314 Studies in Forestry [CHAP. xiv. 



number of noxious insects is chiefly to be feared ; hence the 

 additional importance of keeping such woods or portions of 

 woods carefully thinned and tended so as to remove any sickly 

 stems before they become breeding-places for the insects. 



As a rule conifers are much more exposed to attacks from 

 noxious insects than broad-leaved species of trees. And as they 

 are at the same time comparatively deficient in recuperative 

 power, owing to their not being able to set apart such good 

 reserves of starchy and nitrogenous matters, the damage suffered 

 by them is usually much greater. Spruce and Pine suffer far 

 more from insects than any other species of forest trees ; whilst 

 among broad-leaved kinds Oak, Beech, Poplar, and Willow are 

 more damaged than the Birch, Alder, Ash, Elm, Maple or 

 Sycamore. But there can really be no comparison between the 

 devastations sometimes occurring in coniferous woods and the 

 attacks to which broad-leaved crops are exposed. Even after 

 Oak standards have been defoliated in June by armies of cater- 

 pillars of the Processionary moth (Cnethocampa processionea\ 

 the trees, thanks to their nutrient reserves, flush into leaf again 

 in July ; whereas, when about four-fifths of the foliage of Scots 

 Pine and Spruce have been devoured, the ultimate recovery 

 of the former is extremely doubtful, and the death of the 

 latter is certain owing to the much smaller reserve supplies 

 it stores up. 



Whatever the species may be which forms the crop, damage 

 done to young growth is, for obvious physiological reasons, 

 more serious than when it occurs on older poles and trees ; 

 whilst attacks made in spring are more injurious than those 

 taking place in summer or near the close of the active period 

 of vegetation, when the buds have been formed and the 

 nutrient reserves secreted for the succeeding year's growth. 

 The extent of the damage often also varies according to the 

 parts injured. If the foliage alone be attacked the loss may 

 perhaps be confined to the mere deficiency in increment; 

 whereas when the roots and the cambium are extensively 



