Canopy Gap Characteristics and Disturbance Dynamics in Old-GrowthPicea abiesStands in Northern Fennoscandia: Is the Forest in Quasi-Equilibrium?

Abstract

Emulating natural disturbances in managed forests has been suggested as a potential solution to maintain habitat conditions similar to those observed in old-growth forests. We examined the gap attributes and disturbance history of old-growth Picea abiesdominated stands in the northern boreal vegetation zone of the Pallas-Yllästunturi National Park in northwestern Finland to evaluate the infl uence of gaps on forest dynamics and the temporal patterns of gap creation. Six stands located at two sites were sampled along 400-m-long linear transects so that all intersected gaps were measured and dated. The average proportion of the forest area in the gaps was 43.1% ± 7.5%. An average gap size was estimated to be 221 m 2 ± 198 m 2 , whereas the median gap size was 170.2 m 2 . While only 20% of the gaps were smaller than 100 m 2 , nearly 85% of them were smaller than 300 m 2 . Gap creation was constant with no distinct peaks from 1965 to 2005. Thus, forest dynamics were driven by continuous smallscale disturbances and were characterized by quasi-equilibrium structure. However, the results of the growth release analysis indicated that more severe disturbance(s) may have occurred almost two centuries ago. Emulating this type of forest dynamics would imply selective or group harvesting of trees as the predominant methods, but largerscale, more intensive cuttings could also be carried out periodically.

Natural forest dynamics in boreal Fennoscandia: a review and classification

“…Aakala et al 2009) while at the same area another study had documented patch dynamics in the more distant past (e.g. Caron et al 2009), both results were taken as valid observations. In such cases the studies were considered to be complementary, thus revealing a more complete picture of the disturbance regime at that particular site.…”

“…Aaltonen 1919, Sirén 1955) the research methodology used may not have been up to current standards. This may be the reason for some controversies, e.g., concerning the inherent characteristics of the dynamics of northern spruce forests between older (Sirén 1955) and more recent studies (Hofgaard 1993, Aakala et al 2009and Caron et al 2009 ; for a discussion see Aakala and Keto-Tokoi 2011). However, it was believed that even the more qualitative observations of older studies (e.g.…”

“…Rouvinen et al 2002, Lännen-pää et al 2008. Processes have been somewhat better accounted for in disturbance reconstructions (Wallenius et al 2004, Aakala et al 2009, Caron et al 2009 or in chronosequence studies (Sirén 1955, Lilja et al 2006. However, there are no studies based on long-term monitoring of forest structure and dynamics and the driving factors of change.…”

Spatio-temporal variation of coarse woody debris input in woodland key habitats in central Sweden

“…Several studies have illustrated the importance of small-scale disturbance events, namely gap dynamics, within boreal forests, where frequent deaths of individual trees or small groups of trees may be more important for stand dynamics and structure than infrequent large-scale disturbances (Kuuluvainen 1994, McCarthy 2001, Aakala et al 2007, Fraver et al 2008, Caron et al 2009). Apart from the episodic pulses in tree mortality caused by windstorms, our results further illustrated that the background mortality rate that occurred in periods outside of episodic mortality events varied substantially between stands.…”

Comparing correlative and process-based modelling approaches in a boreal forest identifies important areas for model development

“…Additionally, stand-replacing disturbances (e.g. storms or insect outbreaks) are complemented by small-scale disturbances on the level of individual trees in late-successional boreal forests (Aakala et al 2009;Kuuluvainen et al 2017): continuous tree falls of old individuals more susceptible to physical damage and decay maintain a mosaic of gaps even in the absence of larger disturbances (Caron et al 2009). Here, the generalized process representation that encompasses a wide variety of potential disturbances fitting for different ecosystems in global applications is not detailed enough for our regional application.…”