118 COMPOSITION or rOEEST CB0P8. 



a. An abundant annual production of foliage yielding a rich 

 humus. — ^When several species grow together, they form not only a 

 denser but a deeper mass of continuous foliage, the obvious conse- 

 quence being a more abundant production of leaves, area for area, 

 than if the forest were pure. Besides this, we know that some trees 

 produce more foliage than others, e.g., sal and Terminalia tomen- 

 tosa than teak ; in the hills, the oaks, deodar, and the firs than 

 Pinus longifolia ; and so on ; and that the leaves of some de^mpose 

 more easily and form a richer humus than those of others, Ter- 

 minalia tomentosa and sal, for instance, being better in this respect 

 than teak, and the oaks than Pinus longifolia or any other conifer, 

 and so on. Hence with a mixture of species there is always a better 

 chance of the soil being continually enriched by the decomposing 

 leaves. 



b. The, as much as possible, constant maintenance of a complete 

 leaf-canopy. — This would protect the soil, including its covering of 

 dead leaves (1) from erosion and breaking away; (2) from the suns 

 rays, which would dry up the soil rapidly and hinder the formation 

 of humus; (3) from winds, which would blow away the covering of 

 dead leaves, besides accelerating the evaporation of moisture from 

 the soil; (4) from the action of directly falling rain, which would 

 wash away the surface-soil and covering of dead leaves and humus, 

 besides carrying away in abundance from the soil soluble substan- 

 ces fit for plant food; {5) from being over-run with weeds, which 

 would be an obstacle to reproduction, and would 6hoke out, or at 

 least keep back, advance growth; and (6), to a certain eietent, from 

 fire, which would bum less fiercely if the soil and covering layer 

 of vegetable debris were kept moist as much and as long as possible, 

 and the production of a strong draught of wind, in case a conflagra- 

 tion occurred, were impeded. All these various objects would be 

 most completely attained by means of a mixture of several species. 

 If the species composing a forest are all, or most of them, deciduous, 

 some of them, at any rate, are sure, or at least very likely, to be in 

 kaf while the others are still bare, and thus a green canopy (imper- 

 fect it may be, but nevertheless a green canopy) will be secured 

 during as many months of the year as possible; whereas, when 

 there is only a single species, and that a deciduous one, the whole 

 forest may be leafless for a considerable time, and the soil complete- 

 ly exposed to injurious weather influences and liable to run wild 

 with weeds. 



c. Prevention of fire, which would, besides destroying all the 

 organic matter in the topsoil, bake its surface hard. As shown 



