Environmental Engineering Reference
In-Depth Information
Table 20.2
Change in fynbos ecosystem structure and function with pine invasion indicating key disturbance variables and
disturbance response variables.
Transition
state (see
Figure 20.5)
Description of invasion impacts
Key disturbance
variables
Key response
variables
1
- Main impacts of pine invasions results from the
increased abundance of trees in habitats where
this life form was previously absent or less
common.
Shift in life form
dominance
Increased biomass
Altered composition
and structure of
above-ground
vegetation
2
- Pine invasions reduce native vegetation cover from
75 % to 20% and the total number of species by
58% from 298 to 126 species. Mean plant density
reduced from 260 to 78 plants m
−
2
.
- Pines are more effective users of resources
increasing competition for native species.
- Stands invaded by pine have signifi cantly lower
species richness, native plant cover and density
than pristine fynbos communities.
- Dense pine stands suppress fynbos species,
threatening many taxa with extinction.
- Large fuel loads cause intense fi res in dense pine
stands, causing increased overland fl ow and
accelerated soil erosion.
- Pine invasions might negatively impact on
arbuscular mycorrhizal infectivity after long term
invasion.
- After four decades of pine invasion fynbos seed
banks are depauperate
(Richardson & van Wilgen 1986, Richardson &
Higgins 1998, Holmes
et al
. 2000)
Increased resource
competition
Increased fi re
intensity
Altered microbial
systems
Decline in species
richness
Decline in functional
groups
Depleted native seed
bank
Figure 20.5
Pinus
invasion of
fynbos illustrating different
ecosystem states and thresholds as
invasion intensifi es. The triangles
represent invasion impacts by alien
Pinus
and the disturbance variables
that lead to each system state; the
matrix represents the fynbos
ecosystem and its response variables.
Thresholds are indicated by the thick
black lines. Appropriate
management actions to restore the
ecosystem are listed in the right-
hand column.
