Soil & Tillage Research 103 (2009) 197–202

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, Belgiumb Physical and Regional Geography, K.U. Leuven, Leuven, Belgiumc Division Soil and Water Management, K.U. Leuven, Leuven, Belgium

A R T I C L E I N F O

Keywords:

Desertification

HighLand2006

Land rehabilitation

Mountains

Nutrient management

Soil erosion

A B S T R A C T

Land degradation is not uniform, even in the same landscape, but nevertheless an overall consensus

seems to grow on the fact that many areas are under way of rehabilitation. It is a debateable question

whether the improving areas are improving because of interventions—or whether this has more to do

with processes of innovation and adaptation. The international symposium ‘HighLand2006’ on land

degradation and land rehabilitation, held in Mekelle (Ethiopia), from 21 to 25 September 2006, created a

forum for those conducting research in East African Highlands as well as in similar regions around the

globe to discuss findings. Tropical highlands (>1000 m a.s.l.) cover 4.5 million km2 with an average

population density of 33 inhabitants km�2. 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.

� 2008 Elsevier B.V. All rights reserved.

Contents lists available at ScienceDirect

Soil & Tillage Research

journa l homepage: www.e lsev ier .com/ locate /s t i l l

1. Land degradation in tropical mountain areas and scope forrehabilitation

Due to their important altitudinal gradients, mountain regionsreceive much attention (Becker and Bugmann, 2001). Mountainagriculture systems are vulnerable to environmental change forvarious reasons, such as the cost of accessibility and infrastructureas well as the limited opportunity for production gains associatedwith scale of operation (Becker and Bugmann, 2001). Besides, inmost tropical mountains, there are high population densities. InEast Africa and Central America, there are far more than 100inhabitants km�2 in all areas with an elevation over 2500 m a.s.l.(Table 1). Short-term increase in agricultural production is oftenobtained through increased pressure on the land, i.e. reducedfallowing, removal of vegetation between cropland, conversion offorest and woodlands on steep slopes into rangeland and marginalarable land.

According to the ‘Global Assessment of Soil Degradation’ map(Oldeman et al., 1991), more than 50% of the northern Ethiopian

* Corresponding author.

E-mail address: jan.nyssen@ugent.be (J. Nyssen).

0167-1987/$ – see front matter � 2008 Elsevier B.V. All rights reserved.

doi:10.1016/j.still.2008.08.002

highlands, for instance, suffer from extreme loss of topsoil due tosheet and rill erosion. Water erosion is a generalised problem innearly all tropical mountains.

In many tropical mountains, not the least in northern Ethiopia,huge efforts are undertaken to rehabilitate the land.

However, the overall productivity of such areas is oftenperceived to be so dramatically damaged by human impact thatrecovery is deemed impossible (Rasmussen et al., 2001; Reij andSteeds, 2003). However, several impact studies have demonstratedthat investments in tropical mountains do pay off in economicterms (Holden et al., 2005; Boyd and Turton, 2000).

Degradation is not uniform, even in the same landscape, butnevertheless an overall consensus seems to grow on the fact thatmany areas are getting substantially better. In a recent exchange ofthoughts, Stocking (2006) stated that it is a debateable questionwhether the improving areas are improving because of soil andwater conservation interventions—or whether this has more to dowith boserupian (Boserup, 1981) processes of innovation andadaptation.

Over the past decade, significant advances have been made byresearchers analysing land rehabilitation efforts in these areas, andthis special issue aims at presenting a representative set of studies(Fig. 1).

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

Sub-continent Major highland

and mountain

regions

Area (1000 km2)a Population (106)a Population

density (km�2)a

Countries with

mountain

population >40%a

Farming systemsb,c Land

degradationc

>1000

m a.s.l.

>2500

m a.s.l.

>1000

m a.s.l.

>2500

m a.s.l.

>1000

m a.s.l.

>2500

m a.s.l.

Southeast Asia Truong Son,

Ningling

Shan,

Wuhi Shan

554 50 11 0.4 21 8 Upland intensive

mixed s., upland

extensive s.,

sparse forest s.

W(3–4)

Oceania New Guinea Papua

New Guinea

W(1) S

South Asia Himalaya 684 367 23 4 34 11 Bhutan Highland mixed

s.; sparse mountain s.

