Natural forest management in Sahelian ecosystems of southern Niger

Journal ofArid Environments(1995) 30:129-142

Review Natural forest m a n a g e m e n t in S a h e l i a n e c o s y s t e m s of southern Niger

Blair Orr School of Forestry and Wood Products, Michigan Technological University, Houghton, All 49931, U.S.A. (Received 24 October 1992, accepted 20 ~ l y 1993) During the previous decade management plans have been developed to utilize rationally the natural ecosystems of the Sahel. This paper discusses Guesselbodi Forest, one of the first natural reserves placed under intensive management, in relation to general trends in the Sahel and natural patterns of forest change and structure. Successional patterns, open areas, and the role of fire and grazing are emphasized in developing recommendations for improved forest management. Modifications of current practices can further enhance natural forest management in the Sahel.

Keyworfls: fire; forest management; forest succession; grazing; Niger; Sahel; silviculture

Introduction T h r o u g h o u t the Sahel the cost and failure of m a n y tree plantations c o m b i n e d with the continued overexploitation of forests have led foresters to develop schemes for m a n a g i n g the natural vegetation on a sustainable basis. T h e p u r p o s e of this p a p e r is to identify properties and processes o f the natural ecosystem which should be incorporated in a natural forest m a n a g e m e n t plan. T h e p a p e r begins with a brief section that describes the geographic range for the r e c o m m e n d a t i o n s and some of the terminology used. T h e second and third sections summarize ecosystem processes i m p o r t a n t to the r e c o m m e n d a t i o n s and the recent, h u m a n - i n d u c e d changes in Sahelian forests, respectively. T h e fourth section examines the m a n a g e m e n t of Guesselbodi Forest in Niger, one of the oldest natural forest m a n a g e m e n t plans in the Sahel. T h e work at Guesselbodi is best s u m m a r i z e d in H e e r m a n s & M i n n i c k ' s (1987) guide to natural forest m a n a g e m e n t . T h e i r guide briefly describes the current state of natural forests in Niger, focusing on Guesselbodi Forest, and then describes techniques which can be used to restore vegetation in the Sahel. T h e work at Guesselbodi is s o m e o f the m o s t comprehensive work in the Sahel and it is being used as a m o d e l for the d e v e l o p m e n t of natural forest m a n a g e m e n t plans in other parts o f the Sahel. T h u s , this section 0140-1963/95/020129 + 14 $08.00/0

© 1995 Academic Press Limited

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includes a discussion of those parts of the Guesselbodi management plan that, in light of more recent investigations, might require modification. The paper concludes with recommendations that may enhance natural forest management. T h e recommendations .are made within the context of three premises embodied within the current Guesselbodi management plan: (1) Local participation is a necessary component of a natural forest management project; (2) Natural forests will continue to be exploited and managed use of the forests is preferable to overexploitation; and (3) T h e existing degraded land can and should be restored. This paper acknowledges the first two premises and focuses on the third. T h e first two premises may place constraints on the range of restoration techniques available to land managers.

Background: geographic scope and terminology For the purposes of this paper 'Sahel' is used in the popular sense as that area which is sub-Saharan with some woody vegetation, but not dense forest, a rainfall zone of 400 to 800 m m of precipitation. This zone is described by White (1983) as the Sahel wooded grassland and the Sudanian woodland zones. In the Yangambi classification (FAO, 1974) this is zones 26 and 31. T h e recommendations are based upon observations in the western part of Niger south of the 14 ° 30' N o r t h latitude. With appropriate modifications the recommendations extend to other parts of the Sahelian and Sudanian zones described in White (1983). These classification systems would not describe the ecosystem as true forest, however, current management of these areas is generally described as 'natural forest management' (Heermans & Minnick, 1987; Fries, 1990). T h e G o v e r n m e n t of Niger classifies the protected zones in this area as 'forests' or 'forest reserves'. T h e land managers are 'foresters'. While the terminology is not ecologically correct, it is the common language of land managers in the Sahel.

