African
Journals Online
Southern African Forestry Journal
Issue 190, March 2001
Abstracts
The African Acacias - a thorny subject
Barnes, R.D.
Abstract: There are 129 Acacia species in Africa.
They are intermediate in plant succession and colonize degraded land.
They restore fertility and can be maintained indefinitely in
agricultural systems. They provide many benefits but are disliked for
their thorns and invasiveness. Seed was collected across the ranges of
Acacia erioloba, A. karroo, A nilotica, A.senegal,
A. tortilis and Faidherbia (formerly Acacia) albida.
Screening trials indicated that, with selection, all had potential
both inside and outside their natural ranges. Subsidiary studies
showed that some acacias obtain their nitrogen from groundwater rather
than from the atmosphere, that they can produce more crude protein per
hectare than a grain crop, that there are annual rings in the wood,
and that gum arabic could be a lucrative cash crop. Farmers will
resist planting acacias until the benefits can be translated into
cash. The challenge for breeders in the new millennium is to produce
trees that are inherently so good that they sell themselves to the
farmer.
Breeding strategies for forest trees: concepts and
challenges
White, T.
Abstract: This paper describes some recent developments that
affect the way forest geneticists think about breeding strategies for
forest trees. The topics are grouped into several categories: (1)
General Concepts ; (2) Breeding Population Size ; (3) Breeding
Population Structure ; (4) Management of the Breeding Population ; and
(5) Incorporating New Technologies in Tree Improvement Programs. The
last major section on new technologies highlights: (1) The increasing
importance of hybrid breeding in tree improvement programs: (2) The
potential of somatic embryogenesis as a biotechnology leading to
clonal forestry for some commercially-important species ; and (3) The
need for forest tree breeders and molecular geneticists to work
together to incorporate promising new technologies into applied
breeding programs.
Growth and provenance variation of Pinus
caribaea var. hondurensis as an exotic species
Hodge, G.R.; Dvorak, W.S.; Romero, J.L.
Abstract: CAMCORE has visited 33 populations of Pinus
caribaea var. hondurensis in Belize, Guatemala, Honduras,
El Salvador, Nicaragua, and Quintana Roo, Mexico. Seed collections
have been made in 29 provenances from 1, 325 mother trees. A total of
21 provenances and sources of Pinus caribaea var. hondurensis
were tested in 48 provenance / progeny trials in Brazil, South Africa,
and Venezuela. Growth rates in Brazil and Venezuela were quite
promising, and were less encouraging in Colombia. In Brazil and
Venezuela, heights were around 12 m and mean DBH was around 18 cm at
age 8. Growth in Colombia was substantially slower, with mean height
less than 8 m at age 8, and mean DBH around 13 cm. Assuming 1111 stems
/ ha with 85% survival, these growth rates correspond approximately to
volumes (outside bark) of 14 - 15 m3 of wood/ha/year on
sites in Brazil and Venezuela, and 4 - 5 m3 / ha / yr in
Colombia. Since these data represent the mean of unimproved material
from all provenances, substantially larger values should be expected
from selected material from the best provenances planted on suitable
sites.
Forking and foxtailing percentages were high in some tests in
Brazil and Venezuela. There were generally higher incidences of
foxtailing in Venezuela (greater than 25% at ages 5 and 8) than in
Brazil (7 to 13% at ages 5 and 8). Forking was more similar, with
means around 30% in Brazil and Venezuela.
Provenances had relatively similar growth rankings in the different
countries, with a Type B provenance correlation of 0.59. BLUP
predictions of provenance effects were made for Brazil, Colombia and
Venezuela. The best native provenances were Limon (Honduras) and
Melinda (Belize), and Guanaja (Honduras) also performed well. Improved
sources from Queensland Forest Research Institute (Australia) and
South African Forest Research Institute were 6 to 12% better than the
mean of the unimproved provenances, depending on the country where
they were planted.
Operational deployment of genetic gain
Pallett, R.; Stanger, T.; Morris, A.; Clarke, C.
Abstract: Tree improvement is central to increasing
plantation productivity per unit land area in many countries that rely
on an exotic fast grown plantation resource as a source of wood and
fibre. In order to achieve an acceptable return on the investment made
in tree breeding, it is important that material be deployed with both
good husbandry and on sites where the genetic potential can be
expressed. Apart from the obvious breeding and propagation of
genetically improved material, such a deployment strategy has three
components.
