Research Article |
Corresponding author: Peter Neuenschwander ( p.neuenschwander@cgiar.org ) Academic editor: Ingolf Steffan-Dewenter
© 2017 Peter Neuenschwander, Aristide C. Adomou.
This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Citation:
Neuenschwander P, Adomou AC (2017) Reconstituting a rainforest patch in southern Benin for the protection of threatened plants. Nature Conservation 21: 57-82. https://doi.org/10.3897/natureconservation.21.13906
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In a twenty-year effort at Drabo, southern Benin, small remnant forests, young fallow and agricultural fields were linked and rehabilitated to develop a 14 ha forest reserve. Forest regrowth was encouraged by managing the natural growth of the local fallow vegetation and by bringing in seeds and other propagules from forest islands of Benin. The succession to shade-tolerant woody forest species of Guineo-Congolian origin at the expense of extra-regional herbs, the co-existence of species with slightly different requirements, and the fate of exotic trees in this natural forest are described. A quantitative assessment of a homogeneous lot indicated 397 trees per ha, with stem diameters >10 cm, 43.7% of them below 20 cm, and a rich undergrowth of 72600 smaller plants per ha, proof of active rejuvenation. Only 4.2% of all plants resulted from the 1041 introduction events, i.e., species per date, mostly of the 253 plant species that were new to Drabo. A total of 635 species were recorded, but 50 did not survive and four are yet to be identified. In June 2016, the total of 581 known living species included 224 trees. Among all plants, 244 hailed from the Guineo-Congolian zone with 17 of Upper Guinean and four of Lower Guinean origin, 113 from the three savannah zones, and 224 were of extra-regional origin. Overall, 72.8% of all woody plants, such as many climbers, all shrubs and trees, were of forest and savanna origin (GC, SG, SZ and S), whereas 70.4% of all herbs came from other regions (At, PAL and Pt). Only 7.0% of all species from the GC zone were in decline; but the further away the plants originated from, the larger the decline in numbers and vigour, up to 64.6% among plants of pan-tropical origin. Particularly pan-tropical herbs became ever rarer, with 80.0% of them declining and confined to the few open spaces along paths. In 2017 the forest harboured 52 threatened species, with threat categories EW, CR, EN or VU on the Red List of Benin, out of 73 IUCN-listed species that could possibly survive in Drabo. Some of these species occur in only one or two other locations in Benin. The biodiversity richness of the rehabilitated forests of Drabo now rivals that of natural rainforest remnants of the region. As the surrounding landscape becomes ever more impoverished because of the high human population and its ever increasing impact, the maintenance of such managed islands of biodiversity is critical. By establishing rare local species from other locations we can compensate for direct human destruction and long-term stochastic loss of species in this highly fragmented landscape where natural seed dispersal is difficult.
Benin, sacred forest, threatened plants, IUCN Red List, forest regeneration, Guineo-Congolese semi-deciduous forest
Benin, sacred forest, threatened plants, IUCN Red List, forest regeneration, Guineo-Congolese semideciduous forest
During the quaternary Ice Ages, West Africa’s rain forests receded to two main refuges situated in today’s Côte d’Ivoire/Liberia and southern Cameroon (Figure
Map of West Africa with ecological zones: SS Sahelo-Sahara, S Sahel savannah, SZ Sudan savannah, SG Guinea savannah, GC Guinea-Congolian forest with closed sdh semi-deciduous forest, egh evergreen forest, asterisks Upper Guinean and Lower Guinean ice-age refuges, triangle Sikensi block. According to Arbonnier (2000),
In a highly populated region with sometimes over 250 people per km2 (
Here we describe a 20-year effort to link up tiny forest fragments and to rehabilitate them through selective management of former farm and fallow land by encouraging forest regrowth and introducing plants from other forest islands of southern Benin. The management of this reconstituted, biodiversity-rich forest with its most important inhabitants, the critically endangered, endemic red-bellied monkey, Cercopithecus erythrogaster (Cercopithecidae) and the interactions with the villagers have already been described and compared with management in other forest sites (
