Eucalypt species trials in the Wairarapa and Hawke’s Bay
Luigi Gea and Tony Shelbourne
New Zealand Tree
Grower November 2006
There is interest among New Zealands small growers in growing eucalypts
for sawn timber. Recent research funded by FRST has concentrated
on species introduction and testing of a group of
naturally durable stringybarks along with a few other species with good
reputations for low growth stresses, good sawn timber characteristics
and lack of disease and insect problems. These include
E. pilularis and
E. muelleriana, species
well-known for good sawing and sawn timber
characteristics of appearance-grade lumber.
Recent simulation studies have shown that it is possible to get good
genetic gains from small scale breeding programmes on a single
generation basis. This approach is well suited to progressing
the genetic improvement of promising species of which there are some
genetic resources, but where there is low immediate demand for seed.
Results from trials
Eucalypt species trials have been planted in North and South Island
plantation forests since 1970 by the New Zealand Forest Research
Institute – now Scion, and by New Zealand Forest Products Forests Ltd –
now Carter Holt Harvey Forests Ltd. The National Plant Materials Centre
at Aokautere, Palmerston North also planted a number of eucalypt
species trials to test species for their potential to stabilise
erodable land.
The Scion – Carter Holt Harvey trials in Wairarapa
Two trials were planted near Masterton in 1979, at Kahuiti station and
at Pakaraka. The Kahuiti trial, which included a total of 104 seedlots,
representing 49 eucalypt species was assessed by Ensis in 2001.
The Kahuiti site is 28 km east of Masterton at an altitude of 150 to
180 metres on a steeply sloping site of silt and clay loam over
mudstone. The site is typical of Wairarapa hill country that suffered
severe earthflows during a wet winter in 1977. The mean annual rainfall
is 1000 mm. The total number of trees planted was 16 per provenance and
32 of single provenance species. The trial was not thinned, fortunately
as it turned out, as natural attrition reduced survival to 66% by age
12 years and 43% by age 22. Unfortunately the better grown Pakaraka
trial had been thinned a second time in 2000, which reduced tree
numbers per species so much that assessment was not worthwhile.
Survival, best growth and diameter at breast height
Apart from 10 species, which had six or less survivors, the average
number of surviving trees per species was 23. The 14 species which grew
best in terms of diameter at breast height (DBH) out of the total of 37
species with nine or more trees surviving are listed in the table in
descending order.
E. cordata, an insignificant gum from south east Tasmania, grew
as well
as the better ashes while the other gums, including
E. nitens, ranked
at the lower end of the best 14. Although only nine
E globoidea
and ten
E. muelleriana trees
survived, they had surprisingly outgrown
all other species. Other species of interest for sawn timber that
survived poorly at Kahuiti were
E.
cladocalyx and
Corymbia
maculata,
spotted gum, which ranked in the middle of the range.
Best form
Amongst the best grown group,
E.
delegatensis, E. fastigata, E. obliqua
and
E. regnans had the best
bole straightness and malformation scores
of the ashes. All of the ashes had better form than the selected
members of other groups except
E.
nitens. Stringybarks
E.
globoidea and
E. muelleriana were down
graded by their tendency to fork. The number
of potential sawlogs was by far the highest for
E. delegatensis,
followed by
E. regnans, E. obliqua,
E. nitens and
E. fastigata.
Value of the results
From experience with other species trials in the central North Island
and in Northland there are many changes that occur in relative species
performance up to and beyond age 12 years. These are due to adaptive
responses to environmental factors, to disease and to insect attack.
The results above are imprecise, particularly for those species with
fewer trees assessed. However they have the merit of being from trees
at age 22 years, which represents about two thirds or more of rotation
age for sawlogs on this site. The results should characterise the
species for their long term potential performance, at this relatively
low altitude site in the Wairarapa.
The National Plants Materials Centre trials
Between 1978 and 1986 the
National Plants Materials Centre planted trials with similar objectives
and similar design at a further 13 sites in Hawke’s Bay and the
Wairarapa. These were distributed from near Wairoa in northern Hawke’s
Bay to Longbush and Martinborough in the south Wairarapa. In altitude,
they ranged from 70 metres at Waimarama to 300 metres at Pukeatua, east
of Martinborough.
However they were mainly between 100 metres and 200 metres, with annual
rainfalls varying from 850 mm at Havelock North to 1400 mm east of
Wairoa.
The results
A total of six ashes, five peppermints, 11 gums plus an
E. botryoides x
saligna hybrid seedlot and
E.
robusta, were variously planted at
different sites. A group of nine species was included at most of the
sites. They were ranked for adjusted mean diameter at breast height at
age 12 years over 10 sites.
The Te Whiti trial
A further trial was planted at Te Whiti, close to the Pakaraka site
near Masterton, which included 35 species, planted in three
replications of 12-tree plots. Prior to assessment at age 15 years it
was thinned to leave only two trees per plot and six trees per species.
The 12 species with largest mean diameter at breast height included the
stringybark,
E. muelleriana,
the ashes
E. fastigata. E.
fraxinoides and
E. obliqua,
the peppermints
E. coccifera, E.
pulchella
and
E. tenuiramus, and the
gums
E. nitens, E. ovata and
E. perriniana.
Although the number of trees per species was too small for firm
conclusions, the same group of species are performing well here as at
Kahuiti.
Timber characteristics of different species
Growth and form, and therefore log quality, are important to the
grower. But for sawn timber the sawing behaviour and the
characteristics of the dried product are important in determining
value.
Indications are that with a few exceptions, the fast grown, well formed
ashes and E. nitens are subject to growth stresses, causing sawing
problems and internal checking on drying. These both seriously
down grade their value for solid wood products except veneers.
E. fastigata is a widely adapted and robust contender and the
well
grown stringybark species,
E.
muelleriana and
E. globoidea
show good
prospects for sawn timber if form is improved or managed.
The evidence mounts
The search for eucalypt species in New Zealand that are fast grown,
widely adapted, well formed and free of serious pest and disease
problems is a demanding one and is made even more so when solid wood
use requirements are included. There is growing circumstantial evidence
that the stringybarks, a distinctive group of the subgenus Eucalyptus,
which have rough, persistent and long-fibred bark, contain several
species which are well adapted and have excellent sawing and solid wood
properties, including natural durability. However early assessment of
plots indicates that site specialisation is as strong as any of the
other eucalypt species and careful siting is needed.
Luigi Gea and Tony Shelbourne are both with Ensis
(top)
