Trees of the Calcareous Ashirood 149 



and birchwoods. The elm is more abundant at tlie 

 lower altitudes and in the damper situations, the haw- 

 thorn in the drier situations and at the higher altitudes. 

 When the ash is removed or dies out naturally, the elm 

 or the hawthorn becomes locally sub-dominant, and 

 societies of elm and hawthorn are as characteristic of 

 ashwoods as societies of birch and alder are of oakwoods. 



Two conifers are native in the ashwoods, namely, 

 the juniper {Juniperus communis) and the yew (Taxus 

 haccata) ; but they are somewhat local in their distribution. 

 In Derbyshire, for example, the yew is rather rare, whilst 

 in north Lancashire it is abundant. 



The aspen (Po'pulus tremula) is the only indigenous 

 species of the genus Populus; but sometimes P. serotina 

 is planted at the edges of the woods. An interesting 

 society of P. tremula occurs in upper Cressbrook Dale. 



Of willows which are certainly indigenous, the crack 

 willow (S. fragilis) and the osier willow {8. viminalis) 

 occur by stream sides, and the sallows (S. caprea and 

 8. cinerea) occur in the woods themselves. 8. aurita 

 appears to be absent from the ashwoods of limestone 

 soils. 



In Derbyshire, oaks appear to be absent from the 

 ashwoods, except locally as introduced trees ; but in other 

 localities Quercus Rohur and Q. sessiliflora may occur. 



The beech (Fagus sylvatica) is frequently planted on 

 all kinds of soil in this country, but is probably not 

 indigenous in the north of England. 



The hazel (Corylus Avellana) is a very abundant and 

 characteristic shrub of the ashwoods, where dense thickets 

 of this plant frequently occur. 



The alder (Aln-us rotundifolia) is much less abundant 

 than in the oakwoods. 



In the ashwoods of Somerset and Derbyshire, birches 

 {Betula spp.) are very rare and local; but on the limestone 

 hills of the northern Pennines, particularly at the higher 



