Why Foresters Are Betting on Alternative Eucalyptus Species for a Warmer Future
For decades, South Africa's commercial forestry has relied on a familiar cast of tree species. However, the very foundation of this industry is shifting. Projected climate changes, leading to warmer temperatures and reduced productivity at traditional sites, are forcing scientists and foresters to look for new, resilient tree species that can thrive in the future's challenging conditions1 . This is the story of the quest for the next generation of "green gold"—hardy eucalyptus species capable of securing the nation's forestry sector against the backdrop of a changing climate.
South Africa's commercial forestry has expanded over the past 50 years into the mid- and high-altitude summer rainfall regions. Here, species like Eucalyptus nitens and Eucalyptus macarthurii have been the dominant players1 . But their reign is under threat.
Climate models paint a clear picture: the suitability of these sites is increasingly endangered1 . The search for alternatives is not merely an academic exercise; it is a necessary step for the economic and environmental sustainability of the industry.
Warmer temperatures and altered precipitation patterns threaten traditional forestry sites.
Current commercial species show reduced productivity under projected future conditions.
Research is focusing on several promising eucalyptus species and subspecies known for their superior traits. Two stand out for their proven potential.
A recent study evaluated this subspecies as a potential alternative for high-altitude sites1 . The results were highly encouraging. Four Australian provenances—Butter Leaf, Forest Land, Chaelundi, and Styx River—consistently ranked as top performers in trials conducted at two locations, Windy Gap and The Bends1 .
Crucially, the research found that genotype-environment interactions were negligible. This means that a single, multi-provenance breeding population would be suitable for E. nobilis across South Africa, simplifying breeding programs1 .
Another strong contender is E. globulus subsp. bicostata, a close relative of the well-known E. globulus, which is prized for its superior kraft pulping qualities5 .
The Narrow Neck Ridge provenance emerged as a star performer. It was significantly less susceptible to the fungal disease Mycosphaerella nobilosa and outperformed other provenances in diameter, height, basal area, and volume5 .
| Species/Subspecies | Top Provenances | Key Strengths |
|---|---|---|
| E. viminalis subsp. nobilis | Butter Leaf, Forest Land, Chaelundi, Styx River | Consistent top growth performance; negligible genotype-environment interaction1 |
| E. globulus subsp. bicostata | Narrow Neck Ridge | Superior tolerance to Mycosphaerella; high volume production; good pulping properties5 |
To understand how forest scientists evaluate new trees, let's examine the pivotal E. nobilis trial in detail.
The study was designed with rigor to yield reliable, actionable data1 :
The findings from this experiment were promising for the future of E. nobilis in South Africa1 :
| Parameter | Finding | Implication for Breeding |
|---|---|---|
| Type B Genetic Correlation | Indicated negligible genotype-environment interaction | A single breeding population can be developed for different sites |
| Narrow-Sense Heritability (h²) | 0.30 - 0.35 for DBH, Height, and Volume | Strong potential for successful genetic selection and improvement |
| Estimated Genetic Gain | 2% - 10% for top provenances | Substantial productivity increases are achievable through selection |
Data based on research findings1
Developing resilient forests isn't just about tree genetics. Scientists have a suite of tools to help seedlings survive and thrive in stressful conditions. One powerful biological tool is the use of beneficial fungi.
Arbuscular mycorrhizal fungi (AMF) form a symbiotic relationship with plant roots, acting as a natural extension of the root system. A 2021 study on Eucalyptus camaldulensis demonstrated just how powerful this partnership can be under stress3 .
When eucalyptus seedlings were pre-inoculated with salt-tolerant AMF species (Glomus sp., Gigaspora albida, G. decipiens) and then exposed to high salinity levels, the results were striking3 :
AMF-inoculated plants had higher chlorophyll concentrations (over 50% more) and lower leaf proline (a stress indicator) by more than 20%3 .
AMF increased the critical potassium-to-sodium (K/Na) ratio by three to six times. This helps protect the plant's cellular functions from the toxic effects of sodium3 .
Pre-inoculation with AMF improved overall plant performance by more than 30% under salinity stress compared to non-inoculated plants3 .
This research shows that pairing the right tree with the right biological allies can dramatically boost its ability to withstand environmental challenges like soil salinity.
| Tool/Reagent | Function in Research | Practical Application |
|---|---|---|
| Salt-Tolerant AMF Inoculum | Forms symbiotic relationship with roots to improve water/nutrient uptake and stress tolerance3 | Used as a bio-fertilizer in nurseries to produce hardier seedlings for outplanting in marginal soils |
| Randomized Complete Block Design | Statistical experimental design that minimizes the impact of variability in field conditions1 | Ensures that the performance data collected for different tree provenances is reliable and accurate |
| WINRHIZO Pro System | Scans and analyzes root systems for length, diameter, surface area, and tissue density3 | Allows scientists to non-destructively study how root architecture contributes to drought and soil stress tolerance |
The journey of introducing and testing new tree species is a long-term endeavor, but the results for alternative eucalypts like E. nobilis and E. globulus subsp. bicostata are promising. By combining strategic genetic selection with advanced silvicultural tools like AMF inoculation, South Africa's forestry sector is building a resilient and productive future.
The work ensures that the country's commercial forests will continue to provide essential resources, support rural economies, and remain a vibrant part of the landscape for generations to come. The "green gold" of the future is being cultivated today in the research trials of the summer rainfall region.
Forestry research requires decades of observation and data collection to yield meaningful results.
Identifying high-heritability traits allows for effective breeding of resilient tree varieties.
Beneficial fungi like AMF enhance tree resilience to environmental stressors.
Scientific methodologies ensure reliable data for informed decision-making.