W(3–4)

Central America

and Carribean

Sierra Madre,

Cordillera de

Salamanca,

Sierra Maestre

85 5 9 1 107 200 Guatemala,

Costa Rica,

El Salvador,

Honduras

Maize-bean

(mesoamerican) s.

W(3–4)

South America Andes 2033 1114 38 21 19 19 Bolivia,

Colombia,

Peru, Ecuador

Intensive highland

(N Andean) s.; high

altitude mixed

(Central Andean) s.;

sparse forest

(S Andean) s.

W(2–4)

E(2–4)

Central Africa Mitumbar,

Mutchinga,

Congo-Nile

crest

170 6 6 0.4 38 67 Rwanda,

Burundi

Highland perennial s.,

maize mixed s.

W(2–3)

East Africa Ethiopian and

East African

highlands

710 83 56 11 79 135 Eritrea,

Ethiopia

Highland perennial s.,

highland temperate

mixed s., maize

mixed s.

W(2–4)

Southern Africa Drakensberg

and Madagascar

range

308 9 6 0.3 20 33 Lesotho,

Swaziland

Maize mixed s.,

rice-tree crop system

W3 P3 C3

West Africa Hilly coastal

areas

17 0 0.4 0 24 Tree-crop s.

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.

} {

J. Nyssen et al. / Soil & Tillage Research 103 (2009) 197–202198

2. Northern Ethiopia, a focal place for studies on landdegradation and rehabilitation in tropical mountains

Following the International Soil Conservation Organisation’s(ISCO) conference in Addis Ababa in 1989 (Hurni and Kebede,1992; Kebede and Hurni, 1992), it was the second time thatEthiopia could host a major international scientific event on landdegradation and rehabilitation. In the framework of the UnitedNations proclamation of 2006 as the International Year of Desertsand Desertification, the international symposium ‘HighLand2006’(Poesen et al., 2006), held in Mekelle (Ethiopia), from 21 to 25September 2006, created a forum for those conducting research ineast African highlands as well as in similar regions around theglobe (Fig. 1) to discuss results and to exchange experiences duringin-door sessions and excursions (Fig. 2).

The most important present-day geomorphic processesobserved during the excursions are sheet and rill erosionthroughout the country, gullying (Fig. 2) in the highlands, andwind erosion in the Rift Valley and the peripheral lowlands(Nyssen et al., 2004a).

With respect to recent environmental changes, temporal rainpatterns, apart from the catastrophic impact of dry years on thedegraded environment, cannot explain the current desertificationin the driest parts of the country and the accompanying landdegradation elsewhere. Causes are to be found in changing landuse and land cover, which are expressions of human impact on theenvironment. Deforestation over the last 2000–3000 years was

probably not a linear process in Ethiopia. Studies on land use andland cover change show however a tendency, over the last decades,of increasing removal of remnant vegetation, which is sloweddown or reversed in northern Ethiopia by a set-aside policy(Nyssen et al., 2004a).

Given its physical geography and land use history, the northEthiopian highlands were an ideal location to discuss these andrelated questions. ‘HighLand2006’ has allowed participants (1) toreview current understanding of, (2) to report progress in, and (3)to identify priorities for future research in environmental change,geomorphic processes, land degradation and rehabilitation intropical and subtropical highlands.

Two major questions will be addressed in this special issue:

1. W

hich factors control the intensity of land degradation, its on-site and off-site impacts, in tropical mountains? This questionaddresses the role of natural and anthropogenic factors in thedegradation of the vegetation cover and in controlling theintensity of hydrological processes, soil erosion, landsliding,reservoir sedimentation and flooding.

2. W

hat is the effectiveness and efficiency of traditionally andrecently introduced soil and water conservation techniques? Intropical highlands, large efforts have been made to conserve soiland water through a range of techniques (e.g. stone bunds(Fig. 3), grass buffer strips, in situ land surface management,check dams (Fig. 2), exclosures (Fig. 4), small reservoirs, nutrientmanagement, sediment excavation from reservoirs). Many

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

J. Nyssen et al. / Soil & Tillage Research 103 (2009) 197–202 199

lessons can be learned regarding their effectiveness, efficiencyand implementation in rural societies.

In parallel with this special issue of ‘‘Soil & Tillage Research’’, anumber of selected papers on environmental change andgeomorphological processes in tropical highlands are publishedin a special issue of ‘‘Catena’’ (Billi, 2008; Ciampalini et al., 2008;Fubelli et al., 2008; Kimaro et al., 2008; Moeyersons et al., 2008;Munro et al., 2008; Nigussie et al., 2008; Oliveira et al., 2008;Schmid et al., 2008; Turkelboom et al., 2008; Van de Wauw et al.,2008).

