Land Degradation and Soil and Water Conservation in Tropical Highlands

Soil & Tillage Research 103 (2009) 197–202

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Soil & Tillage Research

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Land degradation and soil and water conservation in tropical highlands

Jan Nyssen a,*, Jean Poesen b, Jozef Deckers c a Department of Geography, Ghent University, Gent, Belgium b Physical and Regional Geography, K.U. Leuven, Leuven, Belgium c Division Soil and Water Management, K.U. Leuven, Leuven, Belgium

ARTICLE INFO ABSTRACT

Keywords: Land degradation is not uniform, even in the same landscape, but nevertheless an overall consensus Desertiﬁcation seems to grow on the fact that many areas are under way of rehabilitation. It is a debateable question HighLand2006 whether the improving areas are improving because of interventions—or whether this has more to do Land rehabilitation with processes of innovation and adaptation. The international symposium ‘HighLand2006’ on land Mountains degradation and land rehabilitation, held in Mekelle (Ethiopia), from 21 to 25 September 2006, created a Nutrient management forum for those conducting research in East African Highlands as well as in similar regions around the Soil erosion globe to discuss ﬁndings. Tropical highlands (>1000 m a.s.l.) cover 4.5 million km2 with an average population density of 33 inhabitants kmÀ2. Nearly all tropical highlands suffer from land degradation, especially medium to very high water erosion. Exchange of experiences during in-door sessions and excursions led to results which are condensed in this special issue. Studies presented tend to invalidate hypotheses on irreversibility of land degradation in tropical mountain areas. Circumstances are that in highly degraded environments, with high pressure on the land, no other alternatives are left open but to improve land husbandry; and that this is particularly successful in places where decision making processes at different levels in society give the highest priority to the implementation of soil and water conservation and other land rehabilitation, in situ and at catchment level. ß 2008 Elsevier B.V. All rights reserved.

1. Land degradation in tropical mountain areas and scope for highlands, for instance, suffer from extreme loss of topsoil due to rehabilitation sheet and rill erosion. Water erosion is a generalised problem in nearly all tropical mountains. Due to their important altitudinal gradients, mountain regions In many tropical mountains, not the least in northern Ethiopia, receive much attention (Becker and Bugmann, 2001). Mountain huge efforts are undertaken to rehabilitate the land. agriculture systems are vulnerable to environmental change for However, the overall productivity of such areas is often various reasons, such as the cost of accessibility and infrastructure perceived to be so dramatically damaged by human impact that as well as the limited opportunity for production gains associated recovery is deemed impossible (Rasmussen et al., 2001; Reij and with scale of operation (Becker and Bugmann, 2001). Besides, in Steeds, 2003). However, several impact studies have demonstrated most tropical mountains, there are high population densities. In that investments in tropical mountains do pay off in economic East Africa and Central America, there are far more than 100 terms (Holden et al., 2005; Boyd and Turton, 2000). inhabitants kmÀ2 in all areas with an elevation over 2500 m a.s.l. Degradation is not uniform, even in the same landscape, but (Table 1). Short-term increase in agricultural production is often nevertheless an overall consensus seems to grow on the fact that obtained through increased pressure on the land, i.e. reduced many areas are getting substantially better. In a recent exchange of fallowing, removal of vegetation between cropland, conversion of thoughts, Stocking (2006) stated that it is a debateable question forest and woodlands on steep slopes into rangeland and marginal whether the improving areas are improving because of soil and arable land. water conservation interventions—or whether this has more to do According to the ‘Global Assessment of Soil Degradation’ map with boserupian (Boserup, 1981) processes of innovation and (Oldeman et al., 1991), more than 50% of the northern Ethiopian adaptation. Over the past decade, signiﬁcant advances have been made by researchers analysing land rehabilitation efforts in these areas, and * Corresponding author. this special issue aims at presenting a representative set of studies E-mail address: [email protected] (J. Nyssen). (Fig. 1).

Table 1 Tropical mountain regions (>1000 m a.s.l.)

