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Technical Article No. 10.2

Performance of PlantedNative Conifer Trees

SINTRODUCTION

everal of our highest profile native conifer trees inNew Zealand are amongst our most widely plantednative timber tree species. Tãne’s Tree Trust (TTT) hasrecently completed a survey of native tree plantationsthroughout the country. Growth and stand managementinformation on the performance of significant plantingsof native tree species has been collated and included inthe Tãne’s Tree Trust Indigenous Plantation Database.Details on the survey and the database are givenin Technical Article No. 10.1 in this handbook.

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There is increasing interest in establishing a resource ofnative tree species as a future specialty wood supply,especially the major native conifer trees. Many of theseconifers have been widely utilised in the past and continueto be highly prized for their valuable wood propertiesand uses.

This article provides a summary of the growthperformance of native conifer trees planted throughoutNew Zealand. Growth models for both height anddiameter have been developed based on selected standsfrom the TTT Indigenous Plantation Database and theplantation surveys.

MEASUREMENT OF STANDS

Most of the plantations identified in the recent surveywere inspected and trees assessed for growth. PermanentSample Plots (PSPs) or inventory growth plots wereestablished within representative areas within most plantedstands of known age and management history. Themethods for establishing PSPs followed those of Ellisand Hayes (1997). This data has been added to otherdatasets, including a survey by the Forest Research Institutein the mid-1980s (Pardy et al. 1992).

DBH (diameter at breast height – 1.4 m above groundlevel) of all planted trees within plots were recorded andheights measured for a minimum sample of 12 trees perplot using a Vertex. Stand stocking was calculated frombounded plots of know area and estimates of stemdensity of non-bounded inventory plots was calculatedusing a minimum of 30 intra-tree distances within stands.

Site factors and the history of site and stand managementwas collated from owners and managers, or from earlyarchives of plots established by the former New ZealandForest Service or the Forest Research Institute. Datasetsfrom both the earlier plantation survey and the recentTTT survey were combined. The combined datasetincludes a small number of stands that were remeasuredduring both surveys and where individual trees could berelocated.

Measuring thediameter at breastheight of a 32-year-oldplanted kauri in one ofmany kauri plantationsassessed in the upperNorth Island.

Stands of 48-year-old rimu (above) and totara (below), Holt’sForest Trust, northern Hawkes Bay.

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Conifers make up the bulk of native tree species measured,comprising over half of the nearly 10,000 trees in theTãne’s Tree Trust Indigenous Plantation Database (Table1). These are spread over 270 plots established in eithersingle-species stands, mixed species stands, scattered plotssuch as in established gardens, or as single or multi-rowshelterbelts.

Stands were located in virtually every region of NewZealand from Northland to Southland and from lowlandcoastal sites to inland sites over 500 m above sea level.Stand density average 2200 stems per ha and ranged fromonly 200 stems per ha to over 5000 stems per ha. Veryfew plantations had been pruned or thinned, with themost common treatment being only a low pruning forimproved access.

The conifers most commonly planted nationwide included:- Totara – Podocarpus totara- Kauri – Agathis australis- Rimu – Dacrydium cupressinum- Kahikatea – Dacrycarpus dacrydioides

Stand selection for modelling

Many of the conifers have been planted as single-species woodlotsor plantations on private land and in urban parks and most at aregular spacing. Wherever possible, data used for developing thegrowth models was restricted to those stands that had been plantedat regular spacing and which had minimal edge effects. Trees plantedin the open or on edges will have significantly faster diametergrowth, in particular, due to less competition compared to treesgrowing within plantations where stand densities can be determined.

GROWTH MODELS

SPECIES AND NUMBERS PLANTED

Table 1: Number of trees and plots by species within the Tâne’sTree Trust Indigenous Plantation Database.

