THE VEGETATION OF THE JUAN FERNANDEZ ISLANDS 



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1901 02 03 04 05 06 11 12 13 14 15 16 17 18 19 20 21 22 29 30 31 32 33 34 35 36 37 38 39 



Fig. I. Masatierra, Meteorological station in Bahi'a Cumberland. \'ariation in rainfall 1901 — 1939. 

 Figures in left margin denote millimetres. No observations 1907— 1910 and 1923 — 1928. 



numerous aneroid readings is 590. For comparison between the two stations see 

 Table III. Due to the much cooler nights in the mountains, the average tempe- 

 rature is much lower; the difference in day temperature is very small. With the 

 character of the vegetation in mind I was surprised that the difference in rain- 

 fall was not much greater. An}-body who has lived for some time on Masatierra 

 will tell you that it rains much more in the mountains than near the coast, and 

 our experience is the same; we could see the rain clouds gather over the high 

 ridges while the settlement had sunshine, and a longer series of observations 

 would, I presume, show a much more pronounced difference between the coast- 

 land and the mountain range. It goes without saying that when the moisture- 

 laden air current from SE to SW meets the high coast and is forced to rise, 

 condensation is at its greatest over the south border of the mountain range. 



There is another climatic factor of very great importance, dense fog fre- 

 quently covering the mountains above 400 — 500 m. Between March 25 and April 

 30 the Portezuelo pass was visited 18 times, and 9 times mist was recorded. 

 The photograph, Fig. 2, of the east part of the south side of the island which 

 rises precipitoush- from the sea, shows the sharp lower boundary of the cloud- 

 bank; this is a common sight. 



Returning to the temperature, observations were taken during every excur- 

 sion jointly with the aneroid readings, a condition for working out the altitude. 

 These observations are given in Table IV. 



We have no exact knowledge of the climate of the lower, barren western 

 part of Masatierra. The backbone of the island, which rises abruptly to 500 — 

 900 m above the south coast from Cape Guasaballena to Cerro Piramide, and 



