Plant Formations of the Dublin Mountains

Plant Formations of the Dublin MountainsThe Vegetation of the District Lying South of Dublin by G. H. Pethybridge; R. Lloyd PraegerReview by: W. G. SmithThe Irish Naturalist, Vol. 15, No. 5 (May, 1906), pp. 126-130Published by: Irish Naturalists' Journal Ltd.Stable URL: http://www.jstor.org/stable/25522883 .

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126 The Irish Nanurahisf May,

PLANT FORMATIONS OF THE DUBLIN MOUNTAINS.

The Vegetation of the District tying South of Dublin. By

G. H. PJrHYBRIDGO, PH.D, B.Sc., and R. LirO4D PRAEGIR, B.E., M.R.I.A. Proceedings of the Royal Irish Academy, xxv., B. Dec., I90$.

Pp. 57. Coloured Map. Five plates. Price, 2s.

The publication of this paper marks the opening of a new era in the

investigation of the plants of Ireland. The collector ajnd enumerator

of species has placed on record what plants are to be found, and during

the last decade one of the authors of this paper has perfected the frag mentary county lists until they are now a representative census. The Watsouian side of distribution has also received attention, and the great

botanical divisions of the Irish flora are known, as well as something of

their origin. Here and there a County Flora deals specially with the

plants of a district and their distribution. Thus, from the oft depre cated collecting of plants and making of lists; there has arisen a record

of the plants of Ireland which has claims to be considered at least

fairly complete. The progress, like that in most countries, has been

mainly along floristic lines. Meanwhile, another branch of the out-door study of plants has been opening from a prolonged bud-stage, and the

authors of this paper decided to test the merits of this recent growth,

the study of plant associations. It is unnecessary to define or to

describe this study, because in the introduction to the paper under review there is an excellent summary of the objects and the develop

ment of the subject. This introduction, although it formns the first part

of the paper, was probably the last part written, because the authors

state (p. 138): "We decided . . . to avoid reading up the detailed

work done in Scotland and England) and thus to start devoid of pre

conceived notions as to what the associations (if any) might, could,

would, or should be, and to let them force themselves upon us as they

actually existed in this area." This was the best test to make, and the

result was,:-" We were not long in recognizing that associations did

exist, and in deciding that they could be mapped, but only on a mnap of

a fairly large scale." The writer of this review was in some mieasure

the means of suggesting the study of Irish vegetation on these lines, for

one of the authors was present at the Glasgow meeting of the British

Associatibn (i9oi), when an attempt was made to explain the work of

Robert Smith (died I899), and to encourage its development in Britain.

The criticism of one who had already done so much topographical work as

Mr. R. Lloyd Praeger was awaited with somewhat mixed feelings, and

it was a relief when, in course of time, one learned that tlhe method

was approved, because from his many-sided investigations on the Irish

flora, Mr Praeger was better prepared than most men to judge of its

value. Hence, though at first sight " The Vegetation of theiJistrict South

of Dublin " may appear to be merely of local interest. it has a much

wider vglue as a study in plant geography, and isin reality an important

contribution.



x906. Reviews. 127

The district chosen for the survey is a good one fo r examining zones of vegetation, Starting from sea level, it includes a plain of cultivation which changes in the south into the granitic mass of the Wicklow Mountains, and rises to 2,473 feet on Kippure. A short account of the geology and physiography, and a general floristic account forms an Introduction. The main part of the paper is concerned with the plant associations. These fall into four zones-Seaside, 'Agrarian, Hill Pasture, and Moorland. The sea coast of this particular area is not,

however, a good example of this zone. but it is satisfactory to find that

in the area north of Dublin, which will, we hope, be the subject of a further paper, the authors will be able to deal more fully with this interest ing form of vegetation. From our own experience, we are not surprised that the authors have decided to leave out of this paper the peculiar problems of the Agrarian or Farmland. The chief interest, therefore, centres in the zones of Hill Pasture and Moorlanid, where the influence of man is less evident. This is just the kind of vegetation which has been most thoroughly examined elsewhere, and one turns to the results of the Dublin District with interest. The results may be considered from three aspects;-(a) the methods of survey, (b) the map, (c) the text and illustrationis descriptive of the plant associations.

