IndexIntroductionRehabilitation of Dryland EcosystemsDegradation FactorsPassive vs Active RestorationAtacama Desert ExperimentsEffect of Precipitation, Temperature and SoilEffect of Herbivores on Seedling SurvivalRehabilitation in NigerAgroforestry as a way to restore the dry forestConclusionDiscussionIntroductionEcosystems are dynamic by nature. Throughout history, biomes around the world have changed. Currently, several dry forests are (or have already) altered their structure and are losing their function as a dry forest ecosystem (as in Ethiopia and Ghana). Along with the degradation of dry forests into savannas comes the loss of the ecosystem services they provide. Say no to plagiarism. Get a tailor-made essay on "Why Violent Video Games Shouldn't Be Banned"? Get an Original Essay However, dryland ecosystems, such as savannas, are of great importance to human societies. According to the Aridland Systems Research Program (CGIAR), approximately 2.5 billion people (about 30% of the human population) live in and rely on dryland ecosystems for the natural resources they provide. These ecosystems are home to 50% of raised livestock, 44% of cultivated land (one-third of all cultivated crops come from arid areas), and store approximately 36% of global soil carbon (CGIAR). One can therefore understand the importance of maintaining, as well as enhancing, the dryland ecosystem and the ecosystem services they provide through the regeneration of lost dry forest ecosystems. Resilience thinking is a tool that can be used to increase the productivity of dryland ecosystems. Resilience is an ecological concept that illustrates the ability of an ecosystem to remain intact in a stable state while disturbances occur. If disturbances are too large for an ecosystem to remain in a stable state, there are two ways in which an ecosystem can react to changes in (a)biotic factors, namely through adaptation and transformation. Resilience thinking, as described by Folke et al, will be used to investigate what factors have caused the degradation of dry forest ecosystems and how this could be used to transform savanna/semi-arid ecosystems into dry forests. Therefore, this paper summarizes the results of a literature review, 2 experimental articles and an article reflecting on a success story in the Maradi and Zinder region. The findings from these papers will be used to think about what factors cause degradation of dry forests and maintain the resilience of savanna/semi-arid ecosystems. Finally, a conclusion and discussion is provided that attempts to answer the research question and integrate the knowledge gained from the articles reflected on, with that of resilience thinking. Rehabilitation of dryland ecosystems Yirdaw et al (2017) wrote a review article on the rehabilitation of dryland ecosystems. This article provides an overview of the factors influencing dry forest degradation and offers options for restoration. Degradation factors One of the reasons for the degradation of dry forests is the occurrence of fires, which, although sometimes beneficial (increase soil fertility and favor the composition of species in fire-resistant species), prevents the natural succession of savannas in dry forest ecosystems. Furthermore, factors such as overgrazing, herbivory activity, land conversion to agriculture and firewood collection are causesof the degradation of dry forest and savannah. Passive and active restoration When it comes to restoration, site conditions require different management strategies. Areas that have a low degree of degradation (where degradation is the result of fire, overgrazing, firewood collection and/or cultivation) can be restored through “passive restoration”. Passive restoration involves excluding human and animal disturbances through isolation, allowing the dry forest to regenerate naturally. Heavily degraded dry forests have been shown to not recover under passive restoration, and active restoration is required instead. Active restoration is practiced when an area is so degraded that the natural seed bank in the soil has diminished. In addition to isolating the area from animal and human disturbances, replanting of multiple species is carried out. This should include late and rare species for rapid recovery of the natural succession process. To do this, local knowledge of tree species is often needed, as scientific knowledge about which tree species grow in subtropical areas is often lacking. Experiments in the Atacama Desert These two articles examine how an ENSO event could trigger the creation of trees. In this way they reveal multiple (a)biotic factors that influence the resilience of semi-arid areas. Therefore, herbivores, soil conditions, precipitation and temperature affect resilience. Effect of Precipitation, Temperature and Soil During an ENSO event (El-Nino Southern Oscillation event), climate conditions change leading to higher precipitation patterns in some areas (such as the West Coast of South America) and drought in other areas (such as the Philippines). Increased precipitation has a significant influence on semi-arid vegetation