A floristic analysis of forest and thicket vegetation of the Marakele National

One of the major plant communities identified in the Marakele National Park was forest. It became clear that this major forest community contained various forest and thicket communities. Relevés compiled in the forest were classified by TWINSPAN and Braun-Blanquet procedures identified six communities that are hierarchically classified. The forests dominated by Podocarpus latifolius and Widdringtonia nodiflora represent Afromontane Forests, whereas the Buxus macowanii-dominated dry forests and Olea europaea subsp. africana represent Northern Highveld Forests. A further group of communities represent thickets on termitaria with floristic affinities to both savanna and forest. The floristic composition and relationships of the forest and thicket communities are discussed.


Introduction
In an overview of the vegetation of Marakele National Park, Van Staden & Bredenkamp (2005) recognised five major plant communities, of which one represents forests.These forests are mostly restricted to moist, sheltered valleys, and represent typical Marakele Afromontane Forest (Von Maltitz 2003).Although Du Preez et al. (1991) classified this type of forest as typical Afromontane Forests, the Marakele forests exist under much drier conditions than in the Drakensberg (Von Maltitz 2003).These forests occur in specific niches in deep valleys, protected gorges and ravines along the eastern and western slopes of the Drakensberg mountain range.
Indeed, some of the Marakele forests are very dry and represent a very rare and restricted plant community classified by Von Maltitz (2003) under Northern Highveld Forests.
Van Staden (2002) indicated that various plant communities occurred within these forests, though they are not yet described.This paper aims to describe the forest plant communities of the Marakele National Park, to provide an inventory of the biodiversity of the plant community at the plant species level.

Study area
The study area was described in detail by Van Staden (2002) and Van Staden & Bredenkamp (2005), and are therefore only briefly mentioned here.The study area covers 290.51 km² in the southwestern part of the Limpopo Province between 27°30'E-27°45'E and 24°15'S-24°30'S.Marakele National Park is situated mainly in the Waterberg Moist Mountain Bushveld (Low & Rebelo 1996), in the Savanna Biome (Rutherford & Westfall 1994).The vegetation of the study area includes Acocks' (1988) Sour Bushveld (Veld Type 20), Mixed Bushveld (Veld Type 18), Sourish Mixed Bushveld (Veld Type 19) and North-Eastern Mountain Sourveld (Veld Type 8).The underlying parent rock of the biggest part of the study area consists of sandstone of the Kransberg Subgroup, Sandriviersberg Formation.Sandstone of the Matlabas Subgroup, Aasvoëlkop Formation, occurs in the southwestern and southern parts; shale and mudstone of the Matlabas Subgroup Aasvoëlkop Formation, Groothoek Mudstone Member; a conglomerate outcrop of the Matlabas Subgroup, Aasvoëlkop Formation are found in the western part.These rock formations resulted in the complex mountain topography of the Waterberg.Within this complex topography, the forests are restricted to the relatively moist kloofs, mostly with small rivers.
The soils that have developed on the parent materials range from shallow sandy to deep sandy soils on sandstone and clayey soils on diabase and mudstone.
The rainfall varies from 556 mm to 630 mm per annum and occurs mainly during the summer months.This is considerably lower than the rainfall limits described for forests in summer rainfall area by Rutherford & Westfall (1994).The study area experiences warm, wet summers with temperatures of up to 32 ºC and cool dry winters with frost in the low-lying areas.

