A brief botanical survey into Kumbira forest, an isolated patch of Guineo-Congolian biome.

Kumbira forest is a discrete patch of moist forest of Guineo-Congolian biome in Western Angola central scarp and runs through Cuanza Norte and Cuanza Sul province. The project aimed to document the floristic diversity of the Angolan escarpment, a combination of general walk-over survey, plant specimen collection and sight observation was used to aid the characterization of the vegetation. Over 100 plant specimens in flower or fruit were collected within four identified vegetation types. The list of species includes two new records of Guineo-Congolian species in Angola, one new record for the country and one potential new species.

Introduction

Angola lies almost wholly within the southern zone of tropical grassland, bounded by tropical rain forest of the Congo in the north and by the Kalahari Desert in the south (Shaw 1947). In general the country comprises four main physiographic components: a coastal plain from the Atlantic seaboard of approximately 200 m above sea level, and from 12 to 200 km wide; a narrow steep escarpment, from 200 to 1000 m altitude; PageBreakan interior plateau, occupying nearly 80% of the country lying between 1000 and 1600 m, and a mountain belt rising above the escarpment and plateau of about 2620 m in central plateau (Huntley and Matos 1994).

Between the Karoo-Namib phytochorion of the coastal belt and the dominated Zambesian phytochorion of the interior plateau, a discontinuous series of moister vegetation type extends southwards from the Guinea forest and Congo savanna systems following the escarpment (Huntley 1974, White 1983). The Angolan escarpment is dominated by semi-deciduous forest and a mosaic of forest-savanna and gallery forest of Guineo-Congolian affinity, which is restricted to the interior of Cabinda province and large but discontinuous patches of forest in Zaire, Uíge, Cuanza Norte and Cuanza Sul provinces (Barbosa 1970, Huntley 1974).

These vegetation formations, as referred above, cover large areas of Cabinda with a tree strata of about 30 to 40 m height, while in the south are restricted to extensive “Coffee forests” in Dembos, Cazengo and Gabela regions (Huntley 1974). In this latter Kumbira forest, located in Conda, Cuanza Sul province is no doubt the most important and, probably the most southerly and most isolated patch of this biome, with various elements of Congo basin and West African affinities, dominated by genera , , , and (Barbosa 1970).

To these formations can be added the afro-montane forests, also of great biogeographic interest (Hall 1960a), restricted to small and isolated patches of forest in Benguela, Huambo and Huíla provinces. The total area of these forest patches was estimated to be approximately 200 ha, the best known of which is Mount Moco in Huambo province which provides habitat for its flora and avifauna (Huntley 1974, Olmos 2008 unpub., Maiato 2009, Mills 2010). The Angolan escarpment with approximately 1000 km of extent is unique, beautiful and constitutes the section of the Great Escarpment of Southern Africa poorly known in terms of its biodiversity, but high level of endemism (Huntley and Matos 1994, Figueiredo 2008, Clark 2011).

Despite the recent published checklist of Angolan vascular plants (Figueiredo and Smith 2008), data on the Angolan flora is mostly limited to the literature of pre-independence era, and current knowledge on Angolan plants is poor and restricted to isolated and focused studies carried out by individuals or institutions. Increasing interest and efforts are being made in order to document and obtain baseline data of areas with high socio-ecological importance (for example The Future Okavango Project – http://www.future-okavango.org and the Okavango Wilderness Project – http://www.wildbirdtrust.com/portfolio/okavango-widerness-project) which focus on the Cubango and Cuito river catchments respectively). However large parts of the country, such as the Angolan escarpment, remain to be studied biologically.

In terms of biodiversity, only the avifauna has been investigated in any detail (Hall 1960a, Cagan and Riley 2005, Mills 2010, Cáceres et al. 2015). Recommendations have being made to undertake botanical surveys in the Kumbira area (Barbosa 1970, Huntley 1974). The ecological importance of Kumbira forest in maintaining the highest number of Angolan endemic avifauna highlighted the area as important for conservation of biodiversity. But at the same time concerned due to the increasing human pressure PageBreak(Huntley 2011 unpub.). To fill in the gap in terms of botanical diversity, we undertook a botanical survey into Kumbira forest. Here we document our current knowledge of the plant diversity and phytogeographical affinities of Kumbira Forest, the findings are based primarily on a rapid botanical assessment conducted between 10th and 18th June 2014.

