spontaneous regeneration, but mainly over the long term and in areas with
low-density invasions.
Most restoration studies in South Africa are short term and are vegetationorientated (e.g. Galatowitsch and Richardson 2005; Blanchard and Holmes 2008;
Ruwanza et al. 2013a; Kerr and Ruwanza 2016; Ndou and Ruwanza 2016).
Recovery of other taxa is less well quantified, largely because of the untested
assumption that the recovery of native vegetation will facilitate the recovery of
other taxa and subsequently ecosystem services and functions (Kaiser-Bunbury
et al. 2017). Recent South African studies do indicate spontaneous recovery of
other taxa and a link to ecosystem services (Mgobozi et al. 2008; Colvin et al.
2009; Magoba and Samways 2010; Samways et al. 2011; Maoela et al. 2016;
Modiba et al. 2017). Invasive alien plant species were found to negatively impact
most on seed dispersers and nectar-feeding bird pollinators (Mangachena and Geerts
2017). Although a few bird species were still absent 10 years after vegetation
recovery, bird species richness and abundance recovered, and all feeding guilds—
including pollinators and seed dispersers—were represented (JR Mangachena,
unpublished data). However, this is likely to be context-dependant as invasive
alien species may contribute additional food sources to the benefit of some pollinators (Geerts and Pauw 2009). Ecosystem processes such as pollination might not
automatically be reinstated by restoring target plant species. But assessing these
processes will provide an indication of the sustainability of restoration projects
(Forup and Memmott 2005). A keystone species approach to restore ecosystem
services might be a cost-effective way to achieve this (Traveset and Richardson
2006).
More studies are required to measure the extent to which the removal of invasive
alien plant species will result in a restored ecosystem. In particular, clearing of
invasive alien plant species can hamper native vegetation recovery through overuse
of herbicides or the lack of follow-up clearing. This also adds additional cost to
restoration, enhancing the uneconomical nature of some restoration interventions.
Therefore, we argue that high quality alien control should be prioritised. Furthermore, invasive alien plant control is making very little progress, or none at all in
many areas (e.g. McConnachie et al. 2012). We caution against claiming large
potential ecosystem service benefits from the clearance of invasive alien plants
(Stafford et al. 2017), since the desired goal of restoring ecosystem structure and
function in support of these services might not materialise.
23.5 Best Practice: Restoration Implementation
23.5.1 Legacy Effects, Ecosystem Functions and Drivers
It is important to assess how different invasive alien species, and different levels of
density and duration of invasion, affect restoration potential. For example, N-fixing
alien Acacia species have higher negative impacts on the recovery potential of
678
P. M. Holmes et al.
low-density invasions.
Most restoration studies in South Africa are short term and are vegetationorientated (e.g. Galatowitsch and Richardson 2005; Blanchard and Holmes 2008;
Ruwanza et al. 2013a; Kerr and Ruwanza 2016; Ndou and Ruwanza 2016).
Recovery of other taxa is less well quantified, largely because of the untested
assumption that the recovery of native vegetation will facilitate the recovery of
other taxa and subsequently ecosystem services and functions (Kaiser-Bunbury
et al. 2017). Recent South African studies do indicate spontaneous recovery of
other taxa and a link to ecosystem services (Mgobozi et al. 2008; Colvin et al.
2009; Magoba and Samways 2010; Samways et al. 2011; Maoela et al. 2016;
Modiba et al. 2017). Invasive alien plant species were found to negatively impact
most on seed dispersers and nectar-feeding bird pollinators (Mangachena and Geerts
2017). Although a few bird species were still absent 10 years after vegetation
recovery, bird species richness and abundance recovered, and all feeding guilds—
including pollinators and seed dispersers—were represented (JR Mangachena,
unpublished data). However, this is likely to be context-dependant as invasive
alien species may contribute additional food sources to the benefit of some pollinators (Geerts and Pauw 2009). Ecosystem processes such as pollination might not
automatically be reinstated by restoring target plant species. But assessing these
processes will provide an indication of the sustainability of restoration projects
(Forup and Memmott 2005). A keystone species approach to restore ecosystem
services might be a cost-effective way to achieve this (Traveset and Richardson
2006).
More studies are required to measure the extent to which the removal of invasive
alien plant species will result in a restored ecosystem. In particular, clearing of
invasive alien plant species can hamper native vegetation recovery through overuse
of herbicides or the lack of follow-up clearing. This also adds additional cost to
restoration, enhancing the uneconomical nature of some restoration interventions.
Therefore, we argue that high quality alien control should be prioritised. Furthermore, invasive alien plant control is making very little progress, or none at all in
many areas (e.g. McConnachie et al. 2012). We caution against claiming large
potential ecosystem service benefits from the clearance of invasive alien plants
(Stafford et al. 2017), since the desired goal of restoring ecosystem structure and
function in support of these services might not materialise.
23.5 Best Practice: Restoration Implementation
23.5.1 Legacy Effects, Ecosystem Functions and Drivers
It is important to assess how different invasive alien species, and different levels of
density and duration of invasion, affect restoration potential. For example, N-fixing
alien Acacia species have higher negative impacts on the recovery potential of
678
P. M. Holmes et al.