Sub-continent Major highland Area (1000 km2)a Population (106)a Population Countries with Farming systemsb,c Land and mountain density (kmÀ2)a mountain degradationc regions population >40%a >1000 >2500 >1000 >2500 >1000 >2500 m a.s.l. m a.s.l. m a.s.l. m a.s.l. m a.s.l. m a.s.l.

Southeast Asia Truong Son, 554 50 11 0.4 21 8 Upland intensive W(3–4) Ningling mixed s., upland Shan, extensive s., Wuhi Shan } sparse forest s. Oceania New Guinea { Papua W(1) S New Guinea South Asia Himalaya 684 367 23 4 34 11 Bhutan Highland mixed W(3–4) s.; sparse mountain s. Central America Sierra Madre, 85 5 9 1 107 200 Guatemala, Maize-bean W(3–4) and Carribean Cordillera de Costa Rica, (mesoamerican) s. Salamanca, El Salvador, Sierra Maestre Honduras South America Andes 2033 1114 38 21 19 19 Bolivia, Intensive highland W(2–4) Colombia, (N Andean) s.; high E(2–4) Peru, Ecuador altitude mixed (Central Andean) s.; sparse forest (S Andean) s. Central Africa Mitumbar, 170 6 6 0.4 38 67 Rwanda, Highland perennial s., W(2–3) Mutchinga, Burundi maize mixed s. Congo-Nile crest East Africa Ethiopian and 710 83 56 11 79 135 Eritrea, Highland perennial s., W(2–4) East African Ethiopia highland temperate highlands mixed s., maize mixed s. Southern Africa Drakensberg 308 9 6 0.3 20 33 Lesotho, Maize mixed s., W3 P3 C3 and Madagascar Swaziland rice-tree crop system range West Africa Hilly coastal 17 0 0.4 0 24 Tree-crop s. areas

Total 4561 1634 151 38 33 23

a According to Huddleston et al. (2003). b According to Dixon et al. (2001). c Dominant types, according to Oldeman et al. (1991); W water erosion, E wind erosion, C chemical deterioration, P physical deterioration, S stable terrain; codes for degree of severity: 1 low, 2 medium, 3 high, 4 very high.

2. Northern Ethiopia, a focal place for studies on land probably not a linear process in Ethiopia. Studies on land use and degradation and rehabilitation in tropical mountains land cover change show however a tendency, over the last decades, of increasing removal of remnant vegetation, which is slowed Following the International Soil Conservation Organisation’s down or reversed in northern Ethiopia by a set-aside policy (ISCO) conference in Addis Ababa in 1989 (Hurni and Kebede, (Nyssen et al., 2004a). 1992; Kebede and Hurni, 1992), it was the second time that Given its physical geography and land use history, the north Ethiopia could host a major international scientific event on land Ethiopian highlands were an ideal location to discuss these and degradation and rehabilitation. In the framework of the United related questions. ‘HighLand2006’ has allowed participants (1) to Nations proclamation of 2006 as the International Year of Deserts review current understanding of, (2) to report progress in, and (3) and Desertification, the international symposium ‘HighLand2006’ to identify priorities for future research in environmental change, (Poesen et al., 2006), held in Mekelle (Ethiopia), from 21 to 25 geomorphic processes, land degradation and rehabilitation in September 2006, created a forum for those conducting research in tropical and subtropical highlands. east African highlands as well as in similar regions around the Two major questions will be addressed in this special issue: globe (Fig. 1) to discuss results and to exchange experiences during in-door sessions and excursions (Fig. 2). 1. Which factors control the intensity of land degradation, its on- The most important present-day geomorphic processes site and off-site impacts, in tropical mountains? This question observed during the excursions are sheet and rill erosion addresses the role of natural and anthropogenic factors in the throughout the country, gullying (Fig. 2) in the highlands, and degradation of the vegetation cover and in controlling the wind erosion in the Rift Valley and the peripheral lowlands intensity of hydrological processes, soil erosion, landsliding, (Nyssen et al., 2004a). reservoir sedimentation and flooding. With respect to recent environmental changes, temporal rain 2. What is the effectiveness and efficiency of traditionally and patterns, apart from the catastrophic impact of dry years on the recently introduced soil and water conservation techniques? In degraded environment, cannot explain the current desertification tropical highlands, large efforts have been made to conserve soil in the driest parts of the country and the accompanying land and water through a range of techniques (e.g. stone bunds degradation elsewhere. Causes are to be found in changing land (Fig. 3), grass buffer strips, in situ land surface management, use and land cover, which are expressions of human impact on the check dams (Fig. 2), exclosures (Fig. 4), small reservoirs, nutrient environment. Deforestation over the last 2000–3000 years was management, sediment excavation from reservoirs). Many J. Nyssen et al. / Soil & Tillage Research 103 (2009) 197–202 199