Ecological zones in West Africa (Figure
Within the Guinea-Congolese forest zone, the limits for the vegetation and the outer limits of still existing semi-deciduous and evergreen rainforests are therefore given separately. The site of a detailed study of plant cover (
The Dahomey Gap as shown in Figure
Drabo Gbo (6°30'N; 2°18'E; ca 60 m asl) (Figure
The "Monkey Sanctuary of Drabo Gbo" (Figure
Map of Drabo forests with year of purchase and start of forest management, major clearings: 1 nursery-garden 1997 (house constructed 1997-1998) 2 papa-garage 1999, 2000 3 Lissanou 1999–2003 4 mill 2000 5 Gaston part of Cooun cleared in 2010 6 Cooun 2001 7 corridor-Dansou 2004, 2010 8 Emile 2001–2007 partly cleared 2012 9 ‘Maison de Jeunesse’ (MdJ house constructed 2005) 1998, cleared in 2013 10 Tofinou 1998-2000 11 Pierre 1999–2001 12 Kakpo 2004 13 Grande Forêt 1996, local fire in 2012 14 AgoXwè 2000–2003 15 Corridor north 1998, 2002–2003, Orojamè 1998, Fanto 1998–2000, partly cleared 2014, Dodja 2011, partly cleared 2016. Natural forests grey with border line, wood lots light grey with border line, compact villages light grey, unsurfaced roads as lines.
Speed, quality and abundance of regrowth depend much on the previous occupation of the land (
A flimsy fence of concrete poles, which support five lines of barbed wire, surrounds most of the forest lots; however, effective protection is provided by the "vodun adogba" , i.e., by traditional cults to which the first author has been initiated. Interactions with the surrounding population were described in detail in
Management consists of freeing trees from an excessive burden of climbers and maintaining small paths. Exotic timber species, such as Cassia siamea, Acacia auriculiformis and Tectona grandis (teak), are cut on demand by villagers, but under the supervision of the owner. Among the indigenous commercially important species, oil palm (Elaeis guineensis) is by far the most important. On demand, its fruits are collected where easily accessible. During successive fallow cycles, this indigenous species had been protected and enriched to a degree where in many places areas of up to 0.5 ha were so densely stocked that all other vegetation was suppressed. Cutting these oil palms produced sunlit habitats, which triggered the emergence of pioneer trees and offered open space for planting young trees. These were sometimes shaded by cut palm leaves until full rooting was achieved.
During the twenty-year period of establishing the forest, numerous collecting trips were made to other patches of forest in southern Benin. Plant material was collected mainly in the following locations (Figure
Most collecting expeditions were conducted in the main rainy season to benefit from conditions favourable for transplanting. To facilitate establishment at Drabo, plants, seeds, or cuttings were first held in a 50 m2 nursery in open forest near the house, where they could be provided with additional shade if needed, water, and mulch. Most plants remained there for up to a year, awaiting the next significant rains. Recalcitrant seeds were scarified or treated with hot water. Some plants were planted out directly into particular microhabitats, mostly into 5 ha near the habitation of the owner. Watering and mulching during the first year made it possible that also plants from slightly moister forests could survive in Drabo.
On "Cooun" (Figure
To register all plant species, parts of the forest were inspected since 1998 daily for "Cooun" and surroundings, weekly for "Grande Forêt" and surroundings, and monthly for Drabo Fanto and Dodja by PN and/or a local guide. Unknown plants were marked with a yellow plastic band for later identification by AA. First identifications in 1997 and 1998 had been made by the late Prof. Paul Houngnon of the National Herbarium of Benin. Plants were identified by means of
A list of all species registered in these forests is given as supplementary file. Species from aquatic, semi-aquatic, coastal-sand, or rocky habitats as well as horticultural species are excluded because they are not part of the natural flora of Drabo and, where present, survived only under special conditions, i.e., in pots or concrete ponds. The supplementary file lists:
– Taxa (Pteridophytes as 1Pteri, Gymnosperms as 2Gym, Monocotyledons as 3Mono, Dicotyledons as 4Dicot, and non-identified as 5nonid.
