10.3: Restoring Damaged Ecosystems
Ecosystems are regularly disturbed by natural phenomena such as floods from cyclones/hurricanes, or wildfires started by lightning. Nevertheless, natural disturbances typically lead to succession and a return to ecological conditions that can sustain high levels of biodiversity. In contrast, ecosystems that humans have damaged or destroyed through activities such as unsustainable agriculture and deforestation, overgrazing, or pollution tend to lose their ability to rebound without human intervention.
Ecological restoration aims to restore damaged ecosystems to a point where their ecosystem functions and species composition resemble their original or near-original state.
Ecological restoration is the practice of restoring damaged ecosystems to a point where their ecosystem functions and species composition resemble their original or near-original state. Restoration ecology, in turn, is the scientific study of restoring damaged ecosystems, communities, and populations. Ecological restoration is often the best method for providing for the long-term use of degraded sites, whether considered from the perspectives of ecology, social benefit, or even economic benefit. Consequently, and unsurprisingly, this practice and the science originally developed in response to attempts to restore economically valuable ecosystem functions: creating wetlands to prevent flooding, reclaiming mining sites to prevent pollution and soil erosion, revegetating overgrazed rangelands to increase grass production, and planting trees on cleared areas to improve agroforestry.
Best practices in ecological restoration have undergone major advances in recent decades. In the past, restoration methods mostly aimed for quick economic benefit, which resulted in simplified ecosystems that either failed to establish or degraded after a short time. To avoid such costly mistakes, restoration plans of today increasingly aim for the permanent re-establishment of healthy ecosystems that could support sustainable industries such as ecotourism, wildlife management, carbon sequestration, and low-level grazing by livestock. Ecological restoration often also makes economic sense; a study from South Africa found that every US $1 invested in restoring ecosystem services would generate US $8.30 for the local economy (de Wit et al., 2008).
Many grassroots conservation groups are at the forefront of initiatives that use ecosystem restoration to help make the connection between healthy ecosystems and socio-economic well-being. One prime example is the Green Belt Movement, a Kenyan initiative led by rural women to combat deforestation and restore degraded forests. They do this by helping rural women work together to grow and plant trees. Since its founding in 1977, the organization has overseen the planting of over 51 million trees, which has helped restore forests on Mount Kenya, the Aberdares, and the Mau Complex. The planted trees have prevented erosion, stored rainwater, and provided firewood, timber, and food. In addition, over 30,000 women have been trained in sustainable trades such as forestry, beekeeping, and food processing.
Ecological restoration approaches
There are four main approaches to ecological restoration (Figure 10.10):
- Natural regeneration. Degraded areas, such as abandoned fields or logged areas, are allowed to naturally reseed and return to grasslands or forests. Land managers often choose this approach when active restoration is too expensive, when earlier restoration attempts have failed, or when experience has shown that the ecosystem is resilient and can recover on its own (e.g. Crouzeilles et al., 2017).
- Rehabilitation. Land managers improve conditions of a degraded ecosystem by transitioning it to another, different ecosystem type. For example, land managers could rehabilitate a degraded forest by transitioning it to a tree plantation. Rehabilitation could involve replacing just a few species or many species.
- Partial restoration. Land managers restore some ecosystem functions and some of the species that were dominant or characteristic of the ecosystem. For example, as a part of a grassland restoration, land managers might initially replant a few key species that are hardy and contribute to ecosystem functioning; they could delay restoration of rare species until later phases.
- Complete restoration. Land managers restore an area to benchmark ecosystem structure, mix of species, and ecosystem functioning. Complete restoration usually requires an active program to modify the site, reintroduce native species, and eliminate or reduce the factors that were degrading the ecosystem.
Before a restoration project is initiated, and the type of approach is decided upon, land managers must consider how quickly the ecosystem can recover, resource needs and availability, the availability of locally adapted taxa, and the work that might be required to allow the restored community to persist over the long term. Examples of specific considerations include how to prepare soils, how to handle translocated organisms, when and how much fertiliser and water to add, and how to prevent invasions by unwanted species (Galatowitsch and Richardson, 2005; Zabbey and Tanee, 2016). It is also important to remember that ecosystems generally fail to recover if the factor that caused them to become degraded in the first place is not removed or reduced. For instance, efforts to reverse desertification (Section 5.3.4) would require a reduction of grazing pressure and unsustainable agricultural practices.
