DAMAGE CAUSED BY LOW OR HIGH TEMPERATURE. 7 



Frost-shakes are a peculiar effect of hard frost during winter, 

 which will also, like the freezing and lifting of the soil, be treated 

 of in a paragraph by itself. 



6. Factors determining the Extent of the Damage done ly late 

 and early Frosts. 



The extent of the injury that may be done is mainly dependent 

 on the Species of Tree, although numerous other factors are also 

 of more or less influence, among which the age of the timber 

 crop, the nature of the soil and situation, the time of the oc- 

 currence of the damage, and the kind of weather accompanying 

 the frost, are often of the most importance. 



The temperature at which young portions suffer from frost 

 varies greatly according to the different Species of Trees, many 

 of which bear exposure to 5 or 7 C. below freezing point. The 

 leaves and flowers of most of our trees bear exposure to a few 

 degrees below the freezing point, but the concurrent circumstances 

 then become of importance, and prolongation of the frost, or 

 simultaneous hoar-frost, stimulated by rapid evaporation of 

 moisture from ponds and meadows, heightens the danger, whilst 

 aerial movement decreases it. In many plants the leaves appear 

 yellowish and drooping after a frosty night, but may gradually 

 raise themselves again and recover their normal green appearance. 

 The flowers appear to be invariably more sensitive than the 

 leaves, but in the case of the hardy kinds of trees they aie 

 still less sensitive to late frost than those of other species. 



In regard to late and early frosts our indigenous and ac- 

 climatised trees may be classified as under : 



Very sensitive: Ash, Sweet Chestnut, Oak, Beech, Acacia, 

 Silver Fir. 



Somewhat sensitive : Spruce, Lime, Maple and Sycamore, Larch. 



Hardy, or least sensitive : Hornbeam, Birch, Alder, Elm, Aspen, 

 Willow, Mountain Ash, then Scots, Black and Wey- 

 mouth Pines. 



The hardy species mostly break out early into leaf, as may be 

 noted in the case of Alder, Hornbeam, and Birch, whilst the young 

 flush of leaves of the more sensitive species takes place later, in 

 some cases as late as the middle or end of May, as in the Oak, 

 Sweet Chestnut, and Acacia, so that the danger from late frosts 

 is to a great extent obviated. The Beech, which breaks into leaf 



