Managing ground cover

weeds for biodiversity gain in

New Zealand lowland forests

Kate McAlpine (DOC)

Shona Lamoureaux (AgResearch)

Susan Timmins (DOC)

Acknowledgements

• Funding from FRST (now MBIE) under Beating Weeds II

programme, and DOC.

• Landowners/managers: Ian Nobel, Tim & Heather Ryan,

Ed & Sue Harvey, Chris Clark (DOC), Kerry Watson

(Trustpower), Greg Shaw (South Waikato DC).

• Graeme Bourdot, Tom Belton, Sarah Crump, Simon

Fowler, Trevor James, Kris Kramer-Walter, Carolyn

Lusk, Walter Stahel, Mike Trolove, Nancy van

Nieuwenhove, Ian Westbrooke.

1. Impacts on native vegetation

2. Controlling weeds for

biodiversity gain

3. Effects of seed size and predation

on native recruitment

Ground cover weeds

Tradescantia fluminensis

Plectranthus ciliatus

Asparagus scandens

Impacts on native

regeneration

• 48, 2 x 2 m plots per site

• Range of weed cover 0-100%

• Measured weed abundance,

native abundance, native diversity

Weed biomass (% cover x height)

Na

tive

ab

un

da

nce

< 1

m

05

10

15

20

25

0 10 20 30 40 50

Asp 1

510

15

20

25

30

Asp 2

010

20

30

40

50

Plec 1

510

15

20

25

Plec 2

010

20

30

Trad 1

0 10 20 30 40 50

05

10

15

20

25

Trad 2 ***

***

***

*

***

Weed biomass (% cover x height)

Na

tive

sp

ecie

s d

ive

rsity

0

5

10

15

0 10 20 30 40 50

Asp 1 Asp 2

Plec 1

0

5

10

15

Plec 2

0

5

10

15

Trad 1

0 10 20 30 40 50

Trad 2

*

***

*** ***

*

Controlling weeds for

biodiversity gain

• 32, 2 x 2 m plots per site

• All plots with 100% cover of weed

• Applied 3 treatments

Herbicide

at full

strength

Herbicide

at half

strength

Manual

control

No

treatment

Treatments

Treatment

Ch

an

ge

in

na

tive

ab

un

da

nce

-10

0

10

None Manual Half Full

Asp 1

None Manual Half Full

Asp 2

Plec 1

-10

0

10

Plec 2

-10

0

10

Trad 1 Trad 2

What else might affect

native recruitment?

• Native seed supply?

• Native seed size?

• Seed/seedling predation?

Extra 32, 50 x 50 cm plots per site

Weed cover class % cover

High > 95%

Medium ~ 60-80%

Low ~ 20-40%

Zero < 1%

Species Common name Avg seed

weight (g)

Geniostoma ligustrifolium hange hange 0.0005

Melicytus ramiflorus mahoe 0.001

Macropiper excelsum kawakawa 0.002

Myrsine australis mapou 0.003

Pseudopanax arboreus five-finger 0.005

Coprosma grandifolia kanono 0.02

Knightia excelsa rewarewa 0.03

Hedycarya arborea pigeonwood 0.24

Vitex lucens puriri 0.37

Beilschmiedia tawa tawa 1.38

• More weed = less native biomass

• More weed = fewer native species

• Manual control is best for natives

• Half strength herbicide gives good

control, but damages natives

Results so far:

Galeobdolon luteus

Hedera helix

Selaginella kraussiana

Vinca major

Plectranthus ecklonii

Photo: Clayson Howell