4. OTHER FACTORS POTENTIALLY INFLUENCING TIMBER PRODUCTIVITY
4.4 Growth of Pines at North East Cape Forests and their Timber Properties
4.5.4 Fertilization
4. That growth response to vegetation management is affected by site and planted pine species.
The important outcome of this study was that specific mechanisms of competition will vary as a function of the climatic and soil conditions of the site and that the impact of different types of competitors on tree growth will change as the seedlings mature and compete in different spatial zones. Results also indicated that although grasses and herbaceous broadleaves were initially vigorous competitors, woody plants were the most detrimental to early pine growth. Tree growth was greatest where herbaceous and woody vegetation was controlled, that is on the weed free plots. Here there was no competition for light, water or nutrients, and tree growth occurred at a maximum rate. This is the ideal situation (Rolando and Little, 2000).
Fertilization in pine stands of Swaziland is strongly age-dependent. Thinning may also affect nutrient status of plantations (Du Toit and Carlson, 2000).
Substantial research results have been published on fertilization at establishment (Donald, 1990; Morris 1986; Donald et al., 1987; Herbert, 1996a; Herbert and Sch6nau, 1989a and 1989b; Sch6nau, 1983). Phosphorus (P) was the main limiting nutrient for all three genera in the North East Cape Forests. Pines have also shown early responses to Nitrogen, Phosphorus, Potassium (NPK) mixtures, but the only sustained responses with fertilization at planting were to P applications. However, in other trials initial responses to P applied to pines at planting were not sustained (Du Toit and Carlson, 2000).
From 1990 until 1993 all stands in the study area were fertilized at planting time with various fertilizers, application techniques and application quantities.
(K.M. Basset, pers. comm., North East Cape Forests, 2001). Following a management decision in 1993, fertilization of pines were discontinued until proper weed control regimes were put in place (Darrow, 1996). Limited fertilizer applications were conducted on scalped lands due to the fact that this land preparation technique removed the mineral topsoil. Several forest nutrition research projects were conducted in NECF with variable and inconclusive results.
4.6 Abiotic Risk
NECF has been exposed to severe fire damage during dry season winters, this is when the amount of fuel is largest, the fuel (dry grasses) and weather (frequent and strong winds) conditions are hazardous, and frequent controlled fires applied by farmers increase the probability for destructive fire. However, when damaging fires do occur the chance for tree survival depends on the species susceptibility to fire damage. Local experience showed that some species, such as P. leiophylla and P. elliottii are more tolerant to damage than, for example, P. patula.
Therefore, planting species less susceptible to fire damage on hazardous sites will reduce timber and growth losses when various other means of fire prevention fail (De Ronde and Zwolinski, 1997).
It is important to note that fire, seasonal drought and seasonal floods contribute to the utilisation of available resources and thereby directly and indirectly contribute to stand variability. The resulting impact has not been quantified, but it remains an important factor in the evaluation of current stand performance in NECF.
4.7 Human Factor
When the project was initiated in 1989 not all the personnel recruited had forestry backgrounds and qualifications (Botha, 1996). It was a difficult time as infrastructure was extremely limited and the high target that was set increased the difficulty of the project. By 1993 it became obvious that the local forestry management staff was not in a position to maintain the schedules and quality
standards for plantation establishment that had been envisaged in the initial years.
A new management team was subsequently deployed. The first management intervention consisted of a reduction in the rate of planting to a more manageable level as well as a discontinuation of the intensive site management techniques and fertilisation until the weed management practises were in line with the new
standards (Darrow, 1997).
4.8 Products and Regimes
The project was initiated with an objective of producing 1,1 million tons of thermo mechanical pulpwood on a land base of 80 000 ha based on a 60% eucalypt and 40% pine composition. Following the strategic review by Zobel in 1991 it was decided to discontinue the production of hardwood and focus on softwood for thermo mechanical pulp (TMP) production. Subsequent market movements and strategic realignment resulted in a decision to manage the plantations for a dual industrial sawlog and pulpwood regime based on an afforestation area of approximately 35 000 ha (Botha, 1996; Darrow, 1997). These strategic realignments had an impact on the silvicultural prescriptions and regimes and contributed to the variability in current stand parameters.
4.9 Land Acquisition and Suitability of Soils
Initial strategic planning entailed the purchasing of 80 000 ha of land (Harvett, 1989). The strategy behind this was to keep farm prices low (demand-supply principle). Market indications where that if less land would be purchased the price per hectare would be higher (in excess of R1 OOD/ha). The average price paid at
the end of the land acquisition project equated to R775/ha. The strategy to keep land prices low thus worked well, however, in order to make this strategy a success the land purchases had to be conducted over a limited time period and across all the landholdings identified in early strategic reconnaissance based on soil and climate data (Mills et. al. , 1988). There was thus an inherent trade-off between the capital outlay for land and the quality of the afforestation potential information available in support of the purchase decision-making process, this was further complicated by the unique geology and climate parameters associated with the Eastern Cape as proven by the subsequent ongoing research.
During 1993 a re-evaluation of the NECF landholdings found 24 000 ha of the original acquired area to be unsuiTable for afforestation due to low rainfall, inaccessibility, shallow soils or steep slopes (Botha, 1996). The identified 24 000 ha represents consolidated units. NECF was authorised to alienate all marginal and uneconomical land and to replace this with land of high afforestation potential.