Species

Totara

Kauri

Rimu

Kahikatea

Tanekaha

Kawaka

Miro

Matai

TOTAL

No. of trees

2072

1820

579

685

94

54

47

42

5393

No. of plots

82

70

35

32

14

8

8

21

270

A handful of three other conifers that had been plantedand were measured during the plantation survey includedtoatoa (Phyllocladus toatoa), Halls totara (Podocarpuscunninghamii) and kaikawaka (Libocedrus bidwillii).

Smaller numbers of other conifers planted included:- Tanekaha – Phyllocladus trichomanoides- Matai – Prumnopitys taxifolia- Miro – Prumnopitys ferruginea- Kawaka – Libocedrus plumosa

Consequently, stand edge trees, those planted inthe open, trees planted at wide spacings in scatteredstands such as in established gardens or urbanparks, and those native conifers planted asshelterbelts were excluded from the data used todevelop growth models. Growth modelling wastherefore based on a restricted number of plotsand trees that represented stands. For the fourmajor conifer species, this comprised23-47 plots and from 400 to nearly 1500 treesmeasured for diameter (Table 2). Mean age acrossall eight conifer species varied from 20-46 yearsalthough the age range across individual plantationsvaried from eight to over 100 years.

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Table 2: The number of plots and trees measured for each of the conifer species for only those plantations selected for developingthe height and diameter growth models.

Species name

Totara

Kauri

Rimu

Kahikatea

Tanekaha

Kawaka

Miro

Matai

No. plots

47

41

23

23

9

5

4

2

Height

538

641

281

281

37

25

5

4

DBH

1468

976

401

408

43

26

13

7

No. trees measured

Mean

46.3

32.4

39.4

29.5

33.6

20.8

32

41.3

Min

9

8

9

8

9

9

9

23

Max

102

84

84

78

64

30

55

55

Age (years)

Height/age cur ves

Plot mean heights along withfitted height/age regressioncurves for the eight coniferspecies are given in Figure 2 forthe individual species. This variedfrom 60-100 years of age for thedifferent species depending ondata available in the IndigenousPlantation Database.

Data analysis

Sigmoidal growth curves of the Bertalanfy-Chapmanform were fitted using nonlinear regression. Models wereobtained for mean height and mean DBH. Fits of modelsusing either separate slope or asymptote parameters foreach species were tested. For both height and DBH,models with separate asymptote parameters were fittedfor each species performed best. For the height model,an intercept of 0.5m representing height at planting wasused. For the DBH models, a zero intercept at age 4 yearswas used, this being the average age at which breast heightis achieved by native conifers.

The tallest conifers were kauri and kahikatea which averaged25 m at 80-90 years after planting (Figure 2). This wasfollowed by rimu at a mean height of 22 m 90 years afterplanting, then totara over 20 m at over 100 years afterestablishment. Of the minor conifer species, where datawas only available for 40-70 years, kawaka and tanekahahad similar growth trajectories to totara with miro andmatai the slowest growing conifers at 8 m and 11 m meanheight growth respectively 60 years after planting.

Mean annual height increment for the faster growingconifers kauri and kahikatea exceeds 30 cm for kauri andkahikatea, 20 cm for totara, and around 15 cm for theslowest growing conifers miro and matai.

miro

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Figure 1: Height/age regression curves for the conifersassessed from data in the TTT Indigenous Plantation Databasethat included the recent nationwide survey of native plantations.

Diameter/age curves

DBH/age curves up to 100 years are shown for theconifers in Figure 2 and the order of species in terms ofgrowth rate for DBH is the same as for height growth.Kauri has the fastest diameter growth rate exceeding 40cm within80 years of planting. This is followed by rimu and kahikateawhich have a similar diameter at 80 years of less than40 cm followed by totara at 35 cm but only when 100years of age after establishment.

The limited data on kawaka up to 30 years predicts DBHof 20 cm but with a growth rate on a similar trajectoryto tanekaha and totara. The smaller and younger datasetsfor matai and miro indicate significantly slower diametergrowth rates (Figure 2).

Figure 4: Mean DBH/age regression curves to age 110 yearsfor the conifers based on growth data collated in the TTTIndigenous Plantation Database.

