Diversity, above-ground biomass, and vegetation patterns in a tropical dry forest in Kimbi-Fungom National Park, Cameroon.

RESEARCH HIGHLIGHTS: This study is one of few detailed analyses of plant diversity and vegetation patterns in African dry forests. We established permanent plots to characterize plant diversity, above-ground biomass, and vegetation patterns in a tropical dry forest in Kimbi-Fungom National Park, Cameroon. Our results contribute to long-term monitoring, predictions, and management of dry forest ecosystems, which are often vulnerable to anthropogenic pressures.
BACKGROUND AND OBJECTIVES: Considerable consensus exists regarding the importance of dry forests in species diversity and carbon storage; however, the relationship between dry forest tree species composition, species richness, and carbon stock is not well established. Also, simple baseline data on plant diversity are scarce for many dry forest ecosystems. This study seeks to characterize floristic diversity, vegetation patterns, and tree diversity in permanent plots in a tropical dry forest in Northwestern Cameroon (Kimbi-Fungom National Park) for the first time.
MATERIALS AND METHODS: We studied associations between above-ground biomass and species composition, and how different vegetation types vary in terms of species composition, diversity, and carbon storage, in a dry forest in Kimbi-Fungom National Park, Cameroon. Vegetation was inventoried in 17 permanent 1-ha plots. Allometric equations were used to calculate above-ground biomass and carbon.
RESULTS: We found an average of 269.8 tree stems ha-1 and 43.1 species ha-1. Five vegetation types: semi-deciduous, gallery, mixed vegetation, secondary and the grassland/woody savanna forest were classified using TWINSPAN analysis. The five vegetation types had an average above-ground biomass of 149.2 t ha-1 and 74.6 tC ha-1 of carbon in the 17 ha analyzed. Canonical correspondence analysis (CCA) showed the importance of semi-deciduous forest over grassland/woody savanna forest.
CONCLUSIONS: This study demonstrated that the forest of the Kimbi-Fungom National Park is poor in plant diversity, biomass, and carbon, highlighting the need to implement efficient management practices. Fine-scale inventory data of species obtained in this study could be useful in developing predictive models for efficient management of tropical dry forests.

Introduction

Forest inventory and monitoring are key tools in understanding the structure, composition, diversity, above-ground biomass, and carbon storage of different vegetation types and habitats, and are also key in achieving targets for international agreements [1]. Dry forests rank among the most threatened ecosystems globally, creating a need for detailed assessments of biodiversity hotspots, carbon stocks, and the extent and preservation of these forests [2, 3]. Anthropogenic factors, such as agriculture, pastoral nomadism, and population expansion, are reducing dry forest extents, and natural factors like drought and fire also affect this biome; these ecosystems appear highly vulnerable even to small increases in temperature [4].

Cameroon, situated at the juncture of West and Central Africa, holds important extents of Lower Guinean forest [5, 6], holding rich biodiversity totaling around 9000 species, 1800 genera, and 230 families of vascular plants [7, 8, 9]. Cameroon holds three main biomes: dry savanna, moist savanna, and tropical rain forest. Dry savanna covers the northern parts of the country, and moist savanna and tropical rainforest form a mosaic across much of the rest of the country, except for montane areas. The dry savanna and moist semi-deciduous forest of Kimbi-Fungom National Park (KFNP), in the northwestern part of the country, are assumed to be relatively species-poor, albeit based on few studies [10, 11]. Indeed, fewer than 70 herbarium sheets, representing fewer than 60 plant species/100 km2, have been collected from the KFNP area [8, 9, 12]. Although the vegetation of the Bamenda Highlands has been studied extensively [13, 14, 15], much remains to be understood regarding forest structure, species composition, species diversity, distribution, and carbon stocks across different vegetation types [10, 11]. Furthermore, few or no studies on carbon storage have been undertaken in dry forests in this region.

Generally, the vegetation of the newly-established KFNP remains poorly understood; since this park represents an important conservation effort in the region, a detailed understanding of its vegetation and biodiversity is paramount. A preliminary assessment of forest cover in KFNP during 1979–2015 based on images from the sensor revealed potential significant forest cover reduction through deforestation (Figure 1), further prioritizing research attention to this area. Hence, in this study, we aimed to determine the forest structure, composition, and abundance, and estimate existing biomass and carbon storage. Results are discussed in terms of carbon storage, and are placed in the context of other vegetation types in central Africa.

Figure 1

A. 60 m Landsat MSS (Multispectral Scanner) of 1979, B. 30 m Landsat 8 of 2015 for Kimbi Fungom National Park, Cameroon.

Materials and Methods

Study site

The study site lies in the Bamenda Highlands, in the North West Region of Cameroon, at latitude 6.5–6.9°N and longitude 9.8–10.5°E (Figure 2), covering 953.8 km2. This site holds a mixture of humid semi-evergreen forest, woody savanna, grassland savanna, and gallery forest of the Sudano-Zambazien forest ecosystem [16] including habitats such as swampy Pandanus forest, Raphia forest, and inselberg. KFNP is surrounded by several other protected areas: Mt Oku, Mbembe Forest Reserve, Mt Tabenken, Nkom-Wum Forest Reserve, Mbi Crater, Kagwene Wildlife Sanctuary, Bali Ngemba Forest Reserve, and Bafut Ngemba Forest Reserve.

Figure 2

Map of vegetation types and sample locations across Kimbi-Fungom National Park, Cameroon.

The climate of KFNP has two seasons within the Equatorial Cameroon climate type [11], with a dry season in November through mid-March with <100 mm; December to February are the driest months. The rainy season occurs in April–October each year, with August and September being the wettest months. No detailed climatic data are available for this area; however, it is not expected to deviate much from the nearby Mbembe Forest, <100 km away, which has the following climatic conditions: rainfall 1824–1958 mm, and annual mean temperature 21–24 °C. It's unfortunate that the KFNP area does not have a climate station. The nearest small rain gauge station is at Ako which is > 50 km away, and a weather station in Bamenda which is further away from the field site. KFNP soils are ferruginous, brown to gray in color [17], and with an acidity of around pH 5.6. Plots were established in the central part of the park, at elevations of 429–898 m.

Field sampling

Representative plots occurring in clusters of pre-classified vegetation formations (dry semi-deciduous, grassland savanna, gallery forest, swamp and secondary forest), as described in Letouzey 1985 [16] were sampled. Plots were selected using a simple random approach in each cluster. Four and a half hectares were sampled in a dry semi-deciduous forest: 10.1 ha in grassland/woody savanna, 1 ha in secondary forest, 0.8 ha in gallery forest, and 0.4 ha in mixed vegetation (Table 1). However, 0.2 ha of fallow land with no trees were recorded in plot 11 (Table 1). During the study period, the savanna areas of the reserve were under intensive cattle grazing, and the semi-deciduous forest was subjected to subsistence crop farming.

Table 1

Mean above-ground biomass, carbon, basal area, and species richness, across five vegetation types in Kimbi-Fungom National Park, Cameroon.

