Potential impacts of climate change on the climatically suitable growth areas of Pinus and Eucalyptus:: results from a sensitivity study in South Africa

Global average surface temperature has increased by approximately 0.74 degrees C over the most recent 100-year period. At a regional level in South Africa, detectable changes in both the rainfall and temperature patterns have occurred in the past 50 years. Climate change has become a reality that can no longer be ignored. Given the relatively long timescales of plant-to-harvest rotations in the commercial production forestry sector in South Africa, and the significant investment implied, climate change has the potential to have substantial impacts on forestry productivity and profitability. Under climate change conditions the climatically optimum areas for specific forest species are hypothesised to shift, with optimum areas changing in extent and location between and within provinces. This paper focuses on the Eucalyptus and Pinus genera. From the ICFR Forestry Productivity Toolbox, climate criteria for three Pinus species plus one hybrid, and four Eucalyptus species plus one hybrid, were used in combination with gridded maps of present mean annual temperature and mean annual rainfall to assess climatically optimum, moderate- and high-risk growth areas, as well as unsuitable growth areas over southern Africa. The temperature and rainfall variables were then perturbed through plausible ranges of projected future climates to determine the potential impacts of climate change on the climatically optimum, moderate and unsuitable growth areas of the Pinus and Eucalyptus families. For both families, rising temperatures may slightly increase the optimum growth area in Mpumalanga and the Eastern Cape, whereas in KwaZulu-Natal the area may reduce. The Pinus species showed less sensitivity to rising temperatures than eucalypts. The two hybrids exhibited less sensitivity than other species of their genera. The hybrid Pinus ExC emerged as least sensitive to increasing temperature. Declining rainfall concomitant with rising temperature will have an especially negative effect on total area of optimal growth. An increase in rainfall will, however, offset all negative impacts of temperature and increase total optimum growth area for both families.