Climate change including drought and temClimate change including drought and temperature extremes

Climate change including drought and temperature extremes

Understanding the physiological limits of the Wollemi Pine is particularly important in the context of climate change, where extreme weather events (such as heat waves and droughts) are predicted to occur more frequently and with increasing intensity (Seneviratne et al. 2012; Ukkola et al. 2020).

Wollemi Pine is known to incur tissue damage at and above 37.5 °C, which is the lowest temperature for damage initiation among its Australian Araucariaceae relatives (Offord 2011). By contrast, the Wollemi Pine has the greatest tolerance for cold, with damage only beginning at -6.8 °C (Offord 2011), and cultivated Wollemi Pines growing in cooler regions, such as at BMBGMT, appear to suffer less heat-stress related damage and mortality than those growing in hotter regions, such as at ABGMA (C. Offord, pers. obs cited in Offord & Zimmer 2023; see Offord & Zimmer 2023 for climate profiles of these locations). Additionally, the response of Wollemi Pine to drought in laboratory experiments was noted as remarkably different to other Australian species within the Araucariaceae (Zimmer et al. 2015b). These other Australian Araucariaceae species were isohydric, meaning they close stomata in response to water stress, ceasing gas exchange and photosynthesis, with the aim of maintaining leaf water potential and avoiding damage. The Wollemi Pine, by contrast, continued to photosynthesise as water stress increased, leading to declining leaf water potentials, and eventually damage—manifested in crown mortality (both stem and branch mortality) (Zimmer et al. 2015b). A contributing factor to the inability of the Wollemi Pine to avoid damage may be the vasoconstriction at its branch bases, as described by Burrows et al. (2007). However, the species is also able to resprout after drought-induced damage, providing some post-drought recovery potential. Furthermore, Lewis et al. (2015) examined the interactive effects of increased CO2 and temperature on Wollemi Pine growth and physiology in glasshouse conditions. While elevated CO2 increased plant growth, they concluded that increasing temperatures may offset these effects by affecting respiration rates.

This research, and the Wollemi Pine’s restricted distribution in a refugia habitat, indicates that the species is vulnerable to the impacts of temperature extremes and drought. Anthropogenic climate change is projected to result in increases in average temperatures, the severity and length of fire seasons and the intensity of extreme weather events, and a decrease in cool season rainfall across much of eastern Australia (CSIRO & Bureau of Meteorology 2022). These changes, which are likely to include a substantial increase in the peak temperature on hot days along the east coast (Dowdy et al. 2015), could severely impact the Wollemi Pine and its habitat. In combination with the increased risk of extreme fire seasons (Canadell et al. 2021; van Oldenborgh et al. 2021), this highlights the need for greater understanding of the nature of climate change impacts on the wild Wollemi Pine population.

A wollemi pine seedling growing in leaf litter