1. A site classification system to determine the geographic
distribution of environmental variables significant to site quality
and tree growth potential
2. The development of cultural best operating practices to promote
growth of improved material, particularly before canopy closure
3. A system of measurement to measure the success of operational
deployment of genetic gain and related future forest productivity
The concept of operational gain integrates genetic improvement with
cultural practices and site growth potential as a measure of the
capture of genetic gain at an operational level. In this paper,
initial results from a trial series testing the interaction of
different levels of genetic improvement in eucalypts, with different
levels of silvicultural after care over two sites are used to quantify
the relative importance of each of the three components.
Are Eucalyptus clones advantageous for the
pulp mill?
Clarke, C.R.E.
Abstract: Eucalyptus clones, the ultimate
exploitation of genetic variation, are perceived to be the ideal raw
material for the pulp mill but is this really true? Their attributes
include uniformity, superior pulp properties and faster growth while
their only limitation is lack of the natural genetic variation which
provides protection against adverse elements. This shortcoming, unless
managed, is likely to have a dramatic impact on a mill. Commercial
compartments of clones rarely exceed 100ha and are more commonly less
than 50ha. The maximum that is planted to an individual clone in one
year is 200ha. At an assumed production of 200t / ha this implies that
parcels of up to 10, 000t of timber (but more often less) from a
single genetic entity will arrive at the mill gate at the same time.
Dramatic differences between clones are likely introduce more
variation in the form 'slugs' than is experienced with seedlings where
the variation is more of a continuous nature. The ten E. grandis
hybrid clones used commercially by Sappi Forests have been evaluated
for wood and dissolving pulp properties across a number of trial
sites. Although wood and pulp properties varied between trees within
clones, most of the variation was found to occur between clones and,
as expected, clones were more uniform than seedlings. Dissolving pulp
yield of clones varied from 43.8 to 45.6%, viscosity from 41.4 to
69.8cps and brightness from 43.7 to 50.7. Wood density was found to
vary between clones from 460 to 570kg / m3, fibre diameter
from 12.05 to 14.49:m and cell wall thickness from 2.40 to 2.64: m.
Differences in wood and dissolving pulp properties between and within
clones are compared here with E. grandis seedlings, the impacts
on daily running of a dissolving pulp mill are discussed and
suggestions are provided for management of clones in the mill to make
best use of their unique properties.
Plantation disease and pest management in the next
century
Wingfield, M.J.; Roux, J.; Coutinho, T.; Govender, P.;
Wingfield, B.D.
Abstract: The extensive development of plantation forestry
in the tropics and Southern Hemisphere marks one of the great
industrial successes of the 20th Century. Early experience led to the
discovery that certain trees, although not particularly impressive in
their areas of origin, can grow rapidly in exotic situations. More
importantly, they are sufficiently genetically malleable to become
outstanding plantation species through breeding. Perhaps the best
examples of such trees are Pinus radiata and Eucalyptus
grandis. By the early 1960's, diseases and pests were recognised
as two of the most important threats to exotic plantation forestry. It
was realised that separation of the crop from its natural enemies was
responsible for the initial outstanding productivity of exotic
plantation forestry. Gradually, new pathogens have been introduced in
plantations in the tropics and Southern Hemisphere. The impact of
these problems has been offset by new technologies that enhance the
production of elite planting stock. During the course of the 21st
Century, we will experience the emergence of many new strategies to
cope with disease and insect pests in intensively managed and
genetically modified plantations. The impact of DNA based technologies
that enhance breeding will be one of the first developments, followed
by the deployment of transgenic trees and microbes. The rapid
emergence of DNA based technologies will bring tremendous
opportunities to forestry, including its capacity to deal with pests
and diseases. However, early experiences are likely to also be beset
with problems. These will include a negative perception of transgenics
by environmental action groups and the public. Successful forestry
will, however, rest on persistence and patience while problems are
addressed. Winning industries will be those that have harnessed new
opportunities and that have developed the strategies to capitalise on
these when concerns linked to safe deployment have been addressed.
Evolutionary relationships of Slash Pine (Pinus
elliottii) with its temperate and tropical relatives
Schmidtling, R.C.; Hipkins, V.
