Risk associated with crop production is probably the main limiting factor to increasing harvests from industrial wood plantations in South Africa, and the yield expectation associated with current silviculture practices is unlikely to be frequently attained in practice. Re-establishment is subject to considerable within-season variability in weather conditions. Periods of low rainfall, high temperature, hail, early and late season frost and extreme winter frost can reduce post-plant survival leading to replanting or the uncertain outcome from blanking operations. Pests and pathogens also contribute to poor re-establishment success, sometime in conjunction with abiotic environmental stress conditions. Resultant below-target stocking and stand variability will detract from harvest yield relative to expectation. Reducing the frequency of these occurrences will contribute to overall wood supply and the success of individual growers.
This research focus area aims to reduce risks associated with tree growing by developing recommendations that will mitigate specific issues, and encompasses biotic, climatic and edaphic risks. The largest component of research deals with pest and pathogen risks, addressing current major threats to different crops in the sector; wattle rust and eucalypt canopy pests. The ability of forestry sites to sustain nutrient supply and productivity over successive rotations, and in the face of changing forestry practice, remains a major uncertainty, and research is underway to address these issue.s