– Plants are described as parasites/epiphytes, herbs, climbers, shrubs or trees based on the description in
– Chorology according to
– The next column indicates the origin of transplanted species (Figure
– Abundance in 2016 is ranked as follows: 1 = 1–4 plants established; 2 = 5–10 plants; 3 = up to 20 plants; 4 = common species; 5 = abundant species.
– The maximum height of trees of each species was estimated in April-June 2016, taking into account all study forests. For most species, biggest trees were found in Drabo; in addition, especially big specimens from Dodja (Do), Fanto (Fa) or Orojamè (Or) were indicated.
– The population tendency was roughly estimated as s = stable, i = increasing, d = decreasing. Where necessary, Cut or Lost (L = lost by July 2016) were indicated.
– Red List status was given according to
– Suspected reasons for difficulty in establishment were given as: - recalcitrant seeds, which were sometimes treated with hot water or by scarifying, - drought, i.e., temporarily too little water, - savannah species, of which we suspect that they do not support transfer to two rainy seasons and are therefore not capable of reaching the coast, - medicinal use, e.g., roots harvested for increasing male potency.
– The number of samples, which include one to maximum 10 plantlets or seeds per species and date, was indicated.
– Plants originally found on the 14 ha and in their vicinity of a few hundred meters were marked with x. Some of them, if they were rare, were also reproduced and transplanted to other sites.
Percentages were compared by a two-way Chi-square test with correction for continuity.
Even before the village of Drabo Gbo had been founded at the end of the 19th century, the area had been under cultivation probably for hundreds of years out of the village of Gbodjo situated at the lagoon near Calavi, with fallow cycles of 15 years or more. Some forests remained untouched and served as sacred forests, like Dodja, the oldest forest in this study. Its Cola gigantea, Celtis milbraedii, Blighia sapida and Antiaris toxicaria are probably several hundred years old and reach 40 m. The forest was not touched for perhaps 100 years; but gaps with trees of only 10 m height that are heavily encumbered by lianas indicate that big trees had been cut before the present inhabitants of Dodja can remember. Another sacred forest, Orojamè, was created around a big Cola tree about 80 years ago and to date is the central site for the "Oro" cult of the entire area. This site of 0.4 ha was bought in 1999 and increased to about 0.8 ha.
In the former teak forest and another fallow lot, two big Cola gigantea trees were included in the newly acquired land. Their preservation was due to a courageous action in the late 1970s by the then "délégué" , who refused political pressure to cut them down because they were reputed to be sites of ghosts. They became islands of biodiversity, from where plants, insects, but also mammals spread to the rest of the developing forest.
About 8 ha, among them "Cooun" where the quantitative study was made, were under forest cover about 50–70 years ago, before the forest was cleared and replaced by maize, teak, Dialium guineense, which were stunted to harvest the sweet seeds, or cow "pasture", effectively bush regrowth since the local cows eat only broad leaves, no grass. Since no heavy equipment was ever used, seeds and roots of the previous forest vegetation remained alive. When fallow or crop land was purchased it was mostly devoid of trees. Once cultivation ended, shrubs, some up to man’s height, developed into big trees within a few years.
In the past, fire in Fanto was ignited along the edge to catch grass-cutters, a large rodent. Moreover, at Drabo Gbo, six big Albizia and Rhodognaphalon trees were set on fire by igniting a car tyre at their base. In the same vindictive action in 2013 by villagers, who were enraged because of a local murder, all 65 trees on the triangle of the "Maison de Jeunesse" (MdJ), were cut. This action was ordered by the "Bokonon" (seer), who claimed a bad spirit was located there. The garden of the MdJ has meanwhile been transformed into an ethnobotanical garden. At present, the protection of the forest is good, i.e., no trees are debarked or felled, few lianas cut, no fire is laid, and no hunting is observed, except for some digging-out of ground squirrels or Gambian rats.
The forests of Drabo are embedded in a landscape of farmland with numerous isolated small houses. The section in Figure
Numerous woodlots have been planted with Cassia siamea, Tectona grandis, and mostly Acacia auriculiformis. The total area of uniform and biodiversity-poor woodlots in Figure
Today, trees in Dodja are around 30 m high, with a few up to 40 m. In Orojamè the canopy is at around 20–25 m. In the oldest, selectively managed fallow land, trees reach 20–25 m, but in Drabo Fanto and on "Emile" in Drabo Gbo on sandy soil, the canopy is at only 10–15 m.
