204 TRANSACTIONS OF ROYAL SCOTTISH ARBORICULTL'RAL SOCIETY. 



Southern Alps. Birch attains to 5300 feet in the Northern Alps, 

 and to 7000 feet in the Central Alps. Professor Schrceter 

 discusses this question at some length. Even assuming that 

 the present tree-limit in Britain is 1000 feet lower than is shown 

 by tree-remains found in our peat, it is still far below the Swiss 

 altitudes. This is an evidence of our oceanic climate, but it is 

 also a result of the lower altitudes attained by even our highest 

 mountains. If Ben Nevis (4400 feet) is compared with a summit 

 in Switzerland of the same height {e.g. the Gabris), the following 

 differences in climate are found on Ben Nevis : lower temperature 

 in July and January, and in the mean annual, but a less 

 marked variation throughout the year ; a larger rainfall and 

 much more fog and wind. As Schroeter says, "A study of 

 meteorological figures conveys some idea of the foggy, rainy, 

 snowy, stormy, and sunless oceanic climate of the Scottish 

 Highlands." So far as statistics show, the upper limit of the 

 birch in the Highlands coincides with a July temperature 

 (ro° Cent.) almost the same as is found towards its upper 

 limit in Switzerland, but in the continental Swiss climate this 

 temperature occurs at much higher elevations. One suggestion 

 appeals to the Scottish forester : it might be well to investigate 

 whether with the help of the larch, which flourishes so well in 

 Scotland, the tree-limit in the Scottish Highlands might not be 

 raised higher, 



A paper by Dr Brockmann-Jerosch ^ also deals with the question 

 of tree-limits, and although it is somewhat technical a short 

 notice may indicate the line of argument. It is shown that the 

 upper tree-limit cannot be determined by any one factor, such as 

 rainfall, snowfall, or the average temperature of the year or of 

 any particular month or period. The tree-limit depends more 

 on the general climate as a whole, and this is determined for 

 each locality by the physiography or lie of the land, in other 

 words by what most foresters call exposure. Dr Brockmann's 

 discussion refers to Switzerland, a continental area, but he 

 shows by statistics that the northern and western parts of 

 Switzerland are more oceanic than the central Alps. A 

 continental climate with its hotter, drier summers and more 

 intense winters, as seen in Siberia, is more favourable to tree- 

 growth in this way that the tree-limit is farther north (I'.g. nearer 

 the pole) than in oceanic western Europe. So also a con- 



^ H. Brockmann-Jerosch in Eui^^/er's Bo/an. /a/irl>iu-ker, ^g, pp. 19-43, 1903^ 