Vegetation Types	Area (ha)	Biomass (t/ha)	Carbon (t/ha)	Basal Area (m2)	Number of Species	Abundance
Semi-deciduous forest	4.5	1453.2 (321.5)	726.6 (160.8)	27.7	126.0	1584.0
Grassland/woody savanna	10.1	728.8 (72.0)	364.4 (36)	1.6	75.0	2817.0
Secondary forest	1.0	161 (167.7)	80.5 (83.9)	12.9	54.0	280.0
Gallery forest	0.8	112.8 (141)	56.4 (70.5)	7.7	53.0	307.0
Mixed vegetation	0.4	81.5 (203.8)	40.7 (101.9)	0.8	36.0	135.0
Total	16.8	2537.3 (149.2)	1268.6 (75.5)	50.7	344.0	5123.0

First values are totals, Values in parenthesis = Corresponding mean values.

We used line transects of 500 × 20 m as plots, established across the various vegetation types (Figure 3). We established 17 plots in total (Table 2), on which all trees and lianas ≥10 cm trunk diameter at breast height (1.3 m, dbh) were sampled. Trees, shrubs, and lianas with trunk dbh <10 cm were measured with calipers, whereas trees and lianas ≥10 cm were measured with a diameter tape. Lianas were measured above the last rooting points, at 1.3 m above the ground [18, 19, 20]. Tree height was determined as the average of visual estimates by 3 field staff. All individuals were measured, and identified to morphospecies; voucher specimens were collected for each morphospecies. Dominant species were defined as species with highest abundance of stems; rare species were those with <5 stems for each vegetation type. Habitat type (swamp SW, flat dry forest FD, slope SL, plateau PL) was recorded for each plot. Finally, outside of plots sampled, observational data were accumulated as we traversed the area, to enhance the general species list for the area.

Figure 3

Field sampling design, showing two equal transect plots, with each plot covering an area of 1ha (500 m × 20 m). The red asterisks at 1, 6, 11, 16, and 21 represent locations of nested plots of 10 m × 10 m with more detailed sampling.

Table 2

Sampling plot locations in the Kimbi-Fungom National Park, Cameroon.

Plot	Vegetation type	Site	Location	Latitude (N)	Longitude (E)	Elevation (m)
1	PSF	KFNP	Kpep	6.79533	10.10048	481.0
2	PSF	KFNP	Kpep	6.79533	10.10048	481.0
3	PSF	KFNP	Kpep	6.79528	10.10029	474.0
4	G/WS_MV_PSF	KFNP	Kpep	6.79339	10.09769	429.0
5	PSF_G/WS	KFNP	Kpep	6.79359	10.09773	433.0
6	G/WS_GF_SF	KFNP	Kpep	6.79267	10.10803	439.0
7	G/WS_GF_SF	KFNP	Kpep	6.79267	10.10803	439.0
8	G/WS_MV_GF	KFNP	Kpep	6.79502	10.11571	396.0
9	G/WS	KFNP	Kpep	6.79484	10.11546	407.0
10	G/WS_PSF	KFNP	Kpep	6.79516	10.11585	410.0
11	SF_GF_G/WS	KFNP	Kpep	6.79534	10.11585	422.0
12	G/WS_GF	KFNP	Tunka-Esu	6.73506	10.11741	898.0
13	G/WS_GF	KFNP	Tunka-Esu	6.73506	10.11741	898.0
14	G/WS	KFNP	Tunka-Esu	6.73506	10.11741	898.0
15	G/WS_GF	KFNP	Tunka-Esu	6.73394	10.11772	846.0
16	G/WS_MV	KFNP	Tunka-Esu	6.73394	10.11772	846.0
17	G/WS_PSF	KFNP	Tunka-Esu	6.73394	10.11772	846.0

GF = Gallery Forest, G/WS = Grassland/Woody Savanna, MV = Mixed Vegetation, PSF = Primary Semi-deciduous Forest, SF = Secondary Forest.

Data analysis

TWINSPAN multivariate analysis was used to classify vegetation types using the PC-ORD package [21]. Species diversity estimates and correspondence analysis were achieved using PAST, version 2.17 [22]. Data for each vegetation type were separated into different life forms: trees ≥10 cm, shrubs ≤10 cm, and lianas ≥1 cm [23, 24, 25]. Forest structure was classified into three strata (life forms): <10 m, 10–30 m (10–29 m), and ≥30 m height.

Above-ground biomass (AGB) was estimated for all trees with dbh ≥10 cm, using the allometric equation of [26] (equation 1). Tree height was estimated following [27] (equation 2):where AGB = above-ground biomass (tons), ρ = wood specific density (g/cm3) at 0% humidity [28], D (dbh) = diameter at breast height (1.30 m), e indicates the exponential function, and H = height (m).

Carbon was estimated for trees ≥10 cm as

Forest structure and composition were described using parameters, including basal area, relative density, relative dominance, relative frequency, and the importance value index [29].

We calculated basal area (BA), the area occupied by plant (species) at breast height, as

The Shannon-Weiner index (SW) is a useful index of diversity in 1-ha plots [29] and is calculated via the following formula:where p is the proportion of individual of a species (number of individual of a species/total number of all species) and ln is the natural logarithm. The natural logarithm of the number of species or ln(S), is the maximum value of SW [29].

Results

Species composition and diversity

In total, 5551 stems of trees, shrubs, and lianas (multiple stems inclusive) were recorded in the 17 1-ha plots, with dbh ≥1 cm. We recorded 4987 stems of trees and lianas, with dbh ≥1 cm, belonging to 201 morphospecies, with an average density of 293 stems ha−1; 564 trees and lianas had multiple stems. We recorded 4607 trees with dbh ≥10 cm, representing 178 species, 110 genera, and 42 families; an additional 350 trees with dbh <10 cm represented 84 species, 72 genera, and 33 families. We also recorded 30 stems of lianas ≥1 cm (27 stems with dbh ≥10 cm) representing 15 species, 15 genera, and 11 families (Table 3). In all, 147 species (76.9%) were identified to the species level; 118 genera (83.6%) were identified. The mean number of trees ha−1 with dbh ≥10 cm was 270 ± 74 trees ha−1 (range 157–404 trees ha−1). Shrubs with dbh <10 cm had an average of 135 ha−1, with a range of 5–495 ha−1. Lianas with dbh ≥1 cm had a mean of 2.8 stems ha−1, with a range of 1–6 stems ha−1. In all, shrubs (dbh ≤10 cm) represent a mean SW index of 1.8, ranging from 0-3.4, lianas (dbh ≥1 cm) 0.26 ranging 0.6–1.8, and trees (dbh ≥10 cm) 3.14 ranging 2.6–3.5. These results reflect highest diversity in trees, followed by shrubs, in the study site (Table 3).

Table 3

Vegetation cover types and corresponding numbers of species, stems, mean Shannon-Weiner diversity index, and range of values of Shannon-Weiner index in Kimbi-Fungom National Park, Cameroon.

