Kalev Jõgiste

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.

Carbon dynamics of North American boreal forest after stand replacing wildfire and clearcut logging

Boreal forest carbon (C) storage and sequestration is a critical element for global C management and is largely disturbance driven. The disturbance regime can be natural or anthropogenic with varying intensity and frequency that differ temporally and spatially the boreal forest. The objective of this review was to synthesize the literature on C dynamics of North American boreal forests after most common disturbances, stand replacing wildfire and clearcut logging. Forest ecosystem C is stored in four major pools: live biomass, dead biomass, organic soil horizons, and mineral soil. Carbon cycling among these pools is inter-related and largely determined by disturbance type and time since disturbance. Following a stand replacing disturbance, (1) live biomass increases rapidly leading to the maximal biomass stage, then stabilizes or slightly declines at old-growth or gap dynamics stage at which late-successional tree species dominate the stand; (2) dead woody material carbon generally follows a U-shaped pattern during succession; (3) forest floor carbon increases throughout stand development; and (4) mineral soil carbon appears to be more or less stable throughout stand development. Wildfire and harvesting differ in many ways, fire being more of a chemical and harvesting a mechanical disturbance. Fire consumes forest floor and small live vegetation and foliage, whereas logging removes large stems. Overall, the effects of the two disturbances on C dynamics in boreal forest are poorly understood. There is also a scarcity of literature dealing with C dynamics of plant coarse and fine roots, understory vegetation, small-sized and buried dead material, forest floor, and mineral soil.

Regeneration in windthrow areas in hemiboreal forests: the influence of microsite on the height growths of different tree species

AbstractNatural regeneration of windthrow areas is an important issue when planning forestry measures after forest disturbances. Seedling recruitment was investigated in storm-damaged hemiboreal mixed forests in eastern Estonia. The establishment and growth of seedlings from natural regeneration was registered for tree species in soil pits and in mounds of uprooted trees in stands that were either heavily or moderately damaged. Seedling growth is expected to be better in large but shallow soil pits created by uprooted Norway spruce [Picea abies (L.) Karst.] and poorer in small but deep pits created by the hardwoods in the area, silver birch (Betula pendula Roth.) and European aspen (Populus tremula L.). The most abundant regenerating species was birch. Pits hosted larger seedling numbers than mounds, due to soil instability in mounds. Rowan (Sorbus aucuparia L.) showed significantly faster growth than the other seedling species. Norway spruce pits were preferred to pits of other species by both birch and spruce seedlings. Black alder [Alnus glutinosa (L.) J. Gaertn.] did not show a preference for pits of a certain species of uprooted tree. Both spruce and rowan preferred hardwood mounds over spruce mounds. Storm severity also affected species composition: birch predominantly occurred on pits and mounds in heavily disturbed areas, while spruce was more abundant in the moderately damaged areas. The effects of advance regeneration and surrounding stands on seedling microsite preferences should be considered in future research and subsequent management recommendations.

Storm disturbance in forest ecosystems in Estonia

Abstract Several storms have damaged Estonian forests in recent years. Individual tree properties such as diameter at breast height (dbh) and tree height affect the type of damage (stem breakage or uprooting) and influence the formation of postdisturbance forest structure. The aim of this study was to analyse how the risk of uprooting and stem breakage varied with respect to tree diameter, height, species and soil conditions. The data were collected from plots located in storm-damaged forests in eastern Estonia. The probability of uprooting increased with increasing diameter for Norway spruce, European aspen and birch. Black alders with large stem diameter usually suffered stem breakage. A high proportion of stem breakage also occurred among small Norway spruce in the understorey, probably damaged by falling canopy trees. Soil conditions influenced the ratio between uprooting and stem breakage of Norway spruce, the ratio being much higher on gley soils than on podzolic soils. The root plate size of Norway spruce was only slightly correlated with dbh, tree height and volume.

The influence of storm-induced microsites to tree regeneration patterns in boreal and hemiboreal forest

We reviewed studies dealing with regeneration under variable conditions in boreal and hemiboreal forests as affected by different microsite types by tree species functional groups. Generally, the importance of storm-induced microsites for regeneration dynamics in boreal forests depends on several factors: (1) distribution and type of microsites (generated by storm characteristics and stand conditions); (2) viable seed supply (stand history, species dispersal traits and status of surviving trees) and their species’ life history strategy; (3) climatic and site conditions (pre-storm conditions and storm-induced changes); and (4) delayed storm effects, such as retarded falling of trees, favoured vegetation growth, etc. Studies acknowledging the significance of microsites were mostly related to intermediate or severe events, causing sufficient changes in resource levels and growth conditions, and influencing extrinsic factors such as frost heaving, erosion and browsing. Also, the dispersal traits of available tree species, including sprouting and response of surviving trees, such as canopy expansion, should be considered in evaluating microsite importance in individual cases. In intermediate to severe windstorm events, pioneer species are generally profiting most from the additional offer in microsites, requiring bare mineral soil and elevated locations for their establishment and growth. Under gap dynamics, shade-tolerant species benefit from dead wood and elevated locations as these offer safe sites in stands with abundant understorey vegetation.

