Agroforestry development in northeastern Nigeria

Forest Ecology and Management, 45 ( 1991 ) 309-3 ! 7 Elsevier Science Publishers B.V., Amsterdam

309

Agroforestry development in northeastern Nigeria I. Verinumbe Department of BiologicaISciences, UniversiO,of Maiduguri, Nigeria

AB~FRACT Verinumbe,I., 199I. Agroforestrydevelopment in northeastern Nigeria. For. Ecol. Manage., 45: 309317. Some results of recent agroforestry development efforts in northeastern Nigeria are summarised, and brieflydiscussed. An initial diagnosticsurvey of farms and local markets identified local practices and selected indigenous species ofAcacia albida, Ziziphus spp., Tamarindus indica, etc. as particularly important sources of food, feed and soil resuscitation. There were indications that seeds of promising tree species suffer heavy insect infestation (28%) and have poor ge=minationas well as seedlingsurvival. Plantations of seven tree species, raised through the taungya system recorded over 75% survival and 4.08 cm annual mean girth increment. Older plantations of Azadiracta indica, Eucalyptus camaldulensis and Prosopisjuliflora also improved soil and increased the dry matter yield of Zea mays, Sorghum vulgaris and drachis hypogeato about five times the yield obtained on soil from the surrounding field. Work in progressand plans to investigate the social and economic prospects of alternative agroforestry systemsamong farmers in the region are also indicated.

INTRODUCTION Northeastern Nigeria is located in the driest part o f Nigeria (Lat. i0~0" N 14°0 ' N a n d Long. 10°0 ' E - ! 5 ° 0 ' E) a n d experiences between 800 m m o f rainfall in the south a n d 200 m m in the n o r t h where the Lake C h a d is located. Higher rainfall in the south ( 8 0 0 - 5 0 0 m m ) s u p p o r t s S u d a n s a v a n n a vegetation. W i t h decrease in rainfall further n o r t h w a r d s (less t h a n 500 m m ) , the Sudan s a v a n n a thins out into the Sahel s a v a n n a at a b o u t Lat. 12°0 , N. In addition to seasonal d r o u g h t ( O c t o b e r - A p r i l ) , the area also suffers f r o m long cycles o f wet a n d dry years. D r o u g h t is characterised b y i m p a i r e d p r i m a r y productivity a n d accelerated soil deterioration ( U N O , 1978; M o r t i m o r e , 1978 ). D r o u g h t also leaves b e h i n d a s o u t h w a r d extension o f the Sahara desert; a p h e n o m e n o n k n o w n as desertification. M o r e than 80% o f the p o p u l a t i o n is rural, being primarily engaged in arable farming, livestock rearing, exploitation o f forest resources a n d fishing a r o u n d Lake Chad. Large n u m b e r s o f pastoralists also c o m e t h r o u g h f r o m the drier countries o f Niger a n d C h a d on t r a n s h u m a n c e a n d back ( M o r t i m o r e , 1987).

0378- ! 127/9 !/$03.50 © 1991 Elsevier Science Publishers B.V. All fights reserved.

310

I.VERINUMBE

In recent years, drought coupled with deforestation caused by factors such as overgrazing, overcultivation and overcutting of trees to satisfy increasing demand for feed, food and wood from domestic sources, has exacerbated the desertification problem. To solve this problem by conventional forest plantations is not feasible because of the lack of large amounts of resources such as land, labour and capital that would be involved. Land, for example, cannot be taken from the already more competitive agricultural sector. A more feasible alternative is to employ agroforestry techniques that break the dichotomy between these enterprises. This will reduce competition between them, maximise their complementary roles, conserve soils, reduce desertification and sustain high yields of food, feed and wood from land. How this can be achieved depends on scientific information about the socio-economic, biological and physical conditions of the area. To obtain such information, which is currently lacking, and to develop suitable systems has been the primary objective of agroforestry work in northeastern Nigeria. AGROFORESTRYIN TRADITIONALPRACTICE As a first step towards the development of agroforestry systems for the region, informal diagnostic surveys of the area were undertaken to identify existing land management practices, examine the role of agroforestry in them and to identify local tree species c t"potential importance to agroforestry and provide a basis for research and development of suitable systems. Visits were made to several locations including farms and markets in the region, during which field observations were made and interviews held with local farmers. The range and sources of forest products available were also identified to guide selection of species for further evaluation. Four major landuse activities, including arable farming, livestock rearing, fishing and forestry, were identified and the role of agroforestry examined.