Mixed conifers, Awhitu, Auckland

Rimu and tanekaha, Cornwall Park, Auckland

Above: Mixed conifers, Whahtwhata, WaikatoBelow: Pruned totara, Northland

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Predicted height and diameter growth

The predicted height and diameter of each of the eightconifers species for selected periods up to 80 years sinceplanting is indicated in Table 3. These predictions arelargely restricted to within the limits of the data so theydo not extend beyond 40 years for the limited numberof stands assessed for kawaka, miro and matai.

Periodic mean annual height increments based onheight/age curves for the tallest conifers kauri andkahikatea after 80 years average 30 cm. This is somewhatslower than they were growing at 40 years after plantingwhere their periodic mean annual height increment was37 cm. Rate of height growth usually slows with age withmaximum growth often recorded when trees are in the20-40 year-old pole phase.

Rimu, totara and tanekaha are predicted to have 22-25cm annual height growth at the 80 year period afterplanting, and again these growth rates are slower than atthe 40 year period. Kawaka, miro and matai have annualheight growth increments after 40 years of 29, 22 and 18cm respectively.

Mean periodic annual diameter increment for the fastergrowing conifers average 5-6 mm for kauri, rimu andkahikatea, less than 5 mm for totara 80 years afterestablishment. Growth rate is slowing compared to the7 mm annual increment at the 40 year period suggestingmany of the stands are over-stocked and require thinningto maintain good diameter growth. Only a 3 mm meanannual increment was predicted for the slowest growingconifers miro and matai at the 40 year period after planting.

Table 3: Predicted height (m) and DBH (cm) for eight native conifer species from the growth models developed for each speciesbased on the assessment of native plantations in the nationwide survey.

Matai

2.03.76.8

3.46.511.1

Age (yrs)

10204080

10204080

Kauri

3.97.814.724.4

9.217.329.743.2

Rimu

3.56.812.721.0

8.616.327.940.6

Kahikatea

3.97.714.423.9

8.415.927.239.6

Totara

3.26.111.418.9

7.113.523.133.7

Tanekaha

3.05.910.918.0

6.211.820.229.4

Kawaka

3.16.111.4

6.812.821.9

Miro

2.64.99.0

4.58.514.5

HEIGHT (m)

DIAMETER (cm)

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CONCLUSIONS

The most popular native conifers for plantingcontinue to be totara, rimu, kauri and kahikatea.This is particularly the case where the objective isto provide a sustainably managed native forestwith potential as a long-term timber resource.

Mean annual diameter growth rates of 5 mm and30 cm for height for the faster growing conifersmeasured in this latest survey are similar to thosereported elsewhere for planted stands of native trees(Pardy et al. 1992). However, variability betweenindividual stands across all species is substantial dueto the wide range of site and climatic factors thatoccur between stand locations.

There are also significant differences in standcharacteristics, particularly stocking, that can influencegrowth. Many of the stands in the survey were notwell managed after planting so that growthperformance particularly within 5-10 years of plantingis likely to have been seriously compromised. Noplanted stands were thinned after planting and thisis reflected in the slowing diameter growth rateacross all species in all highly stocked older plantations.Consequently, these average growth rates do notnecessarily reflect the true potentials of each of thenative conifer species.

ISSN 2230-3014 2011

Printed by Scion Digital Print Centre, Rotorua

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References

A 60-year-old kakahikatea plantation, Mair Park, Whangarei.

The Ministry of Agriculture and Forestry does notnecessarily endorse or support the content of thepublication in any way.

Ellis, J.; Hayes, J. Field guide for sample plots in New Zealandforests. New Zealand Forest Research Institute, Rotorua.FRI Bulletin No. 186. 84p. (1997).

Pardy, G. F.; Bergin, D. O.; Kimberley, M. O. Survey ofnative tree plantations. Forest Research Institute BulletinNo. 175. 24p. (1992).

Contact: Tãne’s Tree TrustWebsite: www.tanestrees.org.nz

Authors: David Bergin and Mark Kimberley, Scion