Processes in Sahelian ecosystems A wide variety of related ecological processes combine to form the vegetation observed in southern Niger. In this paper, four are of particular importance to the recommendations that are made later. (1) Fire has been a natural part of the environment. (2) Grazing and browsing have always had a substantial impact on plant communities in the Sahel. (For the sake of brevity, in the remainder of this paper, grazing implies browsing as well.) (3) W o o d y vegetation does not form a total canopy over the landscape and is frequently grouped in clusters. (4) T h e r e are patterns of woody plant succession. Each of these properties must be considered when developing a rational forest management plan. Walker (1993) also lists these components of arid and semi-arid ecosystems. T h e remainder of this section is divided into two parts, the first discusses fire and grazing and the second vegetation and stand dynamics. This division is not arbitrary; fire and grazing have functioned as both evolutionary factors and as more recent human-induced factors of the ecosystem.

Fire and grazing Arid and semi-arid ecosystems have evolved to exist successfully in an environment with fire and grazing. For example, following the work of Schlising (1969) and others, Onyekwelu (1990) determined that Combretum bauchi~nse Hutch. & Dalz. exhibited

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cryptogeal germination; a pattern where the plumule emerges and then reburies itself. Cryptogeal germination is competitively advantageous in a fire-prone environment. Gombretum bauehiense and several other Combretum species have evolved gradually and taken advantage of the fire. Also, plants that coppice tend to withstand fire regimes more effectively than those that do not (Kruger, 1984). The majority of the woody species in the Sahel reproduce successfully by coppicing. Le Hou6rou (1989) has speculated that the ratio of annual to perennial grasses in the Sahel is due to fire frequency. White (1983) includes a short section of references on various aspects of fire on African vegetation. A substantial body of knowledge suggests that, throughout the Sahel, long-term burning and grazing, continuing to the present (Kelvin, 1989), are the result of human activity. Traditional human land management practices have successfully incorporated natural ecosystem processes. Boaler & Hodge (1964) discuss the use of fire by Somali nomads to increase the production of palatable grasses. Similarly, plants in the arid and semi-arid regions of Africa have evolved under moderate grazing pressure. McNaughton (1979) studied a grazing regime in the Serengeti where the herbivores were wild animals. Traditional, domestic grazing patterns in the same area are similar to those of the wild animals studied. Also, traditional grazing intensity was light relative to grazing by wildlife. McNaughton has hypothesized that such grazing is necessary to maintain maximum biomass production and specifically cites this as an example of co-evolution. He lists nine reasons why grazing is beneficial to animals and plants. Bite patterns, particularly height of the defoliation, and intensity might alter conclusions about optimal grazing levels if the animal is a domestic species. In addition, grazing patterns can have an impact upon plant succession (Davidson, 1993). Belsky (1986) has argued that strong evidence to support beneficial effects of herbivory is lacking, at least from the standpoint of increased biomass production, Even if one accepts her argument, herbivory clearly has an impact upon seed germination through seed transport, scarification, nutrient recycling, and condition of the soil surface (Chapman et al., 1991; Tybirk, 1991). Finally, fire and grazing often occur simultaneously. Lemon (1968) found that moderate grazing (a maximum of 60 to 80% utilization) plus burning did not harm the vegetation. This level of utilization includes the optimum level of grazing determined by McNaughton (1979). Lemon recommends burning to increase forage for large grazing animals. Lemon concludes, 'if burning is frequent and mild, a fireconditioned community, which many ecologists would consider "natural", may be maintained'. When synthesizing work in similar semi-arid southern African ecosystems Mentis & Tainton (1984) concluded that frequent burning improved the quality and quantity of the available forage. Grazing and fire have been linked as a traditional management practice for thousands of years. They should be included in natural forest management plans.