Arablefarming Three types of arable farming systems identified as shore farming, irrigated farming and rainfed farming were observed. Shore farming is found near the shores of Lake Chad. The lake water level rises and floods its extensive shores between the months of October and December each year, after which it recedes. The residual moisture left is used by small scale, rural farmers to produce crops like beans, maize, millet, cassava and vegetables during the remaining nine months of the year. For successive years, the lake never rises to its previous level for one or two decades. It thu~ leaves some dry land that is useless for arable crop farming. Between 1972 and i983, about 15 km of dry

AGROFORESTRYDEVELOPMENTIN NORTHEASTERNNIGERIA

31 |

TABLE I List of tree species on farmers" fields and in local markets together with their local uses and extent of seed insect infestation in northeastern Nigeria Name of Species

Local uses Fuelwood

Acacia albida Acacia nilotica Acacia senegal .,Icacia tortilis Acacia seyal .4cacia sieberiana ,4dansonia dijitata Annogeisus /eiocarpus .4:adiracta indica Bauhinia rufescens Balanites aegyptiaca Callotropis procera Diosp),rus mespill~fonnis ttyphene thebaica Khaya senegalensis Maerus spp. Mitra:(rna ira,trois Piliostiqma reticulata Phoeni.v dactil~fera Prosopis africana Prosopis jtd(flora Salvadora persica Schlerocao,a birrea Tamarimlus indica Ziciphus spp. Sterculia setigera

Food

Feed

Soil Industrial or Medicinal %seed fertility commercial damaged by insects

X

×

×

× × × X

x × × X

× × X x X X

× X

45 24 57 38

14 0

× ×

0

X ×

X

X

30

× x ×

X x

×

X

~ X

× × X

X

0

X

15 13 0 -

× X

X

X

X

X

X

x X

X X

X

-

x

X X

X

5I

X ×

x ×

×

X

X

x

X 42 48

X

X

-

N o t e : - = Not evaluated.

unproductive land was created in this way. Since the farmers use branches of trees to fence out livestock on their farms, trees could be incorporated into the farming system in alley cropping agroforestry to serve as live fences, to improve soil fertility and to produce wood especially during the dry fallow period. Irrigated farming activities are associated with the government and located near sources of water. This sometimes involves large scale clearing of land using modern equipment to uproot all trees and construct irrigation canals, etc. Trees are needed on such farms to protect canal banks and to act as windbreaks. They are also needed to maximise the use of water and nutrients by extracting those leached beyond reach of crops. Rainfed farming is widespread and involves the bulk of the rural popula-

312

I. VERINUMBE

tion. The farmers depend on the short, erratic rainfall (June-September) to grow their early maturing clops of sorghum, millet, groundnuts and cowpea. In unfavourable years, the crops fail to mature and the farmers rely heavily on wild fruits and leaves growing on their land to survive; a form of insurance. Those in the more arid areas need trees to stabilize sand dunes that are often a threat to their land and homes. Integrated management of trees, crops and livestock among the farmers is very common. Some of the common useful species found on farms are listed in Table I. Farmers look for yield-improving species like Acacia albida and Ziziphus spp. even if the rest of the field is not crop~ ed. In some cases, trees are maintained in high population densities on farms. The fruits and leaves of the trees are fed to livestock during the dry season. The farmers themselves consume the leaves and fruits of species like Adansonia digitata, Balanites aegyptiaca, and Tamarindus indica, while Khaya senegalensis and Piliostigma raticulata provide medicinal extracts. Results of market surveys further confirmed the importance of some of these species by the presence of their products on sale.

