After years of toil I finally handed my PhD thesis in. Some people hate their thesis – but not me… I actually quite enjoyed the process. Would have been better without the pressure in the last 6 months though and the long weekends sitting at my desk! I’m very pleased to let it go – and oddly looking forward to hearing what the examiners have to say.
As few people will read it otherwise, my PhD abstract is below (if anyone is interested!):
How mature forest impacts adjacent disturbed forest, or “forest inﬂuence”, is a poorly understood ecological concept that is important for sustainable forest management worldwide. Specifically, this thesis investigated whether beetles can recolonise disturbed areas from adjacent mature forests, and how this changed with forest succession. Furthermore, I applied a combined functional trait and phylogenetic approach to better understand what processes were important for succession and recolonisation. This involved a review and three studies based on two large-scale experiments.
Functional trait approaches for beetles lack consistent methodology and conceptual basis. Chapter 2 reviews previous beetle functional trait studies and outlines a broadly applicable trait framework, including a potentially useful list of traits, analysis approaches and future challenges for this discipline. This manuscript is accepted for publication in Ecological Entomology.
Chapter 3 illustrates that forest influence operates for beetle communities, and that these effects changed greatly over time. This was based on analysing beetle community composition from pitfall traps at fifteen sites, using replicated transects across mature forest boundaries into adjacent harvested stands, over a chronosequence of three secondary forest stages (~7, ~27 and ~45 years old). Environmental characteristics were measured at each plot and used to model how beetle communities were responding across the forest boundaries, and to assess if successional beetle communities were responding to the same environmental forces. Within 200 m from mature forest, the beetle community in ~45 year old secondary forest had largely recovered. The important environmental factors differed in each forest age, yet leaf litter variables and microclimate were consistently correlated with species distribution. This manuscript is accepted in Ecological Applications.
Chapter 4 uses functional trait and phylogenetic approaches on data collected from the experiment described in Chapter 3 to gain deeper insights into community assembly processes underlying beetle succession. I also test whether different beetle trophic groups (decomposers/primary consumers versus predators) assembled the same way. A molecular phylogeny constructed from two DNA barcoding regions and 14 functional traits were calculated for 133 common species. Successional patterns in the phylogenetic and trait datasets were modelled using 16 environmental variables. Environmental filtering was the dominant process shaping beetle community succession for both trophic groups, yet the traits driving this pattern, and evolutionary forces underpinning them, were strongly divergent. Microclimate and leaf litter were key trait filters, particularly for decomposers/primary consumers. This manuscript is in pre–review with Axios.
Microclimate and leaf litter inputs were manipulated in an experimental trial (Chapter 5) to understand the role of dispersal limitation and habitat on beetle recolonisation. The trial was established within a recently harvested site with a mature forest boundary nearby, and beetle communities were sampled using pitfall traps under sterilized leaf litter, artificial shade plots and control (no litter or shade) in a randomized block design. Litter addition and shading significantly altered beetle abundance and community composition and allowed some species adapted to older forest to successfully recolonise. Species functional traits and phylogenetic relationships were also used to explore how environment affects community assembly. Environmental filtering was also the dominant process overall, yet biotic interactions were important for community assembly in open control plots. This manuscript is submitted to Animal Ecology.
My results demonstrate that forest influence is important for beetles in production forests and that forest influence may alter the successional trajectory of beetle communities. Microclimate and leaf litter were both important in facilitating recolonisation, yet dispersal limitation still plays a role. Furthermore, this thesis has helped elucidate what forces shape beetle community assembly over succession, and demonstrates that litter addition and shade not only alters species composition it also changes how beetle communities assemble.