SPABIO - Dynamic spatialized bioeconomy of biological invasions: proof of concept for the management of Ludwigia sp. in Brière

Approaches

To address these shortcomings, SPABIO relies on transdisciplinary collaboration between ecologists, economists and natural environment managers to

(1) develop a new class of bio-economic models that are ecologically realistic and directly applicable to the concrete problems encountered by managers,

(2) provide proof of concept for this new theoretical framework using the case of water primrose (Ludwigia sp) in the Brière Regional Nature Park, and

(3) prepare the application of the theoretical framework to other IAS problems in various contexts.

SPABIO required a significant amount of work to digitise the spatial records of water primrose abundance and removal in Brière.

We then developed a Bayesian model adapted to the structure of the data collected by managers. The ecological model is a multi-state (4 abundance classes), dynamic (22 years) and spatialised (17,000 square cells of 1 ha) model. the model of the cost-effort relationship for removal is a multiple linear regression, and the bio-economic coupling of the two models is carried out via a cost-effectiveness calculation (cost weighted by the probability of reducing the abundance of water primrose).

Results

On managing the dynamics of water primrose

The ecological model suggests that the effect of uprooting depends on the abundance of the plant. When water primrose is very abundant in the environment, uprooting promotes a transition to lower abundances. On the other hand, when the environment is not heavily invaded, uprooting accelerates the invasion.

The economic model suggests a quasi-linear cost-effort relationship and therefore no economies of scale. Finally, the bio-economic coupling suggests that weeding is only bio-economically effective in heavily invaded areas.

Our results on water primrose in Brière suggest that the strategy of attempting to eradicate the plant when it is still not very abundant (known as the ‘invasion curve’ strategy) can be counterproductive. This is an extremely interesting and original finding that challenges the main golden rule of invasion management, namely the imperative to control lightly invaded areas as a priority in order to respond cost-effectively to the dynamics of invasion. Without calling into question the importance of early management actions, this result calls for a case-by-case application of this rule, categorising the invasions to which it applies and those to which it does not apply.

On the prioritisation of water primrose management efforts

Our bioeconomic analysis has produced fundamental results in terms of spatial prioritisation of management efforts, taking into account dispersion dynamics on the one hand and spatialised management costs on the other. In practical terms, and for the management of water primrose in particular, this result should lead to the abandonment of interventions in areas with low levels of invasion in favour of prioritising efforts in areas with high levels of invasion, and in particular focusing removal efforts on large canals with high levels of invasion (i.e. river transport routes).

On the form of data that can be integrated into modelling

The availability and quality of data from managers can limit the implementation of bio-economic models adapted to their needs. In Brière, the water primrose abundance data was already in GIS format, and formatting it for modelling did not pose a major problem. However, data on removal sites (spatial coverage, costs) were not available in sufficient quality. The future development of bio-economic models to support managers requires them to acquire a greater understanding of scientific data.

Participants

INRAE units involved

• UMR DECOD - Dynamique et durabilité des écosystèmes : de la source à l’océan
• UMR CEE-M - Centre d’Économie de l’Environnement de Montpellier - Université de Montpellier
• UMR PSAE - Paris-Saclay Applied Economics - Université Paris-Saclay / AgroParisTech

Partners

• UMR Ecobio - Ecosystèmes, Biodiversité, Evolution - Université Rennes
• AMSE - Aix-Marseille School of Economics 
• Parc Naturel Régional de Brière