establishment and early performance of planting trials...

Establishment and early performance of planting trials with indigenous woody shrub species in the Rotorua district David Bergin 2008

1

ESTABLISHMENT AND EARLY PERFORMANCE OF

PLANTING TRIALS WITH INDIGENOUS WOODY SHRUB

SPECIES IN THE ROTORUA DISTRICT

David Bergin

2008

This Scion contract report is prepared for the Farmers of the Central Plateau Sustainable Farming Fund project 03/065 in collaboration with local community

groups and landowners at Rerewhakaaitu and Horohoro, and PGG Wrightson Ltd. The opinions provided in the Report have been provided in good faith and on the basis that every endeavour has been made to be accurate and not misleading and to exercise reasonable care, skill and judgment in providing such opinions. Neither Scion nor any of its employees, contractors, agents or other persons acting on its behalf or under its control accept any responsibility or liability in respect of any opinion provided in this Report By Scion.

2

ESTABLISHMENT AND EARLY PERFORMANCE OF PLANTING TRIALS WITH

INDIGENOUS WOODY SPECIES IN THE ROTORUA DISTRICT

David Bergin

Scion, Private Bag 3020, Rotorua

ABSTRACT

Indigenous species planting trials were established on three sites in the Rotorua district at

Horohoro, Rerewhakaaitu and Ngongotaha in mid-2005 and mid-2006 as part of a Sustainable

Farming Fund project in collaboration with local community groups and landowners, PGG

Wrightson Consulting, and Scion. The objectives of the trial were to establish demonstration

areas that evaluated a range of planting practices including plant spacing, nursery stock types and

maintenance requirements for a range of riparian sites.

Preliminary results indicate that near canopy cover can be achieved at high density planting of

10,000 stems per hectare using relatively fast-growing indigenous shrub hardwoods. Lower

densities of 5000 and 2500 stems per hectare will require 3-4 further years to achieve near

canopy cover. Effective weed control is required for at least the first two years to ensure sites do

not become dominated by exotic brush weeds.

With only one year after planting, preliminary results indicate that containerised seedlings

perform better than bare-rooted stock. Application of copper to the interior surfaces of containers

prevent root spiralling, but there may be an early detrimental effect on height growth. Further

monitoring is required to determine if these trends continue.

.

KEYWORDS: indigenous, planting, revegetation, site preparation, nursery-raised seedlings,

containers, open-grown, weed control.

INTRODUCTION

Catchment protection has been an ongoing focus in the Rotorua district over the last 3 decades.

Since the 1970s, Environment Bay of Plenty, and formerly the Bay of Plenty Catchment

Commission, has been working with landowners to develop catchment protection areas along

stream banks and on erosion-prone land (Stace et al. 2003). Revegetation of these areas retired

from grazing required fencing and the planting of woody species. Early plantings involved

planting of various mixtures of exotic and indigenous plant species, the choice often depending

on the commercial availability of suitable planting stock. Spacing of plants and planting

practices also varied according to resources available. Maintenance of retirement areas

frequently lapsed with regard to control of invasive brush weeds such as blackberry, gorse and

barberry. Inadvertent grazing in some retired areas destroyed newly planted areas, further

contributing to brush weed invasion.

Planting trials using indigenous shrub species were established on three sites in the Rotorua

District in mid-2005 and mid-2006 as part of a Sustainable Farming Fund project by the local

landowner group, the Farmers of the Central Plateau, PGG Wrightson Consulting and Scion. The

trials were established as demonstration areas in high profile sites and evaluated a range of

factors including site preparation, nursery stock types, plant spacing and weed control. The sites

3

selected for the trials were typical of areas that had been retired either recently or some years ago

from pastoral farming and were a high priority for revegetation with appropriate woody

indigenous species to reduce the impact of farming landuse on water quality in the district. For

many of riparian and erosion-prone areas in the Rotorua District, planting appropriate local

indigenous species is favoured and a limited range of the key indigenous shrub species was used

in these trials.

Building on information from previous trials and management programmes, planting trials in the

Rotorua district are aimed at refining propagation and establishment practice for the planting of

indigenous woody species on retired erosion-prone sites.

PREVIOUS WORK

There are numerous guidelines for the planting of indigenous species for a wide range of reasons

and covering many different sites including relatively sheltered inland sites and exposed upland

forest sites (eg., Evans 1983; Pollock 1986; Beveridge et al. 1985, 1987; Bergin and Gea 2005).

However, there is ongoing conjecture regarding choice of appropriate regimes for establishing

natives on different sites. Choice of site preparation, planting pattern, plant density, species,

nursery stock type and size, maintenance requirements and long-term management will depend

on the site to be revegetated including the type and propensity for weed growth, the resources

available for undertaking the programme, and the commitment of locals and/or agencies

involved in management (Bergin and Gea 2005).

A survey commissioned by Environment Bay of Plenty in collaboration with the Department of

Conservation and the New Zealand Forest Research Institute found that many cleared sites not

actively managed as exotic forestry or pastoral farming, or recently retired from pastoral grazing,

were prone to invasion by woody brush weeds, particularly blackberry (Bergin and Shaw 1993).

The survey found that blackberry quickly invades recently retired open sites even where a dense

sward of rank grass was present. For sites that had been retired from grazing for at least five

years, blackberry had often formed a dense canopy over significant areas within the Rotorua

basin and in the greater Bay of Plenty region. Sites surveyed included those that had been

planted as part of the Kaituna Catchment Scheme where riparian sites were retired from grazing

and planted with woody indigenous species to improve water run-off to Lake Rotorua. Some two

decades later, such sites often comprised only a few indigenous shrubs and trees surviving from

the original planting programmes scattered amongst a dominant 4 m high cover of blackberry. In

contrast, there was no evidence of indigenous regeneration amongst the large blackberry

colonies. Blackberry was also found to invade many wetland areas and to persist within the

understorey of established exotic plantations.

