876 



II. THE INFLUENCE OF EXTERNAL FACTORS 

 ON THE VEGETATION. 



The vegetation of the Færoes bears the impress of the peculiar 

 climatic conditions which result from the geographical position of 

 the islands. 



The decidedly insular chmate \vith cool summers and absence 

 of extreme cold in winter, with an all-prevailing humidit}^ and 

 abundant rainfall, all these together produce moist conditions in 

 the soil al most everywhere and favour the rapid production of 

 humus. 



Excellent accounts of the Færoese climate are given by Wil- 

 laume-Jantzen in »Geografisk Tidsskrift« (1899) and »Atlanten« 

 (1905). In »Bot. of Fær.«, Vol. I. (Ostenfeld 1901 a) I have given a 

 short abstract of the first of these papers. 



These accounts show at once a climate with characteristics so 

 marked that they must of necessity have a determining influence 

 on the vegetation. It ^\i\\ therefore be advantageous to consider 

 in some detail these climatic conditions in so far as they influence 

 plant life. 



Vegetation is affected not by climate alone, but also by edaphic 

 factors, nor can the influence of man and animals be left out of 

 account. There are thus three main groups of factors to be inves- 

 tigated vv'hen considering the relation between external conditions 

 and the vegetation. 



1. Climatic factors. 



a. Temperature. Willaume-Jantzen s sketch of the cli- 

 mate makes it quite evident that there is an unusually slight variation 

 in the temperature of the air in the different seasons of the year. 

 The climate is decidedly insular. The coldest season extends 

 into the middle of March, and the highest temperatures begin to 

 be registered in July and August. 



Observations made at Thorshavn over a period of 30 years^ 

 give the following averages (in Centigrade) for the months of the 

 year : 



' In mj' abstract (Ostenfeld 1901 a) I have only been able to use Willaume- 

 Jantzen's first paper which is based upon observations during 25 years; therefore 

 the figures given there do not exactly correspond with those pnblished here. 



