Ill] SCRUB ASSOCIATIONS 91 



alder {Alniis glutinosa), hazel {Corylus Avellana), mountain ash 

 {Pyrus Aucnparia), and willows (probably chiefly S. cinerea) 

 occur more or less rarely ; and in one locality Scots pine (Pinus 

 sylvestris) was found. 



The highest examples of buried timber consisted wholly of 

 birch, and were encountered on the southern extremity of the 

 plateau of the Peak at an altitude of nearly 1800 feet (549 m.) ; 

 and generally it may be concluded that the buried timber 

 proves that in former times trees ascended the southern 

 Pennines about 200 feet (61 m.) or 250 feet (76 m.) higher 

 than they do at the present time, that this ancient forest was 

 composed principally of birches, and that more or less uncommon 

 associates were the aspen, oak, the alder, the hazel, the mountain 

 ash, the willow, and the Scots pine. 



Degeneration of Woodland 



There can be no doubt that a certain amount of the 

 degeneration of the woodland of this district has been brought 

 about by the indiscriminate felling of trees, the absence of 

 any definite system of replanting, and the grazing of quad- 

 rupeds. It is doubtful, however, if these causes are quite 

 sufficient to account for so great a lowering of the upper limit 

 of forest as 250 feet (76 m.), and for so general a phenomenon. 

 It must be remembered that the population of the remoter 

 valleys, many of which are now treeless or almost so, is very 

 small ; and the district does not appear to have ever been a 

 great grazing district. 



The inability of certain forests to rejuvenate per se has 

 been pointed out by many foresters and plant geographers. 

 In discussing the causes of the succession of forest to heath in 

 north German}', Krause (1892) emphasized the view that the 

 narrowing of the forest area has been largely due to errors in 

 sylviculture, especially to the grazing of cattle in the forest. 

 That such a factor is a causa vera in the degeneration of forests 

 is indisputable. Graebner (1901), on the other hand, lays stress 

 on the gradual impoverishment of the soil caused by the removal 

 of the tree trunks, by the gradual washing out by rain of the 

 soluble mineral salts originally present in the soil, and the 

 spreading of heath vegetation on the forest floor consequent 



