Southern Boreal Region Research Articles

Structure of a pristine Picea abies forest in northeastern Europe

Abstract. 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.

The palaeoecology of a treed bog in western boreal Canada: a study based on microfossils, macrofossils and physico-chemical properties

The developmental histories of a wetland and the surrounding upland vegetation in the southern boreal region of western Canada are traced through microfossil, macrofossil, physico-chemical and radiometric analyses of a 425 cm deep core consisting of sandy gyttja and peat. Microfossil analysis includes algal, fungal and zoological ‘Types’ which are illustrated and described, with notes on their occurrence as observed in several peat sequences of western boreal Canada. Local wetland development started in the central area of a 65 ha closed depression at c. 5000 BP, due to a rise in the groundwater table related to a gradual increase in effective precipitation in the region. Initial stages were characterised by Typha-dominated marsh communities that suggest marked seasonal fluctuations in local water levels. The accumulation of organic matter could not keep pace with the ever-rising groundwater table, and a shallow eutrophic pond with aquatic macrophytes developed locally. The body of open water was surrounded by marsh vegetation that was gradually being displaced towards the margins of the depression. At 4330 BP moist conditions became prevalent throughout the growing season. A brown-moss dominated treed rich fen replaced the shore marsh community and gradually began to encroach on the small pond. The basin completely terrestrialised at 3260 BP. Autogenic processes caused by peat accumulation resulted in a transition towards a Sphagnum-dominated treed poor fen. At 2790 BP a treed bog became established, firstly dominated by Sphagnum angustifolium and S. magellanicum indicating moist local conditions. After 1870 BP S. fuscum became dominant, indicating drier conditions locally. The upland vegetation just before local wetland formation was characterised by Picea in relatively wet depressions and by Populus in drier areas. Some grassland patches were present, most probably on the more southerly exposed slopes of the hills. Picea was locally displaced by wetland vegetation at c. 5000 BP, whereas deciduous forest and some grassland stands continued to dominate the surrounding hills. The coniferous taxa Pinus and Picea began to invade the uplands after 4330 BP, contemporaneously with the development of the local peatland. This marks the time at which the modern southern boreal ecosystem dominated by peatlands in lowlands and mixed wood forest in uplands became established in the area.

Riparian edge effects on boreal balsam fir bird communities

Riparian forests are often identified as prime habitat for wildlife because of the presence of particular plant communities and edges creating a highly developed and diversified vegetation structure. However, in the northeastern boreal forests of Canada, where narrow land–water ecotones with abrupt edges are quite common, the relative habitat value of riparian forests remains to be demonstrated. We compared bird communities of eight pairs of riparian and nonriparian plots, similar in vegetation structure and composition, to verify the relative value for breeding birds of typical coniferous riparian forest stands of the southern boreal region of eastern Quebec. Bird abundance (P = 0.02), richness (P = 0.03), and diversity (P = 0.02) were significantly higher in the riparian stands, where the spatial sequence of three distinct habitats (a balsam fir (Abiesbalsamea (L.) Mill.)–northern white cedar (Thujaoccidentalis L.) forest, a narrow alder (Alnusrugosa (Du Roi) Spreng.) - grass wetland, and water) created high horizontal vegetation diversity. In riparian stands median bird richness and density were, respectively, 23.5 species and 437.5 territories/km2 compared with 19.0 species and 348.2 territories/km2 for interior stands. Nine species were observed exclusively in riparian plots. In addition to the species usually found in the studied nonriparian forests, the riparian plots were used by species typically related to the water edge such as the Northern Waterthrush (Seiurusnoveboracensis Gmelin) and Rusty Blackbird (Euphaguscarolinus Miiller) as well as species associated with the shrub and grass wetland such as the American Robin (Turdusmigratorius L.), the Veery (Catharusfuscescens Stephens), and the Common Yellowthroat (Geothlypistrichas L.). The shrub-foraging guild showed higher abundance in riparian stands. The tree-foraging and tree-bole foraging guilds, however, were comparable in both groups of stands. In this study, the natural conditions prevailing along he riparian sites appeared mostly positive for the breeding-bird community; it created what is perceived as being an "edge effect." The edge effect can be defined, in this case, as being the additional density and number of species induced by the added horizontal vegetation diversity created by the close association of three extremely different ecosystems: a forest stand, an aquatic ecosystem, and a narrow but distinct shrub-grass wetland. This also confirms the necessity of distinguishing natural edges that are permanent features of the landscape from induced edges created by human activity.