ABSTRACT
The “Manzanar Project,” initiated in the 1980s by late Dr. Gordon Hisashi Sato, brought new approaches to restoring ecosystem services in coastal regions. Although initially controversial, these innovative practices culminated with the planting of approximately 700,000 mangrove trees on the muddy coast of Eritrea and helped restore mangrove ecosystems on the Mauritanian side of the Senegal River Delta. Moreover, it formulated the daring proposal in early 2011 that irrigating the deserts with seawater and growing mangroves trees and Spartina grasses could be a giant step in combating hunger and poverty in many parts of the world. Subsequent field work at Nouakchott Autonomous Seaport, Mauritania, suggested the truthfulness of the proposal. Through trial and error at an inland sabkha (supratidal mudflat or generally flat salt-encrusted desert) in Nouakchott, we learned to grow mangrove trees on a sabkha without any irrigation water inputs. Moreover, we grew other halophyte species in the desert (Sesuvium portulacastrum, Nitraria retusa, Spartina maritima), and demonstrated that deserts can be converted into mangrove forests and grassy meadows. Based on the success of these projects, we believe large desert areas can be afforested using simple technology with a minimum carbon footprint. This paves the way for new initiatives to curb climate change and could constitute a major solution for providing key ecosystem services such as carbon storage, soil erosion control, water conservation, and wood production in desert areas.
The impacts of climate change on human health (Rodríguez-Verdugo et al. 2020), wildlife (Staudinger et al. 2013), worldwide socio-economic development (Carleton and Hsiang 2016), and the environment (Malhi et al. 2020) are alarming. Moreover, the competitive economic advantage of agricultural land development compared to the long-term benefits of forests often leads to environmental destruction and undermines efforts to sustain poverty alleviation achievements (Shyamsunder et al. 2020). Therefore, it is urgent that the mechanisms linking forests, poverty, and the environment (Razafindratsima et al. 2021), the negative trade-offs with food security (Doelman et al. 2020), as well as the tradeoffs between poverty reduction and environmental protection be explored in depth (Kenneth 2007). Otherwise, the deteriorating relationship between humans and nature will turn into an existential threat.
Forests remain central to reshaping the human-nature relationship due to their contribution to climate change mitigation and biodiversity conservation (Reid and Huq 2005), global green recovery (FAO 2022), and even global poverty alleviation (Jagger et al. 2022). Afforestation is predicted to be a major solution to curb climate change effects by providing key ecosystem services such as carbon storage, soil erosion control, water conservation, and wood production (Gu et al. 2022), as well as preserve cultural services and values (Moore et al. 2022). However, limitations on land combined with freshwater resource exploitation leave little room for forest planting in conventional agricultural, pastoral, or other suitable areas. In southern Mediterranean countries plagued with recurrent droughts, pressure for freshwater resources from sectors such as agriculture, municipalities, and industry is intense. The environmental water (Harwood et al. 2017, Horne et al. 2017) needed to maintain the sustainable resource base of the rivers, wetlands, and other water sources on which all water users depend is sacrificed at the altar of intensive water usage (Zeggaf Tahiri 2022). Likewise, the pressure exerted by the aquaculture industry, namely shrimp farming in Bangladesh, on mangrove ecosystems leads to deleterious impacts such as environment degradation, loss of land security, food insecurity, rural unemployment, loss of livestock resources, social unrest, and conflicts (Hossain et al. 2013). In this context, desert afforestation can constitute a revolutionary solution. A variety of afforestation materials (seeds, seedlings, and cuttings) have been used for this purpose in conjunction with numerous methods (mechanical, chemical, and site water management) (Duan and Abduwali 2021).
However, all these techniques are constrained by the fact that afforestation and other ecological projects in arid and semi-arid regions can aggravate the shortage of water there (Liu et al. 2018). For instance, in the Gobi Desert, water resources are scarce and cannot support sustainable growth of shrubs, namely Haloxylon ammodendron (Yao et al. 2021). The shrubs survived for the first two years under irrigation conditions but withered and died once irrigation stopped. Paradoxically, the pit excavation method used in such projects resulted in an increase of dust and increased intensity of dust storms (Wang et al. 2013). Moreover, the vulnerability of afforested areas to future climate change will remain a rising concern (Watts et al. 2018).
This paper describes successful desert afforestation, mangrove restoration, and desert greening with the sole use of nontreated seawater. We highlight the scientific acumen of the late Dr. Gordon Sato and celebrate the vision and the achievements of the Manzanar Project in Eritrea (Sato et al. 2005), Morocco (Sato et al. 2011), and Mauritania (Auriol et al. 2010, Zeggaf Tahiri 2023) which Sato pioneered. Our objective is to demonstrate for other practitioners the feasibility of establishing sustainable mangrove forests in the barren fields of sabkhas (supratidal mudflat or generally flat salt-encrusted desert) deep in the desert. The approach we adopted is turning desert constraints such as vast barren lands with high temperatures, high solar radiation, abundance of brackish water and/or seawater (especially in coastal areas) into opportunities for desert greening. Hence, the restoration of ecosystem services is improving the lives of Eritreans and Mauritanians with limited resources.
