MODE OF DECOMPOSITION. 765 



decomposition; the high relative-humidity of the air and low 

 mean temperature in mountain tracts cause dec]) layers of raw 

 humus to accumulate in forests.* 



(e) Density of Standing Crop of Trees. Neither a dense 

 crop of trees, nor an open, light crop, such as that of light- 

 demanding trees, when they become old, and weeds cover 

 the ground, afford the most favourable conditions for the 

 decomposition of litter and its admixture with the mineral soil, 

 as ordinary neutral mould ; in both cases, the humus accumu- 

 lates in an incompletely decomposed, sour condition, as peat. 

 Peat hinders the absorption of water by the roots of the trees 

 and prevents the aeration of the soil, it interrupts the normal 

 loosening of the soil, and by the infiltration of solutions of 

 humus under its superficial layers causes the formation of a 

 hard pan. The important influence of the various systems 

 of management result from the above considerations. Clear- 

 cutting yields the densest even-aged crops ; selection forests, 

 resembling virgin forest most closely, affords the most favour- 

 able conditions. It is evident that in the tending of a woqd, by 

 thinnings, setting the older trees free, underplanting light- 

 demanders, etc., the forester has the best means for regulating 

 and maintaining the normal decomposition of the soil-covering 

 of litter. 



If litter and humus are to produce the most advantageous 

 effects on forest-growth, the litter must be decomposed chiefly 

 by bacteria and fungi, this decomposition must be moderately 

 fast and uninterrupted. 



Although it is difficult to decide absolutely the proper period 

 for the decomposition of humus, it may be said, that for 

 ordinary forest localities, this is most beneficial, when broad- 

 leaved litter is converted into humus within three years, and 

 coniferous litter in three or four years, while the layer of 

 humus below is only a few centimeters thick. 



The hurtful effects of breaking up the soil and mixing litter 

 and humus on poor soil, by pigs, a comparison of the humus 

 in such areas, with others in which pannage is not allowed, 

 will demonstrate clearly. 



* Ramann, li Die kliinati.schc.n Uoden/oneii Eurojuis." Bodenkunde, 1'JOl, 

 St. Petersburg. 



