New Insights into the Consequences of Post-Windthrow Salvage Logging Revealed by Functional Structure of Saproxylic Beetles Assemblages

Abstract

Windstorms, bark beetle outbreaks and fires are important natural disturbances in coniferous forests worldwide. Wind-thrown trees promote biodiversity and restoration within production forests, but also cause large economic losses due to bark beetle infestation and accelerated fungal decomposition. Such damaged trees are often removed by salvage logging, which leads to decreased biodiversity and thus increasingly evokes discussions between economists and ecologists about appropriate strategies. To reveal the reasons behind species loss after salvage logging, we used a functional approach based on four habitat-related ecological traits and focused on saproxylic beetles. We predicted that salvage logging would decrease functional diversity (measured as effect sizes of mean pairwise distances using null models) as well as mean values of beetle body size, wood diameter niche and canopy cover niche, but would increase decay stage niche. As expected, salvage logging caused a decrease in species richness, but led to an increase in functional diversity by altering the species composition from habitat-filtered assemblages toward random assemblages. Even though salvage logging removes tree trunks, the most negative effects were found for small and heliophilous species and for species specialized on wood of small diameter. Our results suggested that salvage logging disrupts the natural assembly process on windthrown trees and that negative ecological impacts are caused more by microclimate alteration of the dead-wood objects than by loss of resource amount. These insights underline the power of functional approaches to detect ecosystem responses to anthropogenic disturbance and form a basis for management decisions in conservation. To mitigate negative effects on saproxylic beetle diversity after windthrows, we recommend preserving single windthrown trees or at least their tops with exposed branches during salvage logging. Such an extension of the green-tree retention approach to windthrown trees will preserve natural succession and associated communities of disturbed spruce forests.

Effects of natural disturbances and salvage logging on biodiversity – Lessons from the Bohemian Forest

“…From this amount, 50,000 m 3 were concentrated on four larger windthrow areas ($300 m 3 ha À1 ) and were experimentally excluded from the salvage-logging operations in the management zone (Thorn et al, 2014). Since the establishment of the Bavarian Forest National Park and the Šumava National Park, the effects of windstorms and bark beetle outbreaks have been increasingly scientifically studied.…”

“…Salvage logging affects saproxylic species assemblages not only because dead wood is removed, but also because microclimatic properties of remaining dead wood is altered. For example, cut branches that remain on the forest floor become rapidly overgrown by grass, and saproxylic beetle species adapted to dry branches suffer from this alteration (Thorn et al, 2014).…”

“…Hence, they can be retained as important dead-wood legacies and post-disturbance habitats for a number of species (Beudert et al, 2015;Jonasova and Prach, 2008;Müller et al, 2008). In particular, sun-exposed dry branches, a characteristic legacy in storm-felled forests, can be retained by preserving branches of intact spruce crowns or complete dead trees of low economic value (Thorn et al, 2014).…”

Natural regeneration determines wintering bird presence in wind-damaged coniferous forest stands independent of postdisturbance logging

“…These windthrown areas were logged, except for four compact areas consisting of 50 000 m 3 of downed trees of unlogged windthrow (see, e.g., Thorn et al 2014). When postdisturbance logging was completed in spring 2008, six census transects were established through 21 logged, 21 unlogged, and 18 mature forest plots, with plots at least 100 m apart.…”

The forest biodiversity artery: towards forest management for saproxylic conservation

“…The results obtained through the silvicultural management intensity indicator by Schall & Ammer (2013) highlighted that modern continuous-cover systems, such as selective logging, may preserve productivity without an intense environmental alteration. Nevertheless, canopy closure can affect the distribution of heliophilous species, thus the effect of the amount of retained trees on microclimate should be tested (Thorn et al 2014). …”