Analysis of weather trends in the forestry areas of South Africa shows that warmer temperatures and more erratic rainfall patterns are already a reality. However, foresters have not adapted their modus operandi to the change. To bridge the gap between climatologists and foresters, the ICFR is busy developing ready-to-use spatial tools to enable foresters to understand and evaluate the possible impact of climate change on their plantations.
by Ilaria Germishuizen 

Recent analysis of climate patterns indicates that the southern African region is moving towards a warmer and more erratic climate, and there is evidence that some of these trends are already occurring.

The analysis of rainfall and temperature data by the ICFR for the forestry areas of Mpumalanga and KwaZulu-Natal during the period 1950 to 2007 has highlighted that, although average rainfall and temperature in these areas is not changing significantly, year-to-year variability has drastically increased.

Furthermore, the study identifies a definite trend towards heavier rainfall events over fewer days.

These changes are likely to affect the vulnerability of plantation forests in a number of ways, including the occurrence of drought and fire events and the susceptibility of trees to existing and new pests and pathogens.

Analysis of climate patterns
Climate patterns in South Africa's forestry areas in Mpumalanga and KwaZulu-Natal were analysed over a 50-year period to pick up changes in rainfall and temperature trends that may affect our plantations.

With regard to rainfall, results showed a general trend of increased rainfall variability from year to year, particularly during the drier months, and a decrease in the number of rainy days per year. This last finding is particularly important to foresters as it indicates that the intervals between rainy days are getting longer, exposing our trees to increased drought risk and putting them under increasing physiological stress.

Another clear trend observed was the move towards a warmer climate, with an increase in the frequency of 'hot' days, where the temperature was equal to or in excess of 30oC. Year-to-year mean annual temperature fluctuations were also a discern- able trend, confirming an overall tendency towards less predictable weather patterns. The only exception was observed at Commondale, near Piet Retief, where weather records showed that lower minimum temperatures are becoming more frequent.

This simple analysis has confirmed the percep- tions of foresters on the ground and has highlighted the need to review common practices such as regional planting windows and to re-evaluate seasonal fire and drought risks.

How is the ICFR supporting forestry through this change?
The first easy step was to incorporate the available intermediate (2046-2065) and future (2081-2100) climate change projections for southern Africa into the site classification system that the ICFR has adopted as a platform for research uptake. The ICFR site classification is based on Mean Annual Precipitation (MAP) and Mean Annual Temperature (MAT), and stratifies the South African forestry landscape into site classes that can be considered climatically homogenous. By substituting the current MAP and MAT layer with the projected intermediate and future layers developed by the Climate System Analysis Group based at the University of Cape Town, a picture of the 'future' climate in the forestry landscape was created.

This 'projected' site classification (see figure at bottom of page) shows an increase in warmer and moister sites in the forestry areas, and a decrease in frost- and snow-prone sites.

The 'projected' site classification was used to map changes in site-species' suitability for the main commercially-grown species and to identify possible changes in species importance, with species that are currently marginal, potentially becoming more prominent in the forestry landscape. Furthermore, it highlighted how resistance to certain pests and diseases, and drought and species robustness, are highly desirable traits in a changing environment.

The projected site-species suitability maps provide some basic information that could help identify priorities in future tree improvement research and germplasm conservation.

Climatic conditions are one of the main drivers of forest productivity, and climate change will definitely have an impact on our plantations. Climate change represents both a challenge and an opportunity, and a proactive approach is needed to secure the profit- ability of growing trees sustainably into the future.

Enquiries
For more information visit www.icfr.ukzn.ac.za, or contact Ilaria at ilaria.germishiuzen@icfr.ukzn.ac.za.

Current (above) and future (below) site class distribution in the forestry areas of South Africa. Coefficient of correlation: 0.8

Published in June 2013