A. P.G. Schönau

Fertilising Commercial Forest Species in Southern Africa: Research Progress and Problems (Part 1)

SYNOPSIS Since the inception of forest fertiliser research in Southern Africa in 1926, eight eucalypt, six pine and four acacia species have been tested, encompassing a wide range of sites in summer, winter and uniform rainfall areas. Marked deficiencies of P, Mn and sometimes N, usually associated with hydromorphic and elluviated soils derived from sandstone, are easily diagnosed and corrected at planting or after canopy closure. On the other hand, ferralitic soils showing adequate growth rates respond mainly to applications of P and Ca but balanced for N and K at planting. However, requirements after canopy closure are difficult to determine, varying with site, species and stand development. Fertilising at planting promotes the development of a vigorous root system, which allows for continually improved growth. Thus responses increase with the effective rooting depth and soil water availability of sites, as well as being larger for the faster growing species. Hence MAI has been increased up to 11 m3/ha ...

7. Problems in Using Vegetation or Soil Classification in Determining Site Quality

SYNOPSIS This paper discusses the concepts of site and site quality and reviews briefly the determination of the latter. Site quality is viewed primarily as productive capacity of forest land, although other aspects are considered also. It is concluded that nowadays site index, or the top height of a stand at a certain reference age, is used more frequently than any other indicator. The various methods of determination of site quality, i.e. stand parameters, site factor analysis and classification are discussed. Main emphasis is given to vegetation or soil classification as determinant. The main problems in using vegetation are that it does not work well where it has been significantly altered or when the abundance of species increases. Soil classification also gives rather poor results since these systems are developed mainly for agricultural use. The trend is to include factors important for tree growth in the classification systems thereby improving determination. Better results are achieved with broad...

Preliminary Biomass Studies in Young Eucalypts

SYNOPSIS The wet and oven-dry biomass of various above-ground components of four to five-year-old Eucalyptus deanei, E. globulus ssp. globulus, E. nitens, E smithii and E. viminalis were determined from small samples on the Transvaal Highveld. Close relationships were established between the oven-dry mass of twigs and branches, leaves, stem wood and stem bark respectively and the square of breast height diameter. Tree height was not significant as an additional predictor variable because of the close relationship between height and diameter, the trees being the same age and growing on the same site. Total above-ground biomass and the relative proportions of the various components for various diameter classes is given for each of the above species. There are considerable differences in these proportions between the species. However, the results of this study indicate that the total biomass production for young eucalypts can be increased by 40 to 55 % by making use of above-ground components other than stem...

Fertilisation in South African forestry.

SYNOPSIS The history of forestry fertiliser research in Southern Africa is described briefly. Fertiliser investigations in wattle started in the 1920s and in pines in the 1930s, but investigations with eucalypts started only in the 1950s. Nevertheless, it is noted that today more is known about the nutritional requirements of eucalypts than of the other species, mainly owing to the application of foliar analysis in combination with suitable experimental designs. The importance of the various nutrients for the different species is discussed with reference to experiments undertaken in Southern Africa. The controversial issue whether gains from fertilising are maintained is examined and the conclusion is reached that unsatisfactory design and insufficient replication are the main causes that initial responses have not been shown to be maintained. An indication of the commercial use of fertiliser in wattle, eucalypt and pine growing is given and the high profitability of fertilisation for these species indica...

The Importance of Complete Site Preparation and Fertilising in the Establishment of Eucalyptus grandis

SYNOPSIS The background and results of an experiment involving the response of Eucalyptus grandis up to the age of three years to site preparation and fertilising are described. Full cultivation gi...

