Chapters 5.45

5.45 -Potential For Combating Climate Change With Acacia Trees Globally By Smallholder Farmers

Ashley Martin, University of Guelph, Canada

Suggested citation for this chapter.

Martin,A. (2022) Potential For Combating Climate Change With Acacia Trees Globally By Smallholder Farmers, In Farmpedia, The Encyclopedia for Small Scale Farmers. Editor, M.N. Raizada, University of Guelph, Canada. http://www.farmpedia.org

Detailed overview of genus

The Genus Acacia is a tree or shrub has over 1250 different species under its umbrella, with 170 of those being native to Africa (Hayward, 2004). In addition to Africa, the genus is also native to Australia, South East Asia, and the Middle East (Brenan, 1983). A non-demanding plant, it is most commonly grown from seed, requiring less labour and being more cost effective than other trees (ANPSA, 2012). It grows optimally in a range of soil types ranging from sand dunes to lateritic soils, and flourishes in a temperature between 12 and 25 degrees Celsius (Murray et. al, 1990). The plant does best in a pH range between 5 and 8, with an annual rainfall between 280 mm and 450 mm, thus making it ideal for some subtropical regions of the world (Mwove, 2020). It is sensitive to frost and waterlogging (Mwove, 2020). Most species live for 12 to 15 years, and are generally fast-growing plants (ANPSA, 2012). There is variation in terms of the optimal growing conditions amongst Acacia species, but the most widely cultivated species thrive in the above conditions.

How acacia trees can help combat climate change

According to a study conducted by the U.K.’s Department for International Development’s Forestry Research Programme, the following species are suitable for dry and degraded soils, and are highly drought tolerant: Acacia erioloba, Acacia karroo, Acacia nilotica, Acacia senegal, and Acacia tortilis (Hayward, 2004). Their drought tolerance comes from their deep taproots and results in less than 50% hydraulic conductivity loss (Crous et. al, 2011), meaning that planting them would create the potential to increase forest cover in arid and semi-arid areas – leading to more greenspace, effectively boosting air quality and allowing space for more wildlife habitat across Africa. At the same time, as the roots associate with underground bacteria that convert atmospheric nitrogen gas to nitrogen fertilizer, the genus Acacia has the ability to improve soil quality and help to prevent desertification (Desertlands Foundation-Kenya, 2018).

Benefits to the farmer of growing Acacia trees

Though each species and variety of Acacia offers its own unique properties and products, the species above tend to be multipurpose. Farmers can generate income from numerous Acacia products - such as livestock fodder, dyes and tannins, famine food, firewood, charcoal, timber for building/pulp/tools/musical instruments, as well as gum arabic from the A. senegal species. The flowering and shrub varieties are used and sold as ornamentals (Kew Science, 2020). Gum arabic is used as a food additive and has the highest economic potential out of all these products - growing best in the “gum-belt” which spans North Africa to Ethiopia in the west (Hayward, 2004). Smoke from burning the wood also acts as an effective and natural insect repellent (Wickens, 1995). The thorny branches of many species can serve as crude but effective fencing to keep out wandering animals who might graze on the tree (Hayward, 2004).

As previously mentioned, Acacia trees improve soil quality, therefore allowing farmers to produce higher quality and more nutritious food crops for their own consumption as well as for sale (Desertlands Foundation-Kenya, 2018). Weeds do not tend to be an issue with Acacias, as the tree grows quickly and “shades out the weeds” (Murray et. al, 1990). Fertilizer application is not a huge concern, but it would be best to establish using a slow-releasing fertilizer (ANPSA, 2012). According to Ogodo (2009), the tree itself acts as a fertilizer. Acacia leaves also serve as a nutritional fodder for livestock, delivering around 17% crude protein compared to maize at less than 10% (Hayward, 2004). All of the benefits and ease of cultivating this tree can positively impact smallholder women farmers, allowing them highly increased crop yields, improved soil quality, additional products to sell or use, and as a natural fertilizer for just the initial cost and upkeep of the tree.

