CRITERIA FOR ASSESSING THE FAVOURABLE CONSERVATION STATUS OF Pelobates fuscus

Transcription

1 CRITERIA FOR ASSESSING THE FAVOURABLE CONSERVATION STATUS OF Pelobates fuscus PROJECT REPORT Securing Leucorrhinia pectoralis and Pelobates fuscus in the northern distribution area in Estonia and Denmark LIFE08NAT/EE/ RIINU RANNAP WOUTER DE VRIES LARS BRIGGS Tallinn 2012

2 Introduction Pelobates fuscus is a widely distributed amphibian species in Europe having an overall decreasing population trend. A particularly dramatic decline is seen within its northern and western distribution range (e.g. Fog 1997; Nyström et al. 2002, 2007; Briggs et al. 2008; Van Delft et al. 2010; Jooris et al. 2012), which explains the species being listed in Annex IV of the EU Habitats Directive (92/43/EEC). Such a status demands conservation efforts and an explicit understanding of the species habitat requirements to achieve favourable conservation status across the EU. The determination of the criteria for assessing the favourable conservation status of P. fuscus for Estonia and Denmark has been one of the targets of the LIFE-Nature project (LIFE08NAT/EE/000257) Securing Leucorrhinia pectoralis and Pelobates fuscus in the northern distribution area in Estonia and Denmark (DRAGONLIFE). In the framework of the project Estonian and Danish experts have simultaneously worked out the criteria for assessing the favourable conservation status of P. fuscus. This work has been based on several activities carried out in the course of the project. First of all the results of the evaluation of aquatic and terrestrial habitat characteristics gave a wider understanding of the species habitat requirements. This action provided new knowledge on the preferable breeding sites and terrestrial habitat components of P. fuscus, which are closely connected to the criteria for assessing the favourable conservation status of the species. Favourable conservation status When assessing the favourable conservation status of P. fuscus, the effective population size, structure of meta-populations (number of ponds, distance between ponds) and other parameters have been taken into account. In the course of the project, we have come to recognize that there are mainly two types of P. fuscus population structures present in Estonia and Denmark:

3 1. Isolated populations that do not have possibilities for immigration. Each isolated population is dependent on a single breeding pond or very few ones within a few hundred metres. 2. Meta-populations formed by several sub-populations of P. fuscus, which are connected to one another by migration corridors and ponds, functioning as stepping stones for the toads. Thus, individuals can migrate freely between sub-populations. Even if each subpopulation has only a single breeding pond, the whole meta-population system offers several breeding possibilities due to connectivity and retains in this way the stability of whole population. The criteria for assessing the favourable conservation status of P. fuscus differ according to the type of population structure. Isolated population The population must have regular reproduction success that provides on average several hundreds of juveniles annually. A complex of at least three source ponds, each 1,000 m 2 and in optimal conditions, can ensure such numbers of juveniles. Although populations can use only one breeding site and still survive during a long period, especially in the case of large waters with flood zones (> 0.5 ha) that give regular breeding success with a high number of juveniles, several breeding sites are still required to ensure a favourable conservation status of a species. The breeding waters must be large ( 1,000 m 2 ), fish-free, with naturally clean water (low conductivity) and an extensive zone of shallow water (up to 30 cm). The preferred sediment type of the breeding pond is clay for P. fuscus. Additionally, the breeding sites have to be sun-exposed (without shade), particularly in Estonia and to a lesser extent also in Denmark. The terrestrial habitat has to contain sandy and loose soil (at least within a 100-m radius around the breeding pond). Deciduous forest should be avoided in the close vicinity of the breeding pond. The presence of open landscapes with areas without intensive agricultural practices around the breeding site (e.g. extensive fields, vegetable gardens, dunes, gravel/sand pits and paths habitats with loose sandy soils where the toads can dig in and forage around) is important.