Vegetation patterns and stand dynamics The Sahelian, Sahelo-Sudanian, and the drier parts of the Sudanian forests have numerous grassland openings between patches of trees and bushes. The most dramatic of these is a pattern called brousse tigr~e (Fig. 1). This dry season aerial photograph shows alternating stripes of dark, the trees and shrubs, and light, the openings of bare ground or annual forbs and grasses. Vegetation stripes run on the contour so that rainfall and eroding soil from the bare ground areas run down into the woody vegetation stripe where they are captured (White, 1970; Ambouta, 1984). Ambouta (1984) speculates that during a dry year the downhill edge of the vegetation stripe does not receive enough water from the overland flow to maintain itself and dies. During the

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subsequent years of low and average rainfall, this new equilibrium width is maintained. In good rainfall years the perennial grasses, followed by the woody vegetation, become established in what was previously the annual grass-bare soil zone just above the woody vegetation stripe. Thus, a form of succession occurs as the stripes move upslope (Fig. 2). Vegetation patterns similar to Nigerian brousse tigr~e have been found in other arid and semi-arid zones, though evidence of stripe movement is not always apparent (Boaler & Hodge, 1964; White, 1969; Mauchamp et al., 1993). In addition, there is some evidence that mixed patterns of brush and grass may be linked to burning. Sweet (1982), in a 22-year study of ungrazed plots in Botswana, dominated by Acacia nigrescens, Oliv., and Combretum apiculatum Sond., found that frequent burns reduced the amount of brush cover by eliminating juveniles. U n b u r n e d stands had a higher woody biomass and the mature trees in these stands also suppressed juveniles. In his study, burning did not change the grass composition or density nor did it affect soil properties. Burning may alter the forage quality of the vegetation, leading to a change in grazing patterns which ultimately changes plant succession patterns (Davidson, 1993).

Figure 1. Aerial photo of brousse tigrre at Gogueze Koara Plateau, Niger. Dark areas are woody vegetation and lighter areas are open. Scale: 1:9000. Further information about brousse tigrhe is available in Ambouta (1984). Photograph Source: Institut G~ographique National, St. Mendr, France, by permission of the Government of Niger.

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T h e implication of the brousse tigr~e pattern, and other brush-grass mosaics, is that open areas are part of the natural landscape (Boaler & Hodge, 1962; Wickens & Collier, 1971). Therefore, while foresters should consider revegetation strategies for degraded open areas, reforestation should not be the objective. Grassed areas are natural parts of the landscape and are economically and culturally important. Finally, open areas with natural crusts are also part of the ecosystem in some areas, including the brousse tigrhe m e n t i o n e d above. W h e r e barren areas generate additional moisture (a)

(b)

(c)

(d)

Figure 2. Cross-section of brousse tigr$e showing plant response to rainfall patterns. Adapted from Ambouta (1984). (a) stable vegetation during an average rainfall year; Co) downslope dieback during a dry year; (c) new equilibrium; (d) upslope expansion during a wetter year.

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for adjacent patches of vegetation, the barren areas should be maintained as they are (Le Hou6rou, 1984; Pickup, 1985). As with other forest types, the Sahelian forests have natural patterns of tree succession. For example, within the shrub and tree portions of the mosaic and in nearby farm fields, Guiera senegalensis appears to be an early successional species. Many abandoned farm fields in Niger are now nearly pure stands of Guiera senegalensis ]'.F. Gmel. Heavy grazing also appears to increase the amount of Guiera senegalensis. In the farm fields of Senegal Guiera senegalensis is lopped each year before planting peanuts and millet (Louppe, 1991). Root sprouts are removed during the weeding. Nevertheless, Guiera senegalensis resprouts during the fallow dry season. In some cases Guiera senegalensis resprouts before the field becomes fallow. This successional pattern and others must be considered in management plans (Davidson, 1993).

