SOIL AND SURFACE CONDITIONS 127 



increase the fertility of a poor soil by a very small, and 

 in many cases inappreciable, extent. The differences 

 in the growth of timber due to variations of soil and 

 situation are as distinctly marked in natural forests, 

 thousands of years of age, as in newly planted ground, 

 although in the former this difference may be relatively 

 reduced by mutual shelter, and improvement of the local 

 climate, and these are probably the greatest factors. 



Take, for instance, two lots of trees of the same species, 

 one planted on poor land recently cleared of timber, such 

 as larch or beech, and the other on good fertile soil which 

 has been under grass for perhaps a century. For the 

 first two or three years, the trees on the poor soil will 

 probably make a better growth than those on the grass, 

 owing to the more favourable conditions of the first few 

 inches of surface, and the greater fertility due to the decay 

 of the humus left by the old crop. But when once the 

 trees are thoroughly established, and the roots in each 

 case have penetrated to a depth of a foot or so, the better 

 soil will quickly show its influence on the growth of the 

 trees, and the difference becomes more marked as time 

 goes on. If the trees on the poor soil are sheltered by old 

 crops from prevailing winds, while the others are fully 

 exposed to them, the difference may be less marked ; but 

 given similar altitude, exposure, etc., the natural fertility 

 of the soil will make itself felt in a comparatively short 

 time, according to the species and general climatic features 

 of the locality. 



The successful growth of trees at high elevations in 

 Central Europe is closely connected with the superiority 

 of the soil over that found in the British Isles generally 

 above the 1000 or 1500 feet contour line. Bare rock, or 

 thin, poor soils may be as abundantly represented in the 

 one case as the other, but in the British Isles certain 

 types occur at a much lower level, and consequently the 



