Could the vulnerable great Capricorn beetle benefit from the introduction of the non-native red oak?

Abstract

Introduced plants are often identified as the major conservation concern worldwide, however, they also may offer conservation benefits, among others, provide habitat and/or food resources to protected animals. Here we aimed to assess the ability of the great Capricorn beetle Cerambyx cerdo, a highly specialised species associated with mature oaks, to use non-native red oak Quercus rubra as a host plant. To test which factors influenced oak colonisation, we surveyed native and non-native oaks in ‘Nowosolska Dolina Odry’, a site within the ‘Natura 2000’ network (Western Poland). The beetle was detected in 34 native oaks (10.9% of examined trees), demonstrating clear preferences for trees in a more open environment. Comparison of observed numbers of occupied oaks and values expected from their random colonisation showed that C. cerdo avoided non-native red oaks. Logistic regression revealed that variables with the greatest predictive importance for C. cerdo occurrence were canopy extent around the tree and trunk diameter, followed by an autocovariate (distance-weighted number of occupied trees in the neighbourhood of the target tree). Oak species was a poor predictor of tree occupancy, however, it added considerably to the predictive capability of the models when combined with the remaining variables. We argue that physicochemical properties of the wood and/or phloem and structure of the cortex may also influence colonisation of trees. Our results do not provide arguments for the introduction of non-native oaks to benefit C. cerdo. Instead, we recommend maintaining semi-open conditions around host trees and high density of old oaks in the landscape.