Analysis
In the overview of the vegetation of the Marakele National Park, Van Staden (2002) used 130 sample plots, located in a stratified random manner in physiographically and physiognomically homogeneous units, delineated on 1:50 000 scale aerial photographs (Bredenkamp & Theron 1978;Westfall 1981;Gertenbach 1987).The number of sample plots for each delineated physiographic-physiognomic unit was determined according to the size of each delineated unit.Termitaria were not included in the placing of the sample plots.Although they could be recognised on the aerial photographs, they were too small to delineate.Additional sample plots were subjectively placed within the termitaria vegetation.
For the purpose of this study, a standard sample plot size of 10 m x 20 m was fixed and used throughout the study area.This plot size is considered adequate for surveys in savanna vegetation by Coetzee (1975), Coetzee et al. (1976), Westfall (1981), Van Rooyen (1983) and Gertenbach (1987).
At each sample plot a list is compiled of all the species that occur.A cover-abundance value was given to each species according to the cover-abundance scale, used by Braun-Blanquet and given by Mueller-Dombois & Ellenberg (1974) and Werger (1974), and modified by Barkman et al. (1964): 5 -Any number of plants, with cover >75 % of the sample plot.4 -Any number of plants, with cover > 50-75 % of the sample plot.3 -Any number of plants, with cover > 25-50 % of the sample plot.2a -Covering between 5-12 % of the sample plot area independent of abundance (indicated as A in the tables).2b -Covering between 13-25 % of the sample plot area independent of abundance (indicated as B in the tables). 1 -Numerous, with cover of 5 % or less.+ -Individuals with cover of < 1 %.r -Usually a single individual with a cover of < 1 %.
Although Van Staden (2002) recorded various habitat variables, only the following habitat classes are used in this study (see Table 1): The altitude of each sample plot was recorded using an altimeter and is given in meters.
The slope of the terrain of each sample plot was measured in degrees, using an optical clinometer.
The following classification of slope units (Westfall 1981), were used in this study:

Synthesis
The full dataset was captured on the mainframe computer of the University of Pretoria, in the BBNEW software package.It was then exported to be used in the software package BBPC (Bezuidenhout et al. 1996).After a TWINSPAN classification (Hill 1979), the output of the resulting classification was imported into a spreadsheet, for refinement by Braun-Blanquet procedures (Behr & Bredenkamp 1988).The final classification of the relevés was then interpreted for identification of major communities for the entire park.The relevés representing the forests and thickets were then extracted, subjected to TWINSPAN (Hill 1979) and exported to be used in the software package BBPC (Bezuidenhout et al. 1996) for refinement by Braun-Blanquet procedures.The results are summarised in a phytosociological table (Table 1).

Results
The phytosociological classification of forests and thickets in the study area resulted in the identification of five forest communities with one of the communities having two sub-communities.Although different plant communities can be recognised within these forests and bush clumps, certain species, e.g., Olea europaea subsp.africana, Ficus sur, Cryptolepis transvaalensis, Cussonia paniculata and Euphorbia ingens were prominent throughout the range of this major community.

Olea europaea
The forest communities occur in the kloofs, or as thickets in bush clumps on south and east-facing slopes and also as dense thickets on termitaria on the plains.The kloofs are the most sheltered of the geomorphology classes found in the study area, with water in the watercourses draining down the kloofs.These kloofs are also protected against the veld fires that occur frequently in the adjacent savanna or grassland vegetation.Geldenhuys (1994) described a similar situation for forests in the Western Cape.A dendrogram showing the habitat relationships of the various plant communities is shown in Fig. 1.

Olea capensis-Cheilanthes viridis Forest
This community represents all the forests that occur in moist kloofs or sheltered valleys in the Marakele National Park.Based on species composition, this vegetation can be regarded as Afromontane Forest (White 1978).According to the classification of
The shrub layer is on average 1.4 m tall, with an average canopy cover of 22 % (Table 2).Prominent shrubs occurring in this community are Myrsine africana and Ochna holstii (species group C) (Table 1).The woody liana Secamone alpinii (species group C) is frequently found in the tree and shrub strata.

Habitat
The Rhus leptodictya-Mimusops zeyheri Termitarium Thickets are found from 1160 m-1300 m a.s.l.This widespread community occupies an even drier habitat than that of the Buxus macowanii-Kirkia wilmsii Low Forest, though the termitaria are moister than the surrounding savanna (Van der Meulen 1979).They are therefore classified with the forests.The bush clumps on termitaria are restricted to the Ad Land Type on level and gentle slopes (Land Type Survey Staff 1988) (Fig. 1).
Before proclamation of Marakele National Park, this community was subjected to heavy grazing by cattle and the field layer varies in height and cover depending on soil salinity and the amount of grazing (Coetzee et al. 1981).The vegetation developed on huge termite mounds to form this specific plant community.The size of these termitaria determines the type of vegetation that occurs.The trees are usually very tall because of the depth and aeration and the fine texture and higher nutrient status of the soil (Coetzee et al. 1976).
This community is a representative of Acocks' (1988) Sour Bushveld, with the structure as a short closed woodland (Edwards 1983)

