Ecosystem Guidelines for Environmental Assessment

MAINLAND THICKET
appear to recover naturally, and are invaded
by exotic species or other non-thicket
species.
Over-grazing and wild fires in hot, dry
conditions hold a significant threat to thicket.
Although thicket is essentially a fire-proof
vegetation, overgrazing of the succulent
component results in the system being open
to the invasion of shrubs and C4 grasses.
Such areas may then become flammable,
allowing fires to penetrate vegetation that
otherwise never would have been exposed to
fire in recent times. This can result in the
elimination of many fire-intolerant thicket
plants. Fires can also penetrate into Thicket
and Valley Thicket in some situations, such
Mosaic thicket depends on maintaining a fine balance
as when areas are cleared for stock grazing.
between grazing and fire.
The occurrence of alien invasive acacias in
fynbos increases the likelihood of fire
penetrating thicket vegetation at the fynbos/thicket boundary.
The loss of connectivity of thicket patches affects ecosystem function. Historically, thicket was more
connected than it is now. Transformation has resulted in a fragmented pattern that reduces resilience
to environmental change and causes isolation of gene pools and the loss of gene flow within and
between patches. Isolation due to human-induced fragmentation may result in some species losing
their adaptive potential, increasing the risk of species or varieties becoming extinct.
Game fences prevent some animal and plant species from migrating, and may ultimately threaten
their survival. The introduction of non-indigenous game also presents a threat to thicket vegetation.
Due to historical transformation of adjacent, non-thicket habitat such as Coast Renosterveld or Dune
Thicket may provide the only connectivity between Mainland Thicket types that occur in inland-trending
valleys. Coastal development threatens to sever these surviving linkages.
JAN VLOK
What are the “bottom lines” and non-negotiables
Avoid over-grazing in Valley or Arid Thicket - otherwise the system will disappear.
Avoid the introduction of extra-limital, non-thicket game species.
Avoid severing or fragmenting patches of intact thicket. Where this has occurred, set aside corridor
areas to reconnect the patches.
Avoid transitional or boundary areas where thicket abuts or forms mosaics with vegetation
associated with the adjacent biome. Such areas accommodate the highest levels of biodiversity and
require special conservation measures.
Many of the mosaic thicket vegetation types are maintained by a fine balance between specific fire
and grazing regimes. Retain appropriate grazer-browser ratios in game species as well as the required
fire regime.
Avoid disturbance to riparian areas or steep slopes and valleys where thicket vegetation is present.
Avoid disturbance to rocky outcrops, geological/soil type boundaries and islands where thicket
vegetation is present.
Never underestimate the restoration potential and importance of thicket in areas where it used to occur.
64 : MAINLAND THICKET ECOSYSTEMS