II 
THE STRUGGLE FOR EXISTENCE 
21 
Blangsted, strikingly illustrates our subject. 1 The chief com¬ 
batants are the beech and the birch, the former being every¬ 
where successful in its invasions. Forests composed wholly 
of birch are now only found in sterile, sandy tracts; every¬ 
where else the trees are mixed, and wherever the soil is 
favourable the beech rapidly drives out the birch. The latter 
loses its branches at the touch of the beech, and devotes all 
its strength to the upper part where it towers above the beech. 
It may live long in this way, but it succumbs ultimately in 
the fight — of old age if of nothing else, for the life of the 
birch in Denmark is shorter than that of the beech. The 
writer believes that light (or rather shade) is the cause of the 
superiority of the latter, for it has a greater development of 
its branches than the birch, which is more open and thus 
allows the rays of the sun to pass through to the soil below, 
while the tufted, bushy top of the beech preserves a deep 
shade at its base. Hardly any young plants can glow under 
the beech except its own shoots ; and while the beech can 
flourish under the shade of the birch, the latter dies im¬ 
mediately under the beech. The birch has only been saved 
from total extermination by the facts that it had possession of 
the Danish forests long before the beech ever reached the 
country, and that certain districts aro unfavourable to the 
growth of the latter. But wherever the soil has been enriched 
by the decomposition of the leaves of the birch the battle 
begins. The birch still flourishes on the borders of lakes and 
other marshy places, where its enemy cannot exist. In the 
same way, in the forests of Zeeland, the fir forests are dis¬ 
appearing before the beech. Left to themselves, the firs are 
soon displaced by the beech. The struggle between the latter 
and the oak is longer and more stubborn, for the branches and 
foliage of the oak are thicker, and ofl’er much resistance to the 
passage of light. The oak, also, has greater longevity; but, 
sooner or later, it too succumbs, because it cannot develop 
in the shadow of the beech. The earliest forests of Denmark 
were mainly composed of aspens, with which the birch was 
apparently associated ; gradually the soil was raised, and the 
climate grew milder; then the fir came and formed large 
forests. This tree ruled for centuries, and then ceded the 
1 See Nature, vol. xxxi. p. 63. 