In one area, the Waimangu Scenic Reserve, there were extensive areas of blackberry typical of

many areas surveyed (Bergin and Shaw 1993). Stock was excluded from the area in the late

1960s with only local blackberry control since then. Atkinson (1972) reported that blackberry

was widespread in the reserve forming an unsightly tangle in some areas and suggested these

locally dominant stands of blackberry may have been established for 20 years or more.

In another survey of large-scale revegetation programmes in the Bay of Plenty, Stace et al.

(2003) found that low planting densities resulted in poor survival of planted seedlings and sites

becoming dominated by exotic brush weeds, particularly blackberry compared to more densely

planted sites. Eight species were identified as the best to use in revegetation programmes as they

best survival and fastest growing canopy cover, thereby reducing the period for post-plant weed

control and significantly reduce the period when invasive exotic brush weeds could invade and

become dominant. The high-percentage cover indigenous species favoured for revegetation were

4

black mapou, akeake, kohuhu, harakeke, taupata, manuka, lemonwood and kanuka. Mahoe,

karamu, karo, lacebark, cabbage tree and pohutukawa were found to medium percentage cover

species while the most erect small diameter crown species five finger and rewarewa were

categorised as low percentage cover species. A model for designing using a mix of the high

percentage cover species and optimum plant spacing to give a desired level of canopy closure

within 5 years of planting was presented. Results indicated planting densities of at least 2000

stems per hectare using the high percentage cover species resulted in a 80-90% canopy cover of

targeted indigenous tree and shrub species within 5 years. However, spacing trials were

recommended to provide refined estimates of canopy closure and weed control requirements.

Most woody indigenous plants raised in nurseries for revegetation are grown in containers such

as polythene planter bags PB2 or PB3 or similar size containers (Bergin and Gea 2005). Smaller

alternative containers such as rootrainers are an attractive option as they take less space and

potting material in the nursery, are lighter to transport, and can be more easily distributed around

the planting site. However, anecdotal evidence suggests that there may be more difficulties

achieving reasonable survival and growth rates where smaller seedlings are planted, particularly

on difficult sites. Early results from a current trial comparing larger PB container stock with

rootrainer stock on inland sites along riparian zones shows better survival and growth for several

indigenous shrub species tested (Colin Stace, Environment BOP, pers. comm.).

With planting stock, there are concerns with root distortion and the effect on plant survival,

growth and stability. Plants raised in containers are vulnerable to root distortion especially where

they are not ‘potted-on’ before they become root bound. In addition, distortion of roots can occur

where seedlings are incorrectly placed in pots, with leaving roots upturned during transplanting

the most common failure (Bergin and Gea 2005).

Building on existing knowledge and experience, trials that will provide practical revegetation

options for replacing weed infested areas dominated by blackberry with indigenous woody

species are required. This includes determining appropriate planting densities and the trade-off

with varying periods of weed maintenance, and a comparison of different nursery stock types to

improve plant performance on difficult sites.

OBJECTIVES

The overall objective is to provide guidelines on choice of planting stock and optimum planting

density and weed control requirements for difficult weed infested riparian sites in the Rotorua

district. The project comprises two trials – a plant spacing trial and a nursery treatment trial.

The objectives of the plant spacing trial are:

• To compare a range of planting densities for establishment of indigenous shrub hardwood

species used in revegetation of exotic brush weed infested riparian sites after mechanical

clearance.

• To determine optimum planting densities for revegetation with indigenous hardwood

shrub species on two typical sites in the Rotorua district.

• To compare weed control requirements between different planting densities of

indigenous shrub species

The objective for the nursery stock treatment trial is to compare growth performance of planted

seedlings raised under different propagation methods in the nursery.

5

PLANTING SITES

The trials are located across three different sites in the Rotorua district to cover a range of sites

typical of riparian revegetation sites in the region and local community input (Figure 1). The

plant spacing trial is located on two sites – Horohoro and Rerewhakaaitu. The nursery stock trial

is located on two sites – Rerewhakaaitu and Ngongotaha.

Horohoro site

This site on Parekarangi Trust land near Horohoro south of Rotorua is located approximately 6

km along State Highway 30 from the junction of this highway to State Highway 5. The site was

fenced off from grazing in 1990 and is typical of many riparian sites retired over the last 2-3

decades from grazing where early plantings of indigenous shrub species have been largely

overgrown by invasion of dense exotic brush weeds, particularly blackberry. The trial is located

within a 2.5 ha demonstration area near the state highway gently sloping northeast with scattered

springs draining into a stream that runs through the block.

Rerewhakaaitu site

Both the spacing trial and nursery treatment trial are located immediately adjacent to the

Rerewhakaaitu School near the junction of Rerewhakaaitu and Ash Pit Roads. The trial sites

comprise relatively flat pumice terraces that make up a wide riparian zone that runs into Lake

Rerewhakaaitu. This riparian area is for the most part a dry stream bed but occasional floods do

occur and a small stream is evident for short periods during wetter months. The dominant cover

before clearing for the trials was a mixture of broom on the higher drier terrace where the

spacing trial is located and dense blackberry and scattered willow on lower terraces near the

stream bed where most of the nursery treatment trial is located. The area was retired decades ago

although attempts at planting some natives has been attempted by the local community but

mostly failed. A small number of 2-3 m high kohuhu and totara were found are scattered during

clearing that were probably left over from earlier plantings.

Ngongotaha site

This site immediately adjacent to the Ngongotaha Stream approximately 3 km upstream and

from the Ngongotaha township had been recently fenced off from grazing. The site was in short

pasture that had been recently grazed before final exclusion of stock.

