IMPACT OF HERBIVORY AND COMPETITION ON COMPENSATORY GROWTH IN WOODY-PLANTS - WINTER BROWSING BY MOOSE ON SCOTS PINE

The potential for compensatory growth in plants can depend on growth form and environmental conditions experienced by individual plants. We determined the degree to which a conifer, Scots pine (Pinus sylvestris), compensates for biomass losses. By systematically clipping current annual shoots at four different intensities during three consecutive years we simulated winter browsing by moose (Alces alces). To assess the impact of between-tree competition on compensatory growth, clipping was performed at two different tree densities. In terms of current annual shoot growth, individual pines did not overcompensate in response to clipping in any of the treatments, although a tendency towards overcompensation was observed at low clipping intensities under crowded conditions. Densely-grown pines compensated for lost biomass more frequently than open-grown pines. Regrowth was delayed the year after intense clipping, suggesting that under natural conditions trees are temporarily released from herbivory. The compensatory growth response was not qualitatively different from that observed in sympatric, early successional deciduous Betula spp. It is suggested that compensatory growth may be a plastic trait in slow-growing coniferous woody plants. Although pines under specific conditions tended to show over-compensation, we do not consider it a specific adaptation to herbivory.