84 



caused marked vertical differences in temperature in the vegetational 

 stratum. He summarizes these results as follows (p. 309) : "The 

 temperature results show that the highest layers of the vegetation pos- 

 sess a greater diurnal range of temperature than either the free air 

 above or the lower layers of the vegetation. Regularly, especially in 

 clear weather, both the higher day and the lowest night temperatures 

 were recorded in this position." 



Dachnowski ('12: 292-297) studied the temperature conditions in 

 a cranberry bog substratum in central Ohio. He found that at a time 

 when ice formed from 8 to 15 inches thick on the adjacent lake, in the 

 bog it was only 3 to 5 inches thick, and there were small patches where 

 it did not form at all. At a depth of 3 inches in the peat the tempera- 

 ture ranged from 33° to '/'/° F. (.5 "-25.0° C). In the bordering 

 maple-alder zone, at 3 inches depth it ranged from 33° to 72° F. (.5''- 

 22.0° C. ). His observations indicate that the temperature relations 

 within the maple-alder zone are more stable than those in the open 

 central area. 



Cox ('10) has also shown that the character of the vegetation in 

 Wisconsin cranberry bogs has much influence upon temperature rela- 

 tions in this habitat. 



It seems very probable that similar conditions hold over prairie 

 vegetation, but I do not know of any observations on this point. We 

 are all familiar with the common practice of gardeners of using a mulch 

 of straw to retard temperature changes under it ; prairie vegetation 

 must have a similar influence. (Cf. Bouyoucos, '13: 160.) 



The relative air temperatures within and without the forest show 

 a distinct tendency to reduce the maxima and minima, and to lozver 

 the mean annual temperature. Harrington ('93:53) concludes, 

 therefore, that ''the forest moderates (by reducing the extremes) and 

 cools (by reducing the maxima more than the minima) the tempera- 

 ture of the air within it. The moderating influence is decidedly greater 

 than the cooling effect." These effects are not uniform, but are much 

 more marked in the summer, and Harrington further says : "The cool- 

 ing effect tends to disappear in winter. The moderating effect is the 

 most important one and it is the most characteristic" (p. 56). 



The temperature relations within the forest crown show that in 

 general the effects are similar to those found at an elevation of about 

 5 feet. The maxima are lowered, the minima are elevated, and there 

 is a cooling effect. The differences are most pronounced during the 

 summer, and the temperatures are intermediate in position between 

 those at the five-foot level and those in the open (I.e.: 66). At a 

 height of 24 feet, deciduous trees showed a marked summer cooling 



