Risques d'erosion au tiers monde: le point de vue de l'utilisateur

SOIL T E C H N O L O G Y

vol. 2, p. 301-311

C r e m l i n g e n 1989

R I S Q U E S D ' E R O S I O N A U TIERS M O N D E : LE P O I N T D E V U E D E L ' U T I L I S A T E U R EROSION HAZARD MAPPING IN THE THIRD WORLD: A LAND USERS PERSPECTIVE Y. Biot, P. Blaikie & M. Stocking, Norwich

R~um~ L'analyse des 6checs de n o m b r e u x prog r a m m e s de c o n s e r v a t i o n des eaux et des terres a r6v616, entre autres, des lacunes sev~res d a n s les processus d'identification des causes et des cons6quences de la d 6 g r a d a t i o n des terres. Ces lacunes sont bas6es, n o n p o i n t sur u n e analyse scientifique erron6e, mais sur u n p o i n t de d6part qui ne tient suflisamment compte du p o i n t de vue de l'utilisateur des terres a u Tiers Monde. Les a u t e u r s pr6sentent u n e approche diff~rente bas6e sur l'identification de l ' e n v i r o n n e m e n t social, politique et ~ c o n o m i q u e de l'utilisateur en deux parties: l'6tude des liens entre la d 6 g r a d a t i o n des terres et le d 6 v e l o p p e m e n t des soci6t6s h u m a i n e s et l'6tude d u d+clin de la productivit6 des terres r~sultant de l'6rosion. Les m & h o d e s propos6es dans cette c o m m u n i c a t i o n r e n d e n t possible l ' 6 l a b o r a t i o n d ' u n e strat+gie de conservation des eaux et des terres qui tient c o m p t e d u savoir, des conditions de vie et des possibilit6s de l'utilisateur et de la soci+t6 qui l'enveloppe. ISSN 0933-3630 (~)1989 by CATENA VERLAG, D-3302 Cremlingen-Destedt, W. Germany 0933-3630/89/5011851/US$ 2.00 + 0.25

SOIL TECHNOLOGY A cooperating Journal of CATENA

Summary Recent studies of failed soil and water conservation programmes in the Third World have revealed, amongst others, serious flaws in the process of identification of the causes and consequences of land degradation. These flaws are not caused by an erroneous scientific analysis, but originate in a theoretical framework which is not targetted at the user of the land. The authors propose an alternative approach to the analysis of land degradation problems. The method is based upon the identification of the social, political and economic environment of the land user and can be divided into two parts: (i) a study of the relationship between land degradation and development and (ii) a study of productivity decline caused by erosion. It is believed that this methodology permits the design of soil and water conservation programmes which take into account the knowledge, present day conditions and prospects of the land user and the society which supports him/her, hence be more likely to succeed.

I

Introduction

L'~tude et la cartographie des risques d'~rosion o n t ~t+ j u s q u ' ~ r+cemment le d o m a i n e de la gbomorphologie, hydrologic et agronomic. L'6chec des prog r a m m e s de c o n s e r v a t i o n des eaux et des terres de par le m o n d e a instigu6 u n effort de recherche accentu~ a u d6but des ann+es 80. Cette recherche co-

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incide avec l'initiation d'une conception nouvelle en l'+tude des probl+mes agricoles au Tiers Monde: l'6tude des syst~mes de production (Farming Systems Research) et la recherche participative (Farmer Participatory Research) qui mettent l'accent sur les besoins, le savoir et les capacit6s des utilisateurs du terroir plut6t que sur l'application de quelque th~orie macro-~conomique ou politique de dbveloppement. C'est dans cette perspective que se situent la m+thodologie d'incorporation du savoir de l'utilisateur des terres dans les programmes de conservation des eaux et des terres propos6e par ROOSE (1988) et les btudes par BONVALLOT (1986), M A R C H A L (1986), M I E T T O N (1986) et ROOSE (1986). Le parti pris pour l'utilisateur des terres permet aussi l'+tude et la cartographie des risques d'6rosion d'un, ou plut6t de plusieurs angles diff+rents, dont deux sont le sujet de la communication pr~sente: • l'~tude des liens entre la d6gradation des terres et le d~veloppement des soci6t~s humaines, • l'6tude (plus restreinte) du d~clin de la productivit+ des terres r+sultant de l'~rosion. Le but de cette communication est de r+sumer le savoir acumulb par les auteurs pendant les derni~res ann~es, et d'ouvrir le d6bat sur l'6valuation de la d6gradation des terres ~t de nouvelles perspectives.