To measure restoration success, biologists often aim to restore degraded areas to conditions (ecosystem functions or species composition) comparable to a chosen benchmark or reference site. Reference sites provide practical targets for restoration and can be used to quantitatively assess of the success of a restoration project. Comparing restoration progress against a reference site also allows land managers to intervene or adjust their methods if restoration goals are not being met. This approach, in which land managers monitor conditions and adjust their protocols as and when needed, is known as adaptive restoration. (For a general discussion on adaptive management, see Section 10.2.3.)
Major restoration targets
Many human-altered ecosystems in Africa have proven to be good candidates for ecological restoration. These include tropical rainforests, wetlands, rangelands, and coral reefs. In addition, restoration projects in urban areas (Box 10.4) have become popular in recent years in part due to the enhanced quality of life for people living in the area.
Samuel Kiboi
School of Biological Sciences, University of Nairobi,
Nairobi, Kenya.
Deforestation is one of the main driving forces of biodiversity loss in Africa. Many rural and urban communities rely on wood biomass for energy in the form of either charcoal or firewood. This means that they must continuously source for the firewood or charcoal by harvesting living or dead trees. In many cases, the available energy source is live trees on farmlands which are planted as border trees, or random remnants of pre-existing vegetation within the farm. In some instances, farmers who have land in less densely populated areas have portions of forested areas or woodlots which are under continuous disturbance from wood harvesting. This is more common in rangelands or areas that have lower agricultural productivity. In other areas, such as urban settlements bordering forests, such as Kibera in Nairobi Kenya, there has been extensive harvesting of firewood and sometimes selectively for medicinal purposes or wood carving (Furukawa et. al., 2011).
Given the known benefits of intact forests, including improving food security and climate change mitigation, there are currently several efforts aimed at increasing Kenya’s forest cover both in protected and unprotected areas. The Kenya Forest Service has always been at the forefront of restoration in protected areas, particularly in gazetted forest areas. Despite the general enthusiasm to increase forest cover, many structural and informational challenges remain. Most reforestation programs classify seedlings as either “exotic” or “indigenous”, but do not consider which species are best suited to local conditions. In addition, despite the numerous reforestation programs initiated by individuals, government entities, and corporations, there is generally minimal follow-up maintenance after planting, which can jeopardise an entire project. The first three years after planting are especially crucial for proper seedling establishment and require intensive management, including weeding, mulching, and protection from herbivores. Perhaps the biggest challenge to the sustainability of these reforestation initiatives is the slow growth rate of many valuable indigenous trees that does not meet short-term harvest demands while also allowing for longer-term forest regeneration.
At the University of Nairobi, successful urban forest islands with potential natural vegetation have been established using the “Miyawaki method” (Miyawaki, 2004). This method uses native trees to restore indigenous forests at timelines shorter than if natural regeneration was allowed to take its course (Figure 10.D). To create an urban green space on the university property, we selected 16 native tree species using a vegetation science study of remnant forests around Nairobi. Within 16 months, many of the trees had established well, with the best performing species, Ehretia cymosa, growing to over 2 m (Kiboi et. al., 2014). This study illustrates the importance of selecting locally adapted species in forest restoration initiatives.
Sustainable restoration practices can alleviate the short-term pressure from restored ecosystems while they mature to a self-sustaining structure. Not only should locally adapted species be promoted, but also native species that can be continuously coppiced, where new shoots rapidly replace harvested branches and portions of branches. Exotic species, such as Australian gum, pine, and mesquite (Prosopis juliflora) often display these characteristics, but those species are often invasive with detrimental effects on native ecosystems and communities. Fortunately, many African plant species are also good candidates for sustainable restoration initiatives, including camphor bush (Tarchonanthus camphoratus), sickle-leaved false-thorn (Albizia harveyi), silver clusterleaf (Terminalia sericea), and weeping wattle (Peltophorum africanum) (Kennedy, 1998; Kaschula et al., 2005). Although coppices may have more variable increases in biomass compared to initial planted stands, it is a sustainable way of biomass management especially in areas that experience high demand for harvestable wood. In addition, planting native trees and shrubs in farmlands typically provides beneficial ecosystem services through increasing the abundance and diversity of native insectivorous birds and pollinators of crops. In these various ways, the right management practices can lead to benefits for local people, biodiversity, and sustainable conservation practices.
