performance of planted native shrubs
TRANSCRIPT
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T e c h n i c a l H a
n d b o o k S e c t i o n 1 0 : N
a t
i v e
T r e e
P l a n t a t
i o n s
1 0 . 4
P e r f o r m
a n c e o f P l a n t e d N a t i v e S h r u b s
Technical Article No. 10.4
Performance of
Planted N ative S hrubs
M
IN TRO DUCTIO N
The use of quick-growing, generally hardy shrub species
is a favoured m ethod for providing shelter on an exposed
site and a canopy cover to reduce the time needed for
weed control. These hardy early successional species
also tend to be those that are less expensive to raise as
seedlings com pared to m ost native tree species.Consequently, many native revegetation programmes
throughout New Zealand initially focus on establishing
a cover of shrubby vegetation using a selection of hardy
species.
In a recent survey of native plantations by Tane’s Tree
Trust, a selection of early successional native shrub and
small tree species of know age since planting were
assessed for growth. This article provides an indication
of the growth rates of a range of the hardy native
species m ost often used to provide initial cover in
revegetation programm es on open sites including a
generic growth m odel across the m ore com m only
planted native shrubby species
illions of seedlings of a range of com mon hardy
pioneer species are raised in nurseries for planting
throughout New Zealand each year. This often includes
revegetation of riparian areas in pastoral landscapes
and establishm ent of native vegetation on erosion-
prone steep hill country that once was forested.
M ost of the native conifer and hardwood tree species
establish naturally am ongst pioneer vegetation which
provides initial protection from extrem es of climate
(Bergin and Gea 2007). Planting of a cover of hardy
species in advance of establishing selected native tree
species found in high forest can mimic this process of
natural succession. M any native
tree species favoured for
timber production grow
slowly in early years, but
performance of som e
is improved when
planted within shelter.
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Table 1:Predicted height and root collar diameter (RCD) for shrub and small tree species based on the assessment of planted
native stands in the nationwide Tane’s Tree Trust survey. Order is based on the fastest mean height growth in the first 10 year period.
1020
40
10
20
40
10
20
40
10
20
40
10
20
40
10
20
40
10
20
40
10
20
4010
20
40
10
20
40
10
20
40
10
20
40
10
20
40
10
20
40
10
20
40
Age
interval
(years)
5.17.8
11.1
4.9
7.4
10.5
4.8
7.3
10.4
4.7
7.1
10.1
4.6
6.9
9.8
4.6
6.9
9.8
4.5
6.8
9.7
4.4
6.6
9.34.4
6.6
9.3
4.2
6.3
8.9
4.1
6.1
8.6
4.0
5.9
8.4
3.9
5.9
8.3
3.4
5.1
7.1
3.1
4.6
6.4
Height
(m)
5137
28
49
37
25
48
36
25
47
35
25
46
35
22
46
35
24
45
34
24
44
33
2344
33
24
42
32
21
41
30
21
40
30
22
39
30
21
34
25
18
31
23
16
Height
increm ent
(cm)
13.720.3
21.3
12.4
18.4
19.3
11.3
16.7
17.5
9.2
13.7
14.4
10.0
14.8
15.5
13.3
19.7
20.7
11.6
17.2
18.0
15.6
23.2
24.314.2
21.1
22.1
11.7
17.3
18.1
8.4
12.5
13.1
12.6
18.7
19.5
8.6
12.8
13.4
14.3
21.2
22.2
10.3
15.2
16.0
Root Collar
Diam eter
(cm)
1.41.0
0.5
1.2
0.9
0.5
1.1
0.8
0.4
0.9
0.7
0.4
1.0
0.7
0.4
1.3
1.0
0.5
1.2
0.9
0.5
1.6
1.2
0.61.4
1.1
0.6
1.2
0.8
0.5
0.8
0.6
0.3
1.3
0.9
0.5
0.9
0.4
0.3
1.4
1.1
0.6
1.0
0.8
0.4
Root Collar
Diam eter
increm ent
(cm)
Houhere (Hoheria spp.)
Tarata (Pittosporum eugenoides)
Akeake (Dodonea viscosa)
Rautawhiri (Pittosporum colensoi )
Kanuka (Kunzea ericoides)
Makomako ( Aristotelia serata)
Mahoe (Melicytus ramiflorus)
Ti kouka (Cordyline australis)
Manatu (Plagianthus regius subsp.
regius)
Kohuhu (Pittosporum tenuifolium)
Manuka (Leptospermum scoparium)
Whauwhaupaku (Pseudopanax
arboreus)
Karamu (Coprosma robusta)
Kapuka (Griselina littoralis)
Mapou (Myrsine australis)
Species
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.PIO N EER SPECIES M EASURED
O f the 10,000 plant measurem ents in the Tane’s Tree
Trust Native Plantation Database, 20% are planted native
shrub and small tree species used widely in revegetation
programmes. The selection of hardy native species used
in revegetation programm es vary from site to site
depending on the objectives of revegetation, which species
are native to the local area, and characteristics of the site
such as degree of exposure, level of fertility or moisture
regimes.
Up to 43 shrub and small tree species were measured in
58 plots from 39 different locations nationwide. Invariably
all planted stands were mixed species assemblages and
most were planted in riparian areas with a small num ber
on retired hill country or planted for amenity or aesthetic
reasons in established gardens and urban parks. None
had been planted specifically as a nurse crop for the laterinter-planting of conifer or hardwood trees. Shrub and
small tree plantings ranged in age from 3 to 40 years since
establishm ent.
