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Zefferman E, Stevens JT, Charles GK, Dunbar-Irwin M, Emam T, Fick S, Morales LV, Wolf KM, Young DJN, Young TP. Plant communities in harsh sites are less invaded: a summary of observations and proposed explanations. AOB PLANTS 2015; 7:plv056. [PMID: 26002746 PMCID: PMC4497477 DOI: 10.1093/aobpla/plv056] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/18/2015] [Accepted: 05/11/2015] [Indexed: 05/22/2023]
Abstract
Plant communities in abiotically stressful, or 'harsh', habitats have been reported to be less invaded by non-native species than those in more moderate habitats. Here, we synthesize descriptive and experimental evidence for low levels of invasion in habitats characterized by a variety of environmental stressors: low nitrogen; low phosphorus; saline, sodic or alkaline soils; serpentine soils; low soil moisture; shallow/rocky soils; temporary inundation; high shade; high elevation; and high latitude. We then discuss major categories of hypotheses to explain this pattern: the propagule limitation mechanism suggests invasion of harsh sites is limited by relatively low arrival rates of propagules compared with more moderate habitats, while invasion resistance mechanisms suggest that harsh habitats are inherently less invasible due to stressful abiotic conditions and/or increased effects of biotic resistance from resident organisms. Both propagule limitation and invasion resistance may simultaneously contribute to low invadedness of harsh sites, but the management implications of these mechanisms differ. If propagule limitation is more important, managers should focus on reducing the likelihood of propagule introductions. If invasion resistance mechanisms are in play, managers should focus on restoring or maintaining harsh conditions at a site to reduce invasibility.
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Affiliation(s)
- Emily Zefferman
- Department of Plant Sciences, University of California, Davis, CA 95616, USA Present address: Department of Earth and Planetary Sciences, University of Tennessee, Knoxville, TN 37917, USA
| | - Jens T Stevens
- Department of Plant Sciences, University of California, Davis, CA 95616, USA John Muir Institute for the Environment, University of California, Davis, CA 95616, USA
| | - Grace K Charles
- Department of Plant Sciences, University of California, Davis, CA 95616, USA
| | - Mila Dunbar-Irwin
- Department of Plant Sciences, University of California, Davis, CA 95616, USA
| | - Taraneh Emam
- Department of Plant Sciences, University of California, Davis, CA 95616, USA
| | - Stephen Fick
- Department of Plant Sciences, University of California, Davis, CA 95616, USA
| | - Laura V Morales
- Department of Plant Sciences, University of California, Davis, CA 95616, USA
| | - Kristina M Wolf
- Department of Plant Sciences, University of California, Davis, CA 95616, USA
| | - Derek J N Young
- Department of Plant Sciences, University of California, Davis, CA 95616, USA
| | - Truman P Young
- Department of Plant Sciences, University of California, Davis, CA 95616, USA
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152
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Ens E, Hutley LB, Rossiter-Rachor NA, Douglas MM, Setterfield SA. Resource-use efficiency explains grassy weed invasion in a low-resource savanna in north Australia. FRONTIERS IN PLANT SCIENCE 2015; 6:560. [PMID: 26300890 PMCID: PMC4523779 DOI: 10.3389/fpls.2015.00560] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/06/2015] [Accepted: 07/07/2015] [Indexed: 05/18/2023]
Abstract
Comparative studies of plant resource use and ecophysiological traits of invasive and native resident plant species can elucidate mechanisms of invasion success and ecosystem impacts. In the seasonal tropics of north Australia, the alien C4 perennial grass Andropogon gayanus (gamba grass) has transformed diverse, mixed tree-grass savanna ecosystems into dense monocultures. To better understand the mechanisms of invasion, we compared resource acquisition and usage efficiency using leaf-scale ecophysiological and stand-scale growth traits of A. gayanus with a co-habiting native C4 perennial grass Alloteropsis semialata. Under wet season conditions, A. gayanus had higher rates of stomatal conductance, assimilation, and water use, plus a longer daily assimilation period than the native species A. semialata. Growing season length was also ~2 months longer for the invader. Wet season measures of leaf scale water use efficiency (WUE) and light use efficiency (LUE) did not differ between the two species, although photosynthetic nitrogen use efficiency (PNUE) was significantly higher in A. gayanus. By May (dry season) the drought avoiding native species A. semialata had senesced. In contrast, rates of A. gayanus gas exchange was maintained into the dry season, albeit at lower rates that the wet season, but at higher WUE and PNUE, evidence of significant physiological plasticity. High PNUE and leaf (15)N isotope values suggested that A. gayanus was also capable of preferential uptake of soil ammonium, with utilization occurring into the dry season. High PNUE and fire tolerance in an N-limited and highly flammable ecosystem confers a significant competitive advantage over native grass species and a broader niche width. As a result A. gayanus is rapidly spreading across north Australia with significant consequences for biodiversity and carbon and retention.
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Affiliation(s)
- Emilie Ens
- Research Institute for the Environment and Livelihoods, Charles Darwin University, Darwin, NTAustralia
- Department of Environmental Sciences, Macquarie University, North Ryde, NSWAustralia
| | - Lindsay B. Hutley
- Research Institute for the Environment and Livelihoods, Charles Darwin University, Darwin, NTAustralia
| | | | - Michael M. Douglas
- Research Institute for the Environment and Livelihoods, Charles Darwin University, Darwin, NTAustralia
- School of Earth and Environment, University of Western Australia, Perth, WAAustralia
| | - Samantha A. Setterfield
- Research Institute for the Environment and Livelihoods, Charles Darwin University, Darwin, NTAustralia
- *Correspondence: Samantha A. Setterfield, Research Institute for the Environment and Livelihoods, Charles Darwin University, Darwin, NT 0909, Australia,
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