European regional assessment: Vulnerable (VU)
EU 27 regional assessment: Vulnerable (VU)

Aeshna grandis has shown a mostly continuing declining trend throughout the lowlands, and is threatened in Croatia, France, Germany, Italy, and Slovenia. Distribution trends show that it has declined in the Netherlands and in France. Most worrying however is the strong decreasing trend in countries where it is supposed to have its strongholds, such as in Denmark, Finland, Lithuania, and Sweden. The reason for the decline is likely climate change in combination with nutrient deposition that leads to a degradation of its habitats. The species is therefore expected to continue to gradually decrease in the lowlands but increase its range and occupancy in the far north. In the southern part of its range, it is likely that the species will be increasingly dependent on sites in higher altitudes. Based on occupancy modelling and distribution trends the species has been estimated to have declined by at least 30% during the past 10 years and the threats are not likely to cease during the next 10 years. A. grandis is hence considered to be Vulnerable (A2ac+3c) in Europe as well as in the EU27.

A. grandis is found in the temperate and boreal zones from Ireland in the west to Lake Baikal in the east. It is widespread in northern and north-eastern Europe, and mainly found in lowland environments. It has shown a slight expansion in Ireland and the UK and there is possibly a northern range shift in Scandinavia. Roughly from southern Germany onwards, the species becomes increasingly restricted to mountain areas, with isolated outposts in the Pyrenees and the Balkan Peninsula. Most populations are found below 1,000 metres, but breeding has been confirmed at 2,250 metres (Kalkman et al. 2015, Taylor et al. 2022). It is one of only three species of dragonflies that have been observed in Iceland (Aug 2011), although it most probably was ship assisted (Billqvist et al. 2019).

A. grandis is widespread and common to abundant in the north-eastern part of its distribution. In Central Europe it gets gradually scarcer with more scattered and relatively small populations. Even further south it is more confined to higher elevations (Kalkman et al. 2015). It has increased in occupancy in both Ireland and Wales, and a colonisation of Scotland looks possible if the northward movement in England continues (Taylor et al. 2022). A. grandis otherwise has a mostly declining trend and is threatened in Croatia, France, Germany, Italy, and Slovenia. Distribution trends show that it has severely declined in the Netherlands and in France. Most worryingly however is the strong decreasing trend in countries where it is supposed to have its strongholds, such as in Denmark, Finland, Lithuania, and Sweden. The reason for the decline is likely climate change in combination with nutrient deposition that leads to a degradation of its habitats. The species is expected to continue to gradually decrease in the lowlands but increase its range and occupancy in the far north. In the southern part of its range, it is likely that the species will be increasingly dependent on sites on higher altitudes and face local and rapid extinction.

A. grandis occurs in many different types of stagnant and slow-flowing, vegetation-rich aquatic habitats, but the largest populations are found in open to semi-open forests. It is usually absent in open areas and distinct agricultural settings, but in areas with strong populations, it can locally occur in lower numbers in more eutrophic environments, as well as man-made habitats in early succession, as long as there is some nearby tree cover. In Central Europe most populations are found in man-made habitats in a later stage of succession. Strays are found in cities and in gardens, seemingly far from suitable aquatic environments (Billqvist et al. 2019, Kalkman 2010).

A. grandis has a very long flight period, is very characteristic and easily recognisable. It is often seen some distance from breeding habitats and sometimes in the dozens. They forage quite high in clearings, along forest roads or over treetops. On warm evenings, it can be active until very late. Mating takes place very early in the morning and is often hidden in dense vegetation. The species is also active when it is overcast and can be seen when it is raining. They then fly low over and through vegetation to flush prey. The eggs are laid in soft, organic material such as rotten wood. The larval development lasts two to four years. The exuviae can be found either low or a bit higher up on upright straws, leaves or similar in and along water edges (Billqvist et al. 2019).

A. grandis has for a long time shown a decline, but as it is widespread and common in large parts of northern Europe, the decline has until recently not been perceived as serious on a European scale. It is threatened in Croatia, France, Germany, Italy, and Slovenia. 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 likely that it will suffer altitudinal range shifts and distributional shrinkage which may result in rapid decline and local extinction of isolated occurrences. This suggests that the species is mostly under threat all over its lowland distribution. Even though A. grandis is not wholly dependent upon oligotrophic habitats the threats to the species are probably similar to those that more 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 an increased intra-guild predation from thermophilic species that previously were rare or did not occur in these environments. Higher water temperatures lead to a 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 often and more severely, there are fewer suitable sites to disperse to and from. The drought also fundamentally affects the wetland's plant communities. When a bog is trenched and dewatered, the peat is oxygenated, the levels of pH changes 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 an accelerated and ongoing afforestation which is occurring on a large scale, at least in Scandinavia. 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, the opposite can 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).

There is no trade or use of this species.

A. grandis 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. The development in the lowlands and the more isolated occurrences in the southeast and southwest should be followed closely. If the downward trend continues, it may be relevant to apply local measures for populations that are under threat.

A. grandis is not wholly dependent on nutrient-poor habitats but there is a great need to raise the awareness of the dragonfly species associated with these habitats. Fieldwork and studies are needed on cold-adapted species in general to establish the exact threats and if they are reversible or not. They are often missed and lacking as 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. Climate-adaptive management plans of mires is imperative. A review and analysis of experiences from different restoration projects from different countries is needed. Perhaps more knowledge on 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 to 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. Perhaps controlled fires can be a tool in keeping habitats open. It is crucial that water levels are stable over time.