Methods

Study area

The central escarpment of western Angola on which Kumbira forest is part of, runs through Cuanza Norte and Cuanza Sul provinces. Barbosa (1970) recognized three types of moist high forest along this escarpment occurring in discrete geographic and climatic zones. North to south, these are:

i. forests of subtype Cazengo to the north of the Cuanza River;

ii. forests of subtype Amboim, between the Cuanza and Keve (Queve) Rivers, of which the most significant is the area of forest around Gabela;

iii. forests of subtype Uku (Vila Nova do Seles) to the south of the Keve River;

Kumbira forest () is a discrete patch of moist forest vegetation in this third zone, SW of Conda (Figure 1), where cloud gathers under the knife-edge ridge of the Njelo mountain which reaches around 1500 m in elevation and prevents the cloud from moving further inland. The forest forms part of about 200 000 ha of semi-deciduous moist forest (Cagan and Riley 2005) and occurs on middle altitude slopes at around 700–900 m. Below this altitude dry open vegetation predominates, and at higher elevation the forest gives way to woodland and ultimately open rocky mountain slopes into rocky gorges in Njelo mountain.

Figure 1.

Map of Angola and its provinces, Cuanza Sul province highlighted and Kumbira in Conda municipality (black dot). Kumbira forest (top), the forest with Njelo mountain in the background (bottom).

Kumbira forest is considered to be part of Gabela Important Bird Area (Dean 2001), and holds unique and threatened bird community (Cagan and Riley 2005). Although its ornithological importance the area is not protected by law, the proposed implementation of Gabela Natural Reserve, recently reinforced (Huntley 1974; Huntley 2011 unpub.) is unfortunately far from being achieved.

Sampling strategy

The botanical team consisted of staff from the Royal Botanic Gardens Kew, UK and from the Herbarium of Lubango, Angola. The team used a combination of general walk-over survey (Filgueiras et al. 1994), plant specimen collection and sight observations to aid the characterization of the vegetation and the compiling of an inventory of the plant species present. Over 100 herbarium specimens were collected, mostly of flowering and fruiting plants, but some sterile collections (lacking flowers or fruits) PageBreakwere made of the more common or important species which were not flowering or fruiting at the time of our visit.

Due to the limited time available, no plot-based surveys to quantify the composition of the different vegetation types were conducted. Plant specimens were collected in duplicate or triplicate, with one set deposited in Lubango for incorporation into the main collection, the remaining set(s) being taken back to the UK where they were identified by comparison with material housed in the Kew herbarium. A range of botanical specialists were consulted to help in the identification of difficult plant groups.

Due to the paucity of useful literature on Angolan plants, and to the limited previous botanical work in the region, it was not possible to name all collections made, particularly sterile material, but we were able to name the large majority. Those named only to genus are nevertheless included within the checklist in Appendix 1. We have not included the additional species listed by Gossweiler and Mendonça (1939) and Barbosa (1970) from this forest subtype in the Appendix 1, as it is not possible to say which forest patch they are from.

The recent Angolan plant checklist by Figueiredo and Smith (2008) was used as the baseline for assessing species records and distributions in the country. The African Plants Database (http://www.ville-ge.ch/musinfo/bd/cjb/africa/recherche.php) and the World Checklist series (http://apps.kew.org/wcsp/home.do) for a number of plant families were used as the standards for up-to-date taxonomy of African plant species.

Results

From the vegetation survey carried out in Kumbira forest, four main vegetation types were identified. Here we provide a very brief overview of the forest types and their dominant species as recorded by the rapid botanical survey. The habitat types outlined here are also assigned to each of the species listed in (Appendix 1).