Vegetation cover	Number of species	Number of stems	Mean Shannon-Weiner diversity index
shrubs	84	350	1.8 (0–3.4)
lianas	10	30	0.26 (0.26–1.8)
trees	178	4607	3.12 (2.6–3.5)

Species richness and diversity varied among plots and life forms, with a mean of 43 ± 13 species ha−1, ranging 27–65 species ha−1. The Shannon-Weiner diversity index was invariably ≥2.5, with an average of 3.1, ranging 2.7–3.5 (Table 4). In all, 144 species were collected outside sample plots as observational effort (Table 5).

Table 4

Summary of density, number of species, above-ground biomass, carbon, and basal area in 17 ha plot across five vegetation types in Kimbi-Fungom National Park, Cameroon.

Plot	Vegetation type	Elevation (m)	Stem density	Tree density	Number of species	AGB (t/ha)	Carbon (t/ha)	BA (m2/ha)
1	PSF	481.0	407.0	404.0	65.0	346.8	173.4	30.2
2	PSF	481.0	389.0	389.0	63.0	360.3	180.2	30.6
3	PSF	474.0	381.0	375.0	58.0	361.9	181.0	32.4
4	G/WS_MV_PSF	429.0	353.0	335.0	58.0	199.7	99.9	18.5
5	PSF_G/WS	433.0	237.0	213.0	43.0	137.2	68.6	14.6
6	G/WS_GF_SF	439.0	313.0	292.0	57.0	149.6	74.8	14.8
7	G/WS_GF_SF	439.0	356.0	311.0	50.0	86.2	43.1	11.9
8	G/WS_MV_GF	396.0	251.0	190.0	29.0	48.3	24.2	6.8
9	G/WS	407.0	314.0	250.0	32.0	68.9	34.5	9.6
10	G/WS_PSF	410.0	241.0	183.0	32.0	60.8	30.4	7.5
11	SF_GF_G/WS	422.0	202.0	157.0	27.0	89.4	44.7	8.6
12	G/WS_GF	898.0	289.0	244.0	36.0	80.6	40.3	10.6
13	G/WS_GF	898.0	297.0	292.0	34.0	86.0	43.0	10.9
14	G/WS	898.0	298.0	249.0	30.0	93.9	47.0	11.7
15	G/WS_GF	846.0	280.0	250.0	33.0	88.0	44.0	11.1
16	G/WS_MV	846.0	221.0	194.0	34.0	78.8	39.4	10.1
17	G/WS_PSF	846.0	296.0	259.0	52.0	200.4	100.2	17.4
	Total		5125.0	4587.0	733.0	2537.2	1268.9	257.4
	Mean		301.5	269.8	43.1	149.2	74.6	15.1
	Standard deviation		60.4	74.1	13.3	104.8	52.4	8.2

GF = Gallery Forest, G/WS = Grassland/Woody Savanna, MV = Mixed Vegetation, PSF = Primary Semi-deciduous Forest, SF = Secondary Forest.

Table 5

Plant species recorded in observational efforts (i.e., outside of sampling plots) in Kimbi-Fungom National Park, Cameroon.

Family	Species
Acanthaceae	Acanthus montanus (Nees) T.Anderson
Acanthaceae	Asystasia decipiens Heine
Amaranthaceae	Amaranthus sp.
Anacardiaceae	Lannea kerstingii Engl. & K.Krauce
Annonaceae	Artabotrys aurantiacus Engl. & Diels.
Annonaceae	Uvaria sp.
Annonaceae	Xylopia sp.
Apocynaceae	Baissea axillaris (Benth.) Hua
Apocynaceae	Landolphia sp.
Asclepiadaceae	Marsdenia sp.
Asparagaceae	Asparagus flagellaris (Kunth) Baker
Asparagaceae	Chlorophytum macrophyllum (A.Rich.) Aschers.
Asteraceae	Chromolaena odorata (L.) R.M.King & H.Robinson (nat.)
Asteraceae	Vernonia kotschyana Sch. Bip.
Bignoniaceae	Crescentia cujute Billb. & Beurl. (exo.)
Chrysobalanaceae	Dactyladenia barteri (Hook.f.ex Oliv.) G.T.Prance & F.White
Chrysobalanaceae	Magnistipula cuneatifolia Hauman
Clusiaceae	Garcinia cf barteri Oliv.
Colchicaceae	Gloriosa simplex L.
Combretaceae	Agelaea pseudobliqua G.Schellenb.
Commeliniaceae	Palisota ambigua (P.Beauv.) C.B.Clarke
Connaraceae	Connarus griffonianus Baill.
Connaraceae	Jaundea pubescens (Baker) G.Schellenb.
Costaceae	Costus spectabilis (Fenzl) K.Schum.
Dichapetalaceae	Dichapetalum sp.
Dilleniaceae	Tetracera masuiana De Wild. & T.Durand
Dilleniaceae	Tetracera sp.
Dioscoreaceae	Dioscorea alata L.
Ebenaceae	Diospyros monbuttensis Gürke
Euphorbiaceae	Shirakiopsis elliptica (Hochst.) Esser
Fabaceae	Albizia adianthifolia (Shum.) W.F.Wright
Fabaceae	Anthonotha macrophylla P.Beauv.
Fabaceae	Crotalaria macrocalyx Benth.
Fabaceae	Dalbergia sp.
Fabaceae	Dalbergiella welwitschii Baker
Fabaceae	Desmodium hirtum Guill. & Perr.
Fabaceae	Desmodium velutinum (Wild.) DC.
Fabaceae	Dialium zenkeri Harms
Fabaceae	Oddoniodendron micranthum (Harms) Baker
Fabaceae	Pseudarthria hookeri Wright & Arn.
Fabaceae	Sesbania sp.
Fabaceae	Tamarindus indica Linn.
Fabaceae	Tephrosia barbigera Welw.ex Bak.
Gentianaceae	Anthocleista liebrechtsiana De Wild
Hypericaceae	Psorospermum glaucum
Hypericaceae	Psorospermum sp.
Hypericaceae	Psorospermum sp.3
Lamiaceae	Lippia africana Moldenke
Lamiaceae	Vitex myrmecophila Mildbr.
Lamiaceae	Vitex thyrsifolia Baker
Leeaceae	Leea guineensis G.Don
Loganiaceae	Strychnos spinosa Lam.
Loganiaceae	Strychnos tricalysioides Hutch. & M.B.Moss
Malvaceae	Cola millenii K. Schum.
Malvaceae	Microcos mollis Juss.
Malvaceae	Sida corymbosa R.E.Fr.
Malvaceae	Sterculia setigera Delile
Marantaceae	Megaphrynium macrostachyum (Benth.) Milne-Redh.
Melastomataceae	Dissotis brazzae Cogn.
Moraceae	Ficus craterostoma Mildbr. & Burret
Musaceae	Ensete livingstonianum (J.Kirk) Cheesman
Myristicaceae	Coelocaryon botryoides Verm.
Myrtaceae	Eugenia obanensis Baker.f.
Ochnaceae	Campylospermum calanthum (Gilg.) Farron
Ochnaceae	Campylospermum excavatum (Van Tiegh.) Farron
Ochnaceae	Campylospermum flavum (Schum. & Thonn.) Farron
Ochnaceae	Rhabdophyllum affine (Hook.f.) Van Tiegh.
Olacaceae	Strombosia grandifolia Hook.f.
Orchidaceae	Ancistrochilus rothschildianus O'Brien
Orchidaceae	Ancistrorhynchus serratus Summerh
Orchidaceae	Bulbophyllum colubrinum (Rchb.f.) Rchb.f.
Orchidaceae	Bulbophyllum vulcanicum Kraenzl.
Orchidaceae	Eulophia euglossa (Rchb.f.) Rolfe
Orchidaceae	Habenaria longirostris Summerhayes
Orchidaceae	Habenaria malacophylla Rchb.f.
Orchidaceae	Liparis caillei Finet
Orchidaceae	Liparis guineensis Lindl.
Orchidaceae	Nervilia sp.
Orchidaceae	Polystachya odorata Lindl.
Orchidaceae	Vanilla imperialis Kraenzl.
Passifloraceae	Adenia cissampeloides (Planch.ex Hook.) Harms
Passifloraceae	Adenia sp.1
Petiveriaceae	Hilleria latifolia H.Walter
Phyllanthaceae	Bridelia micrantha (Hochst.) Baill.
Phyllanthaceae	Macaranga assas Amougou
Phyllanthaceae	Phyllanthus muellerianus (Kuntze) Exell
Pittosporaceae	Pittosporum viridiflorum Sims subsp. Dalzielii (Hutch.) Cuf.
Proteaceae	Protea madiensis Oliv.
Rhizophoraceae	Cassipourea zenkeri (Engl.) Alston
Rosaceae	Prunus africana (Hook.f.) Kalkman
Rubiaceae	Euclinia longiflora Salisb.
Rubiaceae	Gardenia lutea Fresen.
Rubiaceae	Gardenia vogelii Hook.f.ex Planch
Rubiaceae	Ixora anemodesma K.Schum
Rubiaceae	Ixora bauchiensis Hutch. & Dalziel
Rubiaceae	Leptactina sp.
Rubiaceae	Polysphaeria arbuscula K.Schum.
Rubiaceae	Psychotria cf ebensis K.Schum.
Rubiaceae	Psychotria peduncularis (Salisb.) Steyerm.
Rubiaceae	Psychotria vogeliana Benth.
Rubiaceae	Psychotria sp.
Rubiaceae	Psydrax kraussioides (Hiern) Bridson
Rubiaceae	Rothmannia ebamutensis Sonké
Ruscaceae	Dracaena aubryana Brongn.ex E.Morren
Ruscaceae	Dracaena surculosa Lindl.
Rutaceae	Clausena anisata (Wild.) Hook.f.ex Benth.
Sapindaceae	Paullinia pinnata L.
Sapotaceae	Porteria pierrei (A.Chev.) Baehni
Smilacaceae	Smilax kraussiana Meisn.
Thymelaeaceae	Dicranolepis disticha Planch.
Violaceae	Rinorea dentata (P.Beauv.) O.Kuntze
Zingiberaceae	Aframomum daniellii (Hook.f.) K.Schum.
Zingiberaceae	Renealmia sp.

