D. G.M. Donald

Mycorrhizal Inoculation for Pines

SUMMARY The effects of methyl bromide soil sterilization and inoculation with spores from ground sporocarps of Rhizopogon luteolus on the growth of Pinus radiata seedlings is described. It is concluded that although Rhizopogon luteolus may not be the most efficient mycorrhizal fungus available to South African foresters, the ease with which it can be introduced into practice, together with the improvement in growth that it can achieve, warrants its use. Sample material is available to anyone wishing to try the original source. Screening of other Rhizopogon species and other strains of R. luteolus to check for greater efficiency are recommended.

The Control of Phytophthora cinnamomi Rands in a South African Forest Nursery

SUMMARY Tests of several fumigants which control Phytophthora cinnamomi Rands under field and glasshouse conditions are reported. The soil fumigant basamid is the cheapest effective treatment available, at present. The implications of failure to control Phytophthora cinnamomi for forestry, agriculture and the indigenous flora are briefly discussed.

Micropropagation of Eucalyptus radiata ssp. radiata Using Explants from Mature and Coppice Material

SYNOPSIS Nodes from young field-grown coppice regrowth and branches of a mature tree of Eucalyptus radiata ssp. radiata were cultured on a MS medium containing BA and NAA. BA at 0,5 mg/l and NAA at 0,01-0,1 mg/l were most effective in promoting axillary shoot proliferation from both coppice and adult tissue. BA concentration of the medium was reduced (0,1 mg/l) to induce axial growth in regenerated bud primordia. 50–70 shoots could be obtained from one nodal culture. Multiplication rate was higher from the mature tree than from the coppice shoots. Rooting was achieved from shoot cultures on half strength MS salts supplemented with 2,5 mg/l of IBA for mature shoots and 5 mg/l for coppice shoots. The percentage of rooting of coppice shoots (90%) was much higher than for mature shoots (35%). Summer was the best season to take explant material for shoot multiplication.

The Application of Fertilisers to Pines in Southern Africa

SYNOPSIS Phosphate is the major limiting element for tree growth in Southern Africa. Once phosphate requirements have been met responses to N and K may also occur. N and K applied without P will cause a growth reduction. Manganese deficiency in some areas of the Southern Cape is the only example of a trace element deficiency causing crop failure in South Africa. With the exception of P. pinaster which has not responded consistently, all the commercial pines have responded to fertiliser application. Response to fertiliser application at planting appears likely to last to the first thinning and to be economically viable. Responses in unthinned stands, unless widely spaced or clearfelled at an early age, are less likely to last to clearfelling. The application of fertiliser to older crops at time of thinning holds good promise of an economic return, but the stands must be adequately released to ensure a growth response. Research to date indicates that 10 to 25 kg P per hectare as superphosphate or 2:3:2(22) ...

Litterfall and Nutrient Release in Mature Pinus radiata in the South-western Cape

SYNOPSIS Fast-growing plantations of conifers have replaced areas of mediterranean shrubland in the south-western Cape. This study arises from the need to quantify the impacts of major changes in primary productivity, litterfall, and nutrient cycling in terms of the site utilisation and long-term productivity. Litterfall and decomposition were measured over five years in a catchment under mature Pinus radiata in the Jonkershoek valley near Stellenbosch, with seasonality and nutrient cycling rates assessed for the plantation ecosystem. Data are presented for all components of litterfall including needles, strobili, pollen, seed, bark, branches and cones. Total means annual litterfall amounted to 3270 kg/ha per annum, of which needles accounted for 76,7% or 2825 kg/ha, and strobili 8% (295 kg/ha). Decomposition of needles is at least 50 % after three years and litter accumulation is limited. All components of litterfall have been analysed for nutrient content on at least an annual basis, with detailed seaso...

The Application of Fertiliser to Pines Following Second Thinning

SYNOPSIS The results from four trials where fertiliser was applied to pine stands following second thinning are presented. It is concluded that although there is an immense research task still to be done, sufficient information is available to allow the forest industry to turn money into wood without the fear of not making a financial return on the investment. In the oldest trial fifty kilograms nitrogen and fifty kilograms phosphate per hectare increased the current annual increment of Pinus radiata from 13,344 to 17,893 cubic metres per hectare per annum over the 10 years of the trial. This gave an internal rate of return of 18,45%, based on current costs and prices.

The Use of Open-Rooted Pine Seedlings for Afforestation in South Africa

SUMMARY Trials of open-rooted plants of Pinus radiate in the winter rainfall region of South Africa and of P. taeda, P. elliottii and P. patula in the summer rainfall region are described. It is concluded that open-rooted plants can be used with confidence in both regions. Sites which are naturally difficult to establish in the winter rainfall region will require strict weed control. This is also likely to be necessary for the summer rainfall region. Soil sterilization and mycorrhizal inoculation in the nursery can significantly improve both nursery growth and field performance of the pines.

Effect of Nursery Culture and Bud Status on Freeze Injury to Pinus taeda and P elliottii Seedlings

SYNOPSIS The effects of nursery practices on freeze tolerance of P. taeda and P. elliottii seedlings were examined by placing the seedlings in a freezing chamber and lowering the temperature to -10°C. Injury was evaluated 10 days after the freeze treatment by examining cambial tissue (browning test). Top-pruning P. taeda seedlings (three times) increased freeze tolerance while root-wrenching (six times) had no effect. Cambial injury of P. elliottii was negatively related to seedling diameter but injury was not affected by either top-pruning or root-wrenching. Although potassium fertiliser is often recommended for fall fertilisation in the southern United States, this study found no beneficial effects on freeze tolerance. In fact, fertilisation in October decreased freeze tolerance of P. elliottii. Data from the freeze test and from natural freezes in the nursery were analysed to determine if freeze tolerance was related to the presence of a well-formed terminal bud in early November. Covariance analysis f...

In vitro Organogenesis and Plantlet Formation of Paulownia elongata

SYNOPSIS Shoot tips, nodes, internodes and leaves derived from aseptically produced seedlings of Paulownia elongata were cultured on Murashige and Shoog medium (MS) supplemented with NAA and BA. Medium containing 0,1 mg/1 NAA and 0,5 mg/l BA gave the best shoot production from leaf callus (50 shoots per 25 mm2 segment). Shoot tips cultured on medium containing 1 mg/l BA gave rise to a 9,7-fold increase in shoot production in 30 days. The shoots produced could be rooted either on MS medium without growth regulators or treated as straight cuttings and rooted In a 1:1 composted pine bark: vermiculite growing medium.

Cleaning Operations in South African Forestry

SYNOPSIS Intense weed control is practised during establishment and re-establishment; cleaning to improve access during the stands life is done, but has had little effect on the build up of weed populations in South African plantations. The cost of weed control has increased some ten-fold while the efficiency of the cleaning operation has, if anything, improved since the last survey in the late sixties. The use of herbicides has increased significantly since the last survey and appears likely to increase further in the future. Herbicides are more effective than slashing, which stimulates growth in some weed species. Extension work must be increased if current herbicide knowledge is to be effectively utilised. Research to quantify the effect of weed infestation in commercial stands and to examine the possibility of grazing animals controlled by electric fencing to overcome the problem should be given priority.