Flora | Wildflowers

Natural Elements of the area

Introduction

This Introduction is a brief outline of the natural elements of the area that have a direct influence on the nature of the flora.

The barony of Corca Dhuibhne is approximately coextensive with the most northerly of the south-western peninsulas of Ireland. It takes the form of a long ridge that stretches westwards about 50 km into the Atlantic Ocean. Corca Dhuibhne has a mountainous spine that extends from Sliabh Mis (Barr Trí gCom, 851 m) in the east to Cnoc Bréanainn (952 m) and on to Sliabh an Iolair (516 m) in the west. The islands at its western tip (Na Blascaodaí) form an offshore extension of this ridge. The coastline is irregular, and the pen­insula varies between 6 and 20 km in width from north to south, with no point more than 8 km from the sea. The rocks that make up Corca Dhuibhne span a period of more than 400 million years. Shales and volcanic rocks of Silurian age (423-395 million years ago) form the oldest geological deposits of the area. Among the shales are included some sandstones and limestones. The Silurian rocks are exposed at the western end of the peninsula, between Dún Chaoin and Cuan Ard na Caithne and in a narrow strip between An Mhin Aird and Doire Mór. Most of Corca Dhuibhne is composed of rocks of Devonian age (395-345 million years ago). These are divided into three groups: the older Dingle Group and the younger Caherbla Group, and Glengariff Harbour Group. Rocks of the Dingle Group (sandstones and conglomerates and mud-stones) occur generally west of Sliabh. Mis, occupying the central core of the peninsula as far west as Lios PóiI but covering most of the ground west of there. Resting on top of these are the sandstones and conglomer­ates that make up the remaining two groups of Devonian age, formerly referred to as old red sandstone. These rocks form the ground for almost the whole of Sliabh Mis and extend westwards on each side of the peninsula: from Doire Mór to Ceann Sibéal on the northern side and from Cill Mhuire to Doire Mór on the south side. Carboniferous limestone occurs along the northern coast from An Cam to Trá Li; it forms Oileáin an Mhachaire and underlies the sands at Inse and north of An Machaire itself.

The rocks that go to make up the pen­insula of Corca Dhuibhne have been fold­ed, faulted and uplifted at various times. The most significant and the most recent such event took place about 290 million years ago at the end of the Carboniferous period. This resulted from pressure being exerted from the south-east. It resulted in the rocks being folded along axes running approximately north-east to south-west. It is likely that most of Corca Dhuibhne was covered by Carboniferous limestone, and possibly by other rocks deposited in the interval from the close of the Carboniferous period to the beginning of the Ice Age. However, the three hundred or so million years that have elapsed since the close of the Carboniferous period saw all the rocks younger than Devonian being stripped off by processes of weathering and erosion. The 70 million years of the Tertiary period, immediately preceding the Pleistocene (Ice Age) period, probably wit­nessed most of this weathering and erosion.

During the Ice Ages of the Pleistocene period (1,600,000-10,000 years ago) this area was covered by ice sheets and glaciers on more than one occasion. There were both locally generated ice caps and ice sheets that pushed in over the area from the mountains of Uíbh Ráthach to the south and the area to the north and north­east. The result of this was manifold: deep corries and glaciated valleys with steep, dominantly north-facing cliff faces were created in the mountains; many rock sur­faces were scraped bare and contain either very shallow soils or no soil at all; rock was ground down by the ice and deposited as till (boulderclay), sand, and gravel, chiefly on the lower ground and in valley bottoms; and glacial deposits from outside the area were introduced by the ice sheets both from the north and the south. Such extraneous influences include the introduc­tion of substantial amounts of limestone included in glacial deposits resting on the old red sandstone of the northern slopes of Sliabh Mis.
Except for those of Inse and An Machaire, and some very isolated pockets in the areas of Silurian limestone, the soils of Corca Dhuibhne are acidic, reflecting the generally acid nature of the bedrock. Poor drainage reflects high annual rainfall, uneven ground, and the widespread devel­opment of an iron-pan a few decimetres below the ground surface. Drainage is fur­ther influenced by local microclimate, which in turn is controlled by height above sea level, openness to sunshine, shade offered by north-facing cliffs, and shelter offered from prevailing winds.

Following the close of the glacial period 10,000 years ago, the sea level, which had been low, rose gradually to its present level, forming a splendid spit and beach at Inse and the tombolo (spit connecting an island to the mainland) at An Machaire, along with the other beaches and coastal features of the area. Poor drainage coupled with high rainfall has resulted in the wide­spread occurrence of blanket bog on hill slopes and in the mountain, and high-level valleys late in the postglacial period.

Overall, the climate of Corca Dhuibhne, while variable depending on height above sea level and position relative to the sea, is generally wet and mild. Thus rainfall varies from an average of about 1,250 mm per year between sea level and 150 m to approximately 2,000 mm on Cnoc Bréanainn; mean daily air temperature in January varies from about 6°C at Trá Li to more than 7°C at Dun Chaoin. Frost is rare and occurs with decreasing frequency westwards. Snow hardly ever lies on the ground at sea level and is rare even in the mountains.
The scenery of Corca Dhuibhne, although splendid, is not that of a natural landscape. Humans arrived in this area very early in the postglacial period. The first people to live in Corca Dhuibhne came about 9,000 years ago. These were hunters and gatherers of the Mesolithic period and did not significantly alter the landscape. Neolithic people, who were farmers, arrived about 6,000 years ago and began a process of altering the landscape that has continued to the present day. The total lack of natural tree cover in the area is one result of this. The existence of place-names such as Doire M6r and Ard na Caithne indicate the fairly recent existence of nat­ural oakwoods and arbutus stands; the common occurrence of the terms coill and doire in the place-names of the area indi­cates that these are not isolated examples.

This above information was sourced from Flora Chorca Dhuibhne Aspects of the Flora of Corca Dhuibhne and provided to dodingle.com courtesy of Oidhreacht Chorca Dhuibhne. Republication of the extract or any part therin, in any form or capacity, is strictly prohibited without the express permission of the publishers. © Oidhreacht Chorca Dhuibhne.

(Flora Chorca Dhuibhne Aspects of the Flora of Corca Dhuibhne by Máirín Uí Chonchubhair with photographs by Aodhán Ó Conchúir. Botanical editor: Caroline Mhic Daeid. 1995 (reprint 1998). Hardback. 270 + xviii pages.) The archive of this survey is also housed in Músaem Chorca Dhuibhne and may be consulted by researchers by appointment.