Limestone lovers

Berry Head in South Devon is quickly becoming one of my favourite haunts with its rich botanical landscape and marine wildlife. Last September I blogged about one of its specialities, the White Rock-rose (Helianthemum apenninum), a nationally rare species (see http://nicksnaturenotes.blogspot.co.uk/2011/09/last-white-rock-rose.html). The unusual mix of physical geography and chemistry provided by the Devonian limestone sea cliffs of Berry Head provide conditions for the White Rock-rose shared only by a handful of other sites in the South West. I was visiting it again this weekend with friends and showed off the White Rock-rose amongst other more common plants. Towards the end of the afternoon we wandered up to the remains of the fort in search of summer migrant birds amongst the scrub. Resting my arms on the battlements and enjoying a Whitethroat and possibility of Cirl Buntings, I became curious about a stunted-looking plant which I had almost leant on. Closer inspection revealed what looked like a bonsai version of an umbellifer, a dwarf parsley or carrot plant. My companion with much pleasure eventually identified it as Honewort (Trinia glauca), which is indeed a member of the carrot family and another local limestone specialist. Apparently, in turf closely grazed by rabbits, plants of Honewort grow to no more than a few centimetres tall (BRC, 2012), as was the case with many of the Berry Head plants that we observed.

When I got home I looked at the distribution map on the National Biodiversity Network's Gateway (see http://data.nbn.org.uk/gridMap/gridMap.jsp?allDs=1&srchSpKey=NBNSYS0000003662) and fascinatingly it is found in almost the same isolated areas as the White Rock-rose. These rare fragmented habitats of dry limestone, with short-grazed south facing aspects have created almost identical conditions for such specialists to cling on to their slopes. However their hold is truly precarious, the species being listed as ‘Near Threatened’ (BRC, 2012). The challenge for the Honewort is made more challenging as it is dioecious (having separate male & female plants, requiring cross-pollination) and has poor seed dispersal, most likely reliant on ants (Carvalheiro, et al., 2008).

These two limestone loving species are literally hanging on in Britain, exposed to human disturbance.  This makes it all the more important to value these wonderful wildlife hotspots and for me to take more care where I lean my tired ‘binocular-ed’ arms.

BRC (2012) Online Atlas of the British and Irish flora [online] http://www.brc.ac.uk/plantatlas/index.php?q=plant/trinia-glauca [Accessed 7/5/12]

Carvalheiro, L.G., Barbosa, E.R.M. and Memmott, J.(2008) Pollinator networks, alien species and the conservation of rare plants: Trinia glauca as a case study. Journal of Applied Ecology, 45: 1419–1427

National Biodiversity Network's Gateway  (NBN) (2012) Grid map of records on the Gateway for Honewort (Trinia glauca) [online] http://www.brc.ac.uk/plantatlas/index.php?q=plant/trinia-glauca [Accessed 7/5/12]

The last White Rock-rose

With my daughters recently back to school I was keen to get out and do some serious birdwatching and try and spot a few summer migrants on their way back to winter quarters. Berry Head seemed like a good option, a headland jutting out beyond Brixham at the extreme tip of the southern arm of Torbay. I was pleased to see so many resident pebble-chinking stonechats, but not much sign of migrants. A solitary Wheater flitted discretely on the steep slopes.

It did not take long before my eyes were heading downwards rather than to the skies – the abundance of late summer wild flowers caught most of my attention. Berry Head’s thin limestone soils mixed with salty air have created a special botanical habitat. The last blue flowers of Viper’s-bugloss (Echium vulgare) clung to the tips of arching flower branches ending their summer show, whilst the tiny blue lily flowers of Autumn Squill (Scilla autumnalis) were in their prime scattered widely on the cliffs. Sea specialist, Rock Samphire (Crithmum maritimum) was most abundant on less accessible rocky slopes providing late yellow warmth to the cliffs. However it was a nationally rare species that I was eager to find, the White Rock-rose (Helianthemum apenninum), a limestone specialist restricted to a few locations in the South West. It occurs on dry, rocky limestone grassland on south facing slopes (Countryside Trust, 2011), typical of montane Mediterranean habitats where is more commonly found. However the conditions provided by the Devonian limestone sea cliffs of Berry Head provide sufficient conditions for the White Rock-rose to prevail, although threats from scrub invasion, trampling and dog fouling put this at risk (Countryside Trust, 2011). In the UK it is at its northern European limit (Preston, 2007).

The White Rock-rose flowers between April & July (Rose, 2006), and so I was being rather optimistic to see it at its best. Just when I was giving up any hope of finding it, there was one last solitary flower already in decline having shed one of its petals. This contrasts with the small silvery downy leaves, strongly inrolled at their margins. Next year I will be visiting much earlier, perhaps to time in with the return of the summer migrants.

Countryside Trust (2011) [online]. www.countryside-trust.org.uk/bap [Accessed September 24th 2011]
Preston, C.D (2007) Which vascular plants are found at the northern or southern edges
of their European range in the British Isles? Watsonia (26): 253–269
Rose,F (2006) The Wild Flower Key – How to identify wild flowers trees and shrubs in Britain and Ireland. London: Penguin Books Ltd.