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 Carbon sequestration

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

19% New Zealand’s land area 53,000 km 2 83% cleared 3% protected ~50% NZ’s threatened flora

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

Native biological diversity

Common management approaches 1.Land retirement ► changes in grazing, fertiliser, and burning (‘tenure review’) 2.Weed control 3.Rabbit control 4.Predator control to conserve native biodiversity

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 CO 2.. 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

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

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

‘Grazing removal’ study Aims 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)

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)

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

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

Results: matagouri Grazing did not affect allometric relationships (e.g. age/diameter) Similar results for plant weight, volume and height C2 = P Williams data

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

GrazedUngrazed Native vegetation richness 20 P = Results: native plant richness

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

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’

Management recommendations For 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

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