4 Intensive agriculture in the close surroundings of the breeding sites has to be avoided. Thus, agricultural land should be provided with a buffer zone (uncultivated land) with a minimum width of 10 m around each pond to avoid the direct influence of fertilizers and pesticides. In addition, fertilizer-free areas with loose soil (sand) should be available within 50 m from the pond to increase the survival of juveniles and adults during the breeding period. The habitat components (breeding sites, terrestrial foraging area, digging sites for hiding and hibernation sites) must be safeguarded in the area where the population occurs. The components of the habitat complex should be preferably situated within a distance of m. According to the knowledge gained from the DRAGONLIFE project, effective population size must be at least 500 adult toads, which means that the population must count during each decade peaks of at least 1,000 adults. Meta-population A meta-population can live in a landscape with a complex of aquatic sites. The specimens can easily migrate between different breeding sites, which allows for the exchange of individuals. The distance between sub-populations can be over 2 km in landscapes with larger source ponds (annual breeding success from 100 s to 1,000 s of offspring). In the case of smaller breeding sites the distance between sub-populations should be within one kilometre. Each sub-population must have nearly annual breeding success of hundreds to over 1,000 individuals. In large areas with numerous smaller sites, over 10 breeding sites are required, whereas in areas with larger breeding waters 2 to 3 reproduction sites with annual breeding success per sub-population should be assured. The breeding waters must be large (preferably > 1,000 m 2 ), fish-free, with naturally clean water (low conductivity) and an extensive zone of shallow water (over 30 cm). The preferred sediment type for P. fuscus is clay. Additionally, the

5 breeding sites have to be sun-exposed (without shade) in Estonia and to a lesser extent in Denmark. The terrestrial habitat has to contain sandy and loose soil (at least within a 100-m radius around the breeding pond) and no deciduous forests in the close vicinity of the breeding pond. The presence of open landscapes around the breeding site (e.g. extensive fields, vegetable gardens, dunes, gravel/sand pits habitats with loose sandy soils where the toads can dig in and forage around) is important. Intensive agriculture in the close surroundings of the breeding sites has to be avoided. Thus, agricultural land should be provided with a buffer zone (uncultivated land) with a minimum width of 10 m around each pond to avoid the direct influence of fertilizers and pesticides. In addition, fertilizer-free areas with loose soil (sand) should be available within 50 m from the pond to increase the survival of juveniles and adults during the breeding period. The habitat components (breeding sites, terrestrial foraging area, digging sites and hibernation sites) must be safeguarded in the area where the population occurs. The distance between two sub-populations with large breeding success should not be more than 2 km and there should be easily permeable migration corridors and foraging habitats. Thick brushwood, intensively used agricultural fields, roads with heavy traffic, etc. should be avoided. Migration possibilities between sub-populations have to be assured for the toads by maintaining sandy roads and pathways, uncultivated areas in field margins, fenced-out road verges, gardens, etc. Examples from the project During the LIFE-Nature project, several P. fuscus populations have been restored to achieve favourable conservation status. The following provides some examples from each country.

6 Estonia Karula National Park In Karula NP, the terrestrial habitats of P. fuscus consist mostly of coniferous forests, unfertilized grassland (pastures and hay fields) and fields, small gardens and farmyards. The main breeding sites for the toads are beaver floods and man-made ponds. The population of P. fuscus had probably been functioning earlier as one meta-population in Karula NP. However, in the beginning of the LIFE project successful breeding was recorded in only 13 water bodies. Currently, after large-scale breeding habitat creation and restoration (started in 2010), one larger meta-population and six isolated populations of P. fuscus exist in Karula NP. Each of the isolated populations needs to be developed, at least five potential breeding ponds have to be created or improved. It is vital to grow the populations to a size of 1,000 adult toads, and to a minimum of three ponds with annual breeding success. Thereafter the isolated populations should be connected to each other by creating and restoring high-quality breeding sites as potential stepping stones between the populations. Only in this way can the conservation status of P. fuscus be considered favourable in the entire Karula NP. However, in the core area of the park, where most of the project activities have been developed, the conservation status of P. fuscus can already be considered favourable. Emajõe-Suursoo A small and isolated P. fuscus population inhabits the southern border of Emajõe- Suursoo peat bog. The population is found in Ahunapalu village, which is situated on a sandy ridge surrounded by the bog and dense forest. Currently there are two ponds with annual breeding success of P. fuscus. The terrestrial habitat consists of small gardens, grasslands and sand paths. In the coming years the number of potential breeding ponds has to be increased up to 10. The actual number of water bodies depends on the size of the ponds. If at least five smaller ponds have annual breeding success, the population of P. fuscus will be considered to have a favourable conservation status for an isolated population.