METHODS

Site preparation

Both the Horohoro and Rerewhakaaitu sites were sprayed with herbicide and mechanically

cleared by contractors. Clearing involved the use of a small rubber-tracked mulching unit and a

tracked 12 tonne excavator with long reach bucket. The details on spraying and mechanical site

preparation along with time taken and costs are provided in Whyte (2007).

Spraying of the site with herbicide followed by mechanical clearing left a consistent planting site

for the trials. The excavator cleared steep bank sites at both the Rerewhakaaitu and Horohoro

sites and the wet spring sites that occurred over much of the latter site.

Standard site preparation for the nursery treatment trial involved spot-spraying grass with

herbicide at the required plant spacings.

6

Figure 1: Location of the three planting trials in the Rotorua District – the plant spacing

trial at Horohoro and Rerewhakaaitu, and the nursery treatment trial at

Rerewhakaaitu and Ngongotaha.

7

Species

Three indigenous shrub hardwood species used extensively in revegetation programmes in the

Rotorua district were used for the spacing trials. These were:

Coprosma robusta karamu

Leptospermum scoparium manuka

Pittosporum tenuifolium kohuhu

The nursery treatment trial comprised one species rautawhiri (Pittosporum colensoi) which is

one of the main native shrub hardwood species planted in riparian zones and retired hill sites in

the Rotorua basin.

Manuka and kohuhu were categorised as high percentage cover species and karamu as medium

percentage cover species in the canopy cover model described in earlier work of Stace et al.

(2003).

All plants were raised in polythene planter bags PB3 at Treeline Nursery. Seedlings were one-

year-old when planted. All seedlings were bare-rooted immediately before planting as per

standard practice used by local community groups for plantings at the Awahou and Ngongotaha

Stream plantings (Jaap van Dorsser, pers. comm).

Trial design and treatments

Spacing trial

The trial consisted of two replicates at each of the two sites. Each replicate contained three

blocks each with a single spacing as follows:

• 1x1 m (10,000 stems per hectare)

• 1.4x1.4 m (5100 stems per hectare)

• 2x2 m (2500 stems per hectare)

Each replicate comprised approximately 20 m x 60 m rectangular blocks split into 3 sub blocks

for each spacing:

• 2 x 2 m spacing – 45 plants/species

• 1.4 x 1.4 m spacing – 48 plants/species

• 1 x 1 m spacing – 68 plants/species.

Within each spacing block, each of the three species were planted within single species stands

with adjacent blocks used as buffers where they are contiguous and with a single buffer planted

around all external boundaries. Species were allocated randomly within each spacing block as

Randomised Complete Block design. The trial for each species therefore comprised:

2 sites x 2 replicates x average 54 plants for each of 3 spacings = 648 plants/species

With 3 species, approximately 2000 seedlings were planted in the trial across both sites.

Allocation of species to each planted block is given in Appendix 1 for both planting sites. Trial

layout for the spacing trial at Rerewhakaaitu is given in Figure 2 and at Horohoro in Figure 3.

Figure 2: Trial layout for the spacing trial at Rerewhakaaitu. Three species were planted at three densities. Species are K – karamu;

P – Pittosporum; M – manuka.

Figure 3: Trial layout for the spacing trial at Horohoro. Three species were planted at three densities. Species are K –

karamu; P – Pittosporum; M – manuka.

Nursery treatment trial

Jaap van Dorsser has been working with Dianne Edmonds of Treeline Nurseries, Kaharoa, for 12

months to produce a line of rautawhiri seedlings using several nursery raising treatments. Seed

for all treatments was collected from the same location and prepared and sowed using standard

nursery procedures.

The nursery treatments comprised various combinations of:

• containers (Hillsons rootrainers, polythene planter bags PB3),

• bare-root seedlings produced in open nursery beds,

• with and without application of a copper chemical coating to the inside or containers to

reduce root growth near edges of containers, and

• preparation of root systems immediately prior to planting (root treated).

As per standard practice, newly germinated seedlings were transplanted from seed trays into

small containers which were Hillson rootrainers. When approximately 15-20 cm high, seedlings

were transferred to either PB 3 polythene bags or lined out in open nursery beds for bare-root

production with various combinations of copper.

There were 5 treatments with a full complement of seedlings and 2 additional treatment

variations with a reduced sample of seedlings. The treatments were:

1. Rootrainer Hillsons with copper then lined out in open beds.

2. Rootrainer Hillsons then lined out in open beds.

3. Rootrainer Hillsons then potted into PB 3 then root systems bare-rooted prior to planting.

4a. Rootrainer Hillsons with copper then potted into PB 3 with copper.

4b. Rootrainer Hillsons with copper then potted into PB 3 with copper then root systems

bare-rooted prior to planting.

5a. Rootrainer Hillsons with copper then potted into PB 3.

5b. Rootrainer Hillsons with copper then potted into PB 3 then root systems bare-rooted prior

to planting.

A minimum of 200 seedlings were raised for each of the 5 main treatments.

The trial at each site had 10 replicates. Each replicate comprised 10 seedlings of each of the 5

main nursery treatments. For one site the trial consisted of:

5 nursery treatments x 10 seedlings x 10 replicates = 500 seedlings.

As part of the Randomised Complete Block design, treatments were assigned randomly with

each replicate. A split block design was used to accommodate the variations to treatments 4 and

5. Allocation of nursery treatments for each site are given in Appendix 1.

Each replicate comprised 50 seedlings planted on a uniform site planted in 5 lines of 10 trees

each. At 1.4 m spacing between plants, each replicate require a block that was 7 m x 14 m. The

total area required at each site to accommodate 500 seedlings was approximately 1000 m2 or a

block approximately 30 x 35 m. The trial was sited on a relatively uniform area at each site. Trial

layouts for Rerewhakaaitu and Ngongotaha are given in Figure 4 and Figure 5 respectively.

Figure 4: Trial layout for the nursery treatment trial at Rerewhakaaitu.