Basal area

The 17 ha plots gave a total basal area (dbh ≥10 cm) of 257.4 m2, with a mean per plot of 15.1 m2 ha−1 (range 6.8–32.4 m2 ha−1). The dominant family was Fabaceae (87.0 m2, 33.2%; Table 6) followed by Chrysobalanaceae (27.3 m2), Phyllanthaceae (21.6 m2), Anacardiaceae (19.0 m2), and Combretaceae (11.0 m2). Dominant genera were Brachystegia (31.4 m2), Maranthes (26.3 m2), Uapaca (17.7 m2), Daniellia (17.1 m2), Pseudospondias (11.3 m2), and Terminalia (10.3 m2) (Table 6). Dominant species were Brachystegia eurycoma, Maranthes glabra, Daniellia oliveri, Uapaca togoensis, Pseudospondias microcarpa, and Terminalia glaucescens (Table 7). The total basal area for trees <10 cm dbh was 1.7 m2 ha−1 whereas lianas gave 3.6 m2 ha−1. Semi-deciduous forest had the largest basal area of 27.7 m2 ha−1, followed by secondary forest (12.9 m2 ha−1), gallery forest (7.7 m2 ha−1), grassland/woody savanna (1.6 m2 ha−1), and mixed vegetation (0.8 m2 ha−1) (Table 1).

Table 6

Eleven plant families with the highest above-ground biomass, and carbon stock in 17 1-ha plots in Kimbi-Fungom National Park, Cameroon.

Family	Biomass (t/ha)	Carbon (t/ha)	BA (m2/ha)	Abundance	Relative abundance (%)
Fabaceae	914.9	457.5	83.3	887	17.3
Chrysobalanaceae	436.5	218.3	27.2	282	5.5
Phyllanthaceae	184.0	92.0	19.7	503	9.8
Anacardiaceae	159.8	79.9	18.6	331	6.5
Rubiaceae	138.8	69.4	7.7	783	15.3
Combretaceae	111.0	55.5	10.3	294	5.7
Ochnaceae	92.0	46.0	8.9	229	4.5
Arecaceae	56.0	28.0	5.5	49	1.0
Moraceae	49.3	24.7	7.3	198	3.9
Myristicaceae	46.0	23.0	5.7	40	0.8
Euphorbiaceae	45.7	22.8	9.0	159	3.1
Total	2234	1117.1	203.0	3755	73.3

Table 7

Ten species with highest above-ground biomass, and carbon stock in 17 1-ha plots in Kimbi-Fungom National Park, Cameroon.

Species	Biomass (t/ha)	Carbon (t/ha)	Basal Area (m2/ha)	Abundance	Relative abundance (%)
Brachystegia eurycoma Harms	439.3	219.6	31.4	77.0	1.5
Maranthes glabra (Oliv.) G.T. Prance	426.2	213.1	26.2	263.0	5.1
Daniellia oliveri (Rolfe) Hutch. & Dalziel	145.4	72.7	16.9	174.0	3.4
Erythrophleum suaveolens (Guill. & Perr.) Brenan	132.6	66.3	7.5	51.0	1.0
Pseudospondias microcarpa (A.Rich.) Engl.	113.0	56.5	11.2	99.0	1.9
Terminalia glaucescens Planch.ex Benth.	102.9	51.5	9.5	271.0	5.3
Uapaca togoensis Pax	100.5	50.3	10.8	256.0	5.0
Lophira lanceolata Tiegh. Ex Keay	89.5	44.8	8.6	213.0	4.2
Pycnanthus angolensis (Welw.) Exell	46.0	23.0	5.7	40.0	0.8
Ricinodendron heudelotii (Baill.) Pierre ex Baill.	23.4	11.7	6.1	45.0	0.9

Forest structure

Average tree height in the five vegetation types ranged from 2–45 m. The 17 ha plots held 4607 trees of 178 species, 110 genera, and 42 families in morphospecies for trees ≥10 cm dbh. Trees <10 m tall formed the bulk of abundance, representing 66.6% (3068 tree stems). Trees 10–29 m tall represented 29.0% (1336 tree stems), and trees of height ≥30 m represented 4.1% (190 stems) of the total stems. Based on the different vegetation types, for trees <10 m tall, gallery forest represented 6.6% (201 stems), woody and grassland savanna 66.2% (2029 stems), mixed vegetation 2.1% (63 stems), semi-deciduous forest 19.8% (606 stems), and secondary forest 5.5% (169 stems), of total numbers of stems.