Recent changes in the forests o f the Sahel Many parts of the Sahel are experiencing a shift to a degraded landscape dominated by the more xerophytic species of trees and shrubs. For example, Prosopis africana (Guill. & Perr.)Taub. is dying out or completely absent in many Nigerian stands where it had formerly been present. Total volume per hectare and average tree size are declining. These changes are the result of a combination of causes. Some changes are the result of natural climatic change within the region (Nicholson, 1978). Recently, an expanding population has increased pressure upon the natural forests of the Sahel and the impact is first evident in the d e m a n d placed upon forest Table 1. Sustainable population in five ecologicalzones of arid and semi-arid west Africa for three land uses Zone

Rainfall

Land use

(mm) Crops

Livestock Forest (sustainable population (people. km-2))

Saharan

0-200

0

0-3

0

Sahelian

200-400

6

2

1

Sahelo-Sudanian

400-600

11

5

10

Sudanian

600-1000

16

7

20

800 +

25

7

20

Sudano-Guinean

Compiled from Gorse & Steeds (1987). resources by livestock. Table 1 shows that the human-carrying capacity in almost all zones of sub-Saharan West Africa will first be exceeded by the associated livestock use rather than the direct extractive demand for forest resources. Overgrazing is the first stage of land degradation. Although some land may be degraded locally due to fuelwood demand, on a national scale the pressure from livestock grazing is greater than from fuelwood harvesting. In many of the southern Nigerian forests grasses and forbs are now absent, though a degraded stand of trees and shrubs remains. Once the protective grasses and forbs are destroyed, soil erosion increases. Overgrazing also causes soil compaction. Next, a hard crust forms on the soil surface,

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causing reduced infiltration and available water for the remaining vegetation. Only the m o r e xerophytic w o o d y species can survive. This process explains the decline of mature Prosopis africana and other less drought-resistant species as well as decreases in total stand volume.

Guesselbodi

Forest

M a n y forests t h r o u g h o u t the Sahelian and Sudanian zones have been designated as national forests or reserves, but are only nominally m a n a g e d as such because of shortages of funding and personnel. T h e results of the inadequate oversight and m a n a g e m e n t have led to overgrazing and overharvesting of forest products, particularly fuelwood. In the late 1970s, Guesselbodi Forest, in s o u t h - w e s t e m Niger, was a clear example of these destructive patterns. Its proximity to Niamey, the capital of Niger, led to levels of overexploitation that were severe by Nigerian standards. Aerial photographs showed that by 1980 '40 to 60 percent of the vegetative cover had disappeared in ... 30 years' (Fries, 1990). T h e resulting barren areas have two distinct soil surfaces, often found in a mosaic across the open area (Fig. 3). T y p e one has a hard crust that sometimes includes a mixed-pebble desert p a v e m e n t , a surface generally indicative of substantial surface erosion (FAO, 1983). T y p e two is sand that has been redistributed by wind and water action. T h e hard crusts have no vegetation growing on them, while the redistributed sand areas have limited a m o u n t s of annual grasses and forbs during the wet season. In less-disturbed areas, the hard crust surface occurs less frequently. T h e exposed roots

• i ~. ~

Figure 3. Degraded land near Guesselbodi Forest, Niger. Grass and small forbs cover areas or redistributed sand while bare areas have a hard crust that often contains small pebbles. Photograph taken during the rainy season, 1991.

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of a young Guiera senegalensis in Fig. 4 illustrate the dramatic nature of erosion and crust development. In 1983 Guesselbodi was one of the first forests to be placed under a rigorous natural forest management plan (Heermans & Minnick, 1987). T h e Guesselbodi plan integrated marketing, local management, and silvicultural components. Both a mechanism and an incentive for local management were necessary. The mechanism was a co-operative that would regulate harvest, sell wood, and implement land restoration projections. Money (a universal incentive) derived from the sale of wood to fuelwood merchants in Niamey, the capital of Niger, would cover the costs of cooperative management and pay for wood purchased fxom co-operative members. Niamey is close enough to Guesselbodi Forest to provide a ready market for harvested wood.

