6. RESULTS
6.6 Pollen analysis
67 Zone D4: 25 - 0 cm; 550 - present cal yr BP
In Zone D4, both δ15N and δ13C values decrease at the top of the zone. Total Nitrogen and Total Organic Carbon both increase overall, reaching the highest content at the top of the core, while the C:N ratio decreases negligibly, and Zone D4 indicates a dominance of C4 vegetation.
68 Table 6.4 Classification of taxa according to regional, local, arboreal and non-arboreal groupings (*indicates taxa with total counts of <1%)
Regional Taxa Local Taxa
AMARANTHACEAE non-arboreal CYPERACEAE undiff. non-arboreal
ASTERACEAE Artemisia non-arboreal ERIOCAULACEAE Eriocaulon non-arboreal
ASTERACEAE Stoebe* non-arboreal HALORAGACEAE non-arboreal
ASTERACEAE undiff. non-arboreal LILIACEAE non-arboreal
ASTERACEAE Vernonia* non-arboreal POACEAE non-arboreal
BORAGINACEAE Heliotropium* non-arboreal MONOLETE spore
COMMELINACEAE* non-arboreal TRILETE spore
DIPSACACEAE Scabiosa non-arboreal TRILETE Mohria spore
ERICACEAE non-arboreal
EUPHORBIACEAE Euphorbia non-arboreal Neophytes
EUPHORBIACEAE undiff. non-arboreal POACEAE Zea mays non-arboreal
FABACEAE non-arboreal MIMOSOIDEAE Type II arboreal
GERANIACEAE* non-arboreal PINACEAE Pinus arboreal
HYPERICACEAE Hypericum* non-arboreal
IRIDACEAE undiff. non-arboreal Non-pollen Palynomorphs
LAMIACEAE undiff. non-arboreal Pseudoschizea
LAMIACEAE Leonotis* non-arboreal Undetermined
OXALIDACEAE Oxalis* non-arboreal Non-pollen palynomorphs
THYMELIACEAE non-arboreal
ACANTHACEAE arboreal
ANACARDIACEAE arboreal
APIACEAE* arboreal
AQUIFOLIACEAE Ilex mitis* arboreal
ARALIACEAE arboreal
BORAGINACEAE Cordia arboreal
BRASSICACEAE arboreal
CELASTRACEAE* arboreal
CELTIDACEAE Celtis arboreal CORNACEAE Cornus* arboreal EBENACEAE Diospyros* arboreal
EBENACEAE Euclea arboreal
EBENACEAE undiff.* arboreal MYRICACEAE Myrica* arboreal
MYRTACEAE arboreal
OLEACEAE arboreal
PODOCARPACEAE Podocarpus arboreal POLYGALACEAE Polygala* arboreal
PROTEACEAE arboreal
ROSACEAE Cliffortia arboreal ROSACEAE Leucosidea arboreal ROSACEAE undiff.* arboreal
69
70
71 Zone D1: 144-110 cm; ca.12,100 - 9690 cal yr BP
Regional taxa dominating this zone are Asteraceae, Ericaceae, Anacardiaceae and Podocarpus. Asteraceae declines at 12,100 cal yr BP, however the majority of the zone indicates high frequencies of this taxon. Ericaceae is found in highest concentration in this zone, and frequency of Anacardiaceae increases later in the zone. Podocarpus does not show drastic change in this zone, although concentrations are relatively high. Brassicaceae and Celtis concentrations show a marked decline, whereas Cordia indicates a positive increase.
Liliaceae concentrations are slightly lower at the early parts of the zone, but increase towards the later in the zone. There are no systematic changes in the concentration of Poaceae, however Cyperaceae frequencies decrease briefly at ca. 12,000 cal yr BP and ca. 10,300 cal yr BP. Generally, Afromontane forest/arboreal taxa increase in this zone, and regional pollen signals are high.
Zone D2: 110 - 83 cm; 9690 - 7970 cal yr BP
Asteraceae, Ericaceae, Anacardiaceae and Podocarpus dominate this zone in terms of regional taxa, although there is also a marked increase in the frequency of Brassicaceae towards the early part of the zone. Asteraceae decreases marginally, whilst Anacardeaceae and Celtis increase towards the early part of the zone. There are no systematic changes in the frequency of Podocarpus and Ericaceae. There is a brief increase in Protea between ca.
8900 and ca. 8500 cal yr BP, and Liliaceae frequency begins to increase towards the early part of the zone. Poaceae and Cyperaceae frequencies are mirrored in this zone, with Poaceae increasing in the mid-zone and decreasing towards the early and late stages if the zone. Overall, Afromontane forest/ arboreal pollen signals decrease marginally in this zone, with local pollen signals strengthening towards the early stages of the zone.
Zone D3: 83 - 25 cm; 7970 - 550 cal yr BP
Zone D3 represents a significant portion of the record of Dartmoor Vlei. Dominant regional taxa in this zone are Asteraceae, Anacardiaceae, Brassicaceae, Celtis and Podocarpus.
Overall, Asteraceae frequencies are lower in this zone. There is a brief decrease between ca.
2260 and ca. 1160 cal yr BP, and a slight increase towards the younger part of the zone.
There are no significant changes in Anacardiaceae frequencies, although a relative increase in frequencies can be noted at ca. 1930 and ca. 720 cal yr BP. Brassicaceae and Podocarpus
72 show a generally increasing trend in the frequencies from the base of the zone towards the younger region of the zone, whereas Celtis increases significantly in the mid-range of this zone. Protea frequencies also increase between ca. 7500 and ca. 3650 cal yr BP, however decrease again towards the younger region of the zone. Zea mays occurs for the first time in the records between ca. 1600 and ca. 650 cal yr BP, however it is the only exotic taxon recorded in this zone. Locally, Liliaceae frequencies increase. There are no significant changes in Poaceae and Cyperaceae frequencies; however a relative increase in Poaceae frequency at ca. 5100 cal yr BP indicates a corresponding decrease in Cyperaceae. Similarly, an increase in Cyperaceae at ca. 2700 cal yr BP is mirrored by a decrease in Poaceae frequencies. There are no notable changes in the proportion of regional and local pollen taxa, however the local signal is stronger in this zone than the previous zones. Forest and grassland taxa, however, indicates that there is a slight increase in the number of Afromontane forest taxa in this zone, increasing marginally from the base of the zone towards the top.
Zone D4: 25 - 0 cm; 550 - present cal yr BP
Zone D4 indicates a decrease in Ericaceae, Celtis and Protea, which were more frequent in Zone D3. Brassicaceae and Anacardiaceae frequencies are high in this zone, and Thymeliaceae frequencies increase from previous zones. Leucocidea sericea is present for the first time in the record. Zea mays is once again found at the base of the zone at ca. 530 cal yr BP only, and Mimosoideae Type II occurs singly at ca. 240 cal yr BP. Podocarpus frequencies decrease notably in zone D4, whilst Pinus is present for the first time in the record, and increase significantly from ca. 450 cal yr BP towards the top of the zone.
Regional pollen taxa increase marginally from the previous zone. Asteraceae frequencies are high, although Liliaceae decreases towards the top of the zone. Poaceae and Cyperaceae frequencies do not differ significantly from the top of the previous zone, however the proportion of Afromontane forest taxa increases slightly.