The Manzanar Project, Eritrea
Mangroves grow in only about 15% of the approximately 1,500 km coastal intertidal zone of Eritrea (including islands). They typically occur in areas called “mersas” where the seasonal rains are channelled to enter the sea each year (Sato et al. 2005). Prior research has demonstrated that seawater contains the same mineral elements of a complete algal growth medium, “Zarrouk’s medium” (Zarrouk 1966) in sufficient quantity to support plant growth except for nitrogen, phosphorus, and iron (Fox 1996). Given that mangroves can grow on Zarrouk’s medium, but not on seawater alone, Sato correctly deduced that the freshwater at mersas was bringing these three essential elements from land (Sato et al. 2005, 2011). Simple experiments by the Manzanar staff confirmed this and constituted a radical departure from the conventional explanation that freshwater per se is required for mangrove growth (Spalding et al. 1977). Accordingly, it was predicted that the treeless intertidal areas of Eritrea, which occupy 85% of the coast, could be successfully planted with mangroves and irrigated with seawater if provided with the missing three elements.
Novel approaches to mangrove planting in desert countries based on planting methods, fencing, and participatory approach have been published (Sato et al. 2005, 2011) and proved establishing mangrove in treeless intertidal areas of Eritrea (Figure 1) was possible if the trees were provided with adequate mineral nutrition (i.e. nitrogen, phosphorus and iron). The Manzanar Project culminated with the planting of around 700,000 mangrove trees, chiefly Avicennia marina, on the muddy coast of Eritrea where they had never grown before. Such forests provided forage for herds of goats (Figure 2), harboured fish nurseries, and ultimately raised living standards of the Hergigo villagers (Sato et al. 2005).
I first met with Dr. Sato in December 2005 at the 8th International Conference on Desert Technology, Nasu, Japan. In January 2007, at his invitation, I visited the Manzanar Project in Massawa, Eritrea. By then, Dr. Sato was already a retired professor from the University of California San Diego, a recipient of the Lifetime Achievement Award from the Society for In Vitro Biology 2002 and the Blue Planet Award 2005 among others. I was greatly impressed by in-field project achievements, by how science can change peoples’ lives in deserts, and above all by his humility. We immediately agreed to extend the project’s outcomes to other African countries. We began a journey which brought us to Mauritania, Senegal, Morocco, United Arab Emirates, and finally Egypt before he died in March 2017. The most salient outputs of this journey are summarized below.
Mangrove Ecosystem Restoration at Diawling National Park (DNP), Mauritania
Mangrove ecosystems in Mauritania are biogeographically marginal and have received little attention (Dahdouh-Guebas and Koedam 2001). In addition, the building of two large dams (Manantali Dam in Mali and the Diama Dam just upstream of the Senegal River Delta) caused major economic impacts on downstream farmers, fishers, and herders (Faye 2018, Ficatier and Niasse 2008) and later completely disrupted the normal tidal hydrology, cutting off water from large areas of the delta (Hamerlynck and Duvail 2003). Subsequently, the pristine mangrove forests that once covered the flood plains of DNP turned to large dry and infertile plains with scattered linear bands of mangrove trees matching the contours of the tidal channels (Diawara 1995).
In this context, a three-year project for mangrove ecosystem restoration at DNP, Mauritania, was launched in 2009 by UNESCO-Morocco Office under the UN-MDG program. Four sites (Gahra, Birette, Dar Essalam, and Dar Errahma), all located within the DNP area and covering an area of 25 ha, were selected for restoring the predominantly degraded Avicennia germinans stands. By the end of the project, using mostly the same approaches as those previously used in Eritrea, we planted around 42,000 mangrove trees with survival rates exceeding 95%. Two years after planting, the mangrove trees reached a height of about 2 m and constituted a source of forage for herds of camels and goats (Figure 3). The success of the project was reported (Tandia 2011, Zeggaf Tahiri 2023).
Planting mangrove trees was not the only virtue of this project. Through numerous explorations of the delta mangrove ecosystems, we located scattered individual mangrove specimen in the Bell basin (less than 10 trees) and a mangrove stand at Hassi Ba site (less than 20 trees), both few kilometers away from the fringes of water bodies of the delta (Figure 4). These mangrove stands show the unusual capacity of trees to grow in dry areas out of water for a long period of the year. For DNP staff, these remnant trees were a testimony of past extensive mangrove ecosystems before the huge delta hydrology changes caused by construction of the Diama dam. For us, it was evidence that mangrove trees are geographically limited by the successive concurrence of three events: natural transport of propagules to new sites (tide or flood), successful germination of propagules, and soil water availability for mature mangrove trees growth.
Desert Greening at Nouakchott, Mauritania
A Manzanar Project-funded initiative was launched one year before mangrove ecosystem restoration at DNP, near Nouakchott Autonomous Seaport (Figure 5) and was supposed to yield an answer for the daring proposal mentioned earlier in background section. At first, we attempted planting mangrove saplings in the intertidal area on the Atlantic Ocean coast (Figure 5, A) but failed because strong waves washed away all plants on shore. (It is worth noting this was the same fate for the Tarfaya, Morocco, initiative years later, where we confronted the added difficulty of strong and continuous winds [Sato et al. 2011]).
