In semi-arid ecosystems, restoration success can be limited by poor establishment
from actively seeded species (Madsen et al. 2016). Seed enhancement technologies,
such as polymer seed coatings containing germination stimulants (e.g. smoke
extract), have been shown to improve restoration success (Turner et al. 2006).
Embedding the broadcast seed into the soil by raking and sowing at the optimal
time of year greatly improved recruitment response (Turner et al. 2006).
Hydroseeding is one mechanised method commonly used in roadside revegetation
projects, but can be useful, albeit expensive, in areas accessible by vehicles (Martin
et al. 2002). If the application slurry includes additives such as germination stimulants, mulch and organic soil binders, this can improve restoration efficiency compared to dry broadcasting methods.
For both seed and cuttings, it is important to collect material from the nearest
remaining natural remnant, and also to match the habitat type for edaphic, hydrological and climatic variables, to improve the chances of establishment. Propagated
material should be grown to develop strong rooting systems relative to shoot growth
and preferably be grown in local soil and hardened off before planting to minimise
planting shock and optimise establishment. Many plant communities develop in
clumps rather than as regularly-spaced individuals, as positive interactions among
individuals such as simple sheltering effects, can promote establishment. Where
clumps or windbreaks may facilitate establishment, artificial wind breaks or alien
slash should be used to create shelters. Furthermore, careful species selections that
maximise trait diversity, or match niche requirements of the invasive alien species
likely to re-invade, can enhance the likelihood of restoration success (Funk et al.
2008; Laughlin 2014).
Increasing surface roughness after fire, for example by using felled alien
branches, can help to reduce surface erosion by raising the boundary layer and
promoting the trapping of wind-dispersed native seeds from neighbouring intact
remnants. Transferring seed-bearing branches of native pioneer shrubs to a burnt
riparian zone resulted in good recruitment and augmented a sowing treatment
(Pretorius et al. 2008). Where soil erosion may be a potential problem on steep
slopes after alien control, both physical and biotic interventions should be considered. Alien logs or biomass may be pegged or stacked across the slopes to trap
sediment and short-lived, commercially-available, non-invasive species sown to
provide short-term soil surface stability. An example of the latter is the use of
commercial wheat in nutrient-poor fynbos ecosystems, as it does not grow too
vigorously or produce a viable seed bank under such conditions.
Granivores such as mice and gerbils may be prominent and voracious following
alien clearance, therefore faunal control could be considered. For small mammals,
the encouragement of raptors through erecting suitable perches on the restoration site
may have a positive impact. Herbivores such as antelope preferentially browse or
graze young vegetation, targeting the establishing plants, and the use of exclosures
may be justified to ensure establishment.
Restoration of highly-degraded ecosystems to sustainable, fully functional natural
ecosystems could take a long time, representing several generations or recruitment
events (e.g. 45+ years for 3 generations in fire-driven fynbos). The reasons for this
23 Biological Invasions and Ecological Restoration in South Africa
689
from actively seeded species (Madsen et al. 2016). Seed enhancement technologies,
such as polymer seed coatings containing germination stimulants (e.g. smoke
extract), have been shown to improve restoration success (Turner et al. 2006).
Embedding the broadcast seed into the soil by raking and sowing at the optimal
time of year greatly improved recruitment response (Turner et al. 2006).
Hydroseeding is one mechanised method commonly used in roadside revegetation
projects, but can be useful, albeit expensive, in areas accessible by vehicles (Martin
et al. 2002). If the application slurry includes additives such as germination stimulants, mulch and organic soil binders, this can improve restoration efficiency compared to dry broadcasting methods.
For both seed and cuttings, it is important to collect material from the nearest
remaining natural remnant, and also to match the habitat type for edaphic, hydrological and climatic variables, to improve the chances of establishment. Propagated
material should be grown to develop strong rooting systems relative to shoot growth
and preferably be grown in local soil and hardened off before planting to minimise
planting shock and optimise establishment. Many plant communities develop in
clumps rather than as regularly-spaced individuals, as positive interactions among
individuals such as simple sheltering effects, can promote establishment. Where
clumps or windbreaks may facilitate establishment, artificial wind breaks or alien
slash should be used to create shelters. Furthermore, careful species selections that
maximise trait diversity, or match niche requirements of the invasive alien species
likely to re-invade, can enhance the likelihood of restoration success (Funk et al.
2008; Laughlin 2014).
Increasing surface roughness after fire, for example by using felled alien
branches, can help to reduce surface erosion by raising the boundary layer and
promoting the trapping of wind-dispersed native seeds from neighbouring intact
remnants. Transferring seed-bearing branches of native pioneer shrubs to a burnt
riparian zone resulted in good recruitment and augmented a sowing treatment
(Pretorius et al. 2008). Where soil erosion may be a potential problem on steep
slopes after alien control, both physical and biotic interventions should be considered. Alien logs or biomass may be pegged or stacked across the slopes to trap
sediment and short-lived, commercially-available, non-invasive species sown to
provide short-term soil surface stability. An example of the latter is the use of
commercial wheat in nutrient-poor fynbos ecosystems, as it does not grow too
vigorously or produce a viable seed bank under such conditions.
Granivores such as mice and gerbils may be prominent and voracious following
alien clearance, therefore faunal control could be considered. For small mammals,
the encouragement of raptors through erecting suitable perches on the restoration site
may have a positive impact. Herbivores such as antelope preferentially browse or
graze young vegetation, targeting the establishing plants, and the use of exclosures
may be justified to ensure establishment.
Restoration of highly-degraded ecosystems to sustainable, fully functional natural
ecosystems could take a long time, representing several generations or recruitment
events (e.g. 45+ years for 3 generations in fire-driven fynbos). The reasons for this
23 Biological Invasions and Ecological Restoration in South Africa
689