The Ecology and Conservation of Puma concolor in North America

Puma concolor. Source: U.S. National Park Service

The Ecology and Conservation of Puma concolor in North America

The cougar, Puma concolor, is a large American cat, up to 2.6 m in length, with a comparatively small, rounded head with muscular jaws and characteristically rounded ears. It has a uniformly beige coat; the uniformity of colour is expressed in the cougar’s Latin name, concolor, and differentiates it from any other American cat species, all of which, for example the lynx, are patterned to some degree (Miller, 2007).

Taverna et al. (1990) describe the habitat of the cougar as being the most wide-ranging of any large American carnivore, inhabiting rocky outcrops, low to dense shrub, chaparral, and densely wooded areas. Maehr et al. (2004) even identifies shopping centres in Florida as viable habitat for the cougar, where the animals exhibit similar traits to populations living in naturally sparse landscapes.

The cougar was once widespread throughout the whole of the United States (Sweanor, et al.,1999). Human persecution forced the cougar into remote western regions, effectively removing it from the eastern states. P. concolor has a range encompassing 13 western states, while subspecies P. concolor coryi and P. concolor stanleyana exist in Florida (Maehr et al., 2002).

Habitat fragmentation, mainly by the building of roads is leading to cougar ranges being limited (Beier, 1993), and a need for a minimum habitat area study for cougars has been identified in order to properly maintain cougar numbers in the face of social, industrial and economic progress.

Husseman et al. (2003) found that wolves and cougars share a prey base. Elk form the main prey item for wolves and cougars. Mule deer, bighorn sheep and mountain goats make up the rest of the prey base. However, wolves were found to be more likely to take juveniles of all prey species, while cougars were able to take adults, reducing direct competition.

Beier (1993) reported that the independent nature of adult female cougars acted to regulate density, and that male density was separately defined by the territorial nature of adult males. Female density is primarily regulated by vegetative land cover, geological factors, and prey accessibility, since it is her responsibility to raise young and provide suitable cover and sustenance for them. Male numbers are affected by competition for females, and so their range is partially delimited by the same abiotic factors that influence distribution of females. However, since ground cover is less of an issue for the adaptable cougar, it is behaviours, particularly sexual and parental, that govern range, with ranges being relative to those of other adults, and density regulation may therefore been seen as an extension of behavioural factors.

Population dynamics are further affected by competition from bears and wolves, where those species’ ranges overlap with cougar territories (Riley et al., 2004). Wolves are being actively reintroduced throughout the western United States, and there is a projected conflict of interests between both conserved species (Sweanor et al., 2000). White-tailed deer are colonising many valley locations in the western states(Ripple, 2006), and these are being followed by cougars not normally associated with valley environments. In fact, wolf habitation of valleys may have affected cougar range at the time when these two species were first learning to live together, and may have been the deciding factor in limiting cougars to higher altitudes in those areas.

The recent cougar colonisation of valleys, such as those in Yellowstone National Park, has led to confrontations between wolves and cougars, in some cases leading to mortality in both species (Knopf, 2009). Wolf conservation is therefore impacting on cougar regeneration, forcing the cats to live in less desirable habitats, such as rocky areas to which the cougars are better adapted than the wolves.

The sampling and monitoring techniques currently employed by scientists looking at the regeneration of P. concolor in North America are various and range from active trapping (Sweanor et al., 2000) to passive tracking (Miller, 2007).

Spring activated animal snares were set up around Wyoming by Sweanor et al. (2000) to capture independent adults and mature cubs. These animals were ear-tagged, radio-collared and marked with coded ear tattoos. In a separate study in Florida, radio-tagged cougars were monitored by aircraft (Maehr et al., 2002)

Bounties were regularly paid to cougar hunters (Knopf et al., 2009; Riley et al., 2004), and although this practice has ceased, the term bounty is still used to refer to hunted animals. However, cougars have been reclassified as game animals and are still hunted in all states except California and Oregon. Bag counts are currently limited to one kill per day per season, and kills are recorded, leading to a reliable system of cougar population assessment. Changes in hunting style have led to conflict with new legislation, however: the practice of treeing has been banned in all states except Texas (Sweanor, et al., 2000). This entails hunting a cat with dogs until it runs up a tree. The cat is then surrounded and shot at close range. Although curtailing overt cruelty towards cougars, the ban on treeing has had the knock-on effect of reducing the amount of time a hunter has to look at the animal before killing it. Legislation limits the killing of females; when treeing an animal, hunters could differentiate between males and females and spare the latter. Now, however, both sexes are shot indiscriminately.

