FORESTRY AND CONSERVATION 351 



it should be culled of its weeds, the poor kinds, which we do not 

 care to reproduce, and which, like all other weeds, propagate them- 

 selves only too readily. This weeding must not, however, be done 

 all at once, as it could be in a field crop, for in a full-grown piece 

 of woodland each tree has a value, even the weed trees, as soil cover. 



The great secret of success in all crop production lies in the 

 regulating of water supplies ; the manuring in part and the cultivat- 

 ing entirely, as well as drainage and irrigation, are means to this 

 end. In forestry these means are usually not practicable, and hence 

 other means are resorted to. The principal of these is to keep the 

 soil as much as possible under cover, either by the shade which the 

 foliage of the tall trees furnishes, or by that from the underbrush, 

 or by the litter which accumulates and in decaying forms a humus 

 cover, a most excellent mulch. 



A combination of these three conditions, viz., a dense crown 

 cover, woody underbrush where the crown cover is interrupted, and 

 a heavy layer of well-decomposed humus, gives the best result. 

 Under such conditions, first of all, the rain, being intercepted by the 

 foliage and litter, reaches the ground only gradually, and there- 

 fore does not compact the soil as it does in the open field, but leaves 

 it granular and open, so that the water can readily penetrate and 

 move in the soil. Secondly, the surface evaporation is considerably 

 reduced by the shade and lack of air circulation in the dense woods, 

 so that more moisture remains for the use of the trees. When the 

 shade of the crowns overhead (the so-called "crown cover," or "can- 

 opy") is perfect, but little undergrowth will be seen ; but where the 

 crown cover is interrupted or imperfect, an undergrowth will appear. 

 If this is composed of young trees, or even shrubs, it is an advantage, 

 but if of weeds, and especially grass, it is a misfortune, because these 

 transpire a great deal more water than the woody plants and allow 

 the soil to deteriorate in structure and therefore in water capacity. 



Some weeds and grasses, to be sure, are capable of existing where 

 but little light reaches the soil. When they appear it is a sign to 

 the forester that he must be careful not to thin out the crown cover 

 any more. When the more light-needing weeds and grasses appear 

 it is a sign that too much light reaches the ground, and that the 

 soil is already deteriorated. If this state continues, the heavy drain 

 which the transpiration of these weeds makes upon the soil moisture, 

 without any appreciable conservative action by their shade, will 

 injure the soil still further. 



The overhead shade or crown cover may be imperfect because 

 there are not enough trees on the ground to close up the interspaces 

 with their crowns, or else because the kinds of trees which make up 

 the forest do not yield much shade; thus it can easily be observed 

 that a beech, a sugar maple, a hemlock, is so densely fohaged that but 

 little light reaches the soil through its crown canopy, wnile an ash, 

 an oak, a larch, when full grown, in the forest, allows a good deal 

 of light to penetrate. 



Hence, in our weeding process for the improvement of the wood 

 crop, we must be careful not to interrupt the crown cover too much, 



