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.
My 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.
In 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.
The 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.Gamle trær er nøkkelstrukturer i landskapet, de er viktige for biologisk mangfold og de har høy kulturell verdi. De minker globalt, og dette truer artene som er avhengige av dem samt de økosystemfunksjonene disse trærne fremmer. Økosystemfunksjoner er de fysisk-kjemiske og biologiske prosessene som forekommer i økosystemer og som støtter opp om liv. Artenes egenskaper utgjør en sentral kobling mellom biologisk mangfold og økosystemfunksjoner. Dette mangfoldet av egenskaper er også kjent som funksjonelt mangfold, og høye nivåer av funksjonelt mangfold i et samfunn fremmer flere økosystemprosesser og gjør disse prosessene mer motstandsdyktige mot endring. Mye forskning peker
på at biologisk mangfold påvirker økosystemfunksjon, men få studier tar for seg dette i sammenheng med mangfold av insekter i gamle trær. Forskningen min har utforsket de flersidige driverne for taksonomisk og funksjonelt mangfold i insektmiljøer som forekommer i gamle eiketrær, og målt bidragene fra disse til økosystemfunksjoner.
Resultatene fra forskningen min støtter oppfatningen om at gamle trær er viktige for biologisk mangfold, og peker på at gamle trær og samfunnene deres bidrar til viktige økosystemfunksjoner, eksempelvis predasjon av insekter og nedbrytning av organisk materiale. Resultatene fremhever også viktigheten av samfunnskompleksitet og habitatsmangfold for å fremme biologisk mangfold og viktige økosystemfunksjoner. Forskningen min viser dessuten at det finnes mulige synergier mellom bevaring av gamle trær og bærekraftig jordbruk. Å beskytte og verdsette gamle trær og lokalsamfunnene deres, samt integrere disse på nytt i landbrukspraksis, er et viktig skritt mot et mer bærekraftig forvaltningssystem som har mulighet for å forbedre folks velvære samtidig som det fremmer biologisk mangfold
