Coarse woody debris pools and their decay class dynamics were studied in three areas of unmanaged boreal forest in northern Finland, and in the Murmansk and Arkhangelsk provinces in northwestern ...Russia. The study areas had varying climatic and edaphic conditions, and disturbance histories. Living and dead trees (diameter at 1.3
m height ≥10
cm) were measured in five late-successional
Picea abies-dominated stands in each of the three areas. Wood density and time since death were determined from randomly sampled dead
P. abies, and their decay class dynamics were modeled using stage-based matrix models.
Volumes and decay class distributions of coarse woody debris reflected each site's productivity and disturbance history. Volumes ranged from 41 to 170
m
3
ha
−1, and as a proportion of total wood volume varied from 28% in an area with constant tree mortality, to 38% and 53% in areas with past episodic disturbances. Expected residence times (or half-lives) of snags varied from 12 to 27 years, and for down woody debris from 20 to 40 years, so that the residence times for both decreased from north to south.
The results imply naturally variable quantities and residence times of coarse woody debris in late-successional European boreal forests. These data also indicate the role of a site's disturbance history as a determining factor for quantity and decay class distributions. The developed models for decay class dynamics are applicable for both assessing the habitat availability for deadwood-dependent organisms, and carbon dynamics.
Severe droughts have the potential to reduce forest productivity and trigger tree mortality. Most trees face several drought events during their life and therefore resilience to dry conditions may be ...crucial to long-term survival. We assessed how growth resilience to severe droughts, including its components resistance and recovery, is related to the ability to survive future droughts by using a tree-ring database of surviving and now-dead trees from 118 sites (22 species, >3,500 trees). We found that, across the variety of regions and species sampled, trees that died during water shortages were less resilient to previous non-lethal droughts, relative to coexisting surviving trees of the same species. In angiosperms, drought-related mortality risk is associated with lower resistance (low capacity to reduce impact of the initial drought), while it is related to reduced recovery (low capacity to attain pre-drought growth rates) in gymnosperms. The different resilience strategies in these two taxonomic groups open new avenues to improve our understanding and prediction of drought-induced mortality.
The aim here was to review and summarize the findings of scientific studies concerning the types of forest dynamics which occur in natural forests (i.e. forests with negligible human impact) of ...boreal Fennoscandia. We conducted a systematic search for relevant studies from selected reference databases, using search terms describing the location, structure and processes, and degree of naturalness of the forest. The studies resulting from these searches were supplemented with other known works that were not indexed in the databases. This procedure yielded a total of 43 studies. The studies were grouped into four types of forest dynamics according to the information presented on the characteristics of the native disturbance-succession cycle: 1) even-aged stand dynamics driven by stand-replacing disturbances, 2) cohort dynamics driven by partial disturbances, 3) patch dynamics driven by tree mortality at intermediate scales (> 200 m) and 4) gap dynamics driven by tree mortality at fine scales (< 200 m). All four dynamic types were reported from both spruce and pine dominated forests, but their commonness differed. Gap dynamics was most commonly reported in spruce forests, and cohort dynamics in pine forests. The studies reviewed provide the best obtainable overall picture of scientific findings concerning the characteristics and variability of the unmanaged boreal forest dynamics in Fennoscandia. The results demonstrate that the unmanaged Fennoscandian forests are characterized by more diverse and complex dynamics than has traditionally been acknowledged.
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Disturbance regimes are changing in forests across the world in response to global climate change. Despite the profound impacts of disturbances on ecosystem services and biodiversity, assessments of ...disturbances at the global scale remain scarce. Here, we analyzed natural disturbances in boreal and temperate forest ecosystems for the period 2001–2014, aiming to 1) quantify their within‐ and between‐biome variation and 2) compare the climate sensitivity of disturbances across biomes. We studied 103 unmanaged forest landscapes with a total land area of 28.2 × 106 ha, distributed across five continents. A consistent and comprehensive quantification of disturbances was derived by combining satellite‐based disturbance maps with local expert knowledge of disturbance agents. We used Gaussian finite mixture models to identify clusters of landscapes with similar disturbance activity as indicated by the percent forest area disturbed as well as the size, edge density and perimeter–area‐ratio of disturbed patches. The climate sensitivity of disturbances was analyzed using Bayesian generalized linear mixed effect models and a globally consistent climate dataset. Within‐biome variation in natural disturbances was high in both boreal and temperate biomes, and disturbance patterns did not vary systematically with latitude or biome. The emergent clusters of disturbance activity in the boreal zone were similar to those in the temperate zone, but boreal landscapes were more likely to experience high disturbance activity than their temperate counterparts. Across both biomes high disturbance activity was particularly associated with wildfire, and was consistently linked to years with warmer and drier than average conditions. Natural disturbances are a key driver of variability in boreal and temperate forest ecosystems, with high similarity in the disturbance patterns between both biomes. The universally high climate sensitivity of disturbances across boreal and temperate ecosystems indicates that future climate change could substantially increase disturbance activity.
