Effects of simulated winter browsing on mountain birch foliar chemistry and on the performance of insect herbivores

Authors

  • M. Riipi,

  • K. Lempa,

  • E. Haukioja,

  • V. Ossipov,

  • K. Pihlaja


M. Riipi, K. Lempa and E. Haukioja, Dept of Biology and Kevo Subarctic Research Station, Univ. of Turku, FIN-20014 Turku, Finland (mariipi@utu.fi).–V. Ossipov and K. Pihlaja, Dept of Chemistry, Univ. of Turku, FIN-20014 Turku, Finland.

Abstract

Winter browsing by mammalian herbivores is known to induce a variety of morphological and physiological changes in plants. Browsing has been suggested to decrease the carbohydrate reserves in woody plants, which might lead to reduced tannin production in leaves during the following summer, and consequently, to increased herbivore damage on leaves. We conducted a clipping experiment with mature mountain birch trees and measured the effects of clipping on birch growth, leaf chemistry and toughness, as well as on the performance of insect herbivores. Leaves grew larger and heavier per unit area in the clipped ramets and had a higher content of proteins than leaves in the control trees. Clipping treatment did not affect the total content of sugars in the leaves (mg g−1), suggesting that a moderate level of clipping did not significantly reduce the carbohydrate pools of fully-grown mountain birch trees. Furthermore, the contents of proanthocyanidins (condensed tannins) and gallotannins were slightly higher in the leaves of clipped ramets, contrary to the hypothesis of reduced tannin production. The effects of clipping treatment on leaf and shoot growth and on foliar chemistry were mainly restricted to the clipped ramets, without spreading to untreated ramets within the same tree individual. The effects of clipping on leaf characters varied during the growing season; for instance, leaf toughness in clipped ramets was higher than toughness in control trees and ramets only when leaves were mature. Accordingly, clipping had inconsistent effects on insect herbivores feeding at different times of the growing season. The generally small impact of clipping on herbivore performance suggests that the low intensity of natural browsing at the study area, simulated by our clipping treatment, does not have strong consequences for the population dynamics of insect herbivores on mountain birch via enhanced population growth caused by browsing-induced changes in food quality.

Ancillary