2 AN INTRODUCTION 



areas, when compared to the temperature of the atmosphere 

 in the open country. As a general rule, it may be stated that 

 the average temperature throughout the year is less within 

 woodlands than that which obtains in the open. And 

 furthermore, that the average summer temperature is con- 

 siderably less in woodlands than in the open ; whereas the 

 average -winter temperature is usually about the same or 

 very slightly lower than in the open. 



Then again, extremes of heat and cold are lessened 

 within woodland areas. It has been found that during the 

 hottest days in the year, the maximum temperatures 

 registered within woodlands are always far below those 

 registered in the open; and conversely, the minimum 

 temperatures registered within woodlands during the coldest 

 days of the year are never so low as those registered in the 

 open ; especially is this so in the case of woodlands consisting 

 of ever-green trees. 



So also, there are daily variations in the temperature of 

 the air within woodlands, when compared to the temperature 

 of the air in the open. 



Within woodland areas, the night temperature is practi- 

 cally always warmer than, and never falls so low as, the tem- 

 perature in the open ; whereas, during the daytime, the 

 average atmospheric temperature within woodlands is always 

 less than the average temperature in the open. 



The chief reason for these differences can be ascribed to 

 the fact that the canopy of the trees prevents the soil from 

 being rapidly warmed by the sun's rays ; and also, when once 

 the soil has become warmed, the canopy of the trees prevents 

 any rapid radiation of heat from the soil. 



And so, also, in the case of -woodland soils, it has been 

 found that the average temperature of such soils is always 

 less than that of soils in the open country. The greatest 

 difference is observed in the summer months, whereas in the 

 winter the difference is practically nil. 



As regards the Moisture in the Atmosphere. The 

 presence of woodlands probably does not materially affect 

 the absolute humidity of the atmosphere if the neighbouring 



