HARDWICKE'S SCIENCE-GOSSIP. 



169 



THE DANISH FOREST. 



By JOHN WAGER. 

 V. — The Relationship of Associated Trees. 



AVING indicated 

 the zones of the 

 several species of 

 Danish trees, I 

 pass on, continues 

 Dr. Vaupell, of 

 part of whose 

 works this and the 

 following chapters 

 are merely a sum- 

 marised transla- 

 tion, to consider 

 their relation to 

 each other when 

 associated in the 

 forest ; for there 

 is, in reality, not 

 a mere aggrega- 

 tion of different 

 trees and species, 

 but also a certain 

 relationship between them. They influence each 

 other— form and transform, so that they may be 

 regarded as parts of an organism, which absorbs 

 and appropriates the natural elements. As re- 

 gards the occurrence of the different species in the 

 Danish forest, they are most unequally distributed ; 

 while of one spefies large associations are found in 

 nearly every forest district, there are of several other 

 species but few unmixed collections, such being, in 

 general, dispersed on plots in the forests, or upon 

 their outskirts. The reason why they appear with 

 comparatively so few individuals in mass, or do not 

 form entire woods, must not be sought in sterility, or 

 in want of capacity for associated growth ; for each 

 species of our trees would certainly extend itself, and 

 form entire woods, if not prevented by other species. 

 Thus the oak copses of Jutland are of oak only ; there 

 are purely oak-woods in South Zealand and Holland, 

 and woods exclusively of hornbeam, of lime, of birch, 

 and of alder, are also found. Thus we see, that not 

 No. 224.— August 1883. 



the beech only, but other species of trees tend to pre- 

 dominate and exclude the rest. 



The growth and extension of a species of plant is 

 in general determined by the physical conditions — 

 the presence of warmth, moisture, and nutritive soil, 

 in sufficiency to enable it to grow and develop ripe 

 seed. But these conditions, which suffice for the 

 isolated plant, are not determinate when different 

 species are associated during years of growth ; for 

 then the relative growth depends also upon the 

 degree in which one species can endure the proximity 

 of another, and the interference and influence it 

 exerts. In this respect there is great difference ; not 

 because the one tree by respiration or contact can 

 injure the other, but because it withholds from the 

 other some portion of light. Conditions of light 

 exercise a far greater influence upon the existence and 

 growth of forest trees than of herbaceous plants. 



The different species of trees have a difference of 

 adaptability to local physical conditions ; but each 

 endeavours to cover the ground with growths of its 

 own kind, and contention among them results. Some 

 species of willow send forth an immense quantity of 

 seeds ; the mass of winged fruit which in a single 

 year falls from the ash, and is carried around by the 

 wind, is so great that it could cover all Zealand with 

 ash-forest if the seed got leave to develop itself ; and 

 the same, in part, may be said of the birch and the 

 elm. Birds every year sow all the forests with 

 rowan-seed, yet it is rare to meet with even a small 

 rowan-wood. Thus every species presses forwards, 

 and there is struggling and strife in the woods. As 

 with animals, so with trees, the one species oppresses 

 the other. The beech dislodges the oak, the oak 

 dislodges the fir ; the species which is in harmony 

 with the special physical conditions obtains the sway. 

 Meantime the fight is not without end ; when the 

 tree has got the better of difficulties, it can peace- 

 ably unfold its properties, and form forest after its 

 nature. In the forests of former times the contest 

 was between the aspen, the birch, the Scotch fir, and 



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