A roadkill survey in Florida by Lotz and Land (2007) estimated the Florida cougar population and set out to discover the relationship between road deaths and recorded births. The lowest annual estimate of cougar births was determined by analysing birth and death rates of known cougar populations as well as numbers of cougar bodies found on local roads. It was found that the amount of Florida cougar roadkills formed a set percentage of the total numbers of the cougar population, suggesting that the roads were disturbing established cougar ranges.

Cougars have dog-like tracks (Miller, 2007), but a number of features easily distinguish the two species. Kill sites can also identify predators: kill efficiency, wound depth and length, subcutaneous haemorrhaging, carcass entrance and covering of prey are all indicative of predator identity.

Ever since Europeans colonised the land mass now known as the United States, any dangerous animal was considered fair game (Knopf et al., 2009), and could be destroyed to protect livestock as well as the settlers. All wild animals were considered a food source in the early days of the formation of the United States, so cougars may well have been hunted for sustenance as well as for homeland security reasons.

Three waves of cougar management have occurred in modern times: firstly, an attempt at total annihilation, succeeded by managed sport hunting to ameliorate livestock depredation, and finally an ostensibly concerted effort to protect the cougar’s place in natural American ecosystems (Riley, 2004).

It has been demonstrated (Ripple et al., 2006) that the removal of cougars has allowed populations of their prey species, particularly ungulates, to multiply exponentially. These large numbers of unpredated ungulates in turn over-graze the native herbaceous biomass, leading to the collapse of trophic cascades and causing localised secondary extinctions.

However, P. concolor is now regaining some of its former North American territories (Gloyne et al., 2001; Maehr et al., 2002; Sweanor et al., 2000). This is due in large part to a relaxation of human persecution and a coordinated effort on behalf of the majority of states (Knopf et al., 2009), with the notable exception of Texas, where cougars are regarded as a pest species and hunting remains unregulated. Wildlife underpasses are also being used in Florida to counter habitat fragmentation (Lotz, M., Land, D., 2007) and are shown to be positively affecting local cougar populations.

In terms of habitat, the eastern regions of the United States present large, viable ecosystems into which the cougar can be reinserted. The cougar should be able to pick up its role as a top predator relatively easily in those areas where habitat allows, and suitable prey species still exist (Taverna, 1999). However, the cougar’s main obstacle to reintroduction in Northern America is the public. Beier (1991) suggests that the cougar’s negative image, caused mainly by an increase in attacks on humans as the cougar’s range extends towards concentrations of human habitation, could be positively altered through information campaigns, and by providing visitors to areas of known habitation with advice regarding possible encounters.

References

Beier, P., (1993). Determining Minimum Habitat Areas Habitat Corridors for Cougars.

Conservation Biology, 7, 94–108.

Gloyne, C., Clevenger, A., (2001). Cougar Puma concolor use of wildlife crossing

structures on the Trans-Canada highway in Banff National Park, Alberta.

Wildlife Biology, 7: 17-124.

Husseman, J., Murray, D., Power, G., Mack, C., Wenger, C., Quigley, H., (2003).

Assessing differential prey selection patterns between two sympatric large

carnivores. OIKOS, 101: 591–601.

Knopf, K., Jalkotzy, M., Boyce, M., Anderson, C., Lindzey, F., (2009). Cougar

Management in North America. Cougar: Ecology and Conservation, 4: 41–54.

Lotz, M., Land, D., (2007). Florida Panther Roadkills. Wild Cat News,

www.cougarnet.org.

Maehr, D., (2002). Florida panther dispersal and conservation. Biological

Conservation.106: 187–197.

Maehr, D., Larkin, J., Cox, J, (2004). Shopping centers as panther habitat: inferring

animal locations from models. Ecology and Society, 9: 1–9.

Miller, K., (2007). Puma Identification Guide. www.cougarnet.org.

Monroy-Vilchis et al., (2009). Cougar and jaguar habitat use and activity patterns in

central Mexico. Animal Biology, 59: 145–157,

Riley et al., (2004). Dynamics of early wolf and cougar eradication efforts in

Montana: implications for conservation. Biological Conservation, 120: 155 -167.

Ripple, W., Beschta, R., (2006). Linking a cougar decline, trophic cascade, and

catastrophic regime shift in Zion National Park. Biological conservation, 133:

397 –408.

Sweanor, L., Logan, K., Hornocker, M., (2000). Cougar dispersal patterns,

metapopulation dynamics and conservation. Conservation Biology. 14: 789-

808.