Critical analysis and practical

Seeds

In South Africa, the retail cost of Acacia seeds online is on average between 12-20 Rand, or between $0.79 and $1.30 USD per pack of ten seeds (Seeds for Africa, 2020), depending on the species. This is equivalent to a half-day day’s worth of earnings for many smallholder farmers. More affordable seeds could potentially be distributed by seed banks or by trade in Sub-Saharan Africa and SouthEast Asia, though it is difficult to find governments or NGOs that are distributing seeds to smallholder farmers.. There appears to be a need for organizations to purchase seeds from suppliers such as Seeds for Africa (mentioned above), or connect local entrepreneurs to seed suppliers.

Seeds shed annually from pre-existing plants, and can be harvested by striking the branches until they fall off (ANPSA, 2012). Due to the widespread nature of Acacias over the world the seed is not difficult to obtain. Seeds could potentially be distributed by existing seed banks as well (links below). As with many plants, Acacia seeds have a hard outer coat which needs to be treated prior to germination in order for it to grow successfully (ANPSA, 2012). The simplest way to pretreat the seeds is to pour boiling water over them and let them soak overnight. The seeds should puff up to nearly double their size, at which point they will be ready to plant. In some cases, the seeds will not puff up after only one round of pretreatment, in which case it can be repeated as many times as necessary. Alternatively, the seeds can be rubbed in between sandpaper in order to wear down the seed coat. These two methods should work for most species of Acacia, excluding those which originate from tropical areas. The seeds from most tropical species however, can be planted without treatment (Murray et. al, 1990).

Cultivation and potential issues

Aside from occasional and light pruning in its initial years, the Acacia requires minimal maintenance (ANPSA, 2012). As long as it is grown in a suitable climate, watering and fertilizing are not required.

A non demanding tree, the Acacia does not suffer from many pests or diseases. Notably though, the borer has been studied to affect black Acacias such as A.decurrens, A.parramattensis and A.mearnsii (ANPSA, 2012). When affected by borers, the tree can still grow strongly for 7 to 8 years, around half of its natural lifespan. If necessary, a wire can be inserted into the trunk or branch to remove the pest.

As previously mentioned, the genus Acacia grows well in poor soils. It is usually unnecessary to introduce new compatible rhizobia bacteria to facilitate underground atmospheric nitrogen fixation (Thrall et. al, 2005). If this optional step is taken and results in the inoculation of Acacia, it has the potential to further rejuvenate degraded soils. Inoculated Acacia species have also shown an overall increase in the efficiency of seed establishment and tree growth (Thrall et. Al, 2005). One notable supplier of inoculants is BASF Agricultural Solutions in South Africa (BASF, 2017). Poaching of the sapling/tree may or may not be a concern, but wild or domestic animals may graze on the leaves, inhibiting their growth (Pasternak et., 2010).

Harvest

The most practical way to harvest Acacia wood for sale is through the use of machinery such as harvesters for logging, though on the smaller scale it can be done manually. Harvesting for gum arabic is simple, as it oozes out naturally under harsh climate conditions when the bark breaks. In order to speed up the process, the tree can be tapped (Mwove, 2020). Ideally, one should wait until the tree is mature in order to reap the full benefits. This means that the end product of wood should be harvested after at least 7 to 8 years of growth. Products such as gum arabic, seed/seed pods, etc. can be harvested along the way as they are shed annually. The soil improvement benefit in terms of nitrogen also lasts the entirety of the tree’s lifespan (ANPSA, 2012).

Helpful Links and Videos

Though the World Agroforestry Centre or other NGOs do not appear to be directly supplying acacia seeds to smallholder farmers, a book was published by the World Agroforestry Centre on how organizations can begin to adopt seed distribution: https://www.worldagroforestry.org/sites/default/files/Toolkit.pdf

Based in Tunisia, “Acacias For All” project aims to combat desertification and empower women farmers at the same time. Projects such as this can lay out a foundation for other organizations - supplying seeds, teaching women how to cultivate, harvest, and create/sell products for income. The website below is in French, though translated sources can be found as well. http://acaciasforall.tn/?v=947d7d61cd9a

Manual seed harvesting tutorial - https://www.youtube.com/watch?v=f-GEh8dQEoA

Brief summary of propagation and cultivation practices - https://uses.plantnet-project.org/en/Acacia_(PROSEA_Timbers)

Case studies and detailed information on Acacias for international development from ICRAF - http://apps.worldagroforestry.org/icraf-subject/acacia

Further information on Acacia products, specifically medicinal/pharmaceutical - https://www.sciencedirect.com/topics/agricultural-and-biological-sciences/acacia

FAO Conservation Guide 27, a book full of information on management and usage of Acacias - http://www.fao.org/3/v5360e/v5360e00.htm

References

1. Australian Native Plants Society Australia (2012, December). ANPSA Plant Guide: Acacia. http://anpsa.org.au/acacia.html.

