11] WOODLAND ASSOCIATIONS 69 
distinction is sometimes made inaccurately. Further, none of 
these maps attempts to distinguish between natural and semi- 
natural woods on the one hand and obviously artificial planta- 
tions on the other. 
Trees and Shrubs 
The ash (Frazinus excelsior) is dominant throughout the 
length and breadth of the ash woods (see figure 9); and in 
them it is not confined, as it is in the oak woods, to the damper 
situations. It seems clear that, in any given natural station, 
the abundance of the ash is due to one of two causes, either to 
a high water-content or to a high lime-content. Some of the 
local foresters are of opinion that the timber of the ash grown 
on the lhmestone soils is harder and more durable than that 
grown on the wet, non-calcareous soils. 
The two most frequent arboreal associates of the ash are the 
wych elm (Ulmus glabra = U. montana) and the hawthorr 
(Crataegus Oxyacantha), both of which are here more generally 
distributed than in the oak or birch woods. The elm is more 
abundant at the lower altitudes and in the damper situations 
(see figure 10), the hawthorn in the drier situations and at 
the higher altitudes. When the ash, the most valuable timber 
tree of the dales, is removed or dies out in a degenerating 
wood, the elm or the hawthorn, as the case may be, becomes 
locally subdominant ; and societies of elm and hawthorn are as 
characteristic of the ash woods as birch and alder societies are 
of oak woods. On the vegetation maps, these societies are in- 
dicated by the same colour as the ash association of which they 
form a part; but, where practicable, the initial letter or letters 
of the genus of the locally subdominant tree is printed on 
the general woodland colour. An example of a society of wych 
elms occurs in upper Middleton Dale; and hawthorn societies 
are typical of most of the upper parts of drier dales. 
Two conifers are native in the ash woods. One of these, 
the juniper (“Juniperus communis”) is very rare, and ap- 
parently confined to one place: the other, the yew (Taxus 
baccata) is not common; but small specimens occur here and 
there on the ledges of limestone cliffs in the ash woods. It is 
rather curious that these plants should be so uncommon here, 