Introduction Until recently, both the study and mapping of erosion hazards have been restricted to geomorphologists, hydrologists and agronomists. The failure of soil and water conservation programmes worldwide has prompted renewed research in the early

Blot, Blaikie & Stocking

'80's. This effort coincides with the initiation of new concepts in the study of the agricultural problems of the Third World: Farming Systems and Farmer Participatory Research - approaches which emphasise the needs, the know-how and the capabilities of the land user rather than macro-economic or political theories of development. The methodology of incorporation of farmers' knowledge within soil and water conservation programmes proposed by ROOSE (1988) and the recent studies by BONVALLOT (1986), M A R C H A L (1986), M I E T T O N (1986) and ROOSE (1986) are examples of Farming Systems and Farmer Participatory Research in soil and water conservation planning. The emphasis on the land user also allows the study and mapping of erosion hazards from two different angles: • the study of the relationships between land degradation and development, • the study of productivity decline caused by erosion. The present paper summarises the authors' past experience in such studies in an attempt to open up the debate on land degradation assessment and land conservation planning to new perspectives.

Etude des liens entre la d~gradation des terres et le d~veloppement des soci~t~s humaines Les probl6mes d'brosion dans les soci6t~s en voie de d6veloppement ont tendance ~tre plus importants que dans les communaut6s en ~quilibre plus ou moins stable. Malgr~ les ann+es de recherche en la nature physique du probl+me et son arret, voire renversement, l'+rosion acc616r6e est toujours pr6sente, sinon amplifi+e: les images provenants des terres de montagnes en Ethiopie et des plaines d+sertiques du continent Indien en sont t~moins. L'analyse des 6checs des programmes de conservation des eaux et des terres a d6montr6 l'importance de nombreux facteurs regroup+s en trois niveaux d'organisation humaine :

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1. le niveau politique national et international, 2. le niveau r6gionale,

de

l'~conomie

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3. le niveau des d6cisions prises par l'utilisateur des terres vis ~t vis de l'6conomique et du social. A u premier niveau, plusieurs domaines ont trait aux probl6mes d'6rosion au Tiers M o n d e : la conservation de l'eau et des terres, l'aide ext6rieure, le gouvernement national, les activit6s des bureaucrates, les activit+s des services coloniaux. A u niveau de l'6conomie politique r6gionale la recherche a d~montr+ l'importance de l'acc+s et l'utilisation des ressources naturelles des soci~t~s agraires, ainsi que de l'allocation des terres, du cr6dit, du capital et des droits coutumiers. A u niveau le pus bas ce sont les d6cisions prises par les utilisateurs vis ~t vis de l'~conomique et du social qui d&erminent surtout le risque d'+rosion des terres. Ces d+cisions sont influenc~es non point par la nature du terrain seule, mais par l'effet des d+cisions prises aux niveaux sup6rieurs: le village, la r6gion, la nation, le jeu des nations puissantes et des compagnies trans-nationales (fig.l). Deux examples d6montrent l'utilit6 de ce genre d'analyse: • A u N6pal une des causes de l ' a b a n d o n des syst+mes de conservation des terres a ~t~ attribute au d6cimage de la population la plus active par le biais du service des G h u r k a s dans l'arm6e britannique ( B L A I K I E , 1985). • L'infusion d'argents gagn6s en dehors du cercle de la famille et du village a des effets tr~s n~fastes sur la fa~on dont le terrain est prot~g~ contre l'~rosion et augmente consid~rablement les risques

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de d6gradation des terres - - les examples de d~gradation des p~turages et des terres agricoles au Botswana et au Zimbabwe en sont les plus r~cents ( A B E L et al., 1987; A B E L et B L A I K I E , 1988). Plusieurs 6tudes par les auteurs ont d~montr+ que l'6rosion, et le d+clin des rendements s'ils s'en suivent sont la consbquence d ' u n ou d'une s6rie de d6s6quilibres au niveau social, ~conomique et/ou politique l'6rosion n'est d o n c que s y m p t 6 m e d ' u n ou de plusieurs d6sordres qu'il se faut bien conna~tre avant de d~cider de la strat6gie de conservation des eaux et des terres. Les diff6rentes strat6gies possibles sont illustr6es dans la fig.2. I1 n'est pas impensable, par example, qu'une diminution du poids des dettes ~trang~geres soit plus efficace ~ arr~ter la destruction syst+matique du couvert v6g&al de larges r6gions tropicales au Tiers M o n d e q u ' u n p r o g r a m m e de plantations d'arbres.

