Boreal Forest Species Research Articles

Start of reproduction and allozyme heterozygosity in Pinus sibirica under different techniques of artificial forest stand establishment

Siberian stone pine (Pinus sibirica Du Tour) is one of the main forest-forming tree species in boreal forests of Eurasia. Large edible seeds of this species have an important resource value because of their high nutritious properties. Development of approaches to establishment of early cone producing Siberian stone pine stands including utilization of corresponding genetic background is one of the priorities of forest resource management. The goal of our study was to evaluate the effect of stand density on the differentiation of trees by the age of first reproduction and the relationship of allozyme heterozygosity and morphological traits variability in Siberian stone pine. Morphological and allozyme variability in artificial Pinus sibirica stands with high and low density was investigated. In the high-density stand the distance between trees was 0.7 and 3 meters (4080 trees per ha) while in the lowdensity stand it was 8 and 8 meters (144 trees per ha). Age of formation of first male and female cones was evaluated by retrospective method based on analysis of tracks of cones on a shoot bark. Tree height, diameter and number of male, female and vegetative shoots in a crown of model trees were measured. Genotypes of the trees were determined by 29 isozyme loci coding for 16 enzymes (ADH, FDH, FEST, GDH, GOT, IDH, LAP, MDH, MNR, PEPCA, 6-PGD, PGI, PGM, SDH, SKDH, SOD). In the low-density stand, the portion of generative trees was higher and differentiation of trees by age of reproduction starting was lower in spite of the smaller age of trees as compared to the high-density stand. In both samples, the age of formation of first generative organs was related negatively with stem height, stem diameter and number of female shoots. In the high-density stand, positive relation of age of first reproduction with total number of shoots and number of male shoots was found. In both samples nonreproductive trees were less heterozygous at isozyme loci as compared to trees starting cone production. Allozyme heterozygosity correlated positively with the age of first cone production in the high-density stand only. We conclude that the degree of competition between trees due to different stand density determined age and timing of first reproduction and development of tree crowns. The relationship of allozyme heterozygosity and the age of first reproduction was expressed more in the high-density stand of Siberian stone pine.

Significance of woodland key habitats for polypore diversity and red-listed species in boreal forests

Preservation of woodland key habitats has become an integral part of biodiversity-oriented forest management in northern Europe. In Finland, brook-side spruce forests constitute the most important key-habitat type in terms of total area and timber volume. Our aim was to compare polypore diversity and the occurrence of red-listed species between brook-side key habitats and comparable sites of managed forest as controls. Furthermore, we assessed the importance of stand structural features to polypore communities, and contrasted regions with different land-use history. Altogether 69 key habitats and 70 controls were inventoried in four regions across southern Finland. A total of 28,023 surveyed dead-wood units had 3,307 occurrences of 114 species of which 25 species were red-listed. Key habitats hosted on average 28% (about two species) more polypore species (mainly deciduous-specialists) than controls because of a larger average volume of dead wood and a higher proportion of dead deciduous wood. However, the average number of red-listed species was low and did not differ between the two forest categories. We detected a landscape effect connected with the intensity and length of forest management history, with the highest numbers of all and red-listed species per site in eastern Finland. Volume and diversity of dead wood were the most important variables explaining variation in species richness. Presently, key habitats in managed forests appear to contribute only little to the conservation of red-listed polypore species.

Comparative phylogeography and demographic history of the wood lemming (Myopus schisticolor): implications for late Quaternary history of the taiga species in Eurasia

