Ecology and management of alien plant invasions in South African fynbos: Accommodating key complexities in objective decision making

Abstract

a b s t r a c tInvasive alien trees and shrubs pose significant threats to biodiversity and ecosystem services in South African fynbos ecosystems. An ambitious initiative, the Working for Water program, commenced in 1995 to reduce the extent and impact of plant invasions. Despite substantial progress, the problem remains immense, and innovative ways of improving the efficiency of control operations are urgently needed. This study sought to develop a robust conceptual framework for effective management of the most important invasive alien plant (IAP) species. Two methods were applied in exploring the complexity of problems, thereby identifying appropriate response strategies. The DPSIR (Driving forces-PressureState-Impacts-Responses) framework and the Analytic Hierarchy Process (AHP) tool were used to design a strategy for prioritizing management actions. This strategy considers explicitly the most influential factors that determine the distribution, abundance, spread and impacts of IAPs. Efficient management of IAPs is constrained by multiple interacting environmental and socio-economic factors. Factors related to the fire-prone nature of the ecosystem and the characteristics of the invasive stands emerged as pivotal features for setting spatially-explicit priorities for management. Results of the analyses provide an objective and quantifiable perspective for improving the management efficiency. We conclude that considerable progress in controlling the spread of IAPs in fynbos ecosystems could be achieved by better coordination of management practices and by improving the quality of species distribution data.

Prioritizing species, pathways, and sites to achieve conservation targets for biological invasion

“…Krug et al 2009), or multiple species in particular regions or within particular taxa (e.g. invasive alien trees and shrubs that pose a threat to particular ecosystems; Roura-Pascual et al 2009). By contrast, prioritization schemes for action must often simultaneously consider many species, pathways and sites, but nonetheless need to be straightforward and quick to conduct (see right of Fig.…”

“…The invasibility of sites is rarely singled out to be quantified (Catford et al 2011), but in practice, species and site prioritization happen simultaneously (Forsyth et al 2012;Roura-Pascual et al 2009), although spatial heterogeneity is seldom explicitly incorporated into prioritization models (Leung et al 2012). Heat maps have been used with species distribution models, along with information on climate suitability to identify areas most vulnerable to multi-species invasion (Gallardo and Aldridge 2013).…”

A Cost–Benefit Approach for Prioritizing Invasive Species

“…Finally, Kumschick and Nentwig (2010) and Kumschick et al (2012Kumschick et al ( , 2015 developed frameworks to prioritize actions against alien species according to their impacts, incorporating expert opinions as well as the diverging interests of various stakeholders, thereby capturing, to some degree, a political issue that often underlies prioritization. Although the scoring approach has proven useful for guiding management prioritization (Roura-Pascual et al, 2009), the method has been developed outside of any formal optimization framework. In particular, this approach exhibits four major flaws: i) the assessment inevitably reflects expert judgments and scores can be controversial, ii) scores' aggregation is problematic, iii) management constraints and in particular costs associated with management activities are rarely explicitly taken into account, iv) interactions among species are, at best, superficially accounted for.…”

“…Echoing the increasing demand for simple tools that guide managers and politicians to optimize their investments based on objective and measurable criteria (Tilman, 2000;Roura-Pascual et al, 2009;Dana et al, 2014;Koch et al, 2016), we define the theoretical groundwork of a general ranking formula that could be used as a rule of thumb in order to design a reliable, easy to apply, and economically sound tool to derive management decisions. The paper proceeds as follows.…”

Assessing the flexibility of the Analytic Hierarchy Process for prioritization of invasive plant management

“…Existing applications of AHP in invasion management are often region or species-specific (e.g., Roura-Pascual et al 2009, Forsyth et al 2012, Hohmann et al 2013. Moreover, these studies do not directly demonstrate to managers that the AHP tool is adaptable to their specific management scenarios.…”