Classification and vegetation patterns

Multivariate analyses using TWINSPAN revealed five vegetation types, a dry semi-deciduous forest (here termed primary forest), and four dry forest types (here identified as secondary forest, gallery forest, mixed vegetation, and grassland/woody savanna) in Cameroon (Figure 4), with 4607 stems in 178 morphospecies, 110 genera, and 42 families. Twenty-one and twelve individuals were not identified to genus and family, respectively. Main and secondary forest matrices were based on abundances of tree species ≥10 cm that were all identified to species, measured for dbh, and with data on elevation (Figure 4).

Figure 4

TWINSPAN dendrogram of 120 species of vascular plants with dbh ≥10 cm in 17 1-ha plots each in Kimbi-Fungom National Park, Cameroon.

In all, seven plots held elements of semi-deciduous forest, representing 4.5 ha of 17 ha sampled, with a total of 1559 stems in 130 species, 89 genera, and 39 families. Dominant species were Maranthes glabra, (227 stems), Sorindeia grandifolia (95 stems), Spondianthus preussii (93 stems), Pseudospondias microcarpa (85 stems), Chrysophyllum ubanguiense (75 stems), and Brachystegia eurycoma (70 stems). In this vegetation type, 37 species were rare, with one individual each, such as Beilschmiedia gabonensis, Bridelia atroviridis, Daniellia oliveri, Englerophytum stelechanthum, and Shirakiopsis elliptica.

Secondary forest (three plots), with 0.96 ha of the 17 ha sampled, had 259 stems pertaining to 55 species, 44 genera, and 26 families. One morphospecies was identified only to genus and one only to family. Dominant species were Hallea stipulosa (36 stems), Ricinodendron heudelotii (18 stems), Albizia zygia (17 stems), Trema orientalis (12 stems), and Anthocleista djalonensis and Sterculia tragacantha with 10 stems each. Eighteen species were rare in this vegetation type, with one individual each, such as Alstonia boonei, Daniellia oliveri, Erythrophleum suaveolens, Irvingia wombulu, and Quassia sylvestris.

Gallery forest, found in eight plots representing 0.8 ha of the 17 ha sampled, had a total of 276 stems belonging to 53 species, 44 genera, and 24 families. Dominant species were Uapaca togoensis (96 stems), Daniellia oliveri (20 stems), Vitex doniana (13 stems), and Hymenocardia acida (11 stems); 19 rare species included Afzelia africana, Albizia adianthifolia, Cassia arereh, Cola cordifolia, and Pterocarpus erinaceus.

Mixed vegetation (four plots), representing 0.4 ha, had 129 stems belonging to 37 species, 31 genera, and 21 families, with two morphospecies not identified to genus or family. Dominant species were Uapaca togoensis (20 stems), Maranthes glabra (15 stems), Vitex doniana (9 stems), and Nauclea latifolia (8 stems); 16 rare species included Annona senegalensis, Beilschmiedia anacardioides, Brachystegia eurycoma, Elaeis guineensis, and Vitex rivularis.

Grassland/woody savanna (14 plots), representing 10.1 ha of the 17 ha sampled, had a total of 2383 stems belonging to 77 species, 55 genera, and 29 families (three morphospecies were not identified to genus, 28 morphospecies were not identified to family). Dominant species in this vegetation type were Hymenocardia acida (237 stems), Terminalia glaucescens (231), Crossopteryx febrifuga, Nauclea latifolia (225 stems), Lophira lanceolata (186 stems), Daniellia oliveri (147 stems), Entada abyssinica (116 stems), Piliostigma thonningii (111 stems), Cussonia arborea (105 stems), and Uapaca togoensis (86 stems). Rare species totaled 21, including Albizia adianthifolia, Antidesma chevalieri, Erythrina senegalensis Maesopsis eminii, Magnistipula butayei, Milicia excelsa, Morelia senegalensis, Pterocarpus erinaceus, and Uapaca paludosa (Table 1). Five quadrats were devoid of trees, shrubs, and lianas, representing 0.2 ha. As such, a total of 16.8 ha was sampled for woody vegetation at an elevation of 396–481 m.

Above-ground biomass and carbon

Our 17 ha of sample plots yielded a total above-ground biomass of 2537.3 t, and carbon content of 1268.6 t (Table 4). Among the 11 families with highest AGB, Fabaceae had the highest AGB (914.9 t ha−1), corresponding to 457.5 t ha−1 of carbon (Table 6). Brachystegia eurycoma had the highest AGB of any species (439.3 t ha−1), equivalent to 219.6 t ha−1 of carbon (Table 7). Mean AGB by vegetation type was 203.8 t ha−1 in mixed vegetation forest, 72.0 t ha−1 in grassland/woody savanna, 141.0 t ha−1 in gallery forest, 167.7 t ha−1 in secondary forest, and 321.5 t ha−1 in semi-deciduous forest (Table 1).

An overall species list and abundance in the 17 1-ha permanent plots is represented in Table 8. The correspondence analysis showed that the first two axes accounted for 82% (axis 1 = 65% and axis 2 = 17%) of total variation in this study. Axes 1 and 2 explained over 71% of the variance. The correspondence analysis revealed two distinct associations among the variables; low number of species, low above-ground biomass, and grassland/woody savannah were associated, whereas high number of species, high above-ground biomass and semi-deciduous forest were associated (Figure 5).

Table 8

Species list and abundance (number of individual stems) in 17 ha of sampling plots, Kimbi-Fungom National Park, Cameroon.