Abstract: llozymes in bud tissue and monoterpene contents in
xylem oleoresin of slash pine (Pinus elliottii) were analyzed
from populations across the natural distribution, as well as those
from other species in the AUSTRALES pines. Allozyme diversity measures
of slash pine were similar to those found in other southern pines. The
two slash pine varieties, the slower-growing south Florida variety
(var. densa) and the more commercial "typical"
variety (var. elliottii), were not separated in the cluster
analysis of allozymes. Variation was continuous from south to north in
Florida in slash pine, with no distinct transition between the two
varieties. The monoterpene data also showed continuous variation
between the two slash pine varieties. Expected heterozygosity declined
from south to north, supporting the hypothesis that slash pine resided
in a Pleistocene refugium in south Florida or the Caribbean, migrating
northward at the close of the ice age. Allozyme frequencies as well as
monoterpene compositions of slash pine and its AUSTRALES relatives
showed a very close relationship between slash pine and Bahamian
Caribbean pine (P. caribaea Morelet var bahamensis).
Alternative eucalypt species for Zululand: seven
year results of site: species interaction trials in the region
Gardner, R.A.W.
Abstract: The ICFR initiated a search for alternative
eucalypt species for the Zululand Coastal Plain region during 1992 by
establishing a series of site: species interaction trials in the area.
Sixteen pure species (seedlings), one E. grandis intra-specific
clone and five inter-specific hybrid (E. grandis x either
camaldulensis or urophylla) commercial clones were planted
at three sites ranging in climatic condition from warm and wet in the
south to hot and dry in the north. Final measurements, assessments and
wood-sampling for pulping properties was carried out during 1999.
These results together with relevant recommendations are discussed in
this paper. On a growth, disease-resistance and pulpwood-quality
basis, the top performing pure species at the southern (highly
productive) site at Terranera were E. longirostrata and E.
pilularis, and on the drier, more marginal sites at Teza and False
Bay, E. henryi, E. citriodora, E. longirostrata
and E. tereticornis gave impressive results.
Prospects of eucalypt species, including
interspecific hybrids from South Africa, for hardwood plantations in
marginal subtropical environments in Queensland, Australia
Lee, D.J.; Nikles, D.G.; Dickinson, G.R.
Abstract: In Australia, there has been rapid expansion in
recent years of commercial plantations of hardwood timber species,
especially of Eucalyptus and Corymbia. In tropical and
sub-tropical Queensland the land most likely to be readily available
for this planting is in the marginal 650-1000 MAR zone where,
potentially, millions of hectares could be planted on cleared land.
Optimal forestry plantation practice requires matching of taxa
(species-provenances-hybrids) and sites. However, experiment-based
identification of taxa with commercial potential has not been
accomplished for many regions in this rainfall zone of Queensland. In
Brazil, China and South Africa, large viable plantation estates have
been developed on marginal lands through use of hardy, high-yielding
interspecific eucalypt hybrids (Eldridge et al. 1993). Eucalypt hybrid
breeding is in its infancy in Queensland so the potential exists to
accelerate the identification of superior hybrids through introduction
and testing of material developed elsewhere. Based on this overseas
experience, bulk seedlots of selected eucalypt hybrids have been
introduced, in strict accordance with quarantine requirements, and are
now being tested against Eucalyptus and Corymbia species
and provenance controls in key regions of Queensland and northern NSW.
This paper presents two-year results for three trials in
sub-tropical Queensland, indicates the taxa with fastest early growth
and considers the potential and suitability of several eucalypt
hybrids (seedlings) to marginal sites in Queensland.
An industrial evaluation of a stand level grading
system for Pinus patula
Turner, P.; Megown, K.A.; Grzeskowiak, V.; Megown, R.A.;
Pauck, J.; Alborough, D.
Abstract: This paper reports on progress made in the
development and implementation of a stand level wood quality grading
system for P. patula identified for processing in Mondi
Merebank's stone ground wood and thermo-mechanical pulp lines. The
grading system stratified the resource using fiber collapsibility as
the selection criteria.
The paper evaluates the impact of the grading system on the process
parameters and the basic characteristics of pulp produced by the
different pulp lines. The grading system was found to have a positive
impact on desired pulp quality criteria.
Variability inherent in the resource and the production process
declined significantly upon implementation of the grading system. The
results indicate the level of improvement that can be realized from a
simple wood quality grading system. It is anticipated that a more
detailed understanding of factors impacting on wood and pulp
characteristics, and resource and process variation will support a
process of continuous pulp quality improvement.
This work was co-sponsored by Mondi Forests, Mondi Merebank and the
CSIR.
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