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Shrubs and Invasive Mammals on Retired Crown Land

Shrubs and Invasive Mammals on Retired Crown Land. Andrea Byrom Richard Clayton, Roger Pech, Amy Whitehead. Crown land reform. More than half a million hectares may be used primarily for conservation by 2015 Biodiversity protection Soil protection Water conservation Landscape values

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Shrubs and Invasive Mammals on Retired Crown Land

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  1. Shrubs and Invasive Mammalson Retired Crown Land Andrea Byrom Richard Clayton, Roger Pech, Amy Whitehead

  2. Crown land reform More than half a million hectares may be used primarily for conservation by 2015 • Biodiversity protection • Soil protection • Water conservation • Landscape values • Carbon sequestration

  3. Strong tendency for woody succession Special habitats • Shrublands • Cushionfield • Herbfields • Grasslands • Tussocklands • Wetlands • Inland sand dunes • Saline habitat • Forest

  4. 19% New Zealand’s land area 53,000 km2 83% cleared 3% protected ~50% NZ’sthreatened flora

  5. A sequence of large-scale biological impacts • Kiore (1000 yr bp) • Burning (800 yr bp) • Burning and livestock grazing (150 yr bp) • Rabbits (150 yr bp) • Ferrets, stoats, weasels, (cats) (130 yr bp) • Exotic pastures and fertiliser (130 yr bp) • Hares, hedgehogs, mice, rats, possums, goats • Broom, briar, gorse, hawthorn • Cropping, viticulture, horticulture, dairying, forestry • Housing subdivisions

  6. Native biological diversity

  7. Common managementapproaches • Land retirement► changes in grazing, fertiliser, and burning (‘tenure review’) • Weed control • Rabbit control • Predator control to conserve native biodiversity

  8. Public perceptions “The Department of Conservation is priding itself on the return of a huge section of Mesopotamia Station into its fold… how does it intend to manage .. land taken under the tenure review process?” “.. the loss of any [wilding] pine is a loss to New Zealand’s ability to store CO2 .. millions of wilding pines are helping to stop climate change.” Letters to The Press, 2008 “.. money that could be spent on fencing is spent instead trying to control the weeds that spring from seeds blown from DOC land… Christine Fernyhough, ‘The Road to Castle Hill’, 2007

  9. Former pastoral lease land • Successional plant communities • How to manage weeds and pests? • How to mitigate threats to biodiversity? • Potential for these systems to accumulate carbon

  10. Focus on major changes • Grazing ceases when land retired to Crown • Removal of livestock can start successional change in plant communities • Grazing removal = ‘experimental manipulation’ • Paired sites close to fencelines have similar physical characteristics

  11. ‘Grazing removal’ studyAims • Measure changes in weed and pest animal abundance • Measure changes in indigenous biodiversity • Provide in-depth understanding of ecosystem responses • Point to what to do next(research & management)

  12. Hypotheses Removal of grazing will: • Influence shrub growth rates • Faster growth on ungrazed sites • Alter shrub recruitment processes • Release seedlings from grazing pressure • Increase competition from grasses • Increase plant species richness • Provide habitat for invasive mammals Manuka and matagouri (native shrubs)

  13. Sites chosen • Land retired from grazing in last 30 years • Well-maintained fence separated DOC land from grazed land • Paired grazed and ungrazed plots on each side of fence (n=8) • All located in Canterbury high country

  14. Methods • Shrub measurements: volume, height, age (growth rings), stem diameter, weight(n = 10-30 shrubs/site) • Index surveys of invasive mammals • Plant richness (site and quadrat scales)

  15. F3 C2 • Grazed +Ungrazed B1 C1 Ln (stem diameter at 8 cm) B2 Ln (plant age) Results: matagouri • Grazing did not affect allometric relationships (e.g. age/diameter) • Similar results for plant weight, volume and height C2 = P Williams data

  16. 1.0 0.8 0.6 Cumulative number of shrubs 0.4 0.2 Grazed Ungrazed 0.0 0 5 10 15 20 25 30 Age (years) Results: manuka • Significant effect of grazing on shrub volume, weight, & stem diameter • Evidence of a pulse in recruitment on ungrazed sites ~10-20 yr ago

  17. Results: native plant richness 20 15 10 Native vegetation richness 5 0 P = 0.015 Grazed Ungrazed

  18. Results: pest animal responses 1.0 1.0 F1 F3 Rabbit Hedgehog B1 M1 F3 Rat M2 B2 M2 NMDS axis 2 0.0 NMDS axis 2 0.0 Wallaby B2 Non metric multidimensional scaling ordination (NMDS) & analysis of dissimilarity (ANODIS) F1 B1 Hare Possum F2 C M1 Mouse F2 C -1.0 -1.0 -1.0 0.0 1.0 2.0 -1.0 0.0 1.0 2.0 NMDS axis 1 NMDS axis 1 Grazed Ungrazed ANODIS: P<0.001

  19. Crown Land Reform: summary ► Release from grazing ► Shrub succession • Grazing effects on shrub dynamics & growth vary depending on species • Higher richness of native plants in ungrazed areas • Different guilds of invasive mammals associated with grazed vs. ungrazed areas • All have implications for ‘successional trajectories’

  20. Management recommendationsFor retired Crown land • Embrace complexity • take a broad ‘ecosystem’ view(surprises always around the corner) • General rules don’t always apply • Evidence-based science can support management programmes • Think long-term(high country is changing, but changing slowly) • Invest in monitoring

  21. Thanks to • Foundation for Research, Science & Technology (funding) • DOC (logistic support) • Susan Walker, James Reardon, Susan Timmins, Liz Rayner & Peter Williams (discussions and reviews)

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