NATURAL REGENERATION OF PINE AND BIRCH ON THE HEATHER MOORS OF NORTH-EAST YORKSHIRE

Both pine (Pinus sylvestris L.).and birch (Betula pubescensEhrh.) usually invade after a fire, the invasion reaching greatestforce after 3 to 5 years, then falling off rapidly probablywith the return of the heather (Calluna). Pine seedlings onlygrow vigorously if their tap-roots reach the pan, when secondaryroots are developed extensively. In birch the tap-root is notwell developed, but secondary roots spread vigorously sendingdown sinkers to penetrate the pan. Regeneration of birch ishelped by rotten stumps and roots which its mycorrhizal rootsexplore. The root forms are compared and contrasted and thefindings compared with the work of Laitakari and Erteld.