• Moist high forest (F)

Surveyed at former coffee plantation at foot of Serra Njelo, c.7 km SW of Conda [centred on ]). The canopy trees in this part of the forest were retained as shade for the coffee grown underneath (, ), and there has been considerable regrowth of forest understorey since the plantations were abandoned. The canopy is c. 25-30 m high, and the commonest tree is the seasonally deciduous , , , and several species of are common elements. We also encountered , , , , and in some areas. An arborescent and a species of were also noted (sight records only).The understorey was rich in , and the herbaceous flora included many ferns and occasional epiphytes, is recorded from Angola for the first time.

Hook.f. ex Benth, Exell & Mendonça ex R. Germ., (Hiern) Exell & Mendonça, Welw. ex Oliv., , Bremek, Sims, Gürke

• Submontane forest/woodland (W)

(Upper margins of Moist High Forest). The moist high forest gives way to deciduous woodland at higher elevations (above c. 900 m). Characteristic trees and shrubs include , , , , and . We also encountered , an afromontane element, in the gullies at high altitude.

•

(Surveyed at: mostly at Monte Belo estate, former coffee plantation at foot of Serra Njelo, c. 11 km SW of Conda [centred on ]). The exotic, evergreen trees ( from northern South America) planted initially as shade for the coffee are now overgrown and let little light through the canopy, seriously reducing the development of a shrub or herb layer except in gaps. was recently referred as one of the most impressive and worrying invasive species of western Angola, forming dense stands in localized sites as observed in Kumbira forest (Rajmánek et al. 2016). Nevertheless, we did record a variety of ferns and other herbaceous plants in this area, in addition to the very large fig , the first record of this Guineo-Congolian species from Angola. We observed some regeneration of from PageBreakPageBreakseed, demonstrating its potential as an invasive species. A second exotic mimosoid legume tree was encountered in this area – – also native to the New World.

• Ruderal and secondary habitats (Sec)

There is extensive encroachment of agriculture in the vicinity of villages, roads and tracks, and extraction of timber trees in some areas of forest. We did not survey this beyond making occasional observations. The commonest subsistence crops grown in the region are manioc (cassava) and plantain. The oil palm is widely planted. We also encountered dense stands of the pigeon pea in one area. Disturbed areas of forest, recently cleared, had large patches of the invasive shrub .

• Plant diversity

Our records are a brief snapshot, based on a visit of just six collecting days, at just one time of the year (June). They are by no means comprehensive. Nevertheless, we recorded 92 species from the forest.

• New plant records for Angola

We report two new records of Guineo-Congolian forest species for Angola – the tree and the herb . In addition, is newly recorded for the country, and may represent an undescribed subspecies. We also report a potential new species in sp. nov. (Appendix 2).

Discussion

Phytogeographical context

Coastal regions of Angola are strongly influenced by the Benguela cold-water current which reduces surface evaporation and rainfall. Although the current moves off-shore north of Namibe, corresponding with the northern limit of the Namib Desert, coastal vegetation north of the desert remains dry, and is dominated by dry scrub woodland and succulents such as aloes, euphorbias and baobabs.

Kumbira Forest is a very localized patch of forest between this dry coastal vegetation and the moist savannas of the plateau. Barbosa (1970) regarded the forest as typically Zambezian, the canopy dominated by species that lose their leaves in the dry season. Barbosa also quoted from Gossweiler and Mendonça (1939) who commented on the high percentage of species. However, we found that most of the species within the forest are Guineo-Congolian rather that Zambezian in PageBreakfloristic affinity sensu White (1983) - the species recorded are generally widespread within the Guineo-Congolian phytogeographical region but often rare or previously unrecorded in Angola.

And it must be noted that which we encountered in the forest, is distributed widely across tropical Africa, and not just in the Zambezian region. Kumbira Forest must be one of the most southerly areas in western Angola with significant Guineo-Congolian vegetation. The upper limits of the forest contain occasional afromontane elements, and the forest merges into moist woodland characterized by widespread species.

