Sentence:  Geltsdale Forsest is an extensive tract of mountain, forming the south-east portion of Castle Carrock parish, and is a royal forest leased by the Earl of Carlisle. Part of it abounds in birch and <WSD>alderwoods</WSD>, and gives rise to the river Gelt, which flows northwards. 
Meaning of the word marked with <WSD> tags:  A wood largely populated with alder trees.