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  • (2022) Mackenzie, Berin
    Climate change and anthropogenic ignitions are driving rapid changes in global fire regimes, including the seasonal timing of fire. Species with physiological seed dormancy (PD) constitute a significant proportion of the floristic diversity in fire-prone ecosystems worldwide, yet their seed ecology in these systems remains poorly understood with many species regarded as difficult to germinate. In this thesis, I investigate mechanisms of fire-stimulated germination of PD species and the influence of fire seasonality on emergence patterns using shrub species in the genus Boronia (Rutaceae). Using freshly dispersed seeds (Chapter 2), I demonstrate the important role of seasonal temperatures in mediating the speed and magnitude of fire-stimulated germination, and the importance of both fire-related heat (soil heating) and smoke as germination cues. Using buried seeds (Chapter 3), I develop novel conceptual models of how seasonal patterns in dormancy and germination interact with the seasonal timing of fire and moisture availability to drive emergence patterns. Fire seasonality effects vary in strength and direction—even amongst sympatric congeners—with fires in certain seasons predicted to delay and reduce germination of some species and accelerate and increase germination of others. Given the importance of seasonal temperatures as drivers of germination and soil seed bank dynamics, I critically review conventional methods of simulating seasonal and diurnal temperature regimes in laboratory studies (Chapter 4). I find that alternating constant temperature profiles based on meteorological data systematically underestimate post-fire soil temperatures and lead to excessive cumulative exposure to daily temperature extremes. These findings raise important questions about the predictive accuracy of laboratory studies predicated on such approaches. I highlight alternative incubation profiles that better approximate the thermal conditions seeds experience in situ and recommend comparative studies to assess the adequacy of the current methodological paradigm. New knowledge presented herein will be pivotal to seed scientists, fire ecologists and conservation managers in fire-prone ecosystems worldwide as they strive to understand the germination requirements and seed ecology of PD species to support effective ex situ conservation, and to integrate fire seasonality and fire intensity into fire management frameworks to ensure best-practice conservation of regional floras.