502 JOURNAL OF FORESTRY 



for a time after the departure of their betters. Scrub also in time 

 finally gives place to something else. Grass-land of various classes 

 follows woodland on the true clays ; heathland on the limestones, and 

 moorland on the sands and gravels. 



The author raises the question : "Why should a pure wood of any 

 species terminate except for two reasons, namely, soil exhaustion 

 for the species or change of climate?" He adniits that his reasoning 

 for "woodland succession" from soil exhaustion is inconclusive in 

 that it is difficult to distinguish it from succession due to change in 

 climate. In the opinion of the reviewer the illustrations drawn and 

 the arguments presented by the author are not at all convincing. 



The trend of progressive succession is always toward the mixed 

 forest and away from the pure stand. The climax type is seldom of 

 a single species. Even were it proved that a single species, as illus- 

 trated in the beech or white pine, did in time exhaust the soil for 

 that species (a condition which is as yet far from being proved) its 

 chief importance in succession would be in stimulating a change from 

 a pure to a mixed stand, not a change from one pure stand to another. 

 When a mixture of several species has been attained, soil exhaustion 

 for any one can have no possible effect in causing succession because 

 the several species can continue shifting places and no two genera- 

 tions of the same species are likely to grow in exactly the same 

 places in the stand. J. W. T. 



Quarterly Journal of Forestry, July, October, 1917, pp. 193-99, 253-63. 



That trees suffer when a stand becomes so 



Grass open grasses are able to enter, is a well recog- 



and nized principle in silviculture. Better growth in 



Ash Trees young trees is got when they are grown on land 



that is plowed or otherwise cultivated so that 



grasses and weeds are kept down. "Even old trees suffer through the 



presence of grass on the forest floor. This is clearly shown when a 



middle-aged or mature stand is heavily thinned and the ground 



"grassed over," 



All species are not alike sensitive to the destructive influences of 

 grass. As a rule, conifers^ are less effected than hardwoods, though 

 in the former the various cedars are more sensitive than pines. 



Professor Somerville, the writer of the article under review, calls 