and can be used as a trigger to transform vegetation in ways that have long-term effects on local water and nutrient cycles. The article by Squeo et al (2007) examines three sites, namely Piura, Mejia and Fray Jorge, located respectively in the north, center and south of the Atacama Desert (the area itself has a semi-arid ecosystem). To simulate an ENSO event, all plants were watered in addition to natural rainfall. The three sites had different precipitation patterns (which take into account the different effect that ENSO has on rainfall patterns), average temperature, and slightly different soil types (sandy, loamy, and sandy-loamy). These three factors significantly influenced the growth rate of Prosopis Pallida (in Peru) and Prosopis chilensis (in Chile) trees. The researchers concluded that these trees have better growth rates in areas where it rains in the summer season (when temperatures are higher) and where the soil is sandy, allowing for easier root establishment. A tree ring analysis conducted by Holmgren et al (2006) further supports the idea that rain during the summer season causes higher growth rates. The experiment also revealed that in Peru the P. pallida tree became established twice during ENSO years compared to non-ENSO years, however the same was not found for P. chilensis. Furthermore, the tree ring growth rate doubled during ENSO events for the P. pallida tree. Similarly, a significant correlation was found between tree ring growth rate and annual precipitation for the P. chilensis tree. Differences between the species played no role, as when planted together both species grew better in Peru than in Chile. Differences in temperature and soil probably explain the better rate ofsurvival and growth in Peru compared to Chile. Effect of herbivory on seedling survival In the article Holmgren et al (2006), the influence of herbivory on tree establishment during ENSO events was tested. The study area once again was in Fray Jorge and Piura. Herbivory had a clear effect on seedling survival in both Peru and Chile. Without herbivores, 85% of P. pallida seedlings survived (even under low water treatments), whereas only 31% survived when they were present herbivores. P. chilensis fared less well, especially with low-water treatments (no seedlings survived after 1 year with water availability below 450 mm, even without herbivory). Rehabilitation in Niger The article written by Sendzimir, Reij and Magnuszewski (2011) describes the deforestation of the Maradi and Zinder regions in Niger after the 1920s, and the socio-ecological policies implemented to regreen these areas of grass-covered savannah . Deforestation in Niger occurred mainly due to a sharp increase in population (and therefore land conversion).from forest to agriculture), centralization of natural resources during colonialism in 1935, high export of natural resources in 1950, as well as deforestation following the drought of the early 1970s, when local people were desperate for food and fuel. forestIn the 1980s, a new agricultural technique (farmer-managed natural regeneration) was introduced, in which particular species of trees and shrubs (drought-resistant) were planted among the crops. After another drought in 1985 it became clear that this strategy prevailed over previous agricultural techniques. However, due to corruption among forestry officials and paramilitary forces, this farming technique was not adopted by farmers nationwide until 1987, when political upheaval following the death of Niger's president allowed rural farmers to experiment with the new farming technique . Farmers realized that agroforestry The farming technique provided multiple benefits, including increased rainfall by up to 30%, reinforcing a positive feedback loop that increased tree density and crop yield. Additionally, the trees provided shade for the livestock, as well as additional fodder. Soil fertility increased naturally thanks to tree litter, as well as bird and livestock dung. Tree roots fixed nitrogen through rhizobial bacteria, further increasing soil fertility. The shelter that the trees provided for the birds also improved seed dispersal, which meant farmers saved costs as they had to replant crops less frequently. Farmers, seeing these benefits, were motivated to implement the new agricultural technique. In addition to increasing crop yields, they would receive additional benefits from ecosystem services, such as protection from drought, natural fertilization of crops and fuel wood. Conclusion Savanna ecosystems appear to be an alternative stable ecosystem to dry forest. To transform a savannah ecosystem into a dry forest the following (a)biotic factors have proven to be relevant: the occurrence of fires; land conversion for agriculture; overgrazing/herbivory; climate (temperature, precipitation and ENSO events); soil conditions. If one wanted to restore these areas to their original state (there is a debate as to whether this is morally/culturally appropriate or not, for more information), then these factors need to be adequately addressed by multiple actors. Discussion Farmers can.