In 2016 a quantitative assessment of the vegetation was made in a mixed Albizia forest with rich undergrowth on "Cooun ", after 15 years of fallow combined with cow pasture (Figure
All above named species are part of the 328 naturally occurring species classified as abundant (category 5), yet they account for only 11.6%. For 64.6% of all local species, less than 20 specimens are known, and for 25.0% only 1–4 specimens could be found despite regular and intensive search. Among the 253 introduced species, only one reached a total population of more than 20 specimens.
Identification, particularly of juvenile plants without flowers and fruits, proved to be challenging. Up to 1998 a total of 168 plants of local origin had been identified. By 2004, when the bulk of the land had been acquired, the number increased to 317. Up to 2010 only 7 more species were discovered, and 4 more up to 2016, bringing the total of local species to 328. Another 253 species were introduced from forests from southern Benin (Fig.
The supplementary file lists 635 plant species, among which four could not yet be identified. Identification or description as a new species will become possible as soon as flowers will be produced. Two have been tentatively attributed to the genus Monanthotaxis (Annonaceae).
Among the 631 remaining species, 50 or 7.9% were lost during the last 20 years, 49 of them introduced species. For five of the 10 extra-regional (At, PAL, Pt) and 10 of the savanna (SG, SZ, S) species, loss is attributed to seeds that would not sprout in the forest environment. By contrast, only one out of seven forest (GC) species that had been collected only as seeds failed to produce seedlings.
This leaves 581 species (Table
Since locally occurring rare species were also transplanted to other parts of the forest, the total number of introduction events in the course of the last 20 years was a high 1041, with a maximum of 10 introductions per species with up to 10 individuals from one collection date.
During the last 20 years, changes in composition were observed. Declines in number of plants and, sometimes, plant vigour were unevenly distributed among growth forms and origins (Table
Change to a more mixed composition of large trees with a larger proportion of evergreen species is reflected in the frequent breaking of large branches of Albizia trees during storms, while Celtis and Blighia spp. resist better and become gradually more important.
The decline in numbers and vigour of particular species in Table
A total of 224 tree species are growing on these 14 ha. Among them, 69 are big trees of 10 m height or more. In the Drabo forest under total protection, the number of Cola gigantea, which had been largely destroyed in the area, increased steadily. The timber trees Afzelia africana, Celtis milbraedii, Diospyros mespiliformis, Milicia excelsa and Triplochiton scleroxylon, which had all disappeared from Drabo, grew well in the study forest. Erythrophleum suaveolens raised from seeds became common and reached 25 m, while Rhodognaphalon brevicuspe planted as sticks reached 22 m.
Some formerly rare plants like Oxyanthus racemosus and Pavetta corymbosa, of which only one plant each could be found in 1995-1996, became common. Similarly, some tree species like Albizia ferruginea, Borassus aethiopum, Ceiba pentandra, Celtis milbraedii, Parkia biglobosa, Psydrax parviflora, Vepris verdoorniana, and Zanthoxylum leprieuri existed in only one lot, but grew well when planted elsewhere. Several trees, which were the last ones in the area and were subsequently felled, provided seeds and sticks that were reared in the nursery and then planted out: Cynometra megalophylla, Elaeophorbia drupifera, Kigelia africana, and Pentaclethra macrophylla.
Some species from the Guineo-Sudanian transition zone or even further north reach the coast and were found in Drabo, like Adansonia digitata, Crossopteryx febrifuga, Lawsonia inermis, Parkia biglobosa, and Tamarindus indica, of which only a few big trees survived in the area. Lophira lanceolata from the isolated population near Pahou survived only on sandy soil.