Livestock rearing This tsetse-free area houses a large number of livestock which come from both domestic sources and from the neighbouring countries of Chad, Niger and Cameroun. Livestock rearing is, therefore, widespread in the region with apparent shortage of dry season feed. Since annual grasses provide feed only during the short wet season, most of the feed for the rest of the year comes from wild perennial shrubs and trees. Young trees are lacking on the fields, having been overgrazed, desiccated and burned before establishment. Older trees are weak and unhealthy possibly due to old age and constant trimming of branches to feed livestock. These observations imply that development of suitable browse species and silvopastoral systems would considerably improve feed supply to the livestock industry.

Fishing The main focus of fishing activity is the inland fresh water Lake Chad. Other smaller lakes like Lake Aloa and rivers like the Yobe are also popular fishing centres. According to Sagua (1982), more than 80% of the fish caught is smoked either for local consumption or for export. The fishery industry, therefore, needs wood and consumes large quantities of it to the detriment of the environment. Full-time fishermen live in association with shore farmers who produce food for them. A profitable agroforestry system involving shore farmers would,

AGROFORESTRYDEVELOPMENTIN NORTHEASTERNNIGERIA

313

therefore, find a ready market for its firewood product. Acute shortage of wood is apparent and fishermen presently use grass and very inferior wood ( Callotropis procera) to smoke their fish.

Forestry Widespread exploitation of forest resources including fuelwood is going on with very little effective afforestation. The government raises large quantities of exotic tree seedlings of mostly Azadiracta indica at the nurseries scattered all over the area, hut this is not adequately reflected on the plantation sites. Most of the seedlings planted in the harsh field conditions die because of lack of water and care. A feasible alternative may be to convince the farmers to plant the seedlings among their crops and to care for them together. BIOLOGICAL INVESTIGATIONS

Treeseeds Based on results obtained from the surveys, seeds of promising tree species were collected locally for further investigation. On the discovery that they were heavily eaten by beetles, a preliminary assessment was made to quantify the damage. The results (Table l ) indicated that the indigenous species, with the exception of A. digitata and K. senegalensis, suffered heavy damage averaging up to 28 _+20%. This probably accounted in part for the very low natural regeneration rate of the species noticed during the diagnostic survey. The introduced exotics, namely Azadiracta indica and Prosopis juliflora, suffered no damage. The implication is that insect pests are a major problem and need to be considered if indigenous tree species are to be used in agroforestry practices in the region.

Tree seedlings Only about 30-40% of the apparently healthy seeds germinated and the seedlings survived to the end of their three months life at the nursery. This high rate of failure led to suspicions that the potting mixture (top soil only) used was not adequate and needed investigation. Varying proportions of sand or cowdung were added to the topsoil and planted with Leucaena leucocephala, Azadiracta indica and Khaya senegalensis. After three months ofgrowth, the aerial biomass was estimated and related to the soil mixture. The addition of about 50% sand or 30% cowdung to the topsoil improved growth. The improvements were, however, very small and statistically nonsignificant ( P > 0.05 ), indicating that the poor performance of the seedlings

314

I.VERINUMBE

was largely caused by factors other than potting mixture quality. While the problem remains unsolved, large quantities of seeds need to be collected and raised in order to obtain a desired minimum number of healthy seedlings for field planting.

Young trees It was impossible to do field trials on all tree species collected and raised at the nursery. Some of them did not produce enough seedlings to warrant meaningful field testing. Also the land allocated for the whole investigation was small; about 0.5 ha, half of which was already being used as a nursery. Mean tree girth of seven species planted in pure stands on 20 m × 20 m plots at 2 m X 2 m spacing for four years using the taungya system was 19.65 cm for Leucaena leucocephala, 18.64 cm for Acacia nilotica, 16.69 cm for Khaya senegalensis, 16.51 cm for Acacia Senegal, 16.15 cm for Azadiracta indica, 14.84 cm for Prosopisjuliflora and I 1.88 cm for Eucalyptus camaldulensis. E. camaldvlensis had the lowest survival rate of 59% whereas more than 75% of all the other species survived. Canopy closed and growth of the species stagnated at about the age of 3 years. This suggested a three year period for thinning, harvesting or rotation of agroforestry practices involving the species planted at that spacing. Within species, growth was largely uniform and statistically non-significant (P> 0.05 ). However, between species, E. camaidulensis grew significantly slower (P<0.05). The rest of the species exhibited uniform growth and showed no statistical differences between them (P> 0.05). The success of these species, including a n~wly introduced le~acaena, indicate a favourable future for their use in agroforestry systems in the area.