The main species planted that are grouped into one of
three broad categories were:
native shrubs – m anuka (Leptospermum scoparium),kohuhu (Pittosporum tenuifolium), tarata (Pittosporum
eugenoides), akeake (Dodonea viscosa), koromiko (Hebe
stricta); wineberry (Aristotelia serratus), karamu
(Coprosma robusta);m onocot – ti kouka or cabbage tree (Cordyline australis);
sm all native trees – kanuka (Kunzea ericoides), mahoe
(M elicytus ramiflorus), whauwhaupaku or five finger
(Pseudopanax arboreus), houhere species (Hoheria populnea,
H. sextylosa), kapuka (Griselinia littoralis).
O nly a sm all selection of the m ost com m on species
planted had sufficient num ber of stands and plants across
a range of ages to be included in growth sum maries by
species. Growth data of all species were combined in the
development of a preliminary growth model for mixed
native shrub and small trees.
M EASUREM EN T OF STAN DS
Site factors and the history of site and stand management
was collated from owners and m anagers. For sites
dominated by shrub hardwoods of known age since
planting, a representative sample of up 30 plants for each
of the m ajor species was m easured. As m any of the
shrubby species are m ulti-leadered from near ground
level and often heavily branced, especially when young,
measuring diameter at breast height is often impractical.
Consequently, root collar diameter (RCD) was measured
using large callipers or diameter tapes to measure the one
or more stems at approxim ately 10 cm above ground
level. All plants in the sample were measured for height
growth using an extendable height pole.
Stand stocking was calculated using a m inimum of 30
representative intra-tree distances within stands taking
care to avoid stands edges. Stand stocking was variable
from less than 1000 stems per hectare to several thousand
stems per hectare.
GROW TH M ODELS
H eight/age curves
Plot mean heights along with fitted height/age regression
curves for the eight shrub and small tree species are given
in Figure 1 for the individual species. This varied from
25-40 years of age for the different species depending
on growth data available.
All species had rapid early height growth from an average
planting height of 50 cm with m ean heights of 4-5 m 10
years after planting. Height growth of the tallest species
houhere, tarata, kanuka and ti kouka were on average
approaching 10 m high 40- years after planting.
Figure 1:Height/age regression curves for selected native
shrub and small tree species commonly planted on open sites
as assessed during the recent nationwide survey of nativeplantations.
Diam eter/age curves
RCD/age curves to 30 years after planting are shown for
selected native shrub and small tree species in Figure 2.
M ean root collar diameter is up to 15 cm within 10 years
for the fastest growing species ti kouka, kapuka and
houhere, a mean annual growth rate of 1.5 cm .
Growth rate decreases across all species from 10-20 years
after planting and then largely plateau, which is likely
related to increasing com petition as many stands were
established at high stocking. At 20 years mean root collar
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ISSN 2230-3014 2011
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4
Figure 4:Mean RCD/age regression curves based on growth
data for planted stands up to an approximated age of 30 years
for selected native shrub and small tree species.
Predicted height and root collar diam eter
Predicted m ean height and RCD for the major native
shrub and small tree species com monly planted on open
sites is given in Table 1. As expected, these species are
fast growing in early years with most exceeding on average
40 cm height growth per year over the first 10 years.
Rapid height growth reduces in subsequent decades to
less than half initial growth rates.
Virtually all species exceed an annual root collar diameterincrement of 1 cm over the first 10 year period but as
for height, this reduces only half that rate a decade later
as growth levels off (Table 2).
CON CLUSIO N S
References:
The results of this survey confirm that the early growth
rate of selected native hardy shrub and small tree species
planted on open sites of over 40 cm height and over 1
cm diameter are substantially faster compared to growth
rates of both native conifer and native hardwood tree
species (refer to Handbook Articles 10.2 and 10.3). This
is also reflected in nursery production where m ost shrub
hardwood species take less than a year to reach a planting
height of 50 cm compared to most conifer and hardwood
trees that take at least two years (Bergin and Gea 2007).
Planting of early successional pioneer species is therefore
a practical option for establishing a woody cover of native
vegetation and this mimics natural regeneration strategies
for most sites. N ot only are seedlings of m ost of the
shrub species cheaper to obtain than the slower growing
native high forest species, their role in provide a coverof native vegetation is a practical option on exposed open
sites where performance of most conifers and hardwood
trees would be poor. In addition, faster growing pioneers
will have a greater chance of outcompeting m ost invasive
weeds.
W hile som e of the small native species listed above will
grow for a century and more (e.g. kanuka, kapuka), most
are shrubby species that will only form low canopies and
understorey tiers in high forest. However, their role as
‘nurse cover’ in providing sheltered m icrosites for theestablishment by natural regeneration or by inter-planting
of conifers and hardwood trees species is essential.
Bergin, D.O.; Gea, L. 2007: Native trees – planting andearly m anagement for wood production.New ZealandIndigenous Tree Bulletin N o. 3. New Zealand ForestResearch Institute. Revised edition. 44p.
diameter varies from 12 cm for manuka and kanuka to
20 cm or more for ti kouka, kapuka and houhere.
The M inistry of Agriculture and Forestry does not
necessarily endorse or support the content of the
publication in any way.
Pardy, G. F.; Bergin, D. O.; Kimberley, M . O. 1992:Surveyof native tree plantations. Forest Research InstituteBulletin No. 175. 24p.
Contact: Tãne’s Tree Trust
W ebsite: www.tanestrees.org.nz
Authors: David Bergin and M ark Kimberley, Scion