76 FOEESTS, WOODS, AND TKEES 



silted up. At present, on our treeless catchment areas, as 

 Mr. Margerison (6) pointed out, " the heads of great reser- 

 voirs are being very seriously and rapidly silted up, and 

 some day they will cost an enormous sum for cleaning out. 

 Where is the silt to be deposited so that it is not again 

 quickly washed back ? And what are those corporations to 

 do with it who do not own the adjoining freeholds ? Herein 

 afforestation will prove beneficial. Plantations will prevent, 

 or greatly minimise, silt-laden surface-water rushes by block- 

 ing them and by promoting percolation and filtration." It 

 has been objected that wooded catchment areas may pollute 

 the water supply on account of the enormous masses of dead 

 leaves which decay on the watersheds, or are blown about 

 and carried down by streams to rot in the reservoirs. The 

 humus in the forest is, however, antagonistic to pathogenic 

 bacteria, and the decayed leaves themselves are absolutely 

 innocuous. In order to prevent the leaves being blown 

 into the reservoir, a band of ground next the water may be 

 planted with gorse and other small-leaved shrubs, which 

 form traps for the leaves of the trees. A narrow belt of 

 spruce trees, which have dense, small, evergreen leaves, is a 

 more efficient screen for this purpose. Only a small part of 

 the foliage of the spruce is shed annually, namely, the leaves 

 on the oldest and innermost parts of the branches. These 

 leaves, as they are shed, fall on the ground beneath and 

 are not blown to a distance. The falling leaves of oak, 

 beech, ash, and other broad-leaved trees are blown to con- 

 siderable distances by the wind, and, in the absence of a 

 screen of spruce, may constitute somewhat objectionable 

 litter in the water of the reservoir. 



To sum up, the effect of trees on the yield and quantity 

 of the water supply collected on upland areas cannot be 

 otherwise than beneficial. In the U.S. Year -Book of 

 Department of Agriculture, 1902, it is laid down : " A forest 

 furnishes the best possible cover for watersheds of storage 

 reservoirs. For this reason fully as much as the financial 

 one, several water companies are planting extensively in the 

 Eastern States, especially in Massachusetts and Connecticut." 