Family	Species	GF	G/WS	MV	PSF	SF	Total
Anacardiaceae	Lannea microcarpa Engl. & K. Krauce	-	2	-	8	1	11
Anacardiaceae	Lannea schimperi (Hochst.ex. A. Rich.) Engl.	3	50	2	-	-	55
Anacardiaceae	Lannea sp.1	-	1	-	1	-	2
Anacardiaceae	Lannea sp.2	10	27	4	13	6	60
Anacardiaceae	Pseudospondias microcarpa (A.Rich.) Engl.	1	-	4	85	7	97
Anacardiaceae	Sorindeia grandifolia Engl.	-	-	-	95	-	95
Annonaceae	Annona senegalensis Pers.	2	56	1	-	-	59
Annonaceae	Cleistopholis patens (Benth.) Engl. & Diels.	-	-	-	3	-	3
Annonaceae	Cleistopholis staudtii Engl. & Diels.	-	-	-	2	-	2
Annonaceae	Cleistopholis sp.	-	-	-	2	1	3
Annonaceae	Monodora tenuifolia Benth.	-	-	-	1	1	2
Annonaceae	Monodora sp.2	-	-	-	2	-	2
Apocynaceae	Alstonia boonei De Wild	-	-	-	1	1	2
Apocynaceae	Funtumia elastica (Preuss) Stapf	-	-	-	20	1	21
Apocynaceae	Holarrhena floribunda (G.Don) Dur & Schinz	1	6	-	2	-	9
Apocynaceae	Rauvolfia caffra Sond.	-	-	-	6	-	6
Apocynaceae	Rauvolfia vomitoria Afzel.	-	-	-	1	-	1
Apocynaceae	Rauvolfia sp.	-	-	-	6	-	6
Apocynaceae	Voacanga africana Stapf	-	-	-	1	-	1
Araliaceae	Cussonia arborea Hochst.ex.A.Rich.	3	105	2	-	-	110
Araliaceae	Polycias fulva (Hiern) Harms	1	9	-	7	1	18
Arecaceae	Elaeis guineensis Jacq.	-	-	1	43	5	49
Bignoniaceae	Markhamia tomemtosa (Benth.) K.Schum.	-	-	-	2	-	2
Bignoniaceae	Newbouldia laevis (P.Beauv.) Seeman ex Bureau	-	-	-	35	-	35
Bignoniaceae	Spathodea campanulata P.Beauv.	-	6	-	-	7	13
Bignoniaceae	Stereospermum kunthianum Cham.	-	5	-	-	-	5
Bombacaceae	Bombax buenopozense P.Beauv.	1	12	-	11	9	33
Burseraceae	Canarium schweinfurthii Engl.	1	1	1	12	-	15
Burseraceae	Dacryodes sp.	-	-	-	1	-	1
Cecropiaceae	Musanga cecropioides R.Br.ex Tedlie	-	-	-	2	-	2
Cecropiaceae	Myrianthus arboreus P.Beauv.	-	-	-	1	-	1
Chrysobalanaceae	Magnistipula butayei De Wild.	-	1	-	-	-	1
Chrysobalanaceae	Magnistipula butayei subsp. balingembeaensis De Wild.	-	-	-	2	-	2
Chrysobalanaceae	Maranthes glabra (Oliv.) G.T.Prance	1	5	15	237	2	260
Chrysobalanaceae	Parinari curatellifolia Planch.ex Benth.	-	14	-	-	-	14
Chrysobalanaceae	Parinari sp.1	-	-	-	1	-	1
Clusiaceae	Garcinia cf mannii Oliv.	-	-	-	1	-	1
Clusiaceae	Garcinia epunctata Stapf	-	-	-	10	4	14
Clusiaceae	Mammea africana Sabine	-	-	-	3	-	3
Clusiaceae	Symphonia globulifera L.f.	-	-	-	1	-	1
Combretaceae	Combretum sp.	2	12	4	3	-	21
Combretaceae	Terminalia glaucescens Planch. ex Benth.	6	231	1	2	2	242
Ebenaceae	Diospyros sp.	-	-	-	1	-	1
Euphorbiaceae	Alchornea cordifolia (Schum. & Thonn.) Müll.Arg.	1	3	-	-	-	4
Euphorbiaceae	Macaranga spinosa Müll.Arg.	-	-	-	-	2	2
Euphorbiaceae	Neoboutonia velutina Prain	-	6	-	-	-	6
Euphorbiaceae	Ricinodendron heudelotii (Baill.) Pierre ex Baill.	4	4	-	17	18	43
Euphorbiaceae	Shirakiopsis elliptica (Hochst.) Esser	-	-	-	1	-	1
Fabaceae	Afzelia africana Sm.	1	1	-	5	-	7
Fabaceae	Afzelia bipindensis Harms	2	-	-	4	-	6
Fabaceae	Albizia adianthifolia (Schum.) W.F.Wright	1	1	-	5	6	13
Fabaceae	Albizia zygia (DC.) J.F.Macbr.	-	2	-	-	-	2
Fabaceae	Albizia sp.	5	5	-	11	17	38
Fabaceae	Angylocalyx pynaertii De Wild.	-	-	-	2	-	2
Fabaceae	Anthonotha macrophylla P.Beauv.	-	-	-	13	4	17
Fabaceae	Baphia buettneri Harms subsp. hylophila (Harms) Soladoye	-	-	-	12	5	17
Fabaceae	Baphia sp.	-	-	-	2	-	2
Fabaceae	Brachystegia eurycoma Harms	-	-	1	70	6	77
Fabaceae	Cassia arereh Delile	1	4	-	-	-	5
Fabaceae	Daniellia oliveri (Rolfe) Hutch. & Dalziel	20	147	1	1	1	170
Fabaceae	Dialium cf pachyphyllum Harms	-	-	3	10	-	13
Fabaceae	Dialium sp.	-	-	-	2	-	2
Fabaceae	Entada abyssinica Steud. ex A.Rich.	3	116	-	1	-	120
Fabaceae	Erythrina senegalensis A.DC.	-	1	-	-	-	1
Fabaceae	Erythrophleum ivorense A.Chev.	-	-	-	12	-	12
Fabaceae	Erythrophleum suaveolens (Guill. & Perr.) Brenan	3	14	4	28	1	50
Fabaceae	Parkia africana R.Br.	1	13	-	1	8	23
Fabaceae	Parkia filicoidea Welw. ex Oliv.	-	-	-	3	-	3
Fabaceae	Penthaclethra macrophylla Benth.	-	-	-	3	-	3
Fabaceae	Pericopsis laxiflora (Benth.) Van Meeuwen	3	39	-	-	-	42
Fabaceae	Piliostigma thonningii (Schum.) Milne-Redh.	4	111	4	-	-	119
Fabaceae	Pterocarpus erinaceus Poir	1	1	-	-	-	2
Fabaceae	Pterocarpus osun Craib	-	-	-	7	-	7
Fabaceae	Pterocarpus soyauxii Taub.	-	-	1	14	-	15
Gentianaceae	Anthocleista djalonensis A.Chev.	-	1	-	4	10	15
Hymenocardiaceae	Hymenocardia acida Tul.	11	237	1	-	-	249
Hyperaceae	Harungana madagascariensis Poir.	7	29	-	-	7	43
Hypericaceae	Psorospermum febrifugum Spach.	2	29	-	-	-	31
Hypericaceae	Psorospermum sp.4	-	-	-	1	-	1
Icacinaceae	Rhaphiostylis sp.	-	-	-	1	-	1
Irvingiaceae	Irvingia grandifolia (Engl.) Engl.	-	-	-	1	-	1
