Spatial variation in the ongoing and widespread decline of a keystone plant species

Catherine R. Dickson, David J. Baker, Dana M. Bergstrom, Phillippa K. Bricher, Rowan H. Brookes, Ben Raymond, Patricia M. Selkirk, Justine D. Shaw, Aleks Terauds, Jennie Whinam, Melodie A. McGeoch

Research output: Contribution to journalArticleResearchpeer-review

Abstract

Extensive dieback in dominant plant species in response to climate change is increasingly common. Climatic conditions and related variables, such as evapotranspiration, vary in response to topographical complexity. This complexity plays an important role in the provision of climate refugia. In 2008/2009, an island-wide dieback event of the keystone cushion plant Azorella macquariensis Orchard (Apiaceae) occurred on sub-Antarctic Macquarie Island. This signalled the start of a potential regime shift, suggested to be driven by increasing vapour pressure deficit. Eight years later, we quantified cover and dieback across the range of putative microclimates to which the species is exposed, with the aim of explaining dieback patterns. We test for the influence of evapotranspiration using a suite of topographic proxies and other variables as proposed drivers of change. We found higher cover and lower dieback towards the south of the island. The high spatial variation in A. macquariensis populations was best explained by latitude, likely a proxy for macroscale climate gradients and geology. Dieback was best explained by A. macquariensis cover and latitude, increasing with cover and towards the north of the island. The effect sizes of terrain variables that influence evapotranspiration rates were small. Island-wide dieback remains conspicuous. Comparison between a subset of sites and historical data revealed a reduction of cover in the north and central regions of the island, and a shift south in the most active areas of dieback. Dieback remained comparatively low in the south. The presence of seedlings was independent of dieback. This study provides an empirical baseline for spatial variation in the cover and condition of A. macquariensis, both key variables for monitoring condition and ‘cover-debt’ in this critically endangered endemic plant species. These findings have broader implications for understanding the responses of fellfield ecosystems and other Azorella species across the sub-Antarctic under future climates.

Original languageEnglish
Number of pages15
JournalAustral Ecology
DOIs
Publication statusAccepted/In press - 1 Jan 2019

Keywords

  • Azorella
  • climate change
  • dieback
  • sub-Antarctic
  • terrain variables

Cite this

Dickson, C. R., Baker, D. J., Bergstrom, D. M., Bricher, P. K., Brookes, R. H., Raymond, B., ... McGeoch, M. A. (Accepted/In press). Spatial variation in the ongoing and widespread decline of a keystone plant species. Austral Ecology. https://doi.org/10.1111/aec.12758
Dickson, Catherine R. ; Baker, David J. ; Bergstrom, Dana M. ; Bricher, Phillippa K. ; Brookes, Rowan H. ; Raymond, Ben ; Selkirk, Patricia M. ; Shaw, Justine D. ; Terauds, Aleks ; Whinam, Jennie ; McGeoch, Melodie A. / Spatial variation in the ongoing and widespread decline of a keystone plant species. In: Austral Ecology. 2019.
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Dickson, CR, Baker, DJ, Bergstrom, DM, Bricher, PK, Brookes, RH, Raymond, B, Selkirk, PM, Shaw, JD, Terauds, A, Whinam, J & McGeoch, MA 2019, 'Spatial variation in the ongoing and widespread decline of a keystone plant species' Austral Ecology. https://doi.org/10.1111/aec.12758

Spatial variation in the ongoing and widespread decline of a keystone plant species. / Dickson, Catherine R.; Baker, David J.; Bergstrom, Dana M.; Bricher, Phillippa K.; Brookes, Rowan H.; Raymond, Ben; Selkirk, Patricia M.; Shaw, Justine D.; Terauds, Aleks; Whinam, Jennie; McGeoch, Melodie A.

In: Austral Ecology, 01.01.2019.

Research output: Contribution to journalArticleResearchpeer-review

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AU - Brookes, Rowan H.

AU - Raymond, Ben

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AB - Extensive dieback in dominant plant species in response to climate change is increasingly common. Climatic conditions and related variables, such as evapotranspiration, vary in response to topographical complexity. This complexity plays an important role in the provision of climate refugia. In 2008/2009, an island-wide dieback event of the keystone cushion plant Azorella macquariensis Orchard (Apiaceae) occurred on sub-Antarctic Macquarie Island. This signalled the start of a potential regime shift, suggested to be driven by increasing vapour pressure deficit. Eight years later, we quantified cover and dieback across the range of putative microclimates to which the species is exposed, with the aim of explaining dieback patterns. We test for the influence of evapotranspiration using a suite of topographic proxies and other variables as proposed drivers of change. We found higher cover and lower dieback towards the south of the island. The high spatial variation in A. macquariensis populations was best explained by latitude, likely a proxy for macroscale climate gradients and geology. Dieback was best explained by A. macquariensis cover and latitude, increasing with cover and towards the north of the island. The effect sizes of terrain variables that influence evapotranspiration rates were small. Island-wide dieback remains conspicuous. Comparison between a subset of sites and historical data revealed a reduction of cover in the north and central regions of the island, and a shift south in the most active areas of dieback. Dieback remained comparatively low in the south. The presence of seedlings was independent of dieback. This study provides an empirical baseline for spatial variation in the cover and condition of A. macquariensis, both key variables for monitoring condition and ‘cover-debt’ in this critically endangered endemic plant species. These findings have broader implications for understanding the responses of fellfield ecosystems and other Azorella species across the sub-Antarctic under future climates.

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Dickson CR, Baker DJ, Bergstrom DM, Bricher PK, Brookes RH, Raymond B et al. Spatial variation in the ongoing and widespread decline of a keystone plant species. Austral Ecology. 2019 Jan 1. https://doi.org/10.1111/aec.12758