Forestry is a topic that doesn’t often make headlines — except when runaway fires destroy thousands of trees, as happened recently across the country on a large scale, in what was described as the worst forest fires in South African history.
More than 50Â 000ha of commercial plantations were destroyed (and another 18Â 000ha in Swaziland). The cost to timber companies ran into hundreds of millions of rands.
Forestry contributes an impressive 9% to the country’s GDP, with a total commercial forestry resource of about 1,5-million hectares and an annual export value of more than R9-billion.
Since the early 1980s, there has been a rise in the intensity of forest management practices locally. The principle of ecologically sustainable forestry development and yield management is therefore increasingly emphasised in the plantation context, as well as in the broader ecosystem perspective.
But a profound improvement in the understanding of the factors controlling tree growth and the limitations of the sites on which tress are planted is necessary before the idea of sustainability in plantation timber production can become a practical reality, says Professor Mary Scholes of the University of the Witwatersrand. “This understanding further needs to be linked to the social constraints of the area.”
Predicted shortages in forestry products are increasingly putting pressure on the local industry to maximise yield on a sustainable basis by correctly using existing forestry resources.
There are a number of restrictions limiting the expansion of the industry and the improvement of current yields.
The limited availability of suitable land often results in the unwanted afforestation of marginal land, increasing conflict with other land-users, including residents.
This necessitates the acknow-ledgement first of forestry as a legitimate user of nutrients and water — the limited availability of water and the major impact the forestry industry has on this resource; and second of site degradation under existing afforestation –mainly as a result of the interplay between soil compaction, soil erosion and nutrient depletion.
Scholes says the latest research results have emphasised that, in general, the nutrient balance in plantation ecosystems is negative, especially with respect to nitrogen and phosphorus, and therefore unsustainable in the long term in the absence of fertilisation.
She points out that the negative effect on forest productivity will be apparent long before the nutrient stock is depleted.
Water and nutrient interactions are widely recognised as key factors in determining forest productivity in many parts of the world. South African forest sites are no exception with the growth rate and health of plantations highly dependent on the variation of soil moisture availability. In local conditions soil water availability is often limited, while evaporative demand is high.
Scholes says many of the forest soils in the country are inherently low in fertility since they are situated on ancient weathering surfaces in relatively high rainfall areas. The expected effects of climate change on water availability will exacerbate the issue of sustainable development, she says.
Of the recent fire damage, she says: “We believe that some of the forests will have to be felled, whereas others that were not so badly burned can be saved, but the products from these plantations will probably be different to what was initially intended. We intend to measure the impacts on nutrient cycling; we know that the rates of nitrogen mineralisation will be enhanced for a short period, but the major loss will be the nutrients that were in the litter layers. These will have been lost to the atmosphere in the fires.”
To maintain a competitive forestry industry, continuous observations and monitoring of key indicators of social, economic and environmental processes and conditions are essential.
The continuing evaluation of the complex relationship between soil moisture availability, nutrient status and tree growth on different sites is crucial to both the interpretation of results from silvicultural experiments and to the development of sound management practices.
The need to both understand and quantify site-tree relationships therefore receives high priority in South African forest research.
Six individual projects form part of Scholes’s overall project on the indicators for forest sustainability. These involve the measurement of the effect of residual P and K fertiliser on the growth of Pinus patula at Usutu in Swaziland; optimising site selection and tree breeding; measuring the effects of acidic deposition in the Mpumalanga highveld areas on biogeochemistry and forestry; reviewing carbon sequestration in plantations; as well as research into root dynamics in selected clones; and, a new area, that of studying litter fall dynamics and light fraction carbons across permanent sampling plots.
This research will provide Sappi with important information on how to make its timber plantations sustainable, as well as on potentially increasing its yield at different sites.
This is novel research that has never been attempted before. Technology transfer takes place on a regular basis and the expected technology outputs include technology for faster growing of trees, the ability to estimate nutrient loss with burning and the effect on the environment. Recommendations on optimising the fertilisation programme for young eucalyptus trees have been put forward to Sappi, the technology partner of the project.
The project is contributing a great deal with its ability to recommend how to manage pine and eucalyptus plantations growing under changed climatic conditions, especially in relation to elevated temperatures and reduced water availability.
Says Scholes: “The potential impact of global change on the forestry industry is large with respect to finding suitable planting material able to withstand and flourish under changed temperature regimes, a changed suite of pathogens and pests and reduced availability of water. The project will provide information on suitable planting materials able to adapt to these conditions. The production of the new planting material will lead to local job creation.
“A direct benefit from sustainable plantations is the spin-off of other commercial products like organic foods, homeopathic remedies and foods like honey and mushrooms, which co-habit with forests. Nature tourism also benefits from sustainable forestry.”
Scholes says: “The project is fundamentally about cleaner production and sustainability, enabling South Africa to comply with international protocols in this regard. Water quality remains one of our biggest concerns. Leaching of nitrates found in fertilisers are damaging to the water supply, to say the least. This has already been observed in Mpumalanga and this research directly assesses water quality and the impact of atmospheric pollution on tree growth.
“Therefore the conceptual framework we work from is that water and nutrient cycling, and the processes regulating the rate of transfer of these elements in the landscape will determine the sustainability of our forests, making not only an environmental statement, but also taking into account the commercial value of our forests and the practical as well as the economic implications of long term sustainability.”