Cusseque - Vegetation

The vegetation of the Cusseque core site is Table 1: Vegetation of the Cusseque core site in numbers: sampling size and very different from the other three core biodiversity indices. sites of the TFO study area. It forms part of Ecoregion Angolan Miombo the larger Miombo region extending over Sampling period: 2011 - 2013 large parts of southern and central Africa. 2 Compared to the middle and lower reaches 1,000 m plots sampled 15 of the Okavango Basin, the humid climate 100 m2 plots sampled 90 of the Angolan highlands supports a Vegetation unit Miombo forests with species-rich and dense vegetation. In this (MODIS classification) exfoliatum ssp. pseudotaxus, Miombo undulating landscape the topographic forests dominated by deciduous tree position is paramount in determining species, Miombo forest dominated by spatial patterns of the vegetation. While Julbernardia paniculata, Cryptosepalum the elevated parts comprising plateaus and maraviense , capensis (on humid soils), ridges are covered by Miombo forests and wet grasslands and peatlands woodlands, the mid-slopes leading down to the valleys feature an open landscape Dominant families (cover) (s.l.), Ixonanthaceae, dominated by geoxylic dwarf shrubs and , Apocynaceae grasses. At the valley bottom, where Dominant families (richness) Fabaceae (s.l.), Combretaceae, drainage lines converge, permanently wet Euphorbiaceae, Poaceae peatlands have established. Species richness on 1,000 m² 49 (34 - 61) Most woody species are brevi- deciduous losing their leaves at the end of Species richness on 100 m² 36 (13 - 60) the rainy season, however, some Evenness (J´ ) on 1,000 m² 0.512 (0.389 - 0.710) evergreen species like Cryptosepalum Evenness (J´) on 100 m² 0.607 (0.263 - 0.843) exfoliatum ssp. pseudotaxus play a major Simpson index (D ) on 1,000 m² 0.735 (0.621 - 0.906) role in the vegetation, too. A few weeks SI before the onset of the first rains, are Simpson index (DSI ) on 100 m² 0.816 (0.347 - 0.939) resprouting and the fresh leaves flourish in colours ranging from deep red, orange to and relatively low stand height (mostly of the core site exhibit mixed stands of fresh green. In the following the < 12 m) resulted from cohort Brachystegia spiciformis, Brachystegia vegetation units are described in reference regeneration after major disturbance bakeriana and Cryptosepalum exfoliatum to the mapping units of the land cover map events or is due to low fertility of the ssp. pseudotaxus including various (Schneibel et al. 2013). predominantly ferralitic soils (Fig. 1). Combretum species. The canopy is less Closed Miombo forests cover large b) The woodlands in the central parts closed and trees are mostly semi- areas of the core site and reach heights of up to 15 m. They are dominated by tree species of the Fabaceae family, mostly of the Caesalpinioideae subfamily. Three subunits can be distinguished: a) Very dense woodlands with stands dominated by evergreen Cryptosepalum exfoliatum ssp. pseudotaxus trees covering large areas of the western section of the core site. Here, shifting cultivation is currently absent and hence woodlands are mostly unfragmented. As these woodlands are hardly affected by fire a thick moss layer covering the ground can establish. This subunit is further characterized by a high abundance of lianas such as Landolphia camptoloba forming a hardly penetrable thicket. Within this vegetation subunit stems do not reach large diameters resulting in a low Fig. 1: Closed Miombo forests dominated by Cryptosepalum exfoliatum ssp. standing woody biomass. It is not clear yet pseudotaxus with thick moss layer on the ground and stems covered by lichens if this homogeneous vegetation structure (photo: R. Revermann).

