The objective of this work is to describe risk reduction measures for the terrestrial life stages of amphibians that can be recommended independent from the approval of plant protection products (PPP). These measures should be able to reduce the risk of PPP exposure, as well as promote amphibians in agricultural areas and compensate for the negative effects caused by PPP at the population level. In particular, we evaluated existing measures for ecological compensation and PPP risk reduction, and took changes in agricultural practice also into account.
With the help of a literature review and a survey of cantonal advisory agencies, we compiled potential risk reduction measures. In addition, existing measures for other organism groups and measures defined by the Federal Council by means of new regulations for the application of PPPs were examined with regard to their effect on amphibians. All measures were evaluated by interviewing experts with regard to their effectiveness for the protection or promotion of amphibians, their feasibility on a farm, as well as their controllability. The impact on production was not quantified as part of this project.
A total of 30 measures were considered conceivable in Switzerland. Of these, nine risk reduction measures are proposed for practical application, whereby a forward-looking and constructive cooperation between agriculture and amphibian conservation will be important for their implementation. In part, these measures are already being implemented or promoted, but they can be adapted more specifically for amphibians based on this work; in turn, the measures would benefit other animal groups in addition to amphibians. In principle, the combination of measures can increase their impact.
Workshops for farmers and agricultural advisors: raising awareness forms the basis for the successful implementation of risk reduction measures and promotes the conscious and careful use of plant protection products and thus the protection of amphibians.
No local application of plant protection products on migration routes during the main migration period of amphibians in spring: this measure requires a differentiated consideration depending on the occurrence of the species and the time of migration. The expected impact would be very high, as direct contact of migrating amphibians with pesticides would be avoided. It mainly benefits the most common species (common frog, common toad, alpine newt). A prerequisite for implementation is a good forecasting model for the timing of amphibian migration; furthermore, it would have to be clarified whether the measure would lead to yield losses.
No (or time-limited) application of plant protection products in area B of amphibian breeding sites of national importance: with area B comprising terrestrial habitats adjacent to breeding sites and parts of migration corridors, they are intended to protect populations of rare species and also significant populations of common species. For individual populations, this measure would have a high impact. In sum, only a few breeding sites would be affected. Approximately 10 % of all amphibian breeding sites are included in the inventory of amphibian breeding sites of national importance. Across Switzerland, about 1008 ha of pesticide-relevant crops are cultivated within area B perimeters.
Spatial arrangement of biodiversity promotion areas: the spatial arrangement of biodiversity promotion areas is very important to their protective function and enhancement of terrestrial habitat. Biodiversity promotion areas could, for example, be targeted along migration routes or near breeding sites. Basics provided in this work should simplify the implementation. The measure is considered to be well feasible and effective, but needs a differentiated consideration and good advice.
Site-specific creation of small structures that can serve as hiding places for amphibians in the terrestrial habitat: these include, for example, wood and stone piles, but also other structural elements such as groups of shrubs and water ditches. These provide suitable habitat for amphibians and are already familiar to farmers. The creation of small structures at field edges, in biodiversity promotion areas or around amphibian breeding sites is considered to be particularly effective and easy to implement. This measure can help to increase the survival of juveniles in particular, which are especially important for the viability of populations.
Integrative water management: climate change requires a reconsideration of agriculture. Retention ponds, for example, can be created to ensure the irrigation of agricultural crops. If these are planned appropriately, they would also create new breeding habitat for amphibians. This is a future-relevant topic with a lot of potential for amphibian protection. The feasibility requires a combined planning of land and water management along with amphibian and nature conservation.
Construction of new amphibian breeding sites: the construction of new breeding waters was judged by herpetologists to be an extremely effective risk reduction measure. While proven methods can be used for the construction of breeding waters, their acceptance by farmers may be low (e.g. because of legislation over the distance requirements of the use of plant protection products near water bodies). Agricultural advisors could play an important role here. Population models show that the establishment of breeding waters is the most effective measure to promote metapopulations of amphibians at the landscape level. Analysis of migration routes between breeding waters provides an overview of where new breeding waters can contribute to population connectivity.
Establish wet rice as a special case of amphibian breeding waters: wet rice fields could substantially support amphibian populations, especially the late breeding species that prefer temporary waters. At the same time, a niche product is produced (Swiss rice), which can be sold at attractive prices directly from the farm. Ecological cultivation of wet rice will be financially supported as a biodiversity promotion area type starting in 2024. This measure is proposed based on new research results (www.nassreis.agroscope.ch); it was not part of the evaluation procedure of the project.
Adapted management in the vicinity of amphibian breeding waters: this refers, for example, to extensive agriculture or the use of drift-reducing nozzles. This was evaluated as a very effective measure, especially since the choice of nozzles does not affect agricultural production and the nozzles are already widely used.
Further research contributions from this project provide a scientific basis for the selection of locally adapted measures and their implementation. With models of the dynamics of populations and metapopulations of amphibians, we describe the potential effects of plant protection products and provide information on how amphibian populations respond to risk reduction measures. In this way, measures can be identified that have the greatest effect on amphibian populations. We also analyzed amphibian use of agricultural landscapes on a national scale and show where populations potentially live on agricultural lands where PPPs are used. This work provides baseline information on where and when to best protect which species and life stages and how. For example, based on modeling, protecting tadpoles and especially juveniles (after metamorphosis) appears to have the greatest protective effect on populations. Regionally, the creation of new breeding waters (with suitable terrestrial habitat) represents the most efficient measure. At the local level, small structures in terrestrial habitat or on seasonal migration routes are also considered effective. Risk reduction measures should be selected and implemented on a species-specific basis. For example, in the natterjack toad field study, the toads were observed to use cropland as terrestrial habitat because they prefer open soils. Therefore, biodiversity enhancement areas with open soils would be a promising enhancement measure to promote natterjack toads. Although enhancement programs are often species-specific and species vary in local occurrence, mapping indicates that amphibians are not exceptional in agricultural areas, but are potentially widespread. Highly endangered species, in particular, have a high likelihood of coming into contact with plant protection products, especially on potential migration routes between amphibian breeding sites.