Figure 4. Dramatic evidence of erosion near Guesselbodi Forest, Niger showing exposed roots of a young Guiera senegalensis and the hard crust which has subsequently developed.

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A wide variety of erosion control and land reclamation techniques and structures have been used t h r o u g h o u t Guesselbodi Forest. Structures ranged from small crescent shaped m i c r o c a t c h m e n t s to larger stone check d a m s and berms, in m o s t cases c o m b i n e d with planted grasses and trees. T h e b e r m shown in Fig. 5 is typical of early reclamation efforts at Guesselbodi. Although planted vegetation m a y have survived (in this case Andropogon gayanus K u n t h and Acacia species), it has rarely spread across the landscape through natural processes. Generally, the out-planting survival rate of trees is low. A recent and m o r e promising technique has been to spread branches of recenfly harvested trees on the ground and let termites incorporate the detritus into the soil. This technique aids nutrient cycling, improves soil structure, and loosens the surface crust. Direct seeding of tree species in these slash piles has been successful in some trials ( H e e r m a n s & Minnick, 1987; Hopkins, pers. c o m m . ) . Neither the larger structures nor the m i c r o c a t c h m e n t s have dramatic out-planting success and effectively cover only a small proportion of the open area. Planting strategy is one area where the m a n a g e m e n t plan has strayed f r o m the natural p a t t e m s of stand development in the Sahel. O p e n areas are a part of the natural forest and, hence, should not be reforested. T h e Guesselbodi plan did not utilize natural p a t t e m s of plant succession in developing a harvesting schedule because the necessary information was not available to early planners. Failure to incorporate natural p a t t e m s of succession remains the second p r o b l e m associated with the silvicultural prescription of the forest. Specifically, the plan allowed co-operative m e m b e r s to harvest annually Guiera senegalensis; Combretum micranthum G. Don; Combretum nigricans Lepr. ex Guill. & Perr., and Combretum glutinosum Perr. ex D C . T h e 5000-ha forest was divided into ten 500-ha parcels, one of which would be cut each year in a 10-year cycle. In the parcel,

Figure 5. Berms for rainfall detention. Planted Andropogon gayanus has survived but has not spread over the exposed soil surface. Surface crust is evident in the foreground. Photograph taken in Guesselbodi Forest, Niger, rainy season, 1991.

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Combretum nigricans and Combretum glutinosum greater than 4 cm in diameter and Combretum micranthum and Guiera senegalensis greater than 3 c m in diameter would be harvested. It was believed that after 10 years sufficient regeneration, primarily due to coppicing, and the growth of the smaller, residual trees would allow re-entry into the forest for another harvest of equal volume. Revenue from the harvest would make the project sustainable. T r e e planting and erosion control structures would help d e n u d e d areas recover and would eventually produce m o r e wood for the future harvests. Figure 6 (adapted from Hopkins, 1991") shows that the regrowth in Guesselbodi has been disproportionately Guiera senegalensis. T h e increasing proportion of Cruiera senegalensis occurs because the removal of a substantial proportion of the w o o d y biomass approaches the open-field, early successional conditions preferred by Guiera senegalensis. Figure 6 also shows that the total growth does not return to the preharvest level. Stem-size is greatly reduced. Combretum nigricans and Combretum glutinosum are the preferred fuelwood species and u r b a n w o o d merchants prefer relatively larger diameter fuelwood. H o p k i n ' s (1991) preliminary results and knowledge of locally preferred species indicate that the m a n a g e m e n t plan should be revised. T h e above description of the Guesselbodi plan is abbreviated, but a closer attention to details would not be likely to alter the general conclusions; the structure and composition of the forest is changing and the standing volume o f the forest is decreasing. T h e natural processes of forest succession and growth control this change. Although this section of p a p e r discusses some of the limitations of the Guesselbodi plan, specifically the recovery of areas with a hard soil crust and the.unexpected shift to a forest dominated by small Guiera senegalensis, it is important to realize that the direction provided by the Guesselbodi natural forest m a n a g e m e n t plan is desirable.

