CHAP, xcvi SUCCESSION OF VEGETATION 363 



Jutland. In these places the beech does not thrive, attaining compara- 

 tively low stature and maturing its seeds imperfectly ; thus it is that 

 the oak gains the mastery. Moreover, on sandy soil the beech readily 

 produces raw humus, and is incapable of natural regeneration. 



For some centuries ling-heath has spread at the expense of forest in 

 Denmark and northern Germany. Jutland was formerly clad with ''oak- 

 forests, or less probably with one continuous forest ; now, patches of 'oak- 

 scrub on heaths are the solitary relics of such forest. The forest has been 

 devastated by careless and ignorant felling, by utilization of the wood in 

 the production of iron from bog-ore an industry largely pursued in 

 Jutland during the Middle Ages and by the west wind. As soon as the 

 soil dries, a covering of raw humus arises and the vegetation changes, as 

 was shown by P. E. Miiller. 1 The earthworms disappear and the soil 

 consolidates. In the layer of raw humus humous acids are produced ; and 

 in the subsoil, as rain-water washes out the mud, layers of hard pan arise. 2 

 At the same time the vegetation on the ground of the forest is utterly 

 changed. In the beech-forest, with its wealth of humus, there grows 

 a vegetation consisting of Anemone, Corydalis, Asperula odorata, and 

 others. 3 When the soil acquires raw humus it is invaded by Aira caespi- 

 tosa, Trientalis, Maianthemum, and others, and becomes well fitted for 

 the growth of Calluna vulgaris. This enters and gradually converts the 

 vegetation into heath, since the beech is incapable of natural regenera- 

 tion. This metamorphosis takes place especially on windy hills and on 

 the western sides of forests. 



Both oak-forest and beech-forest succumb in the struggle with heath, 

 when felling of the trees on the washed-out soil allows the wind free play. 

 Continental parts of Europe are unfavourable to the production of raw 

 humus ; here bad forestry and wind do not lead to the production of 

 heath, but, when afforestation is checked by strong winds or by drought, 

 there arise many allied communities familiar in the south-east of Europe 

 namely bushland, steppe, scrub, or communities of perennial herbs 

 belonging to the sunny (Pontic) hills in Germany. 4 



A development in the reverse direction takes place when ling-heath 

 is irrigated with water rich in nutriment. Even one year after the com- 

 mencement of irrigation ling vanishes, and after a lapse of three years 

 the heath may be replaced by a carpet of grass and the soil may be 

 inhabited by earthworms. 5 



1 P. E. Miiller, 1887 a, 1899. * See p. 62. See p. 332. 



4 See Sect. XII, p. 290. 



The evolution of the European flora has been dealt with by many botanists, 

 including Ad. Engler (1879-82), G. Anderson (1896), Clement Reid (1899), and Marie 

 Jerosch (1903). Concerning change of species in North American forests, 

 E. Bruncken's work (1904) should be consulted, as should those of Clements (19040, 

 1905, 1907), C. MacMillan (1895), and Transeau (1905 a, 1906) on 'Zonation '. 



