beetles in climate change | Mirage News
How do canopy insects react to the abrupt disappearance of their host tree? A study in floodplain forests along the Elbe shows surprising results.
As a result of the droughts of recent years, pronounced tree mortality has been observed in Germany, which has left clearly visible gaps in forests and parks. All climate projections indicate that such events will occur more frequently in the future.
It also affects insects and other animals in the canopy, which harbor much of the biodiversity and perform many functions without which no forest can exist.
In response to tree mortality, forest scientists plan to convert commercial forests to hardier mixed forests, which includes planting drought-tolerant tree species from other countries.
But this strategy carries risks and is controversial: if plants or animals are introduced into regions where they are not native, it can disrupt ecosystems, their biodiversity and their functioning. “The nature and extent of these disruptions cannot be predicted based on current knowledge.” This is reported by scientists Andreas Floren and Tobias Müller from the Departments of Ecology and Bioinformatics of the Julius-Maximilians-Universität Würzburg (JMU) in the scientific journal Sustainability together with Peter Horchler from the Federal Office of Hydrology in Koblenz .
Exotic trees as rescue species
The researchers show that non-native trees may also provide opportunities in times of climate change by becoming rescue species for insects when their host trees die locally.
Evidence of this has been found in the floodplain forests of the Midlde Elbe Biosphere Reserve in Germany, where Red Ash (Fraxinus pennsylvanica) is found in close proximity to European Ash (Fraxinus excelsior). F. pennslyvanica was planted there in the early 20and century due to their high flood tolerance.
“In 2016 and 2017, we analyzed beetle biodiversity in the crowns of both tree species,” explains Andreas Floren from the JMU Systems Ecology working group, which combines animal ecology and bioinformatics. The results showed that the highest beetle diversity was found on European ash trees, clearly differing from the beetle communities of red ash trees.
Almost complete dieback of the European ash following the drought
According to Floren, ash dieback caused by water stress and fungal infections was not evident in 2016/2017. But in 2020, when the team repeated the analyses, the situation was completely different: by that time, more than 80% of the native ash trees had died – which is close to a “coup de grace” of this species. of tree. The heat and drought of the past years had taken their toll. North American ash trees, on the other hand, were little affected.
The beetle fauna in the trees had changed drastically by 2020. “This indicates a functional restructuring of the ecosystem,” says Floren. Many species had switched to red ash and several endangered and Saxony-Anhalt Red List beetle species had increased in number and become secondary pests of F. excelsior. These beetles burrow into the bark of native ash trees and destroy their bast layer.
Surprisingly, herbivorous beetles were absent from all trees. On the other hand, more wood-eating and xylophagous beetles were collected. Predatory beetles and those that feed on fungi are now being harvested in greater numbers from Red Ash trees.
Data were obtained by fogging individual trees with a highly specific insecticide; beetles and other insects fall into collection sheets installed under the tree and are collected for identification. Natural pyrethrum has been used as an insecticide which is destroyed in sunlight within hours without residue, so the disturbance to the ecosystem remains low.
Red ash trees are the second best habitat
“Overall, our data suggest that F. pennsylvanica could become a rescue species for native fauna if European ash were to become extinct, as red ash provides the second best habitat,” says Floren. “That neophytes become important for the preservation of native fauna is highly unusual and is only possible because the two ash species are closely related.”
In biology, neophytes are plants that have been introduced to non-native sites by human activities. Further research is now needed on the diversity and function of tree canopy fauna, including neophytes, to prepare for the possible consequences of climate change, as what has happened in floodplain forests could get to other forests.