Potential interaction between two allogenic ecosystem engineers, beaver and emerald ash borer
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Beaver (Castor canadensis Kuhl), the quintessential ecosystem engineer, cause alteration of forest hydrology through dam construction that creates new habitats, modifies the previous forest state, and regulates resource availability to a wide range of different organisms [1,2,3,4]. Emerald ash borer [EAB] (Agrilus planipennis Fairmaire) is native to eastern Asia and has caused significant mortality of ash since first discovered in North America in 2002 [5,6]. Since all North American ash species are vulnerable to infestation, the removal of the three most common ash species (black, green, and white) from forests is expected to cause drastic changes within ecosystems these species dominate [7,8].
Several riparian tree species are used by beaver as food sources, including green ash, [9,10]. Selection of food trees by beaver is related to the abundance of certain species within the foraging areas [10,11]. In forests with high green ash densities, it would then be appropriate to hypothesize that beavers would preferentially select green ash as a food source. The feeding behavior of beaver produces a girdled tree that resembles a girdled trap tree used in EAB survey and research programs. The goal of a girdled trap tree, with a band of removed bark and phloem, is to induce volatile production by the stressed individual in an effort to attract EAB adults to the tree. Removing these trap trees would theoretically act as a sink for EAB larvae, reducing the population potential within a given forest. Although attractiveness varies on study [12,13], the focus for identifying an effective lure for EAB detection has focused on volatiles produced by stressed ash trees. As a result of beaver-induced stress in green ash, there is a possibility for EAB populations to reach density levels that can cause tree mortality more quickly; increases in stress hosts may increase the EAB population potential, as illustrated in other forest insects due to beaver feeding .
This observation was made during an emerald ash borer trapping experiment. Within an ash dominated forest, a beaver pond was discovered surrounded by girdled green ash trees. Beaver feeding resulted in ash trees with thinning canopies, fading foliage color, and a missing band of bark and phloem that resembled trees girdled for emerald ash borer survey and research.
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Published on Tuesday 28th October, 2008 at 20:56:34.
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Marshall, J. (2008). Potential interaction between two allogenic ecosystem engineers, beaver and emerald ash borer. PHILICA.COM Observation number 50.