Conclusions

We surveyed key sites in a small portion of Kumbira Forest in Cuanza Sul Province, reporting on diversity and floristic affinities of the flora. The vegetation types were identified: moist high forest, submontane forest & woodland, and -dominated former coffee plantation. In addition, ruderal or disturbed areas also occur.

Species composition is overwhelmingly Guineo-Congolian, and this forest represents one of the most southerly areas of such vegetation along the Angolan escarpment. Most species have a wide geographic distribution, but some such as are more restricted, and are reported from just Cuanza Sul and Cuanza Norte. is restricted to riverine lowland habitats from Cuanza Sul to Cameroon.

Much of the area surveyed had good regeneration of the understorey since coffee cultivation ceased, but we observed large trees being taken out of the forest, and evidence of village agriculture encroaching in a number of places. Areas formerly planted with New World legume species, particularly , were in less favourable condition as the overgrown shades out the understorey. There is some evidence of this species reproducing and spreading naturally, and we observed other potentially invasive species such as . In addition, some coffee estates are being reestablished, which will reduce the extent of undisturbed or recovering forest further. Three species are newly recorded for Angola, , and . We also report a potential new species of .

List of the vascular plants collected and observed in Kumbira Forest, Cuanza Sul, Angola. Habitat types in Kumbira forest relate to the phytochoria recognised by White (1983) as follows: Forest = I. Guineo-Congolian; Woodland = VIII. Afromontane. Most species found in secondary forest and -dominated forest are also Guineo-Congolian in distribution and affinity.

