Long-term dynamics of and potential management strategies for the beaver (Castor fiber) population in Poland

Abstract

In the medieval period, beavers were widespread throughout Poland. In the 13th century, the number of animals began to decline. After the Second World War, it was assumed that Eurasian beavers were no longer present in Poland. In 1974, the programme “Active protection of European beavers in Poland” was launched. Reintroduction was a very important element of the active protection of beavers. According to an inventory carried out in 1977, there were estimated to be over 1000 individuals. Long-term reintroduction efforts by hunters and scientists have caused beavers to be present throughout Poland. In recent years, the beaver population has increased significantly. This situation has created conflicts between farmers, foresters and beavers. In Poland, the beaver is considered a partly protected species. This manuscript discusses the dynamics of the beaver population in Poland and needed actions for future sustainable management.

Keywords:

• Eurasian beaver
• beaver population
• beaver management
• Poland

Historic distribution and population trends

In the medieval period, beavers were widespread throughout Poland (Sawicki 1989). Nobles and kings created protections for the beavers. In the 11th century, King Boleslaw the Brave forbade beaver hunting on his land. He created a beaver protection office, which looked after the beavers (Wdowińśka & Wdowiński 1975). The number of beavers began to decline rapidly in the 13th century. The Lithuanian Statute that had been enforced since the middle of the 16th century contained provisions concerning the protection of beavers in Polish lands. After 1805, beavers were only present in the Neman, Pisa and Pasłęka regions (Linstow 1908). In the 19th century, hunting intensification led to a reduction in the entire beaver population. There were no beavers in Poland during that time period (Łoziński 1881). It has been estimated that approximately 1200 specimens survived the 19th century in Europe (Halley & Rosell 2002). In the interwar period, beavers were found in the Neman and Pripyat basins. After the Second World War, it was assumed that Eurasian beavers were no longer present in Poland. Naturalists from the USSR were then asked to deliver a number of beavers to establish a population in Poland. In 1948, the first beavers from Voronezh, Russia, were brought in. Recovery of the beaver population was unsatisfactory until 1970 due to incomplete protection of the species. Therefore, in 1974, the programme “Active protection of European beaver in Poland” was launched (Kasperczyk 1990). The programme was implemented in cooperation with scientists from the Polish Academy of Sciences and hunters from the Polish Hunting Association. The reintroduction was a very important element of the active protection of beavers. According to an inventory carried out in 1977, the number of individuals in Poland was estimated at over 1000 individuals (Żurowski 1979), and in 1987, the number of Eurasian beavers in Poland was estimated at approximately 3000. At the end of the 1990s and after 2000, the beaver population in Poland was so large and widespread across the country that the species was no longer threatened with extinction. According to various data, the size of the beaver population ranged from 15 000 to 20 000 individuals (Czech 2000). The long-term reintroduction efforts of hunters and scientists have resulted in the presence of beavers throughout Poland. The dynamic population growth observed in recent years has been replaced by the stabilization of the population. (Figure 1). The diagram of the population growth is a sigmoidal curve. This curve effectively describes population increase in the past and present stabilization of the beaver population in Poland. This pattern has been confirmed by the studies of various authors (Hartman 1994, 1995; Korablev et al. 2011; Šimůnková & Vorel 2015).

Figure 1. Beaver population in Poland (Rozkrut 2018)

Genetics

The beaver population in Europe was restored with specimens from Eastern Europe. The expansion of the population from the west might have caused genetic enrichment. Studies have demonstrated genetic differences between the western and northeastern populations in both the control region of mitochondrial DNA and microsatellite markers (Biedrzycka et al. 2014). There has been no documented reintroduction of Western European beavers to Poland, so the observed situation may be a consequence of natural migration. Considerable differentiation was also identified within the mtDNA control region. This finding points to the possibility that additional relic populations survived in Poland and Germany (Biedrzycka et al. 2014) in addition to the eight known populations that survived the 19^th century (Halley & Rosell 2002).