The association between demographic history, genealogy and geographical distribution of mitochondrial DNA cytochrome b haplotypes was studied in the wood lemming (Myopus schisticolor), a species that is closely associated with the boreal forest of the Eurasian taiga zone from Scandinavia to the Pacific coast. Except for a major phylogeographic discontinuity (0.9% nucleotide divergence) in southeastern Siberia, only shallow regional genetic structure was detected across northern Eurasia. Genetic signs of demographic expansions imply that successive range contractions and expansions on different spatial scales represented the primary historical events that shaped geographical patterns of genetic variation. Comparison of phylogeographic structure across a taxonomically diverse array of other species that are ecologically associated with the taiga forest revealed similar patterns and identified two general aspects. First, the major south-north phylogeographic discontinuity observed in five out of six species studied in southeastern Siberia and the Far East implies vicariant separation in two different refugial areas. The limited distribution range of the southeastern lineages provides no evidence of the importance of the putative southeastern refugial area for postglacial colonization of northern Eurasia by boreal forest species. Second, the lack of phylogeographic structure associated with significant reciprocal monophyly and genetic signatures of demographic expansion in all nine boreal forest animal species studied to date across most of northern Eurasia imply contraction of each species to a single refugial area during the late Pleistocene followed by range expansion on a continental scale. Similar phylogeographic patterns observed in this taxonomically diverse set of organisms with different life histories and dispersal potentials reflect the historical dynamics of their shared environment, the taiga forest in northern Eurasia.

Fine root morphological adaptations in Scots pine, Norway spruce and silver birch along a latitudinal gradient in boreal forests

Variability in short root morphology of the three main tree species of Europe's boreal forest (Norway spruce (Picea abies L. Karst.), Scots pine (Pinus sylvestris L.) and silver birch (Betula pendula Roth)) was investigated in four stands along a latitudinal gradient from northern Finland to southern Estonia. Silver birch and Scots pine were present in three stands and Norway spruce was present in all stands. For three fertile Norway spruce stands, fine root biomass and number of root tips per stand area or unit basal area were assessed from north to south. Principal component analysis indicated that short root morphology was significantly affected by tree species and site, which together explained 34.7% of the total variability. The range of variation in mean specific root area (SRA) was 51-74, 60-70 and 84-124 m(2) kg(-1) for Norway spruce, Scots pine and silver birch, respectively, and the corresponding ranges for specific root length were 37-47, 40-48 and 87-97 m g(-1). The range of variation in root tissue density of Norway spruce, Scots pine and silver birch was 113-182, 127-158 and 81-156 kg m(-3), respectively. Sensitivity of short root morphology to site conditions decreased in the order: Norway spruce > silver birch > Scots pine. Short root SRA increased with site fertility in all species. In Norway spruce, fine root biomass and number of root tips per m(2) decreased from north to south. The differences in morphological parameters among sites were significant but smaller than the site differences in fine root biomass and number of root tips.

Habitat suitability models of saproxylic red-listed boreal forest species in long-term matrix management: Cost-effective measures for multi-species conservation

Understanding of how a large landscape or network of conservation areas and habitats of red-listed species change in time is an important topic when addressing the temporal interplay between protected areas and matrix. We developed models of habitat suitability indices (HSI) for saproxylic red-listed invertebrate and fungal species, accounting for roughly 70% of all red-listed boreal forest species of the study area in eastern Finland. By using a forestry planning program that incorporates various optimisation methods we analysed trade-offs between timber production and amount of habitats of saproxylic red-listed species within a 60-year period. We also produced production possibility frontiers that show how to increase quality of the matrix with least costs. Moreover, we analysed how habitat suitability criteria used in optimisations affect the area of different habitat quality classes. Our analysis shows that by adopting HSI models in long-term matrix management, it is possible to increase habitats for several red-listed species without substantial losses in timber production. The increase in habitat area is achieved mainly by decreasing the area that is thinned compared to intensive timber production plan. In the long term, this seems to be a novel cost-effective method to increase the quality of the matrix for red-listed saproxylic species. However, the selected optimisation method and the criteria or specification of the management objective for red-listed forest species have a strong effect on results when HSI models are used in conservation planning. Therefore any practical application must be performed with great care.