Fig. 1. Location map of the case studies presented in this special issue (STR), as well as in the parallel special issue of ‘Catena’.

lessons can be learned regarding their effectiveness, efficiency high-investment and nearby-monitored NGO-type of interven- and implementation in rural societies. tions. One might therefore question to what extent reports on recovery are representative of wider areas. Such impact studies In parallel with this special issue of ‘‘Soil & Tillage Research’’, a typically do not include detailed botanical, hydrological and number of selected papers on environmental change and geomorphological components either (Rohde and Hilhorst, 2001). geomorphological processes in tropical highlands are published It is precisely in the area around Mekelle that photo-monitoring in a special issue of ‘‘Catena’’ (Billi, 2008; Ciampalini et al., 2008; studies could demonstrate an increase in vegetation cover over the Fubelli et al., 2008; Kimaro et al., 2008; Moeyersons et al., 2008; last 30 years as well as a decrease in soil erosion rates (Munro et al., Munro et al., 2008; Nigussie et al., 2008; Oliveira et al., 2008; 2008; Nyssen et al., 2007a). Schmid et al., 2008; Turkelboom et al., 2008; Van de Wauw et al., An interesting aspect of landscape-wide studies is that they are 2008). beyond the scale of experimental plots and represent necessarily the ‘real world’. Similarly, in northern Ethiopia, Nyssen et al. (2008a) 3. Land degradation and rehabilitation studies show that reforestation of the uplands has not only benefits for in situ soil conservation and regeneration, but has also led to strongly Needless to say, due to steep slopes and high population improved spring discharge in the bottomlands, leading to a major density, severe land degradation may occur in tropical highlands land use change with the expansion of irrigated farmland. when not properly managed. Whereas on-site impacts of land degradation (and of 4. In situ surface and nutrient management for conservation of conservation activities) are immediately felt by the farmers tropical highland farms (as demonstrated in the studies presented in Section 4), the overall impact is much wider than the sum of individual losses Several studies on the evaluation of physical and biological soil or benefits. and water conservation technologies in Ethiopia have been Case studies on land rehabilitation are often limited in space, published (Bosshart, 1997; Descheemaeker et al., 2006a, 2006b; time and scope; they may include better endowed regions and/or Desta et al., 2005; Eweg et al., 1998; Fiedler and Gebeyehu, 1988; Hurni and Kebede, 1992; Kebede and Hurni, 1992; Kru¨ ger et al., 1997; Lakew and Morgan, 1996; Nyssen et al., 2000a, 2000b, 2004b, 2007b, 2008b; Vancampenhout et al., 2006; Wolde et al., 2007; Yohannes and Herweg, 2000), as in other tropical highlands (to name but a few: Braud et al. (2001), De Noni et al. (2000) and Dercon et al. (2003) in the Andes, Kloosterboer and Eppink (1989) in Cabo Verde, or Mati and Veihe (2001) in savannah environments in Africa). A new paradigm was confirmed at the HighLand2006 conference, which is also reflected in the composition of this special issue: the great importance that is accorded to in situ management for soil conservation and land rehabilitation. Attention is given to experiments with alternative soil nutrient management systems, whereby soil nutrient replenishment treatments were tested in the Kenyan highlands (Shisanya et al., 2008); and simulation models Fig. 2. HighLand2006 participants and farmers discussed land rehabilitation issues, developed for the Ethiopian highlands (Assefa and van Keulen, such as gully rehabilitation in the north Ethiopian highlands. 2008) that can be used to explore long-term dynamics of soil C, N 200 J. Nyssen et al. / Soil & Tillage Research 103 (2009) 197–202

