Broad and local-scale factors modifying ecosystem recovery after restoration

The practice of restoration is one pillar of land stewardship that can reduce the impacts of ecosystem degradation. However, the complexity of biotic and abiotic interactions that underlie ecosystem responses to restoration renders it difficult to predict restoration outcomes and the extent of recovery, consequently affecting restoration success. At broad global scales, ecosystem responses to restoration may be influenced by climate, and at local scales, biotic interactions may play a stronger role. The overarching goal of my PhD research was to identify climatic and biotic factors that affect ecosystem responses to restoration at broad and local scales and to determine to what extent these factors can predict restoration outcomes. At the broad global scale, I investigated the role of a changing climate in ecosystem recovery across ecosystems and different disturbances. In a meta-analysis of 130 restoration studies across Asia, Europe, North America, and South America, I quantified the extent of recovery following restoration and tested whether the extent of deviation from historical climates and extreme climate events predicts ecosystem responses to contemporary restoration. I found that restoration is not achieving complete recovery, and that the effects of deviation from recent past climate on recovery after restoration were dependent on the ecosystem characteristic measured. Deviation and anomalies in mean annual temperatures from the recent past mostly decreased recovery following restoration. At the local-scale, I investigated the role of plant-soil interactions in facilitating dominance of non-native plants in the montane grasslands of Banff National Park, Canada, a critical habitat for wildlife. I first identified the plant, arbuscular mycorrhizal, and plant-pathogenic fungal communities in a field survey of reference ecosystems and partially restored ecosystems where non-native plants dominate. I found that the arbuscular mycorrhizal fungal community composition did not differ across ecosystems, suggesting establishment of native plants is not limited by this fungal group. However, distinct fungal pathogen communities coincided with the presence of non-native plant species. These pathogens, possibly conditioned by non-native plants, may impede the restoration of montane grasslands by affecting the establishment of native plant species. To test this hypothesis, I next performed a set of experiments using soil from the field as inoculum and growing plant species present in the montane grasslands to test whether different plant species condition distinct communities of soil pathogenic and arbuscular mycorrhizal fungi, and whether soil conditioned by different plant species has different effects on con- and heterospecific plant growth that may explain non-native plant dominance. I found plant species conditioned distinct communities of soil pathogenic fungi in some cases, but not arbuscular mycorrhizal fungi. Most plant species had less biomass in conspecific than in heterospecific soils (negative conspecific feedback), suggesting non-native plant dominance is not driven by increased positive feedbacks, and that soil pathogens affect the growth of native and non-native plants. In the field, non-native plant species may offset negative conspecific feedbacks by untested mechanisms explaining their dominance in the montane grasslands of Banff National Park. Overall, by addressing multiple scales and using a variety of methods, my research shows that climate and biotic factors can influence ecosystem responses to restoration and helps identify opportunities and limitations to the predictability of ecosystem responses to restoration at global and local scales.

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