In Sweden, the majority of forest area has been altered by industrial forestry over the decades. Almost 30 years ago, a shift towards biodiversity-oriented forest management practices occurred. Here ...we took advantage of long-term data collected by the Swedish National Forest Inventory to track developmental changes in forest structural components over this time. We assessed changes in structural components that play an important role in biodiversity (dead wood, large living trees, tree species composition, and understory vegetation) in four forest types with descending tiers of biodiversity protection: protected areas, woodland key habitats, low-productivity forests and production forests. Overall, we found a positive trend in the volumes of dead wood and large living trees, as well as in tree species diversity, while there was a general decline in understory vegetation coverage. Most observed changes were consistent with the intended outcomes of the current forest policy, adapted in the early 1990s. The implementation of retention forestry is likely driving some of the observed changes in forest structural components in the south. In contrast, we observed no changes in any of the focal structural components in the north, which could be attributed to the ongoing clear-cutting of forests previously managed less intensively. Dead wood and large living trees increased not only in managed, but also in unmanaged forests, likely reflecting historical management. The increased tree species diversity can be explained through current forest management practices that encourages maintenance of additional tree species. Decreasing understory vegetation coverage in both dense managed and unmanaged forests suggests that factors other than forestry contribute to the ongoing changes in understory vegetation in Swedish forests. Overall, the observed increase in structural components has not yet been reflected in documented improvements for red-listed forest species, which may be due to delays in species responses to small improvements, as well as a lack of detailed monitoring. Similarly, the increased availability of forest structural components might still be insufficient to meet the specific habitat requirements of red-listed species.
•Biodiversity important structural components were assessed in Swedish forests.•Dead wood and large living trees increased over time, but not in the north.•Tree species diversity increased due to more deciduous tree species.•Understory vegetation coverage declined, probably due to denser forests.•The observed trends are in line with the increased conservation concern.
In boreal forests fires often ignite and spread within the dominant moss and lichen cover of the ground layer vegetation, which thus greatly influences fire hazard. We used an experimental set-up in ...greenhouse conditions to study the differences in how (1) fuel moisture and (2) wind velocity influence the ignition probability and fuel consumption among four common circumboreal ground vegetation fuels, Pleurozium schreberi (Willd. ex Brid.) Mitt., Hylocomium splendens Schimp., Dicranum spp. and Cladonia rangiferina (L.) F. H. Wigg. Our results show that the reindeer lichen C. rangiferina was clearly the most flammable species, with high ignition probability even at high moisture contents and low wind velocities. Of the mosses, Dicranum was the least flammable, with low ignition probability and mass loss at low wind velocities regardless of moisture content. P. schreberi and H. splendens behaved somewhat similarly with wind velocities quickly increasing the initially low ignition probability and mass loss observed in the absence of wind. However, especially for mass loss, among-species differences tended to disappear with stronger winds. The observed differences can be explained by the different structures and growth forms of the studied species and open a potential avenue for improving forest fire risk predictions.
