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

Figure 3.1. Disturbance factors at various spatial and temporal scales in boreal
forests. The spatial scale will run from single trees to several stands or parts of
catchment areas and the temporal from sub-annual to centuries
Time scale
Often Rare
Rot + wind,
competition,
scenesence
Flooding,
erosion
Wind-throws,
droughts
Insect attacks,
large storms
Severe fires
Small
Spatial scale
Large
Modified from Jonsson & Siitonen 2012.
Shorohova et al. (2011) summarized current understanding of natural
disturbance regimes and the related dynamics determining the natural
prevalence and development of old-growth boreal forests (Table 3.1).
They concluded that in contrast to forests in western North America and
western Siberia, boreal forests of northwest Europe tend to be dominated
by less severe, non-stand-replacing fires and other disturbances, letting
more varied and smaller scale disturbances shape forest development and
structure, between the rather infrequent severe, stand-replacing fires.
Forests are then mainly dominated by small-scale gap dynamics, with
cohort dynamics where fires of medium severity occur, giving a complex
and fine-grained forest structure. As the proportion of old-growth forests
in a landscape is determined by the frequency and severity of recurrent
stand-replacing disturbances (fires, storms, insect outbreaks), the low
frequency between severe disturbances in boreal forests in Fennoscandia
should imply that old-growth, multi-aged forests may originally have covered
a considerable area and lasted for rather a long time. In western and
northern Norway, the broken topography and moister climate should
have made large, stand-replacing fires very rare, but local storm damage
and avalanches would probably have been quite common.
Studies of natural forest dynamics in the Nordic countries have been
concentrated to boreal forests (mainly of the northern and middle boreal
zones), with little specific information on the natural dynamics of
temperate forests (Peterken 1996). This is mainly due to the long-lasting
and extensive human influence in temperate forests (cf below), leaving
virtually no suitable cases for studies of such dynamics, although some
selected forest tracts with long forest continuity can be found, e.g., the
Biodiversity, carbon storage and dynamics old northern forests 29