8 PROTECTION OF WOODLANDS. 



earlier, suffers much more frequently from late frost than the 

 more sensitive Oak, which does not commence its active period 

 of vegetation until later ; in the case of the Silver Fir the side 

 shoots may often be seen killed by frost, whilst the vertical 

 shoot still lies protected in the terminal bud which is the last to 

 develop. At the precise moment of the development of the bud, 

 the Larch is the most sensitive species ; but as soon as the needles 

 are somewhat strengthened, it becomes much more hardy. 



So far as the influence of the Soil and Situation is concerned, 

 coombs or hollows on the hillsides, and depressions in the 

 crowns of the timber crops, appear to be most exposed to danger, 

 especially when the soil is moist, as the heavy cold layers of air 

 produced by the evaporation of the moisture have no means of 

 being wafted away, owing to the free circulation of air being 

 impeded : such patches, often contrasting sharply with their 

 immediate surroundings, either through inferior growth and 

 development, or through the occurrence of the more hardy 

 species, are called frost-holes. Woods skirting the edge of low- 

 lying meadows in valleys, and those in the vicinity of ponds 

 and moist meadows frequently suffer damage from frost as late 

 as even the middle of summer, in consequence of the cold pro- 

 duced by the increased evaporation. Eastern and south-eastern 

 aspects exposed to the cold, frost-bringing east winds, and southern 

 exposures, with their tendency to early awakening of active 

 vegetation, are more liable to danger from frost than the other 

 aspects. 



The Soil-covering, more or less dependent on the nature of soil 

 and situation, is also of influence, as young plants surrounded by 

 a dense growth of grass are more exposed to danger from frost 

 than those on cleaner soil, in consequence of the stronger radiation 

 of warmth by the grass, whilst a high, lightly shadowing soil- 

 covering of thorns, juniper, broom, &c., acts as a protection. 



Young plants are, of course, always most exposed to the danger ; 

 young seedlings that have just germinated are usually killed 

 outright by late frosts, which not infrequently also happens to 

 one and two-year-old seedlings of the sensitive species of trees 

 when the frost is hard. With advancing age the liability to 

 suffer from this danger diminishes, especially when the plants 

 have attained to over the so-called frost-height or normal level 

 of the cold layers of air, which is often very distinctly marked on 





