Taxonomic Notes
The nominate subspecies occurs in Northern America. In Europe and Asia A. subarctica elisabethae (Djakonov 1922) is found. Two colour morphs of A. subarctica elisabethae occur in Europe which mainly differ in the amount of yellow pattern in the thorax. It seems that in cooler climates the darker type prevails while in the lowland of central Europe the paler type is more common. These morphs can be found together and are at least partly determined by climatological circumstances and are therefore not considered to be subspecies.
Justification
European regional assessment: Near Threatened (NT)
EU 27 regional assessment: Near Threatened (NT)
Aeshna subarctica is widespread and common in a large part of its most northern range but is undergoing a decades long decline in Central Europe. A. subarctica is threatened in Austria, Belgium, Bulgaria, the Czech Republic, Denmark, France, Germany, Italy, the Netherlands, Slovakia, Slovenia, and Switzerland. In its main distribution in the north, a decline is inferred in southern Sweden. The species is adversely affected by climate change, which may result in rapid decline and local extinction in parts of its range. This is particularly true of the Central European populations which have declined dramatically. These, however, only constitute a small part of the species range and a decline in this region would not affect its conservation status on a European scale. Should the species disappear from here, however, its European extent of occurrence (EOO) would be drastically reduced. It is expected that the species in the south and locally elsewhere will become even more restricted to higher altitudes. The decline in southern Sweden indicates that the species can be at risk also in the lowlands in the north, and it can therefore be expected that its distribution will gradually shift in a northerly direction. Occurrences in the southern parts of the northern range will most probably be increasingly threatened and isolated and this development, as well as the populations in the scattered Central European range, must be followed closely. The decline is inferred to have been less than 30% (around 25%) in the past 10 years and is expected to be less than 30% (at least 20%) in the next decade. The species is thus assessed as Near Threatened (A2c+3c) in Europe as well as in the EU 27.
Geographic Range Information
In Europe, the subspecies A. subarctica elisabethae occurs mainly in lowlands in the north central parts, approximately from the Benelux countries in the west in a belt to the east and northeast. Its strongholds are found in Finland, Norway, Sweden, and northern Belarus and it is probably also common in large parts of northern European Russia. The species is moderately represented in the Baltic states and northern Poland. South of this core area, it is scarce in the northern parts of Central Europe. Even further south, the species is found more fragmentarily with frequently isolated occurrences at higher altitudes in the central and eastern Alps, the Hautes Fagnes (Belgium), Jura Mountains (France), western Carpathians, Vosges Mountains (France), and in the Black and Bohemian Forests (Germany, Czechia). More recently, the species has also been found in the Carpathian Mountains in Romania, which gives some credence to a previously very isolated and unconfirmed record from Bulgaria (unmapped). This seems to imply that the species might have a wider distribution in the mountainous parts of the southeast than what was previously assumed. On the other hand, the possible localities are very scant and the dubious Bulgarian record was made as early as 1954, and the species has shown a decline for decades, especially at the fringes of its European distribution (Kalkman 2010, Kalkman et al. 2015, Kitel 2022).
A. subarctica is a Holarctic species that occurs in the northern parts of Europe, Asia, and North America.
Population Information
The specific habitat requirements of A. subarctica make the species unusual and rare in large parts of its range. In Europe, the species has its strongholds in the lowlands of Finland, Norway, Sweden, and northern Belarus. It is probably also common and widespread in large parts of the northern European part of Russia. A. subarctica is moderately represented in the Baltic states and northern Poland. It is rare and local in Denmark, northern Germany, the Netherlands, and in Hautes Fagnes in Belgium (+/- 600 m). Further south, the species is limited to high elevations in the central Alps, the Jura Mountains, the western Carpathians, the Vosges and in the Black and Bohemian Forests. Here A. subarctica occurs very fragmentedly, and it has been declining here for a long time. Most of the occurrences in South Central Europe are small and isolated, and although some may consist of more individual-rich populations, it is vulnerable to local extinction. An isolated observation in southern Belarus in 1999 may suggest that the species is also found in northern Ukraine. More recently, the species has also been found in the Carpathian Mountains in Romania, but the possible localities in that region are very scant and the species has shown a decline for decades, especially at the fringes of its European distribution (Kalkman et al. 2015, Kitel 2022). In recent years A. subarctica has been found in several new regions in Sweden, Switzerland, and Italy, but this does most probably not reflect an expansion but is more due to intense citizen science as well as targeted research with visits to suitable environments (Assandri et al. 2022, Billqvist et al. 2019, Monnerat et al. 2021).
Habitat and Ecology Information
A. subarctica is almost exclusively found in quagmires in nutrient-poor wetlands such as bogs, vegetation-rich peat pits in a forest environment or on the edges of smaller lakes. The species can be found temporarily outside these habitats but is very rare where habitats with Sphagnum are missing, such as in open agricultural landscapes. Because of its specific habitat requirement, it is restricted in Central Europe to occurrences at higher altitudes, mostly above 700 meters (Billqvist et al. 2019, Kalkman et al. 2015).
