Gap dynamics in a hemlock–hardwood forest

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Abstract
The dynamics of small openings in a hemlock-hardwood stand at the Harvard Forest, Petersham, Massachusetts, USA, were studied. Rates of lateral growth of canopy tree species into openings ranged from 6-14 cm/yr with a maximum of 26. Red oak (Quercus rubra L.) (RO) had the highest rate of lateral expansion. In small openings (r < 0.25 .times. tree height), regenerating species ranked by rate of height growth were as follows: black birch (Betula lenta L.) (BB) > red maple (Acer rubrum L.) (RM) > yellow birch (B. alleghaniensis Britton) (YB) > hemlock (Tsuga canadensis (L.) Carr.) (HK) = RO; in moderate size openings (r = 0.25 to 0.5 .times. tree height), the ranking was birches = RM > RO > HK; in open grown even-aged stands, the ranking was RO > BB = RM = YB > paper birch (B. papyrifera Marsh.) .mchgt. HK. A comparison of rates of height growth with opening closure rates indicates that tree reproduction is not successful in openings of less than about 0.5 .times. tree height in diameter. This is primarily because small openings close quickly by lateral growth of the surrounding canopy trees and is not simply a factor of changes in rates of height growth with opening size.