Timo Kuuluvainen

Forest management and biodiversity conservation based on natural ecosystem dynamics in northern Europe: the complexity challenge.

Abstract Recent research in northern Europe has revised many long-held conceptions of the complexity of forest ecosystems and their natural structure and dynamics. The unveiling of the picture of natural characteristics of forest ecosystem structure and dynamics reveals much more diversity than its traditional complement, highlighting the importance of non–stand-replacing disturbances and the associated heterogeneous and dynamic stand and landscape structures. This increasing detail is a reflection of a fundamental change in the ecological understanding of forests as complex ecosystems. In particular, the generalization that the boreal forest is regulated by fierce stand-replacing disturbances, leading to the dominance of even-aged stand successions, has been disproved. However, this misconception has, until now, been repeated and used to legitimize the dominant practice of clear-cutting as a nature-based way to manage the forest. The practical conclusion of this review paper is that the dominating forest management model in North European boreal forests, which is based on the clear-cut harvesting of timber and growing of even-aged stands, is in contradiction with the variable and complex characteristics of the disturbance-succession cycle observed in naturally dynamic forests with negligible human impact. As a consequence, the structural variation of the boreal forest under management has been grossly truncated compared with its natural range. Because of this, and due to the scarcity of protection areas in many regions of northern Europe, it is not likely that the conservation of native biodiversity and ecological sustainability will be attained, assuming that the model of forest management remains unchanged. Thus, there is a strong incentive for change in the prevailing forest management model toward one that is based on natural ecosystem dynamics and an understanding of forests as complex systems.

Boreal forest health and global change.

The boreal forest, one of the largest biomes on Earth, provides ecosystem services that benefit society at levels ranging from local to global. Currently, about two-thirds of the area covered by this biome is under some form of management, mostly for wood production. Services such as climate regulation are also provided by both the unmanaged and managed boreal forests. Although most of the boreal forests have retained the resilience to cope with current disturbances, projected environmental changes of unprecedented speed and amplitude pose a substantial threat to their health. Management options to reduce these threats are available and could be implemented, but economic incentives and a greater focus on the boreal biome in international fora are needed to support further adaptation and mitigation actions.

Natural stand structures, disturbance regimes and successional dynamics in the Eurasian boreal forests: a review with special reference to Russian studies

Abstract• This review summarizes early stand-scale studies of pristine forest structures, disturbance regimes and successional patterns carried out in boreal Eurasia. We attempt to reveal, characterize and classify stand dynamic types that can be used as templates for nature-based forest management.• The studies reviewed demonstrate multiple successional pathways in stand development in all types of pristine forests. All-aged stands driven by small-scale disturbances are formed over successional development of several hundreds of years. This endogenous development can be interrupted by stand-replacing or partial disturbances leading to successions with even-aged or cohort-structured stands, respectively. In Western Europe, the most common disturbances are windthrows, surface fires and fluctuations in moisture regime; in Eastern Europe and Siberia, the most common disturbances are crown and surface fires and insect outbreaks. Type, return interval and severity of disturbances are strongly influenced by the site conditions and successional stage of a stand.• Based on characteristics of forest stands and disturbance regime, four main types of pristine boreal forest stand dynamics can be distinguished: (1) even-aged, compositional change dynamics, (2) even-aged, mono-dominant dynamics, (3) cohort dynamics and (4) fine-scale gap dynamics. These types can be mimicked in developing scenarios of ecological sustainable forest management in Eurasian boreal forests.Résumé• Cette revue bibliographique résume les résultats de nombreuses études anciennes sur la structure des peuplements forestiers, sur les régimes de perturbation et sur les dynamiques de succession en forêt boréale eurasienne. Une typologie des modes de succession est proposée pour servir de cadre à une gestion forestière proche de la nature.• Les études analysées montrent l’existence de multiples modes de succession et de développement des peuplements dans tous les types de forêts vierges analysées. Des peuplements mélangés comportant des arbres de tous âges se développent en réponse à des perturbations locales avec des dynamiques de plusieurs siècles. Ce développement endogène peut être interrompu par des renouvellements massifs ou des perturbations partielles qui conduisent à des successions basées sur des peuplements équiennes ou structurés en cohortes, respectivement. En Europe occidentale, les perturbations les plus fréquentes sont les chablis, les incendies de surface et des fluctuations des régimes hydriques ; en Europe oriental et en Sibérie, ce sont les incendies de surface et de canopée, et les attaques massives par des insectes.• En se basant sur les caractéristiques des peuplements et des types de perturbations, nous avons pu identifier quatre types principaux de dynamiques forestières : (1) une dynamique de changement de composition spécifique avec une structure équienne ; (2) une dynamique de domination par une espèce avec une structure équienne ; (3) une dynamique de cohortes ; et (4) une dynamique de trouées locales. Ces types de succession peuvent servir de base pour le développement de scénarios de gestion forestière durable de ces forêts boréales eurasiennes.

