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Induced Long-Term Resistance of Birch Foliage against Defoliators: Defensive or Incidental?

Erkki Haukioja and Seppo Neuvonen
Ecology
Vol. 66, No. 4 (Aug., 1985), pp. 1303-1308
Published by: Wiley
DOI: 10.2307/1939183
Stable URL: http://www.jstor.org/stable/1939183
Page Count: 6
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Induced Long-Term Resistance of Birch Foliage against Defoliators: Defensive or Incidental?
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Abstract

The long-term increase in foliage resistance of white birch subjected to artificial defoliation, which has been previously documented, may be a defensive response against leaf predators, or it may be passive deterioration in foliage quality due to lost nutrients. We tested these hypotheses by two experiments in which foliage quality was assayed by the growth response of a geometrid caterpillar that is the tree's major herbivore in our area. Fertilization of the soil around defoliated trees did not eliminate the change in foliage quality caused by mechanical damage, contrary to the prediction of the nutrient-stress hypothesis. Another result consistent with the defensive hypothesis was that insect damage was a more effective inducer of changes in birch foliage than mechanical damages was. Artificial defoliation was an effective inducer in a nutrient-poor but not in a nutrient-rich site; this result can be explained by either of the two hypotheses.

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