Effects of competition and herbivory over woody seedling growth in a temperate woodland trump the effects of elevated CO2
A trend of increasing woody plant density, or woody thickening, has been observed across grassland and woodland ecosystems globally. It has been proposed that increasing atmospheric [CO2] is a major driver of broad scale woody thickening, though few field-based experiments have tested this hypothesis. Our study utilises a Free Air CO2 Enrichment experiment to examine the effect of elevated [CO2] (eCO2) on three mechanisms that can cause woody thickening, namely (i) woody plant recruitment, (ii) seedling growth, and (iii) post-disturbance resprouting. The study took place in a eucalypt-dominated temperate grassy woodland. Annual assessments show that juvenile woody plant recruitment occurred over the first 3 years of CO2 fumigation, though eCO2 did not affect rates of recruitment. Manipulative experiments were established to examine the effect of eCO2 on above-ground seedling growth using transplanted Eucalyptus tereticornis (Myrtaceae) and Hakea sericea (Proteaceae) seedlings. There was no positive effect of eCO2 on biomass of either species following 12 months of exposure to treatments. Lignotubers (i.e., resprouting organs) of harvested E. tereticornis seedlings that were retained in situ for an additional year were used to examine resprouting response. The likelihood of resprouting and biomass of resprouts increased with lignotuber volume, which was not itself affected by eCO2. The presence of herbaceous competitors and defoliation by invertebrates and pathogens were found to greatly reduce growth and/or resprouting response of seedlings. Our findings do not support the hypothesis that future increases in atmospheric [CO2] will, by itself, promote woody plant recruitment in eucalypt-dominated temperate grassy woodlands.
KeywordsEncroachment Global change Recruitment Resprouting Seedling growth
We thank Steven Wohl, Vinod Kumar, Craig Barton, and Craig McNamara for maintaining the Western Sydney University Free Air CO2 Enrichment (EucFACE) facility, as well as several employees at Western Sydney University and volunteers who assisted with routine surveys of understorey vegetation plots and the experimental plantings. The EucFACE experiment is funded by the Australian Government, through the Education Investment Fund, the Department of Industry and Science and the Australian Research Council, and Western Sydney University. The growth and resprouting components of this research were funded by Australian Research Council Discovery Grant number DP130102576. Establishment and continued monitoring of the long-term vegetation plots was funded by the Hawkesbury Institute for the Environment, Western Sydney University. Victor Resco de Dios acknowledges funding from a Ramón y Cajal fellowship (RYC-2012-10970). Raul Ochoa Hueso acknowledges funding from a Juan de la Cierva-Incorporación fellowship (IJCI-2014-21252).
Author contribution statement
LC, MB, RB, VRD, and SP conceived the ideas and designed the experiment; LC, EB, SH, JP, and ROH collected the data; LC analysed the data; LC led the writing of the manuscript. All authors contributed critically to the drafts and gave final approval for publication.
This study was funded by the Australian Research Council (DP130102576) and the Hawkesbury Institute for the Environment, Western Sydney University.
Compliance with ethical standards
Conflict of interest
The authors declare that they have no conflict of interest.
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