Taverna, K., Halbert, J., Hines, D., (1990). Habitat suitability analysis for the Central

Appalachians. www.heartwood.org.

Is There a Threat of Malaria in Britain and Ireland as a Result of Global Warming?

 Anopheles stephensi. Source: CDC

This blog post is based on my article called Climate Change Bites, originally published on Yahoo. That was in turn based on an essay I wrote as part of my degree studies. The essay won a Highly Commended award at the Undergraduate Awards in 2012. The information here is still valid, and there is, in my opinion, still a significant risk of widespread indigenous malaria occurring in the British Isles if temperatures continue to rise; this situation will be exacerbated by a stalling economy, which constitues a contributing factor not mentioned in the original essay, or in the article based upon it, which is reproduced below.

Malaria is one of the biggest health problems facing developing nations at present. It can cause severe fevers and is often fatal if untreated. But what is perhaps less well known is that malaria was once a problem native to Western Europe, including Britain and Ireland. Could it ever return to these countries? Given the suitability of a large percentage of land cover for mosquito breeding, and the possibility of global temperatures rising by at 2.5°C this century, it seems likely that malaria will once again become indigenous in Britain and Ireland within our children’s lifetime.

Let’s look at the reasons why malaria might become a problem in these countries. First of all, Britain and Ireland are particularly wet places, with a lot of standing water, such as lakes, wetlands, and fields impeded by slow-draining soils. This water cover provides ample habitat for indigenous Anopheles mosquitoes, the species that carry malaria. Anopheles mosquitoes behave as generalist aquatic breeders and will reproduce in almost any wet environment if undisturbed.

So the habitat,and the mosquito species that carry malaria are already present. But what about malaria itself? Malaria does occur in Britain and Ireland, but it is not yet indigenous. It is brought in by people returning from countries where malaria is a daily fact of life. But the infection is usually treated, and in those cases where it is not, malaria hits a brick wall. Why? The only reason that the species of Plasmodium responsible for this blood-borne disease do not multiply in these countries at present is because ambient temperatures are currently too low. The bottom line: it is too cold here for malaria to get a foot-hold. But that could change if temperatures rise. And that is precisely what climatologists are predicting.

What if that happens, and temperatures hit the required level for Plasmodium to reproduce? Well, another three prerequisites must be satisfied for malaria to become native: (1) people return from abroad carrying the disease and it goes untreated, (2) the specific mosquito hosts then bite the infected person/s, and (3) the parasite develops within the mosquito. Once all of these prerequisites have occurred, the infection may spread and malaria will soon have become indigenous.

But there may be some hope, even if that does happen. Because of the localised nature of the human-mosquito-Plasmodium relationship, the first outbreak of indigenous malaria is likely to be small and limited to a particular area, which will probably be marshy or coastal. If infections go unchecked, however, it is likely that the outbreak will spread; a worst-case scenario would involve an outbreak in an area with a high population density, such as London, Dublin, or Cork.

The mosquito species that carry malaria are already present in Britain and Ireland, as are the parasites responsible. It is only a matter of time before the climate in these countries changes sufficiently to allow malarial Plasmodium species to multiply and become indigenous. Whether it will then become epidemic is largely a matter for public health infrastructures to decide.

The Biodiversity and Conservation of Pollardstown Fen

Tufted Duck. Source: Wikimedia Commons

The Biodiversity and Conservation of Pollardstown Fen, County Kildare 

The protection of fen habitats and species in Ireland can be said to have begun in the late 1960s, when An Foras Forbartha conducted the first major national survey of peatlands, which concluded in 1974. This was the government‟s first organised response to losses of large tracts of peatland through increased development and turf cutting. The main objective of the survey was to identify which raised and blanket bogs required the most immediate conservation action. Dúchas took on the second survey which lasted from the early 1980s into the early 1990s, aiming to identify which sites had scientific importance. The sites identified by this survey were designated Areas of Scientific Interest (ASIs) but these had no legal basis. A further survey then resurveyed these ASIs and assessed them for redesignation as Natural Heritage Areas (NHAs). These were better protected than the ASIs, since NHAs were given statutory status under the Wildlife Act (1976).