Nitrogen and Water Availabilities and Competitiveness of Bluejoint: Spruce Growth and Foliar Carbon‐13 and Nitrogen‐15 Abundance

How resource availabilities affect the competitiveness of Canada bluejoint grass [Calamagrostis canadensis (Michx.) P. Beauv., hereafter referred to as bluejoint] is poorly understood. Bluejoint is a widespread grass species in boreal forests and competes with tree species such as white spruce [Picea glauca (Moench) Voss] for belowground resources (e.g., soil N and water) when their supply is limited. In this greenhouse‐based study, we tested the following hypotheses: (i) bluejoint competition reduces white spruce growth when belowground resource availabilities are limited; (ii) greater N and water availabilities may increase bluejoint competition and its adverse effects on white spruce growth; and (iii) white spruce foliar δ13C and δ15N are affected by soil N and water availabilities and bluejoint competition. A 2 × 2 × 2 (competition × N availability × water availability) factorial experiment was conducted using pots of planted white spruce seedlings with or without bluejoint. Bluejoint competition reduced the volume index (diameter2 × height) of white spruce by 50%. The competitiveness of bluejoint appeared to be independent of resource availabilities, but bluejoint had greater growth response to increased N availability than white spruce. Bluejoint competition depleted white spruce foliar δ13C and δ15N by 1.2 and 1.2‰, respectively, even under adequate water supply, indicating that N deficiency caused by bluejoint competition had a dominant effect (increasing 13C discrimination during photosynthesis) compared with the potential effect of drought stress on foliar δ13C, and that strong NH4 uptake by bluejoint may have prevented significant soil N losses and 15N enrichment through nitrification and subsequent denitrification.

Exotic plant species in the southern boreal forest of Saskatchewan

Exotic species possess abilities to harm the ecosystems they invade. This study assesses the density, frequency and cover of exotic plants in roadside right-of-ways, logged areas and wildfire sites within mixedwood sections of the southern boreal forest of Saskatchewan. A total of 23 exotic species were observed including nine species of Gramineae, seven species of Leguminosae and five species of Compositae. Average density of exotic species in areas recently disturbed by timber harvesting or wildfire was 0.2 stems m −2 with a frequency of 72%. Exotic species adapted for wind dispersal were best represented including common dandelion ( Taraxacum officinale), perennial sow thistle ( Sonchus arvensis) and annual hawksbeard ( Crepis tectorum). Only two exotic species, T. officinale and Canada bluegrass ( Poa compressa), were observed in mature forest; both occurred with a frequency of 13% and an average density of 0.002 stems m −2. A total of 22 exotic species was found in the right-of-ways quadrats with an average density of 117 stems m −2 and a frequency of 94%. The most frequently observed exotic species in the roadside right-of-way areas were T. officinale, alsike clover ( Trifolium hybridum), S. arvensis, creeping red fescue ( Festuca rubra) and smooth brome grass ( Bromus inermis). These species are either common agricultural weeds or were part of the original seed mixture used to establish a plant cover in the roadside right-of-ways. Each of the exotic species observed was ranked to determine its current and potential threat to ecosystem attributes. The majority were considered a lesser threat and easy to control, with eight species ranked as a lesser threat and hard to control, and one species, B. inermis, ranked as a serious threat and hard to control. The distribution of exotic species was closely related to the management of roadside right-of-ways, wildfire events and timber harvesting. An increased distribution of exotic species was observed within roadside right-of-ways areas which had been subjected to more intensive management. Although the exotic species observed in this study are maintained and dispersed by management activities, the majority of exotic species are not a threat to this forest ecosystem in the southern boreal forest of Saskatchewan.