The Methods of Survey.-The survey of this area of about 200 square miles was carried out during four years, and the authors point out the advantages and disadvantages of this system. The coniclusions arrived at after several years are, we consider, more valuable than if they were the result of a short vacation study, such as some workers consider sufficient to grasp the vegetation of a district. If the work extends over a long period miiuch depends on the method of taking notes. The system used in the Dublin District has been carefully thought out, and is a model for future workers. The authors used "Isix-inch " Ordnance

Survey maps, and, by means of a system of initial letters, they record

on the map the plants found; we have seen some of their field maps,

and can vouch for the very careful way in which the area has been

traversed acre by acre, and we can picture the wading over wet bog and

the scrambling on rocky hill-sides in all kinds of weather. In addition to map records, a system of lists was also kept, and from these the

plants of each association were finally determined. An example of these comparative results is given, which shows at once how the final lists of a plant association are arrived at. The system is that generally

used, but it is a distinct advantage to have it described in detail, and a

similar precision is strongly to be recommended to all who carry on

this work. The Vegetation Map.-The maps in papers of this kind always attract

attentiotn, and there, we believe, the interest of many a reader ceases. We have said before, and say again, that the map is only " the principal

picture" illustrating the paper, and is not the paper. The map of the Dublin District has the particular interest that it is the first vegetation map printed throughout at the Ordnance Survey Office The coloMrnl



t28 The Iish Naturalist. May,

have been printed on the " one-inch " Ordnance maps, and the result

is so satisfactory in clearness and detail that it is to be hoped the

method will be followed in all future vegetation maps. The colour scheme has been adopted by the authors after careful consideration, and otn grounds stated (p. 177). It differs to some extent from that used by other workers, and will probably be criticised on this accoutt It

must be borne in mind, however, that the earlier colour-schemes were

experimental, and that a standard scherne can only be prepared after

the vegetation of the British Isles is better known than it iS. the

vegetation maps published up till now fall into two groups-those pub

lished on the "2 miles to an inch' maps (I : 126720), and those on

the " one inch to a mile"t (i 6336o). The Dublin District belongs to

the "one inch" group, along with the maps of Westmoreland (GCe graphical Journal, March and Sept., i1o4). Two different systems are

represented on these maps: the -"solid," where each association has a

distinct colour (Dublin map), and the "dot and dash" system, where a

few ground colours are used, and differences are indicated by dotting

and cross-hatching. The " solid system " is certainly the most distinct

on a map, but the other system aims at grouping the associations.

Comparing the " one-inch " maps with the " half-inch," it is evident that

the former allows of much greater detail being shown; thus, the asso

ciations designated as Pteris, Juncus, andI Ulex in the Dublin map are

too small to be separately colouired in a "half-inch" map, and are

there included under some other colour, although described as separate associations in the text. It is easy to criticise, but it is no easy task to

fix on a definite colour scheme. The Dublin map has many points of

value which will aid in fixing such a system.

The Zones of Vegeiaiion.-The district south of Dublin has not many

features of interest as a woodland area, and in itself is not large eniough

to allow of much discussion regarding the distribution of trees. Con

pared with England and Scotland, we find a general agreement. Oak

forest in the mait valleys gives way to a Bireh scrub in the uplands,

with remains of Birch in the peat up to I,700 feet. The existing plan

tations of Scots Pine are found on the moorland edge, but the existence

of an earlier forest is indicated by stems found in the peat up to 1,250

feet. The occurrence of Ash with a Hazel scrub on the Mountain Lime

stone recalls what has been observed in the valleys of this geological

formation in Yorkshire. The Hill Pasture formus a zone on the upper limits of cultivation. In

the earlier "half-inch " maps this was represented by one colour, but

in the Dublin District map it is broken up into Pteris association, Nardus Heath, and two Ulex associations The main interest centres

round the Bracken and Gorse associations, none of which have been so

fully dealt with in any of the preceding British papers, but the limited extent of the Nardus Heath will be noted by workers in areas where this is a prominent association. The authors note a strong competition,

between Bracken and Gorse in which the Bracken is the aggressor,



1906. Reviews. 129

Again, Bracken and Ling are competitors on undulating ground; Calluna occurs on the slopes exposed to the prevailing westerly winds, while Pteris occupies the sheltered slopes. There is evidence that the Bracken requires a fairly deep, well-drained soil, and, given this, its deep rhizomes, with their rapid apical growth, are capable of invading the more primitive Calluna and Gorse vegetation. These conclusions, arrived at on a favourable area, will serve as useful guides to other workers. The paper on the South Dubliii District will be a land mark as a study of Ulex Gailii and U. europz4us. The authors have demonstrated that over a wide area these form two distinct zones U. Ga/Hii the higher, U. europrus the lower. The reasons for this are suggested, but we hope that the authors will be able to make it the subject of more detailed study. The same distribution was pointed out to me some years ago by Mr. C. E. Moss as a result of his observations