12

Figure 5: Trial layout for the Ngongotaha Nursery Treatment trial located on the true right bank of the Ngongotaha Stream

approximately half way between the Agrodome and the township.

13

Planting

Spacing trial

Seedlings preparation for the spacing trial involved removing seedlings from bags and carefully

washing most potting mix from the root system. This allowed roots to be inspected and any

distortion was removed or reduced by root pruning.

Planting occurred in mid 2005 using community groups. Animal repellent were applied as per

standard practices to deter animal browsing, particularly rabbits, even though pest control was

undertaken at both sties.


Nursery treated plants were planted in early spring 2006 at two well prepared riparian sites in the

Rotorua basin typical of revegetation sites in the region - Rerewhakaaitu and Ngongotaha. Both

sites had been mechanically cleared of blackberry and willow. Plant spacing was 1.4 x 1.4 m

(5000 stems per ha). 500 seedlings (100 of each main nursery treatment) was available for each

site.

Maintenance

Maintenance at both sites involved spraying grass regrowth with glyphosate and brush weeds

with grazon. at both sites… Joe….and Kolleen…

Fertiliser application at Rere…

Monitoring

For the spacing trial, emphasis was on quantifying degree of canopy cover, and hence weeds

suppression that would occur at the different stocking rates for each species. For the nursery

treatment trial, assessment focussed on determining differences in growth performance based on

differences in nursery stock treatments.

For both the spacing and nursery treatment trials, planting height and plant cover (length x

breadth) were measured for a minimum sample of all planting stock by species to provide a

baseline on which to determine growth rate.

Sites were inspected regularly by local community groups after planting to record early mortality

and determine possible causes such as browsing by rabbits or hares, disturbance by recreational

users, and most importantly, competing weed growth.

A full survival and plant growth assessment was carried out approximately one and two years

after planting for the spacing trial and one year after planting the nursery treatment trial. The

major parameters to be measured were:

- survival

- plant height (in cm)

- plant cover – length and breadth of the live crown of each plant (in cm)

- subjective assessment of plant vigour and health as one of five categories:

1 - very unthrifty - few or no leaves, just alive

2 - unthrifty - loss of leaves, poor foliage colour and plant vigour

3 - average - moderate health and vigour

4 - good - minor browsing or leaf discolouration, otherwise good growth

5 - excellent - healthy plant with good foliage colour and growth

- comments - any addition information on plant condition (eg., browsing)

14

The subjective assessment of plant vigour and health was based on a comparison of seedling

condition within each species, not between species. Dead seedlings wre entered as a dash (-).

Plant growth assessments were entered onto a customised Scion Field Record Forms (Appendix

2). All seedlings were identified and measured separately. This not only allowed for the history

of each seedling to be followed but also enabled a more robust statistical analysis of the data

compared with using plot averages.

Field measurements were entered into the computer directly off field sheets for processing and

statistical analysis using standard techniques. Plant cover for each plant was calculated as the

square root of length x breadth.

Data analysis

Analysis of variance and least significant difference tests were used to determine statistical

significance of treatments in both the spacing trial and the nursery treatment trial at each site.

The factorial design for the nursery treatment trial has allowed an overall comparison of plant

performance one year after planting of the key factors that are tested in each of the seven

treatments. These are with and without the effect of copper application to containers, bare-rooted

seedlings vs container-grown seedlings, and with and without root treatment immediately prior

to planting.

RESULTS

Spacing trial

Overall there was good survival for all species at the Rerewhakaaitu site (Fig. 6) compared with

the Horohoro site (Fig. 7). Of the three species planted, karamu survival was significantly less at

the Horohoro site with only 50% surviving one year after planting and dropping to 40% survival

after two years (Appendix 3). Both manuka and kohuhu achieved over 80% survival at both sites

after one year although significant mortality of manuka occurred at both sites between the first

and second year after planting. By the end of the second year, kohuhu had maintained close to

90% survival at both sites.

0

10

20

30

40

50

60

70

80

90

100

Karamu Manuka Kohuhu

Survival (%

)

2006

2007

Figure 6: Survival of each species planted in the spacing trial in mid-2005 at the

Rerewhakaaitu site.

15

0

10

20

30

40

50

60

70

80

90

100

Karamu Manuka Kohuhu

Survival (%

)2006

2007

Figure 7: Survival of each species planted in the spacing trial in mid-2005 at the Horohoro

site.

Compared to karamu, significantly taller planting stock of both kohuhu and manuka is reflected

in the significantly greater heights in the first and second years of growth after planting at both

sites (Appendix 3 & 4). Plant spread was also significantly lower for karamu at planting but this

trend did not continue after planting at the Horohoro site (Appendix 3) where all species had 80-

90 cm2 canopy spread at the end of the second year after planting.

Overall, average plant height was close to 1.2 m two years after planting for most species at both

sites and plant spread was 70-90 cm2 (Appendix 3 &4). Karamu height was significantly less

than the two other species at only 70 high at the Rerewhakaaitu site and 105 cm high at the

Horohoro site.

For those karamu that survived at the Horohoro site, height increment nearly doubled in the

second year to 45 cm compared to growth in the first year after planting (Fig. 8). Kohuhu and

manuka had similar height increments in the first year at around 35 cm although height

increment in the second year was up to 50 cm for kohuhu compared to less than 40 cm for

manuka.

0

10

20

30

40

50

60

Karamu Kohuhu Manuka

Height Increment (cm)

2005-06

2006-07

Figure 8: Height increment of each species planted in the spacing trial in mid-2005 at the

Horohoro site.

16

In contrast at the Rerewhakaaitu site, growth was poor in the first year for all species (Fig. 9).

Height increment for karamu did not improve in the second year and was significantly different

to that of kohuhu and manuka at this site (Appendix 4). Height increments for both kohuhu and

manuka at Rerewhakaaitu had improved to similar rates to that of the Horohoro site by the

second year.