7 Denmark Gribskov and Hilleroed municipalities Before the DRAGONLIFE project started, P. fuscus was recorded in 8 30 sites in Gribskov municipality and in sites in Hilleroed municipality, depending on the year of registration. Those existing sites were remnants of a former meta-population. In Gribskov municipality, all P. fuscus sites were situated outside Natura 2000 areas, while in Hilleroed, four P. fuscus sites were inside the Natura 2000 network. So far one former source pond of P. fuscus has been restored in Gribskov municipality (it was done in 2009, before the DRAGONLIFE project started). This pond became a very productive breeding site for the toad, giving hope for further colonization into the Natura 2000 area, because it is planned to dig and restore breeding sites also inside the Natura 2000 areas in Gribskov municipality. However, the populations in Gribskov municipality are very small and populating rather hostile landscapes; therefore, natural colonization of new breeding sites and the expansion of the population is questioned still. Thus, conditions for migration should be improved or artificial breeding and rearing programmes for the toad considered. In Hilleroed municipality, four existing P. fuscus populations form two sub-populations, which are currently isolated from each other, but one population is partly connected to the meta-population of Gribskov municipality. In Hilleroed municipality several ponds will be restored and created in the near future. For the rather fragmented meta-population which crosses the border of Gribskov and Hilleroed municipality, an estimated 100 ponds will be needed to reconnect the fragmented meta-population. In addition, a minimum of 50 smaller terrestrial habitats of 0.5 ha each should be created and 10 larger areas of 5 10 ha of dry grasslands on sandy soils established. For the other population in Hilleroed municipality, an estimated 30 ponds, 15 smaller terrestrial habitats and 2 larger areas of 5 10 areas with dry grassland on sandy soils should be established to reconnect this population to the larger population in the border region with Gribskov municipality.

8 References Briggs, L., Rannap, R., Bibelriether, F. (2008): Conservation of Pelobates fuscus as a result of breeding site creation. RANA, Sonderheft. 5: Fog, K. (1997): A survey of the results of pond projects for rare amphibians in Denmark. Memoranda Societatis pro Fauna et Flora Fennica. 73: Jooris, R., Engelen, P., Speybroeck, J., Lewylle, I., Louette, G., Bauwens, D., Maes, D (2012): De IUCN Rode Lijst van de amfibieën en reptielen in Vlaanderen. Rapporten van het Instituut voor Natuur- en Bosonderzoek 2012 (22). Instituut voor Natuur- en Bosonderzoek, Brussel. Nyström, P., Birkedal, L., Dahlberg, C., Brönmark, C. (2002): The declining spadefoot toad Pelobates fuscus: calling site choice and conservation. Ecography 25: Nyström, P., Hansson, J. Månsson, J. Sundstedt, M. Reslow, C., Broström, A. (2007): A documented amphibian decline over 40 years: Possible causes and implications for species recovery. Biological Conservation 138: van Delft, J.J.C.W., Creemers, R.C.M., Spitzen-van der Sluijs, A.M. (2007): Basisrapport Rode Lijst Amfibieën en Reptielen volgens Nederlandse en IUCN-criteria. Stichting RAVON, Nijmegen.