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

A modern clearcut with aggregated retention trees from Nordmarka, Oslo,
SE Norway
Photo: Anne Sverdrup-Thygeson, NINA.
3.3 Ecological factors and variation in forest types
The characteristic distributions of tree species and vegetation types of
forests in the Nordic countries are mainly shaped by the natural variations
in climate and site factors (primarily nutrient and water supply),
the immigration of organisms since the last ice age, various natural disturbance
regimes, as well as human resource use and management
through the ages (cf the previous sections).
The climate, especially the overall temperature regime, has long been
recognized as a major determinant of forest biodiversity, as represented
by the vegetation zones from the nemoral in the southern lowlands of
Fennoscandia to the alpine of the northern or mountainous parts (e.g.
Ahti et al. 1968, Påhlsson 1994, Moen 1998; Figure 3.2). The temperature
regime distinguishes the broadleaved deciduous temperate forests
of the nemoral zone from the spruce, pine or birch-dominated boreal
forests of the southern to northern boreal zones, with the mixed forests
of the boreonemoral (hemiboreal) zone in between. An additional factor
is the humidity gradient of high precipitation in the oceanic parts in the
west and low precipitation in the continental parts in the east or in the
interior, as reflected in Moen’s vegetation sections (Moen 1998). The
humidity gradient tends to influence ground vegetation composition
rather than the major shifts in tree species composition. These climate
Biodiversity, carbon storage and dynamics old northern forests 39