Coppice-with-standards with an overmature coppice component enhance saproxylic beetle biodiversity: A case study in French deciduous forests
Highlights
► We studied the effects of overmature coppice on saproxylic beetle diversity. ► Overmature coppice stands have a higher saproxylic beetle richness. ► Few red-listed beetle species, but tends to increase in the overmature coppice. ► Results in line with the observe shift in deadwood profile. ► Conserving overmature coppice can be a useful tool in biodiversity restoration management.
Introduction
Coppicing is a management technique in which the coppice is harvested in short rotations (10–25 years) to mainly produce firewood or charcoal. Trees are cut to the ground purposefully to stimulate resprouting from stumps and roots (Spitzer et al., 2008). Coppice-with-standards (CWS) is a silvicultural system where some trees among the coppice, called “standards”, are left to grow to a larger timber size. This traditional two-story woodland management system was developed over the past thousand years in Western and Northern Europe to sustain both permanent forest cover and a continuous flow of a wide range of forest products (construction timber, fencing and furniture parts, fruits and wild game). More recently, mainly during the 19th century, CWS have progressively been converted to high forests, e.g., by selecting the most vigorous coppice shoots in order to achieve a structure akin to generative high forest. Yet, even today, traditionally-managed CWS still represent a large part of the forested surface area in France (about 30%, (National Forest Inventory (NFI)). However, some of these stands have been abandoned and the coppice component unmanaged for decades, especially in private forests. This is due to several reasons: fragmented ownership and the cost of felling operations, the decrease in firewood demand due to the development of fossil fuels, and declining timber prices (Coppini and Hermanin, 2007). In these abandoned forests, also called “overmature CWS stands”, the ordinary rotation age of the coppice component has been exceeded and changes in stand structure and biodiversity have potentially occurred.
Recent changes in forest management perspectives and a heavier emphasis on increasing profitable harvesting tend to favor the development of multifunctional forests and the structural diversification of stands (Wohlgemuth et al., 2002). Indeed, current energy use projections for Europe, and more specifically for France, predict that woody biomass will be an important source of renewable energy in the forthcoming decades. Depending on the location, the forestry and the dominant tree species, changes in forestry practices to provide fuelwood will imply (i) an extension of traditional fuelwood collection, (ii) the development of specialized forestry practices (whole-tree extraction, harvesting logging residues and stumps) and (iii) mono-specific plantations or short-rotation coppices of fast-growing species (Bouget et al., submitted for publication). A resurgence in the interest for coppices and CWS may bring about the felling of previously unmanaged woodlots and a broad-scale increase in cutting.
Though the effects of coppicing on biodiversity have been explored in previous studies (Key, 1990, Fuller and Warren, 1993, Van Calster et al., 2008), the influence of overmature CWS stands in particular has not yet been investigated. The ecological value of overmature CWS is not known.
Longer coppicing rotations cause changes in the forest structure over the years as a result of forest growth. Globally, habitat conditions such as spatial structure, structural density, vegetation complexity, shade and humidity and deadwood profiles change as the CWS stands age from mature to overmature and these changes subsequently impact forest biodiversity. Young managed CWS are expected to have a high number of small stems and low amounts of dead wood, particularly of large-diameter logs or snags (Kirby et al., 1991). Deadwood-associated species may respond to changes in micro-climate and deadwood substrate availability along the maturity gradient of CWS. Saproxylic beetle assemblages, for instance, are known to be driven by deadwood volume (Müller et al., 2007, Lassauce et al., 2011) and by deadwood type quality, e.g., in terms of dimension (Brin et al., 2011).
Consequently, our study compared CWS with mature and overmature coppices in terms of stand features and saproxylic beetle diversity. We endeavored to answer the following questions: Does overageing in CWS induce significant changes in stand structure, especially as regards the deadwood profile? Do these potential changes impact saproxylic biodiversity? Are saproxylic assemblages more original or richer in overmature than in mature CWS? We also discuss the possible loss of biodiversity associated with coppice harvesting operations, and the potential benefits of preserving some of these overmature CWS as set-aside areas.
Section snippets
Study area, sample plots and stand characteristics
The study was conducted in northern France, i.e., in the central part of the European temperate forest zone. Twenty-nine study plots (1 plot = 1 stand) were established in 2009 in 12 forests in five regions (Fig. 1). The selected stands (higher than 3–5 ha in area) were oak–hornbeam forests (Quercus petrea (Matt.), Quercus robur (L.); Carpinus betulus (L.)), accompanied by beech (Fagus sylvatica (L.)), birch (Betula pendula (L.)) and aspen (Populus tremulus (L.)). Oak (Q. petrea (Matt.) or/and Q.
Results
A total of 24,305 specimens corresponding to 247 species was recorded. This includes 1695 red-listed individuals belonging to 30 red-listed species. The most abundant species were: Xyleborus dispar (Scolytidae) (25% of the catches), Xyleborinus saxesenii (Scolytidae) (18%) and Isorhipis marmotanni (Eucnemidae) (6%).
Structural changes in CWS with an overmature coppice component
Our study shows how the CWS structure evolves from mature (i.e., “harvestable”) to overmature stands. Indeed, as already found in previous studies focusing on coppices (Kirby et al., 1998, Coppini and Hermanin, 2007), the 60-year-old coppices were characterized by higher volumes of small and total lying deadwood as well as standing deadwood compared to the younger 20-year-old coppices. This increase is related to the self-thinning process, which decreases the number of living sprouts per stump.
Acknowledgements
We thank Carl Moliard for his technical assistance, and Yoan Paillet for his advice. We are also grateful to Benoit Nusillard, Thierry Noblecourt, Olivier Rose and Jacques Chassain for their help with species identification and lab work, and Victoria Moore for checking the English language. Two anonymous reviewers significantly helped to improve the manuscript. This work was funded by the French Environment and Energy Management Agency and the Cemagref. Considerable assistance was provided by
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