3. Land degradation and rehabilitation studies

Needless to say, due to steep slopes and high populationdensity, severe land degradation may occur in tropical highlandswhen not properly managed.

Whereas on-site impacts of land degradation (and ofconservation activities) are immediately felt by the farmers(as demonstrated in the studies presented in Section 4), theoverall impact is much wider than the sum of individual lossesor benefits.

Case studies on land rehabilitation are often limited in space,time and scope; they may include better endowed regions and/or

Fig. 2. HighLand2006 participants and farmers discussed land rehabilitation issues,

such as gully rehabilitation in the north Ethiopian highlands.

high-investment and nearby-monitored NGO-type of interven-tions. One might therefore question to what extent reports onrecovery are representative of wider areas. Such impact studiestypically do not include detailed botanical, hydrological andgeomorphological components either (Rohde and Hilhorst, 2001).It is precisely in the area around Mekelle that photo-monitoringstudies could demonstrate an increase in vegetation cover over thelast 30 years as well as a decrease in soil erosion rates (Munro et al.,2008; Nyssen et al., 2007a).

An interesting aspect of landscape-wide studies is that they arebeyond the scale of experimental plots and represent necessarily the‘real world’. Similarly, in northern Ethiopia, Nyssen et al. (2008a)show that reforestation of the uplands has not only benefits for insitu soil conservation and regeneration, but has also led to stronglyimproved spring discharge in the bottomlands, leading to a majorland use change with the expansion of irrigated farmland.

4. In situ surface and nutrient management for conservation oftropical highland farms

Several studies on the evaluation of physical and biological soiland water conservation technologies in Ethiopia have beenpublished (Bosshart, 1997; Descheemaeker et al., 2006a, 2006b;Desta et al., 2005; Eweg et al., 1998; Fiedler and Gebeyehu, 1988;Hurni and Kebede, 1992; Kebede and Hurni, 1992; Kruger 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) andDercon et al. (2003) in the Andes, Kloosterboer and Eppink (1989)in Cabo Verde, or Mati and Veihe (2001) in savannah environmentsin Africa).

A new paradigm was confirmed at the HighLand2006 con-ference, which is also reflected in the composition of this specialissue: the great importance that is accorded to in situ managementfor soil conservation and land rehabilitation. Attention is given toexperiments with alternative soil nutrient management systems,whereby soil nutrient replenishment treatments were tested in theKenyan highlands (Shisanya et al., 2008); and simulation modelsdeveloped for the Ethiopian highlands (Assefa and van Keulen,2008) that can be used to explore long-term dynamics of soil C, N

Fig. 3. Stone bunds for soil and water conservation are aligned along the contour in May Leiba catchment, Tigray, Ethiopia.

J. Nyssen et al. / Soil & Tillage Research 103 (2009) 197–202200

and P in support of the design of appropriate farmland manage-ment for higher yields and improved livelihoods.

Of particular interest in semi-arid mountains and other tropicalareas is the in situ conservation of water and soil. The effectiveness ofstone bunds and exclosures for soil and water conservation on theslope was studied earlier (for instance in Ethiopia: Descheemaekeret al., 2006a; Descheemaeker et al., 2006b; Desta et al., 2005; Nyssenet al., 2007a; Vancampenhout et al., 2006). At the same time it washowever shown that these interventions (1) still allow soil and waterto be lost and that (2) the conserved soil and water is being kepteither outside of the farmland, or in narrow strips at the lower side offarmland. Hence the large number of emerging studies on farmlandsurface management. Engel et al. (2008) demonstrate how no-tillagecultivation in the Santa Catarina highlands, southern Brazil stronglyreduces runoff and soil loss; and Tewodros et al. (2008), show how inEthiopia, conservation agriculture with beds and furrows, shapedusing the local ‘ard’ plough, leads to strong decreases in runoff andincreases in soil water content. To broaden the picture, Govaertset al. (2008) report on long-term experiments in the Central Mexicanhighlands, whereby selected soil quality indicators (i.e. time-to-pond, aggregate distribution and soil moisture) are investigated togive insight into the feasibility of conservation agriculture as part ofa sustainable production system in tropical highlands. Stroosnijder(2008) reviews soil water drought in Africa, which occurs whereplant production suffers because water is not available due todeteriorated physical properties of soil. There is great potential to

Fig. 4. Land resilience on steep slopes (exclosure since 9 years in Hechi, Tigray).

mitigate this type of drought via appropriate land managementpractices.