Tropical forests: Tropical forests cover less than 10% of Earth’s land surface; yet, they contain more than half of all terrestrial species (Cortlett and Primack, 2011). When these forests are lost, we lose substantial biodiversity and ecosystem services. For this reason, tropical forest restoration initiatives in Africa and elsewhere have received much attention in recent years. Towards the end of this chapter we will discuss a major global effort focussed on restoring degraded tropical forests, known as REDD+.
Africa has already lost over 40% of its wetlands through human activity, with current loss rates among the highest in the world .
Wetlands: Africa has already lost over 40% of its wetlands through human activity, with current loss rates among the highest in the world (Davidson, 2014). Because of the recognized importance of wetlands in providing flood control and other ecosystem services (Section 5.5.3), damaged wetlands are frequently targeted in restoration efforts. Wetlands are defined by their hydrology; therefore, wetland restoration projects often the focus on restoring a site’s original hydrology. One such example comes from South Africa, where authorities (with support from the World Bank) have been working on restoring Africa’s largest estuarine lake at iSimangaliso Wetland Park—a multistep process that involves restoration of the estuary’s hydrology, controlling invasive plants around the wetland, and improving farming practices in the surrounding area (Whitfield et al., 2013). Wetland restoration can also occur through activities like dam removals (Section 11.3.2) or replacing exotic vegetation that deplete groundwater with native vegetation to promote groundwater retention (Sirami et al., 2013). Importantly, true wetland restorations are notoriously difficult to accomplish. It can be relatively easy to replant a wetland to look as it previously looked, but to restore the foundational hydrology often requires sophisticated engineering. In many cases, partial wetland rehabilitation is the best that can be achieved.
Mangrove swamps (Figure 10.11) provide nursery grounds for many economically important fisheries, protect coastal communities against powerful storms, and prevent saltwater from intruding into freshwater systems (van Bochove et al., 2014). They are also among the world’s most important carbon sinks, storing four times more carbon per hectare than other types of tropical forests (Donato et al., 2011). Yet, over 35% of the world’s mangrove swamps have already been degraded by agriculture, urban expansion, pollution, and commercial shellfish farming (MEA, 2005; Giri et al., 2011). To regain these lost services, several communities are now restoring their mangroves, while also adopting more sustainable practices to reduce damage to these important habitats (Feka et al., 2009). One of Africa’s most ambitious mangrove restoration projects have been initiated in Senegal, where more than 300,000 local citizens planted more than 150 million mangrove trees across 140 km 2 between 2006 and 2013 (Cormier-Salem and Panfili, 2016). Mangrove (as any other) restoration projects do need to be planned carefully to ensure success. For example, it is important to choose ecologically-appropriate species to plant, rather than the fastest growing species that promises quick (but not necessarily optimal) results. Studies from Eritrea have also shown how fertiliser runoff caused by wave action could reduce lead to project failure (Sato et al., 2005). Another concern is that mangroves are often exploited, restored, and managed as forests, while the primary determinants of their function and structure—hydrology, soils, and nutrients—are neglected (Lewis, 2005; Gopal, 2013). Recent work showed that natural regeneration of mangrove swamps may produce more diverse, resilient, and productive ecosystems compared to planting efforts (Wetlands International, 2016). These issues will need to be addressed to ensure the long-term sustainability of mangrove restoration efforts.
Seasonal drylands: Through extensive land mismanagement (primarily overgrazing and unsustainable agriculture), a large portion of Africa’s seasonal drylands are undergoing desertification, the conversion of once-productive land to desolate man-made deserts—large dry unproductive dust bowls with no vegetation. The degradation of these lands has crippled agriculture, obliterated natural biological communities, and displaced millions of people. While many drylands seem to regenerate naturally when pressures associated with land mismanagement are removed at an early stage, extended periods of mismanagement hamper recovery by leading to a loss of natural seed banks, nutrients, and microsites that allow for seedling establishment.