0

10

20

30

40

50

60


Height increment (cm)

2005-06

2006-07

Figure 9: Height increment of each species planted in the spacing trial in mid-2005 at the

Rerewhakaaitu site.

Plant spread increment across all species at both sites one year after planting was similar at 15-

20 cm2 (Fig. 10 & 11). There was an increase in growth of crown spread for all species at both

sites in the second year after planting. However, this was not consistent across the two trial sites.

At the Horohoro site, karamu spread increment was significantly greater at over 60 cm2

compared to little more than half that for both kohuhu and manuka (Appendix 3). In contrast, at

the Rerewhakaaitu site, kohuhu spread increment increased to 40 cm2, significant greater than

the other species (Appendix 4).

0

10

20

30

40

50

60


Plant spread increment (cm

2)

2005-06

2006-07

Figure 10: Plant spread increment of each species planted in the spacing trial in mid-2005

at the Horohoro site.

17

0

10

20

30

40

50

60


Plant spread increment (cm

2)

2005-06

2006-07

Figure 11: Plant spread increment of each species planted in the spacing trial in mid-2005

at the Rerewhakaaitu site.

Across all species and at both sites, there was increasing plant spread over time (Fig. 12). Plant

spread almost doubled in the first year after planting and then doubled again in the second year

to reach around 80 cm2. There was however, no significant difference between spacing

treatments in both the first and second years after planting (Appendix 3 & 4). Similarly, there

were no significant differences in any of the species and plant spacing interactions tested.

0

10

20

30

40

50

60

70

80

90

2005 2006 2007

Plant spre

ad (cm

2)

1.4x1.4 m

1x1 m

2x2 m

Figure 12: Average plant spread for both trial sites across all species planted in the spacing

trial in mid-2005.

There were no significant differences for plant vigour between virtually all treatments and

treatment combinations at both sites (Appendix 3 & 4).

18

Nursery treatment trial The performance of the seven nursery treatments at both trials sites is given in Appendix 5 for

survival, plant spread and height, spread increment and height increment, and plant vigour. There

was significant variability in both plant height and spread at planting between treatments which

have contributed to these preliminary results. However, this initial variability does not account

for all the variation between factors.

Significant differences occurred between most parameters measured across the seven nursery

treatments (Appendix 5). To simplify interpretation of these differences, results of growth

performances are summarised based on the three key factors tested – containers vs open-grown

seedlings (Fig. 13), effect of application of copper to containers vs no copper application (Fig.

14), and the effect of root treatment of seedlings immediately before planting vs planting

seedlings straight from the container (Fig. 15).

Approximately one year after planting, performance of containerised stock was in general better

than for open-grown stock (Fig. 13). Survival, height increment, and spread increment were

significantly greater for container-grown seedlings compared to open-grown stock at the

Ngongotaha trial site. While differences were not always significant for parameters assessed at

the Rerewhakaaitu site, there was a similar trend of better performance of potted seedlings

compared to bare-root seedlings.

The use of a copper coating on the inside of containers significantly affected growth of seedlings

at both sites (Fig. 14). There was no difference in survival between those seedlings raised with

copper treatment compared to those not treated. Height increment was up to 10 cm less for

seedlings treated with copper one after planting compared to seedlings without copper.

Of the three factors tested, root treatment, whereby potted seedlings were bare-rooted

immediately before planting, showed the greatest effect on growth one year after planting. Root

treatment significantly reduced growth of both height and crown spread compared to

containerised seedlings that were planted directly into the ground (Fig. 15). This was particularly

pronounced at the Ngongotaha trial site where there was at least 15 cm increase in height

increment and 10 cm2 increase in spread increment with directly planted containerised stock

compared to seedlings that were root treated.

DISCUSSION

Spacing trial

While survival was high for all species at the Rerewhakaaitu site, growth in terms of plant height

and spread was significantly less than at the Horohoro site reflecting the colder more exposed

conditions of that site. Plants at the Rerewhakaaitu site, in particular karamu, had upper crown

foliage browned with considerable purple coloured foliage on most plants, evidence of probably

heavy frosting or cold winds or both. Survival of karamu at Horohoro was severely affected at

the end of one replicate due to rabbit browsing that occurred soon after planting.

19

0

10

20

30

40

50

60

70

80

90

100

Ngongotaha Rerewhakaaitu

Survival (%

)

Containers

Open grown

0

10

20

30

40

50


Height increment (cm

)

Containers

Open grown

0

10

20

30

40

50


Spread increment (cm

2)

Containers

Open grown

Figure 13: Survival, height increment and plant spread increment of seedlings raised in

PB3 planter bag containers compared to seedlings raised as open-grown plants in tractor-

prepared nursery beds.

20

0

10

20

30

40

50

60

70

80

90

100


Survival (%

)

No copper

Copper coating

0

5

10

15

20

25

30

35

40

45

50



No copper

Copper coating

0

5

10

15

20

25

30

35

40

45

50


Spread increment (cm)

No copper

Copper coating


containers treated with a copper coating applied to the inner surfaces to deter root

distortion compared to containers without copper treatment.

21

0

10

20

30

40

50

60

70

80

90

100


Survival (%

)

Containers

Root treated

0

10

20

30

40

50



Containers

Root treated

0

10

20

30

40

50


Spread increment (cm

2)

Containers

Root treated


containers and then root treated involving immediate pre-plant removal of most potting

mix and remedial treatment to ensure root system distortion is minimised compared to

container-grown seedlings planted without root treatment.

22

While rapid height growth is important in the first year so that planted seedlings have less

likelihood of being overtopped by vigorous weed growth, vigorous growth of plant spread is

desirable as this will lead to more rapid canopy cover and thereby suppression of problems

weeds. While height growth of karamu was the least of the three species tested in the spacing

trial at both sites, it has a more spreading habit reflected in the significantly higher spread

increment (Appendix 3). Karamu was, however, categorised as a moderate canopy cover species

by Stace et al. (2003) compared to kohuhu and manuka which were identified as high percentage

cover species.