Fig. 3. Stone bunds for soil and water conservation are aligned along the contour in May Leiba catchment, Tigray, Ethiopia. and P in support of the design of appropriate farmland manage- mitigate this type of drought via appropriate land management ment for higher yields and improved livelihoods. practices. Of particular interest in semi-arid mountains and other tropical areas is the in situ conservation of water and soil. The effectiveness of 5. Conclusions stone bunds and exclosures for soil and water conservation on the slope was studied earlier (for instance in Ethiopia: Descheemaeker Studies presented in this special issue tend to invalidate et al., 2006a; Descheemaeker et al., 2006b; Desta et al., 2005; Nyssen hypotheses on (a) irreversibility of land degradation in tropical et al., 2007a; Vancampenhout et al., 2006). At the same time it was mountain areas; and (b) futility of SWC programmes. The studies however shown that these interventions (1) still allow soil and water furthermore demonstrate that (a) land management has become to be lost and that (2) the conserved soil and water is being kept an inherent part of the farming system in several tropical mountain either outside of the farmland, or in narrow strips at the lower side of areas, (b) it is possible to reverse environmental degradation in farmland. Hence the large number of emerging studies on farmland these areas through an active, farmer-centred SWC policy, and (c) surface management. Engel et al. (2008) demonstrate how no-tillage keeping small-scale farmers on their land by providing adequate cultivation in the Santa Catarina highlands, southern Brazil strongly levels of subsidies is an effective way to sustain the agricultural reduces runoff and soil loss; and Tewodros et al. (2008), show how in system of tropical mountain areas in the long term and to provide Ethiopia, conservation agriculture with beds and furrows, shaped ecosystem services to the society. using the local ‘ard’ plough, leads to strong decreases in runoff and The challenges to be met include (a) in situ SWC of farmland in increases in soil water content. To broaden the picture, Govaerts addition to contour terracing, (b) appropriate and concomitant soil et al. (2008) report on long-term experiments in the Central Me´xican nutrient management and (c) involving local communities in highlands, whereby selected soil quality indicators (i.e. time-to- decision making about farmland management. pond, aggregate distribution and soil moisture) are investigated to Coming back to the issue whether land rehabilitation is due to give insight into the feasibility of conservation agriculture as part of interventions or to ‘‘boserupian’’ (Boserup, 1981) processes of a sustainable production system in tropical highlands. Stroosnijder innovation, the papers in this special issue tend to demonstrate (2008) reviews soil water drought in Africa, which occurs where that rehabilitation is linked to both. In highly degraded environ- plant production suffers because water is not available due to ments, with high pressure on the land, no other alternatives are left deteriorated physical properties of soil. There is great potential to open but to improve land husbandry (‘‘more people – less erosion’’ – Tiffen et al., 1994). Furthermore, such rehabilitation will be particularly successful in regions where the highest priority at different levels in society is given to the implementation of soil and water conservation and other land rehabilitation.

Acknowledgements

Organisers and participants in the HighLand2006 conference are especially thanked for fuelling discussions during in-door and field sessions. This contributed significantly to shaping the papers published in this special issue. As a post-conference activity, some 50 scientists visited the May Zegzeg Integrated Watershed Management area, jointly with 200 farmers from the wide surroundings; again many issues regarding conservation could be raised there. The HighLand2006 conference was financially supported by Fig. 4. Land resilience on steep slopes (exclosure since 9 years in Hechi, Tigray). VLIR, the Flemish Interuniversity Council (Belgium) and K.U. J. Nyssen et al. / Soil & Tillage Research 103 (2009) 197–202 201

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