5

7 4

o

3

2

gs

cm

cn

cg

other

l

total

Species

Figure 6. Volume change by species at Guesselbodi Forest from 1985 to 1990. 1985 volumes are pre-harvest volumes, gs = G-uiera Senegalensis; cm = Combretum micranthum; cn = Combretum nigricans; cg= Combretum glutinosum; os = other species. Source: Hopkins (1991). ([TA= 1985; • = 1990.) *Hopkins' work is preliminary.Evidence suggests that trends indicated by the data are correct, but certain inconsistencies and large standard deviations imply that a larger sample will be necessary to provide figures reliable enough for a detailed management prescription.

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For example, the project wisely included substantial participation by local residents and a provision for grazing. Livestock would be excluded from parcels for the 3 years following a planting. On a 10-year rotation this would leave seven other parcels available for grazing. In addition, fodder collection was allowed in those areas temporarily closed to grazing. Not only has the number of livestock increased in the Sahel, but the pattern of ownership has changed. In Niger, and other countries, large herds are now owned by wealthy 'civil servants', merchants, and ... farmers' from outside of the villages or tribal areas where they are grazed (White, 1984). Thus, not all of the local increase in overgrazing can be attributed to local people. Regaining local control of the land through forest co-operatives could help reduce grazing pressure ff regulations limit non-local use. The changes in stand characteristics in Guesselbodi, particularly the increase in Guiera senegalensis and the limited success of tree planting in barren areas, indicate that some parts of the Guesselbodi plan need revision. The next section of the paper recommends four modifications for the Guesselbodi plan. Since the Guesselbodi plan is a model for other forests in the Sahel and the problems and dynamics of forests have general similarities throughout the Sahel, these recommendations should have wide applicability.

R e c o m m e n d a t i o n s for forest m a n a g e m e n t in the S a h e l

Good natural management of Sahelian ecosystems should closely mimic the natural ecosystem. Therefore, grazing and fire should be part of the management plan and open areas, both grassed and barren, should be maintained. Planting and cutting patterns should be re-evaluated given the position of Guiera senegalensis in the successional patterns. Four recommendations are proposed:

1. Study the role of fire in Sahelian ecosystems and determine how fire can best be included in the management plan Foresters have been reluctant to accept the role of fire in African forests because it can destroy plantations of exotic species. For decades plantation establishment has been a primary focus of foresters in arid and semi-arid Africa. Standard works on forestry in arid areas such as Weber & Stoney (1986) promote fire prevention as a part of plantation management. However, older farmers in Niger have complained about the ban on fires, view fires as beneficial, and will start fires. Fries (1990) states 'uncontrolled forest fires are a major problem in forest management', but goes on to list forest fires and their controlled use in forest management as an important area for further research. While fire may be beneficial in natural ecosystems which are relatively undisturbed, the impact of fire, even at modest levels, may be detrimental in already degraded landscapes. For example, annuals which benefit from the removal of dead plant material that hinders germination, may be harmed by fire on a nearly barren site. Severely degraded landscapes have dramatically reduced biomass and, therefore, lack the fuel continuity which is necessary for the spread of fires. Therefore, researchers and foresters must be aware of differences between degraded areas and undisturbed stands as they explore use of fire in Sahelian ecosystems.

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2. Plant grasses, rather than trees and shrubs, in many of the barren areas. In areas where bare soil is a component of the ecosystem, leave some areas unplanted Attempt to improve the bare soil first and plant the early successional grasses in open areas, rather than planting trees. This operation mimics the natural forest with its numerous grassed openings. An area with good grass cover will still result in land reclamation and erosion control. T r e e planting alone will not restore severely degraded landscapes. Further, since grazing is placing a greater stress on the ecosystem than fuelwood harve.sting, restoration to grass will help relieve some pressure on the resource base. Grazing, at traditional levels, is a natural part of the ecosystem. Plans such as the Guesselbodi management plan already consider grazing and fodder production as a positive benefit of management. T h e Guesselbodi plan also incorporates local control over the forest area through the co-operative. In combination these may make a larger contribution to improved livestock management than would initially be apparent.

