IMPORTANCE FOR WOOD- PRODUCTION. 589 



from the soil, and heuce retain much moisture in the surface- 

 soil. [Not, however, iu the soil containing their roots, which is 

 well drained by the demands of the growing poles for water, 

 transpired by their crowns into the atmosphere. — Tk.] Hence 

 in dense pole-woods of spruce, beech and silver-fir, especially 

 on northerly aspects, there is always plenty of half-decom- 

 posed litter and humus. Woods of old light-demanding trees 

 show opposite phenomena. The Scotch pine loses its soil- 

 improving character soon after light gains admission to the 

 ground. [In Britain, generally at an age of about 60 years. 

 -Tk.] 



(f) System of Management. — Decomposition of litter is un- 

 doubtedly slowest in even-aged high forests, and here (unless 

 it is removed periodically) the greatest amount of undecomposed 

 and partly decomposed litter is found. Coppice forms the other 

 extreme ; litter there decomposes the more quickly, the shorter 

 the rotation and the more open the crop (as in oak-bark cop- 

 pice). A light growth of herbage may be then considered 

 beneficial. Coppice-with-standards also resembles coppice in 

 this respect. Whilst under the above-mentioned systems the 

 rate of decomposition varies with the age of the crop, in Selec- 

 tion-forest this rate is invariable, though owing to the moderate 

 access of heat, light and air and the moisture preserved in the 

 soil by the groups of underwood, it is moderately fast. For this 

 reason, in the still existing virgin forests of Germany the 

 amount of humus and litter imagination may have pictured 

 does not exist ; under otherwise equal conditions, the amount 

 of humus in them is frequently less than in any dense pole- 

 woods of Scotch pines or spruce managed under the clear-cutting, 

 high forest system. 



8. Products of Deeompositioit of the Soil-Cover uig. 



The nature of the products of the decomposition of the soil- 

 covering depends on the rapidity with which it proceeds. 

 According to Ebermayer (op. cit. p. 580), they may be classed 

 under three principal heads as sour, dry and mild humus. 



(a) Sour humus. — Sour humus is formed on wet soils which 

 exclude the air and do not contain enough oxygen ; the decom- 

 position of the soil-covering, therefore, proceeds very slowly and 



