Ecosystem Guidelines for Environmental Assessment

LOWLAND FYNBOS
INCORPORATING SAND FYNBOS AND LIMESTONE FYNBOS
LOWLAND FYNBOS
ECOSYSTEMS
LOWLAND FYNBOS ECOSYSTEMS
Nick Helme, Pat Holmes and Tony Rebelo
What are the key ecological “drivers” in terms of
maintaining ecosystem function, pattern or structure
Limestone Fynbos and Sand Fynbos often occur in a matrix, and ecological processes that affect the
one may be closely inter-related with the other.
Fire frequency must ensure sufficient seed-set in slow-maturing species such as the Proteaceae.
This can be up to 30 years in arid areas.
The appropriate seasonal fire regime must be retained. Fire should occur in summer to early autumn
(December to March).
Under natural regimes fires are slow moving, ignition is extremely rare (most fires start "elsewhere")
and fires burn unimpeded over large areas. End boundaries of fires are usually other vegetation types
and young veld.
Allow for sufficient seed-set in slow-maturing species.
In Limestone Fynbos and Sand Fynbos, there can be a high incidence of species turnover along
habitat or environmental gradients, i.e. beta diversity is high. Many edaphic gradients are found on
edges of Limestone Fynbos and Sand Fynbos communities. Subtle edaphic variations, such as the depth
of overlying sand, have a dramatic effect on community structure. There are also substantial unexplained
variations in species richness, and concentration of rare and endemic plants, from area to area.
Patch size and connectivity with other limestone outcrops may be important to retain certain species.
Seasonal wetlands and seeps are important to retain certain distinct communities. Regional and
local natural water drainage patterns are thus also important drivers of biodiversity pattern.
Natural grazing and physical soil disturbance by fauna may be important to retain a high incidence
of spring annuals, which is unusual in fynbos.
What are the key issues, vulnerabilities and threats
There can be a very high occurrence of rare and regionally endemic plant species in Limestone Fynbos
and Sand Fynbos, many of which are very localised within what might appear to be fairly homogenous
habitat. In Sand Fynbos, the incidence of rare and endemic plant species is particularly high in the
South.
Vulnerable habitats include wetlands, sink-depressions and moister soil facies. These ecotypes are
at risk due to their higher agricultural potential.
Both Limestone Fynbos and Sand Fynbos are vulnerable to changes in the natural fire regime (to
promote grazing, for example) and invasion by alien plants.
They are also at risk from veld clearance and ploughing, over-harvesting of species (flowers and
whole plants), and changes in water availability due to abstraction of groundwater.
Limestone Fynbos is highly susceptible to invasion by rooikrans Acacia cyclops, especially on deeper
sands in valleys between rocky outcrops. However, in areas of severe invasion even the rocky pavements
are affected. Besides being vulnerable to rooikrans, Sand Fynbos is also susceptible to invasion by
Port Jackson Acacia saligna, Eucalyptus gomphocephala and Leptospermum laevigatum, and annual
grasses (Avena, Briza).
COLIN PATERSON-JONES
38 : LOWLAND FYNBOS ECOSYSTEMS