Response of Montane Plant Communities to Wildfires in the South Island of Aotearoa New Zealand

Budha Magar, Shanta
Hannah L., Buckley
Nicola J., Day
J Curran, Timothy
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Doctor of Philosophy
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Auckland University of Technology

Measuring and predicting the response of plant communities to ecological disturbances require characterising community dynamics over multiple timescales, both before and after disturbance events. With global climate change, fire regimes are expected to increase in some regions, including parts of New Zealand. These increases are predicted to be particularly impactful in ecosystems in regions with historically low fire frequencies, such as montane plant communities in New Zealand’s South Island. Species functional traits or sets of traits such as those represented by growth form and biostatus, can influence the ecological effects of fire and are likely to influence rates of recovery of individual plants and plant communities after fire. Thus, flammability at the plant community level can be estimated using plant community composition, plant traits and experimental measurements of plant shoot flammability. In this thesis, I measured plant community structure and trait variation of plants within South Island montane plant communities that had been impacted by wildfires over a range of sites and timescales. This research showed that most plants in these communities can survive wildfires and that most aspects of plant community structure recover rapidly, in less than 15 months after fire. However, longer-term data from permanent monitoring plots showed that historical fires have a lasting signature on plant community composition. In addition, plants with different biostatus (native or exotic) and growth forms (forbs, graminoid, or woody) showed different responses to fire. These long- and short-term dynamics in plant community structure result in dynamics in estimated plant community flammability that primarily reflects changes in key plant traits and species’ relative abundance. However, both experimentally measured shoot flammability and plant traits, including leaf nutrient concentrations, show phylogenetic patterns suggesting both ecological and evolutionary processes that drive plant flammability, and therefore influence community flammability. This study highlights the need for ongoing future trait-based fire ecology research in these montane plant communities because, although native plants were not disproportionately impacted by these instances of wildfires compared to exotics, long-term data show that repeated fires are likely to alter community structure over longer timescales.

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