in Yorkshire, but the limited amount of Gorse did not allow of any definite conclusion being drawn up. Somne readers of this paper may think that the distinction by colour on a map of this scale of two plants so closely allied as to be almost varieties is rather " fine." If such be

the first impression, a careful reading of this paper will correct it. The two dominant plants-U. europaus and U. Ga/Hit-are, as it happens nearly related, but the ecological features of the two associations are distinct in regard to plants present, and, better still, on comparing their growth-" The most marked clhange (in the U. Ga//ii association) is the smaller structure of the plants, the absence of tall-growing species, and of such as have large leaves; in short, a tendency to more pronounced serophytism in characters" (p. 154). Cases of nearly allied plants forming dominant species in associations characteristic of very different conditions are by no means rare, and our general impression is that varieties and sub-species of the systematists are in most cases the out come of growth of the parent species under different external con ditions. The study of the two Ulex associations in this paper will serve onie good purpose if it only directs the attention of systematists to this aspect of ecology.

The Moorland, zone includes the vegetation which caps the mountains.

The six most important associations shown by colours on the map

are :-Calluna, Vaccinium, Juncus, Eriophorum, Scirpus, and Racomi trium. The Calluna association is a familiar one in Britain, and in

Dublin District occupies the greater part of the moorland. The authors record observations on its conditions of life, the chief of which is that it requires a well-drained, peaty soil. Vaccinium, which forms an asso ciation covering square miles in the Scottish Highlands, occurs only in

a few places in the Dublin District, although the species of Vaccinium and other plants of the association are common in the other hill associa

tions. The Juncus associations, which have already been referred to in other papers, were found so extensive in the Dublin District that a special

colour has been assigned to them. The authors distinguish a juncus

Polytrichum association, generally in wet places where springs emerge



130 The Irish Natiwalist. May,

on the hill sides, and a second Juncus association in the lower grounds. The distribution of species of Juncus and the plants occurring with them is another example of survey work where systematists would find a relation between the species and the soil-conditions. Where the peat bog becomes ill-drained and wet, Calluna loses its dominant place and gives way to other plants better adapted to the coinditions. The authors record three of these associations-Eriophorum, Scirpus, and Racomitrium moors,-of which the two latterare new. The distinc tion between the Eriophorum and Scirpuis moors does not appear to be strongly marked in this district, except in regard to abundance of cotton-grass in the one, and the Scirpus-sedge in the othler. The authors

are, however supported in their distinction of a Scirpus moor by some

later observations made in the North-west of Scotland, and criticismi which might be made ought to be reserved until greater areas of these

inaccessible and difficult peat bogs have been surveyed. The Racomi trium association occupies small areas near the summits of the hill mass.

The name is used to designate a somewhat mixed vegetation of Calluna, Eriopborutu, and Scirpus, which has one common feature, the abundance of the moss Raconiitriun lanuginosum. The association occupies bosses of peat with intervening wet hollows, and its characteristic appearance is shown by an excellent photograph It is an association which is probably not uncbmmoni on sumumit peat-bogs, and we suspect that the recording of it has been overlooked by other workers. This paper has therefore added materially to our knowledge of the plants, which by their growth and decay have made most of our peat deposits, and it shows how much

may be expected from future work on the vegetation of peat. Ireland,

above all, offers such opportunities for observing plant life on peat-bogs, and for investigations on the history of peat, that it is to be hoped that

Messrs. Pethybridge and Praeger may not only be enabled to give more

time to this work, but may also be supported by assistance from others. The investigation of peat bogs is slow and arduous work, hardly to be undertaken seriously in slatches of leisure. In the peat we have a record of the succession of recent plant growth on the earth, and so far as Britain is concerned, the work of readinlg the record has scarcely begun. The " Vegetation of the District South of Dublin' in many other ways opens out a new field for tlle out-door botaniist in Ireland. The Royal Irish Academy are to be congratulated on the excellent way in which this paper has been illustrated. If our hearty appreciation of the work of the authors is not obvious, then this review has failed in its object. To one who has watched the various papers on botanical survey in Britain grow in the field and come into print, it is interesting to see how each one opens out new questions and improves on its predecessor; this, the latest, has repeated history and stands as a model.

W. G. SMITH.

The University, Leeds.



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Plant Formations of the Dublin Mountains