1884.] DECAY OF FALLEN LEAVES. 241 



DECAY OF FALLEN LEAVES. 



^X t^e following brief remarks it is })rofessed rather to seek for 

 ^ and invite information than to provide it, on this rather intricate 

 ^ subject. In the course of an article on ' Leaf Canopy and 

 Pruning,' the decay of fallen leaves had necessarily to be referred to, 

 and in connection with that incidental reference an explanation has 

 been specially requested. A few words may therefore be offered, 

 attemjDting to make the position plainer. 



It can hardly be controverted that it has been sufficiently proved 

 by thousands of instances, both in leaf woods and needle woods, that 

 the decay of fallen leaves in sitit is most beneficial to the growth of 

 the trees that have shed them. This much then we may take for 

 granted. 



In tracing further the more superficial or visible aspects of the pro- 

 gress of decay, the following details seem very probable. The leaves 

 decay most rapidly when they are exposed to the greatest extremes of 

 alternating moisture and dryness, and the most violent changes 

 from heat to cold. That is, leaves decay most rapidly when quite 

 exposed to weather in the open. 



Under the shade of trees excluding much of the sunlight and much 

 of the rain, leaves decay more slowly. This latter protracted process 

 of decay is, however, in general, more favourable to vegetation, and 

 especially to the growth of trees, and adds an increased quantity of 

 useful substances to the soih The rapid rotting of leaves or other 

 vegetable matter is, chemists will tell us, a process analogous to 

 thorough combustion. Leaves decaying rapidly in the open will thus 

 vanish for the most part into thin air, and leave hardly any residuum 

 to be added to the soil. On the other hand, leaves decaying under 

 the shade of leaf canopy undergo a mouldering process more 

 analogous to charcoal burning or charring, and the result is a much 

 greater (j^uantity of powdery humus to be added to the soil. In the 

 latter case, too, the carbonic and nitric acids evolved in the process of 

 decay have better opportunity of sinking into the ground, or, at any 

 rate, less chance of being wafted away by winds. Therefore, as was 

 stated nuder fourthly, the shade of leaf canopy usefully moderates 

 and retards the decay of the fallen leaves and organic refuse. The 

 leaf canopy must not, however, be too dense, nor the trees too close 

 together. Instances have occurred, most frequently in Beech woods, 

 where the coverts have been maintained too dark, the trees being too 

 close together, owing to procrastination or insufficiency of thinning. 

 Here, although the crowded trees shed great wealth of leaves, no 



