
Hamra National Park, Sweden
The original part of Hamra National Park is a small (28 ha) but genuine virgin forest1 2. It was protected in 1909, making it one of the oldest national parks in Europe. As early as the beginning of the 1900s, Hamra National Park was described as “probably the most remarkable primeval forest remaining in all of Sweden” 3. On the shores of Lake Svansjön, which borders the original part of Hamra to the northwest, the odd tree has been felled, possibly by fishermen; otherwise the original part is completely untouched by axe and saw3. However, slash-and-burn agriculture near the virgin forest may have influenced the fire regime4. Later, the national park was enlarged and Hamra now covers almost 14 km2. The newer part consists of formerly managed forest and bog – not old-growth forest.
Hamra is located in the mid-boreal zone5, the original part at 410–420 m elevation. The mean annual temperature is 2.6°C and the average annual precipitation 582 mm 2. The bedrock consists of granite2 and the soils are meagre3.
Three quarters of the original part of Hamra is coniferous forest, the rest being bog and water surface3. Drier forest sites are dominated by Scots pine (Pinus sylvestris), with an undergrowth of bilberry (Vaccinium myrtillus), lingonberry (Vaccinium vitis-idaea), crowberry (Empetrum nigrum), common heather (Calluna vulguris), mosses and lichens. Moister sites are covered by mixed Scots pine and Norway spruce (Picea abies) or almost pure spruce. It is a dense forest whose undergrowth is totally dominated by bilberry and mosses (photo below). A striking feature of the spruce forests is the dense growth of fishbone beard lichen (Usnea filipendula) hanging from the spruce branches, and tree lungwort (Lobaria pulmonaria) on spruce trunks. In absence of forest fires, spruce is slowly invading somewhat drier sites, too. Silver birch (Betula pendula), downy birch (B. pubescens) and common aspen (Populus tremula) are the most common deciduous trees. The tallest spruce I measured (with Nikon Laser 550A S instrument) was 37 m tall. There are pines that are over 400 years old1.

Since 1700 there have been five forest fires in dry pine forests, the last in 1854, but only one or two in mesic forests2. The mean fire interval in the period 1400–1850 was 67 years, with most fires having been surface fires that killed mainly spruce, deciduous trees and small pines, but not the larger pines4.
Almost uniquely for boreal forest, two permanent study plots were established as early as 1922 2. The structure of the forest has changed considerably since then due to fire prevention2.
A 3-kilometre virgin forest loop trail („Urskogslingan“) starts at the main entrance of the national park. A shortcut allows a 2 km variant, but the longer trail is highly recommended as it shows some of the finest sites such as picturesque small lake Näckrostjärnen, dry pine forest, and tall and dense spruce forest southwest of Näckrostjärnen. The dense growth of mosses on the forest floor and lichens hanging from the trees create a very primeval impression. Next to the trail there is also a recent blowdown area with research markings. Camping is not permitted in the virgin forest but is possible throughout the newer part of the national park.
KR & TM
References:
- Hamra National Park, Ancient Woodlands, Quiet Wetlands and Wild Rapids.
- Linder, P. (1998): Structural Changes in Two Virgin Boreal Forest Stands in Central Sweden over 72 Years. Scand. J. For. Res. 13: 451–461.
- Hanneberg, P. & Löfgren, R. (1998): Sweden’s National Parks. Swedish Environmental Protection Agency.
- Linder, P. & Östlund, L. (1998): Structural changes in three mid-boreal Swedish forest landscapes, 1885–1996. Biological Conservation 85/1–2, 9–19.
- Ahti, T., Hämet-Ahti, L. & Jalas, J. (1968): Vegetation zones and their sections in northwestern Europe. Ann. Bot. Fennici 5: 169-211.