Family	Species	Habitat type	Collectors	Voucher number(s)
PTERIDOPHYTA
Dennstaedtiaceae	Blotiella currorii (Hook.) R.M.Tryon	Forest	Goyder & Maiato	7701, 7719, 7720, 7722
Dryopteridaceae	Bolbitis gemmifera (Hieron.) C.Chr.	Forest	Goyder & Maiato	7702, 7726
Lomariopsidaceae	cf. Lomariopsis	Forest	Goyder & Maiato	7718
Polypodiaceae	Platycerium sp.	Forest	Sight record
Pteridaceae	Pteris catoptera Kunze var. catoptera	Inga	Goyder & Maiato	7783
Thelypteridaceae	Christella dentata (Forssk.) Brownsey & Jermy	Forest	Goyder & Maiato	7721, 7727
GYMNOSPERMAE
Podocarpaceae	Podocarpus milanjianus Rendle	Woodland	Goyder & Maiato	77800
ANGIOSPERMAE
Araceae	Culcasia angolensis Welw. ex Scott	Forest	Goyder & Maiato	7802
Asparagaceae	Asparagus africanus Lam. var. puberulus (Baker) Sebseb	Forest	Goyder & Maiato	7751
	Dracaena sp.	Forest	Sight record
Commelinaceae	Aneilema beniniense (P.Beauv.) Kunth	Forest	Goyder & Maiato	7741
	Palisota cf. schweinfurthii C.B.Clarke	Forest	Goyder & Maiato	7715
Dioscoreaceae	Dioscorea praehensilis Benth.	Forest	Goyder & Maiato	7758
Marantaceae	Marantochloa leucantha (K.Schum.) Milne-Rendh.	Forest	Goyder & Maiato	7778
Acanthaceae	Acanthus montanus (Nees) T.Anderson	Forest	Goyder & Maiato	7707
	Justicia flava (Vahl) Vahl	Secondary forest	Sight record
	Justicia paxiana Lindau	Forest	Goyder & Maiato	7717
Apocynaceae	Motandra guineensis (Thonn.) A.DC	Forest	Goyder & Maiato	7804
	Oncinotis sp.	Forest	Goyder & Maiato	7777
Bignoniaceae	Markhamia zanzibarica (Bojer ex DC.) K.Schum.	Forest	Goyder & Maiato	7710
Bixaceae	Cochlospermum angolense Welw. ex Oliv.	Woodland	Goyder & Maiato	7796
Cactaceae	Rhipsalis baccifera (J.S.Muell.) Stearn	Forest/Inga	Sight record
Cannabaceae	Trema orientalis (L.) Blume	Forest	Goyder & Maiato	7765
Cleomaceae	Cleome sp.	Forest	Goyder & Maiato	7713
Combretaceae	Combretum angolense Welw. ex M.A.Lawson	Forest	Goyder & Maiato	7712
	Combretum collinum Fresen.	Woodland	Goyder & Maiato	7792
	Combretum platypetalum Welw. ex M.A.Lawson	Forest	Goyder & Maiato	7757, 7766
	Pteleopsis diptera Engl. & Diels	Forest/woodland	Goyder & Maiato	7725, 7793
Connaraceae	Rourea thomsonii (Baker) Jongkind	Forest	Goyder & Maiato	7703
Dichapetalaceae	Dichapetalum crassifolium Chodat	Forest	Goyder & Maiato	7704
Ebenaceae	Diospyros heterotricha (Welw. ex Hiern) F.White	Forest	Goyder & Maiato	7704
Euphorbiaceae	Acalypha paniculata Miq.	Forest	Goyder & Maiato	7762
	Antidesma venosum E.Mey. ex Tul	Forest	Goyder & Maiato	7768
	Croton gratissimus Burch.	Forest	Goyder & Maiato	7801
	Mallotus oppositifolius (Geiseler) Müll. Arg.	Forest	Goyder & Maiato	7734
Gentianaceae	Anthocleista schweinfurthii Gilg.	Forest	Goyder & Maiato	7774
Hypericaceae	Harungana madagascariensis Lam. ex Poir.	Woodland	Goyder & Maiato	7791
Lamiaceaee	Clerodendrum poggei Gürke	Forest	Goyder & Maiato	7736
	Clerodendrum volubile P.Beauv.	Forest	Goyder & Maiato	7714
	Vitex welwitschii Gürke	Forest	Goyder & Maiato	7770
Leguminosae: Mimosoideae	Acacia pentagona (Schumach. & Thonn.) Hook.f.	Forest	Goyder & Maiato	7748
	Albizia adianthifolia (Schumach.) W.Wight	Forest	Goyder & Maiato	7740, 7764
	Inga vera Willd. subsp. vera	Inga	Goyder & Maiato	7759, 7764
	Leucaena leucocephala (Lam.) de Wit	Inga	Goyder & Maiato	7780
Leguminosae: Papilionoideae	Cajanus cajan (L.) Millsp.	Secondary forest	Goyder & Maiato	7784
	Dalbergia saxatilis Hook.f.var. saxatilis	Forest	Goyder & Maiato	7769
	Desmodium repandum (Vahl) DC	Forest	Goyder & Maiato	7742
	Erythrina sp.	Forest	Sight record
	Millettia drastica Welw. ex Baker	Forest	Goyder & Maiato	7787
