Community level consequences of adaptive management through Climate Matching: oak galls as a model system

Abstract

In the present century, ecosystems across the globe will be subject to profound changes in climate. Forests are expected to be particularly sensitive to such change as the long life span of trees limits the potential for rapid adaptation. In order to preserve commercial viability and the essential ecosystem services provided by forests, there has been much interest in strategies for managing the adaptation of trees to their climatic environment. Climate Matching has emerged as one such strategy, whereby climate models are used to identify provenances – tree populations at a particular locality - with seed expected to be well adapted to the future conditions of a particular planting site. Debate continues about the feasibility and merit of this and other approaches, but it has yet to be demonstrated that the underlying assumptions of Climate Matching are valid for focal European tree species. Furthermore, a potentially major omission thus far has been consideration of how the Climate Matching strategy might influence associated organisms. Given the widely demonstrated bottom-up effects of foundation species genotype that have emerged from the field of community genetics, it is possible that planting seed of non-local provenance could effect forest organisms such as insect herbivores. In this thesis, I investigate the underlying assumptions of Climate Matching and its community level consequences using a model system of cynipid oak galls on Quercus petraea. Following a general introduction to Climate Matching and the study system, in Chapter 2 I use data from a provenance trial of Q. petraea in France to explore a central assumption of the Climate Matching strategy: that provenances of focal tree species show climate associated variation in adaptive phenotypic traits. In Chapter 3, I explore correlations between these phenotypic traits and the abundance, diversity, and community composition of an associated guild of specialist gall-inducing herbivores. Tree phenological traits in particular showed strong patterns of adaptation to climatic gradients, and influenced the abundance and community structure of galling species. However, as the response to non-local tree provenances was not strongly negative, it was considered unlikely that mixed planting of local and Climate Matched provenances would have sever impact on the gallwasp community. Having assessed the bottom-up effects of provenance phenotypic variation on the galling community, my ultimate aim is to extend analysis to include associated hymenopteran inquilines and parasitoids. However, interpretation of effects at this level is hindered by taxonomic uncertainty, with a growing appreciation that morpho-taxa may not represent independently evolving lineages (i.e. ‘true’ species). In Chapters 4 & 5 I therefore develop approaches for addressing taxonomic uncertainty with this ultimate aim in mind. In Chapter 4, I apply a DNA barcoding approach to parasitoid and inquiline specimens reared from the provenance trial, and compare taxa based on barcodes with those based on morphology to identify points of taxonomic uncertainty. I also investigate the extent to which networks based on morphological and molecular taxa support contrasting conclusions of network properties. In Chapter 5 I explore the potential for molecular based resolution of species level taxonomic error in a challenging group of parasitoids: the genus Cecidostiba. Beginning with a framework of single locus DNA barcoding, I use data from multiple nuclear loci to reveal the existence of cryptic species. Finally, in Chapter 6 I explore the practicalities of Climate Matching in light of my empirical results, and suggest fruitful avenues for further research.