Veteran oaks, biodiversity and ecosystem functioning in southern Norway

Field: Environmental Science (Physical Sciences)

Veteran trees are keystone structures in landscapes, hotspots for biodiversity and have high cultural value. They are also declining globally, and this threatens the species that are dependent on them, and the ecosystem functions they promote. Ecosystem functions are the physicochemical and biological processes that occur within ecosystems that maintain life. A key link between biodiversity and ecosystem functioning is the traits of the species. This diversity of traits is also known as functional diversity, and high levels of functional diversity in a community promote multiple ecosystem processes and make these processes more resilient to change. There is a large amount of evidence to support the conclusion that biodiversity influences ecosystem functioning, but few studies address this related to invertebrate diversity in veteran trees.\n\nMy research has explored the multifaceted predictors of taxonomic and functional diversity of veteran oaks invertebrate communities, and measured the contribution of these communities to ecosystem functioning. In Paper 1, I considered three possible ecosystem functions promoted by veteran oak beetle communities (decomposition, predation and pollination), and explored how the veteran oaks and their landscape contexts influence this diversity (both taxonomic and functional). In the two corresponding papers (Papers 2 and 3), I focused more closely on predation and decomposition (respectively), and examined the differences in these processes and beetle communities involved in them between veteran and young oaks. Lastly, in Paper 4 I used a mesocosm experiment to explore how community complexity influences biotic interactions and decomposition in tree hollows. All my research was conducted around veteran oaks in southern Norway.\n\nIn Paper 1, I found that the features of veteran trees (e.g.: senescence, circumference and regrowth) and the landscape that they were in had different influences on species richness and functional diversity within the different groups of decomposers, predatory and flower visiting beetles. In Paper 2, I found that there were more species of predatory beetles with greater functional diversity around veteran oaks than young oaks, and this corresponded with greater invertebrate predation rates. In Paper 3, I found a similar effect on the wood decomposing beetles, with a greater number of species and higher functional diversity around veteran trees than young trees. However, I found the opposite effect on decomposition of the small diameter wood, with slower rates around the veteran trees. In Paper 4, I found that community complexity increased decomposition rates and wood mold production in tree hollows, and that macrofauna influenced the decomposition pathway and nematode community structure and maturity. \n\nThe findings from my research support the concept that veteran trees are important for biodiversity, and indicate that veteran trees and their communities influence ecosystem functions, such as invertebrate predation and decomposition. They also highlight the importance of community complexity and habitat heterogeneity for promoting biodiversity and ecosystem functioning. Results from my work indicate that there is the potential for synergies between the conservation of veteran trees and sustainable agriculture and forestry. Protecting and valuing veteran trees and their communities, and reintegrating them into land use practices, is an essential step towards a more sustainable system of management, and has the possibility of enhancing the wellbeing of people while promoting biodiversity.