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Summary BOT251 semester test 1
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ALBANY THICKET BIOMECHARACTERISTICS
• Dense, woody, semi-succulent, and thorny vegetation type, with an average height of 2-3m –
IMPENETRABLE in an unaltered condition
• Thicket does not fit within the Forest biome definition as it does not have the required height
nor the many strata below the canopy
• Found in semi-arid areas of Eastern Cape and Western Cape
• Two prevailing climate systems
• all year rainfall towards the southwest
• summer rainfall towards the northeast
• Therefore, converge in the region is ALL YEAR RAINFALL with spring and autumn maxima
THREATS GEOLOGY
1. Bush-clearing for crop cultivation • Dominant geological feature = CAPE FOLD
2. Urban expansion along the coast BELT.
(residential & industrial) • Consists mostly of folded strata of the Cape
3. Illegal collecting Supergroup (coarse-textured rock)
4. Invasion of alien species • Rocks of the Karoo Supergroup (fine-textured
rock) form the African escarpment (another
major topographical feature)
CLIMATE VEGETATION
• Changes in rainfall result = changes to • Varied structure & growth form
vegetation • impenetrable, evergreen, closed shrubland of
• Increase in summer rainfall towards the sclerophyllous or succulent trees
northeast = change in vegetation towards • Main growth forms of the biome:
grassland and savanna -leaf and stem succulents
• Increase in winter rainfall towards the -woody shrubs
southwest = change towards fynbos- -grasses
dominated vegetation -annuals
• Seasonal rainfall pattern determines the fire -geophytes
regime • Its thickness and impenetrability comes from
• Selective force for fragmented Thicket a distinct guild of spinescent woody plants
pattern is: (Woody species of this guild all produce edible
-fire regime fruits – seeds bird dispersed)
-determined ultimately by seasonal
precipitation
• Unreliable rainfall
• Common droughts
• Region experiences high and low
temperatures with frost in winter especially
inland
• Lower temperature range near the coast
SOILS NATURAL PROCESSES
• Vary considerably • No regular or widespread fire regime (Not
• Soils from KAROO SUPERGROUP: deep, well- much fuel (e.g. grass) and succulents helps
structured exclude fires)
• Soils from CAPE SUPERGROUP coarse, • But fire is increasing in degraded -
unstructured soils, shallow and nutrient-poor replacement of the non-flammable succulent
(dominant soil-type) unit with a potentially flammable field layer
• Regions with BOTH poor and fertile soils (i.e. grass and shrub layer)
• Known for deep soils rich in nutrients but is • Herbivory = important role in shaping
, not restricted to this vegetation and ecosystem properties.
• Clumping of vegetation also distinguishing • Megaherbivores (elephants and rhinos)
feature, facilitated by belowground animal maintain thicket structure.
activity (termite mounds, active mole rat • Large browsers (elephant, rhinoceros, greater
colonies, aardvark burrows and earthworm kudu) limit the spread of thicket
activity) • Results in higher mineral, organic • If large browsers removed, thicket becomes
and moisture content compared with invasive and spreads into other vegetation
adjacent soils types (savanna & grassland)
• low resilience, regenerate slowly after
disturbance
VEGETATION UNITS
1. DUNE THICKET
• Narrow seaward-facing side of coastal dunes
• Lianas fairly abundant
• Vegetation has many Pondoland flora affinities
• Eg’s of common species: Mimusops caffra, Brachylaena discolor and Carissa bispinosa
2. VALLEY THICKET
• From coast up river valleys, many species prominent in this unit (floristically the richest)
• closed canopy reaches ca. 6 m in height
• Vegetation usually woody evergreen species
• Eg’s of common species: Euphorbia triangularis, E. tetragona
3. SUCCULENT THICKET
• Mainly in drier areas and river valleys
• High number of both succulent and endemic species; overall species richness is lower
than other thicket veg units
• Sparse thicket with canopy usually 2 – 2.5 m in height
• Eg’s of common species: Grewia robusta, Brachylaena ilicifolia and Spekboom
Portulacaria afra
ANIMAL BIODIVERSITY
• low species richness
•48 medium to large animals: (elephant, antelope, rhino, cape buffalo)
•birds: (2 near endemic species: orange breasted sunbird, cape siskin)
•6 endemic reptiles
DEGRADATION
• Thicket biome is prone to degradation for TWO reasons:
• low annual production and
• the very slow recovery rate of the main forage species which can take up to 18 months
to recover from 50% defoliation e.g. by goats.
OVERGRAZING
• Albany thicket is relatively resilient to browsing by indigenous herbivores, but is highly
vulnerable to browsing by domestic goats
• Excessive grazing transforms thicket from a closed-canopy shrubland into an open community
comprising scattered and degraded thicket clumps and isolated trees in a matrix of short-lived
herbs
BIOME COMPARISONS
• Thickets are SIMILAR to FORESTS in that their distributions are restricted to fire protected sites
(eg. Valley)
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