January 12, 1905 j 



NATURE 



257 



PLANT ASSOCIATIONS IN MOORLAND 

 DISTRICTS. 

 TOURING the last four years systematic observations have 

 ■^ been made on the distribution of the various associ- 

 ations of vegetation covering the moorland region lying 

 to the east of the \'ale of Eden." The boundarins of each 

 plant association have been traced out in tlie liclil and laid 



-Succe-sioii of moorlanj vegetal ii.n 

 ss Heath developed on the slopes bel 

 , gently sloping toregroun ' 



hed. 



down on the six-inch Ordnance map, and reduced to the 

 one-inch map for publication. The factors governing the 

 distribution of plant associations over such a limited area 

 are mainly edaphic, although the 

 differences in altitude, which amount 

 to about 2500 feet in the area 

 in question, produce changes in the 

 vegetation which are chiefly due to 

 climatic conditions. Much of the vege- 

 tation at present covering cultivated 

 areas in Britain owes its distribution 

 to artificial agencies, edaphic and 

 climatic factors being to a great extent 

 masked. The more reinote moorland 

 districts of the north of England and 

 Scotland, however, give opportunities 

 for studying plant associations the dis- 

 tribution of which is chiefly delenninrd 

 by edaphic and climatic factors, ihe 

 artificial factors due to the influen c of 

 man being secondary. 



The most important artificial ag''ni ics 

 tending to modify the natural di^iriliu- 

 tion of vegetation covering our irocr- 

 lands at the present day appear to be 

 drainage operations and grazing of 

 cattle. On many of the alpine moof- 

 lands these factors are almost nej; le- 

 gible, and any change in the vegetation 

 has been caused, not by artificial 

 agencies, but by secular changes in 

 climate. The evidence of a change in 

 vegetation, both on the alpine moor- 

 lands of England and Scotland, is un- 

 mistakable, and it is possible to a certain 

 extent to reconstruct the waves of 

 vegetation which have occupied the areas inentioned since 

 the passing away of the last ice sheet. 



The district in which mapping has been carried on by 

 the author consists of a great extent of bleak, gently sloping 

 moorland, of which about lo per cent, lies above 2000 feet. 

 The author has found that considerable and marked changes 

 take place in the plant associations at about 2000 feet ; tree 

 vegetation ceases, and many alpine plants make their 

 appearance which are absent from the lower moorlands. 



The geological formation in the south 

 and west of the district is chiefly 

 Carboniferous limestone yielding only a 

 small amount of detritus, whilst in the 

 north and east the limestone thins out 

 and is replaced to a great extent by 

 sandstones, grits, and shales which 

 yield a much larger amount of detritus. 

 This feature has an important effect 

 upon the vegetation, the wetter types of 

 associations being developed upon those 

 rocks yielding a large amount of 

 detritus. 



The moorlands first resolve themselves 

 into two chief types, grass moorland and 

 heather moorland, and these are fre- 

 quently linked together by several inter- 

 mediate plant associations. Dry heather 

 moors or heaths do not cover any great 

 extent of ground, and are chiefly found 

 in the limestone districts of the south. 

 The wetter types of heather moors are 

 well developed, and the whole district 

 can be briefly described as a wet heather 

 and dry grass moorland country. These 

 features are well shown in many of the 

 " hopes " and gills leading out of Wear- 

 dale and South Tynedale. The steep 

 lower slopes of the hills are covered 

 with an association having Nardus 

 stricta as the dominant plant. Above 

 1500 feet to 1800 feet the slope of 

 the ground becomes more gradual, and 

 shales and grits make their appearance. At the same time 

 the Xardiis stricta association yields to heather associations 

 in which Eriophorum is always a prominent plant. The 



Nardu 



Fig. 2.— Calluna and V, 

 vegetation developed 

 Ci-og rapk icat Journal. 



Ri^ 



' Geographical Distributions ( 

 rs Eden, Tees, Wear and Tynt 

 ember, r904.) 



f th. 



Vegetation of the 

 (Ccografhical Jour,, 



il. Ma 



■ the 



succession of different types of moorland is often well shown 

 along some of the " edges " in the north-east of the district. 

 At Redbourne Edge the almost flat, poorly drained summit 

 is entirely covered by Erlophoriuin bog, developed on deep 

 wet peat. As the edge of the bog is approached the peat 



NO. 1837. VOL. 71] 



