CHAP, xi.] Effects of Underplanting 241 



re-formation of close canopy, and consequent sinking of the 

 assimilative power of the lower and inner foliage. 



With regard to Prof. R. Hartig's theory, that heavier and 

 better timber is formed when underwood protects the soil, 

 Riinnebaum's experiments confirmed its correctness, at any 

 rate so far as Scots Pine is concerned, but without yielding 

 other final results of a satisfactory nature when criticised from 

 a purely academic point of view. In a general way, it might, 

 however, be deduced that the undergrowth, though in other 

 physical respects of favourable influence, does not (as has been 

 hitherto generally accepted) directly stimulate to enhanced 

 annual increment, owing to the fact that it utilizes a portion 

 of the soluble nutrient salts contained in the soil for its own 

 growth and development. But the quantity of nutriment thus 

 diverted from the standards is, especially on the better classes 

 of soil, not sufficient to justify the objections of the opponents 

 of underplanting. Their argument, that after heavy thinnings 

 or partial clearance a spontaneous growth of grasses and weeds 

 covers the ground, and annually restores to the soil the 

 nutrients previously extracted from it, ignores the researches 

 of Vonhausen, who proved 1 that a soil-covering of grass 

 extracts from four to five times as much mineral food (salts) 

 from the soil as is required by Beech underwood, whilst the 

 humus or mould formed by such herbage is almost entirely 

 consumed by the soil-covering of weeds annually without the 

 standard timber trees being able to reap any benefit therefrom. 

 It must also be remembered that the quantity of nutrients 

 annually extracted from the soil by the underwood is compara- 

 tively so small as hardly necessary to be taken into considera- 

 tion, at any rate on the better classes of soil, so far as the 

 food-supplies of the standard trees are concerned ; whilst the 

 influence that may thus be exerted on the productive capacity 

 of poorer classes of soil must be more than outweighed by the 

 greater increment due to the thinnings or partial clearances in 

 1 Allgemeine Forst- und Jngd-Zdtung, 1872, p. I. 

 R 



