European regional assessment: Near Threatened (NT)
EU 27 regional assessment: Near Threatened (NT)

Somatochlora sahlbergi was previously assessed as Data Deficient (DD). Some studies and fieldwork have been carried out on S. sahlbergi since the last European assessment, so we know more today than before of this enigmatic species’ habitats, behaviour, and ecology. We still lack some information on population trends, population sizes, and distribution. The species may have a fragmented distribution, a small area of occupancy (AOO) (204 km²), and is only known from a few locations (8-10)  however there is very little data available to confirm this. These are all situated in a narrow climate zone where very small changes towards a warmer climate, local events or competition with Somatochlora metallica, quickly can affect the habitat and its surroundings negatively. Some of the observations also concern single individuals only, and at some locations neither larvae nor exuviae have been found despite searches. In other words, it is unclear how many locations the species really reproduces at. There are also indications that the number of individuals fluctuates greatly, with observations of tens of adults in one season and none or only a few in other years. The restricted AOO and small number of locations qualifies the species to be assessed as Near Threatened nearly meeting criterion B. The habitat degradation projected to occur in the future resulting from climate change could push it to a threatened category in the future. More fieldwork is still needed to increase knowledge of this species.

S. sahlbergi is an extremely northern species with a Holarctic distribution that stretches from the northern part of Norway, Sweden and Finland to the Russian Far East and Japan to Yukon in Canada. The known locations are few (8-10), somewhat fragmented, and the areas in between are poorly investigated. Presently we lack knowledge if there are more and/or any cohesive populations (Boudot and Karjalainen 2015, Kohli et al. 2018). There is a complete lack of information on the possible presence of the species from the European part of Russia, or whether there are even suitable habitats.

S. sahlbergi is, in Europe, found only in Russia, the northernmost part of Finland, in Norway's Finnmark and in some smaller areas in Swedish Lapland. Larvae are known from more sites than adults and some observations have not been confirmed but imply that it probably occurs at more locations than we know of today. New sites are however rarely found because of the huge expanses of seemingly appropriate habitats that are daunting and difficult to access, paired with the difficulties of determining best timing for the flight season of adults and the prevailing poor weather. Some studies and fieldwork have been carried out since the last European assessment, so we know at least more today than before of the species habitats, behaviour, and ecology (Billqvist et al. 2019). Some of the observations also concern single individuals only and at some sites neither larvae nor exuviae have been found despite searches. In other words, it is unclear how many locations the species really reproduces at. There are also indications that the number of individuals fluctuates greatly, with observations of tens of adults one season and none or only a few in other years.

S. sahlbergi is in Europe found in open to semi-open areas with permafrost north of 68° N characterised by annual average temperatures lower than 0° C and an average annual precipitation of <450 mm. It has the northernmost breeding range of any dragonfly species, and it is more dependent on the climate than a certain habitat. It is mainly found in small to large lakes just below or above the tree line (in Sweden at 550-650 m asl) with proximity to wind-protected spots with mountain birch (Betula pubescens tortuosa), lower plants such as bog-myrtle (Myrica gale), and low hills or palsas (peat mounds). The habitat tends to be deep and cold, usually at least 50 cm, and have presence of Sphagnum and emergent sedge vegetation. At some sites the habitats are also connected to slowly flowing springs where the larvae live (Billqvist et al. 2019, Kohli et al. 2018).

S. sahlbergi is an enigmatic and rare dragonfly that is difficult to find. The difficulty lies in the fact that it occurs in hard-to-reach places, where the weather is capricious. It is rarely seen with more than a single specimen, and sightings of more than ten individuals are exceptional. The species' flight time is short, and the behaviour seems to vary between different seasons and sites. The flight time begins sometime during the first to second week of July, possibly in some years already at the end of June, and then ends within a few weeks. In hot weather they are very active and shy. On warm, sunny, and windless afternoons the male patrols across open water, often far from the shore, while foraging takes place in protected, warm openings in adjacent mountain birch forest. At lower temperatures, they are easy to get close to but all the harder to find. They rest directly on the ground but take to the trees during night some distance from the breeding habitats. The female lays eggs in flight or while perching at the water surface. Egg-laying takes place in shallow areas of vegetation such as in Sphagnum. The larvae are found in shallow or very shallow parts of the site or in adjacent streams (sometimes fuelled by springs). The larval development probably lasts two to four years. The exuviae are left low on straws that protrude in the water or along the waters’ edge (Billqvist et al. 2019, Kohli et al. 2018, Sahlén 1994).

S. sahlbergi only occurs in a climate zone where the species is completely dependent on several specific external circumstances, not least of which are linked to the local climate. If this is disturbed, the species will likely suffer very negatively very quickly. Small changes in annual rainfall and/or annual average temperature drastically change its habitat fundamentally. There are also some observations and studies that indicate that the species may already be facing habitat loss. In Canada S. sahlbergi seems to have disappeared from seven previously known sites, but the reasons are so far uncertain (Kohli et al. 2018). Another effect of higher temperatures is competition with new species for the habitat, in the case of S. sahlbergi this currently applies to Somatochlora metallica. S. metallica has in the 2000s’ been found on the locations of S. sahlbergi in Finland, in numbers that far exceed individuals of any other species in the area. Since S. metallica is larger and more robust there is a risk that it can out-compete S. sahlbergi. Possibly two moth species, Epirrita autumnata and Operaphtera brumata, might have an impact as well. These cause damage to mountain birch forest and constitute an important and natural cyclical disturbance in these environments. Normally, affected birch forests recover during the years between outbreaks, but due to climate change, the intervals between these outbreaks have become increasingly shorter. Possibly, therefore, enormous areas can be completely deforested and thus affect the basic conditions for species that occur in these environments (Schröter et al. 2012). The previous assessment also mentioned that a part of the European area in Russia where S. sahlbergi is found is under the influence of the atmospheric pollution issued from Russian industry at the north Kola Peninsula (acid deposition and heavy metals). As not much information is available about the species there, it is not sure whether this poses a threat (Boudot 2010).

There is no trade or use of this species.

Presently more research on population trends, sizes, distribution, and dynamics are needed. Larvae are easier located than adults, so studies should focus on finding larvae and hence new sites and populations. S. sahlbergi is a very good candidate for a species where the use of eDNA could be the most effective way to demonstrate its presence. This is because it is found in hard-to-reach areas that are very time-consuming to investigate. Appropriate conservation measures should be applied thereafter.