of a species under specific circumstances as the underlying assumptions are often not
explicit. This can be problematic for species with no previous history of introduction
outside of their native range (no “invasion history”). Trade-offs between the optimal
investment and the optimal outcome need to be made when selecting an approach for
a risk assessment tool. Furthermore, the amount of knowledge available on a taxon
can limit the use of certain approaches. The statistical approach requires the input of
a substantial amount of data to train the model—without adequate knowledge about
the taxon and its behaviour as an invader, such models cannot be developed.
Furthermore, the final model requires data on only a few variables, which increases
the likelihood of this information not being available for some species. This emphasises the need for a risk assessment tool to accommodate situations where information on a species to be assessed is scarce or lacking.
Many tools approach this by applying the precautionary principle—if no data are
available on a species or a certain situation, preventing informed decision-making on
the risks involved, the species is by default deemed to be a high risk (e.g. Nentwig
et al. 2016). This principle is common practice and also anchored in international
agreements. For example, in the management of alien species, the IUCN (2000)
states that “unless there is a reasonable likelihood that an introduction will be
harmless, it should be treated as likely to be harmful”.
20.1.2 Risk Management
To reach sensible and effective management decisions, risk management considerations are fundamental. Ignoring management feasibility, benefits of the taxon, or
potential conflicts between stakeholders, has been shown to lead to unsuccessful and
wasteful management decisions (e.g. van Wilgen and Richardson 2012). The distinction between whether, as opposed to how, to regulate and manage a species relies
on estimating the risks it poses to the recipient environment and economy. For taxa
that are not yet present in an area, and for which decisions on importation are
required, this can be a relatively straightforward process: if the species poses a
high risk its importation should not be allowed, but if it poses a low risk the species
could be considered safe for import (e.g. Keller and Kumschick 2017). However,
decisions regarding taxa that are already present in an area, and in use for various
purposes, cannot solely rely on estimates of the risks they pose, but also depend on
management options available for the species. For example, many trees were
introduced into South Africa for forestry. Even though many of them threaten native
biodiversity, management decisions need to take into account the costs of management, the techniques and tools available, as well as the species life-history traits
(Wilson et al. 2011; Richardson et al. 2015). Further, management does not happen
in isolation from the rest of society; social perceptions and benefits need to be
assessed and accounted for (e.g. van Wilgen and Richardson 2012; Zengeya et al.
2017; see Shackleton et al. 2020, Chap. 24). Unlike in the risk assessment where
clear answers and probabilities are often provided to determine the level of risk, the
inclusion of benefits is dependent on the agendas of various role players, priorities of
578
S. Kumschick et al.
explicit. This can be problematic for species with no previous history of introduction
outside of their native range (no “invasion history”). Trade-offs between the optimal
investment and the optimal outcome need to be made when selecting an approach for
a risk assessment tool. Furthermore, the amount of knowledge available on a taxon
can limit the use of certain approaches. The statistical approach requires the input of
a substantial amount of data to train the model—without adequate knowledge about
the taxon and its behaviour as an invader, such models cannot be developed.
Furthermore, the final model requires data on only a few variables, which increases
the likelihood of this information not being available for some species. This emphasises the need for a risk assessment tool to accommodate situations where information on a species to be assessed is scarce or lacking.
Many tools approach this by applying the precautionary principle—if no data are
available on a species or a certain situation, preventing informed decision-making on
the risks involved, the species is by default deemed to be a high risk (e.g. Nentwig
et al. 2016). This principle is common practice and also anchored in international
agreements. For example, in the management of alien species, the IUCN (2000)
states that “unless there is a reasonable likelihood that an introduction will be
harmless, it should be treated as likely to be harmful”.
20.1.2 Risk Management
To reach sensible and effective management decisions, risk management considerations are fundamental. Ignoring management feasibility, benefits of the taxon, or
potential conflicts between stakeholders, has been shown to lead to unsuccessful and
wasteful management decisions (e.g. van Wilgen and Richardson 2012). The distinction between whether, as opposed to how, to regulate and manage a species relies
on estimating the risks it poses to the recipient environment and economy. For taxa
that are not yet present in an area, and for which decisions on importation are
required, this can be a relatively straightforward process: if the species poses a
high risk its importation should not be allowed, but if it poses a low risk the species
could be considered safe for import (e.g. Keller and Kumschick 2017). However,
decisions regarding taxa that are already present in an area, and in use for various
purposes, cannot solely rely on estimates of the risks they pose, but also depend on
management options available for the species. For example, many trees were
introduced into South Africa for forestry. Even though many of them threaten native
biodiversity, management decisions need to take into account the costs of management, the techniques and tools available, as well as the species life-history traits
(Wilson et al. 2011; Richardson et al. 2015). Further, management does not happen
in isolation from the rest of society; social perceptions and benefits need to be
assessed and accounted for (e.g. van Wilgen and Richardson 2012; Zengeya et al.
2017; see Shackleton et al. 2020, Chap. 24). Unlike in the risk assessment where
clear answers and probabilities are often provided to determine the level of risk, the
inclusion of benefits is dependent on the agendas of various role players, priorities of
578
S. Kumschick et al.