Potential remedies to the population growth

In the early 1990s, the need for local reduction of beavers began to increase in Poland. Beaver can be harvested through trapping and hunting. Under the conditions in Poland, population reductions should be carried out in areas with a very high densities of beavers or in cases where removal of problem animals is required. In Poland, the beaver is considered a partially protected species, and hunting is allowed depending on the damages caused to landowners and forest owners. The regional director for environmental protection may allow the killing of individual animals, translocation of animals to other locations and destruction of dams and burrows unless alternatives are available, with the provision that these actions do not harm the conservation of the wild populations of a protected animal species. The application should describe the damage and hazards that may arise as a result of the activities of the beavers. It is also necessary to describe the place where the damage occurred and to describe alternative activities that were carried out before applying for permission to reduce the beaver population. Shooting is performed by hunters from the Polish Hunting Association. Obtaining a license does not necessarily mean that the number of permitted animals will be shot (Figure 2). Hunting is often ineffective because hunters are reluctant to hunt beavers. The reason for this is the lack of a tradition of beaver hunting, the difficulty of hitting a beaver, or the difficulty of caring for a dead animal because of the difficult terrain. In addition, based on the experience of the countries where hunting is allowed, it can be concluded that this strategy is effective in reducing damage. Killing several individuals usually does not cause the family to leave the territory. Killing all individuals in a family is extremely technically difficult and not very effective because in areas with high beaver abundance, the vacant space is immediately occupied by young, wandering individuals.

Figure 2. Issued permission to reduce beavers (Domańska 2018)

According to the data regarding the use of individual licences for beaver culling, it should be noted that from 2012–2015, licences were issued for the elimination of over 19,000 individuals (Figure 2), while the implementation of those licences accounted for a total of 1,500. This figure indicates that only approximately 8% of the animals that were licensed for removal were killed. This statistic shows the difficulty of regulating the population level of the species in question, which leads a predominantly nocturnal and aquatic lifestyle (Szweda-Lewandowski 2016). The number of licences issued has increased substantially from 2014 (Figure 2), which may have been affected by the increase in conflicts noted during that period (Table I).

Table I. Number of reported conflicts and compensation payments (Domańska 2018)

	2013	2014	2015	2016	2017
Number of reported conflicts	5451	6228	6410	6054	5735
Payment of compensation in thousands Euro	3474	3947	4000	4043	5192

Conflicts

In Poland, the conflicts caused by beavers affect both agricultural and forest areas. Most frequently, the beavers cut down trees and flood the land is flooded, blocking the culverts and destroying the causeways. In addition to damage to agricultural and orchards, the problem is also the destruction of old trees, which are particularly valuable in nature and are impossible or very difficult to replace. In forest areas, beavers most frequently cause the land to fill with water by blocking culverts, destroying dykes, and digging canals. As a consequence, the forest weakens or dies. In the vicinity of the waterfalls, the threat is the shearing of trees. Forest damage caused by beavers is reported to be very rare. In the case of water management, the most important damage is the excavation of pond dykes and flood embankments. The beavers also block drainage ditches and culverts. In the case of communication routes, trees occasionally cut off on roads or on railway lines. In the case of damage to agricultural land, the owners of the farms report noticeable losses and demand compensation. To claim compensation for beaver damage, individuals should apply to the Regional Directorate for Environmental Protection. Since 2015, there has been a noticeable decline in the reported conflicts with a simultaneous increase in the population. The reason for this may be a better understanding by people of the benefits provided by beavers. Education in this field may be related to the improved understanding. In addition, landowners are getting used to the presence of beavers in their area. They are aware of the potential effects of dams and use devices to limit the effects of rapid changes in water levels (Campbell-Palmer et al. 2016; Hawley-Yan 2016).

Between 2013 and 2017, an increase was noted in the value of the compensation payments, along with an uneven rise in the number of reported conflicts (Table I). The maximum number of reported conflicts was in 2015. This may have been due to a rule that had been enforced since 2014 that awarded compensation to people and entities conducting business connected with agriculture, forestry or fishery. Until 2014, people and entities that did not belong to this group could not apply for compensation and therefore did not report the conflicts or have the necessity to resolve them.

