132 AGRICULTURE. 



best sites, it is to be mainly considered and used as a " stop- 

 gap" to make useful those parts which would otherwise be 

 waste. 



2. That a forest growth, besides furnishing useful material, 

 is a condition of soil-cover which affects other conditions, 

 namely, of climate and water-flow, and hence its location 

 should be such as to secure the most favorable influence on 

 these. 



3. That the wood-crop does not live on the soil, but on the 

 air, enriching the soil in nutritive elements by its decaying 

 foliage rather than exhausting it, and hence that no ma- 

 nuring and no rotation of crops is necessary as in field 

 crops; in other words, the location of the wood-crop can be 

 made permanent. 



A wood growth should therefore be maintained on the 

 farm : 



a. Wherever the ground is too wet or too dry, too thin 

 or too rocky or too steep, for comfortable ploughing and for 

 farm crops to do well, or for pasturage to last long, or, in 

 general, where the ground is unfit for field and meadow. 



b. On the highest portions of the farm, the tops of hills 

 and also in belts along the hillsides, so as to interrupt con- 

 tinuous slopes, which might give rise to such a rush of 

 surface-waters as to gully the ground and make it unfit for 

 field crops or pasture ; the gentler slopes which are liable 

 to washing should at least be kept in grass or terraced for 

 crops to prevent the rush of surface-waters. 



c. Along watercourses, where narrower or wider belts of 

 timber should be maintained to prevent undermining of 

 banks and washing of soil into the streams if ploughed too 

 close to the border ; the shade of a forest growth would 

 also check rapid evaporation of smaller watercourses. 



d. Wherever the protection by a wind-break against cold 

 or hot winds is desirable, for which purpose the timber belt 

 is of more far-reaching effect than the wind-break of a single 

 row of trees ; the reduced evaporation from the fields due 

 to this protection has been known to increase the yield of 

 field crops by as much as 25 per cent. 



e. On all unsightly places, which impair the general 



