Long-term patterns of leaf, shoot and wood production after insect herbivory in the Mountain Birch

1. The pattern of responses of adult trees of Mountain Birch (Betula pubescens ssp. czerepanovii) to an outbreak of a folivorous insect (Epirrita autumnata) causing approximate to90% defoliation was studied over 8 years in a subarctic area in northern Sweden. 2. Tree recovery was monitored in terms of the numbers, area, mass and nitrogen content of leaves, the numbers of leaf-carrying long and short shoots, and the widths of annual tree rings in stems. 3. The most prominent characteristic of defoliated trees was a threefold increase in the proportion of long shoots 1 year after defoliation. These shoots subsequently produced many new leaf-carrying short shoots, resulting in shoot populations approximate to50% larger than those of control trees. Thereafter the most strongly defoliated trees showed decreasing leaf area. 4. Defoliated trees produced more female catkins but fewer male catkins than control trees. 5. Released apical dominance did not result in any overcompensation in terms of growth or leaf area production. However, it presumably increased the rate of recovery from herbivory. For the most strongly defoliated trees, the benefits from increased production of long shoots was not sustainable.