Study of the relationships between land degradation and development Erosion problems in developing societies are usually more acute than in communities which live in a more or less stable equilibrium with their environment. The images of land degradation coming from the mountains in Ethiopia and the barren lands in the Indian continent remind us constantly that despite the many years of research in the physical nature of erosion and in methods of conservation, erosion still occurs, often at an even faster pace than before. The failure of many soil and water conservation programmes has been explained at three levels: 1. at the level of national and international politics, 2. at the level of the regional political economy, 3. at the level of the decision making by the land user. Several factors within the level of national and international politics have been demonstrated to

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have serious implications with regards to the extent of land degradation: soil and water conservation strategy, foreign aid, national governments, activities of the bureaucracies and of the colonial powers. At the level of the regional political economy, the access of agrarian societies to natural resources, land allocation, land tenure, credit and capital all have a potential impact on the ways in which land is managed - hence on erosion. At the lowest level, the risk of land degradation is determined mainly by the decisions taken by the land users as conditioned by economic and social considerations. These decisions are not only influenced by the physical attributes of the environment, but especially by the effects which decisions taken at higher levels have on his/her life: the village, the region, the nation, and the powerful nations and transnational companies (fig.l). Two examples illustrate how political and socioeconomic processes may influence land degradation : • Several traditional soil conservation systems have deteriorated since the onset of European expansion. In Nepal, B L A I K I E (1985) partly attributes the abandoning of soil conservation practices to the selective removal of a most active component of society through the Gurka service in the British army, • The infusion of money earned outside the confines of family and village has dramatic impacts on the way in which land is traditionally protected against erosion, and is a major cause of enhanced land degradation - see, for instance, the degradation of rangeland and arable land in Botswana and Zimbabwe (ABEL et al; 1987; ABEL and BLAIKIE, 1988). Past studies by the authors have demonstrated now and again that erosion and productivity decline (if it occurs), are most often the result of a (series of) stress(es) operating at the social, economic and/or political dimensions of society. Erosion is often only a symptom of a (number of) disorders which need to be uderstood fully if an efficient strategy of soil and water conservation is to be devised. Possible strategies are illustrated in fig.2. According to this reasoning, it could, for instance, be argued that a reduction in the foreign debt burden of certain Third World countries could lead to a more effective protection of tropical forest than re-afforestation programmes.

3

Etude du d~clin de la productivit~ des terres r~uitant de l'~rosion

Le deuxi+me sujet de cette communication a trait ~ l'appr~ciation de l'importance des symptrmes physiques, non point en termes physiques (p.e. t/ha/an), mais en termes financiers et/ou ~conomiques. I1 se peut, en effet, que l'+rosion, m~me acc~lrrre par, disons, un changement des pratiques culturales, n'a que peu de consequences financi+res n+gatives pour l'utilisateur et son entourage imm~diat et lointain. Au Tiers Monde l'apprrciation des pertes financi~res et ~conomiques dues l'rrosion est effecture fr~quemment dans le domaine de l'analyse de factibilit+ des programmes de barrages (problrme de s+dimentation des rrservoirs). Des ~tudes rrcentes par la FAO ( S T O C K I N G , 1984; 1985 et 1986) ont trait au d+clin de la productivit6 des terres agricoles ~t cause de l'+rosion. La revue par S T O C K I N G (1984) de la recherche pass~e a d+montr+ que: • la relation entre le d~clin de la productivit6 et l'+rosion cumulative est d'une forme exponentielle n~gative (fig.3). Cette fonction est d&ermin+e surtout par le sol et l'utilisation que l'on en fait: certains sols perdent leur capacit+ productive plus rapidement, certaines cultures r+sistent mieux ~ la d+nudation que d'autres; • les +l+ments nutritifs perdus ~ cause de l'rrosion peuvent ~tre remplac+s et que la perte de la capacit6 de r+tention en eau est irrempla9able. La revue de la recherche passre a permis l'~laboration d'un protocol de recherche adopt6 rrcemment par un

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tiel productif et le calcul de l'aptitude r6siduelle des terres agricoles (ELWELL Au Zimbabwe (STOCKING, 1986), et STOCKING, 1984; STOCKING et les pertes en azote, phosphore et mati+re PAIN, 1983; BLOT, 1988a; b e t c). Un organique du sol sont d6termin6es princi- mod61e d6velopp~ pour l'&ude du d6clin palement par le taux d'~rosion et par les de la productivit~ des p~turages naturels charact6ristiques du sol. Des fonctions au Botswana, T H E P R O M (fig.4) (BIOT, &ablies pour 2058 6v6nements de ruis- 1988b; 1989), a permis la pr6diction du sellement ont permis le calcul th6orique d6clin de la productivit6 du sol (fig.5) du cofit de l'apport d'engrais n6cessaire dont il est facile de d6duire l'aptitude au remplacement de l'azote et du phos- r6siduelle en projetant les niveaux de phore perdus. Ce cofit a 6t6 estim6 ~t 1.5 l'aptitude actuelle et l'aptitude minimale d6termin6e par l'6conomique, le social milliard de dollars am6ricains par an. L'analyse financi6re effectu6e pour le et/ou le politique. Zimbabwe est tr+s simplifi6e, et la recherche actuelle a 6t6 dirig6e vers la mod6lisation du syst+me productif sous l'influence de l'6rosion, permettant ainsi la pr6vision du d6clin du potenSOIL TECHNOLOGY--A cooperating Journal of CATENA

