Cassiope vol. 2
Rhododendron lapponicum, Cassiope tetragona and a fascinating birch forest – excursion guide to Holmevassfjellet near Tromsø by Arve Elvebakk and Kristian Nyvoll. Journal published by Tromsø Arctic-Alpine Botanic Garden at UiT The Arctic University Museum of Noway, April 2021.
This is an excursion guide to a calcareous and easily accessible mountain ridge at 500 m altitude one-hour drive east of Tromsø.
The excursion starts in a birch forest, an ecosystem equally well-known to northerners as exotic to visitors. The whole slope has calcareous bedrocks, and near the start of the path, several
tall ferns are presented as characteristic of such nutrient-rich forests.
Further upslope there is a mosaic of nutrient-rich, moist forest floor communities, alternating with drier and more convex landscape forms with dwarf-shrubs where instead the soil has been modified into a very acidic substrate. When the leaves of the common species break down, they produce a high amount of humic acids, which combine with available nutrients and then disappear from the upper layers through leaching, as shown by strongly reduced pH values. The modified soil is called podzol and has different layers in characteristic colours. This chemical warfare keeps fast-growing, broad-leaved competitors
away, whereas birch and the slow-growing dwarfshrubs can manage with low levels of nutrients. These plants also profit from having mycorrhiza, a symbiosis with fungi, including many edible mushrooms, which increases nutrient availability to both partners.
Above the birch forest the loose calcareous substrate is open and very well-drained, and the vegetation therefore appears more alpine than at corresponding altitudes elsewhere in the area. It is well-exposed and has nice views towards all directions. Several interesting alpine species are presented, but the highlight is the flowering in mid-June of the predominantly arctic species Rhododendron lapponicum and Cassiope tetragona.
Download Cassiope vol. 2 in pdf-format here