3. If any tree planting is to be done and the desired species are in the genus C o m b r e t u m , underplant in the wooded areas Combretum nigricans and Combretum glutinosum are the species preferred by local wood merchants. These Combretum occur in dense vegetation patches and are later in the successional pattern than Guiera senegalensis. It should be possible to underplant Combretum nigricans and Combretum glutinosum in the dense patches two or three years prior to harvest. When the stands are harvested to diameter limits the young Combrerum will be in a position to grow rapidly into the overstory. Since Combretum species coppice readily, any harvest-damaged 3-year-old Combretum seedlings should resprout and grow into the bush overstory.

4. Lengthen the cutting cycle This recommendation is fairly specific to Guesselbodi and nearby forests. However, if Combretum nigricans and Combrevum glutinosum are the preferred species, then longer cutting cycles will probably be necessary. Guesselbodi's 10-year cycle in combination with the diameter limits and planting scheme favor Guiera senegalensis. Combretum nigricans and Combretum glutinosum naturally succeed Guiera senegalensis and stand volume has not returned to the anticipated levels. A longer time between entries into the stand for harvest will certainly help correct the problem of low standing volume, and in conjunction with recommendation 3 above, should develop a stand that has a higher, and more natural, Combretum component. In general, more research on growth rates of Sahelian species is needed before proper cutting cycles can be set. The author thanks Chris Hopkins, Michele Lemettais, and the Government of Niger for their help gathering information for this article and Wayne Clatterbuck, Karlyn Eckrnan, Michael Wagner, Glendon W. SmaUey, and anonymous referees for reviewing earlier drafts of this paper. The author accepts full responsibility for the contents.

References

Ambouta, K. (1984). Contribution fi l'6daphologie de la brousse tigr6e de l'ouest nig~rien. unpublished docteur-ingfinieur thesis. Nancy, l'Universit6 de Nancy. 125 pp.

