Table of contentsIntroductionRehabilitation of dryland ecosystemsDegradation factorsPassive or active restorationExperiments in the Atacama DesertEffect of precipitation, temperature and soilEffect of herbivores on the seedling survivalRehabilitation in NigerAgroforestry as a means of restoring dry forestConclusionDiscussionIntroductionEcosystems are dynamic in nature. Throughout history, biomes around the world have changed. Currently, many dry forests are changing (or have already) changed their structure and have lost their function as a dry forest ecosystem (such as in Ethiopia and Ghana). The degradation of dry forests into savannahs leads to a loss of the ecosystem services they provide. Say no to plagiarism. Get a tailor-made essay on “Why Violent Video Games Should Not Be Banned”? Get the original essay Yet dryland ecosystems, such as savannahs, are of major importance to human societies. According to the Dryland Systems Research (CGIAR) Program, approximately 2.5 billion people (about 30% of the human population) live in and depend on dryland ecosystems for the natural resources they provide. These ecosystems are home to 50% of farmed livestock, 44% of cultivated land (a third of all cultivated crops come from drylands), and store approximately 36% of the world's carbon in their soils (CGIAR). One can thus 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 a concept in ecology that illustrates the ability of an ecosystem to remain intact in a stable state while disturbances occur. If disturbances are too great for an ecosystem to remain in a stable state, an ecosystem can respond in two ways to changing (a)biotic factors, namely through adaptation and through 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 savannah/semi-arid ecosystems into dry forest. summarize the results of a literature review, 2 experimental articles and an article reflecting on a success in the region of Maradi and Zinder. Results from these papers will be used to reflect on the factors that cause dry forest degradation and maintain the resilience of savannah/semi-arid ecosystems. Finally, a conclusion and a discussion are proposed in an attempt to answer the research question and to integrate the knowledge acquired from the articles reflected with that of reflection on resilience. Dryland ecosystem rehabilitation Yirdaw et al (2017) wrote a review article on dryland ecosystem rehabilitation. dryland ecosystems. This article provides an overview of the factors that influence dry forest degradation and proposes rehabilitation options. 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 species composition towards fire-tolerant forests). species), prevents natural succession from savannahs to dry forest ecosystems. Additionally, factors such as overgrazing, herbivory, land conversion to agriculture and crop harvestingfirewood are causes of degradation of dry forests/savannahs. Passive vs. Active Restoration When it comes to rehabilitation, site conditions require different management strategies. Areas with 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 disturbance through isolation, thereby allowing the natural regeneration of the dry forest. It has been shown that heavily degraded dry forests do not recover under passive restoration, and instead active restoration is required. Active restoration is practiced when an area is so degraded that the natural seed stock in the soil has diminished. In addition to isolating the area from animal and human disturbance, the replanting of several species is carried out. This should include rare and late successional species for rapid recovery of the natural succession process. To do this, local knowledge about tree species is often necessary, as scientific knowledge about tree species that grow in subtropical areas is often lacking. Experiments in the Atacama Desert These two articles examine how an ENSO event could trigger tree establishment. In doing so, they reveal multiple (a)biotic factors that affect the resilience of semi-arid areas. As such, herbivory, soil conditions, precipitation and temperature affect resilience. Effect of precipitation, temperature and soil During an ENSO event (El-Nino Southern Oscillation event), climatic conditions change, leading to higher precipitation patterns in certain regions (such as the West). coast of South America) and droughts in other regions (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 lasting effects on local water and nutrient cycles. The article by Squeo et al (2007) examines three sites, namely Piura, Mejia and Fray Jorge, located in the north, central and south of the Atacama Desert respectively (the area itself has a semi-arid ecosystem ). To simulate an ENSO event, all plants were watered in addition to natural precipitation. The three sites had different precipitation regimes (representing the different effect of ENSO on precipitation regimes), average temperatures as well as 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 would rain in summer (when temperatures are higher) and where the soil is sandy, allowing for easier root establishment. An analysis of tree rings conducted by Holmgren et al (2006) further supports the idea that rain during the summer season is a cause of higher growth rates. The experiment also found that in Peru, the P. pallida tree became twice as established during ENSO years, compared to non-ENSO years, but the same was not found for the P. pallida tree. .chilensis. Additionally, the tree ring growth rate doubled during ENSO events for the P. pallida tree. Similarly, there was a significant correlation between tree ring growth rate and annual precipitation for the P tree.chilensis. Differences between the species played no role, because when planted together, both species grew better in Peru than in Chile. Differences in temperature and soil likely account for the better survival and growth rate in Peru than in Chile. Effect of herbivory on seedling survival In the Holmgren et al (2006) article, the influence of herbivory on tree establishment during ENSO events was tested. The study area was again that of Fray Jorge and Piura. Herbivory had a clear effect on seedling survival in Peru and Chile. Without herbivores, 85% of P. pallida plants survived (even under low-water treatments), while only 31% survived in the presence of herbivores. P. chilensis fared less well, particularly with low water treatments (no seedlings survived after one 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 of Niger after the 1920s, and the socio-ecological policies implemented to regreen these bushy savannah areas . Deforestation in Niger is mainly due to a large increase in population (and therefore the conversion of land from forest to agriculture), natural resources were centralized under colonialism in 1935, a large export of natural resources in 1950, as well as deforestation following a drought in the early 1970s, when residents were desperate for food and fuel. Agroforestry as a means of restoring drought 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 cultures. After another drought in 1985, it became clear that this strategy prevailed over previous agricultural techniques. However, due to corruption by forestry officials and paramilitary forces, this agricultural technique was not adopted by farmers nationwide until 1987, when political upheaval following the death of the President of Niger allowed rural farmers to experiment with this new agricultural technique. The agricultural technique brought multiple benefits, including an increase in rainfall of up to 30%, reinforcing a positive feedback loop that increased tree density and crop yield. Additionally, the trees provided shade for their livestock, as well as more fodder. Soil fertility increased naturally thanks to tree litter, as well as bird and livestock droppings. Tree roots fix nitrogen using rhizobia bacteria, thereby increasing soil fertility. The sanctuary the trees provided for birds also improved seed dispersal, saving farmers money because they had to replant their crops less frequently. Farmers, seeing these benefits, were motivated to implement the new agricultural technique. In addition to increasing the yield of their crops, they would receive additional benefits from ecosystem services, such as protection against drought, as well as natural fertilization of their crops and obtaining firewood. Conclusion Savanna ecosystems appear to be an alternative stable ecosystem as opposed to dry forest. To transform a savannah ecosystem into a dry forest, the following (a)biotic factors have proven relevant: fires; land conversion for agriculture; overgrazing/herbivory.