DIFFERENCES OF SOIL TEMPERATURE. 



49 



made some studies of the ettects on soil temperatures of vegetation at 

 different heights and has found that on the whole they increase with 

 the height. 



That the forest litter plays an important part in the matter of soil 

 temperature can not be doubted, but no details are given on this point 

 in the publisjied reports of the forest meteorological services. Numer- 

 ous experimental observations have, however, been taken by Dr. 



■ At surface. 



— AtG inches below surface. 



■ At ifcct below surface. 



Fig. 0. — Diflferencea of temperature for young trees, Liutzel Station, -woods and open fields ( W — O). 



Wollny, the results of which are graphically exhibited in Fig. 7. The 

 unbroiven curve is here the result of several years' observation ; the 

 broken ones represent shorter series, made to test the eftects in indi- 

 vidual soils. The comparison is always made with bare soil, and the 

 positive sign here means a higher tem])erature in the covered soil. 

 The general trend of the curves is strikingly like that in forests. 



Average results. . — — liesvlts on loamy soil. liexvlts on quartz soil. 



l''l(i. 7. — Kftects of littor on soil teuiperatun' (littered .surface — hare). ( 11'— O). 



The material at hand does not ])ermit the study of other modifying 

 influences — .soil, latitude, prevailing cloudiness, Avater in the soil, etc. 

 As a means of comparison, it may be of interest to give the progress 

 of soil temperatures under sod as compared with that under bare soil. 

 This is given in Fig. 8, which represents the means from an eleven- 

 year series of observations by the M^Sl. l>ec(pu'iel. The trend of the 

 curves is quite unlike that of tlu' forest.s. 'J'he .sod is n^latively warm- 

 est in autumn ami coldest in s])ring, and (he mean is in favor of warmer 

 12i4i— No. 7 i 



