Ecology. 23 
The virgin woodlands had certain defined associations of plant and animal 
life, forming through their balanced interdependence a closed barrier to 
invasion by exotic species. Much of the ground they occupied is now 
periodically turned over by the plough. The original soil, rich in humus and 
with a specialised micro-flora and fauna, the result of generations of forest 
growth and decay, has been roughly replaced by an artificial product con- 
stantly subjected to disturbance and alteration to meet economic require- 
ments. The relatively stable, physical and chemical constitution of the 
virgin soil, with its finely zoned and layered structures, upon which the needs 
of the varied species of the virgin associations depended, has been destroyed. 
The virgin forest and virgin soil, within certain limits, were self-supporting 
and self-protective, but the usurping agricultural ground has to be frequently 
doctored to renew the materials carried away in the crop, or wasted in the 
drainage waters. Neglect, or a bad season, results in an invasion of weeds, 
varying in kind with the rotation or fallow, mostly foreign to the original 
vegetation, but now, in ill-assorted groups, occupying all artificially formed 
new ground remote from virgin plant associations. 
Having destroyed the forests, man proceeded to form artificial woodlands 
by planting. In so doing, he not only dislocated various tree-species from 
the habitats to which they were originally closely confined through natural 
selection and adaptation, but further, planted them in parts of the country 
where they were formerly non-existent, and even introduced species (¢.g. larch 
and sycamore) from abroad. Bushes taken from specialised surroundings 
soon formed a network of hedgerows over miles of country, and certain 
species of native trees (¢.g. ash and beech) were selected and spread widely 
beyond their original confines, on account of their usefulness for timber or 
other purposes, or from the ease with which they could be reared in civilised 
surroundings. 
In plantations we often find, side by side, different trees which, in nature 
grow as pure, or almost pure, forest associations. The trees may, further, be 
planted with little consideration as to their natural habitat, in a way that 
often spoils the harmony of the scenery. A natural vegetation, be it vast 
stretches of moor or forest, or scattered, smaller patches of various formations, 
_ always blends harmoniously with the physiography, and, indeed, forms a 
natural clothing in which every earth feature has the appropriate garment 
for the season and the climate. 
Orchards of selected varieties of British and foreign fruit trees present us 
with an entirely artificial type of bushland or scrub, consisting of trees which 
are usually found in nature widely scattered, singly, or as small groups in 
special habitats, where competition with forest trees is limited. As with other 