This protection was further strengthened by the Wildlife (Amendment) Act, 2000. Ireland's programme of peatland conservation was then integrated with the European Natura 2000 system, which consolidated the legal protection of sites using new criteria and included lists of threatened species and habitats in the annexes of its main documents, the Habitats and Birds Directives. Further legislation covering fen conservation includes the Flora (Protection) Order, 1999, and the Planning and Development Act, 2000. The Environmental Impact Assessment Directive further consolidated the criminalisation of the destruction or disturbance of protected habitats and species, requiring that all development projects ensure that the ecology of a site of proposed work is thoroughly investigated before work commences, in many instances leading to the alteration or abandonment of projects on ecological grounds.

In effect, legislation protecting fens in Ireland is three-tiered: legislation is either Irish or European, forming the main two tiers. Non-legal international agreements form a third tier. To use Pollardstown Fen as an example, protection is offered by the following designations:

• Statutory Nature Reserve, with legal basis coming from the Wildlife Act, 1976, and the Wildlife (Amendment) Act, 2000, under which botanical and animal species as well as their habitats are conserved by law.
• Natural Heritage Area (NHA), with legal basis found in the Wildlife (Amendment) Act, 2000, which further conserves Irish species and habitats.
• Special Area of Conservation (SAC), under the Habitats Directive, and protecting annexed habitats and species of European importance from anthropogenic impacts.
• Ramsar Site, with no legal basis, although the convention does require parties to identify and preserve sites falling under the guidelines set out by the convention, typically of international importance, with designation made either by representativeness of the site or by the presence of a rare or endemic species.
• Biogenetic Reserve, designated by the European Council, and providing protection in  addition to that afforded by the Natura 2000 network. Precedes the Natura 2000 network, set up with the aim for scientific research and information exchange.

Of these designations, it is as an NHA and an SAC that Pollardstown Fen is afforded greatest protection, since these designations are founded in law. Any activity impacting negatively on the fen, its habitats or its supported species, may be subject to legal action.

Under the Habitats Directive, Ireland has designated a number of fens as Special Aeas of Conservation (SACs). The legal basis of the protection of SACs (and candidate, or cSACs) comes from Europe, and as such any derogations of legal protections or mitigations included in proposed works must be reported to the European Commission. Special Protection Areas (SPAs) are designated under the Birds Directive in order to conserve rare and threatened bird species, migratory species, and the habitats that they require, and these are also offered European legal protection. SPAs are classified by the presence of Annex I bird species, such as the Golden Plover, Pluvialis apricaria . Migrant species and specialist bird habitats may also be used to designate an area as an SPA. Taken together, areas designated under the Habitats Directive and the Birds Directive are referred to as the Natura 2000 network. 

Another major piece of EU legislation, the EIA Directive, requires that proposed development projects that may affect habitats or species protected under the Natura 2000 work first undertake an in-depth analysis of the ecology of the site. Together with the Natura directives themselves, this directive forms the most far-reaching and practical non-Irish-generated mechanism protecting fenland habitats and species in Ireland.   Many SACs were originally (and many remain to be) Natural Heritage Areas (NHAs). These are sites designated under the Wildlife Act, 1976, and the Wildlife (Amendment) Act, 2000, and are important habitats for botanical or animal species worthy of conservation.

Some fens in Ireland are also Natural Reserves, which are protected by Ministerial Order. National Parks are another means of conserving areas of Ireland‟s fenland, although these have no automatic legal protection. Instead, protection tends to come from any sites within these National Parks being designated as SACs, SPAs, or NHAs (NPWS, 2012). A range of international conventions have been signed by Ireland, and while many such agreements have no legal standing, these international agreements influence wildlife management and protection policymaking in the State. 

As an example, the Convention on Biological Diversity (CBD) gives individual nations sovereign rights over their biological resources. This means that nations are prevented from exploiting the resources of other nations. As part of its commitment to the CBD, Ireland prepares National Biodiversity Plan and Local Biodiversity Plans. These typically cover issues relating to biodiversity in Ireland with an emphasis on threatened habitat types and species, bringing awareness to issues which may affect fenland habitats and species among others. The Nagoya Protocol set out by the CBD then provides a framework for nations to share indigenous genetic material. While this has no direct application to fen or fen species protection, in the case of a future use being found for a fen species, for instance a type of endemic moss, then the Nagoya Protocol offers an internationally agreed best practice for the transferral of said genetic resources. This would effectively protect the species in question from over-harvesting.

The Ramsar Convention currently protects a number of Irish bogs, notably Raheenmore Bog and Clara Bog. However, conventions such as that held at Ramsar must make compromises in order to fit agreements around the disparate legal systems, and political concerns, of many nations. This weakens the objectives of such international agreements (Kruchek, 2003). 

