Biodiversity, carbon storage and dynamics of old northern ... - BPAN.fi

In the boreonemoral and nemoral zones the human influence has
been much stronger and more long-lasting than in the boreal zones (cf
section 3.2 above), leading to stronger modification of the natural tree
species distribution than in the boreal zone. Nevertheless, we can find
similar responses in the forest types to gradients in nutrient supply,
with dwarf shrubs and low herbs dominating the poor to medium types
which often have oak or beech as dominating tree species, with hazel,
birch, pine, aspen or other tree species as additional frequent species. On
richer soils a richer ground flora will often be characteristic, with oak,
hornbeam, elm, lime, ash, maple, and alder constituting key species of
the tree layer. Under particularly poor and/or dry conditions pines may
constitute the dominating tree species even in the nemoral zone. At the
wet end of the moisture gradient, swamp forests with ash, common alder,
birch and various willows tend to dominate in different sub-types.
Figure 3.3. The distribution of boreal forest types along gradients in nutrients and
soil moisture
Dry
Cladonia
forest
Cladonia
calcareous forest
Vaccinium
Empetrum
forest
Vaccinium myrtillus forest
Low-herb
forest
Low-herb
calcareous
forest
Calluna Vaccinium
uliginosum forest
Small-fern
forest
Tall-fern
forest
Tall-herb forest
Tall-herb
calcareous
forest
Pinus mire forest
Picea/Betula swamp
forest
Alnus glutinosa/
Salix forest
Poor
Rich
Adapted from Larsson & Søgnen 2003, cf also Påhlsson 1994, fig. 2:1.
The national forest inventories mainly characterize natural forest variation
by site quality (i.e., a scoring of the stand’s potential production of tree volume)
and tree species composition (mainly based on a few dominating tree
species), cf Figure 3.4 (see also Figure 5.1B for an illustration of the variation
in forest productivity). The Finnish, Norwegian and Swedish forest
inventories also record information on forest types based on characteristics
of the ground vegetation (Figure 3.3). The Danish forest inventory collects
information on the main functional groups of the forest vegetation (Nord-
Larsen et al. 2008). The forest inventories also present information on forest
age (Figure 3.5). This is an important reflection of the effects of forest
management on the age structure of the forests. A number of other
measures of forest conditions are also recorded and presented in reports
Biodiversity, carbon storage and dynamics old northern forests 41