CHAP, xcvii CHANGE OF VEGETATION 365 



human agency. Some changes in the nature of forests may have been 

 simply due to the entry of new species. Possibly it is thus that we must 

 explain the changes which take place in Russian forests, where oak ^ is 

 sooner or later suppressed by beech, and this in turn is vanquished by 

 spruce ; similar changes occur in the north of Germany .- 



If the vegetation occupying an extensive area be left entirely to itself 

 certain formations will suppress all others after the lapse of sufficient time, 

 and will represent the final stage of development. 



We have already discussed the victory of ericaceous heath over forest. 

 Borggreve and E. H. L. Krause^ regard heath as a 'semi-cultivated' 

 community that owes its origin exclusively to cultivation of the soil : 

 this view is certainly incorrect. Ericaceous heath in certain spots in the 

 north of Europe is beyond doubt a natural vegetation in its final stage, 

 not only on the mountain slopes of Blekinge, but even on the poor sandy 

 soil of western Jutland. Heath is quite as independent and natural in 

 origin as oak-forest, and has existed in Denmark, in Jutland, since the 

 Stone Age.* This truth is not affected by the fact that heath has materially 

 spread at the expense of forest, as a result of deforestation. It is, how- 

 ever, worthy of note that Hult ^ has shown that ericaceous heath is 

 exterminated by forest at certain spots in Blekinge. 



As other final stages in the development of vegetation in Blekinge, 

 Hult mentions the following : 



i. Pine-forest on dry sand, on moraine-soil with detritus, and on 

 peat-moor. 



ii. Spruce-forest on less extensive moors near shores. 



iii. Birch-forest with Betula pubescens on deeper moors and on 

 low-moors. 



iv. ' Grove-dell-formation ' on rivers and streams. 



V. Thorn-bushland on the warmest dry places. ' 



vi. Beech-forest on all other soil. 



All other formations change gradually into these : not only grassland, 

 but also Menyanthes-' formation ', marsh, and low-moor change thus, 

 ' even on the rocks there develops a long series of transitional types of 

 vegetation ' before the chmax of forest is attained. 



With the exception of thorn-bushland all these final stages are types 

 of forest, to wit, associations whose distribution over the ground is deter- 

 mined by nature of soil. Forest is in all places the last natural stage of 

 evolution of vegetation, excepting where the development of trees is 

 checked by a substratum of rock, lack of nutriment, water, cold or drought 

 (either due to lack of water or to wind). In such places the final stages 

 are represented by fell-field, dwarf-shrub heath, tundra, meadow, steppe, 

 desert, scrub, or other communities. 



Korzchinsky, 1891. ' Grisebach. 1872. 

 ' Borggreve, 1872 ; E. H. L. Krause, 1892. 



' Sarauw, 1898. " Hult, 1885. 



See Whitford, 1901 ; Cowles, iqoi/j; Kerncr, 1863. 