	Neonotonia wightii (Widht & Arn.) J.A.Lackey	Forest	Goyder & Maiato	7723
	Psophocarpus scandens (Engl.) Verdc.	Secondary forest	Goyder & Maiato	7785
Loranthaceae	Tapinanthus constrictiflorus (Engl.) Danser	Forest	Goyder & Maiato	7789
Malvaceae	Cola welwitschii Exell & Mendonça ex R. Germ.	Forest	Goyder & Maiato	7730, 7747
	Dombeya rotundifolia (Hochst.) Planch. var. rotundifolia	Woodland	Goyder & Maiato	7795
	Grewia flavescens Juss.	Woodland	Goyder & Maiato	7794
	Grewia floribunda Mast.	Forest	Goyder & Maiato	7744
	Urena lobata L.	Secondary forest	Goyder & Maiato	7776
Meliaceae	Turraea vogelii Hook.f.ex Benth	Forest	Goyder & Maiato	7728, 7756
Moraceae	Ficus conraui Warb.	Inga	Goyder & Maiato	7761
	Ficus saussureana DC.	Inga	Goyder & Maiato	7782
	Ficus sp.	Forest	Goyder & Maiato	7739
	Trilepisium madagascariense DC.	Forest	Goyder & Maiato	7733
Passifloraceae	Adenia lobata (Jacq.) Engl. subsp. lobata	Forest	Goyder & Maiato	7752
Phyllanthaceae	Hymenocardia acida Tul.	Woodland	Goyder & Maiato	7798
	Thecacoris trichogyne Müll. Arg.	Forest	Goyder & Maiato	7716
Pittosporaceae	Pittosporum viridiflorum Sims	Woodland	Goyder & Maiato	7797
Primulaceae	Maesa welwitschii Gilg.	Forest	Goyder & Maiato	7709
Rhamnaceae	Gouania longipetala Hemsl.	Forest	Goyder & Maiato	7724
Rubiaceae	Bertiera orthopetala (Hiern) N.Hallé	Forest	Goyder & Maiato	7771
	Coffea canephora Pierre ex A.Froehner	Forest/Inga	Goyder & Maiato	7786
	Empogona glabra (K.Schum.) Tosh & Robbr.	Forest/Inga	Goyder & Maiato	7755
	Mussaenda erythrophylla Schumach. & Thonn.	Forest	Goyder & Maiato	7803
	Pavetta gossweileri Bremek	Forest/Inga	Goyder & Maiato	7760
	Psychotria nigropunctata Hiern	Woodland	Goyder & Maiato	7799
	Rothmannia longiflora Salisb.	Forest	Goyder & Maiato	7745
	Rothmannia whitfieldii (Lindl.) Dandy	Forest	Goyder & Maiato	7746
	Sherbournia bignoniiflora (Welw.) Hua	Forest	Goyder & Maiato	7705
	Tarenna pavettoides (Harv.) Sim?subsp. nov.	Forest/Inga	Goyder & Maiato	7775
	Rytigynia?sp. nov.	Forest	Goyder & Maiato	7788
Sapindaceae	Deinbollia laurifolia Baker	Forest	Goyder & Maiato	7743
	Pancovia golungensis (Hiern) Exell & Mendonça	Forest	Goyder & Maiato	7772
	Paullinia pinnata L.	Forest	Goyder & Maiato	7767
Sapotaceae	Synsepalum cerasiferum (Welw.) T.D.Penn.	Forest	Goyder & Maiato	7754
Solanaceae	Solanum anomalum Thonn.	Forest	Goyder & Maiato	7711
	Solanum mauritianum Scop.	Secondary forest	Goyder & Maiato	7738
	Solanum terminale Forssk.	Forest	Goyder & Maiato	7749
Umbelliferae	Steganotaenia araliacea Hochst.	Inga	Goyder & Maiato	7779
Urticaceae	Urera trinervis (Hochst.) Friis & Immelman	Forest	Goyder & Maiato	7773
Violaceae	Rinorea ilicifolia (Welw. ex Oliv.) Kuntze	Forest	Goyder & Maiato	7750
Vitaceae	Cissus aralioides (Welw. ex Baker) Planch.	Forest	Goyder & Maiato	7790
	Leea guineensis G.Don	Secondary forest	Goyder & Maiato	7708

List of species collected in Kumbira forest which represent new records for Angola.

Family	Species	Notes
Acanthaceae	Justicia paxiana Lindau	Widely distributed in West Africa and the Congo Basin, but not recorded before from Angola
Moraceae	Ficus saussureana DC.	Widely distributed in West Africa and eastern and western margins of the Congo Basin, but not recorded before in Angola.
Rubiaceae	Rytigynia ?sp. nov.	We were unable to match this to any known species of the genus.
Rubiaceae	Tarenna pavettoides (Harv.) Sim	This species has one subspecies distributed across West Africa and northern limits of the Congo Basin, and other subspecies in Eastern and Southern Africa. It has not been reported from Angola before, and our collection may represent a new subspecies.