Post-fire ecological restoration and landscape management on the Port Hills, South Island, New Zealand. (2021)
Type of ContentTheses / Dissertations
Degree NameDoctor of Philosophy
Considering the current and future trends of increasing wildfire events and the global and local demand for research focused on ecological restoration, the overall objective of this doctoral research was to provide restoration strategies for regions in New Zealand that are currently under, or likely to be under fire pressure and to support landscape management towards reducing the negative impacts of wildfires.
This investigation was focused on one of the most catastrophic fires in NZ’s recent history, the 2017 Port Hills wildfire. The study area is described in the following section (Section 1.4), and a short summary of the fire event is presented in Section 1.5. The thesis is then presented in three core research chapters, and a concluding chapter, in which the results are integrated, and restoration and landscape management actions are recommended (Chapter 5).
In order to understand the context in which the 2017 wildfire took place, the history of land cover change that occurred on the Port Hills landscape was investigated through the comparison of aerial photography from the 1970s with orthophotography from 2016 (Chapter 2). This analysis was designed to show the main trends in land cover change and represented a starting point for understanding the interaction of public policies, economic scenarios, and biophysical events that led to these changes. Then, orthophotography from the post-fire landscape was overlapped with the pre-fire image and the burnt area was calculated for each landcover class. Further, the relationship between land cover changes and the 2017 fire event was explored, taking into consideration that changes in landcover generally result in changes in fuel type, availability and spatial distribution, thereby influencing fire outcomes.
In the aftermath of the Port Hills fire, the patches of burnt native forest presented variable post-fire responses, with some species recovering fast and vigorously by resprouting. Resprouting is an important strategy that allows plants to persist after fire and can be a shortcut in the post-fire recovery process (Bond & Midgley, 2001; Vieira & Scariot, 2006). Aiming to understand the variability of post-fire resprouting responses between species, monitoring plots were established across patches of burnt forest (Chapter 3). This analysis was then extended to the community level and the influence of species composition and abundance in the resprouting rate of each plot was investigated. Finally, in order to provide a broader understanding of the resprouting trait in New Zealand woody flora, including the resprouting capacity of species that did not occur in the Port Hills burnt region, this investigation was expanded to the whole country by extensively surveying the current literature.
The occurrence of this fire event in 2017 increased the demand for restoration, which was already significant on the Port Hills. Due to the history of occupation and deforestation, restoration plantings have been ongoing in this region since the 1970s (Reay, 1996). The fire occurrence increased the demand for restoration, not just because patches of native vegetation were burnt, but also because managers of public and private conservation areas in the region, farmers and the local population in general were devastated by the negative impacts of the fire on the landscape (Newsline, 2018; Stuff, 2017a; Stuff, 2017b). Given this increased demand for restoration plantings, and the need to understand the main factors influencing seedling performance, restoration planting plots were established in an experimental design and monitored across the burnt landscape (Chapter 4). In addition, community plantings were randomly monitored with the intention of identifying the most common species planted in the post-fire landscape and determining how these species performed in terms of growth.
The results of the investigations described above were interpreted in an integrated perspective in Chapter 5, which then focused on providing practical restoration and land management recommendations. In summary, the investigation on how land cover changed on the Port Hills over time and how these changes influenced the 2017 fire provided crucial information to support the development of recommendations focused on managing the landscape towards reducing the negative impacts of future wildfires. The post-fire vegetation responses monitored across the patches of burnt forest, especially the identification of species capable of resprouting, provided strategic insights to the development of a restoration approach focused on fire resilience. Finally, seedling performance, monitored in the burnt landscape, supported recommendations for future restoration plantings on the Port Hills, especially regarding species selection, planting location and post-planting silvicultural treatments. While part of the restoration and landscape management suggestions were developed specifically for the Port Hills region, most of the practical recommendations developed from this research can be implemented in other New Zealand regions that are currently under fire pressure.
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