LAND DEGRADATION in ZIMBABWE Geographical Study

. ■ LAND DEGRADATION IN ZIMBABWE Geographical Study Richard Whitlow Geography Department, University of Zimbabwe f % W 'l'5/ ? £ IeB jfc&L . Wp JKOTBW’^PI#* i l l Sa&te- --"fl?***. "v'*»Ji fir?'- ISlfllhk** ^ mk Land Degradation in Zimbabwe A Geographical Study Report prepared on behalf of the Department of Natural Resources by Richard Whitlow Senior Lecturer in Geography University of Zimbabwe 1988 SUMMARY O F R E P O R T v#. w» w^ce for the national erosion survey of on commercial farms are 15 tonfrjttflwriyeftr and 3 ' Zimbabwe were as follows: tonnes/ha/year respectively; the ^Mwalent — the survey method should be simple, systematic and averages for Communal Lands are 50 and 75 quantitively based. tonnes/ha/year. — the survey should have potential for monitoring changes in erosion patterns; - f expressed in terms of soil life span, for the Com .— the survey should generate information on the extent munal Lands in the upper Sabi Catchment cultiva of erosion in both map and statistical forms at scales tion of maize may only be possible for another 10 appropriate for national and regional planning; years before soils become too shallow for crop — the survey method should be economic in terms of growth; sorghum cultivation may be impossible financial and manpower inputs. within 30 years. — Research was initiated during 1984 to develop a suit 1 — the removal of nutrients in eroded soils amounts to, able method for extracting information on erosion from estimated financial losses of $2 540 million each 1: 25,000 aerial photographs. A technique involving year when converted into the cost of replacing lost sampling of 1,000 grid cells per aerial photo within a nutrients with chemical fertilizers. grid framework was developed. The main national survey was carried out in late 1985 using this technique 1— th e consequences of this erosion are seen in and involved detailed examination of nearly 8,500 aerial ■j general declines in crop yields and very high rate* photographs, representing a 22% areal sample of the of siltation of reservoirs, especially o f the smaller country. The data from this survey, combined with dams used for rural water supplies; such small previous scientific research and government reports, dams are likely to fill with sediment within 15 forms the basis of this study. years of construction and even the larger irrigation schemes are being affected adversely by siltation problems. The main report covers the following aspects of land degradation: 1— soil erosion is clearly an important problem in Zimbabwe, especially within the Communal 1. causes and consequences of erosion Lands; it is essential that conservation measures 2. history of the erosion problem be included as a central and key part of develop 3. distribution of erosion ment strategies in these'areas rather than being- 4. influence of physical factors on erosion treated as a token appendage. / 5. influence of human factors on erosion The erosion problems ar^ immensely complicated 2. HISTORY OF THE EROSION PROBLEM involving the interaction of many political, social, economic and environmental factors. It would be unrea — an understanding of the history of the erosion is listic to expect anyone to gain a reasonable familiarity necessary to account for the present patterns of with these problems from reading this brief summary land degradatiop aijd to syssess past successes and alone. failures in tackHrig resources deteriation, so that more effective plans can be developed to over come soil erosion and related problems. 1. CAUSES AND CONSEQUENCES — the review of erosion focuses mainly on the large- OF EROSION scale commercial farming areas and the Commu nal Lands, the former characterised today by high — the erosion system is extremely complex compris standards of conservation and localised erosion ing the interaction of energy forces (e.g. rainfall and the latter by generally p o^ standards of intensity), resistive forces (e.g. stable soil aggrega conservation and widespread erosion; distinct, tes) and protective forces (e.g. plant cover). but not necessarily discrete, historical phases can be identified fpr tljese two main farming areas. — where protective and resistive forces are low in relation to energy forces, as occurs in the Com — the phases in the large-scale commercial farming munal Lands, then high rates of erosion are com areas are as follows: mon; where the protective and resistive forces are high as in tueas of good management and low population pressures, then erosion is localised. Phase 1: Trial and error — pre-1931 — rates of soil formation in Zimbabwe are very slow a combination of ignorance and neglect resulted in (e.g. 400 kgs/ha/year), whereas rates of soil widespread erosion and limited progress was erosion are very much greater; estimates for made in promoting basic mechanical protection of average soil losses on croplands and grazing areas arable lands. i awareness — 1931 — 1948 Phase 3: Agrarian reforms — 1951 — 1962 f