16 PROTECTION OF WOODLANDS. 



also be mentioned the greater danger from fire, and from the 

 numerical increase of injurious insects in consequence of the sickly 

 growth of young crops owing to the heat and the dying off of 

 stems and poles, dry summers being decidedly favourable to an 

 abnormal increase among insects. 



11. Factors determining the Occurrence and Extent of 

 the Damage. 



The above mentioned injurious effects of heat, which can be 

 very considerably increased by continuous east winds, are most 

 apparent in the following cases : 



(a) When the plants are of shallow-rooting species, like Spruce, 



Silver Fir, and Beech ; species that begin from the very 

 first to develop a deep root-system, like Oak, Pines, and 

 Larch, are comparatively little exposed to danger. 



(b) In the case of seedlings and young plants, especially when 



they have been recently planted out and have not had time 

 to fully establish themselves ; older transplants, or young 

 plantations, or crops that have already begun to form 

 canopy, seldom show any injurious effects from heat. 

 Young crops, whether formed by sowing or planting, are 

 often killed off to a very considerable extent by loug-con- 

 continued heat. 



(c) When the soil is shallow, loose, and naturally dry, or 



sandy peat, or very limy soils, and on southern ai 

 western exposures, which suffer more than the fresh* 

 eastern or, better still, the northern aspects. On plaii 

 and in low upland tracts, which also usually have a 

 warmer climate, the injurious effects of heat will be more 

 frequently noticeable than in mountainous tracts with 

 their greater relative humidity, and their more abundant 

 aqueous precipitations. A dense soil covering or rank 

 growth of grass is disadvantageous on areas to be wooded, 

 as it involves the transpiration of a large quantity of 

 moisture, and prevents slight precipitations from reaching 

 the soil. Damage caused by reflection of the heat is also 

 not infrequently to be noted at the edge of the next 

 year's fall of mature timber, or in the vicinity of in- ( 

 dividually isolated stems (standards), not only in the 



