1] 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 catharticus 
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 th 
district. ) 