The Bonn Convention protects migratory species, such as the Pintail and Tufted Duck. However, legislation is only as strong as its weakest link - that is to say, each migratory species is protected only so far as the law allows in each country through which it passes (de Klemm, 1994). The Bern Convention similarly protects the biological resources between nations, though its function has now been largely superseded by the Habitats Directive.

The Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES) is another international agreement, protecting botanical and animal species from the adverse effects of trade.  The legal framework of CITES is somewhat ambiguous, however: parties to the convention are expected to implement CITES, but each individual state must adopt its own legislation in order to do so. In effect, this means that CITES does not replace the legislation of any given state, and therefore is essentially not legally binding, the only obligation being that CITES is implemented, albeit within the pre-existing legal framework of the individual parties.

The European Water Directive acts to preserve waterbodies within the Member States, dividing countries into River Basin Districts. As such, the water quality of any river or other waterway entering aquifers and feeding fens is being managed on a European level, and so this directive could be seen as protecting fen habitats and species either directly or indirectly, depending on a site‟s hydrogeological regime.

The Common Agricultural Policy (CAP) established by the Treaty of Rome in 1957 eventually led to the creation of the Rural Environmental Protection Scheme (REPS) in 1994. All annexed habitats under the Habitats Directive found on the land of participating farms were protected under this scheme, including fens, and so REPS acted as a way of enforcing habitat protection legislation. However, since the breakup of the REPS, landowners have begun converting formerly protected land into agricultural land (IPCC, 2012), partially reversing the conservation aspect of the REPS. REPS was complemented and eventually superseded by Agri-Environmental Options Scheme (AEOS), although AEOS funding is now being withdrawn as well. 

The Irish Red Lists, drawn up in conjunction with the IUCN, protect some species associated with fens, such as the water beetles, Hydroporus scalesianus and Laccornis oblongus. Red Lists exist for other taxa, such as birds and mammals, and provide a basis for focusing conservation efforts on the most threatened species in a hierarchical manner. In summary, the main pieces of Irish legislation protecting fen habitats and species are the Wildlife Act, 1976, and the Wildlife (Amendment) Act, 2000, along with the Flora (Protection) Order, 1999. Major EU regulations that protect fen habitats and species are the Birds Directive, the Habitats Directive, and the Environmental Impact Assessment Directive, all of which have been transposed into Irish law. These mechanisms form the basis for fen protection in Ireland. 

The Flora (Protection) Order,  1999, protects those botanical species listed in Section 21 of the Wildlife Act,  1976, making it an offense to damage or uproot any of these species, to take seeds from them, or to damage their habitats. This is an important piece of legislation for fen conservation, since it is not restricted to SACs. This means that while a fen may be protected by European law, this is only good for as far as the site‟s boundary extends. The Flora (Protection) Order,  1999, protects species such as saw sedge wherever they are found, thereby protecting fenland plants regardless of SAC boundaries. It is therefore a species-based legislation, rather than site-based, such as the SACs and NHAs, which protects the site in which qualifying species are found, but not the species once it leaves that site.

Pollardstown Fen is unique in that it is the largest fen in Ireland fed by springs (O'Donnell, 2006), and also has the longest history as a fen, which it has been for at least 12,000 years. The source of these springs is the Curragh aquifer. Sandstone bedrock filters the waters which then exits the springs and seepages feeding the fen. Pollardstown Fen is an Special Area of Conservation under the Habitats Directive. Three rare species of  Vertigo snails are recorded in the fen, these being  Vertigo geyeri, V. Angustior, and V. Moulinsiana. Any one of these species would qualify the site as an SAC, but all three exist here, the only site in Europe where this occurs. Additionally, the site has three annexed habitat types, also afforded protection under the Habitats Directive, and also qualifying the site as an SAC. These habitat types are Calcareous fens with Cladium mariscus and species of the Caricion davallianae [7210] (one of the largest stands in Ireland), Petrifying springs with tufa formation (Cratoneurion) [7220], and Alkaline fens [7230]. 

The site has also had areas reclaimed from agricultural uses and reflooded, which has led to the site being used by wading birds, raising the biodiversity of the fen (NPWS, 2012), although it has not yet been designated an SPA under the Birds Directive. Examples of notable bird species found at Pollardstown Fen are sedge warblers (Acrocephalus schoenobaenus) and reed buntings (Emberiza schoeniclus), which favour the saw sedge and common reed beds of the fen, while mute swans (Cygnus olor) breed at the edges of the open water areas, as do mallard ducks (Anas platyrhynchos), coot (Fulica atra) and common teal (Anas crecca). The brook lamprey (Lampetra planeri) breeds in the waters of Pollardstown Fen, and the white-clawed crayfish (Austropotamobius pallipes) has also been recorded here, while the resident brown trout (Salmo trutta) is suited to the cold, fast-moving waters of the nearby canal. A predator of the trout, the otter (Lutra lutra) is another resident of the area. Other otter prey items, and conserved species in their own right, are also found here in abundance, the common frog (Rana temporaria) and the smooth newt (Lissotriton vulgaris).

