The Origin of our British Flora 



these one would expect the blaeberries and very likely 

 heather and heath. 



The Scotch pine-forests seem to have soon followed 

 on and dispossessed the thickets of birch and alder. 

 This was, of course, an infinitely more advanced type of 

 vegetation, for many common British plants seem to have 

 accompanied the pines. Mr. R. Smith gives Ranunculus 

 acris, Eyebright, Pyrola, Scabiosa succisa, Galium saxa- 

 tile, Holcus lanata, Festuca ovina, and one or two ferns. 



But the climate was still cold and unpleasant with a 

 June temp, of 9° C, July 12°, August 10° C, which is 

 about that of the Orkney and Shetland Islands. 



The time of pine-forests must have lasted at least for 

 thousands of years. 



The last invasion by the oak-forests has not succeeded 

 in occupying the greater part of Scotland and Wales, 

 for the old English oak-forests, Jed and Dalton forests 

 in Scotland, as well as others, seem to be chiefly in the 

 lowlands. The pines covered many of the hills and also 

 much of the lowlands, where the soil happened to be 

 bad and poor. 



The levels to which oak, pine, and birch have 

 been traced are difficult to determine exactly, but some 

 information can be found in the Botanical Survey maps 

 (see p. 224). 



Unfortunately birch occurs in both pine and oak 

 woods. Nor is it easy to be sure of the natural present- 

 day limit of any of these trees. But such a succession 

 as this is quite natural and understandable ; one can 

 see it on mountain sides or in Northern Europe as one 

 travels north from the temperate to the arctic zone. 

 Moreover, it is the more advanced type, such as the oak, 

 which follows on and dispossesses the simpler associa- 

 tion of pine-woods. On good soil, oaks will anywhere 

 choke out pine-trees,' just as pines will eventually over- 



223 