Relationship between Growth Rate and Foliar Concentrations of Nitrogen, Phosphorus and Potassium for Eucalyptus grandis

SYNOPSIS The growth responses to applications of N, P, K and lime are described briefly for four comprehensive fertiliser experiments with Eucalyptus grandis. Foliar concentrations of N, P and K were determined for these experiments, and their relationship to growth rate and fertiliser application investigated. Highly significant correlations between these factors were established. The combined influence of fertiliser applications and foliar nutrient levels on height growth-rate were studied by multiple regression techniques. Nitrogen and phosphorus were found to be the most important foliar concentrations in these analyses, together with applications of phosphate and lime. In three experiments very close relationships were determined which explained between 42 and 74 % of the variation in height growth-rate. These percentages decrease with increasing age of sampling. It is concluded that foliar N should be 2.0 %. foliar P 0.17 % and foliar K 0,70 % for satisfactory growth of E. grandis. Likewise the foli...

A Tentative Evaluation of Soil Types for Commercial Afforestation in the Transvaal and Natal

ABSTRACT A soil suitability classification for common commercial tree species grown in the Transvaal and Natal is presented using mainly the terminology of the South African Binomial System of soil classification. This was arrived at by using soil depth, texture, morphology, moisture regime and degree of leaching, all of which influence the growth of commercial tree species. A tentative suitability rating of soil series occurring in the forestry zones of the Transvaal and Natal is given for wattle, eucalypts, pines (Pinus elliottii, Pinus taeda and Pinus patula) and Poplar. By making use of the easy soil identification procedure of the Binomial System together with the proposed suitability rating for soil series, the site evaluator can assess quickly the potential of sites for commercial tree growing. An example is given to illustrate the usefulness of this procedure.

Requirements for Intensive Silviculture

SYNOPSIS The fundamentals of intensive silviculture in South Africa are not a recent development but were already indicated at the beginning of this century. The greater emphasis placed on its application today is due to the increased demand for timber and the limited availability of suitable areas for afforestation. As a result more and more land is being afforested where tree-growing conditions are limited and require a greater silvicultural input in order to achieve acceptable production levels. In addition it has been shown that intensive methods are profitable and become more important on marginal sites where a potential loss situation can be turned into a profitable one. This paper describes the basic requirements for intensive silviculture such as an understanding of the limitations set by soil, climate and landscape, and the demands made by the various tree species. The South African silvicultural expertise in respect of site preparation, fertilising, weed control, thinning and coppice management ...

Climatic and altitudinal criteria for commercial afforestation with special reference to Natal.

SYNOPSIS Criteria of altitude and climate such as mean annual precipitation, mean annual. January and July temperatures, mean daily maximum and minimum temperatures for January and July respectively and duration of soil moisture deficit are given for five main commercial tree species in Southern Africa. Using these criteria together with a basic agrohydrological data file compiled from irregularly spaced climate station information at intersections of a 10 km square grid, maps were prepared of optimum growing areas for the five species in Natal. The results are discussed for Acacia mearnsii, Eucalyptus grandis, Pinus elliottii var. elliottii, P. patula and P. taeda. The limitations and possible improvements to the maps and the extension of this technique to other areas are indicated. The maps will be of great advantage in planning future afforestation in Natal.

Role of Eucalypt Plantations in Timber Supply and Forest Conservation in Sub-Saharan Africa

SUMMARY The role of eucalypt plantations in timber supply and forest conservation in Sub-Saharan Africa was investigated. The annual destruction of 11,5 million ha of tropical forest is highlighted, the various causes indicated and the controversy whether fast-growing plantations and woodlots have a role to play in the conservation of these forests is discussed. It is shown that the total eucalypt estate in Sub-Saharan Africa exceeds one million ha of which 75 % are for commercial purposes which represents 16 % of the worlds total area. It is estimated up to 30000 ha of new industrial plantations will be established per year for the next five years while the annual extension of fuelwood plantations and woodlots should amount to at least double that area. Growth rates of eucalypts vary widely from 1,2 to 70 m3/ha per annum, depending on site conditions and silvicultural techniques. Under average conditions rates between 15 and 25 m3/ha are achieved. It is expected that correct site/species matching, impro...