Pollardstown Fen is also important for invertebrates. These include the raft spider (Dolomedes fimbriatus), the amber-winged hawker (Aeshna grandis) and the common darter (Sympetrum stiolatum) and two rare species, Platycherius amplus, a hoverfly, and the moth fly Panimerus goodi, the latter of which is found at Pollardstown Fen and nowhere else in the world. The silky wainscot (Chilodes maritimus) also favours fen habitats and is found at Pollardstown Fen. 

One of the most important botanical features of the fen is the stand of saw sedge (Cladium mariscus), a priority habitat listed in the Habitats Directive, and reportedly the largest in Western Europe (IPCC, 2012). This stand is situated on the north side of the fen where habitat disturbance has been the lowest. Other fen plants found at Pollardstown Fen include the common reed (Phragmites australis), (notable for supporting insect species such as the silky wainscot (Chilodes maritimus)), black bog-rush (Schoenus nigricans), blunt-flowered rush (Juncus subnodulosus), purple moor-grass (Molinia caerulea) and meadow thistle (Cirsium dissectum). Woolly feather-moss (Tomenthypnum nitens) is also found at the fen. The fen margin supports a number of rare orchids, such as fly orchid (Orphrys insectifera), marsh helleborine (Epipactis palustris) and narrow-leaved marsh orchid (Dactylorhiza traunsteineri). 

The characteristic biodiversity of the site is supported by the hydrogeology of the area. There is a constant flow between springs and groundwater seepages at the fen margins, mostly along the south-western edge, which supply the central fen. Where these springs are saturated with calcium, white deposits have formed; these springs are known as tufa (Hajek et al., 2006), and are a protected priority habitat type under the EU Habitats Directive (European Commission, 1992).  Vertigo geyeri and Tomenthypnum nitens are particularly associated with the tufa springs at Pollardstown Fen (Kuczynska et al., 2010). 

The singular nature of this site (it is the oldest of its type in Ireland, for instance) means that its biodiversity is particularly unique and is therefore of high conservation status. Its protected  Vertigo species are rare, but all come from a single genus, making the site of ecological importance. A comparison between Pollardstown Fen and other sites designated as SACs for V. Geyeri, such as Annaghmore Lough, Roscommon, show that Pollardstown Fen is uncommonly species rich for an Irish fen (NPWS, 2012). 

Pollardstown Fen is endangered by the prospect of future drainage (Golder Associates, 2011). Although the site was conserved to a large degree by mitigations to a major road-building project (Foss, 2007), the water table lowered during this construction and despite returning to normal levels, vegetation was allowed to become rank and willow encroachment occurred (Flynn, pers. comm., 2012).  Moorken (2011) noted that  Vertigo declined at the fen margin where it had previously been studied and did not return in its former territory upon normalisation of the water table levels: despite the mitigation measures taken by the road construction, a temporary drop in the level of the water table caused the higher areas of the fen to dry out. This caused an ongoing change in the hydrogeological species zonation, with two notable effects: Salix spp. began encroaching in areas of the site where it had not previously done so; vegetation became rank in areas; and the species of Vertigo for which the fen is famous became absent in the area in which they were first studied. Although Vertigo spp. are still found in the adjacent (more low-lying) area, this is most likely because they were always there and not because they have migrated to the area, although some recruitment may have occurred this way.

This situation is likely to occur again, (Golder Associates, 2011), since the membrane used in the tanking system (whereby the current road sits within a geotextile-lined furrow) is not permanent and so the question of drainage is likely to occur again in the future (Coppinger, 2004). There is currently no scheme in place to replace or upgrade the membrane system, and so permeability, and hence drainage, is likely to be a problem again once the existing geotextile membrane begins to erode (Ciara Flynn, pers. comm., 2012).

The fact that Pollardstown Fen is threatened by the future commencement of drainage means that the distinctive biodiversity of the site will be in greater need of conservation than it is currently. Conservation of this internationally unique site must be accelerated if its distinctive ecosystem and all its components are to be preserved.

References 

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