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EUROPEAN JOURNAL OF ENTOMOLOGYENTOMOLOGY ISSN (online): 1802-8829 Eur. J. Entomol. 116: 64–74, 2019 http://www.eje.cz doi: 10.14411/eje.2019.007 ORIGINAL ARTICLE When is a tree suitable for a veteran tree specialist? Variability in the habitat requirements of the great capricorn beetle (Cerambyx cerdo) (Coleoptera: Cerambycidae) MICHAL PLATEK 1, 2, PAVEL SEBEK 1, DAVID HAUCK 1 and LUKAS CIZEK 1, 2 1 Biology Centre of the Czech Academy of Sciences, Institute of Entomology, Branisovska 31, CZ-37005 Ceske Budejovice, Czech Republic; e-mails: p [email protected], [email protected], [email protected], [email protected] 2 Faculty of Science, University of South Bohemia, Branisovska 1760, CZ-37005 Ceske Budejovice, Czech Republic Key words. Coleoptera, Cerambycidae, saproxylic beetles, deadwood, conservation management, old trees, veteran trees, habitat requirements, realized niche, site-specifi c patterns, great capricorn beetle, Cerambyx cerdo Abstract. Large veteran trees are key structures sustaining biodiversity in wooded landscapes. Many organisms associated with such trees are, however, also able to inhabit suitable trees with smaller diameters or other surrogate habitats. Understanding the mechanisms behind the importance of veteran trees and the conditions enabling veteran tree specialists to exploit smaller trees might help conservation efforts targeted at the diverse and highly endangered biota associated with veteran trees. To investigate this, we studied local patterns in the exploitation of trees by a veteran tree specialist, the great capricorn beetle (Cerambyx cerdo), at three sites with different soil characteristics, namely fl oodplain, dry-sandy and dry-rocky sites, where this beetle exploits oaks of large (~1.5 m), medium (~0.75 m) and small (~0.25 m) diameters, respectively. We recorded the presence and number of exit holes made by C. cerdo on each tree and related these to the characteristics of the trees: their diameters, openness of the canopy around them and their state of health. The probability of occurrence and the number of exit holes increased with tree diameter, canopy openness, and decreasing tree health, but these relationships differed considerably among the study sites. In dry condi- tions, trees of small diameters were more likely to be exploited by the beetle than in the fl oodplain. The number of exit holes, on the other hand, was a function of tree diameter, with large trees sustaining more beetles and thus acting as larger habitat patches. The species of oak affected the probability of exit hole presence as the sessile oak (Quercus petraea) and pedunculate oak (Q. robur) were preferred over Turkey oak (Q. cerris). The slope orientation also affected the presence of exit holes as trees on slopes with either an eastern or northern orientation were not exploited by the beetle. This study revealed a high level of between-site variability in the tree characteristics relevant to predicting the occurrence of C. cerdo, mainly with respect to diameter. Therefore, while the general patterns of habitat use and the fundamental niche of this beetle are well known, survival and protection of local populations is dependent on site-specifi c characteristics. The realized niche of this beetle must therefore be carefully considered when planning conservation management for a particular site. The results also signify that at some sites, small trees can, at least temporarily, substitute for scarce large trees if the state of their health is managed using proper conservation measures. INTRODUCTION opies (Ranius & Jansson, 2000; Sebek et al., 2016; Horák Large veteran trees provide deadwood and a wide range et al., 2018; Parmain & Bouget, 2018). Open conditions of deadwood-related microhabitats, such as hollows, bare also help trees to attain large dimensions and age slowly, wood and fungal fruiting bodies, which offer feeding op- due to the absence of competition from younger trees (Dro- portunities for highly diverse assemblages of biota (Sii- byshev et al., 2008; Miklín et al., 2018). Large old trees are tonen & Ranius, 2015). Due to this, veteran trees are key especially important for saproxylic (i.e. deadwood depend- structures for sustaining biodiversity in wooded landscapes ent) organisms (Siitonen & Ranius, 2015; Horák, 2017). (Buse et al., 2008; Lindenmayer et al., 2014). Large vet- By slowly ageing, living veteran trees provide deadwood erans occur primarily in open places that have escaped and associated microhabitats for decades, therefore creat- intensive forestry or agricultural practices, such as savan- ing temporal continuity in the availability of deadwood re- nas, wood pastures, avenues, hedgerows, orchards, game sources. This is in contrast with already dead trees, which reserves or parks (Manning et al., 2006; Siitonen & Ranius, can offer such habitats only temporarily before they decay. 