Vertical gradients of habitats are a typical characteristic of forest
ecosystems. Sun-exposed dead wood in the upper canopy, for instance,
provides a habitat for saproxylic beetles distinct from that in the more
shaded dead wood below the canopy. Canopy research, however, is
challenging due to both the limited accessibility and potential
confounding effects of temperature on trapping probability when activity
traps are used. We studied saproxylic beetle assemblages along a
complete vertical gradient without bias caused by temperature effects on
activity. Using crane-like constructions attached to the top of large
Silver Fir trees (Abies alba), we exposed bundles of freshly cut
branches of European Beech (Fagus sylvatica), Silver Fir and Norway
Spruce (Picea abies) in three different vertical strata (upper canopy,
mid-canopy and near the ground). The bundles in the upper canopy were
fully exposed to the sun and the bundles in the mid-canopy and near the
ground were in the shade. We allowed beetles to colonize the bundles of
branches for one growing period and then reared beetles from each bundle
over three years. The species composition of saproxylic beetle
assemblages differed between bundles in the upper canopy and near the
ground; bundles in the mid-canopy had an intermediate assemblage
composition. The abundance of saproxylic beetles was higher near the
ground than in the upper canopy, whereas the number of species showed
the opposite pattern. Overlapping confidence intervals of sample-based
rarefaction and extrapolation curves for species diversity indicate that
estimated gamma diversity per stratum is similar across the three
strata. Our results support earlier studies that revealed the importance
of habitat heterogeneity as a driver of the biodiversity of taxa
associated with dead wood. As we controlled for wood diameter and tree
species diversity, our study suggests that the microclimatic variability
within dead wood and thus habitat heterogeneity for saproxylic beetles
is higher in the upper canopy than near the ground. For biodiversity
conservation in forests, our results support a strategy of enhancing the
number of trees with microhabitats, particularly those with dead
branches in the upper tree crown. Dead branches and standing dead trees
should only be removed, e.g. for safety reasons, if no other option is
available.
«
Vertical gradients of habitats are a typical characteristic of forest
ecosystems. Sun-exposed dead wood in the upper canopy, for instance,
provides a habitat for saproxylic beetles distinct from that in the more
shaded dead wood below the canopy. Canopy research, however, is
challenging due to both the limited accessibility and potential
confounding effects of temperature on trapping probability when activity
traps are used. We studied saproxylic beetle assemblages along a
complete vertical grad...
»