Young and old forest in the boreal:critical stages of ecosystem dynamics and management under global change

The circumboreal forest encompasses diverse landscape structures, dynamics and forest age distributions determined by their physical setting, and historical and current disturbance regimes. However, due to intensifying forest utilisation, and in certain areas due to increasing natural disturbances, boreal forest age-class structures have changed rapidly, so that the proportion of old forest has substantially declined, while that of young post-harvest and post-natural-disturbance forest proportions have increased. In the future, with a warming climate in certain boreal regions, this trend may further be enhanced due to an increase in natural disturbances and large-scale use of forest biomass to replace fossil-based fuels and products.The major drivers of change of forest age class distributions and structures include the use of clearcut shortrotation harvesting, more frequent and severe natural disturbances due to climate warming in certain regions. The decline in old forest area, and increase in managed young forest lacking natural post-disturbance structural legacies,represent a major transformation in the ecological conditions of the boreal forest beyond historical limits of variability.This may introduce a threat to biodiversity, ecosystem resilience and long-term adaptive capacity of the forest ecosystem.To safeguard boreal forest biodiversity and ecosystem functioning, and to maintain the multiple services provided to societies by this forest biome, it is pivotal to maintain an adequate share and the ecological qualities of young postdisturbance stages, along with mature forest stages with old-growth characteristics. This requires management for natural post-disturbance legacy structures, and innovative use of diverse uneven-aged and continuous cover management approaches to maintain critical late-successional forest structures in landscapes.

Dead standing pine trees in a boreal forest landscape in the Kalevala National Park,northern Fennoscandia: amount,population characteristics and spatial pattern

Background： After their death, Scots pine trees can remain standing for decades and sometimes up to 200 years,forming long-lasting and ecologically important structures in boreal forest landscapes. Standing dead pines decay very slowly and with time develop into ‘kelo＇ trees, which are characterized by hard wood with silvery-colored appearance. These kelo trees represent an ecologically important, long lasting and visually striking element of the structure of natural pine-dominated forests in boreal Fennoscandia that is nowadays virtually absent from managed forest landscapes.Methods： We examined and mapped the amount, structural features, site characteristics and spatial distribution of dead standing pine trees over a ten hectare area in an unmanaged boreal forest landscape in the Kalevala National Park in Russian Viena Karelia.Results： The mean basal area of dead standing pine trees in the forested part of the landscape was 1.7 m^2·ha^-1 and the estimated volume 12.7 m^3·ha^-1. From the total number of standing dead pine trees 65% were kelo trees, with a basal area of 1.1 m^2·ha^-1 and volume of 8.0 m^3·ha^-1, the remainder consisting of standing dead pines along the continuum between a recently dead tree and a kelo tree. Overall, standing dead pines were distributed throughout the study area, but there was a tendency towards spatial clustering up to 〈100 m distances. Standing dead pines were most commonly situated on flat ground or in the mid slope in the local topography.In addition, standing dead pines contributed to substrate diversity also by commonly having charred wood and broken tops. Based on the presence of dead pine snags in different stage of transition from a recently dead pine to a kelo with silvery surface, it seems evident that the process of kelo recruitment was continuously in action in the studied landscape.Conclusions： Kelo trees are an omnipresent feature in natural pine-dominated forest landscapes with important contribution to forest structural and substrate diversity. Because of their longevity and extremely slow turnover dynamics and importance for biodiversity, protection of vulnerable kelo tree populations, and ensuring their continuous recruitment, should be of high priority in forest restoration and sustainable management.

Conceptual models of forest dynamics in environmental education and management:keep it as simple as possible,but no simpler

Background：Conceptual models of forest dynamics are powerful cognitive tools,which are indispensable for communicating ecological ideas and knowledge,and in developing strategic approaches and setting targets for forest conservation,restoration and sustainable management.Forest development through time is conventionally described as a directional,or ＂linear＂,and predictable sequence of stages from ＂bare ground＂ to old forest representing the ＂climax-state＂.However,this simple view is incompatible with the current knowledge and understanding of intrinsic variability of forest dynamics.Hypothesis：Overly simple conceptual models of forest dynamics easily become transformed into biased mental models of how forests naturally develop and what kind of structures they display.To be able to communicate the essential features and diversity of forest dynamics,comprehensive conceptual models are needed.For this end,Kuuluvainen（2009） suggested a relatively simple conceptual model of forest dynamics,which separates three major modes of forest dynamics,and incorporates state changes and transitions between the forest dynamics modes depending on changes in disturbance regime.Conclusions：Conceptual models of forest dynamics should be comprehensive enough to incorporate both longterm directional change and short-term cyclic forest dynamics,as well as transitions from one dynamics mode to another depending on changes in the driving disturbance regime type.Models that capture such essential features of forest dynamics are indispensable for educational purposes,in setting reference conditions and in developing methods in forest conservation,restoration and ecosystem management.

Tree diametric-species diversity is affected by human impact in old Scots pine dominated forest in boreal Fennoscandia

Background:Forest structural and compositional variability is of fundamental importance for forest ecosystem functioning and species diversity.The purpose of this research was to examine how human impact has affected the compositional-structural diversity of mature pine-dominated boreal forest in boreal Fennoscandia.For this a new approach was used,based on the classification of tree sizes by the diameter at breast height(dbh)and tree species,resulting in a new variable,the diametric-species,the variation of which describes the compositional-structural diversity of the forest.This variable was used to compare the structural-compositional diversity among three forest classes with different degree of human influence,using rarefaction as the main tool of analysis,complemented by analyses based on common diversity indices.Results:The results showed that the near-natural forest was the most diverse and the managed forest the least diverse.On the other hand,the diversity of near-natural and selectively logged forests were similar,suggesting that selectively logged forests are equal to the natural forest in their compositional-structural diversity.The analysis solely on tree species showed no significant differences among the forest classes of different human impact.The Shannon diversity index showed no significant difference between the forest classes for the diametric-species and tree species classifications only,but the Simpson index signaled a slight difference between the selectively logged and managed forest classes for the diametric-species classification.Furthermore,the Sorensen index detected a difference among forest classes in the diametric-species classification.Conclusions:Forest utilization had an adverse impact on forest compositional-structural diversity of mature Scots pine forests.The analysis also shows that the novel approach based on diametric-species classification could be a useful tool for forest diversity analysis and comparison,especially in species-poor forests such as the boreal forest.

Low-level retention forestry, certification, and biodiversity: case Finland

In managed forests,leaving retention trees during final harvesting has globally become a common approach to reconciling the often conflicting goals of timber production and safeguarding biodiversity and delivery of several ecosystem services.In Finland,the dominant certification scheme requires leaving low levels of retention that can benefit some specific species.However,species responses are dependent on the level of retention and the current low amounts of retention clearly do not provide the habitat quality and continuity needed for declining and redlisted forest species which are dependent on old living trees and coarse woody debris.Several factors contribute to this situation.First,the ecological benefits of the current low retention levels are further diminished by monotonous standwise use of retention,resulting in low variability of retention habitat at the landscape scale.Second,the prevailing timber-oriented management thinking may regard retention trees as an external cost to be minimized,rather than as part of an integrated approach to managing the ecosystem for specific goals.Third,the main obstacles of development may still be institutional and policy-related.The development of retention practices in Finland indicates that the aim has not been to use ecological understanding to attain specific ecological sustainability goals,but rather to define the lowest level of retention that still allows access to the market.We conclude that prevailing retention practices in Finland currently lack ecological credibility in safeguarding biodiversity and they should urgently be developed based on current scientific knowledge to meet ecological sustainability goals.