iarmefo began to realise the need for soil conser compulsory conservation, measures were introdu vation; continuing erosion on many European ced by agrarian reforms as dictated by the Native farms and, even more so, within the ‘native Land Husbandry Act (1951); although consider reserves’ prompted an official Commission of able progress was made in mechanical protection Enquiry in 1938; the outcome o f this was the of arable lands, the enforcement of such measures passing of the Natural Resources Act (1941) was unpopular and became a major political issue; the establishment of the Natural Resources Board in addition, the attempt to change from a tribal and the creation of Intensive Conservation Area communal system to an individual system of (ICA) committees to encourage and, where neces land tenure was opposed. sary, enforce conservation measures. Phase 4: Uncertainty — 1962 — 1969 with the abandonment of the Native Land Hus Phase 3: Conservation farming — 1948 — bandry Act and the changing political circumst 1 9 6 5 ances in the country, there was a period of uncer the establishment of the Department of Conser tainty in the 1960’s; some progress was made in vation and Extension (1948) and the introduction improving farming and conservation through the of farm planning (1956) improved greatly the efforts of the Department of Conservation and general standards of conservation; along with Extension who had become responsible tempor mechanical protection, for which subsidies were arily for the reserves* now referred to as Tribal given, better husbandary practices were seen as Trust Lands. In the face of growing population vital in conserving soil and water resources for pressures, land degradation became widespread. increased production. Phase 5: Growing pressure — post 1969 with their political and economic aspirations being Phase 4: Mixed fortunes — post 1965 blocked by the government the peasant farmers farmers were forced to diversify and intensify turned increasingly to supporting the guerrilla production due to difficult political and economic circumstances following the illegal declaration of forces intent upon taking control of the country, independence; despite growing security problems, with the deterioration in security during the civil general awareness on conservation remained at a war, conservation was neglected and this exacer high level, although the need for constant atten bated an already serious problem. Since indepe tion of basic anti-erosion works was stressed. ndence some progress has been made in resolving the conservation problem by, for example, affores the phases in the Communal Lands were as tation and resettlement schemes. follows: Phase 1: Creation of the reserves — pre-1926 the first ‘reserves’, the Gwaai aftl Shangani, Reserves were declared in 1894 and, following 3. DISTRIBUTION OF EROSION pressure from the British government, additional areas bf land were set aside for the exclusive use of — it was estimated that there were just over 1,8 the indigenous population. By 1911 these “ native million hectares o f eroded land in Zimbabwe, that reserves” comprised about 8,5 million hectares, is 4,7% of the country. Most o f this eroded land, barely one fifth of the country; land degradation some 1,5 million hectares were located in the was not a problem at this stage since population Communal Lands. 271,000 hectares of eroded densities were low! land were recorded in the General Lands and only 35,200 hectares of eroded land were observed in non-agricultural areas (e.g. national parks, forest reserves). Phase 2: Centralisation — 1926 — 1951 spatial re-organisation of arable and grazing lands snd settlements was initiated in this phase as e ratals fpr improved farming and conservation erosion was recorded as negligible in just under Despite these efforts extensive erosion took place: two fifths of Zimbabwe and about one quarter Of The Natural Resources Act (1941) was intended the country had very limited erosion (under 4% of to overcome this degradation which was seer the land in a given area being eroded); a forth®" mainly as a product of poor farming methods. one fifth of the country had limited to moderate D^Ianppwer and financial constraints preventing erosion (between 4,1 — 12% of the land, Htts ^pper implementation of this resource legi- eroded); in the remainder of the country (13,2%) j l :,aad destocking measures which were erosion was rated as being severe tp vejry "tjoiit. werevery unpopujgr, compromising that is, over 12% of the land beingefoAjmffo iservationefforts. given locality. ^ n' the most extensive erosion was recorded in the and result in very unstable soil aggregates; such Communal Lands, especially within Natural soils are affected by serious sheetwash erosion Regions IV and V, but also within the higher fain- and, in some areas, very large gully systems have fall areas where nearly one tenth of the land was developed partly due to processes of subsurface eroded. The General Lands were less affected by tunnelling.

Load more