CONCLUSIONS
4. Leaf Characteristics
5.5 Future suggestions for research
The onset of climate change has significant consequences with regards to the future productivity of plant ecosystems worldwide. Climate change predictions suggest that drought events will be more common, earlier snowmelts will occur, higher temperatures and greater variability of rainfall are highly probable (IPCC, 2007). It is likely that there will be significantly longer periods without rainfall, in a number of regions, as well as less rainfall captured by the soil because of more intense storm events (IPCC, 2007). There is no detailed assessment and research dedicated to the potential impacts of climate change on the forestry industry in southern Africa (Warburton and Schulze, 2008). Significant shifts in areas that experience high rainfall are expected, and this is likely to change commercial productivity of the forestry sector. Warburton and Schulze (2008) have suggested that the current areas optimal for planting trees may have to shift in response to changing rainfall patterns.
Conflicting evidence pertaining to physiological responses of trees to elevated CO2, as a consequence of climate change, have been reported. Way (2011) suggested that tree size class and species differences are more important factors determining tree response to drought under elevated CO2 than nutrient availability. An undervalued area of research when considering tree response to changes in water availability is that of the physiology of the water transport system of trees (Brodribb et al., 2010). On a smaller scale, recent research has focussed on venation traits possessed by leaves that correlate with climatic variables or can be directly decoded through models as predictors of plant function (Blonder et al., 2011).
“Venation networks” within leaves can be important predictors of leaf function.
Understanding the importance of leaf venation, xylem transport and resistance to cavitation events, in response to drought, are likely to progressively improve predictions of plant and environmental water use.
The improvement of predictions that govern maximum plant productivity can then be used on local and global scales and in response to future environmental change. There is underestimated potential for the use of water transport physiology to predict the growth and mortality of trees where climate change has altered predictable and reliable rainfall patterns.
The use of FACE experiments to simulate elevated CO2 response in real crop ecosystems has provided interesting results for a number of studies worldwide, but these systems are extremely expensive and substantial maintenance and labour costs are required for meaningful results.
Research that requires great investment cost is not a priority during a period when global financial crisis and budget cuts are prevalent, and the forestry sector in southern Africa is not excluded from the current situation where financial priorities are to cut spending. It would be foolish to make grand, hugely expensive suggestions for future work at SAPPI when it is unlikely, at the current time, that these suggestions would be viable.
Technology transfer of forestry research requires cost-benefit analysis and there is a pressing need to produce conclusions from research undertaken that align with management systems.
Presently, refining choice of species and clones than maintain optimal productivity in response to changing rainfall events and patterns, is more important that continually releasing new clonal varieties.
A number of small-scale research studies could be initiated as a continuation of the current study. Considering the interesting results found in terms of stomatal density (i.e. lack of stomata on the upper leaf surface of GUA leaves), eucalypt clones could be screened for stomatal anatomical differences. Stomatal density determination is rapid, inexpensive and does not require highly skilled technical equipment or staff. It may be useful to assess whether lack of stomata on the upper leaf surface is a common occurrence in all GUA clones, or if it is age-related.
The GUA clone also showed the most pronounced leaf dieback in response to water stress.
Correlations between stomatal absence and leaf dieback in response to soil water deficit of closely related clones could be examined.
Another relatively inexpensive investigation could be determination of δ13C of leaves of clones in areas experiencing significantly different rainfall. Leaf samples could be collected in the field or at tree breeding stations, and the dried leaf samples can be processed locally.
Determination of a site or rainfall gradient can be related to improved water use efficiency may be valuable for future site predictions and commercial clone planting. Another suggestion by Schultze et al. (2006) would be to relate wood δ13C to leaf δ13C, and evaluate whether a relationship occurs between long-term WUE in the leaves and carbon assimilated in the wood.
Existing and future short-term research should focus on facilitating continuous improvement of site-species matching and production management. Should or when the global financial crisis be alleviated and more funds become available for more extensive research programs, there exists great potential in further investigation of water transport physiology (leaf and whole plant hydraulic conductance characteristics) in response to prolonged or severe water stress. The link between plant hydraulic systems, stomatal control of transpiration rate and the concurrent correlation of photosynthetic rates is imperative for comprehending whole- plant responses to changes in water availability. There also exists a huge gap in knowledge of how climate change, especially elevated CO2 and rainfall variability, will change Eucalyptus productivity in southern Africa. Climate change research requires great investment that would require funding from additional research institutions or the corporate sector in order to produce the quality of research being performed worldwide. Research objectives should continuously aim to align with management strategies that benefit the forestry sector in southern Africa.