Gröntjärn Nature Reserve

Geological Marvel of Ice Age Origins

Gröntjärn sits within a dramatic narrow valley surrounded by towering mountains, part of a vast esker deposit from the inland ice's retreat around 8,500 years ago. Massive ice blocks embedded in gravel and sand melted, creating deep kettle holes known as dödisgropar—pits that now form water-filled tarns and lakes. The reserve spans about 150 hectares across Ljusdal and Hudiksvall municipalities, protected since 1978 with renewed decisions in 2016 as a Natura 2000 site.The centerpiece, Gröntjärn tarn, exemplifies this geology with no visible inlet or outlet. Its crystal-clear turquoise water, filtered naturally through permeable glacial gravel, reflects the sky and lake bottom, free from sediment particles carried by surface streams.

Mysterious Water Level Fluctuations

What sets Gröntjärn apart is its extreme hydrological behavior: water levels naturally vary by over 13 meters between high and low points. This stems from complex interactions between surface water, groundwater recharge, and subterranean outflow. Rainy summers swell the tarn via infiltrated precipitation, while dry periods reveal starkly lowered shores, sometimes exposing tree trunks scarred by past high waters and winter ice.Nearby Stråsjö-Långtjärn mirrors this oddity, slowly filling surrounding forest due to a clogged bottom outlet under leaf debris and humus. These phenomena make the reserve a living laboratory for groundwater studies, with the glacial gravel acting as a natural filter for pristine clarity.

Adapted Flora in a Dry Landscape

The reserve's vegetation thrives in arid conditions dictated by porous soils. Vast expanses of pine forest carpet the area, interspersed with berry bushes and colorful lichens. Sunny south-facing slopes and kettle hole edges burst with unusually abundant mosippa, a protected orchid blooming in late spring.Shorelines host a sparse yet intriguing flora, including the Ice Age relict fjällnejlika (arctic sandwort), getväppling (sticky catchfly), and ängsvide (bog whortleberry). Steeper pits support spruce, aspen, and birch, adding diversity to the dominant tall-dominated heathlands.

Trails and Visitor Facilities

Well-marked paths circle the tarn and extend through the reserve, suitable for easy walks amid stunning scenery. A historic logger's cabin adds rustic charm. Accessibility shines with wheelchair-friendly parking, toilets, and a rest area equipped with grill and shelter.Wind shelters dot the routes, inviting pauses to absorb the serene ambiance. The layout encourages exploration of multiple tarns and geological features without strenuous effort, blending nature immersion with practical comforts.

Preservation and Natural Rules

Managed by Länsstyrelsen Gävleborg, the reserve safeguards biodiversity, valuable habitats, and public recreation. Strict rules prohibit damaging vegetation, disturbing wildlife, riding off designated paths, or altering the landscape to preserve its pristine state for future generations.