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Evidence for demographic shift in woody plant species under a changing climate in southwest Australian Mediterranean-type ecosystems

Cowan, Ebony (2018) Evidence for demographic shift in woody plant species under a changing climate in southwest Australian Mediterranean-type ecosystems. Honours thesis, Murdoch University.

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Climate change is projected to cause reduced rainfall, increased temperatures and more frequent fires for many parts of the world, particularly in Mediterranean-type ecosystems (MTEs). Such changes may profoundly impact species demography and ultimately their persistence. However, the impact of climate change on seed demography is not well documented. The MTE region of southwest Australia is a renowned plant biodiversity hotspot and has experienced significant warming and drying over the past 40 years. An iconic and important portion of the region’s biodiversity are serotinous species which retain a canopy seed bank in woody fruits and offer a powerful opportunity to study climate impacts; these species often retain their lifetime reproductive effort as woody fruits which may be quantified, rather than most other plant species which disperse their seeds regularly upon ripening. The drivers of changes to the size of the seed store in serotinous species is unknown, but potential mechanisms include changes in seed/fruit production, seed viability or cone opening. Therefore, these factors were quantified for a selection of 11 serotinous species in the region and compared to data collected in the past (1983-2004) to quantify possible climate change impacts.

Total viable seed production was variable between species and time frames, with 54% of species showing a reduction in seeds produced (reductions of 4-76%). This result was driven by a reduction in fruit production in 57% of species surveyed, while seed viability did not change. Across a broad climatic gradient, there was more rapid cone opening in serotinous species (i.e. seed release into the inter-fire period) in mesic sites compared to xeric sites, with cones also opening at a younger age than they did in the past. This suggests that climate change is influencing the size of the overall seed store in serotinous species, with changes to fruit production and cone opening being most significant. This threatens the long-term persistence of these species under a changing climate, with less seeds available for post-fire recruitment leading to potential population collapse. These findings are applicable to many serotinous species in MTEs globally and warrant further investigation.

Item Type: Thesis (Honours)
Murdoch Affiliation(s): School of Veterinary and Life Sciences
United Nations SDGs: Goal 13: Climate Action
Supervisor(s): Enright, Neal and Fontaine, Joe
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