European regional assessment: Endangered (EN)
EU 27 regional assessment: Endangered (EN)

Aeshna juncea faces threats due to a combination of factors that are amplified by ongoing climate change. These factors entail eutrophication through nitrogen deposition, reoccurring severe droughts, increased rate of afforestation and scrub encroachment, lower oxygen availability through higher water temperatures, increased predation from thermophilic and invasive species, lack of or poor management plans and removal of tree cover essential for the species to escape hot summer temperatures. The decline for A. juncea has been rapid and dramatic. In the UK, the species has declined significantly since 1995 (Taylor et al. 2022). For ten years up to 2020 A. juncea in the Netherlands declined by 10% per year and the current distribution range is down to 15% compared to 1991 (van Grunsven 2020). In Flanders, it was until about 20 years ago widely distributed in appropriate habitats. Since then, and particularly during the last couple of years, the species has declined by more than 62% (De Knijf et al. 2021). Distribution trends for the last 10 years also show a dramatic decline in countries such as the Czech Republic, Finland, the Netherlands and Sweden. In Slovenia, the species is getting scarcer in the last 25 years (Vinko et al. 2022). Due to its decline in Europe A. juncea should be urgently included in the Annexes of the European Habitats Directive and special areas of conservation should be delineated. Based on occupancy modeling and distribution trends the species have been estimated to have declined on a European level by more 60% during the past 10 years. The threats and trends are not likely to cease during the next 10 years, causing suspected declines of at least 50%. A. juncea is hence considered to be Endangered (A2c+3c+4c) in Europe and the EU 27.

Aeshna juncea has the largest range of all Aeshna species, occurring in the northern parts of Europe, Asia, and North America. In Europe, it is widespread and common in the boreal parts of Finland, Norway, Sweden and probably Russia. Towards the south, it becomes gradually scarcer and rarer with a very fragmented distribution. The species occurs between 0 m and 2,500 m elevation.

In Europe the species is widespread and common in the boreal parts of Finland, Norway, Sweden and probably Russia. Towards the south, it becomes gradually scarcer, and the rapid decline of the species, especially in the lowlands, means that it is now mostly known from scattered localities in its southern distribution, such as in the Alps, the Pyrenees, and the mountains of the Balkans and on the Iberian Peninsula.

Aeshna juncea is mainly found in unshaded, nutrient-poor environments with Sphagnum such as peat extracts and bog ponds in moorland and heathland. The species favors cooler climates and can be found in a wider range of habitats in Scandinavia and at high altitudes (>1,000 m) where it also can be found in small lakes or narrow or calm parts of slow-flowing watercourses. In areas with strong populations, it can locally occur in lower numbers in more nutrient-rich environments such as man-made habitats in open agricultural landscapes, garden ponds and quarries (Billqvist et al. 2019, Kalkman 2010).

The male patrols low over water surfaces to examine the vegetation in search of females. Both sexes forage in treetops and are often seen far from water and sometimes late in the day. Both sexes, but mainly females, can be active in less favourable weather. Open, sunlit, insect-rich places such as clearings and forest roads are good places to look for the species, especially close to bogs and other shallow wetlands in or close to forest environments or heathlands. The eggs are partially laid below the water surface. The larval development takes at least two to three years. The exuviae are found either quite low along the waters’ edge or a bit further up on land (Billqvist et al. 2019).

Historically, habitats in Central and Southern Europe and Southern Scandinavia were lost to cultivation, deforestation, and demand for peat. Particularly in the lowlands from Southern Scandinavia and southwards, fragmentation of habitats occurred. Later other factors rapidly worsened the state of lowland habitats but also increasingly sites at higher elevations. Habitat loss locally or regionally can still be a threat, however this is presently not the main concern since most of the known populations of the species in the south are found in nature reserves or at higher altitudes (Billqvist et al. 2019, Kalkman 2010).