In: Oldeland, J., Erb, C., Finckh, M. & Jürgens, N. (2013) [Eds.]: Environmental Assessments in the Okavango Region. – Biodiversity & Ecology 5: 59–63. DOI: 10.7809/b-e.00247. 59 deciduous leading to a significant shrubby inhibited by extensive thickets of the fern suffruticans cover a large fraction of the understorey formed by Copaifera Pteridium aquilinum. ground of this vegetation unit. Further baumiana, Phyllocosmus lemaireanus and Shrubland ecotone: W h e r e dwarf shrubs common in patches include Paropsia brazzaeana as well as a herb environmental conditions slowly start Ochna manikensis and Syzygium layer composed of several tall-growing being unfavourable for tall woodlands we guineense ssp. huillense. White (1976) grasses, e.g. of the genera Hyparrhenia find an ecotone comprising elements of offers different hypotheses for the and Stipagrostis. both, the open dwarf shrub grasslands and occurrence of this growth form, among c) The woodlands east of the Cusseque the woodlands. In some areas, these others unfavourable edaphic conditions, River are covered by another subunit of the ecotones stretch over several hundred frost, and fire. During the vegetation Miombo woodlands where the dominant metres reaching from the topslopes down survey it was shown that these dwarf tree species are Julbernardia paniculata to the midslopes. Tree cover is low and shrubs generally occur on mid- and and Brachystegia spiciformis. The canopy individual trees are separated by large footslopes with either shallow, ferralitic or reaches heights of 15 m and hence is open areas. The most characteristic tree is sandy soils, both exhibiting seasonally considerably higher than in the Monotes glaber; other typical trees changing soil-water conditions and some aforementioned vegetation subunits. include Terminalia brachystemma, Protea hydro-morphic features. Night frosts do Further important tree species occurring gaguedii, Bobgunnia madagascariensis, occur in the dry months of the year, but throughout the woodlands are and Combretum apiculatum (Fig. 2). only on the slopes and in the valleys, Erythrophleum africanum, Burkea Cryptosepalum maraviense hardly on the plateau (Revermann & africana and Pterocarpus angolensis. grasslands: This vegetation unit is very Finckh 2013; Fig. 3 and 4). Miombo (open/disturbed): characteristic of the central plateau and Parinari capensis grasslands (on This vegetation unit comprises the rather referred to as “Anhares de ongote” or sandy soils): This vegetation unit is open parts of the wooded areas that have “Cassamba” in the local languages spatially clearly delimited and is found in been impacted by human activities and are (Barbosa 1970). The dominant life form is the core site on the plains along the eastern exposed to a higher fire frequency. The the so called “geoxylic suffrutex”, side of the Cusseque River. It typically dominant species do not belong to the referring to dwarf shrubs with enormous occurs on sandy deposits along larger river Fabaceae and include for example woody underground biomass and even the systems such as the Longa River. The Monotes caloneurus of the family buds resting underneath the surface. Many main aspect in the late rainy season is Dipteraceae and Uapaca kirkiana and U. species occurring here are very closely shaped by several tall grass species such as nitida of the family Euphorbiaceae. related to tree species of the Miombo Monocymbium ceresiiforme, Stipa- Fallows and early regeneration stages are woodlands and it is often still uncertain if grostis spp., and Hyparrhenia spp. characterized by trees resprouting from they indeed correspond to different amongst others. However, geoxylic root stocks and stem bases left standing species or rather to ecotypes. suffrutices such as Parinari capensis, during the time of cultivation. However, in Cryptosepalum maraviense a n d Ochna arenaria, Ochna cinnabarina, some cases woodland regeneration is Cryptosepalum exfoliatum ssp. Syzygium guineense ssp. huillense, and

Fig. 2: Shrubland ecotone (photo: R. Revermann).

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Fig. 3: Cryptosepalum maraviense grassland (Anhares de Ongote / Cassamba) in October just Fig. 4: Cryptosepalum maraviense grassland on ferralitic soils along the slopes at the end of the before the onset of the first rains showing colourful resprouts of Cryptosepalum maraviense; rainy season in May. At this time, grasses dominate the aspect of this vegetation unit. Peat bogs grasses are not present yet (photo: R. Revermann). are located at the valley bottom in the centre of the photo (photo: R. Revermann).