A. subarctica can occur abundantly under the right conditions, but often goes under the radar since it is almost exclusively found in difficult to access quagmire habitats. The male patrols over areas with Sphagnum where the female oviposit. During foraging, it can be found along warm edge zones and wind-protected clearings near its aquatic environments. Images or hand-held individuals are often required to ensure species affiliation, which is why a certain amount of patience may be required. The larvae are found in shallow water with Sphagnum and their development lasts three to five years. The exuviae are usually found very low, often directly on the Sphagnum (Billqvist et al. 2019).
Threats Information
A. subarctica has for a long time shown a decline, but as it is widespread and still common in large parts of northern Europe, the decline has not been perceived as serious on a European scale. It is threatened in Austria, Belgium, Bulgaria, the Czech Republic, Denmark, France, Germany, Italy, the Netherlands, Slovakia, Slovenia, and Switzerland. Lowland populations throughout Central Europe and especially those along the southern fringes of the distribution range are most severely threatened and climate change is likely making those sites unsuitable for the species in the near future. It is also highly likely that it will suffer altitudinal range shifts and distributional shrinkage in the south which may result in rapid decline and local extinction of isolated occurrences. The populations in South- and South-Central Europe only represent a small part of its European range and the decline in this region does not affect its conservation status on a European scale. Further north the species is mainly found in areas with low environmental pressure and is not under any current threats. The species is however also declining in Southern Sweden (-23%), and this could be an indication of a more severe nature. The decline here is probably largely linked to the southern part where some populations have disappeared. This could suggest that the species is under threat all over its lowland distribution. The threat to the species is equal to those that other cold-adapted species suffer from. Nitrogen deposition in combination with climate change has meant that the habitats have crossed a threshold, where cascade effects have dramatically affected the sites negatively.
The habitats have become less and less nutrient-poor, which has meant that the larvae suffer from increased intra-guild predation from thermophilic species that previously were rare or did not occur in these environments. Higher water temperatures lead to lower oxygen availability for the larvae which leads to higher mortality, change in larval development and flight period. In the past, the species has been able to re-immigrate to places that have dried out during certain years, but as droughts return more and more often and more severely, there are fewer suitable sites to disperse to and from. The drought also fundamentally affects the wetland's plant communities since, for example, the crucial Sphagnum is disappearing. When a bog is trenched and dewatered, the peat is oxygenated, the levels of pH change and metals and nutrients that have previously been bound in the peat are released into the water (Billqvist et al. 2019, Rova and Paulsson 2015).
With more nutrients and lower water levels there is also accelerated and ongoing afforestation which is occurring on a large scale. Trenching of bogs to acquire more land for forestry, as well as old trenches that drain the bogs long after peat extraction has been abandoned, is turning the former open mires into forest. When water levels are lowered it paves the way for the establishment of trees and shrubs, which in turn is increased by nitrogen deposition and climate change. The trees and shrubs that establish themselves also absorb water, which dries out the soil further and accelerates the afforestation (Rova and Paulsson 2015). In the southern part of the species' distribution, besides reafforestation, the opposite can also be a problem, when tree cover essential for the species to escape hot summer temperatures is removed. This is often due to a lack of management plans or plans that are either poor or not designed for cold-adapted species (De Knijf et al. 2021). The Species Temperature Index (STI) shows that a decline or expansion can be explained by a change in a species preferred temperature (Termaat et al. 2019). For A. subarctica this implies that higher mean temperatures can contribute a lot to its rapid decline.
Use and Trade Information
This species is not used or traded.
Conservation Actions Information
A. subarctica still thrives in the most northern parts of its distribution, but the impact of future climate change and nitrogen deposition is difficult to estimate. The diminishing fringe populations and isolated occurrences might only survive locally through altitudinal range shifts. Distributional shrinkage will probably result in rapid decline and local extinction of isolated occurrences. To ensure that A. subarctica and other cold-adapted species survive in the long run, restoration projects might have to be undertaken even in areas where they presently have strong populations.
There is a great need to raise awareness of the dragonfly species associated with nutrient-poor habitats. Fieldwork and studies are needed on cold-adapted species in general to conclude the exact threats and if they are reversible or not. Unfortunately, they are often not included as good indicators in peatland restoration projects. These projects often focus on birds and hence management plans and actions taken can, at least in Central Europe, be averse to the measures needed to restore habitats for dragonflies. Projects in Switzerland have shown that A. subarctica can respond positively to revitalising bogs, such as those carried out in the canton of Neuchâtel (Monnerat et al. 2021). Climate-adaptive management plans of mires are imperative. A review and analysis of experiences from different restoration projects from different countries is needed. Perhaps more knowledge of the exact threats can lead to more appropriate management plans. It should entail keeping scrubs and trees adjacent to sites in open habitats in areas where hot summer days are a threat to the species, but keep afforestation and scrub encroachment to a minimum in smaller, more shaded sites on higher elevations and in the northern distribution range. It is conceivable that natural fires played a role in the past in keeping the bogs from turning into forests, at least in Scandinavia. Perhaps controlled fires can be a tool in keeping habitats open. It is crucial that water levels are stable over time. If the level is too low for longer periods, vascular plants can establish themselves and out-compete the Sphagnum. Likewise, a too-high water level drowns the Sphagnum mosses. A stable water table also makes it difficult for encroaching trees and shrubs to survive.
Monitoring of A. subarctica distribution is needed across Europe and trends in its populations in the scattered Central European range must be followed closely.