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Conference abstract, 2006

Harvesting disrupts biological control of herbivores in a short-rotation coppice system: a plausible mechanism

Björkman, Christer


Disturbances, such as harvesting, often interfere with the ecological processes that lead to stability. One example is biological control of pests in agricultural systems. Instability as a consequence of frequent disturbance is particularly evident in many annual crops. However, it is difficult to study the role of different ecological processes affecting density and stability in systems that are disturbed as frequently. The ideal is a system which is disturbed with an intermediate time interval. Willows, grown as short rotation coppice for biomass production, may provide such a system because harvesting takes place every 3rd to 5th year. Short rotation coppice systems, thus, provide an opportunity to conduct replicated, large-scale field experiments, addressing questions concerning stability and control. In the willow system, population growth rate of the main pests, three species of leaf beetles, are negatively correlated with the density of predatory mirid bugs, especially Orthotylus marginalis. After harvesting, that takes place during winter, leaf beetles recover better than mirids and peak in density three years later. The density of mirids continues to increase during the whole period. One possible reason for this pattern is that leaf beetles, unlike the predators, mainly overwinter outside the plantation. Here we show that the mechanism behind this disruption of biological control most probably is that a vast majority of the mirids are removed from the plantations at harvesting. The reason is that the mirids overwinter as eggs inserted into the willow tissue. We describe in detail the placement of the mirid eggs in the willows. In addition, we show how the abundance of mirid eggs varies with time after harvesting. We also present data on the abundance of mirid eggs in natural willow stands, which have grown undisturbed for more than 10 years. We discuss strategies to conserve the natural enemies in this system

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Authors' information

Swedish University of Agricultural Sciences, Department of Ecology

UKÄ Subject classification

Agricultural Science
Environmental Sciences related to Agriculture and Land-use
Renewable Bioenergy Research

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