2. BASF Agricultural Solutions South Africa (2017). RhizoFlo – Agricultural Solutions. https://www.agro.basf.co.za/en/Products/Overview/Inoculant/RhizoFlo.html

3. Brenan, J. P. M. (1983). Manual on taxonomy of Acacia species: present taxonomy of four species of Acacia (A. albida, A. senegal, A. nilotica, A. tortilis). Food and agriculture Organization of the United Nations, Rome. http://www.fao.org/3/q2934e/Q2934E00.htm#TOC

4. Crous, C. J., Jacobs, S. M., & Esler, K. J. (2011). Drought-tolerance of an invasive alien tree, Acacia mearnsii and two native competitors in fynbos riparian ecotones. Biological Invasions, 14(3), 619–631. https://doi.org/10.1007/s10530-011-0103-y

5. Desertlands-Foundation Kenya. (2018, January 31). Acacia: Answer to Climate Change,Economic Empowerment & Food Security in ASALs. Climate CoLab. https://www.climatecolab.org/contests/2017/exploring-synergistic-solutions-for-sustainable-development/phase/1318866/proposal/1334290

6. Hayward, B. (2004). The Acacia tree: a sustainable resource for Africa. Forestry Research Programme. United Kingdom Department for International Development. https://assets.publishing.service.gov.uk/media/57a08cb2ed915d622c0014ef/ZF0173_-_Acacia_Book.pdf

7. Kew Science, Royal Botanic Gardens (2020). Acacia Mill.: Plants of the World Online: Kew Science. Plants of the World Online. http://powo.science.kew.org/taxon/325783-2.

8. Murray, K., Impara, P., & Stephens, M. (1990). Reforestation in the Pacific Islands (pp. 135–136). Peace Corps ICE. http://www.nzdl.org/gsdlmod?e=d-00000-00---off-0envl--00-0----0-10-0---0---0direct-10---4-------0-1l--11-en-50---20-about---00-0-1-00-0-0-11-1-0utfZz-8-00&cl=CL2.8.4&d=HASHb1669db516271d3af777f8.1&gt=2

9. Mwove, J. (2020, June 29). A-Z of farming acacia trees for Gum Arabic. Nation Kenya. https://nation.africa/kenya/business/seeds-of-gold/a-z-of-farming-acacia-trees-for-gum-arabic-399530.

10. Ogodo, O. (2009, August 28). Acacia tree can boost crops - and more - across Africa. SciDev.Net. https://www.scidev.net/global/farming/news/acacia-tree-can-boost-crops-and-more-across-africa.html.

11. Pasternak, D., Nikiema, A., Haglund, E., & Ndjeunga, J. (2010) Keep Africa Covered Trees-based options to combat land degradation in the Sudano Sahel: A Contribution to the “Great Green Wall” of the Sahel Program. In Dia, A., & Duponnois, R. (Eds.), Le projet majeur africain de la Grande Muraille Verte: Concepts et mise en œuvre. IRD Éditions. doi:10.4000/books.irdeditions.2125

12. Poschen, P. (1986). An evaluation of the Acacia albida-based agroforestry practices in the Hararghe highlands of Eastern Ethiopia. Agroforest Syst 4, 129–143. https://doi.org/10.1007/BF00141545

13. Seeds for Africa (2020) Acacias - Seeds for Africa. https://www.seedsforafrica.co.za/search?q=acacia.

14. Thrall, P.H., Millsom, D.A., Jeavons, A.C., Waayers, M., Harvey, G.R., Bagnall, D.J. and Brockwell, J. (2005), Seed inoculation with effective root nodule bacteria enhances revegetation success. Journal of Applied Ecology, 42: 740-751. https://doi.org/10.1111/j.1365-2664.2005.01058.x

15. Wickens, G. E. (1995). Role of Acacia species in the rural economy of dry Africa and the Near East. Food and Agriculture Organization of the United Nations, Rome.