Somalia is home to one of the world’s most effective desertification reversal programs. Since the early 1990s, when Somalia’s national government collapsed, Somalis have been tormented by warlords and civil war. The lack of effective governance also saw the rise of an unregulated charcoal trade; groves of thorn trees hundreds of years old were set ablaze, before the so-called “black gold” was exported to Arabia. The resultant wildfires and removal of trees caused an erosion crisis, turning grazing lands that once supported a diverse pastoralist community into unproductive wastelands. The resulting famine, exacerbated by droughts, caused even more Somalis to turn to a life of crime, piracy, and terrorism in a desperate effort to support their families. To reverse this decline, the humanitarian NGO Adeso successfully persuaded a regional government to create and enforce a ban on charcoal exports. Adeso also started educating local people about the links between the environment and their own lives, and introduced sustainable alternatives to the charcoal trade, such as promoting the use of solar cookers to reduce the need for charcoal fuel. To reverse desertification and prevent further erosion, Adeso showed local communities how to construct small and simple rock dams; the dams also provide a microenvironment suitable for thorn tree seeds to germinate. Adeso has been so successful in these ventures that they subsequently expanded their work to Kenya and South Sudan.
Coral Reefs: Coral reefs are one of the world’s most important marine ecosystems, both ecologically and economically. They provide food to local communities, support ecotourism industries, and protect coasts by reducing wave energy by as much as 97% (Ferrario et al., 2014). Yet, coral reefs are also one of the most threatened marine ecosystems, impacted heavily by overharvesting, pollution, sedimentation, and climate change. Nevertheless, restoring coral reefs is well worth it; a meta-analysis found that it is nearly 20 times cheaper to restore coral reefs than to construct artificial systems for coastal protection (Ferrario et al., 2014). As such, several initiatives are now in progress to restore coral reefs, ranging from transplanting corals and boosting sea urchin populations for seaweed control to creating artificial reefs that can act as substrate for coral settlements (Lindahl, 2003; Edwards and Gomez, 2007).
The future of ecological restoration
Research in restoration ecology has grown rapidly in recent years. Many reviews (e.g. Suding, 2011) and books (e.g. Falk et al., 2016) have recently been published on the topic. The Society for Ecological Restoration (SER) was established in 1988 to support the field, and two scientific journals (Restoration Ecology and Ecological Restoration) publish hundreds of papers each year on the topic, in addition to the papers published in other ecological and conservation journals. The growth in research provides scientists and land managers more studies and evidence to inform planning and improvement of restoration projects.
A recent development in the field involves biodiversity offsets (ten Kate et al., 2004; MacFarlane et al., 2016). A system generally used by developers, biodiversity offsets aim to achieve no net loss of biodiversity during economic development; some projects even aim for a net overall biodiversity gain. Developers accomplish this by compensating for the ecosystem damage (or loss of threatened species populations, Kormos et al., [2014]) that may be incurred during a development project. This compensation usually follows one or more of three main strategies: (1) reducing the extent of damage at the development site, (2) restoring or protecting natural communities at a different “receptor site” as compensation for what is being lost, and (3) enhancement of the remaining natural communities after development.
While biodiversity offsets (and other restoration initiatives in general) sound good in theory, it is important to remember that the most effective biodiversity conservation strategy remains protecting and managing intact ecosystems. Studies and practical experience have shown that ecological restoration efforts often fail to recreate key characteristics of their reference sites, including species composition or ecosystem functioning, even after years of effort and investment. It is also important to remember than some African ecosystems regenerate very slowly—tropical forests require more than 100 years to develop (Bonnell et al., 2011)—so even effective restorations may take decades to provide the full range of benefits. In cases where biodiversity offsets are pursued, it is critical to ensure that these initiatives indeed offer true conservation gains by mitigating the various associated risks (Coralie et al., 2015; Gordon et al., 2015; Maron et al., 2016).
Because restoring damaged environments takes considerable time and resources, preserving intact ecosystems should be prioritised.