Irvingiaceae	Irvingia wombulu Vermoesen	-	-	-	6	1	7
Irvingiaceae	Klainedoxa gabonensis Pierre	-	-	-	1	1	2
Irvingiaceae	Klainedoxa sp.	-	-	-	1	-	1
Lamiaceae	Vitex cf simplicifolia Oliv.	2	-	-	-	-	2
Lamiaceae	Vitex doniana Sweet	13	55	9	6	1	84
Lamiaceae	Vitex grandifolia Gürke	-	-	-	3	-	3
Lamiaceae	Vitex rivularis Gürke	-	-	1	1	-	2
Lauraceae	Beilschmiedia anacardioides (Engl. & Krause) Robyns & Wilczeck	-	-	1	2	-	3
Lauraceae	Beilschmiedia gaboonensis (meissn.) Benth. & Hook.f.	-	-	-	1	-	1
Lecythidaceae	Napoleonaea imperialis P.Beauv.	-	-	1	8	5	14
Loganiaceae	Strychnos sp.2	-	-	-	1	-	1
Loganiaceae	Strychnos sp.3	-	2	-	-	-	2
Malvaceae	Cola caricaefolia K.Schum	1	-	5	68	4	78
Malvaceae	Cola cordifolia (Cav.) R.Br.	1	-	-	4	-	5
Malvaceae	Cola sp.	-	-	-	1	1	2
Malvaceae	Cola sp.2	1	-	-	-	-	1
Malvaceae	Microcos flavescens Juss	-	4	-	-	-	4
Malvaceae	Sterculia tragacantha Lindl.	4	3	-	13	10	30
Meliaceae	Entandrophragma angolense (Welw.) C.DC.	-	-	2	27	-	29
Meliaceae	Entandrophragma candollei Harms	-	-	-	30	-	30
Meliaceae	Trichilia rubescens Oliv.	-	-	-	-	1	1
Meliaceae	Trichilia sp.	-	2	-	-	-	2
Moraceae	Antiaris toxicaria Lesch.	-	-	-	3	4	7
Moraceae	Ficus abutilifolia (Miq.) Miq.	-	-	-	3	-	3
Moraceae	Ficus adolfi-friderici Mildbr.	-	-	-	-	1	1
Moraceae	Ficus bubu Warb.	-	-	-	1	1	2
Moraceae	Ficus cf sur Forssk.	-	3	-	1	-	4
Moraceae	Ficus exasperata Vahl	-	4	-	3	1	8
Moraceae	Ficus glumosa Delile	3	18	-	1	8	30
Moraceae	Ficus mucuso Welw.ex Ficalho	-	-	-	3	-	3
Moraceae	Ficus natalensis Hochst.	-	-	1	-	-	1
Moraceae	Ficus sur Forssk.	-	-	-	3	-	3
Moraceae	Ficus vallis-choudae Delile	-	9	7	-	6	22
Moraceae	Ficus vogeliana (Miq.) Miq.	-	1	-	-	-	1
Moraceae	Ficus sp.2	-	1	-	-	-	1
Moraceae	Ficus sp.3	-	29	1	-	-	30
Moraceae	Ficus sp.5	1	4	-	-	-	5
Moraceae	Ficus sp.8	-	15	-	-	-	15
Moraceae	Ficus sp.10	2	6	-	-	3	11
Moraceae	Milicia excelsa (Welw.) C.C.berg	-	1	-	5	-	6
Moraceae	Trilepisium madagascariense DC.	-	-	-	6	-	6
Myristicaceae	Pycnanthus angolensis (Welw.) Exell	6	1	1	30	2	40
Myrtaceae	Syzygium guineense (Wild.) DC	8	60	-	1	-	69
Ochnaceae	Lophira lanceolata Tiegh. Ex Keay	8	186	4	-	-	198
Ochnaceae	Ochna afzelii R.Br. ex Oliv.	-	11	-	1	-	12
Ochnaceae	Ochna sp.	-	-	-	1	-	1
Olacaceae	Olax subscorpioidea Oliv.	-	-	-	7	2	9
Pandanaceae	Pandanus candelabrum P.Beauv.	-	-	-	-	6	6
Passifloraceae	Adenia sp.	-	-	-	1	-	1
Passifloraceae	Barteria fistulosa Mast.	-	-	-	2	-	2
Phyllanthaceae	Antidesma chevalieri	-	1	-	1	-	2
Phyllanthaceae	Bridelia atroviridis Müll.Arg.	-	-	-	1	-	1
Phyllanthaceae	Bridelia ferruginea Benth.	-	4	-	-	-	4
Phyllanthaceae	Bridelia grandis Pierre ex Hutch.	-	1	-	3	-	4
Phyllanthaceae	Bridelia scleroneura Müll.Arg.	1	66	1	-	-	68
Phyllanthaceae	Bridelia sp.	1	3	-	-	-	4
Phyllanthaceae	Macaranga monandra Müll.Arg.	-	-	-	-	4	4
Phyllanthaceae	Margaritaria discoidea (Baill.) Webster	3	20	3	20	6	52
Phyllanthaceae	Spondianthus preussii Engl.	-	-	7	93	2	102
Phyllanthaceae	Uapaca guineensis var. guineensis Müll.Arg.	-	-	-	21	-	21
Phyllanthaceae	Uapaca paludosa Aubrév. & Léandri	-	1	-	53	2	56
Phyllanthaceae	Uapaca togoensis Pax	96	86	20	11	-	213
Rhamnaceae	Maesopsis eminii Engl.	3	1	-	34	-	38
Rhizophoraceae	Cassipourea zenkeri (Engl.) Alston.	-	-	-	4	-	4
Rubiaceae	Aidia genipiflora (DC.) Dandy	-	-	-	2	-	2
Rubiaceae	Aidia sp.	-	-	-	1	-	1
Rubiaceae	Craterispermum laurinum (Poir) Benth.	-	-	-	37	-	37
Rubiaceae	Crossopteryx febrifuga (Afzel. ex G.Don) Benth.	8	225	1	-	-	234
Rubiaceae	Cuviera sp.	-	1	-	-	-	1
Rubiaceae	Hallea stipulosa (DC) Leroy	-	-	-	2	36	38
Rubiaceae	Ixora euosmia K. Schum.	-	-	-	31	-	31
Rubiaceae	Ixora sp.2	-	-	-	-	2	2
Rubiaceae	Macrosphyra longistyla (DC.) Hiern	2	-	-	18	-	20
Rubiaceae	Morelia senegalensis A. Rich.ex DC.	2	1	-	8	2	13
Rubiaceae	Nauclea latifolia SM.	3	225	8	-	-	236
Rubiaceae	Pavetta baconiella Bremek.	-	-	-	3	-	3
Rubiaceae	Pavetta calothyrsa Bremek.	-	-	-	1	-	1
Rubiaceae	Rothmannia sp.1	-	-	-	2	-	2
Salicaceae	Homalium africanum (Hook.f.) Benth.	-	-	-	2	-	2
Sapindaceae	Allophyllus bullatus Radlk.	2	17	-	3	-	22
Sapotaceae	Chrysophyllum ubanguiense (De Wild.) Govaerts	2	-	3	75	-	80
Sapotaceae	Englerophytum stelechanthum Krause	-	-	-	1	-	1
Sapotaceae	Pouteria alnifolia (Baker) Roberty	-	-	-	1	-	1
Sapotaceae	Synsepalum stipulatum (Radlk.) Engl.	-	-	-	4	-	4
Simaroubaceae	Quassia sanguinea Cheek & Jongkind	-	-	-	4	-	4
Simaroubaceae	Quassia sylvestris Cheek & Jongkind	-	1	-	-	1	2
Ulmaceae	Celtis philippensis Blanco	-	-	-	7	-	7
Ulmaceae	Trema orientalis (L.) Blume	1	1	-	7	12	21
	Grand Total	276	2384	129	1559	259	4607