5. Conclusions

Studies presented in this special issue tend to invalidatehypotheses on (a) irreversibility of land degradation in tropicalmountain areas; and (b) futility of SWC programmes. The studiesfurthermore demonstrate that (a) land management has becomean inherent part of the farming system in several tropical mountainareas, (b) it is possible to reverse environmental degradation inthese areas through an active, farmer-centred SWC policy, and (c)keeping small-scale farmers on their land by providing adequatelevels of subsidies is an effective way to sustain the agriculturalsystem of tropical mountain areas in the long term and to provideecosystem services to the society.

The challenges to be met include (a) in situ SWC of farmland inaddition to contour terracing, (b) appropriate and concomitant soilnutrient management and (c) involving local communities indecision making about farmland management.

Coming back to the issue whether land rehabilitation is due tointerventions or to ‘‘boserupian’’ (Boserup, 1981) processes ofinnovation, the papers in this special issue tend to demonstratethat rehabilitation is linked to both. In highly degraded environ-ments, with high pressure on the land, no other alternatives are leftopen but to improve land husbandry (‘‘more people – less erosion’’– Tiffen et al., 1994). Furthermore, such rehabilitation will beparticularly successful in regions where the highest priority atdifferent levels in society is given to the implementation of soil andwater conservation and other land rehabilitation.

Acknowledgements

Organisers and participants in the HighLand2006 conferenceare especially thanked for fuelling discussions during in-door andfield sessions. This contributed significantly to shaping the paperspublished in this special issue. As a post-conference activity, some50 scientists visited the May Zegzeg Integrated WatershedManagement area, jointly with 200 farmers from the widesurroundings; again many issues regarding conservation couldbe raised there.

The HighLand2006 conference was financially supported byVLIR, the Flemish Interuniversity Council (Belgium) and K.U.

J. Nyssen et al. / Soil & Tillage Research 103 (2009) 197–202 201

Leuven. During this conference and during the preparation of thisspecial issue, J.N. was at the Division Soil and Water Management,K.U. Leuven, Belgium, and based at Mekelle University.

We thank overseeing editors Rattan Lal and Miroslav Kutılek aswell as the reviewers (Abiye Astatke, Hilaire Desmedt, Hans Hurni,Jan-Peter Lesschen, Roel Merckx, John Quinton, Eric Roose, FrancisTurkelboom, Lieven Van Holm, Bas van Wesemael, Ann Verdoodt,Gert Verstraeten) of the manuscripts submitted for this specialissue. Without their efforts, this special issue would have beenimpossible to realise.

Last but not least, Sofie Bruneel (Department Earth andEnvironmental Sciences, K.U.Leuven), handled in a very profes-sional way the crucial manuscript-submission-despatching-reminding-and-so-much-more process. Thanks a lot, Sofie!

References

Assefa Abegaz, van Keulen, H., 2008. Modelling soil nutrient dynamics underalternative farm management practices in the northern Highlands of Ethiopia.Soil Tillage Res. this issue.

Becker, A., Bugmann, H., 2001. Global Change and Mountain Regions—The Moun-tain Research Initiative. IGBP, Stockholm, p. 86.

Billi, P., 2008. Bedforms and sediment transport processes in the ephemeral streamsof Kobo Basin, northern Ethiopia. Catena 75, 5–17.

Boserup, E., 1981. Population and Technology. Blackwell, p. 255.Bosshart, U., 1997. Catchment discharge and suspended sediment transport as

indicators of physical soil and water conservation in the Mayketin catchment,Afdeyu Research Unit. A case study in the Northern Highlands of Eritrea. Bern,SCRP. Research Report 39, p. 137.

Boyd, C., Turton, C., 2000. The contribution of soil and water conservation tosustainable livelihoods in semi-arid areas of sub-saharan Africa. The Agricul-tural Research and Extension Network, London. Network Paper 102, p. 20.

Braud, I., Vich, A.I.J., Zuluaga, J., Fornero, L., Pedrani, A., 2001. Vegetation influenceon runoff and sediment yield in the Andes region: observation and modelling. J.Hydrol. 254, 124–144.

