152 MASS. EXPERIMENT STATION BULLETIN 170. 



SOIL COVERS, LAWNS, MACADAM, ETC. 



The nature of the soil cover surrounding trees is scarcely less important 

 than that of the soil in which the roots are growing. We find trees growing 

 under many different conditions: e.g., lawns, mowings, cultivated fields, 

 paved and macadamized roads, sidewalks, etc., and it is hardly necessary 

 to point out that cultivation is much superior to all other conditions. 

 The importance of tillage is scarcely appreciated in the case of ordinary 

 crops, even by lifelong farmers. Stirring the soil, even without the use 

 of fertilizers, has enormous influence on the growth of crops, and is also 

 an important factor in the control of various tree pests, a thrifty tree 

 being more resistant to infection. Cultivation not only aerates the soil, 

 but breaks up the capillarity and conserves the moisture, of great 

 importance in dry soils. 



Examples of the good effects of cultivation on shade trees may be seen 

 in the many specimens growing luxuriantly in soil in which crops have 

 been cultivated for years. Trees under these conditions branch freely 

 and produce large leaves of a deep green color. Cultivation of the soil 

 about trees for even one year has a decided effect. 



Next to cultivation, lawn conditions are perhaps the best. The grass, 

 which is constantly being mowed and left on the ground, acts as a mulch 

 and conserves the moisture. Some of our best trees grow in pastures, 

 where the conditions are often unfavorable to the growth of grass or where 

 the grass is kept closely cropped by grazing. A mowing or hay field is 

 one of the worst possible locations for a tree, the elm being particularly 

 susceptible to the ill effects of such an environment. Measurements of 

 elms growing on either side of a road, one series being under partial lawn 

 and the other under partial mowing conditions, showed differences in 

 their development. The average growth of these trees during a period 

 of twenty-five years is as follows: those on the lawn side of the road had 

 a circumference of 56 inches, while those on the other, or mowing, side 

 were only 49 inches. In another case the average circumference of lawn 

 trees was 37 inches, and that of the mowing trees, 26 inches. These trees, 

 which had been growing under these conditions for many years, were of 

 the same age, and were so located that the difference in light intensity 

 cannot be considered a factor in their development. 



The extensive use of various materials for paving roads can hardly 

 have a beneficial influence on tree growth. In some cities a great many 

 trees are found on streets paved with asphalt from one block front to 

 another, allowing nothing but a small space around the trees unpaved. 

 .t is a question in such oases where the trees obtain their moisture, al- 

 though they exist year after year, and make some growth. No doubt 

 some water is obtained from catch basins and sewers; at any rate, moisture 

 is usually found in the soil under the most impervious substance employed 

 in paving, and during the most severe droughts trees on paved streets 

 often suffer less from lack of water than others apparently more favorably 