Fig. 5: Parinari capensis grassland (on sandy soils) at the beginning of the rainy season (photo: Fig. 6: Parinari capensis grassland on sandy soils at the start of the dry season; tall Poaceae and R. Revermann). 61 solitary Burkea africana trees dominate the appearance at this time of the year (photo: R. Revermann). Fig. 7: Drosera burkeana, one of several Drosera species Fig. 8: Horticulture in the peatlands at the headwaters of a small common in the peat lands of the Cusseque area (photo: R. tributary (photo: R. Revermann). Revermann).

Fig. 9: Reed beds and open water along the Cusseque River (photo: R. Revermann).

Fig. 10: The dwarf shrub Cryptosepalum maraviense referred to Fig. 11: Alvesia rosmarinifolia a typical species of the Miombo as “Cassamba” in the local language (photo: M. Finckh). woodlands of the Cusseque core site (photo: M. Finckh).

Protea welwitschii form an integral part of and some sedges. distinctive Limnophyton angolense community composition and dominate the Peatlands: The valley bottoms covered whereas high reeds of Phragmites vegetation at the end of the dry season and by thick peat layers are characterized by mauritianus are present in deeper water the beginning of the rainy season, although typical wetland vegetation dominated by (Fig. 9). with a much smaller underground biomass sedges of the genera Kyllinga, Cyperus, than in the Cryptosepalum maraviense and Eleocharis. Furthermore, several grasslands (Fig. 5 and 6). Drosera species can be found as well as the Wet grasslands: Grasslands on wet dwarf shrub Protea paludosa and many mineral soils occur adjacent to the orchids (Fig. 7 and 8). peatlands or in the heads of the valleys, Reed beds and open water: Species of dominated by tufted, perennial grasses the stream communities include the

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30 Species richness

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0 Vegetation unit

100 m2 Cryptosepalum maraviense Entire core site (n = 90) Miombo forest (closed) (n = 21) grasslands (n = 16) Parinari capensis grasslands Peatlands (n = 11) (on sandy soils) (n = 11) Shrubland ecotone (n = 4)

1,000 m2 Cryptosepalum maraviense Entire core site (n = 15) Miombo forest (closed) (n = 5) grasslands (n = 8)

Fig. 12: Species richness on the Cusseque core site according to vegetation units and on two different spatial scales. Values are shown for vegetation plots sized 100 m2 and 1,000 m2 , indicated by the same colour. Note that sample sizes may be different for the two plot sizes; wetlands were only sampled on 100 m2 plots.

The range of habitats and vegetation study design please refer to the Electronic References communities appearing within the Appendix. Cusseque core site is striking. The Barbosa, L. A. G. (1970): Carta vascular diversity is highest among Fitogeográfica de Angola. – Luanda: the four studied core sites with regards to Acknowledgements Instituto de Investigação Científica de alpha diversity if species richness is Angola. considered. In the Miombo woodlands it This study was funded by the BMBF (The Revermann, R., Finckh, M. (2013): 2 Cusseque - Microclimate. – Biodiversity reaches values of 60 species per 100 m Future Okavango project). For details see & Ecology 5: 47–50. CrossRef with a median of 36. However, some authors' general acknowledgements in this Schneibel, A., Stellmes, M., Frantz, D., volume. vegetation units are dominated by tree Finckh, M., Revermann, R. (2013): species reaching high cover values Cusseque - Earth Observation. – resulting in a rather low evenness if Biodiversity & Ecology 5: 55–57. compared to the woodlands on Kalahari CrossRef sands (Fig. 12). White, F. (1976): The underground forests For details on the applied methods and of Africa: a preliminary review. – The Gardens' Bulletin Singapore 11: 57–71.

Responsible authors: R. Revermann, F. Maiato, A. Gomes, F. Lages, M. Finckh

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