Elevation-for-latitude substitution offers a tool for studying the influence of temperature and precipitation variability on vegetation structure and composition. Understanding how elevation, aspect, ...and slope influence vegetation patterns may help in predicting how climate change influences human forest usage and in developing strategies for ensuring the sustained provision of ecosystem services. However, most ecological studies have been carried out in protected areas, leaving forest areas used by humans to lesser attention. Therefore, we asked how elevation, aspect, and slope impact the vegetation on a human-influenced mountain. We measured woody vegetation size, richness, and composition on a mountain with plots set systematically in four cardinal directions at 100-m elevational intervals from the peak, from 1900 to 4200 m above sea level, in the Hengduan Mountains in eastern Himalaya, southwestern China. We quantified how tree maximum height, basal area, aboveground biomass (AGB), tree and shrub species richness, and woody species composition changed with elevation, aspect, and slope. Based on generalized linear models, the maximum tree height, tree basal area, and woody species AGB followed a unimodal trend along elevational gradients, with tree height and basal area peaking at 3100 m, while AGB was highest at 3300 m and somewhat higher on the southern slope. Basal area increased with slope degree. Neither tree nor shrub species richness was influenced by elevation, aspect, or slope. According to canonical correspondence analysis and TWINSPAN classification, elevation and north-south orientation of the slope were major factors influencing woody species compositions, and vegetation was classified into five types of communities. Our results indicated that the influences of elevation, aspect, and slope on woody vegetation structure were similar in a human-influenced forested mountain area as in protected mountain landscapes based on the literature. However, as forests in this area are used more intensively at low and middle elevations of the southern and western slopes, where aridity restricts tree size and AGB, climate change is likely to challenge traditional harvesting practices and place pressure on moving forest usage to higher altitudes.
Light foraging by trees is a fundamental process shaping forest communities. In heterogeneous light environments this behavior is expressed as plasticity of tree growth and the development of ...structural asymmetries. We studied the relative influence of neighborhood structure and directional solar radiation on horizontal asymmetry of tree crowns in late-successional high latitude (67–68°N) forests in northern Fennoscandia. We described crown asymmetries as crown vectors (i.e. horizontal vectors from stem center to crown center), which we obtained from canopy maps based on crown perimeter measurements in the field. To disentangle the influence of the two main determinants, inter-tree competition and directionality of above-canopy solar radiation at high latitudes, we applied circular statistical models, utilizing cylindrical distributions, to these data consisting of orientations and intensities of crown asymmetry. At the individual tree level, our model predicted crown asymmetry vectors from the current stand structure, and the predictions became better when the intensity of asymmetry (i.e. crown vector length) was higher. Competition was the main determinant of crown asymmetry for 2/3 of trees, and the model predictions improved when we incorporated the directionality of solar radiation. At the stand-level, these asymmetries had resulted in a small increment of the projected canopy area and an increased regularity of spatial structure. Our circular statistical modelling approach provided a quantitative evaluation of the relative importance of directionality of solar radiation and neighborhood stand structure, showing how both of these factors play a role in formation of crown asymmetries in high latitude forests. This approach further demonstrated the applicability of circular statistical modeling in ecological studies where the response variable has both orientation and intensity.
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•North Fennoscandian mountain forests are relatively little affected by human utilization.•They are very important for biodiversity conservation and for their sociocultural ...values.•Fine scale processes are essential features of mountain forests and their dynamics.•Rapid change in climate is predicted to profoundly affect forest ecology and dynamics.•Some of the changes are gradual but also drastic disturbances will become more likely.
North Fennoscandian mountain forests are distributed along the Scandes Mountains between Sweden and Norway, and the low-mountain regions of northern Norway, Sweden and Finland, and the adjacent northwestern Russia. Regionally, these forests are differentiated into spruce, pine or birch dominance due to climatic differences. Variation in tree species dominance within these regions is generally caused by a combination of historical and prevailing disturbance regimes, including both chronic and episodic disturbances, their magnitude and frequency, as well as differences in edaphic conditions and topography. Because of their remoteness, slow growth and restrictions of use, these mountain forests are generally less affected by human utilization than more productive and easily utilizable forests at lower elevations and/or latitudes. As a consequence, these northern forests of Europe are often referred to as “Europe’s last wilderness”, even if human influence of varying intensity has been ubiquitous through historical time. Because of their naturalness, the North Fennoscandian mountain forests are of paramount importance for biodiversity conservation, monitoring of ecosystem change and for their sociocultural values. As such, they also provide unique reference areas for basic and applied research, and for developing methods of forest conservation, restoration and ecosystem-based management for the entire Fennoscandia. However, the current rapid change in climate is predicted to profoundly affect the ecology and dynamics of these forests in the future.
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