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Comparing strategies for surviving browsers

Christina Borzak - Taranna trial 2

Christina sets up trials at Taranna.

Christina Borzak
PhD student
University of Tasmania

Recently I have been busy setting up trials to assess the ability of blue gum (Eucalyptus globulus) seedlings to recover from incidents that result in a loss of biomass, such as mammalian browsing in plantations.  This part of my project aims to investigate the mechanisms behind Eucalyptus recovery and improve our understanding of strategies that have been developed by plants to survive a life with mammalian herbivores.  In July this year, I planted a fenced trial of 556 seedlings at Taranna on the Tasman Peninsula (east coast of Tasmania).  Eight months before planting, the seedlings were cut to two different heights to simulate severe mammalian browsing.  Uncut plants were used as controls.  The two E. globulus populations used for the trial, Blue Gum Hill and St Helens, exhibit extremes of defensive chemistry and possum preference.  Blue Gum Hill trees are relatively more resistant to browsing, while St Helens trees have relatively low concentrations of defensive chemicals and their leaves are preferred by possums.  St Helens trees also exhibit relatively high lignotuber development which leads to the hypothesis that trees with greater lignotuber development might be able to recover from browsing better than trees with less lignotuber development. To assess plant recovery, I will score shoot number, plant and shoot height, plant form and lignotuber size periodically up to one year.

Christina Borzak - Taranna trial 1

Planting trials at Taranna.

Using the same plant stock from St Helens and Blue Gum Hill, in August I set up another common garden trial of 286 E. globulus seedlings at the University of Tasmania.  All seedlings were cut to just above the cotyledonary node eight months ago, and a second 'browse treatment' was done on half of them.  I will assess recovery using the same procedure as for the field trial, with the aim of gaining a better understanding of how E. globulus seedlings can recover after repeated damage.