Two years after planting, the average plant spread across all three species of 70-90 cm2 is

resulting in near canopy closure where planting density was highest at 10,000 stems per ha.

Crowns of many seedlings at these spacings of 1x1 m were beginning to overlap. This is

consistent with other studies with expected time to canopy closure for shrubs about two years

after planting at this density (Bergin and Gea 2007). Tree crowns in both the Rerewhakaaitu and

Horohoro spacing trials planted at the high density of 10,000 stems per hectare would be

expected to overlap within the third year after planting where there has been good survival.

Near canopy cover at the lower densities of 5100 stems per hectare (1.4x1.4 m spacing) and

2500 stems per hectare (2x2 m spacing) will be expected to take 3 and 4 years respectively for

shrub hardwoods (Bergin and Gea 2007). These lower plant densities still have a high proportion

of ground requiring weed control. The high level of weed control over the first two years at both

sites has resulted in no losses of planted seedlings to invasion of exotic grass or brush weeds.

More intensive weed control at the Rerewhakaaitu site is being carried out compared to the

Horohoro site where herbicide spraying stopped approximately 18 months after planting. The

Horohoro site is now dominated by rank exotic grass between particularly where the lower plant

densities occur and where mortality has occurred. The tops of most of the planted seedlings at

least 1 m high are above grass height and do not appear to be negatively affected. There is

virtually no blackberry, gorse or other problem weed invasion 2 years after planting.

Site effects have contributed to the differing performances of each trial at Rerewhakaaitu and

Horohoro. These include heavy frosts and exposure to southerly winds at the Rerewhakaaitu site

that has contributed to dieback of plant growing tips for karamu and manuka. At the Horohoro

site, karamu in one block was damaged by rabbit browsing soon after planting and contributed to

the higher mortality of this species compared to the other species at this site. The Horohoro site

was highly variable with numerous scattered springs draining throughout the site resulting in

variable growth performance of planted seedlings.


Most indigenous trees and shrubs are raised in containers to meet the demand of a diverse market

that requires relatively small quantities of several species for planting programmes. While

methods for successfully raising most indigenous trees and shrubs have been demonstrated

(Forest Research Institute 1980), nearly all planting stock is raised in containers of various types.

A major concern with containerised seedlings is the distortion of the root systems which are not

easily inspected during planting. The nursery treatment trial is evaluating a range of practical

methods that could reduce root distortion in potted seedling compared to open-grown seedlings.

With only one year after planting, however, only preliminary conclusions can be drawn from the

results. Containerised seedlings performed better than bare-rooted stock one year after planting.

While the application of copper to the interior surfaces of containers has deterred root

development in contact with the container, there appears to be an early detrimental effect on

height growth in particular. Preliminary results indicate that preparing containerised seedlings

23

for bare-root planting is having a major effect on both height and crown growth. In general,

although growth was affected by these factors, survival remained high for all treatments after one

year.

This trial will require ongoing monitoring to determine if these trends continue.

ACKNOWLEDGEMENTS

Russell Whyte (AgTech formerly PGG Wrightsons Consulting) was Project Manager and

provided the project brief and organised site selection, site preparation, planting and maintenance

with assistance from Clinton Hemana (PGG Wrightsons Consulting). Jaap van Dorsser organised

the root treatments for the spacing trials with assistance from local community groups and

landowners. Jaap also worked with Treeline Nursery and Ngongotaha Nursery to raise seedlings

for the nursery treatment trial. The local community and landowners at Rerewhakaaitu, the

managers and owners of the Parekarangi Trust Block at Horohoro, and the community at

Ngongotaha assisted with the establishment of the trials and ongoing maintenance. Joe

Warmerdam has undertaken regular weed control of the trial sites and surrounding areas at

Rerewhakaaitu and Michael Bergin carried out the weed control at the Horohoro site. Graphics

was undertaken by John Smith (Scion) and Michael Bergin. Michael Bergin measured all trials

and entered data for statistical analysis by Mark Kimberley (Scion). Photographs are by Jonathan

Barran Photography. The project was funded by the Ministry of Agriculture and Forestry’s

Sustainable Farming Fund.

REFERENCES

Bergin, D.; Gea, L. 2007: Native trees – planting and early management for wood production.

New Zealand Indigenous Tree Bulletin No. 3. Revised Edition. New Zealand Forest

Research Institute, Rotorua. 44p.

Beveridge, A. E.; Bergin, D. O.; Pardy, G. F. 1985: Planting podocarps in disturbed indigenous

forest of the central North Island. New Zealand Journal of Forestry, 30 (1): 144-58.

Beveridge, A. E.; Pardy, G. F.; Bergin, D. O. 1987: Guidelines for planting native trees. Forest

Research Institute Project Record No. 1783. (Unpubl.). 17p.

Evans, B. 1983: Revegetation manual using New Zealand native plants. Queen Elizabeth

National Trust.

Forest Research Institute 1980: Raising native trees. Forest Research Institute, What’s New in

Forest Research No. 85. 4p.

Pollock, K. 1986: Plant materials handbook for soil conservation. Volume 3: Management and

used of native plants for soil conservation. Water and Soil Conservation Publication No.

94.

Stace, C.; Bergin, D.O.; Kimberley, M.O. 2003: Assessment of native revegetation plantings for

catchment protection in the Bay of Plenty. Environment Bay of Plenty Operations

Publication 2003/03. Whakatane. 37p.

Whyte, R. 2007: Riparian restoration demonstration and extension. Farmers of the Central

Plateau Sustainable Farming Fund project 03/065. Final Report. 11p.