The following introduced species came from clines in forests with open water like Pobè and Niaouli; they required irrigation and mulching during the first dry season for establishment: Barteria nigritana, Cleistopholis patens, Dennettia tripetala, Distemonanthus benthamianus, Entandrophragma angolense, Homalium letestui, Mansonia altissima, Monodora myristica, Piptadeniastrum africanum, Pycnanthus angolensis, Tabernaemontana eglandulosa, and Trilepisium madagascariense.
In the course of reforestation of the last 20 years, yearly herbs decreased or disappeared. They resurged, however, immediately wherever an opening provided sunlight habitat. Thus, Trema orientalis trees could not be found anymore, until they suddenly reappeared from dormant seed on MdJ in 2013 in the newly opened up area, hundreds of meters away from the original site. Even in places where Chromolaena odorata was not cut, the encroaching forest within 10 years shaded it out completely. Tithonia diversifolia, another feared invader, appeared only once in 2002 and disappeared the same year, when shaded out.
Commercialized fruits are produced by the following well-established indigenous trees: Chrysophyllum albidum, Dialium guineense, Irvingia gabonensis, and Spondias mombin. Of particular interest is the introduced Synsepalum dulcificum, an endangered plant that has potential for commercialization because of its sugar-free sweet fruits. Tropical crops of closed forests like Coffea canephora, Hevea brasiliensis, Theobroma cacao, and Vanilla planifolia needed irrigation to start growth. By contrast, the exotic fruit trees Anacardium occidentale, Azedirachta indica, Mangifera indica, and Psidium guajava did not last in the closed forest and died within 10-15 years. Similarly, field crops like Ananas sativus, Manihot esculenta, and Musa triploid spp. did not produce any commercial product anymore, but persisted in the closed forest for many years even when shaded.
Among the introduced timber species, Acacia auriculiformis and Cassia siamea grew well in closed forest, whereas Leucaena leucocephala was overgrown by climbers and despite abundant seed-set did not reproduce vigorously. Among the original 1 ha of Tectona grandis many trees were cut; but the remainder grew well in a mixed forest. The one clump of Bambusa vulgaris remains problematic because it is displacing all other plants in the vicinity.
Many medicinal plants, which grow also in the Drabo forest, like Acanthus montanus, Mondia whitei, Acridocarpus smeathmanii and A. alternifolius, as well as Heliotropium indicum are being commercialized and sold on the "juju" markets, without being cultivated or even locally protected.
Number of species alive and percentage declining (d.) in different ecological zones. Drabo July 2016.
Region | Para. & Epi. | Herbs | Climbers | Shrubs | Trees | Total | ||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|
N | %d. | N | %d. | N | %d. | N | %d. | N | %d. | N | %d | |
CG Ϯ | 4 | 23 | 75 | 33 | 109 | 244 | ||||||
0.0 | 13.0 | 9.3 | 3.0 | 5.5 | 7.0 | |||||||
SG | 0 | 17 | 23 | 8 | 33 | 81 | ||||||
64.7 | 13.0 | 25.0 | 18.2 | 27.2 | ||||||||
SZ and S | 0 | 5 | 3 | 4 | 20 | 32 | ||||||
60.0 | 33.3 | 50.0 | 45.0 | 50.0 | ||||||||
At and PAL | 0 | 42 | 17 | 6 | 15 | 80 | ||||||
74 | 29.4 | 33 | 27 | 52.5 | ||||||||
Pt | 2 | 65 | 20 | 10 | 47 | 144 | ||||||
50.0 | 80.0 | 65.0 | 70.0 | 42.6 | 64.6 | |||||||
Total | 6 | 152 | 138 | 61 | 224 | 581 ¥ | ||||||
16.7 | 65.8 | 21.0 | 24.6 | 20.1 | 33.0 |
Table
Most threatened (CR) are Acanthus montanus which was purchased on the market in Calavi, where material from one location near Porto Novo is sold as medicine; Barteria nigritana from Ahozon; Caloncoba echinata from a moist site in Niaouli; Entandrophragma angolense, which originally had only a few trees in Niaouli; and Dennettia tripetala and Nesogordonia kabingaensis from Ewè, where they are not protected. Caesalpinia bonduc is extinct in the wild (EW), but widely maintained (and also stolen!) in the village for its medicinal roots. A few plants of Garcinia cola (EW) also grow in the study forests. Of special interest are Distemonanthus benthamianus (EN), which exists in Benin only in one small, though protected site in Pobè, and Mansonia altissima (CR) from Ewè, where it is not protected. Both species grow as isolated populations at the eastern edge of their continental distribution, and only few trees exist in Benin.