Ciampalini, R., Billi, P., Ferrari, G., Borselli, 2008. Plough marks as a tool to assess soilerosion—a case study in Axum (Ethiopia). Catena 75, 18–27.

De Noni, G., Prat, C., Quantin, P., Viennot, M., Zebrowski, C., 2000. Erosion etconservation, apres recuperation, des sols volcaniques indures de l’Equateuret du Mexique. Etude et Gestion des Sols 7, 25–36.

Dercon, G., Deckers, J., Govers, G., Poesen, J., Sanchez, H., Vanegas, R., Ramınez, M.,Loaiza, G., 2003. Spatial variability in soil properties on slow forming terraces inthe Andes region of Ecuador. Soil Tillage Res. 72, 31–41.

Descheemaeker, K., Nyssen, J., Poesen, J., Raes, D., Mitiku Haile, Muys, B., Deckers, S.,2006a. Runoff on slopes with restoring vegetation: a case study from the Tigrayhighlands, Ethiopia. J. Hydrol. 331, 219–241.

Descheemaeker, K., Nyssen, J., Rossi, J., Poesen, J., Mitiku Haile, Moeyersons, J.,Deckers, J., 2006b. Sediment deposition and pedogenesis in exclosures in theTigray Highlands, Ethiopia. Geoderma 132, 291–314.

Desta Gebremichael, Nyssen, J., Poesen, J., Deckers, J., Mitiku, Haile, Govers, G.,Moeyersons, J., 2005. Effectiveness of stone bunds in controlling soil erosionon cropland in the Tigray highlands, Northern Ethiopia. Soil Use Manage. 21,287–297.

Dixon, J., Gulliver, A., Gibbon, D., 2001. Farming Systems and Poverty: ImprovingFarmers’ Livelihoods in a Changing World. FAO and World Bank, Roma andWashington, D.C..

Engel, F.L., Bertol, I., Ritter, S.R., Paz Gonzalez, A., Vidal Vazquez, E., 2008. Soil erosionunder simulated rainfall in relation to phonological stages of soybeans andtillage methods in Lages-SC, Brazil. Soil Tillage Res. this issue.

Eweg, H.P.A., Van Lammeren, R., Deurloo, H., Woldu, Z., 1998. Analysing degradationand rehabilitation for sustainable land management in the highlands of Ethio-pia. Land Degrad. Dev. 9, 529–542.

Fiedler, H.J., Gebeyehu Belay, 1988. Forests and their importance for soil con-servation in Ethiopia. Archiv fur Naturschutz und Landschaftsforschung 28,161–175.

Fubelli, G., Bekele Abebe, Dramis, F., Vinci, S., 2008. Geomorphological evolutionand present-day processes in the Dessie Graben (Wollo, Ethiopia). Catena 75,28–37.

Govaerts, B., Sayre, K.D., Goudeseune, B., De Corte, P., Lichter, K., Dendooven, L.,Deckers, J., 2008. Conservation agriculture, an option towards sustainableagriculture for the (sub)tropical highlands? Some results from a representativelong-term experiment in central Mexico. Soil Tillage Res. this issue.

Holden, S., Bekele Shiferaw, Pender, J., 2005. Policy analysis for sustainable landmanagement and food security in Ethiopia—a bioeconomic model with marketimperfections. Res. Rep. (Int. Food Policy Res. Inst.) 140, 76.

Huddleston, B., Ataman, E., De Salvo, P., Zanetti, M., Bloise, M., Bel, J., Franceschini,G., Fe d’Ostiani, L., 2003. Towards a GIS-based analysis of mountain environ-ments and populations. FAO, Environment and Natural Resources workingpaper no. 10, Roma.

Hurni, H., Kebede Tato, 1992. Erosion, conservation and small-scale farming, areviewed selection of papers. In: Proceedings of the 6th International SoilConservation Conference. Ethiopia and Kenya, November 6–18, 1989. Geo-graphica Bernensia, ISCO, WASWC, Vol. 2, p. 582.

Kebede Tato, Hurni, H., 1992. Erosion, conservation and small-scale farming, areviewed selection of papers. In: Proceedings of the 6th International SoilConservation Conference. Ethiopia and Kenya, November 6–18, 1989. Geo-graphica Bernensia, ISCO, WASWC, Vol. 1.

Kimaro, D., Poesen, J., Msanya, B., Deckers, J., 2008. Magnitude of soil erosion on thenorthern slope of the Uluguru Mountains, Tanzania: Interrill and rill erosion.Catena 75, 38–44.

