Seeks to improve the yield and quality through:-
- Controlled pollination.
- Extensive provenance and progeny testing and selections.
- Reduction in rotation period.
- Improvement in stem form.
- Increase profitability for the forest industries.
- Introduce new species for both commercial and social forestry.
- Introduce latest propagation technologies.
Contribution of Tree Breeding Research to Climate Change Mitigation
The advent of climate change has brought with it new challenges in tree improvement programs and as such Tree Breeders have been forced to shift their attention to tree species that are fast growing and can easily adapt to the changing environment. The major focus on tree improvement in Zimbabwe is mainly centered on exotic soft and hard woods namely the Pines and Eucalyptus species respectively. In response to this wake up call, the Tree Breeding Unit has embarked on a Breeding Programme to capacitate the forestry sector in light of climate change. In soft woods, the promising species are (P standing for pinus) – P maximinoii and P tecunumanii. These two species have shown great potential especially on growth rate and preliminary indications have shown that the two are outperforming P taeda, P elliottii and P oocarpa in their previously presumed niche areas. Research have shown that P tecunumanii, which is divided into two populations: high elevation population (>1500m.a.s.l) and low elevation population (<1500m.a.s.l), will soon prevent the monoculture of P patula in high altitude areas for the high elevation population and P elliottii and P oocarpa for the low elevation population. With climate change there is emergence of new pests and diseases as well as increased natural disturbances from native pests. To avoid catastrophic events on P patula which is the dominant species in the high altitude areas, P greggii, and P maximinoii were also introduced to reduce monoculture of P patula.
In addition to these fast-growing species, the unit is also working on P roxburghii for adaptability in low rainfall areas. Currently material for this species is coming from three provenances of the country with varying degree of aridness from where the species is showing average performance.
To augment these efforts, the unit is also working on Eucalyptus hybrids targeted mainly for the tobacco growing areas of the country. These have shown great potential in growth rate as well as adaptability. It is envisaged that this initiative will go a long way in providing fuel wood for curing tobacco without impacting negatively on the environment since they have a shorter growing period averaging five years from planting to harvesting. The hybrids are also suitable for plantation forestry and have an added advantage of reducing the rotation cycle due to their rapid growth rate.
Climate change has resulted in the large-scale movement of species and populations within species into climatic zones where they currently do not exist. The aim in tree improvement is to consider physiological adaptations of forest trees under various climate change scenarios. In this regard the Tree Breeding is emphasizing on breeding objectives of drought, disease and frost resistance in tree species. Breeding Eucalyptus hybrids is being conducted with the aim of providing suitable genotypes for planting in areas which are marginal for the parental species in terms of drought, frost and disease resistance.
Table1: Hybrids developed
|Hybrid Cross (E- Eucalyptus)||Breeding Objective|
|E grandis x E camaldulensis||Drought, frost|
|E grandis x E tereticornis||Drought, disease resistance|
|E grandis x E saligna||Fast growth|
|E grandis x E europhylla||Disease resistance|
|E grandis x E pellita||Fast growth, Disease resistance|
Climate change brings a change in temperatures and this affects flowering phenology and abundance and hence seed production. Flowering studies are being conducted in P maximinoii and will be conducted in all new trials of P roxburghii. Modern technologies such as vegetative propagation have been adopted to curb the issue of seeding shyness in certain species such as P maximinoii and P tecunumanii. The Forest Research Centre (FRC) has established a clonal hedge where superior genotypes are mass produced. To date there are 21 individuals for the E grandis x E tereticornis and 24 individuals for the E grandis x E camaldulensis hybrid represented in the clonal hedge at FRC.John Meikle Forest Research Station (JMFRS) is concentrating on vegetative propagation of Pinus species.
Table 2: Number of cuttings propagated at JMFRS
|SPECIES||GROWTH MEDIUM||CUTTINGS WITH SERADIX||CUTTINGS WITHOUT SERADIX|
|P caribaea x P tecunumanii||Pine bark/Sand||220||348|
|P caribaea x P tecunumanii||Pine bark/Sand||52||96|
|P tecunumanii||Pine bark/Sand||59||96|
|P patula||Pine bark/Sand||711||7519|
|P taeda||Pine bark/Sand||48||35|
|P elliottii||Pine bark/Sand||16||303|
|P maximinoii||Pine bark/Sand||1211|
|Grand Total||14 290|
Research into forestry species for the dry zones focuses on the objectives of fuelwood and building wood requirements by establishing tree plantations in the semi-arid regions of the country. The aim is to introduce tree species suitable for introduction into tree, pasture, food crop systems with special emphasis on nitrogen fixing species for the production of forage, fuelwood and shade and with soil protection and improvement properties.
Table below summaries the trials established.
Table 3: Trials established under the dry zone research
|EV133D||Provenance||Azadirachata indica||Forest Hill|
|EB45||Breeding Seedling Orchard||E tereticornis||Forest Hill|
|EB46||Breeding Seedling Orchard||E tereticornis||Forest Hill|
Seven (7) F.albida progeny/provenance trials were established at Matopos, Chesa, Chibhero, Makaholi, Middle Sabi, Kadoma and Chesa. Current work is focused on eucalypts with the dominant species being Eucalyptus camaldulensis and Eucalyptus tereticornis. The bulk of the work is done at Chesa Forest Station in Bulawayo (alt 1460m.asl, natural Region V (mean annual rainfall of 546mm).
The Breeding strategies being used combine genetic improvement of desired attributes and gene conservation. The tree improvement programme has 13 different pine species and 10 eucalyptus species undergoing improvement. The table below shows the number of seed orchards and the level of improvement of seed available in Zimbabwe for plantation and reforestation programmes.
Table 4: Number of seed orchards, area and level of improvement of seed germplasm available in Zimbabwe
|E grandis||6||2nd and 4th||15|
|E camaldulensis||17||1st ,2nd,3rd and 4th||33|
|E tereticornis||9||2nd and 3rd||10|
|P patula||26||1st and 2nd||46|
|P taeda||24||1st and 2nd||33|
|P elliottii||28||1st and 2nd||61|
|P kesiya||17||1st and 2nd||53|
|P caribaea var hondurensis||1||1st||0.6|
|P caribaea var bahamensis||1||1st||0.6|
|P caribaea var
|Pinus spp hybrids||2||1.4|