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Video: Increase biodiversity to strengthen oak resilience

Oaks are keystone species in a wide range of habitats and are of great importance both for maintaining biodiversity and for producing high-quality wood products. But climate change and its impacts on forest ecosystems, such as the increase of pests, poses a great threat to oaks.

Fortunately, several ecological measures are available to improve oak vitality. Parasitoid insects, for example, are natural antagonists of leave-eating caterpillars and can help control forest pests. In the “Oak Resilience” project, the state agency Wald und Holz NRW investigated parasitoids in selected study areas in North-Rhine Westphalia. The team around project leader Dr. Mathias Niesar and his colleague Dr. Wiebke Theisinger first collected parasitoids in the forest. In a second step, they tested in the laboratory if these parasitoids could be bred and potentially released in targeted areas. According to Dr. Niesar this could work “like a kind of vaccination” to support the natural self-regulation of the forest ecosystem.

Wald un Holz NRW team collecting parasitoids for research in a forest in Geisterholz. Photo by Rosa Castañeda.
Dr. Wiebke Theisinger and the Wald und Holz NRW team collecting parasitoids for research in a forest in Geisterholz. Photo: Rosa Castañeda.

Yet, implementing or even scaling up such interventions on a larger scale proves unrealistic. Instead, the most sustainable way to increase oak resilience to climatic changes lies in helping the natural occurrence of parasitoid insects in the forest.

Parasitoids thrive in biodiversity-rich environments, as they need flowering plants for food and other insects as host organisms for reproduction. “[…] if we aim to establish stable, resilient forests in the long term, it’s crucial to strengthen the ecosystem as a whole”, mentioned Dr. Theisinger. Thus, enhancing biodiversity is the best strategy to improve oak resilience.

Forest managers can implement key ecological measures to foster biodiversity:

  1. A great measure to increase the natural self-regulation of forest ecosystems are flowering forest edges, which provide a rich buffet for parasitoid insects. And the high structural and plant diversity of forest edges creates suitable conditions for plenty of species, including alternative hosts for parasitoids.
  2. Another measure that requires less maintenance are wildflower strips and meadows within the stands. With the right flower mix and a low mowing frequency, such areas are a boost for biodiversity. Wildflowers also offer more options: In an impressive initiative in Münsterland, North-Rhine Westfalia, farmers plant specific wildflowers for biogas production as an alternative to maize. If planted on agricultural fields adjacent to forests, the ecological benefits can radiate into the forest ecosystem.
  3. Beyond forest edges, structural diversity within the forest is a driver of biodiversity. Forest management can increase structural diversity by varying plant species and age classes. In addition, they can promote key elements for biodiversity such as habitat trees, deadwood, and small gaps. Forest structural complexity is generally beneficial and can enhance forest productivity and stability.
  4. Finally, light is an important parameter for parasitoid insects in the forest. It influences the availability of food resources in the form of understory vegetation. However, measures in this respect, like thinning or small forest gaps, can have climatic side effects that need to be considered carefully.

Discover more about the “Oak Resilience” project and explore strategies for enhancing forest biodiversity! Download the infographic and watch the documentary produced by the European Forest Institute!

Related blog post: “Oak Resilience”: investigating ecological measures to combat oak decline.

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