From 2011–2013, an analysis was conducted of the proportions of the types of individual sites where beaver damage occurred (Przybycin et al. 2014). This analysis showed that the most common forms of damage were as follows: flooding and other damage in grasslands (meadows and pastures) – 45.5% of all damage; trees gnawed and cut down (excluding to fruit trees) – 27.3%; damage to dykes and embankments of farming ponds (including losses of fish) – 3.3%; flooding and other damage to arable land – 3.1%; damage to orchards (flooding and gnawing of fruit trees or other plantations) – 2.9%; and flooding of forest stand and tree plots (excluding to fruit trees) – 1.6%. Most reports of damage concerned flooding of grasslands and felling of non-fruit trees. The amounts allocated for compensation for these two categories of damage accounted for approximately half of the budget allocated for all compensation for damage caused by beavers.

In addition, it is assumed that the amount of damage reported is not necessarily proportional to the amount of damage actually inflicted. Reports are often the result of the individual decisions of the owners of the damaged properties. Damage caused on land managed by the Treasury is generally not reported for compensation, and this covers 24.1% of the area of the country. Another reason for damage not being reported is that it may be downplayed by the owners and lessors of large farms.

An important element of creating beaver populations in indicated areas is the level of conflict. The methods for solving problems related to the presence of beavers are as follows:

• Compensation - This method is rarely used in other countries (Czech 2000; Schaller 2007; Gaywood 2018) and represents a serious burden on the budget of the voivodships. This strategy does not solve the conflict, but compensates for the damage to a certain extent.

• Resettlement - In the event of a conflict, all the beavers in the given location are caught. However, when the beaver density in a given area is large, the vacated position is rapidly colonized by other beavers, and within a few consecutive years, the conflict reappears.

• Destruction of dams - Dismantling of dams is possible but requires permission from the relevant services. The effectiveness of this method is not high because the beavers quickly rebuild the dam and most often in the same place.

• Securing land and upgrading of dams - Conflicts also occur in the areas that protect culverts, that contain fencing or where dam modernization is occurring. Methods to minimize or mitigate conflicts are based on the application of appropriate technical strategies, such as protection and expansion of the shorelines of watercourses and reservoirs, the protection of valuable trees with wire mesh wrapping, and the protection of potentially threatened culverts through the use of pipes and nets (Campbell-Palmer et al. 2016; Hawley-Yan 2016).

Population stabilization

Since their reintroduction in Poland in 1974, the beaver population has grown to 124 thousand individuals (Rozkrut 2018). The population has been stable in recent years, which is very characteristic and, as mentioned before, has also been seen in other countries. Are we dealing with population stabilization? It is difficult to determine the direct cause of this phenomenon. Staged beaver expansion has been postulated as one of the reasons for the stability (John et al. 2010). Initially, beavers choose habitats that are rich in food. Later, as the rich-in-food habitats become increasingly populated, the beavers expand to those which they had previously rejected. Diminished food reserves result in lower chances of survival. An additional element may be the territorial behaviours of beavers (Nolet & Rosell 1994; Campbell et al. 2005). New individuals that attempt to settle in an already occupied area encounter aggressive responses from the residents as a new member would cause an overcrowded population. Tourists disturb beavers indirectly, affecting their propensity to propagate (Nolet et al. 2005); as a result, beavers begin to look for more isolated territories. It is generally believed wolves, which are natural enemies of beavers, have a considerable effect on reducing the population of the latter. However, there are studies that contradict this thesis (Busher & Lyons 1999; Baker & Hill 2003; Nitsche 2016). An important contribution to this field has been made by observations based on GPS records of confirmed incidents of wolf attacks on beavers (Gable & Windels 2017). It seems, however, that research into this area is insufficient to fully understand effects of wolves on local beaver populations (Gable et al. 2018).

Conclusion

There is no overall pan-European programme or recommendations regarding beaver population management. This lack of cohesive strategy is obvious as the legal solutions that are adopted vary among individual countries. Due to the large number of individuals, none of the methods that have been suggested for conflict resolution work in some areas. This is a major problem that increases dissatisfaction among the people affected by the losses caused by beavers. Therefore, education is an important element. The goal of education is to make people aware of and create the possibility of solving conflict through allowed methods. However, it is necessary to undertake activities that ensure long-term coexistence between beavers and humans.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This work was supported by the Ministry of Science and Higher Education through a Forest Research Institute statutory activity [280122]. The publication is co-financed within the framework of Ministry of Science and Higher Education programme as “Regional Initiative Excellence” in years 2019-2022, project number 005/RID/2018/19.