BRITISH FOREST TREES 17 



the soil, unless underwood is sown or planted. Exception- 

 ally, pure forests may be formed by trees of sparse foliage, 

 when the soil runs no risk of becoming deteriorated through 

 want of protection. Marshes planted up with alders, birch, 

 aspen, and poplars are examples of this, but in such cases 

 wind and sun often act beneficially by stimulating evapora- 

 tion, and thereby decreasing the superfluous amount of soil- 

 moisture. 



In the vegetable kingdom, as in the animal, a constant 

 strife is being waged between species, and in the different 

 species between family groups, and in these again between 

 individual plants a definite struggle for existence in perfect 

 accordance with the laws of nature regarding the survival 

 of the fittest. There is, however, this great difference 

 between the animal and the vegetable worlds, that the 

 struggle carried on by forest trees in the temperate climate 

 of central and northern Europe 1 is one which tends to pro- 

 duce a more or less pronounced, though perhaps never 

 absolute, domination of the principal species over large 

 areas limited only by the conditions best suited to the 

 growth and development of each individual species. 



If the whole continent of Europe were to be planted up 

 quite regularly with an equal number of seedlings of each 

 species of indigenous forest tree, we should find in course 

 of time that a segregation of species would take place, 

 and that, just as has happened in the ethnographic dis- 

 tribution of human races, they would also have their 

 places more or less definitely allocated to them. Certain 

 kinds of trees would be predominant over larger areas- in 



1 This is not the case in the tropical foiv>N <>i equatorial regions, 

 with the exception of the almost pure forests of Dipttroctsrpw tnl>tr- 

 > it/a/its, formed on tracts of Laterite, where soil is the principal factor 

 limiting the growth of species. 



'-' This gregarious tendency wax already noted in KveKn's 

 (iilpin (forest Scenery, I.amler'> edition, 1834, \M|. ii., p. uj 



C 



