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Are ungulates in forests concerns or key species for conservation and biodiversity? Reply to Boulanger et al. ( DOI : 10.1111/gcb.13899)

2017; Wiley; Volume: 24; Issue: 3 Linguagem: Inglês

10.1111/gcb.14029

1365-2486

Camilla Fløjgaard, Hans Henrik Bruun, Morten D. D. Hansen, Jacob Heilmann‐Clausen, Jens‐Christian Svenning, Rasmus Ejrnæs,

Forest Management and Policy

Increasing species richness of light demanding species in forests may not be a conservation concern if we accept a macroecological and evolutionary baseline for biodiversity. Most of the current biodiversity in Europe has evolved in the Pleistocene or earlier, and in ecosystems markedly influenced by dynamic natural processes, including grazing. Many threatened species are associated with high-light forest environments such as forest glades and edges, as these have strongly declined at least partially due to the decline of large herbivores in European forests. Hence, moderate grazing in forests should be an ecological baseline and conservation target rather than a concern. Boulanger et al. (2017) investigated the effect of ungulate grazing on forest understory plant community composition using exclosures in forests, mainly plantations, over a 10-year period. They found increasing richness of herbaceous plant species with grazing, promoting light-demanding species, while shrub richness decreased. Although grazing did not cause changes to forest-specialist species richness, the authors conclude that ungulate grazing—even at relatively low densities—is detrimental to forest specialists, and contributes to a landscape-level biotic homogenization. Thus, they suggest ungulates to be of concern in biodiversity conservation. Boulanger et al. (2017) assess the ecosystem effect using the current managed state of the forest as a baseline, that is, more light-demanding species in the forest is a change of state and therefore also a concern. However, for biodiversity conservation, we would advocate for baselines informed by a macroecological and evolutionary perspective. Most of the current biodiversity in Europe has evolved in the Pleistocene or earlier (Lang, 1994), and in ecosystems markedly influenced by dynamic natural processes, including grazing (Coope, 2004; Kurtén, 1968; Sandom, Ejrnaes, Hansen, & Svenning, 2014; Svenning, 2002). With this baseline for European ecosystems, ungulate grazing must be considered a potential key instrument for biodiversity conservation. Applying this baseline to the study of Boulanger et al. (2017) would not necessarily have changed the analyses and results, but most likely the conclusions and perspectives as regard the plant diversity dynamics in their study. More importantly, an evolutionary informed baseline may change the formulation of study questions and designs in the future. Ungulates and other large herbivores contribute to biodiversity by creating variation in abiotic conditions and diversification of resources, such as dead wood, dung, carcasses, etc. (Figure 1). Investigating biodiversity effects of ungulates, therefore, entails a broader aspect of biodiversity, including specialized fungi and insects, etc., as well as quantifying the abiotic variation (Brunbjerg et al., 2017). The study finds that "ungulates tend to favor ruderal, hemerobic, epizoochorous and non-forest species." However, the properties of plant species hitchhiking on ungulates are extremely dependent on the landscape matrix. Deer are important dispersal vectors for plant species, and if the landscape matrix is mainly farmland, ruderal plants will, of course, be introduced to forest fragments. In contrast, if deer were more or less restricted to natural areas, one should primarily expect dispersal of grassland and wetland herbs into forest glades. In addition, ruderal and hemerobic plant species that today are perceived as negative indicators of conservation status, actually occurred naturally in European landscapes throughout the Pleistocene (see Appendix B in Svenning (2002)), albeit likely at lower densities than in farmland. Applying the evolutionary informed baseline render unjustified the concerns about increased prevalence of light-demanding plant species in forests, as such, unless it is at the large-scale expense of forest specialists. Many threatened species are associated with high-light forest environments such as forest glades and edges, as these have strongly declined at least partially due to the decline of large herbivores in European forests, first the wild species and more recently also free-roaming livestock. Notably, many declining and extinct butterfly species are associated with open woodland habitats (Eskildsen et al., 2015). Thermophilous saproxylic and coprophilic beetles, epiphytic lichens and rare tall herbs confined to the forest–grassland ecocline, are favored by open grazed woodland with ancient trees, as are a suite of bird species (e.g., Bergmeier, Petermann, & Schröder, 2010). Hence, existing evidence points to moderate grazing in forests as an ecological baseline and conservation target rather than a concern. Therefore, results from highly managed forests landscapes focused on taxonomically or functionally narrow aspects of biodiversity, for example, such as the focus on herbaceous plants and shrubs presented by Boulanger et al. (2017) should be considered with caution in relation to nature conservation. This said, field-based evidence on large-herbivore effects on overall biodiversity in contemporary intensively used landscapes are sparse, and further research is much needed. VILLUM FONDEN (VKR-023343 to RE, grant 16549 to JCS) and Carlsbergfondet Semper Ardens (CF16-0005 to JCS). There are no conflicts of interests.