Large solitary oaks as keystone structures for saproxylic beetles in European agricultural landscapes

Abstract

Abstract. 1. Trees outside forests (TOFs) are declining in agricultural landscapes worldwide. Although they provide valuable habitats for saproxylic species, their relative contribution to saproxylic biodiversity with respect to forests is poorly known. Our aim was to investigate the conservation value of oak TOFs for saproxylic beetles in European agricultural landscapes.2. In our design, plots pairing forest trees and TOFs were sampled in sites nested in two French regions. We studied local habitat conditions (deadwood, tree-related microhabitats, openness) and saproxylic beetle assemblages. We measured significant environmental contrasts between forest trees and TOFs, and found that the latter hosted higher microhabitat density and diversity.3. Species assemblages were strongly dissimilar between TOFs and forest trees. Even though a-diversity and abundance were not significantly different in the two contexts, the between-tree b-diversity and the c-diversity of both all and rare species were higher outside than inside forests.4. Furthermore, the potential key drivers of saproxylic beetle diversity were not consistent between forest trees and TOFs. Tree cavity was the only elementary microhabitat whose density significantly affected biodiversity metrics both inside and outside forests. Many more effects on beetle assemblages originating from surrounding conditions were observed in TOFs than in forest trees. We also confirmed that saproxylic beetle diversity is significantly associated to canopy openness.5. Consistent with our results, environmentally friendly forestry practices should include the retention of sun-exposed microhabitat-bearing trees at final harvesting. In addition, environmental policies should favour TOFs as well as oak savanna-like woodlands which are seriously threatened worldwide.

Hollow oaks and beetle functional diversity: Significance of surroundings extends beyond taxonomy

“…Veteran trees are keystone structures in forest, agricultural landscapes, and urban areas (Lindenmayer, Laurance, & Franklin, ; Müller, Jarzabek‐Müller, Bussler, & Gossner, ; Parmain & Bouget, ). The size and age of veteran trees, as well as their coarse bark, structurally complex canopies, and sheltered nutrient‐rich cavities provide features that support high biodiversity (Lindenmayer et al, ; Parmain & Bouget, ). However, veteran trees are in decline globally as a result of intensification of land use and the abandonment of traditional management (Siitonen & Ranius, ).…”

Past levels of canopy closure affect the occurrence of veteran trees and flagship saproxylic beetles

“…Many saproxylic beetles including the three studied species though require open canopy conditions or depend on shade‐intolerant trees (Albert et al., ; Dubois & Vignon, ; Dubois et al., ; Ranius, ). Even if some veterans occur in shady forests, they are thus unlikely to harbour numerous species associated with veteran trees from more open conditions (Parmain & Bouget, ).…”

“…Open-grown, large and hollow trees are keystone ecological structures sustaining woodland biodiversity (Lindenmayer et al, 2012(Lindenmayer et al, , 2014Manning, Fischer, & Lindenmayer, 2006;Müller, Jarzabek-Müller, Bussler, & Gossner, 2014;Siitonen & Ranius, 2015). Recently, more studies have revealed that trees in open conditions are especially important for saproxylic beetles as they host diverse communities with more red-listed species than trees in closed-canopy conditions (Horak et al, 2014;Parmain & Bouget, 2017;Sebek et al, 2016). Although even veterans in closed-canopy conditions may harbour rich saproxylic communities (Parmain & Bouget, 2017), these communities are usually characterized by diverse species composition containing rather generalist species and fewer red-listed individuals (Sebek et al, 2016).…”

When is a tree suitable for a veteran tree specialist? Variability in the habitat requirements of the great capricorn beetle (Cerambyx cerdo) (Coleoptera: Cerambycidae)

“…Although most of the saproxylic species associated with large, veteran trees are also at least occasionally able to utilize small trees (Sláma, 1998;Harvey et al, 2011;Chiari et al, 2013), it is the large trees that are likely to host the bulk of their populations and increase the probability of their survival. This is probably one of the main reasons for the great importance of large trees for C. cerdo (Buse et al, 2007;Albert et al, 2012) and probably also saproxylic biodiversity as a whole (Eckelt et al, 2018;Parmain & Bouget, 2018).…”