Structure of a pristine Picea abies forest in northeastern Europe

. The forest structure in a large, relatively homogeneous area of pristine Picea abies taiga in the southern boreal region west of the Ural mountains was studied along four 500-m long transects. P. abies dominated the forest in association with Abies sibirica and Betula spp. The mean volume of living trees was 216 m3/ha. This value varied among the four transects, from 138 - 252 m3/ha. Mean density of trees (DBH > 1 cm) (and variation over the transects) was 2 064/ha (1670 - 2710). Living trees classified as dying or seriously damaged made up 2.9 (2.5 - 3.5) % of the living tree volume. Betula was an important canopy component and made up 16% of the living tree volume. The number of dead standing trees varied from 195 - 325/ha, corresponding to a volume of 10.8 - 70.7 m3/ha. The density of trees with a broken stem was 90 - 170/ha and their estimated volume 7.6 - 41.3 m3/ha. Standing dead trees and trees with broken stems represented 10.4 and 8.9% of the total standing tree volume (living + dead), respectively. The mean volume of decaying logs on the forest floor was 117 (84.4–156.2) m3/ha, corresponding to 54 (35 - 113) % of the living tree volume. The canopy-forming trees were present in the understory as abundant saplings and suppressed individuals. The size distribution of the dominant tree species resembled the inverse J-shape. Generally, the forest was characterized by a high small-scale structural variation and a larger-scale relative homogeneity. This pattern is consistent with forest dynamics where the forest consists of a small-scale mosaic of patches in different stages of recovery following disturbance. Our results suggest that the ecology and dynamics of extensive areas of natural boreal forests can be driven by small-scale disturbance.

Seedling establishment in relation to microhabitat variation in a windthrow gap in a boreal Pinus sylvestris forest

The characteristics of microhabitats of established Pinus sylvestris and Betula seedlings were studied in a small windthrow gap in a mature P. sylvestris-dominated forest in the Petkeljarvi National Park in eastern Finland. Seedlings were strongly clustered in disturbed microhabitats, particu- larly uprooting pits and mounds, formed by tree falls. They covered 3 % of the 0.3.ha study area consisting of the gap and some of the forest edge. Although Betula occurred only as scattered individuals in the dominant canopy layer of the forest, it accounted for 30 % of the seedlings found in the study area. Betula regeneration was almost completely re- stricted to pits and mounds, where 91% of the seedlings were found. Uprooting spots were also the most important regen- eration microhabitats for Pinus, where 60 % of the seedlings grew, even though the seedlings were found in other substrates as well, particularly on sufficiently decomposed coarse wood. Undisturbed field- and bottom-layer vegetation had effec- tively hindered tree seedling establishment, which emphasises the role of soil disturbance for regeneration. While the estab- lishment of seedlings was found to be clearly determined by the availability of favourable regeneration microhabitats, the early growth of seedlings was affected by a complex interac- tion of environmental variables, including the type of microhabitat, radiation environment and interferences caused by competing seedlings and adjacent trees. In the most impor- tant regeneration microhabitats, i.e. in uprooting pits and on mounds, the distributions of the local elevations of Pinus and Betula seedlings were different. Pinus seedlings occurred closer to ground level, i.e. on the fringes of pits and lower on mounds, while Betula seedlings grew deeper in pits and higher on mounds. The position of the Betula seedlings indicate that they may have a competitive advantage over Pinus seedlings in the dense seedling groups occurring in uprooting spots. We suggest that this initial difference in Pinus and Betula estab- lishment may affect the subsequent within-gap tree species succession and can, in part, explain the general occurrence of Betula in conifer-dominated boreal forests.

Even-Aged and Uneven-Aged Forest Management in Boreal Fennoscandia: A Review

Since WWII, forest management in Fennoscandia has primarily been based on even-aged stand management, clear cut harvesting and thinning from below. As an alternative, uneven-aged management, based on selection cutting of individual trees or small groups of trees, has been proposed. In this review we discuss the theoretical aspects of ecology and economics of the two management approaches. We also review peer-reviewed studies from boreal Fennoscandia, which have aimed at comparing the outcomes of uneven-aged and the conventional even-aged forest management. According to a common view the main obstacle of practicing uneven-aged forestry is its low economic performance. However, the reviewed studies did not offer any straightforward support for this view and several studies have found uneven-aged management to be fully competitive with existing even-aged management. Studies on the ecological aspects indicated that selection cuttings maintain mature or late-successional forest characteristics and species assemblages better than even-aged management, at least at the stand scale and in the short term. We conclude that although the number of relevant studies has increased in recent years, the ecological and economic performance of alternative management methods still remains poorly examined, especially for those stands with multiple tree species and also at wider spatial and temporal scales. For future research we advocate a strategy that fully takes into consideration the interdisciplinary nature of forest management and is better connected to social goals and latest theoretical and methodological developments in ecology and economics.

