Shrubs and Invasive Mammalson Retired Crown Land

Andrea Byrom

Richard Clayton, Roger Pech, Amy Whitehead

Crown land reformMore 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

Figure 1. The New Zealand dryland zone (after Rogers et al. 2005).

New Zealand

Dryland

19% New Zealand’s land area53,000 km2

83% cleared3% protected

~50% NZ’sthreatened 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 Native biological biological diversitydiversity

Common managementapproaches

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 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

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’ 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)

HypothesesRemoval 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

mammalsManuka 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 = 10-30 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

• Grazed+ Ungrazed

Ln (plant age)

Ln

(ste

m d

iam

ete

r a

t 8 c

m)

B1 B2 C1

F3 C2

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

0 5 10 15 20 25 30

0.0

0.2

0.4

0.6

0.8

1.0

Age (years)

Cu

mu

lati

ve n

um

ber

of

shru

bs

GrazedUngrazed

Grazed Ungrazed

05

1015

Nat

ive

vege

tatio

n ric

hnes

s20

P = 0.015

Results: native plant richness

ANODIS: P<0.001

-1.0 0.0 1.0 2.0

-1.0

0.0

1.0

NMDS axis 1

NM

DS

axi

s 2

Hare

Rabbit

WallabyRat

Mouse

Hedgehog

Possum

NMDS axis 1

NM

DS

axi

s 2

B1

B1

B2B2

C

C

F1

F1

F2

F2

F3

F3

M1

M1

M2M2

-1.0 0.0 1.0 2.0

-1.0

0.0

1.0

GrazedUngrazed

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 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

Thanks to• Foundation for

Research, Science & Technology (funding)

• DOC (logistic support)

• Susan Walker, James Reardon, Susan Timmins, Liz Rayner & Peter Williams (discussions and reviews)