24

Appendix 1 – Random allocation of nursery treatments to planting rows for each trial site.

Refer to text for trial design and treatment details.

Rerewhakaaitu trial Ngongotaha trial Replicate Planting

Row Treatment Split treatment Treatment Split treatment

1 1 2 2

2 1 3

3 4a 4b 5b 5a

4 3 4b 4a

5 5b 5a 1

2 1 1 4a 4b

2 2 5b 5a

3 5b 5a 3

4 4b 4a 1

5 3 2

3 1 5b 5a 1

2 4b 4a 5b 5a

3 2 4a 4b

4 1 2

5 3 3

4 1 2 1

2 3 5b 5a

3 5a 5b 4a 4b

4 1 2

5 4b 4a 3

5 1 2 5b 5a

2 3 2

3 4a 4b 3

4 1 4a 4b

5 5a 5b 1

6 1 2 2

2 5b 5a 4a 4b

3 3 5a 5b

4 1 1

5 4b 4a 3

7 1 3 5b 5a

2 2 4b 4a

3 5b 5a 1

4 4a 4b 2

5 1 3

8 1 2 1

2 4b 4a 4b 4a

3 5a 5b 2

4 3 5a 5b

5 1 3

9 1 3 5b 5a

2 4b 4a 1

3 1 3

4 2 4a 4b

5 5a 5b 2

10 1 1 4a 4b 2 4a 4b 3

3 3 5b 5a

4 2 2

5 5a 5b 1

25

Appendix 2 – Field sheet used for annual measurement of planting trials to record height (H), plant spread (length L x width W), plant vigour

(V), and any additional comments.

Trial Site Planted 2005

Recorder

Plot Plant Date Date Date

Block Spacing Species No. H L W V Cmts H L W V Cmts H L W V Cmts

Block = 1, 2; Plot spacings 1=1x1m, 2=1.4x1.4m, 3=2x2m; species K=karamu, P=pittosporum, M=manuka Vigour scores 1=poor, 2=unthrifty,3=average, 4=good, 5=excellent

26

Appendix 3 – Growth performance of the spacing planting trials for karamu, kohuhu and manuka established in mid-2005 at Parakarangi

Station, Horohoro, near Rotorua. Values within each growth performance factor with the same letter are not significant at the 95% level

(p=0.05).

Survival 2006 (%)

Survival 2007 (%)

Height 2005 (cm)

Height 2006 (cm)

Height 2007 (cm)

Height increment 2005-06 (cm)


Plant spread 2005 (cm

2)


2)


2)

Plant spread

increment 2005-06 (cm

2)

Plant spread


2)

Plant vigour 2006 (1-5)*


Species

Karamu 49b 41c 31b 55b 105b 24b 46a 22b 38a 93a 15a 52a 3.2b 3.7a

Kohuhu 95a 92a 41a 74a 126a 34a 50a 26a 47a 83a 21a 35b 3.5ab 3.9a

Manuka 86a 75b 40a 77a 119a 36a 39a 25a 45a 78a 20a 31b 3.9a 3.9a

Spacing

1.4x1.4 m 83a 78a 38a 71a 117a 33a 45a 24a 46a 86a 21a 39a 3.6a 3.8a

1x1 m 73a 65a 37a 77a 128a 38a 47a 24a 47a 85a 23a 35a 3.5a 3.9a


Species x spacing

Karamu 1.4x1.4 m 57a 55a 31a 63a 115a 32a 52a 22a 48a 107a 25a 59a 3.7a 4.3a



Kohuhu 1.4x1.4 m 97a 96a 41a 70a 120a 29a 49a 26a 46a 80a 20a 34a 3.5a 3.7a



Manuka 1.4x1.4 m 91a 80a 40a 76a 115a 36a 37a 25a 44a 79a 20a 33a 3.8a 3.7a



* Vigour scores 1=poor, 2=unthrifty,3=average, 4=good, 5=excellent

27

Appendix 4 – Growth performance of the spacing planting trials for karamu, kohuhu and manuka established in mid-2005 at Rerewhakaaitu

Recreational Reserve. Values within each growth performance factor with the same letter are not significant at the 95% level (p=0.05).

Survival 2006 (%)

Survival 2007 (%)

Height 2005 (cm)

Height 2006 (cm)

Height 2007 (cm)




2)


2)


2)

Plant spread


2)

Plant spread


2)



Species

Karamu 81b 77a 31b 48b 70b 17b 21c 22b 43a 72b 21a 28b 2.9a 3.5b

Kohuhu 90ab 88a 41a 66a 115a 25ab 48a 26a 49a 90a 23a 41a 3.4a 4.1a

Manuka 95c 81a 40a 69a 116a 29a 43b 25a 42a 74b 18a 30b 3.2a 3.1c

Spacing

1.4x1.4m 89a 81a 37a 61a 105a 24a 42a 24a 43a 84a 19a 38a 3.1a 3.7a

1x1m 87a 81a 37a 59a 97a 21a 37a 24a 43a 72a 19a 28a 3.1a 3.5a


Species x spacing

Karamu 1.4x1.4m 80a 74a 31a 47a 77a 16a 28a 22a 43a 80a 20a 36a 2.9a 3.7a


2x2m 83a 82a 31a 51a 75a 20a 24a 22a 47a 79a 25a 31a 3a 3.4a

Kohuhu 1.4x1.4m 91a 90a 41a 65a 115a 24a 50a 26a 47a 93a 21a 46a 3.3a 4.1a


2x2m 93a 90a 41a 68a 116a 27a 48a 26a 51a 97a 25a 46a 3.5a 4a

Manuka 1.4x1.4m 97a 78a 40a 70a 119a 29a 45a 25a 41a 76a 16a 32a 3a 3.2a

1x1m 93a 82a 40a 65a 111a 24a 45a 25a 40a 69a 16a 27a 3.2a 3a


* Vigour scores 1=poor, 2=unthrifty,3=average, 4=good, 5=excellent

28

Appendix 5: Performance of the Nursery Treatment trial at the Ngongotaha and Rerewhakaaitu sites. Values within each growth

performance factor with the same letter are not significant at the 95% level (p=0.05).