Kloosterboer, E., Eppink, L., 1989. Soil and water conservation in very steep areas—acase study of Santo Antao Island, Cape Verde. In: Baum, E., Wolff, P., Zoebisch,M.A. (Eds.), Topics in Applied Resource Management, 1. pp. 111–142.

Kruger, H.J., Berhanu Fantaw, Yohannes Gebremichael, Kefeni Kajela, 1997. Inven-tory of indigenous soil and water conservation measures on selected sites in theEthiopian Highlands. Soil Conservation Research Programme, Addis Ababa, andUniversity of Bern, Centre for Development and Environment, Research Report34, p. 96.

Lakew Desta, Morgan, R., 1996. Contour grass strips: a laboratory simulation of theirrole in erosion control using grasses. Soil Technol. 9, 83–89.

Mati, B.M., Veihe, A., 2001. Application of the USLE in a savannah environment:comparative experiences from East and West Africa. Singapore J. Trop. Geogr.22, 138–155.

Moeyersons, J., Van Den Eeckhaut, M., Nyssen, J., Tesfamichael Gebreyohannes, Vande Wauw, J., Hofmeister, J., Poesen, J., Deckers, J., Mitiku Haile, 2008. Massmovement mapping for geomorphological understanding and sustainabledevelopment, Tigray, Ethiopia. Catena 75, 45–54.

Munro, R.N., Deckers, J., Mitiku Haile, Grove, A.T., Poesen, J., Nyssen, J., 2008. Soillandscapes, land cover change and erosion features of the Central Plateau regionof Tigrai, Ethiopia: Photo-monitoring with an interval of 30 years. Catena 75,55–64.

Nigussie Haregeweyn, Poesen, J., Nyssen, J., Govers, G., Verstraeten, G., De Vente, J.,Deckers, J., Moeyersons, J., 2008. Sediment yield variability in Northern Ethio-pia: a quantitative analysis of its controlling factors. Catena 75, 65–76.

Nyssen, J., Mitiku Haile, Moeyersons, J., Poesen, J., Deckers, J., 2000a. Soil andwater conservation in Tigray (Northern Ethiopia): the traditional dagettechnique and its integration with introduced techniques. Land Degrad.Dev. 11, 199–208.

Nyssen, J., Poesen, J., Mitiku Haile, Moeyersons, J., Deckers, J., 2000b. Tillage erosionon slopes with soil conservation structures in the Ethiopian highlands. SoilTillage Res. 57, 115–127.

Nyssen, J., Poesen, J., Moeyersons, J., Deckers, J., Mitiku Haile, Lang, A., 2004a. Humanimpact on the environment in the Ethiopian and Eritrean Highlands—a state ofthe art. Earth Sci. Rev. 64, 273–320.

Nyssen, J., Veyret-Picot, M., Poesen, J., Moeyersons, J., Mitiku Haile, Deckers, J.,Govers, G., 2004b. The effectiveness of loose rock check dams for gully control inTigray, Northern Ethiopia. Soil Use Manage. 20, 55–64.

Nyssen, J., Munro, R.N., Mitiku Haile, Poesen, J., Descheemaeker, K., NigussieHaregeweyn, Moeyersons, J., Govers, G., Deckers, J., 2007a. Understandingthe environmental changes in Tigray: a photographic record over 30 years.Tigray Livelihood Papers No. 3, VLIR—Mekelle University IUC Programme andZala-Daget Project, p. 82. ISBN 978-90-8826-016-2. http://www.geoweb.u-gent.be/download/TLP_3_Photomonitoring.pdf.

Nyssen, J., Poesen, J., Desta, Gebremichael, Vancampenhout, K., D’aes, M., Gebre-medhin, Yihdego, Govers, G., Leirs, H., Moeyersons, J., Naudts, J., Nigussie,Haregeweyn, Mitiku Haile, Deckers, J., 2007b. Interdisciplinary on-site evalua-tion of stone bunds to control soil erosion on cropland in Northern Ethiopia. SoilTillage Res. 94, 151–163.

Nyssen, J., Getachew, Simegn, Nurhussen, Taha, 2008a. A permanent upland farm-ing system under transformation: proximate causes of land use change in Bela-Welleh catchment (Wag, northern Ethiopian highlands). Soil Tillage Res. thisissue.

