Evidence for ‘demographic shift’ as climate warms and dries in southern Australian Mediterrranean type ecosystems
In 2015 Enright et al proposed the Interval Squeeze model, arguing that a combination of three key drivers – fire interval shift, post-fire recruitment shift, and demographic shift – will combine to drive population declines and extinctions in many woody plant species of fire prone environments world-wide as climate changes through the 21st century. Evidence for the first two drivers (more frequent fire, reduced post-fire recruitment) is accumulating for ecosystems in North America, Australia and elsewhere. However, evidence for the third driver, demographic shift (i.e. declining growth, seed store accumulation, and survival during inter-fire intervals), is less well documented. Comparison of key plant demographic rates for Proteaceae species in the genera Banksia and Hakea from south-western and south-eastern Australia collected in the 1980s and 1990s with new data collected in 2017-2018 shows a strong decline in seed production and storage which correlates with decreased rainfall and increased temperature over the past 30 years, and supports this 3rd pillar of the Interval Squeeze model.
Enright, N.J., Fontaine, JB, Bowman DMJS, Bradstock, RA, Williams, RJ. 2015. Interval squeeze: Altered fire regimes and demographic responses interact to threaten woody species persistence as climate changes. Frontiers in Ecology and the Environment 13: 265–272.