a particularly good year or indeed if they noticed any significant changes in populations. At another Carmarthenshire SSSI the owner thought that the numbers of P chlorantha may be down on the 4000 he counted in 2001.
NB Botrichium has not been recorded at this site since 1998 but populations of this small fern are also known to fluctuate from year to year.
Countryside Council for Wales