page_title: Sommen
section_title: Climate and vegetation
hierarchical_section_title: Sommen / Climate and vegetation
caption_attribution_description: English: Granite cliff at lake Sommen, Southern Swedish highlands. Pines and birches growing on top of the cliff. The cliff is near vertical.
context_page_description: Sommen is a lake in the South Swedish highlands lying across the border of the provinces of Östergötland and Småland. Situated about 147 metres above mean sea level, the lake has an area of 132 km² and has a maximum depth of 60 metres. The lake is shared between the administrative kommunes of Ydre, Kinda, Boxholm and Tranås and the area around it is sparsely populated.
  The lake has very clear water, with a visibility of 8 to 10 metres deep, if conditions are good. This makes Sommen one of the greatest clear-water lakes in Sweden. According to tradition Sommen has 365 islands, one for each day of the year. The actual number is around 260.
  In and around the lake various rare species are protected in a series of nature reserves, bird sanctuaries and areas closed for fishing. Måltorpet Granbo in Sommen is a Natura 2000 area.
  The visitor centre and natural history museum, Naturum Sommen, lies at the northern end of Torpön island, near the central part of the lake.
  According to the Svensk ortnamnslexikon the lake name was given as Sooma in 1447 and is derived from the local dialect word somma meaning an oversized vessel.
context_section_description: Relative to other areas of southern Sweden, Sommen stands out for its low precipitation and low humidity. The rainiest months of the year are September followed by July and August. Each of these months have a precipitation of around 70mm. The driest months are February and March, with around 35mm each. The hottest months are June, July and August averaging 14–15 °C. The coldest months are January and February with an average temperature of about -4 °C. The climate is expected to become warmer and drier in future.
  The growing season around Sommen is of about 216 days with 2614 degree days. The vegetation around the lake is mostly dominated by pine and spruce forest. Broad-leaf forest and open agricultural fields can also be found at some locations. In particular the southern side of the lake contains more lush vegetation and broad-leaf forest than the northern side, which has more cliffs and contiguous pine forest. The rare and endangered flower Anthericum liliago can be found along the lake's rocky shores. This is one of the northernmost locales where it grows.
  On Torpön island is Sweden's largest wych elm and at Asby, a few kilometres from the southern shores, grows Sweden's thickest spruce. The name Ydre, which was formerly applied to most of the area around Sommen, is interpreted to mean "place of yews". One locality in particular appears to be further associated with yews; this is Idebo along Norra Vifjärden.
  Some plants usually associated with carbonate rock areas appear as rarities near Sommen, since there are no known carbonate rock outcrops in the area. The plants are Vicia pisiformis and the orchids Ophrys myoides, Malaxis monophyllos and Herminium monorchis.
caption: Pines and birches along a cliff in lake Sommen, October 2011
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