Specialists in ancient trees are more affected by climate than generalists

Abstract

Ancient trees are considered one of the most important habitats for biodiversity in Europe and North America. They support exceptional numbers of specialized species, including a range of rare and endangered wood-living insects. In this study, we use a dataset of 105 sites spanning a climatic gradient along the oak range of Norway and Sweden to investigate the importance of temperature and precipitation on beetle species richness in ancient, hollow oak trees. We expected that increased summer temperature would positively influence all wood-living beetle species whereas precipitation would be less important with a negligible or negative impact. Surprisingly, only oak-specialist beetles with a northern distribution increased in species richness with temperature. Few specialist beetles and no generalist beetles responded to the rise of 4°C in summer as covered by our climatic gradient. The negative effect of precipitation affected more specialist species than did temperature, whereas the generalists remained unaffected. In summary, we suggest that increased summer temperature is likely to benefit a few specialist beetles within this dead wood community, but a larger number of specialists are likely to decline due to increased precipitation. In addition, generalist species will remain unaffected. To minimize adverse impacts of climate change on this important community, long-term management plans for ancient trees are important.

Keywords: Beetles; climate gradient; coleoptera; precipitation; saproxylic; temperature.

Figure 1

Study sites location with (A) mean temperature during warmest quarter of the year and (B) mean precipitation during warmest quarter of the year in millimeter. Climate data were downloaded from BIOCLIM (variables BIO10 and BIO18) (Hijmans et al. 2005). Axes are longitude and latitude.

Figure 2

Partial regression coefficients (with 95% CI) from six regression models, one for each species group (Generalist and Specialists divided into Northern (N), Southern (S), and Widespread (W) species). In the models, the richness was predicted by summer temperature (A), summer precipitation (B), hollow oak circumference (C), the openness of the immediate surroundings of a tree (D); 1 = partly closed canopy, 2 = closed canopy. 0 = open canopy, used as the baseline in model estimates.