TEMPERATURES IN TREE CROWNS AND AI?OVE TREES. 



61 



February- 

 April. 



^ 

 ^ 



Central Italy*- - -- 

 Eastein Francet.... 

 Alsaiian Mountains J- 



Bavaria^ : 



Eastern Prussia || 



-0.8 

 -1.1 





+0.8 

 -t-1.9 



-0.5+0.2 



'-0.7-1-0.1 









-1-0.4 



-o.y 



—0.3 



May-July. 



—1.4 



+ 1.0 



+ 1.2 

 + 1.9 

 + 1.1 

 +0.5 



a 

 a 

 o 



3 



—1.2 

 —1.0 

 — 

 —0.9 

 —0.4 



August- 

 October. 



a 



r 



3.6+1.1 



2.6 

 -1.9 

 -3.2 

 -1.6 



+ 1.3 



+2.4 

 +1.6 

 +0.2 



—1.3 

 —0.6 

 —0.2 

 -0.8 

 —0.7 



November- 

 January. 



3 



—0.9 

 +0.9 





 —0.3 



a 



Tear. 





-i-0.6— 0.11—1.9 

 +1.7,+1.3— 1.2 



+ 1.2-f0.6 

 — 0. 2,-0. 2 



S 



+ 1.0 



+2.0 

 + 1.0 

 + 0.2 



a 



-0.4 



+ 0.4 

 0.3 

 0.4 



* Station Vallaiabrosa, Tuscauy. t Station Bellet'ontaine, near Nancy. 



; Station Melkerei, in tbe Vosges Mountains. § Stations See.sbaupt and Rohrbrunn. 



II Stations Fritzen and Kurwien. 



TEMPERATURES I:N^ THE TREE CROWN AND ABOVE TREES. 



The observations used in the preceding- section were all taken at the 

 usual height, that is, about 5 feet (1.5 m). The Swiss forest observa- 

 tions are taken at a height of 3 meters or about 10 feet. I have not 

 been able to consult these observations except for a single year, that 

 of 1870. In Lorey's Handbook of Forestry there are given seasonal 

 means for twelve years from three stations, Interlaken, Pruntrnt, and 

 Berne. These give, in Fahrenheit degrees, for winter, ^Y — 0'^.92 for 

 spring, 1'^.33; for summer, 2°.72, and for autumn, 1°.57. These are of 

 the same general character as those taken at an elevation of 5 feet. 

 The large value of W — for spring makes them resemble more the values 

 given in the jireceding section for stations at high elevations above 

 sea level. This is to be expected, as the Swiss stations are at the ele- 

 vation of 2,034 (020 m.), 1,476 (450 m.), and 1,946 feet, (593 m.) respec- 

 tively. Observations are also taken by theBavariau and German services 

 in the tree crown. A place is selected in the top of the tree, but under 

 the thatch of foliage. This is as nearly as practicable vertical over the 

 instruments i)laced at the surface, and observations on temperature are 

 here made at the same time as at the surface. The discussion of these 

 observations lies under two serious disadvantages. In the first place, 

 there is generally no station at the same elevation outside the woods, 

 and, in the second, the tree-top stations are necessarily at dift'erent 

 heights, thus making impossible a direct comparison between stations. 



The first difficulty may be overcome by making' a fictitious outside 

 station and giving- the ground station temperatures a correction for 

 known mean variations of temperatnre with altitude. Unfortunately 

 this reduction of the surface observations to a given altitude can not be 

 made witliout considerable uncertainty. The change of temperature 

 with altitude alters with ivlinost every source of meteorological change, 

 with season and time of day, with the toi)Ography, the cliaractci- of the 

 soil and its covering, and with the weather, and the amount of change 

 is especially variable within the first 50 feet from the surface, within 

 which range must be made the correction we propose to apply. How- 

 ever, the correction is a small one, and over the territory occupied by 

 the German stations it is known with more accuracy than elsewhei'C 

 generally. 



