170 Sub-formation of the Chalk 



seedlings in various stages of growth are often met with. 

 In places, notably on the borders of Sussex and Hamp- 

 shire, considerable aggregations of yews are found 

 forming small groves, or in some oases yew-woods of 

 large extent (Plate XIX). These yew- woods are nearly 

 pure, the whitebeam (Pyrus Aria) being the only tree 

 at all commonly associated. The ground vegetation is 

 extremely poor, much poorer even than that of the beech- 

 woodsj and the soil beneath the shade of the trees is 

 typically bare. 



The origin of these yew-woods is not clear. They 



occupy situations quite similar to those of 

 wood^ *^® typical beechwoods, i.e. the fairly steep 



valley sides of the chalk downs, and in some 

 cases the bottoms of dry chalk valleys. It is suggested 

 that they may originate in the following way. If a 

 beechwood possessing numerous yews is destroyed by 

 total felling of the dominant trees, or if it degenerates 

 owing to various causes, chalk scrub and chalk grassland 

 in which yews are prominent will take its place. The 

 yews can and do sow their seeds and produce seedlings 

 freely under such conditions, and the young trees, pro- 

 bably owing to their poisonous foliage, are largely, if not 

 wholly, immune from the attacks of rabbits and other 

 animals. As soon as a locally closed community of yews 

 is formed, competitors are almost entirely excluded, owing 

 to the very deep shade cast by the trees. In this way 

 local yew groves might be formed and an extension of the 

 process might lead to the formation of extensive, nearly 

 pure, yew-woods, since the intervening scrub and grass 

 association would be gradually destroyed by the extension 

 of the yew. The process would no doubt be slow, owing to 

 the slow growth of the trees. On the other hand it would 

 be very sure, because the equipment of the yew for this 

 kind of competition is overwhelming. Nothing but the 

 formation of a very dense scrub of other species or 