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Study of productivity decline caused by erosion The second topic of this paper deals with the analysis of the importance of the physical symptoms of degradation, not in physical (e.g. t/ha/year), but in financial and economic terms. It is possible, indeed, that erosion, whether enhanced by h u m a n interference with the n o n - h u m a n processes of the environment or not, causes only limited damage to the land user, and his or her near or remote neighbour. In the Third World, the estimation of financial and economic losses caused by erosion is usually confined to feasibility studies of d a m projects (i.e. siltation problems). Recent studies by the FAO

(STOCKING, 1984; 1985; 1986) deal with productivity decline of agricultural land caused by erosion. S T O C K I N G ' s (1984) review of past research has demonstrated 1. the negative exponential shape of the relationship between productivity and cumulative erosion (fig.3). The shape, or rather the curvature of the relationship, is mainly determined by the soil and the land utilisation type: some soils lose their productive potential rapidly; some crops are more resilient than others; 2. that in most past experiments nutrient losses are usually recovered, whereas losses in the soil's capacity to retain water are irreplaceable. Based on these findings, S T O C K I N G (1985) has

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designed a research protocol for the determination genre humain. L a c a r t o g r a p h i e des of productivity/erosion curves which has recently risques d ' r r o s i o n est incompl+te sans une been adopted by a research network coordinated analyse a p p r o f o n d i e des relations soby FAO. In Zimbabwe, losses in soil Nitrogen, Phospho- ciales, ~conomiques e t / o u politiques qui rous and Organic Matter are mainly determined e n g e n d r e n t la d ~ g r a d a t i o n des terres. by rates of erosion and soil type. Relationships L ' i m p o r t a n c e financi~re e t / o u ~conoestablished for 2058 runoff events have permitted m i q u e de l'~rosion n'est pas nrcessairethe theoretical computation of the cost of fertiliser m e n t p r o p o r t i o n e l l e ~ l ' i m p o r t a n c e phyneeded for the replacement of the lost Nitrogen and Phosphorous. This cost has been estimated at sique des p h r n o m + n e s d'~rosion locaux. 1.5 billion US S/year (STOCKING, 1986). L a recherche en les drclins de p r o d u c t i v i The financial analysis carried out for Zimbabwe t6 des terres au Tiers M o n d e a 6t6 initire remains simplified, and presently research has been r r c emment. directed towards the modelling of the productive system as influenced by erosion, thus allowing the Les conclusions d ' a n a l y s e s des causes forecasting of productivity decline and the calcula- h u m a i n e s de l'~rosion et d u co~t de tion of the residual suitability of agricultural land (ELWELL and STOCKING, 1984; STOCKING la d r g r a d a t i o n des terres effectures and PAIN, 1983; BlOT 1988a, b and c). THE- r r c e m m e n t p e u v e n t &re r r s u m r e s en PROM (rigA), a model developed for the study q u a t r e p o i n t s : of productivity decline of rangeland in Botswana (BLOT, 1988b; 1989) - forecasts the decline in pro- 1. ce n'est pas l ' r r o s i o n qui compte, mais ductivity (fig.5) from which it is possible to deduce l'effet de l'~rosion sur la productivit6 the residual suitability on the basis of the present des terres, day and minimum allowable suitability levels. 2. la relation entre ~rosion et drclin de la productivit6 n'est p a s une r e l a t i o n 4 Conclusions simple, mais est fonction d u sol et de l'utilisation que l'on en fait, Vus d ' u n angle social, ~ c o n o m i q u e e t / o u politique, les p r o b l r m e s d ' r r o s i o n ne sont souvent que s y m p t r m e s de d r s r q u i l i b r e s plusieurs n i v e a u x d ' o r g a n i s a t i o n d u

