SLIDE 1 Weeds at home
- bservations 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 4th December 2014
SLIDE 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
- bservation 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.
SLIDE 3 November 2013 | Volume 8 | Issue 11 | e79174
naturalized species
SLIDE 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
- Highest taxonomic similarity and homogeneity among
species assemblages across habitats
- 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
Why? Tests?
SLIDE 5
South Africa’s west coast
SLIDE 6 Climatically: Cape Town = Esperance Bay
(courtesy Dr J Scott, CSIRO)
SLIDE 7
SLIDE 8
SLIDE 9
Fallow fields and thicket – Senecio elegans, boxthorn & bitou
SLIDE 10
SLIDE 11
The rare Cape Weed
SLIDE 12
Granite outcrops – West Coast
SLIDE 13
Crassula natans
SLIDE 14
The lost world of renosterveld
SLIDE 15
Paardeberg flatrock
SLIDE 16 84 species of geophytes
SLIDE 17
Veld grasses perennial and annual Ehrharta calycina Ehrharta longiflora
SLIDE 18
Cape mountains – rainforest and fynbos Asparagas, Dipogon and Psoralea
SLIDE 19
Gladiolus caryophyllaceus – critcally rare in Picketberg landscapes
SLIDE 20
Geophytes are often confined to rock outcrops – why?
SLIDE 21 Georychus capensis Bathyergus suillus Cryptomys damarensis Cryptomys h. pretoriae Cryptomys spp. Cryptomys h. natalensis
Geophagy – eating underground storage organs
SLIDE 22
SLIDE 23
Reprieve from predation – enforced rarity
SLIDE 24 Cabo de Gata-Nijar National Park Las Negras
SLIDE 25 Climatically: Cabo de Gata-Nijar NP = Shark Bay
(courtesy Dr J Scott, CSIRO)
SLIDE 26
SLIDE 27
Corsican and UK coasts
SLIDE 28 Inland Cabo de Gata-Nijar National Park
SLIDE 29 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
SLIDE 30
Granite flora – Serra de Guadarama N of Madrid
SLIDE 31
SLIDE 32
SLIDE 33 From this to this – why?
South Africa Southwest Australian Floristic Region
SLIDE 34
SLIDE 35 Gingin cemetery – extreme sensitivity to topsoil removal and cessation of burning From this for decades ... ... to this overnight weeds
photos S.D. Hopper
SLIDE 36
Why? The vital top 10cm of soil
SLIDE 37 Interactions of soil depth and weed invasion
- n germination of natives and weeds
Fisher et al. 2009 Biological Conservation 142, 256-269
Good condition bushland Invaded bushland
Keith Lightbody
SLIDE 38 Summary
- Weeds may be rare in their native range – natural checks
- n 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.