Thanks to 20 years of careful protection and management, many threatened plants could be established and the species richness of the forest now rivals the one of the forests from where these endangered species come from (Table
Distribution of threatened plant species in southern Benin. Only living woody plants (trees, shrubs, lianas) and species on solid ground (i.e., without plants limited to swamp forests, sandy beaches or rocky outcroppings) are considered. Only VU to EW. Presence = x, origin as in Figure
Family | Species | IUCN Ϯ | Drabo ¥ | Ewè incl. Kétou | Pobè incl. Sakété | Dangbo | Lama | Niaouli | Ahozon (Pahou) | others | Origin§ |
---|---|---|---|---|---|---|---|---|---|---|---|
Acanthaceae | Acanthus montanus | CR | x* | x | Bassila, Porto-Novo | GC | |||||
Anacardiaceae | Antrocaryon micraster | CR+ | xa | GC | |||||||
Apocynaceae | Carissa spinarum | VU | x | (x) | x | x | x | x | x | coast | PAL |
Apocynaceae | Tabernaemontana pachysiphon | EN | x* | x | x | At | |||||
Apocynaceae | Voacanga africana | VU | x* | x | x | (x) | (x) | (x) | (x) | north | At |
Annonaceae | Dennettia tripetala | CR | x* | x | x | GC | |||||
Annonaceae | Monodora myristica | EN | x* | x | x | Lanzron | GC | ||||
Annonaceae | Xylopia aethiopica | VU | x* | x | x | (x) | x | north | At | ||
Arecaceae | Borassus aethiopum | VU | x | (x) | (x) | across country | SZ | ||||
Aristolochiaceae | Pararistolochia mannii | EN | L | (x) | (x) | (x) | x | Zinvié | GC | ||
Asclepiadaceae | Mondia whytei | VU | x | x | x | (x) | x | (x) | SG | ||
Bignoniaceae | Kigelia africana | VU | x | (x) | x | (x) | x | (x) | (x) | SG | |
Burseraceae | Canarium schweinfurthii | CR | xa | GC | |||||||
Capparaceae | Maerua duchesnei | EN | x* | x | x | SG | |||||
Celtidaceae | Celtis milbraedii | EN | x* | x | x | x | GC | ||||
Clusiaceae | Garcinia kola | EW | x* | Ouidah, Porto-Novo | GC | ||||||
Clusiaceae | Pentadesma butyracea | VU | x* | Bassila, Pénésoulou | SG | ||||||
Combretaceae | Terminalia superba | EN | x* | x | x | (x)* | north | GC | |||
Euphorbiaceae | Discoglypremna caloneura | VU | xa | GC | |||||||
Euphorbiaceae | Drypetes aframensis Hutch. | CR | xa | GC | |||||||
Euphorbiaceae | Drypetes gilgiana | CR | xa | GC | |||||||
Flacourtiaceae | Caloncoba echinata | CR | x* | xa | GO | ||||||
Flacourtiaceae | Homalium letestui | EN | x* | x | x | (x) | GC | ||||
Leguminosae- | Afzelia africana | EN* | x* | (x) | x | (x) | x | (x) | (x) | north | S |
Leguminosae. | Albizia ferruginea | VU* | x | x | x | (x) | x | x | Pénéssoulou | GC | |
Leguminosae. | Anthonota fragrans | CR | x* | x | Bonou | GC | |||||
Leguminosae. | Caesalpinia bonduc | EW | x* | (x)* | x* | (x)* | (x)* | (x)* | (x)* | Pt | |
Leguminosae. | Detarium senegalense | VU | x | north | GC | ||||||
Leguminosae | Distemonanthus benthamianus | EN | x* | xa | GC | ||||||
Leguminosae. | Hymenostegia afzelii | EN | x | GC | |||||||
Leguminosae | Parkia bicolor | EN | x* | x | (x) | x | Zinvié | GC | |||
Leguminosae. | Pentaclethra macrophylla | VU | x | x | (x) | x | GC | ||||
Leguminosae. | Piptadeniastrum africanum | VU | x* | x | x | x | Zinvié | GC | |||
Leguminosae | Tetrapleura tetraptera | VU | x* | x | x | x | north | GC | |||
Leguminosae | Amphimas pterocarpoides | EN | x | GC | |||||||
Leguminosae | Pterocarpus erinaceus | EN | x* | (x) | x | north | S | ||||
Malpighiaceae | Acridocarpus alternifolius. | EN | x* | x | (x) | (x) | x | GC | |||
Malpighiaceae | Acridocarpus smeathmanii | EN | x* | (x) | x | GC | |||||