Effect of crown shape and tree distribution on the spatial distribution of shade

Abstract A method for calculating the light extinction probability caused by a forest canopy is presented. With the calculation procedure, it is possible to examine the effect of crown shape, stand density and spatial distribution of trees on the spatial distribution of light extinction probability or on the total shaded area caused by the canopy. At low sun elevations, the momentary projection area of a single crown is greater the more vertically extended the crown is, if the crown volume is held constant. When a longer time period is concerned, the area where the average extinction probability exceeds some arbitrary value is greatest for umbrella-like, horizontally extended crowns. The same is true for a single tree and for a forest stand. When the stand density is low or the tree crown is narrow, the spatial distribution of trees has only a small effect on the amount of shaping; the total amount of shading in random distribution is almost the same as in systematic distribution. In a stand where the total horizontal projection area of crown cones is high, the spatial distribution of trees should be systematic for effective light interception.

Relationship between radiation interception and photosynthesis in forest canopies: effect of stand structure and latitude

Abstract Interception of radiation and the consequent potential photosynthesis was studied, by sing a simulation model, in structurally different forest stands at latitu udes 40° and 60°. The studied stands were of two different types with respect to the leaf-area distribution: horizontally homogenous canopies and canopies with an aggregation of leaves into individual crowns. The effect of canopy structure on interception of radiation and photosynthesis was studied by varying leaf area index, stand density, and crown size and shape. In none of the studied cases was the relationship between accumulated radiation interception and photosynthesis strictly linear, but on a longer time-scale (one growing season) this non-linearity was not very pronounced. Neither canopy structure nor latitude substantially affected the slope of the relationship. In conclusion, while properties of canopy structure and incoming radiation determine the actual amount of radiation intercepted by the canopy, the conversion efficiency between intercepted radiation and photosynthesis appeared to be rather insensitive to differences in canopy structure and in properties of incoming radiation.

A spatial simulation approach to natural forest landscape dynamics in boreal Fennoscandia

Spatially explicit simulation models are needed for predicting the landscape-level effects of historical or potential disturbance regimes. We present a stochastic, grid-based model incorporating a mechanistic model of fire spread, tailored for simulating the fire-driven forest landscapes of boreal Fennoscandia, based on the North American LANDIS model. The approach is semiquantitative, and suited to qualitative predictions on the fire‐landscape interaction. We tested the extent to which the model is able to reproduce the current forest composition of the Ulvinsalo nature reserve (2516 ha) in eastern Finland, based on a GIS map of ecological site types and an empirically-derived fire history of the area. The model satisfactorily predicted the forest composition based on the dominant tree species and the relative occurrence of tree species, as well as the qualitative pattern of the tree age distribution. The major discrepancies were related to the occurrence of sub-dominant broadleaved species and the spatial pattern of fire frequency. We conclude that while the modeling approach is suitable for qualitative exploration, quantitatively accurate predictions require better empirical data on fire behavior, tree autecology, and their interaction, as well as more rigorous methods of model parameterization. The simulated scenario illustrates the change in forest composition from the uneven-aged old-growth pine forests maintained by the historical fire regime to the old-growth spruce forests dominating in the absence of fires. # 2002 Elsevier Science B.V. All rights reserved.

Spatial distribution of soil ergosterol in the organic layer of a mature Scots pine (Pinus sylvestris L.) forest

Abstract The spatial structure of the organic layer fungal biomass estimated from soil ergosterol content of a 1 ha plot in a mature Scots pine ( Pinus sylvestris L.) forest was described from 181 samples and examined in relation to the organic layer properties (thickness, pH, total C, N, K, Mg and Ca) and two above-ground environmental factors: gap fraction, i.e. proportion of sky not shaded by trees directly above the sampling point and throughfall. Ergosterol content of the organic layer had a clear spatial dependence over the studied area, and the spatially structured autocorrelation variance accounted for up to 90% of total sample variance in a 4 m range. Most of the measured properties of the organic layer and the above ground environmental factors were also spatially dependent, although to varying degrees. The spatial pattern of ergosterol was most strongly related to pH, organic layer thickness and total C content. Our analyses did not show any direct influence of gap fraction and throughfall on ergosterol. However, gap fraction and throughfall were related to organic layer thickness indicating the importance of the associated factors (moisture, light, temperature, quality of litter) on forest litter decomposition.