Older trees If farmers are to grow trees on their farmlands at wider spacing and for longer per;ods of time, they need to know the yield to expect at the end of the rotation so as to plan ahead. To obtain an idea of how longer time periods influence growth of trees, use was made of existing plantations ofAzadiracta indica, age from 2 to 19 years, planted at 3 m × 3 m spacing on similar sites. TemporaD' sample plots were established randomly in each of the plantations and diameters of sample trees measured. The diameters were then related to age in regression analysis and the following yield prediction equation obtained: y = 0 . 5 1 2 + 1.976x-0.042x 2 (R2=0.96) where y = diameter of trees (cm) and x = age of trees ( years ).

AGROFORESTRY DEVELOPMENT IN NORTHEASTERN NIGERIA

3|5

Annual girth increment o f about 2 cm was substantial and statistically significant ( P < 0.05). Thus although only one species was used, the results tend to indicate that tree production enterprises can yield substantial return within a short time in the region.

Tree-soil interactions The survey results showed that two species, Acacia albida and Ziziphus spp., are particularly popular a m o n g farmers bf,~cause o f their soil improving qualities. An investigation was, therefore, conducted to assess the magnitude and distribution o f soil nutrients under A. aibida trees during the wet season. Surface soil samples were taken at varying distauces from tree stems and analysed. Table 2 gives a s u m m a r y o f the analysis. Higher soil nutrient content under the trees was confirmed for all the nutrients examined. While nitrogen and potassium decreased continuously away f r o m the stem, organic matter, carbon and sodium increased with distance from the stem up to the centre o f tree crown, after which they decreased progressively. T h e implication is that crown size and tree spacing are i m p o r t a n t factors in A. albida-crop agroforestry and need further evaluation. The use o f relative distance from the tree stem provides a universal basis for comparison o f results.

Tree-crop interactions In order to evaluate some o f the effects trees in agroforestry systems have on crops, surface soil under 12-year-old plantations o f A. indica, P. juliflora and E. camaldulensis were collected and planted with sorghum, groundnut and maize. Surface soil within the same area but outside the plantations served as control. TABLE2 The distribution of soil nutrients under Acaciaalbida trees in northeastern Nigeria during the rainy season Distance from tree stem (in crown radii)

Total N (%) % Organic matter % Carbon Exch. K w.~/100 g Exch. Na me/100 g pH

0.0

0.5

1.0

1.5

2.0

0.088 1.77 I. 12 ! .64 0.73 6.7

0.067 1.87 1.02 1.55 1.23 6.7

0.06 2.09 1.20 1.29 0.93 6.4

0.045 1.52 0.80 1.33 1.09 6.4

0.043 !. 19 0.86 !.46 0.78 6.3

316

I. VERINUMBE

TABLE 3 Biomass yield of crops grown on soil from plantations ofA:udiracta indica, Eucal.l,ptus camalduh'nsis and I'rosopis jul~lh,'a Name ofcrop

Maize Sorghum Groundnut

Mean crop yield (g/plant) A. indica

E. camaldulensis

P. jul(llora

Control

28.57 10.19 3.31

1 ~07 7.23 2. I 0

14.09 6.34 4.54

5.94 3.69 4.66

After two months growth, the crops produced five times higher biomass on forest soils than on the control (Table 3 ). The trees had favourable effects on soil fertility and therefore improved crop yield. While groundnuts gave higher biomass on P~osopis soil, sorghum recorded lower yield. Both P. juliflora and A. indica which produced higher crop yield soil than E. camaldulensis soils looked apparently richer. The variable response of crops to tree species confirms non-uniformity in soil improvements by trees. NEW APPROACHES