Meliaceae | Carapa procera | VU | x | x | GC | ||||||
Meliaceae | Entadrophragma angolense | CR+ | x* | (x) | x | GC | |||||
Meliaceae | Khaya grandifoliola | EN+ | x* | (x)* | Bassila, Zagnanado | GC | |||||
Meliaceae | Khaya senegalensis | EN+ | x* | (x) | (x) | (x) | (x) | (x) | (x) | Bassila, Zagnanado | S |
Meliaceae | Trichilia martineaui | CR | xa | GO | |||||||
Meliaceae | Turraea heterophylla | EN | x* | x | x | x | (x) | GO | |||
Moraceae | Milicia excelsa | EN+ | x | x | x | x | x | x | x | GC | |
Myristicaceae | Pycnanthus angolensis | VU | x* | x | x | x | (x) | GC | |||
Orchidaceae | Angraecum distichum | EN | x* | x | Djrègbè | GC | |||||
Orchidaceae | Graphorkis lurida | EN | L | x | At | ||||||
Olacaceae | Strombosia pustulata | EN | x* | x | x | x | GC | ||||
Oleaceae | Schrebera arborea | EN | x | north | GC | ||||||
Passifloraceae | Barteria nigritiana | CR | x* | x | GE | ||||||
Rubiaceae | Aidia genipifolia | EN | x* | x | x | (x) | x | x | GC | ||
Rubiaceae | Euclinia longiflora | EN | x* | x | x | GC | |||||
Rubiaceae | Gardenia nitida | EN | x* | x | x | x | GC | ||||
Rubiaceae | Nauclea diderrichii | EN+ | x* | x | x | Lokoli | GC | ||||
Rubiaceae | Psilanthus mannii | CR | x* | x | x | GC | |||||
Rubiaceae | Tricalysia reflexa | CR | xa | GC | |||||||
Rutaceae | Afraegle paniculata | EN | x | north | At | ||||||
Rutaceae | Zanthoxylum gilletii | EN | L | x | GC | ||||||
Rutaceae | Zanthoxylum zanthoxyloides | VU | x | x | (x) | (x) | x | (x) | x | GO | |
Sapotaceae | Chysophyllum albidum | VU | x | x | x | (x) | x | GC | |||
Sapotaceae | Mimusops andongensis | EN | x* | xa | GC | ||||||
Sapotaceae | Synsepalum dulcificum | EN | x* | (x) | Porto-Novo etc. | GC | |||||
Sapotaceae | Vitellaria paradoxa | VU | L | x | north | S | |||||
Simaroubaceae | Pierreodendron kerstingii | EN+ | x* | x | (x) | Zinvié, north | GO | ||||
Sterculiaceae | Mansonia altissima | CR | x* | xa | Calavi* | GC | |||||
Sterculiaceae | Nesogordonia cabingaensis | CR | x* | xa | GC | ||||||
Sterculiaceae | Octolobus spectabilis | CR | xa | GC | |||||||
Sterculiaceae | Pterygota macrocarpa | CR | xa | GC | |||||||
Sterculiaceae | Triplochiton scleroxylon | EN+ | x | (x) | x | x | x | north | GC | ||
Tiliaceae | Christiana africana | EN | x | Pt | |||||||
Violaceae | Rinorea dentata | EN | x* | x | x | Bassila | GC | ||||
Violaceae | Rinorea ilicifolia | CR | xa | GC | |||||||
Total threatened plant species: | 73 | 52 | 30 | 48 | 28 | 20 | 32 | 18 |
Biodiversity in general, and of tropical forests in particular, is to be preserved for ethical reasons, for agriculture under the headings of plant protection-biological control (
Because of their small sizes, Benin forests would not satisfy the criteria for a key biodiversity area (
These forest islands harbour plant species with origins in the biodiversity centres of the Upper or Lower Guinea forest blocks. Today, large contiguous forest areas in West Africa are confined to western Côte d’Ivoire and eastern Liberia for the Upper Guinea block and extreme eastern Nigeria to southern Cameroon for the Lower Guinea block. In most areas designated as evergreen or semi-deciduous humid forest (Figure
Because of rapid deforestation eight out of 26 commercial timber species of Côte d’Ivoire and Ghana are listed as threatened (
The fact that plants from zones with yearly rainfalls 200 mm above the one in Drabo, as for instance Baissea zygodioides, Dennettia tripetala, Dracaena phryniodes, Gardenia nitida, Landolphia togolana, Pararistolochia goldieana, Tapura fischeri, and Turraea heterophylla from evergreen forest pockets (