In 2008, we started growing mangrove saplings at an in-situ nursery and then replanting them in a contiguous sabkha (Figure 5, B). These were fertilized with fish waste and irrigated with non-treated seawater. After approximately a year, we barely could sustain the saplings in this harsh environment (Figure 6). Accidentally in October 2009 came a high tide that left our experimental plot in ruins. Adding the fact that seawater pump maintenance and labour costs were prohibitive for the Manzanar Project to finance, we desperately needed a new approach.
At this point, the observations made previously at DNP were inspiring: If mangrove specimen could thrive in year-most dry areas at DNP, could they grow on sabkhas. By digging a hole in the sabkha (Figure 5, Site 3), we noticed the shallow water table level underneath (approximately 40 cm depth) was fluctuating according to ocean tidal movement meaning it was connected to the ocean. We then hypothesized that mature mangrove saplings could grow on sabkhas by benefiting primarily from underground salty water. This simple observation proved useful and led to the vision of dryland forests in deserts.
Afterward, we went further inland into the adjacent sabkha and planted directly mature saplings with elongated roots by drilling holes and adding fish waste with no irrigation at all (Figure 5, Site 3). The mangrove trees had a survival rate of 100%, using exclusively saltwater underneath without any further irrigation (Figure 7). Next, other halophyte species were added to the experiment list: S. portulacastrum, N. retusa, S. maritima (Figure 8). Although the site was not extensive, only about a hectare, we managed for the project duration to transform an infertile sabkha in a salty garden that drew many curious Mauritanians. This work proved successful (Auriol et al. 2009, Sato et al. 2011) and supports the notion that the deserts of the world can be converted into verdant forests and grassy meadows (Zeggaf Tahiri and Sato 2008).
Regretfully, the technical success of this journey was overshadowed by a greater political failure. In July 2012, the site was abandoned for lack of funding from the local administration. Currently, only the remaining mangrove trees at Nouakchott Autonomous Seaport testify to our quest for desert forests.
Discussion
In this paper, we reviewed the failures, the achievements, and the prospects of our field work in Mauritania hoping this will support the quest for desert afforestation worldwide. Through our work and journey in Mauritania, we became deeply convinced of the following:
To combat desertification, halt climate change, and fight poverty, the international community, politicians and scientists alike have declared war on nature calamities. The same belligerent attitude has nurtured current afforestation projects in deserts worldwide. These projects mobilize costly resources and adopt the most sophisticated approaches, including technological and energy consuming tools, and foreign expertise in an aggressive manner. We often put aside simple approaches and the wise thinking that could help us take advantage of the harsh conditions to create a healthier environment, improve production, create wealth for the poor, and reverse the trend of environment degradation. The tools developed by the Manzanar Project are simple solutions based on simple observations leading to sustainable practices. This makes it a sustainable approach in the harsh conditions of deserts with a tremendously reduced carbon footprint on environment. We hypothesize that in these areas, we can take advantage of the “favourable” climatic conditions (high temperatures, high solar radiation, marginal land, seawater, and halophyte species) to devise nature-based solutions which could ultimately transform deserts worldwide into verdant forests and grassy meadows, create wealth, and address present and future climate change impacts on humanity.
Growing mangroves on desert infertile areas, namely sabkhas, is possible and is supported by the existence of inland mangroves in countries like India, Australia, and Mexico where their survival in water-scarce highly saline arid zones is still considered an environmental mystery (Patel 2012). Growing mangroves in arid areas can help to
Ease fodder production pressure on freshwater resources and create wealth for marginalized populations in deserts.
Mitigate the effects of desert encroachment on fertile and productive lands, as well as coastal erosion, curb climate change effects, and support biodiversity conservation on wetlands.
Support green belts across deserts such as the UNCCD’s Great Green Wall initiative in Africa (Nature Editorial 2023) or the Three Norths Shelterbelt Project in China (Wang et al. 2010).
We strongly believe desert greening breakthroughs could originate from scientists who dare to live in and perform research in desert environments, who feel desert biotic and abiotic stress in their skin, who make wise observations and bring simple sustainable solutions.
Dedication
This work is submitted in memory of late Dr. Gordon Hisashi Sato, former president of the Manzanar Project, a brilliant scientist and a great human being. After enduring the horrors of the Manzanar concentration camp, he devoted his life to raising Africans in the inauspicious deserts from the pangs of poverty and famine. Rest in peace.
Readers can learn more about the legacy of Dr. Sato here:
https://senate.universityofcalifornia.edu/in-memoriam/files/gordon-sato.html
https://underthecblog.org/2015/10/29/the-manzanar-project-and-the-worlds-most-unlikely-mangroves/
https://sivb.org/InVitroReport/issue-51-2-april-june-2017/in-memoriam-dr-gordon-h-sato/
Footnotes
Color version of this article is available online at: http://er.uwpress.org
