EVENTS

               Members Reports and Photos

 

SATURDAY 9 aUGUST 2014                  

NORTH BULL ISLAND, DOLLYMOUNT

LEADER: DAVID NASH

Flora  
We met on a breezy but fine sunny morning on the island end of the Causeway conscious of the forecast that the afternoon forecast was for the arrival of some heavy scattered heavy showers as harbingers of the arrival of ex-hurricane Bertha from North America.

We headed towards the Alder Marsh, a freshwater marsh in the island sand dune system which is one of the important features of the island which is a designated UNESCO Biosphere Reserve because of its uniqueness. Responsibility for reporting to UNESCO has recently been devolved to Dublin City Council from the Department of Arts, Heritage and the Gaeltacht, and the Port and Docks Board has handed over ownership of the Bull Wall and some adjacent land to the the Council. So there is an uncertainty  people as to the future management of this unique island.

En route to the Alder Marsh we observed plants such as Wild Pansy Viola tricolor ssp. curtisii, Burnet-saxifrage Pimpinella saxifraga, Wild Carrot Daucus carota, Common Centaury Centaurium erythraea, Cat's-ear Hypochaeris radicata, Marram Ammophila arenaria, Red Fescue Festuca rubra, Sand Sedge Carex arenaria, Sea Buckthorn Hippophae rhamnoides and Eyebright Euphrasia species. The vegetation in the Alder Marsh area was luxuriant and some of the more obvious species present included Alder Alnus glutinosa, Grey Willow Salix cineraria ssp. olefolia, Creeping Willow Salix repens, Meadowsweet Filipendula ulmaria, Field Horsetail Equisetum arvense and Sea Rush Juncus maritimus.  Devil's-bit Scabious Succisa pratensis was just coming into bloom and within days the whole area will be covered with its blue flowers.

Frank Smyth and Bob Aldwell led the Marsh Fritillary hunt. Marsh Fritillary butterfly webs were plentiful and in their hundreds, clustered in what appeared to be the slightly higher or drier areas - on leaves of their food plant Succisa. Some were found on Scabious at the edge of the Marram zone. The brownish caterpillars of various sizes were visible in webs which ranged in development from the 'brown-leaf stage' to more sophisticated white webs marked by the telltale trail of dead leaves and webs left behind when they moved on to munch on their next leaf or plant of Succisa. Eventually, as the weather gets colder the caterpillars, huddled together for warmth, will spin tighter water-resistant hibernacula and disappear out of sight until sunny early spring days arrive and the then black caterpillars emerge to eat and sunbathe. Each year since their discovery, this colony has expanded in area and numbers. To date there have been no reports of parasitoids suggesting that the colony is an introduction, especially since there are currently no other known colonies within County Dublin.

One of our target species, the little fern Adder's-tongue Ophioglossum vulgatum, proved to be very plentiful once we had our "eye in". Richard McMullen, from a previous visit, was quickly able to locate the plant for us. We had been hopeful of seeing Autumn Lady's-tresses Spiranthes spiralis along pathways and short turf in the vicinity of the Marsh, but concluded that we were too early in the season to observe them.

Our major target species was Autumn Gentian Gentianella amarella. One single plant was observed some distance from the Marsh and further on small groups of plants were found along the path in the Marsh and in "the Green".  There have been previous reports of the presence of the Field Gentian Gentianella campestris in the vicinity of the Marsh so we needed to confirm which species were present. The key we used was from Sell and Murrell's Flora of Great Britain and Ireland and the appropriate couplet is shown below:

"Calyx with 4 lobes, the outer 2 several times wider than the 2 inner and overlapping and enclosing them: Gentianella campestris.

Calyx with 4 or 5 lobes (often on the same plant), the widest less than twice as wider as the rest: Gentianella amarella.

G. amarella ssp hibernica: Plant 10-50 cm. Internodes 7-11. Cauline leaves linear lanceolate, more or less acute at apex. Calyx lobes subequal.  Corolla (17-)19-22 mm, dull bluish-purple. Flowers (7-)8-9."

All plants examined were deemed to be G. amarella and of a pale purple hue (= dull bluish-purple?).

Relevés were carried out using one metre square quadrats and a collective decision was made with regard to the coverage of each species on a DAFOR scale as chosen by the BSBI. The following plants were identified within the quadrats: G. amarella, Purging Flax Linum catharticum, Yellow-wort Blackstonia perfoliata, Devil's-bit Scabious Succisa pratensis, Lady's Bedstraw Galium verum, Cat's-ear Hypochaeris radicata, White Clover Trifolium repens, Red Clover T. pratense, Bird's-footTrefoil Lotus corniculatus, Eyebright Euphrasia agg., Quaking Grass Briza media, False Oat-grass Arrhenaterum elatius, Marram Ammophila arenaria, Ribwort Plantain Plantago lanceolata, Dandelion Taraxacum agg., Glaucous Sedge Carex flacca, C. arenaria, Mouse-ear-hawkweed Pilosella officinarum, Selfheal Prunella vulgaris, Meadow-grass Poa species, Yorkshire-fog Holcus lanatus and Field Wood-rush Luzula campestris.

Con Breen lead us to the salt marsh near the tip of the island and on our way we saw Portland Spurge Euphorbia portlandica, a substantial bush of Lilac Syringa vulgaris and a clump of Elder Sambucus nigra and Bramble Rubus fruticosus, the latter providing an excellent source of nectar for many Meadow Brown butterflies. Bittersweet Solanum dulcamara was scrambling through the Brambles. Is this the beginning of island scrub? Along the pathway on the edge of saltmarsh we spied the small Legally Protected Species Lesser Centaury Centaurium pulchellum in flower - this species has no basal rosette - together with a larger number of plants already in fruit. The two lavenders Rock Sea-lavender Limonium binervosum and Lax-flowered Sea-lavender S. humile were coming into flower and the occasional plant of Spear-leaved Orache Atriplex prostrata was noted.This visit should be considered to have been a preliminary saltmarsh visit only. Deposits on the edges of the Saltmarsh provided evidence of the presence of rabbits, an important ingredient in maintaining short turf on parts of the island. On our return journey, Con showed us a substantial patch of Harebell Campanula rotundifolia which is not plentiful on the island and those of us who had not seen Ophioglossum on the outward journey had a visual feast. The threatened precipitation never materialised.

 David Nash

     

     Gentianella amarella                    G. amarella             Ophioglossum vulgatum

   

Succisa pratensis                  Common Blue butterfly                                        Marsh Fritillary web      

       

Filipendula ulmaria                     Salix repens                                          Sagina nodosa               

   

        Solanum dulcamara                       S. dulcamara                               Sonchus arvensis      

         

   

Limonium humile                                 Spergularia species                   Common Blue butterfly                                          

   

Centaurium erythraea                 C. pulchellum               Campanula rotundifolia

   Photographs ©  P. Lenihan

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