Phytogeographical Excursion in the British Isles,

VIII—SOME IMPRESSIONS AND REFLECTIONS.

BY P . E . CLEMENTS (Minneapolis).

S one of those deeply interested in the structure and develop-ment of vegetation, I shall leave to other members of the

party the difficult but pleasant task of doing justice to scenicBritain and to British hospitality. I shall confine myself tosketching the kaleidoscopic impressions of British vegetation, withan occasional reference to the interpretations arising out ofcomparisons with American vegetation.

The three days spent in the Norfolk " Broads " revealed thegeneral features of a fascinating succession with an unusualnumber of structural and developmental problems. The strikingalternation of Scirptis, Typha, Phragmites and Cladiuin affordsunique opportunity for the study of their habitat equivalences andre-actions. It would be difficult, if not impossible, to find a regionquite so favourable for such work, owing to the labyrinthine natureof the " Broads," beside vphich the fabled labyrinths of Crete seemmythical indeed. In the case of the submerged and fioatingpopulations, the light and aeration factors furnish an almostuntouched field, while on the other side, historically, of the reed-swamp plexus, stretch the problems of its conversion into fen andcarr. The ecotone between swamp and fen is an unusually broadone, with corresponding possibilities for studying the change ofdominance in relation to habitat factors.

At Blakeney, the vegetational interest centred in the sharpcontrast between the salt marshes and the shingle beach, whichboth makes the marshes possible and then overwhelms them. Asa dynamic center, the shingle bank is rivalled only by the sanddunes, though it seems to differ in being rather more periodic thancontinuous in growth. The production of new habitats for coloni-zation rarely occurs in such a rapid manner, while the periodicdevelopment of lateral banks would seem to furnish a unique basisfor the study of the sequence of different populations, bothon shingle and in the marsh. The quantitative study so charac-teristic of British ecology, finds perhaps its best exemplification atBlakeney, where also the refinements of exact methods can becarried further than in more complex regions.

English woodlands are an intricate puzzle to the American

178 F. E. Clements.

ecologist familiar with little else than natural forests, rarelychanged except throtigh fire or the hands of lumbermen. Thecontrol by man has been so long and continuous and the effect ofgrazing and of rodents so significant that one is inclined to suspectall comparisons with the virgin forest formations of America. Thevery fact that continuous stretches are rare further complicates

, the task. Naturally one finds many phenomena which he vvouldinterpret in terms of native yegetationj but this is gratuitous lintjlfurther quantitative study has been, made of the respective ages,ofdifferent woody populations, the, relative dominance ,of woodland,scrub and grassland, and the actual inter-relations between 'vegeta-tion and habitat. . . , ,. The problem of the moor, with, its scientific, economic andpractical aspects, appeals to the visitor as the outstanding problemof British vegetation. The divergent opinions among Europeanbotanists as to the nature of moor and its variations,^ of its

' relation on the one hand to swamp and fen, and on the other toheath, constitute a situation in which the American, unfamiliarwith these formations, finds it impossible to discover definite land-marks. He realizes, however, that there is here an almostunparalleled opportunity for recording the movements from yearto year, in addition to securing fundamental evidence by themethods of experimental vegetation. To one impressed withthe complex relations between moor and heath, " Hochmoor"" Flachmoor" and fen, it seems that an exact study of all thefactors and population changes for a long period will be necessaryfor a solution. The importance of doing this is greatly emphasizedby the widespread opportunities for tracing the vegetation move-ments of the past in the almost innumerable peat sections. Theseserve as an invaluable link between the successions of to-day, andof the immediate geological past. It seems beyond questionthat their thorough study will reveal much of the development andstructure of vegetation long since disappeared. British botanycontains no more alluring field than this of correlating the peatdeposits and connecting their successions with those in existenceat present.

It is, perhaps, not altogether idle to speculate in regard to thereclamation of the moors. Their wide extent and almost completelack of use, mark them as an asset of great economic importaace,and one must be allowed to indulge the hope that the BritishVegetation Committee will soon take steps towards the conquest

Phytogeographical Excursion in the British Isles, lyg

of the moor practically, as well as ecologically. One must believethat research is of value only as it broadens and deepens thecurrent of human progress, and that no one should be so wellqualified to apply the results of investigation as the man whoobtained them.

To one sceptical as to the influence of lime, the results of theExcursion were most interesting. One could not fail to beimpressed with the abundant evidences of the distributional signi-ficance of lime, while he was struck by the fact that scarcely asingle '• calciphilous " or " ealciphobous " plant could prove a cleartitle to the term, physiologically. It is useless to add a single lineto the literary solution of this hoary problem, but the Britishexperience serves to emphasize the conviction that nothing butphysiological and competition studies in the field can hope to leadus to a final solution.

Without doubt, the greatest personal return from the Ex-cursion was the first-hand insight into the point of view ofecologists from different countries, and the chance thus affordedof scrutinizing one's own concepts in the light obtained. This mustbe more and more the real value to be derived from such expe-riences, if they are to give more than individual benefits, as theywill. Botanists, like all scientists, are still so highly individualizedthat they have little sympathy or patience with anything whichlooks toward definite and effective co-operation. This would seemto be merely an intermediate stage, and we can hope for the timewhen the ecologists of many countries will work together withsomething of the unity and efficiency which characterize the BritishVegetation Committee.