At the other extreme, these forests harbour also tree species that must be considered remnants of the savannah into which the advancing forests intruded. These include Lophira lanceolata, with its isolated population near Pahou (
The present long-term observations in Drabo describe the succession towards the climax Guineo-Congolese semi-deciduous forest through natural fallow, enriched with plants from other botanical districts of this zone (
As the tree canopies close herbs–most hail from outside the region–gradually decline. This concerns particularly grasses, so that only two forest species, Olyra latifolia and Oplismenus hirtellus, remain. The disappearance of herbs is, however, immediately reversed as soon as free soil appears because of natural tree fall or clearance. Because the Drabo forests are of irregular shape with long edges, many light-demanding species can still survive along the fringes.
Except for bamboo, no plant in Drabo has the potential to become invasive and transform the environment. Even Chromolaena odorata and Imperata cylindrica, two feared weeds, as well as potential invaders like guava or Leucaena leucocephala under the conditions of southern Benin just follow the environmental conditions, but do not transform them (
One cannot step into the same forest twice (paraphrasing Heraclitus); the present text therefore provides only a snapshot. The fact that only a few species were newly detected in the last years indicates that the cumulative list of species has reached a plateau and we can expect only few more discoveries. Since 21 IUCN-listed spp. with good potential for establishment are still lacking (Table
With 585 plant species or about 20% of the Flora of Benin, the Drabo forest have become a sanctuary not only for monkeys but also for rare plants, which themselves again offer the basis for the establishment of rare butterflies and other specialists. The vicinity to big towns and the relatively easy access should allow some eco-touristic development. Since the ownership has been transferred to IITA sustainability should be guaranteed (
The present study shows that with relatively modest means, but much patience and perseverance, it is possible to restore, even create de novo, a rainforest. The techniques are available since long time (
For the future, the major question remains whether in this densely populated area it will be possible to maintain this sanctuary which has become the best known and fully sampled forest of the entire region, while all other forests are all less well known and probably also less well protected. To assure its sustainability the forest will have to be used for scientific studies and bring benefits to the local population. The present study should thereby serve as a basis.
We thank P.O. Agbani (Botanical Garden Université d’Abomey Calavi UAC) and B. Sinsin (rector of UAC), H. Dassou (National Herbarium UAC), M. Tamò (IITA-Bénin), K. Ostertag (Tobè, Bantè) and A. Sessou (forester) and other people, who continue to participate in the protection of these forests, for specimens, encouragement and/or assistance, E. Onasanya (AfricaRice, Cotonou) and G. Goergen (IITA-Benin) for help in literature search and mapping, and G. Kandji and L. Hounguè (Drabo Gbo) for assistance in the field.
Table A. Comprehensive list of all plant species of Drabo Gbo, Benin.
Data type: species data
Explanation note: Status July 2016. Explanations in Materials and methods.