Habitat
The Rhus leptodictya-Carissa bispinosa variation is found at 1160 m-1300 m a.s.l.This variation occurs on level ground or/and gentle slopes (1-160º).The soils are yellow, apedal and well drained and relatively deep (> 500 mm), belonging to one of the following forms: Inanda, Kranskop, Magwa, Hutton, Griffin and/or Clovelly (Land Type Survey Staff 1988) (Fig. 1).
The average diameter of the Rhus leptodictya-Carissa bispinosa variation bush clumps is 25 m.It is represented by seven relevés and an average of 35 species was recorded per sample plot (Table 1).

Floristics and structure
The Rhus leptodictya-Carissa bispinosa variation is differentiated by the following diagnostic plant species (species group F, The shrub layer is on average 1.8 m tall with an average canopy cover of 41 %.Cryptolepis transvaalensis is prominent. The herbaceous layer has an average height of 0.4 m and an average canopy cover of 21 %.The herbaceous layer is dominated by the grass Setaria lindenbergiana and the forb Hypoestes forskaolii (species group K).

General
The Olea europaea subsp.africana-Calpurnia aurea Tall Closed Woodland has floristically strong affinities with the Rhus leptodictya-Mimusops zeheri Termitarium Thickets (species group I) and especially the Rhus leptodictya-Berchemia zeyheri variation, indicated by species group H.The habitat difference between these two bush clump communities is that the Olea europaea subsp.africana-Calpurnia aurea Tall Closed Woodland occurs in deep, sheltered kloofs on rocky substrates without termitaria, while the Rhus leptodictya-Berchemia zeyheri variation occurs on termitaria on the plains without rocks.

Discussion
According to White (1978) 2003).There is also floristic similarity between the kloof forest communities and thickets found on termitaria.Termitaria are known to increase water infiltration and percolation, as well as nutrient availability, compared to the surrounding savanna woodlands (Van der Meulen 1979).Therefore, termitaria do support dense thickets with savanna species, however some forest species are also present.
Low diversity of the woody element places this type close to Drakensberg Montane Forests and Northern KwaZulu-Natal Mistbelt Forests (Von Maltitz 2003).
The distribution of the shrub Buxus macowanii is of biogeographic interest.This species is restricted to coastal forests of the Eastern Cape and forms an outlying population in the Waterberg region (Coates Palgrave 1983).

Fig. 1 .
Fig. 1.A dendrogram showing the habitat relationships of the plant communities classified under the Olea europaea-subsp.africana-Diospyros whyteana Major Community.

subsp. africana-Diospyros whyteana Major Community
Coetzee et al. (1976) type of forest as typical Afromontane Forests, where these forests occur in specific niches in deep valleys, protected gorges and ravines along the eastern and western slopes of the Drakensberg mountain range.Coetzee et al. (1976)described termitaria bush clump communities from the Nylsvley Nature Reserve.These have diagnostic species similar to the bush clump communities on termitaria in the Marekele National Park.Olea europaea subsp.africana-Calpurnea aurea Tall Closed Woodland.
Maltitz 2003))f the tree species in the Afromontane forests are very widespread.Amongst them are Podocarpus latifolius, Ilex mitis and Halleria lucida that occur in the study area.These ISSN 0075-6458 species could almost be used to define the Afromontane region as a whole.Not one species occurs throughout, but most species of the assemblage are represented on virtually every 'island' of Afromontane forest.According to VonMaltitz (2003)the Northern Highveld Forest type is a relict forest type in a progressed stage of 'erosion' from the original Afromontane composition.They are considered remnants of the Magaliesburg Extension(White 1978)-an Afromontane (forest) intrusion linking the forests of Northern Escarpment to those found in sheltered sites of the Central Bushveld and Northern Highveld regions.These forests are Afrotemperate (Afromontane) in character, however Holocene climate changes have caused their confinement to fire-sheltered habitats and a concomitant decline in forest elements, but an increase in woodland elements (VonMaltitz 2003).