Anderson (F.R.S.E. 1952), in A History of Scottish Forestry (1967), pieced together from many varied historical sources a picture of the natural indigenous woodlands of Scotland, which has been confirmed by scientific studies based on pollen counts and botanical analysis (McVean 1964; Durno 1973; Godwin 1975). The species composition of these natural indigenous woodlands was closely associated with geology, soil and elevation. Around the coast and in the lower parts of the river valleys, the moist, fertile mineral soils carried deciduous woodland comprising oak (Quercus robur and Q. petraea), Wych elm (Ulmus glabra), ash (Fraxinus excelsior) and Black alder (Alnus glutinosa). On the drier soils, there was less ash and elm but more birch (Betula pendula and B. pubescens) along with the oak. Above the oak-ash-elm woodlands, on the lower and middle slopes of hills composed of igneous and rich metamorphic rocks, the woodlands included birch, alder, aspen (Populus tremuld), rowan (Sorbus aucuparia), willow (Salix species) and hazel (Corylus avellana). Above this zone were short scrubby stands of birch and willow.