Ngongotaha Trial Site Nursery Treatment*

Survival 2007 (%)

Plant spread at planting 2006 (cm

2)


2)

Plant spread

increment 2007 (cm

2)

Height at planting 2006 (cm)

Height 2007 (cm)

Height increment

2007 (cm)

Vigour 2007 (1-5)†

1 RT with Cu then open grown 68c 12d 35d 23b 32d 64c 33b 2.6c

2 RT then open grown 86ab 15c 52d 36a 31ab 77ab 46a 3.3abc

3 RT then PB3 then root treated 81b 16c 40cd 24b 32cd 65c 33b 2.9bc

4a RT with Cu, then PB3 with Cu 96a 19a 54a 35a 35a 81a 46a 3.4abc

4b RT with Cu, then PB3 with Cu, then root treated 92ab 18ab 45bc 27b 38bc 72b 35b 4.1a

5a RT with Cu then PB3 90ab 17abc 55a 38a 35a 84a 49a 3.7ab

5b RT with Cu, then PB3, then root treated 92ab 17bc 42c 25b 35c 65c 30b 2.9bc

Rerewhakaaitu Trial Site

Nursery Treatment*

Survival 2007 (%)

Plant spread at planting 2006 (cm

2)


2)

Plant spread

increment 2007 (cm

2)

Height at planting 2006 (cm)

Height 2007 (cm)

Height increment

2007 (cm)

Vigour 2007 (1-5)†

1 RT with Cu then open grown 82b 12d 40e 29c 32d 68cd 37b 3.2c

2 RT then open grown 95a 15c 54abc 38a 31d 80a 49a 3.8a

3 RT then PB3 then root treated 96a 16c 45de 29c 32cd 68d 35b 3.4bc

4a RT with Cu, then PB3 with Cu 94a 19a 55ab 36ab 35abc 77ab 41b 3.7ab

4b RT with Cu, then PB3 with Cu, then root treated 96a 18ab 49cd 30bc 38a 75abc 37b 3.5abc

5a RT with Cu then PB3 94a 17abc 56a 39a 35bc 81a 47a 3.8a

5b RT with Cu, then PB3, then root treated 100a 17bc 49bcd 33bc 35ab 72bcd 37b 3.7ab

* Nursery Treatments: RT=root trainer; PB3=polythene bag container; open grown=seedlings grown in nursery beds as bare-root; Cu=copper coating to containers; root treated=seedlings removed from containers before planting and potting mix washed off

† Vigour scores 1=poor, 2=unthrifty,3=average, 4=good, 5=excellent

29

Field-based workshops for local community and farmers allowed sharing of ideas for the

proposed revegetation trials in weed-infested riparian areas at both the Horohoro and

Rerewhakaaitu sites. Practical suggestions for site preparation, planting and weed control

were incorporated into the trials for evaluation.

30

Site preparation at both the Rerewhakaaitu and Horohoro sites involved the use of an

excavator for clearing steep banks and tractor mounted mulching unit to clear and mulch

sites covered in blackberry up to 4 m high. The blackberry stands had been sprayed prior

to clearing. The mulching unit (inset) left an even textured mixture of topsoil and mulched

vegetation that was relatively easy to plant into.

31

Planting of spacing trial was undertaken by the local landowners and community at each

site – Horohoro (above) and Rerewhakaaitu (below)

32

The spacing trial was established at two sites – Rerewhakaaitu (above) and Horohoro

(below). The trial at each site comprised 2 replicates with 3 indigenous shrub species

commonly used in riparian planting programmes in the Rotorua regions (karamu,

manuka, kohuhu) planted in blocks at 3 different densities (10,000 spha, 5100 spha, 2500

spha).

33

Plant densities of 10,000 spha (1x1 m plant spacing)

Plant densities of 5100 spha (1.4x1.4 m plant spacing)

Plant densities of 2,500 spha (2x2 m plant spacing)

The spacing trial comprised randomised blocks of 3 planting densities. These photographs

were taken approximately 1 year after planting.

34

Maintenance involved spraying of grass and woody brush weeds including gorse and

blackberry on a 1-3 monthly basis to ensure planted indigenous seedlings were kept free of

competing weed growth. The Rerewhakaaitu site in particular (below) has been kept

completely weed free with regular spraying by the local landowner Joe Warmerdam.

35

Nursery treatment 1 – seedlings grown in open bed as bare-root transplants

Nursery treatment 3 – Seedlings raised in PB3 planter bags then root treated

Root treatment involved removing seedlings from the container and washing away most

potting mix and checking root system for distortion and undertaking remedial pruning

where required. This technique developed by Jaap van Dorsser has been successfully used

to plant thousands of seedlings in community revegetation programmes along the Awahou

and Ngongotaha streams.

36

Nursery treatments 4a – seedling transferred from a root trainer treated with copper to a

PB3 planter bag also treated copper.

Nursery treatment 4b – seedling treated as for 4a but then root treated before planting

There is a significant difference to the root ball for these two seedling treatments where

copper applied to the interior of the polythene planter bag (upper) has prevented the roots

from circulating around the container. This technique developed by Jaap van Dorsser is

being trialled to determine a practical method for avoiding root distortion in potted

seedlings.

37

Nursery treatment 5a – Rootrainer with copper treatment before transplanting to PB

planter bag without copper

Nursery treatment 5b – Rootrainer with copper treatment, then transferred to PB3 planter

bag without copper, then root treated immediately before planting to remove potting mix

establishment and early performance of planting trials...

Documents