Willow (Salix spp.) and aspen (Populus tremula) regrowth after felling by the Eurasian beaver (Castor fiber): implications for riparian woodland conservation in Scotland

Abstract

ABSTRACT1. A proposed trial reintroduction of the Eurasian beaver (Castor fiber L.) to Scotland has recently been approved (May 2008). A previous proposal was turned down by the licensing authority, partly over the perceived risks to woodland within a Special Area of Conservation.2. This paper presents data on two years of willow (Salix spp.) and aspen (Populus tremula L.) regrowth following tree felling by captive beavers within two large semi-natural enclosures in eastern Scotland. Both willow and aspen are highly preferred by beavers.3. Regrowth of willow stems was quantified from cut stumps, felled logs and partially severed ('incompletely felled') trees, and compared with growth of stems in the canopies of untouched willows.4. Maximum annual regrowth was observed in incompletely felled trees, followed by cut stumps and then unfelled control trees. Mean regrowth rates were ca 18 m regrowth per metre of measured tree section per year in incompletely felled trees. This was approximately 12 times more annual regrowth than that observed in unfelled trees, despite apparently selective browsing of the regrowth of incompletely felled trees by roe deer.5. Although incompletely felled willows represent a relatively small component of felling activity (9% of all felled willow), they contribute disproportionately to the biomass of beaver-engineered riparian woodlands, creating a more multi-layered habitat structure.6. Willow regrowth in inundated areas was avoided by deer, and harvesting of regrowth by beavers was rare. 7. Significant regrowth from 11 stumps of aspen in 2 years post-felling occurred by suckering, with 85 suckers of mean height 2.1 m being recorded, all of which were subsequently avoided by browsing deer and beavers.8. These data suggest that rapid regeneration of willow and aspen will occur in riparian woodlands in the event of major felling activity by Eurasian beaver, even in the presence of low to moderate levels of roe deer browsing, and that the conservation status of both these trees or the wider habitats that they form would not be threatened by a well planned and managed reintroduction of beavers to Scotland.

Reproductive ecology of the Sitka willow (Salix sitchensis ).

“…More beavers are expected to result in more beaver browse of willows which in turn would result in a greater impact on the asexual reproduction of willows. Jones et al (2008) observed that 35% -40% of beaver-felled willows in Scotland showed regrowth. The proportion of stems showing regrowth was variable by habitat (stream and lake) and year (Jones et al 2008).…”

“…Jones et al (2008) observed that 35% -40% of beaver-felled willows in Scotland showed regrowth. The proportion of stems showing regrowth was variable by habitat (stream and lake) and year (Jones et al 2008). In central British Columbia 0% to 51% of beaver felled S. sitchensis showed levels of regrowth.…”

“…Animal browse can induce compensatory growth, alter nutrient and secondary compound concentrations, as well as increase basal area, stem diameter and stem production (Kindschy 1985;Donkor and Fryxell 1999;Veraart et al 2006;Jones et al 2008). All of these animal/plant interactions can alter the proportions of plant sexual and asexual reproduction.…”

“…The association between willows and beavers is more than spatial proximity; beaver browse has been observed to alter the nutrient and secondary compound concentrations in willows (Veraart et al 2006). Stem basal area and diameter; stem and plant abundance; sapling recruitment; stem regrowth; and plant growth rates have also been observed to increase with beaver foraging (Kindschy 1985;Donkor and Fryxell 1999;Jones et al 2008). Conversely, willows have also been found to influence beaver reproduction.…”

“…Jones et al (2008) observed that 35% -40% of beaver felled trees in Scotland showed various levels of regrowth. However, other studies that while not designed to examine beaver impacts, have suggested that beaver activity had a minor impact on the reproduction of Salicaceae species (Barsoum 2002, 25 Cooper et al 2005.…”