Shoot damage effects on regeneration of maples (Acer) across an understorey‐gap microenvironmental gradient

Abstract

Summary We measured whole‐plant survival, frequency of leader (mainstem terminal bud) damage among survivors and growth responses of intact and damaged juveniles of three Acer species over 3 years along a microenvironmental gradient represented by the understorey and two sizes of artificially created canopy gaps in central Massachusetts, United States of America. For all species combined, survival decreased while the frequency of leader damage among survivors increased across the gradient of microsite exposure. Acer rubrum L. (red maple) showed the highest survival (65–93%) but also very high leader damage (80–97%). Acer pensylvanicum L. (striped maple) showed fairly high survival (81–93%) in all but the most exposed microsites (24–36%) and had the lowest leader damage overall (17–44%). Acer saccharum Marsh. (sugar maple) was intermediate for both survival (25–86%) and leader damage (55–96%). Growth differed significantly among sites and species. Both intact and damaged plants showed greater growth in gaps than in understorey, particularly in large gaps. For most growth variables in most microsites, A. pensylvanicum ≥ A. rubrum > A. saccharum when plants were intact, but A. rubrum ≥ A. pensylvanicum > A. saccharum when damaged. Species differences in growth varied among sites, with large gaps producing more pronounced effects than small gaps and understorey for both intact and damaged plants. Growth recovery was inversely related to leader damage frequency among species, and thus at least partially offset the effects of damage on net growth across the populations. The microsite‐ and species‐specific responses to leader damage may influence gap regeneration and forest composition. A. pensylvanicum may be favoured by its regrowth advantage over A. rubrum and A. saccharum in the understorey, where damage is likely to occur during prolonged pre‐gap periods. In contrast, A. rubrum shows a decisive advantage over its congeners in regrowth in the centres of large gaps, where the probability of a juvenile tree capturing canopy gap space is highest.