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sur une jambe de bois. Le vrai probl+me est la gestion des terres, 4. la gestion des terres, et donc aussi l'+rosion, est largement influenc6e par les facteur +conorniques, sociaux et politiques aux niveaux de la famille, de la r+gion, de la nation et du march6 mondial. Conclusions When looked at from a social, economic and/or political viewpoint, erosion problems are often perceived as symptoms of stresses operating at several levels of organisation of humans. It is contended that the mapping of erosion hazards is incomplete without an in-depth analysis of the social, economic and/or political dimensions of land degradation. The financial and/or economic impact of soil erosion is not necessarily proportional to the physical dimension of land degradation. Research in productivity decline caused by erosion in the Third World has been initiated recently. To conclude, the results of recent analyses of the human causes of soil erosion and of the cost of land degradation can be summarised in four points as follows: 1. It is not erosion which is important, but the impact of erosion on the productivity of land, 2. The relationship between erosion and productivity decline is not a simple rationship but a function of the soil characteristics and the land utilisation type, 3. Erosion is not a problem, but the result of a problem - to fight erosion directly is often a misguided strategy. The real problem is land management,

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ABEL, N.O.J., FLINT, M.E., HUNTER, M.D., CHANDLER, D. & MAKA, G. (1987): Cattle keeping, ecological change and communal management in Ngwaketse. International Livestock Centre for Africa (ILCA) and the Integrated Farming Pilot Project (IFPP) and the Overseas Development Group (ODG), Addis Ababa, Gaborone and Norwich. BIOT, Y. (1988): Calculating the residual suitability of agricultural land based on routine land resource surveys. Paper presented at the Symposium on Land Qualities in Space and Time, Wageningen, August 1988. BLOT, Y. (1988): Forecasting productivity losses caused by sheet and rill erosion in semi-arid rangeland: a case study from the communal areas of Botswana. PhD thesis, School of Development Studies, University of East Anglia, Norwich. BLOT, Y. (1988): Modelling productivity losses caused by erosion. In: Proceedings of the Fifth International Soil Conservation Conference, Bangkok, Thailand. BLOT, Y. (1989): THEPROM: an erosionproductivity model. In: Proceedings of the annual meeting of the Institute of British geographers. WASWC/BGRG/IBG. BLAIKIE, P.M. (1985): The Political Economy of Soil Erosion in Developing Countries. Longman, London and New York. BONVALLOT, J. (1986): Tabias et jessours du Sud tunisien. Agriculture dans les zones marginales. Cahiers ORSTOM s~rie P~dologie, 22(2), 163 172. ELWELL, H.A. & STOCKING, M.A. (1984): Estimating soil-life span for conservation planning. Tropical Agriculture 61(2), 148 150. MARCHAL, J.Y, (1986): Vingt ans de lutte anti~rosive au nord du Burkina Faso. Cahiers ORSTOM s~rie P~dologie 22(2), 173-180.

4. Land management, hence erosion, is largely determined by economic, social and political factors at the family, regional, national and international levels.

MIETTON, M. (1986): M&hodes et efficacit~ de la lutte contre l'~rosion hydrique au Burkina Faso. Cahiers ORSTOM s~rie P~dologie 22(2), 181 196.

References

ROOSE, E. (1988): New strategy of water management and soil conservation. Application in development and developing countries. Paper presented at the Vth Int. Soil Conservation Conference, Bangkok, 1988.

ABEL, N.O.J. & BLAIKIE, P.M. (1988): Managing common property resources in rural development: the case of Zimbabwe and Botswana. Research Scheme ESR 322/348/01, ODG/ODA, Norwich/London.

ROOSE, E. (1986): Terrasses de diversion ou microbarrages perm~ables? Analyse de leur efficacit~ en milieu paysan ouest-africain pour la

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conservation de reau et des sols dans la zone Soudano-Sah61ienne. Cahiers ORSTOM, s6rie P6dologie 22(2), 197-208. STOCKING, M.A. (1986): The cost of soil erosion in Zimbabwe in terms of the loss of three major nutrients. Consultant's Working Paper 3, FAO, Land and Water Development Division, FAO, Rome. STOCKING, M.A. (1984): Erosio~ and soil productivity: a review. Consultant's Working Paper 1, FAO, Land and Water Development Division, FAO, Rome. STOCKING, M.A. (1985): Erosion-induced loss in soil productivity: a research design. Consultant's Working Paper 2, FAO, Land and Water Development Division, FAO, Rome. STOCKING, M.A. & PAIN, A. (1983): Soil life and the minimum soil depth for productive yields: developing a new concept. Discussion Paper 150, School of Development Studies, University of East Anglia, Norwich.

Address of authors: Yvan Biot, Piers Biaikie & Michael Stocking School of Development Studies University of East Anglia Norwich NR4 7TJ U.K.

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