Nyssen, J., Poesen, J., Moeyersons, J., Mitiku Haile, Deckers, J., 2008b. Dynamics ofsoil erosion rates and controlling factors in the Northern Ethiopian High-lands—towards a sediment budget. Earth Surf. Process. Landforms 33,695–711.

Oldeman, L., Hakkeling, R., Sombroek, W., 1991. World map of the status of human-induced soil degradation: an explanatory note. Wageningen: ISRIC; Nairobi:UNEP, p. 34.

Oliveira, M.A.T, Behling, H., Pessenda, L.C.R., Lima, G.L., 2008. Stratigraphy of near-valley head quaternary deposits and evidence of climate-driven slope-channelprocesses in southern Brazilian highlands. Catena 75, 77–92.

Poesen, J., Deckers, J., Mitiku Haile, Nyssen, J., Bruneel, S. (Eds.), 2006. HighLand2006Symposium on environmental change, geomorphic processes, land degradationand rehabilitation in tropical and subtropical highlands. Mekelle, Ethiopia,September 19–25, 2006. Mekelle University, K.U. Leuven, VLIR, Africamuseum,UNESCO, Book of abstracts, p. 104.

Rasmussen, K., Fog, B., Madsen, J., 2001. Desertification in reverse? Observationsfrom northern Burkina Faso. Glob. Envir. Change 11, 271–282.

Reij, C., Steeds, D., 2003. Success Stories in Africa’s Drylands: Supporting Advocatesand Answering Skeptics. Centre for International Cooperation, Vrije UniversiteitAmsterdam, 9.

Rohde, R., Hilhorst, T., 2001. A profile of environmental change in the Lake ManyaraBasin, Tanzania. Issue Paper, Drylands Programme, IIED 109. p. 31.

J. Nyssen et al. / Soil & Tillage Research 103 (2009) 197–202202

Schmid, T., Koch, M., DiBlasi, M., Miruts Hagos, 2008. Spatial and spectral analysis ofland cover properties for an archeological area in Aksum, Ethiopia, applyinghigh and medium resolution data. Catena 75, 93–101.

Shisanya, C.A., Mucheru, M.W., Mugendi, D.N., Kung’u, J.B., 2008. Effect of organicand inorganic nutrient sources on soil mineral nitrogen and maize yields incentral highlands of Kenya. Soil Tillage Res. this issue.

Stocking, M., 2006. Personal Communication, School of Development Studies,University of East Anglia.

Stroosnijder, L., 2008. Modifying land management in order to improve efficiency ofrainwater use in the African highlands. Soil Tillage Res. this issue.

Tewodros Gebreegziabher, Nyssen, J., Govaerts, B., Fekadu Getnet, MintesinotBehailu, Mitiku Haile, Deckers, J., 2008. Contour furrows for in-situ soiland water conservation, Tigray, Northern Ethiopia. Soil Tillage Res. thisissue.

Tiffen, M., Mortimore, M., Gichuki, F., 1994. More People, Less Erosion: Environ-mental Recovery in Kenya. Wiley, Chichester, p. 311.

Turkelboom, F., Poesen, J., Trebuil, G., 2008. The multiple land degradation effects ofland-use intensification in tropical steeplands: A catchment study from north-ern Thailand. Catena 75, 102–116.

Van de Wauw, J., Baert, G., Moeyersons, J., Nyssen, J., Nurhussein Taha, AmanuelZenebe, Poesen, J., Deckers, J., 2008. Soil-landscape relationships in the basaltdominated highlands of Tigray, Ethiopia. Catena 75, 117–127.

Vancampenhout, K., Nyssen, J., Desta, Gebremichael, Deckers, J., Poesen, J., Mitiku,Haile, Moeyersons, J., 2006. Stone bunds for soil conservation in the northernEthiopian highlands: Impacts on soil fertility and crop yield. Soil Tillage Res. 90,1–15.

Wolde Mekuria, Veldkamp, E., Mitiku Haile, Nyssen, J., Muys, B., Kindeya Gebre-hiwot, 2007. Effectiveness of exclosures to restore degraded soils as a result ofovergrazing in Tigray, Ethiopia. J. Arid Environ. 69, 270–284.

Yohannes Gebremichael, Herweg, K., 2000. Soil and water conservation—fromindigenous knowledge to participatory technology development, Lang DruckAG, Liebfeld, Bern, Switzerland, p. 52.