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Weeds at home observations and theory from travels in the western Mediterranean and South Africa Stephen D. Hopper AC CENRM & Plant Biology, The University of Western Australia, Albany State Biosecurity Forum Connecting Biosecurity


  1. Weeds at home observations and theory from travels in the western Mediterranean and South Africa Stephen D. Hopper AC CENRM & Plant Biology, The University of Western Australia, Albany State Biosecurity Forum Connecting Biosecurity Esplanade Hotel, Fremantle 11.15 – 11.40 Thursday 4 th December 2014

  2. Abstract OUTLINE • Regions of Australia experiencing a Mediterranean climate have exceptional numbers of , and vulnerability to invasion from, weeds . • Weeds may be rare in their native range due to natural checks on population growth. • However, developing a predictive framework around the population biology and invasive potential of weeds remains fraught . • Each species may have different herbivore/pathogen relationships, and respond differently to climate change, a predictable observation of idiosyncratic behaviour , as seen from the context of Darwinian evolutionary biology. • This presentation offers a review of recent field studies and development of theory pertinent to the southern Australian weed flora .

  3. November 2013 | Volume 8 | Issue 11 | e79174 naturalized species

  4. SWAFR and its naturalized flora are exceptional among Mediterranean Climate Regions • Highest weed species and generic richness (mainly Poaceae, Asteraceae, Fabaceae) • Highest naturalized species density • Iridaceae in highest numbers • Not correlated with geographic and landscape heterogeneity, nor exceptional fire regimes • Lowest human population and urban area, but greatest agricultural area • More OCBILs, less YODFELs (Hopper 2009) • Highest numbers from African and Eurasian origins • Broadest range of habitat types occupied, especially inland riparian and wetland woodlands, forests and tall dense shrublands Why? • Highest taxonomic similarity and homogeneity among species assemblages across habitats Tests? • Low natural stress (OCBILs) and highly disturbed habitats the most invaded Arianoutsou et al. 2013 PLOS ONE 8 (11); Hopper 2009 Plant and Soil 322, 49-86

  5. South Africa’s west coast

  6. Climatically: Cape Town = Esperance Bay (courtesy Dr J Scott, CSIRO)

  7. Fallow fields and thicket – Senecio elegans, boxthorn & bitou

  8. The rare Cape Weed

  9. Granite outcrops – West Coast

  10. Crassula natans

  11. The lost world of renosterveld

  12. Paardeberg flatrock

  13. 84 species of geophytes on Paardeberg flatrock

  14. Veld grasses perennial and annual Ehrharta calycina Ehrharta longiflora

  15. Cape mountains – rainforest and fynbos Asparagas, Dipogon and Psoralea

  16. Gladiolus caryophyllaceus – critcally rare in Picketberg landscapes

  17. Geophytes are often confined to rock outcrops – why?

  18. Geophagy – eating underground storage organs Georychus capensis Bathyergus suillus Cryptomys damarensis Cryptomys h. pretoriae Cryptomys spp. Cryptomys h. natalensis

  19. Reprieve from predation – enforced rarity

  20. Las Negras Cabo de Gata-Nijar National Park

  21. Climatically: Cabo de Gata-Nijar NP = Shark Bay (courtesy Dr J Scott, CSIRO)

  22. Corsican and UK coasts

  23. Inland Cabo de Gata-Nijar National Park

  24. A sixth of WA weeds – 230 species – are native to Cabo de Gata-Nijar National Park (20% of the local flora) • The largest proportion recorded from any one park in the world. • Why? • Young (5-7 Ma), often-disturbed, fertile volcanic soils • 30% of CdGNP’s flora are annuals • Rich in Asteraceae, Fabaceae, Brassicaceae, Apiaceae, Poaceae, Scrophulariaceae, Euphorbiaceae

  25. Granite flora – Serra de Guadarama N of Madrid

  26. Southwest Australian Floristic Region From this to this – why? South Africa

  27. Gingin cemetery – extreme sensitivity to topsoil removal and cessation of burning photos S.D. Hopper From this for decades ... weeds ... to this overnight

  28. Why? The vital top 10cm of soil

  29. Interactions of soil depth and weed invasion on germination of natives and weeds Fisher et al. 2009 Biological Conservation 142, 256-269 Invaded Good condition bushland bushland Keith Lightbody

  30. Summary • Weeds may be rare in their native range – natural checks on population growth • Each species is idiosyncratic (predicted from Darwinian evolutionary theory) and may have different herbivore/pathogen relationships, and respond differently to climate change and habitat contingency • Weeds mainly evolve on young, often-disturbed fertile landscapes (YODFELs) • Exceptional vulnerability to weed invasion occurs on old climatically-buffered infertile landscapes (OCBILs) that endure major soil disturbance and fertilization • Early days – these hypotheses need rigorous critical experimentation and testing • WA needs biosecurity investment equivalent to its globally exceptional challenges with invasive weeds.

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