2015; Horák, 2017; Miklín et al., 2018). Open woodlands However, there has been a rapid global decline in the support rich communities of animals including many light- abundance of large veteran trees (Irmler et al., 1996; Read, demanding species that cannot be found under closed can- 2000; Andersson & Östlund, 2004; Lindenmayer et al., Final formatted article © Institute of Entomology, Biology Centre, Czech Academy of Sciences, České Budějovice. An Open Access article distributed under the Creative Commons (CC-BY) license (http://creativecommons.org/licenses/by/4.0/). 64 Platek et al., Eur. J. Entomol. 116: 64–74, 2019 doi: 10.14411/eje.2019.007 2012, 2014) and this has led to their associated special- 1992), which specifi es species of special conservation in- ists becoming highly endangered (Ranius, 2002; Siitonen terest. It is considered to be an ecosystem engineer; the & Ranius, 2015). In areas with numerous large old trees damage to trees caused by its larvae creates favourable there is often a lack of young trees (Alexander, 1998; conditions for many other saproxylic insects (Buse et al., Bergmeier et al., 2010; Miklín & Čížek, 2014), leading to 2008). Although closely associated with large trees (Buse a potential gap in availability of old trees in the future, and et al., 2007; Albert et al., 2012), C. cerdo occasionally de- thus to a temporal discontinuity in this precious habitat. velops in small trees (Sláma, 1998). Therefore, it is a good Hence, bridging this gap in the availability of veteran trees model for investigating the variability in habitat require- is currently one of the main problems in the conservation ments of saproxylic insects. Understanding the conditions of biodiversity in temperate regions (Gibbons et al., 2008; that enable this beetle to exploit small trees might help to Miklín et al., 2018). bridge a future gap in availability of veteran trees at cur- In order to propose conservation recommendations for rently inhabited sites, and thus increase the effectiveness overcoming the lack of veteran trees, knowledge of the of conservation measures aimed at this beetle and possibly fundamental demands of veteran tree specialists is needed. also other veteran tree specialists. Trees or deadwood of large diameter are often mentioned To address the above issues, we recorded the parameters as an important resource for many endangered saproxylic of trees locally exploited by three populations of C. cerdo. species (Gossner et al., 2013; Seibold et al., 2015; Eckelt One population inhabits large trees growing on a fl ood- et al., 2018; Kostanjsek et al., 2018), but many insects are plain, another inhabits medium-sized trees growing on at least occasionally able to exploit other habitats, such as dry sandy deposits, and the last population depends solely younger and thinner trees or accumulated plant matter. For upon small trees growing on steep, rocky slopes of a river example, a model saproxylic beetle, the hollow specialist canyon. In order to reveal general and site-specifi c patterns Osmoderma s.l. eremita mainly inhabits large hollow trees, in the exploitation of trees, we tested (i) whether the rela- but occasionally it is recorded in small trees with diam- tionship between the probability of C. cerdo occurrence on eters of around 25 cm (Ranius et al., 2005; Barnouin et al., trees and the characteristics of trees or their surroundings 2017). Deadwood of small diameter (around 20 cm) and (diameter, canopy openness and state of tree health) differs even wood chips may serve as a habitat for larvae of an- among the sites, (ii) whether the relationship between the other model beetle, the stag beetle Lucanus cervus (Harvey number of C. cerdo exit holes on a tree and the tree’s char- et al., 2011). In addition, the great capricorn beetle, Cer- acteristics differs among the sites, and (iii) whether spe- ambyx cerdo, can also complete its development in large cies of oak or slope orientation affect the probability of C. branches or occasionally in trees with a diameter less than cerdo occurrence and the number of its exit holes on trees. 20 cm (Schwenke, 1974; Kimoto et al., 2006). It is still unclear as to what extent such marginal habitats may facili- MATERIAL AND METHODS tate the long-term survival of organisms generally associ- Study sites ated with large veteran trees. Furthermore, there is limited This study was conducted at three sites inhabited by C. cerdo knowledge about the conditions that facilitate the exploi- populations in South Moravia, Czech Republic. Each site is cov- tation of such marginal habitats (Ranius, 2007; Harvey et ered with a different type of woodland because of the abiotic con- al., 2011; Macagno et al., 2015). Moreover, since habitat ditions, such as terrain, humidity and substrate (Fig. 1). requirements may vary with biotic and/or abiotic condi- The sampling included: tions (Freese et al., 2006; Strausz et al., 2012), informa- (i) Floodplain site covered by woodlands growing on mostly humid, nutrient rich soils in the Soutok game reserve (48°43´N, tion on the requirements obtained in one part of a species’ 16°55´E; 150 m a.s.l.; mean annual temperature 9.5°C; mean an- distributional range, or habitat type, may not be relevant nual rainfall ~600 mm).