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Belsky, A.J., (1986). Does herbivory benefit plants? A review of the evidence. The American Naturalist, 127: 870-892. Boaler, S.B. & C.A.H. Hodge. (1962). Vegetation stripes in Somaliland. Journal of Ecology, 50: 465-474. Boaler, S.B. & C.A.H. Hodge. (1964). Observations on vegetation arcs in the northern region, Somali Republic. Journal of Ecology, 52:511-544. Chapman, C.A., Chapman, L.J. & Wrangham, R.W. (1991) Ugandan elephants help maintain a useful tree. Agroforestry Today, 3:15 Davidson, D.W. (1993). The effects of herbivory and granivory on terrestrial plant succession. Oikos, 68: 23-35. Food and Agricultural Organization. (1974). Tree Planting Practices in African Savannas. Rome: Food and Agricultural Organization. 185 pp. Food and Agricultural Organization. (1983). Keeping the land alive: soil erosion--its causes and cures. Soil Bulletin No. 50. Rome. Food And Agricultural Organization of the United Nations. 79 pp. Fries, ]'. (1990). Natural forest management in the Sahel: the management of Guesselbodi Forest, a success story. Forest, Trees, and People Newsletter, 11: 28-35. Gorse, J.E. & Steeds, D.R. (1987). Desertification in the Sahelian and Sudanian Zones of West Africa. World Bank Technical Paper No. 61, The World Bank, Washington DC. 62 pp. Heermans, J. & Minnick, G. (1987). Guide to Forest Restoration and Management in the Sahd Based on Case Studies at the National Forests of Guesselbodi and Gorou-Basounga, Niger. Report of the Ministry of Hydrology and the Environment, Forestry Land Use and Planning Project, Niamey, Niger. 155 pp. Hopkins, C. (1991). Presentation to the United States Agency for International Development/ Niger on a preliminary inventory of Guesselbodi Forest. 8 July 1991. Niamey, Niger. Kelvin, G.V. (1989). The earth at night. Scientific American, 261: cover. Kruger, FJ. (1984). Effects of fire on vegetation structure and dynamics. In: Booyseen, P. de V. & Tainton, N.M. (Eds), Ecological Effects of Fire in South African Ecosystems, pp. 219-243. Berlin: Springer-Verlag. 426 pp. Le Hou6rou, H.N. (1984). Rain use efficiency: a unifying concept in arid-land ecology. Journal of Arid Environments, 7: 213-247. Le Hou6rou, H.N. (1989). The Grazing Land Ecosystems of The African Sahd. Berlin: SpringerVerlag. 267 pp. Lemon, P.C. (1968). Effects of fire on an African plateau grassland. Ecology, 49: 316-322. Louppe, D. (1991). Guiera senegalensis Esp~ce agroforesti~re? Bois et For~ts des Tropiques, 228: 41-47. Mauchamp, A., Montafia, C., Lepart, J. & Rambal, S. (1993). Ecotone dependent recruitment of a desert shrub, FTouremia cernua, in vegetation stripes. Oikos, 68:107-116. McNaughton, S.J. (1979). Grazing as an optimization process: grass-ungulate relationships in the Serengeti. American Naturalist, U3: 691-703. Mentis, M.T., & Tainton, N.M. (1984). The effect of fire on forage production and quality. In: Booysen, P. de V. & Tainton, N.M. (Eds), EcologicalEffects of Fire in South Afn'can Ecosystems, pp.245-254. Berlin: Springer-Verlag. 426 pp. Nicholson, S.E. (1978). Climatic variations in the Sahel and other African regions during the past five centuries. Journal of Arid Environments, 1: 3-24. Onyekwelu, S.S.C. (1990). Germination, seedling morphology and establishment of Combretum bauchiense Hutch. & Dalz. (Combretaceae). Botanical Journal of the Linnean Society, 103: 133-138. Pickup, G. (1985). The erosion cell--a geomorphic approach to larMscape classification in range assessment. Australian Rangeland Journal, 7:114-121. Schlising, R.A. (1969). Seedling morphology in Marah (Cucurbitaceae) related to the California Mediterranean climate. American Journal of Botany, 56: 552-560. Sweet, R.J. (1982). Bush control with fire in Acacia nigrescens/Combretum apiculatum savanna in Botswana. Proceedings of the Grassland Society of Southern Africa, 17: 25-28. Tybirk, K. (1991). Regeneration of woody legumes in Sahel. A A U Reports 27, Botanical Institute, Aarhus University, Aarhus, Denmark, 82 pp. Walker, B.H. (1993). Rangeland ecology: understanding and managing change. Ambio, 22: 80-87. Weber, F.R. & Stoney, C. (1986). Reforestation in Arid Lands. Washington, DC: Volunteers in Technical Assistance. 335 pp.

142

B. ORR

White, C. (1984). Herd Reconstitation: The role of credit among lVodaabe herders in central Niger. London: Overseas Development Institute, Pastoral Development Network. 18 pp. White, F. (1983). The Vegetation of Africa: A descriptive memoir to accompany the UNESCO/ AETFAT/UNSO vegetation map of Africa. Paris: UNESCO. 356 pp. White, L.P. (1969). Vegetation arcs in Jordan. Journal of Ecology, 57: 461-464. White, L.P. (1970). Brousse Tigr6e patterns in southern Niger. Journal of Ecology, 58: 549-553. Wickens, G.E. & F.W. Collier. (1971). Some vegetation patterns in the Republic of Sudan. Geoderma, 6: 43-59.