Il] WOODLAND ASSOCIATIONS 71 



R. nigrum, R. rubrum) also occur ; but these, with the possible 

 exception of R. alpinum, are perhaps not indigenous. 



Ericaceous undershrubs are totally absent from the ash 

 woods ; and this appears to apply to all the woods of the ash 

 and beech associations (see page 40) throughout the country. 



One of the most noticeable features of ash woods, both here 

 and elsewhere, is the large number of arboreal and shrubby 

 species which occur in the association. The shrubs are some- 

 times very dense, and almost impenetrable. The following 

 species, which are absent or nearly absent from the oak and 

 birch woods, are characteristic of the ash woods of the Peak 

 District : — 



"Juniperus communis" (rare) Euonymus europaeus 



Taxus baccata (local) Rhamnus catharticiis 



Populus tremula (local) Tilia cordata (rare) 



Ribes alpinum (local) Daphne Mezereum (rare) 



Pyrus Aria (rare) D. Laureola (local) 



Rosa spinosissima (local) Cornus sanguinea 



R. micrantha (rare) Ligustrum vulgare 



Herbaceous Vegetation 



The two most characteristic ground societies of the oak 

 woods, namely the hair-grass society and the soft-grass society 

 (see pages 55 and 56), do not occur at all in the ash woods. The 

 hair-grass society is, it will be remembered, characteristic of 

 those portions of the oak and birch woods whose soils have 

 a high content of acidic humus; and the soft-grass society 

 occurs in the drier parts of the oak woods whose soils have 

 a lower, but still a decidedly appreciable proportion of acidic 

 humus. Such humus does not accumulate in the ash woods. 



The ash woods cannot be separated from the oak woods on 

 the basis of differences in the water-content of the soil of the 

 two plant communities ; for in each case there is a range from 

 very wet to very dry soils. The lime-content in the two cases, 

 however, is always strikingly different ; and there are no soils 

 in the ash woods with a high content of acidic humus such as 

 very frequently characterise the soils of the oak and birch 

 woods. The following divisions of the ground vegetation will 

 illustrate the range in habitat within the ash woods of the 

 district. 



