THE ECOLOGY OF PLANTS. 441 



is moister, so that woods retard evaporation of rain water. 

 The denser the vegetation the greater do these climatic differ- 

 ences becom ; the older the trees, the closer their growth, and 

 the greater the proportion of shade-casting trees (e.g. Beech) 

 in the wood, the moister is the woodland atmosphere and 

 soil. 



Fig. 181. Beech wood with scanty undergrowtn. 

 (From a photograph by W. B, Crump, Esq.,M.A.) 



There is evidence, historical and geological, that at one time 

 Britain was much more extensively covered with trees than 

 at the present day. In prehistoric times the British forests 

 consisted chiefly of Oak and Scots Pine, but there are now 

 very few primitive or " indigenous " Pine woods, this tree 

 having been planted by man in nearly every case. To-day, 

 as in the past, the influence of man and of animals is gradu- 

 ally changing the character of our woodlands. 



Woods are usually distinguished by naming the dominant tree, 

 which largely or entirely makes up the tall vegetation, and to a large 

 extent the character of the trees depends upon the soil. In wet soils 