Agroforestry on vertisols Agroforestry development in the region has so far been concentrated on the predominantly sandy loam entisols derived from aeolian deposit parent material. However, there are also large expanses of black, heavy, cracking clays called vertisols. They swell when in contact with water and prevent infiltration. The soils are, therefore, flooded most of the wet season, after which they are cropped with a special type of sorghum called masakwat. The masakwat uses residual moisture, grows very fast, and matures in the dry season. In 1989, an agroforestry research project, funded by the British Overseas Development Administration, through the University College of North Wales Bangor and the University of Maiduguri, Nigeria, was started on the vertisols. The objective was to evaluate and develop agroforestry systems that would improve the productive capacity of these difficult soils under low rainfall conditions. The site chosen for the project is a 42 ha vertisols land located in the Sahel savanna around Lat. 12 ° 0' N. Five tree species (Acacia nilotica, Acacia senegal, Acacia seyal, Balanites aegyptiaca and Prosopis juliflora) and one control in which no tree species was planted made up six treatments. Plot size was 25 m × 2 5 m with the trees planted at 5 m × 5 m spacing. Each treatment was rcp!icated four times in each of four blocks. Half of the plots in each block were intercropped with masakwat, leaving the other half with trees alone. The

AGROFORES1RY DEVELOPMENT IN NORTHEASTERN NIGERIA

3| 7

procedure is to be repeated over five years to identify effects o f yearly variations in weather. First planting o f trees was done at the end o f the wet season in August, 1987 when the flooded field had dried up. Similarly, a second set oftrees was planted in the first week o f September, 1988. Unlike the usual practice in this region, no irrigation o f the trees in the dry season is involved. Survival rate from preliminary results was 72.4%. Acacia seyal recorded the highest success rate o f 81%, followed by A. nilotica (79%), P. juliflora (74%), A. senegal (69%) and B. aegyptiaca ( 59% ). Yields from masakwat plots were not obtained because the crop failed as a result o f extensive bird and termite damage.

Economics of agroforestry So far, the development o f agroforestry research in the region has e m p h a sised the biological aspects. It is however, known that any biologically feasible system will enly be successful a m o n g the people it found workable and profitable under the prevailing soeio-economic conditions. To address this important aspect early in the d e v e l o p m e n t process, a study aimed at evahtating the economic viability o f biologically promising, alternative agroforestry systems has been proposed with financial assistance from the American Social Sciences Research Council. Further support is still being sought for continuation o f the main study whose results will guide further development o f agroforestry systems in the region. REFERENCES Abdu, H.M.S., 1987. The influence of Acaciaalbida on some soil properties in a Nigerian savanna: University of Maiduguri Campus, Nigeria. M.Sc. Dissertation, University of Maiduguri, 1987. Anonymous, i 987. A report of the National Committee on arid zone afforestation. Report prepared for the Federal Military Government of Nigeria. Von Maydell, H.H., 1987. Tree and shrub species for agroforestry systems in the Sahelian zone of Africa. Plant Res. Dev., 7: 44-59. Mortimore, M., ! 987, Shifting sands and human sorrow: Social response to drought and desertification. UNEP Desertification Control Bull, No. 14, 1987, pp. 1-14. Sagua, V.O., 1982. Lake Chad fisheries and its importance in the green revolution programme. Proc. 2nd Annual Conference of Fisheries Society of Nigeria, Calabar, 25-27 January, 1982. UNO ( United Nations Organisation ), i 978. Round-up plan of action. United Nations Conference on Desectification,29th August-gth September, 1977. United Nations, New York, 1978. Verinumbe, 1., ! 983. Agroforestry:An interdependent system for improved food and wood production in the arid zone of Nigeria. Nigerian J. For., 14( 1 ): 81-84. Verinumbe, l., i 987a, Utilization of indigenous tree species for the control ofdesertification in Northern Borno. In: V.O. Sagua et al. (Editors), Ecological Disasters in Nigeria: Drought and Desertiflcation. Federal Ministry of Science and Technology, Lagos, pp. 276-284. Verinumbe, l., 1987b. Crop production on soil under some forest plantations. Agrofor. Syst., 5 ( 2 ) : 185-188.