A conceptual model of forest stand development based on permanent sample-plot data in Estonia

Abstract Ecosystem management assumes that management practices based on natural disturbance patterns are likely to preserve both natural biodiversity and ecosystem functions. Ecosystem management thus combines traditional natural resource management and forestry practices together with classical notions of protection that are focused on sustaining a naturally evolving ecosystem. Increased knowledge and understanding of natural disturbance dynamics in boreal forest ecosystems allow for the creation of a template for sustainable forest management that is based on mimicking disturbances that are thought to contribute to the biodiversity of the ecosystem. The observed trends of natural development are discussed in this paper. Permanent sample-plot data are used to develop a conceptual model of stand succession following natural disturbance. The distinctive characteristics of disturbances that are relevant to forest management planning are identified and modelled.

A basal area increment model for Norway spruce in mixed stands in Estonia.

An individual tree basal area increment model was developed for Norway spruce [Picea abies (L.) Karst] in mixed stands of spruce and birch in Estonia. Different regression equations were fitted for different combinations of variables to obtain biologically tractable interactions between growth and factors affecting it. The best fit index of the regression model was pursued in trials with variable combinations. The basal area increment was chosen to describe the tree growth and both the diameter and age of the tree were included as independent variables. The logical growth relationships were obtained. The basal area increment has a culmination introduced by the simultaneous influence of tree size and age explicitly included in the model. The stand level attributes contributed modestly to the explanatory power of the model because of the narrow range of stand conditions sampled. The present model is applicable to Estonian conditions.

Variation and ecological characteristics of coarse woody debris in Lahemaa and Karula National Parks, Estonia

Abstract The coarse woody debris (CWD) was inventoried in two boreal Estonian conifer-dominated forest landscapes/national parks, Lahemaa and Karula, with different forestry history and management intensity. The inventoried areas in both national parks consisted of a core with a strict nature reserve (unmanaged) and the surrounding protected special and restricted management zones (management activities in the past). Stands with no records of silvicultural activity since the 1920s (unmanaged) were compared with traditionally harvested stands. CWD was measured as standing dead trees, logs and snags >10 cm in diameter and >1.3 m in length in 304 circular plots (Lahemaa 134 plots, Karula 170 plots; r=11.28 m, 400 m2). The volumes of CWD varied considerably between individual stands. The mean volume of CWD (standing and down combined) in Lahemaa was 48.5 m3 ha−1, ranging from 0.6 to 148.6 m3 ha−1. The mean volume of CWD in Karula was 27.6 m3 ha−1, ranging from 0.2 to 193.7 m3 ha−1 from stand to stand. On average, 19.5 m3 ha−1 (40.2%) of CWD in Lahemaa was standing dead wood and 29.1 m3 ha−1 (59.8%) down dead wood. In Karula standing dead wood formed 15.2 m3 ha−1 (55.7%) and down dead wood 12.2 m3 ha−1 (44.3%). Variation in CWD volumes was clearly dependent on the management history of the stands. Stands with a documented history of management (e.g. cuttings and thinnings) had significantly lower CWD volume than natural stands found mainly in strict nature reserves. Stands selectively logged a long time ago (more than approximately 60 years) did not differ considerably from natural stands in the amount of CWD. The amount of CWD in managed stands (Lahemaa 14.1 m3 ha−1 and Karula 10.6 m3 ha−1) was comparable to other studies in silviculturally managed forests in the boreal zone. The study shows that CWD amounts in Estonian conditions are similar to previous studies in this region.

Vascular plant response to windthrow severity in Norway spruce–dominated Myrtillus site type forests in Estonia

ABSTRACT Species composition and number of species in ground vegetation after windthrow varies depending on damage severity and management actions after a storm event. In this paper we seek to determine the changes in species composition depending on the severity of storm damage. The vegetation response was studied by comparing areas with different levels of windthrow damage (undamaged, partly damaged, totally damaged, and totally damaged and harvested) in Norway spruce–dominated forests in Estonia. A total of 108 herbal and shrub species were found in all areas. Species number was lowest in the control areas and highest in the harvested plots. The number of species that responded to disturbance severity, when compared to the control plots, increased during the second year of the two-year survey period. The groups of species responding to different degrees of storm severity and silvicultural treatments were identified. Early invasion after a storm was observed in the case of several species, such as Epilobium angustifolium, Rubus idaeus, and Ranunculus repens. All the ferns that responded to damage extent seemed to be most favoured in totally damaged areas. Rubus saxatilis showed the clearest response trend, with higher coverage in response to increasing wind severity.

Recovery of advance regeneration after disturbances: Acclimation of needle characteristics in Picea abies

Abstract This study examined the effect of release on needle properties of Norway spruce advance regeneration in a gap clearing. Needle mass is a variable revealing the acclimation capacity of understorey saplings. Correlations between several needle variables were also examined. A model of needle mass increase over time was developed. Needle mass and shoot length in consecutive years help to describe the dynamics of the advance regeneration response. The analysis suggests that needle and shoot properties had reached new stable conditions 5 years after stand clearance.