Data from: Foraging decisions with conservation consequences: Interaction between beavers and invasive tree species

Herbivore species can either hinder or accelerate the invasion of woody
species through selective utilization. Therefore, an exploration of
foraging decisions can contribute to the understanding and forecasting of
woody plant invasions. Despite the large distribution range and rapidly
growing abundance of beaver species across the Northern Hemisphere, only a
few studies focus on the interaction between the beaver and invasive woody
plants. We collected data on the woody plant supply and utilization at 20
study sites in Hungary, at two fixed distances from the water. The
following parameters were registered: taxon, trunk diameter, type of
utilization, and carving depth. Altogether 5401 units (trunks and thick
branches) were identified individually. We developed a statistical
protocol that uses a dual approach, combining whole-database and
transect-level analyses to examine foraging strategy. Taxon, diameter, and
distance from water all had a significant effect on foraging decisions.
The order of preference for the four most abundant taxa was: Populus spp.
(softwood), Salix spp. (softwood), Fraxinus pennsylvanica (invasive
hardwood), Acer negundo (invasive hardwood). The diameter influenced the
type of utilization, as units with greater diameter were rather carved or
debarked than felled. According to the central-place foraging strategy,
intensity of the foraging decreased with the distance from the water,
while both the taxon and diameter selectivity increased. This suggests
stronger modification of the woody vegetation directly along the
waterbank, together with a weaker impact further from the water. In
contrast to invasive trees, for which utilization occurred almost
exclusively in the smallest diameter class, even the largest softwood
trees were utilized by means of carving and debarking. This may lead to
the gradual loss of softwoods or the transformation of them into shrubby
form. After the return of the beaver, mature stages of softwood stands and
thus the structural heterogeneity of floodplain woody vegetation could be
supported by the maintenance of sufficiently large active floodplains. The
beaver accelerates the shift of the canopy layer’s species composition
towards invasive hardwood species, supporting the enemy release
hypothesis. However, the long-term impact will also depend on how plants
respond to different types of utilization and on their ability to
regenerate, which are still unexplored issues in this environment. Our
results should be integrated with knowledge about factors influencing the
competitiveness of the studied native and invasive woody species to
support floodplain conservation and reconstruction.