46 PROTECTION OF WOODLANDS. 



oxycoccos and V. uliginosum), and Marsh Cistus (Ledum) 1 indicate 

 true bogs or swamps. 



Essentially important as a certain degree of soil-moisture un- 

 doubtedly is for the thriving of woodland crops, yet too great a 

 degree of moisture produces many disadvantageous results. 



Most species of our forest trees have a bad, often a crippled, 

 development on wet soils, in consequence of the want of due 

 circulation of air in the soil (deration), of its low temperature, of 

 the incomplete decomposition of the organic debris, and the for- 

 mation of free humic and similar injurious acids. 



Owing to the strong evaporation, damage from frost is especially 

 frequent in wet localities, resulting in the dying off of the tender 

 portions of the plants, and in the lifting of the soft soil and 

 the consequent death of the seedlings or transplants ; this danger 

 can, on very moist soil, assume such proportions as even to lift 

 out of the ground the stronger, larger classes of transplants that 

 have been put out with balls of earth attached to the roots. 



On old stems, and particularly in the case of the Spruce, the 

 appearance of red-rot and disease of the stool is very often 

 directly due to excess of soil-moisture. 



Windfalls are also much more frequent on soils that are 

 constantly soft from moisture, especially when a clayey layer, 

 the cause of the wetness, at the same time prevents the roots oi 

 the trees from working their way down into the subsoil. Tl 

 ordinary operations of forestry, and particularly the preparation 

 and removal of timber for disposal, are also considerably interfered 

 with when the soil is always wet, so much so, in fact, as to 

 only carried out during, and often to be practically dependent on, 

 continuous hard frost during the winter (e.g., massy Alder crops). 



But all species of trees are not affected to anything like 

 similar extent by wetness of the soil and the drawbacks con- 

 sequent thereon. Thus, the common Alder and the majority of 

 the Willow tribe can not only bear, but actually prefer, a high 

 degree of moisture, whilst a few species of Poplar, and also Ash 

 and Hazel in a less degree, can thrive quite well even on a very 

 moist soil ; but in all these cases it is always moisture in circula- 

 tion, and not stagnating moisture, which suits them. Among 

 conifers the Spruce can stand a high percentage of moisture in 

 the soil better than any other species. 

 1 According to Hooker's Flora, it is doubtful if Ledum occurs in Britain. Trans. 