The decline for A. juncea (and several other cold-adapted species found in similar environments) has been rapid and dramatic. In the UK, the species has declined significantly since 1995 (Taylor et al. 2022). For ten years up to 2020, A. juncea in the Netherlands declined by 10% in distribution per year and the current range is down to 15% compared to 1991 (van Grunsven 2020). In Flanders, it was until about 20 years ago widely distributed in appropriate habitats. Since then, and particularly during the last couple of years, the species has declined by more than 62% (De Knijf et al. 2021). Distribution trends for the last 10 years also show a dramatic decline in countries or regions such as the Czech Republic, Finland, the Netherlands, Sweden, North Rhine Westfalia and the UK.

The threat to the species is due to a combination of factors that ongoing climate change amplifies. Nitrogen deposition is causing the habitats to become too rich in nutrients. Droughts have become more recurrent and severe which completely or temporarily causes desiccation of habitats and increases the rate of afforestation. Droughts also increase nutrient concentrations causing water systems to be unbalanced and become more eutrophic. Higher water temperatures bring about a lower oxygen availability for the larvae which leads to a higher mortality, a change in larval development and flight period. The larvae also suffer from increased intra-guild predation from thermophilic species that previously were rare or did not occur in these habitats. A lack of management plans or plans that are either poor or not adapted for cold-adapted dragonflies has meant that sites have become subject to scrub encroachment or the opposite when tree cover essential for the species to escape hot summer temperatures has been removed (Bowler et al. 2021, De Knijf et al. 2021, Taylor et al. 2022, van Grunsven 2020). 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. juncea this implies that higher mean temperatures alone can contribute a lot to its rapid decline.

It is plausible that the decline is further accelerated by the presence of non-native invasive fish species, such as Pumpkinseed sunfish (Lepomis gibbosus), in an aquatic environment that is naturally fishless. Those invasive species do not only predate on the larvae but their presence leads to changes in behaviour (e.g. less active foraging) and finally to a longer larval development increasing the mortality rate. In some regions, such as the Netherlands, the Pumpkinseed sunfish is particularly abundant in moorland pools, i.e. habitats for oligotrophic dragonfly species. Studies show that the average macroinvertebrate abundance in ponds with Pumpkinseed Sunfish was 83% lower than in ponds without the fish, making Pumpkinseed Sunfish predation a plausible explanation for the apparent decline of these taxa in the presence of the alien fish (van Kleef et al. 2008).

The species is not utilised.

A. juncea still thrives in the northern parts of its distribution and locally also in its central European range, but the impact of future climate change and nitrogen deposition is difficult to estimate. The diminishing lowland populations throughout Europe and the isolated occurrences in central Europe, the Iberian Peninsula and the Balkans promptly require immediate attention. Fieldwork and studies are needed on cold-adapted species in general to conclude the exact threats and if they are reversible or not. Climate-adaptive management plans for heathlands are imperative. Some restoration projects have been carried out in the Netherlands but so far they do not seem to have helped the species (van Grunsven 2020). Perhaps more knowledge of the exact threat(s) can lead to (even) more appropriate management plans. Current management plans for fens and similar habitats need to be revised to stop the poor management of sites where the species occurs. This entails keeping scrubs and trees adjacent to sites in open habitats in the lowlands but keeping afforestation and scrub encroachment to a minimum in smaller, more shaded sites on higher elevations.

A. juncea is a good candidate as an "umbrella indicator" of nutrient-poor habitats. Since all species linked to this environment show declining or even alarming trends, A. juncea should be urgently included in the Annexes of the European Habitats Directive and special areas of conservation should be delineated. In the majority of the EU member states, the species' locations are already located within Natura 2000 areas, so what is required is primarily an update on how these should be managed in order to stop the negative development and to benefit the species that are linked to these habitats. For nature conservation planning, it is wise to choose basins that are least susceptible to the introduction of alien invasive species. Conservation practices are best done at distances greater than 250 m from human settlement and 100 m from roads and trails to minimise the chances of introductions of alien species like the invasive species Pumpkinseed Sunfish (Lepomis gibbosus) (van Kleef et al. 2008, Lettevall 2022).
A monitoring program across European countries is needed to obtain an accurate overview of the current distribution and population trends for A. juncea and to elaborate conservation plans.