GF = Gallery forest, G/WS = Grassland/Woody savanna, MV = Mixed vegetation, PSF = Primary Semi-deciduous Forest, SF = Secondary Forest.

Figure 5

Correspondence analysis showing association among variables, such as number of species, vegetation and biomass.

Discussion

Tree diversity, density, and trunk diameter are important indicators in assessing forest above ground biomass and other ecological processes in tropical forests; these indicators vary across regions, vegetation types, and habitats. Average tree density in the dry forest of KFNP was generally lower compared to tropical dry forests in other regions: for example, mean tree densities of 994 stems ha−1 (dbh >10 cm) and 3486 stems ha−1 (dbh >1 cm) were documented in the tropical dry forest of Bannerghatta National Park of the Eastern Ghats in southern India and Hawaiian lowland dry forest, respectively [30, 31]. A study in nearby Mbembe Forest Reserve, in different vegetation types, gave an average of 741 stems ha−1 in woody savanna, 236 stems ha−1 in grassland savanna, and 4963 stems ha−1 in semi-deciduous forest at dbh ≥1 cm [10]. Trees with dbh ≥10 cm in Mbembe Forest had an average of 311 stems ha−1 in woody savanna, 124 stems ha−1 in grassland savanna, and 408 stems ha−1 in semi-deciduous forest [10]. The low tree density in KFNP and indeed in the greater Bamenda Highlands could be attributed to unsustainable practices such as gathering of fuel wood, timber exploitation, pastoral nomadism, and subsistence agriculture. Nevertheless, globally, tropical dry forests are highly threatened: recent reports are that tropical dry forests in Latin America and the Caribbean have been reduced to <10% of their original extent [32]. Our results highlight the poor current state of the dry forest of KFNP and the need for appropriate interventions.

Mean tree species richness (for trees with dbh ≥10 cm) of 43.1 ± 13.3 species ha−1 (27–65 species ha−1) in KFNP was comparable to that in the dry forest of Africa (Cameroon and Congo; 23, 33) and the Western Ghats, India, which ranged from 30-57 species ha−1 [[34], [35]]. Studies of 19 mature tropical forest sites in the Neotropics, Southeast Asia, Australia, and Africa revealed a minimum value for species richness for trees with dbh ≥10 cm of 56 species [33]. However, the mean tree species richness of 43.1 species ha−1 in KFNP (Table 4) is low in comparison to the rainforests of the Rumpi Hills (lowland forest 117.5 species ha−1, submontane forest 75 species ha−1) and Korup National Park lowland rain forest (88.5 species ha−1) [[23], [24], [25],[36], [37]]. Thus, KFNP, with a mean of 43.1 species ha−1 and Mbembe Forest (29.8 species ha−1) can be considered as relatively species-poor.

In this study, the most abundant families were Fabaceae, Rubiaceae, and Phyllanthaceae (Table 6), and the most abundant species were Terminalia glaucescens, Maranthes glabra, and Uapaca togoensis (Table 7). Ten species in our study yielded 1618.8 t of AGB amounting to 63.8% of the total (2537.3 t) with an overall abundance of 1489 tree stems (Table 7). The number of species and basal area were higher in the dry semi-deciduous forest than in the other vegetation types (Table 1), which is expected, since semi-deciduous forest is closer to lowland or mid-elevation rainforest with large trees than the open grassland and woody savanna that are prone to fire annually. It is evident from the maps (Figure 1) presented in the introduction that the forest has been degraded substantially over a 36-year period, from 1979-2015.

This study is one of few in Cameroon and the broader Congo Basin region that have calculated diversity, above-ground biomass, and carbon in a dry forest [10, 11, 38, 39]. In the 17 ha sampled, we calculated a mean AGB of 149.2 t ha−1 and carbon of 74.6 tC ha−1. These values are far lower compared to values of AGB (≥429 t ha−1) and carbon stock (≥249 tC ha−1) documented for other Central African forests [37]. Although the present study revealed that KFNP is poor in mean AGB and carbon, exceptions were observed for some specific plots; for example, plots 1–3 had high mean AGB of 356.3 t ha−1 and mean carbon of 178.2 tC ha−1, and were only slightly lower than values from studies elsewhere in the region [40, 41] (Table 4). In Congo Brazzaville (Iboukikro and Ngambali Forest), a study of 6 1-ha plots in a gallery forest revealed a higher mean of 170.7 tC ha−1 [39] than the gallery forest in KFNP (70.5 tC ha−1).

The semi-deciduous forest showed a strong association of high AGB with number of species, and mixed vegetation had the lowest AGB in KFNP (Table 1, Figure 5). While the low carbon content in the grassland/woody savanna, gallery, and mixed forest may be attributed to the scanty vegetation and/or anthropogenic activities, other factors such as rainfall, duration of wet season, and topography can also influence net primary productivity of tropical dry forest [2]. Our results in some ways reaffirm the assertion that higher species richness could be associated with higher carbon storage in some forests [42]. The study further highlights the need for restorative interventions, such as reforestation, especially in the grassland/woody savanna vegetation.

Conclusions

The forest of the Kimbi-Fungom National Park is generally poor in plant diversity, biomass and carbon, especially in the secondary, mixed vegetation, gallery and grassland/woody savanna vegetation types. This work underlines an urgent need to implement efficient management practices to restore the forest.

Data of this study is part of a general database of species from 70 1-ha permanent plots established by the Tropical Plant Exploration Group on the continental Cameroon Mountains and hosted by the Global Biodiversity Information Facility [43].

Declarations

Author contribution statement

Moses Nsanyi Sainge: Conceived and designed the experiments; Performed the experiments; Analyzed and interpreted the data; Wrote the paper.

Felix Nchu: Conceived and designed the experiments; Analyzed and interpreted the data; Wrote the paper.

Andrew Peterson Townsend: Conceived and designed the experiments; Wrote the paper.

Funding statement

This work was supported by the Rufford Small Grant Foundation through a first booster grant (number 16712-B). Further support was received from the Tropical Plant Exploration Group (TroPEG), Cameroon.

Competing interest statement

The authors declare no conflict of interest.

Additional information

Data associated with this study has been deposited at The Global Biodiversity Information Facility (GBIF).