44 TRANSACTIONS OF ROYAL SCOTTISH ARBORICULTURAL SOCIETY. 



soil deterioration, wliile the larger the openings between the 

 trees the less use is being made of the available light and soil, 

 so that the value of the ultimate crop is less. Violent and 

 spasmodic thinning also means rapid fluctuation of soil moisture 

 conditions, a danger to which trees with their large vascular 

 system may be assumed to be somewhat liable, especially 

 surface-rooting species like spruce. When planting operations 

 are to be undertaken, provided no other cause (such as liability 

 to insect damage) interferes, replanting should be carried out as 

 soon as possible after felling has been completed, especially if 

 the crop has been kept in good canopy to the end of the rotation, 

 since the exposure of the surface of the soil through felling 

 causes intense bacterial and chemical soil activity, the benefits 

 of which decrease rather rapidly and may be entirely lost after a 

 few years. 



In this connection, reference may be made to the work carried 

 out some years ago from the Swedish Forestry Research 

 Institute by Hesselman.^ In one of the two papers summarised 

 in the review, this investigator, inquiring into the factors in- 

 fluencing natural regeneration of coniferous woodlands in 

 Sweden, records the results of an extensive series of soil analyses 

 from the aspect of nitrogenous bacterial activity, and has 

 correlated his results with the quality of natural regeneration 

 found. As far as somewhat casual observations go, his records 

 and conclusions seem quite applicable to conditions in this 

 country, although as regards natural regeneration little evidence 

 is possible, owing to the destructive action of rabbits and game. 



In dense woods of spruce and mixed conifers Hesselman 

 found that no nitrate, only ammonia was formed by bacteria, 

 but when these woods were opened up or felled, widely variant 

 results, depending on the soil itself, were obtained. In the first 

 type of soil, which has an open texture, and is fresh and loamy, 

 a luxuriant growth of herbs at once springs up when the woods 

 are opened out. Natural regeneration is impossible owing to 

 the dense growth of raspberries, dead nettles, and such like. 

 (In this country such an area would be considered rather too 

 valuable for spruce.) Soil of this type ought to be planted at 

 once and with rather vigorous plants as they easily establish 

 themselves, and danger from insects is almost negligible. 



' Summarised in Transactions of the Koyal Scottish Arboricultiiral Society, 

 Vol. xxxiv., Part I, p. 97. 



