34 TREE GROWTH IN RELATION TO 



north aspect at a high elevation a species may break out 

 into leaf so much later than under opposite conditions that it 

 may escape from a frost which does great damage to the 

 same species growing on a south aspect at a lower elevation. 



Taking all things into consideration we may group the 

 species as follows : 



Very frost-tender : Ash, false acacia, sweet chestnut, beech, 

 silver fir. 



Moderately hardy : Oak, Douglas fir, maple, sycamore, 

 spruce, alder. 



Hardy : Lime, elm, aspen, willows, birch, hornbeam, larch, 

 Corsican pine, Austrian pine, Weymouth pine, Scotch pine. 



Of the two varieties of the Douglas fir, the green or Pacific 

 variety appears to suffer most from early frost, and the 

 Colorado or blue variety from late frosts. 



This list may be taken as fairly accurate in most cases, 

 and a little careful observation will easily enable a woodman 

 to modify it according to the local conditions of his own 

 woods. 



Of other species, black walnut, hickories, Turkey oak, 

 and Jeffrey's pine are all frost-tender ; while American ash, 

 Sitka spruce, Japanese larch, white spruce, Lawson's cypress, 

 Wellingtonia, Nordmann's fir, and red cedar are hardy. 



Danger is greatest while the plants are young. A single 

 night of frost while seeds are sprouting may kill a whole bed 

 of seedlings, and danger continues during the first four or five 

 years of life, and is then gradually reduced as the plants grow 

 taller ; it is not at an end till they have grown above the 

 local frost zone, the height of which varies according to the 

 shape of the ground. In damp, deep, narrow valleys forming 

 what are called ' frost holes ', quite tall trees may have their 

 foliage destroyed by a bad frost. Woods on hill sides and 

 high land suffer least. Frosts are worse on north-east, east, 

 south-east, and south aspects, than on north or west ones, and 

 are worse on wet clayey soils than on lighter ones. 