C and N stocks under three plantation forest ecosystems of Chinese fir, Michelia macclurei and their mixture

Chinese fir (Cunninghamia lanceolata), a type of subtropical fast-growing conifer tree, is widely distributed in South China. Its plantation area covers more than 7 × 106 hm2, accounting for 24% of the total area of plantation forests in the country. In recent decades, the system of successive plantation of Chinese fir has been widely used in southern China due to anticipated high economic return. However, recent studies have documented that the practice of this system has led to dramatic decreases in soil fertility and forest environment as well as in productivity. Some forest ecologists and managers recognize the ecological role performed by broadleaf trees growing in mixtures with conifers, and a great deal of studies on mixture effects have been conducted, particularly on mixture species of temperate and boreal forests, but these research results were not completely consistent. Possibilities include dependence of the mixture effects in large part to specific site conditions, the interactions among species in mixtures and biological characteristics of species. Although some researchers also studied the effects of mixtures of Chinese fir and broadleaf tree species on soil fertility, forest environment and tree growth status, little information is available about the effects of Chinese fir and its mixtures with broadleaves on carbon and nitrogen stocks. The experimental site is situated at the Huitong Experimental Station of Forest Ecology, Chinese Academy of Sciences, Hunan Province (26°40′–27°09′ N, 109°26′–110°08′ E). It is located at the transition zone from the Yunnan-Guizhou Plateau to the low mountains and hills of the southern bank of the Yangtze River at an altitude of 300–1,100 m above mean sea level. At the same time, the site is also a member of the Chinese Ecosystem Research Network (CERN), sponsored by the Chinese Academy of Sciences (CAS). This region has a humid mid-subtropical monsoon climate with a mean annual precipitation of 1,200–1,400 mm, most of the rain falling between April and August, and a mean temperature of 16.5°C with a mean minimum of 4.9°C in January and a mean maximum of 26.6°C in July. The experimental field has red-yellow soil. After a clear-cutting of the first generation Chinese fir (Cunninghamia lanceolata) plantation forest in 1982, three different plantation forest ecosystems, viz. mixture of Michelia macclurei and Chinese fir (MCM), pure Michelia macclurei stand (PMS) and pure Chinese fir stand (PCS), were established in the spring of 1983. A comparative study on C and N stocks under these three plantation forest ecosystems was conducted in 2004. Results showed that carbon stocks were greater under the mixtures than under the pure Chinese fir forest and the pure broad-leaved forest, and the broadleaves and the mixtures showed higher values in nitrogen stocks compared with the pure Chinese fir forest. The spatial distribution of carbon and nitrogen stocks was basically consistent, the value being greater in soil layer, followed by tree layer, roots, understory and litter layer. The carbon and nitrogen stocks in soil layer were both highly correlated with the biomass in understory and litter layer, indicating that understory and forest litterfall exerted a profound effect on soil carbon and nitrogen stocks under plantation ecosystems. However, correlations among soil carbon, nitrogen stocks and below ground biomass of stand have not been observed in this study.

Comparative evaluation of five height–diameter models developed for black spruce and jack pine stand-types in terms of goodness-of-fit, lack-of-fit and predictive ability

The objective of this study was to comparatively evaluate five nonlinear models on their ability to describe the relationship between total height ( H; m) and diameter at breast-height ( D; cm) within six commercially-important boreal stand-types. Specifically, the five models evaluated were as follows: (1) the constrained (i.e., H = 1.3 when D = 0) Chapman–Richards-based model proposed by Peng, Zhang and Liu [Peng, C., Zhang, L, Liu, L., 2001. Developing and validating nonlinear height-diameter models for major species of Ontario's boreal forests. NJAF 18, 87–94; denoted Model 1] which excludes consideration of stand-level effects; (2 and 3) the constrained Chapman–Richards-based models proposed by Sharma and Zhang [Sharma, M., Zhang, S.Y., 2004. Height–diameter models using stand characteristics for Pinus banksiana and Picea mariana. Scand. J. For. Res. 19, 442–451; denoted Models 2 and 3] which includes consideration of stand-level density effects through the explicit inclusion of density-based predictor variables (density ( N; stems/ha) and basal area ( G; m 2/ha)); and (4 and 5) constrained and unconstrained allometric-based models (denoted Models 4 and 5, respectively) derived from a multivariate expansion of the equation of simple allometry which includes consideration of stand-level effects via the explicit inclusion of density and stand developmental predictor variables (relative density index ( R; %/100) and mean dominant height ( H D; m), respectively). The six stand-types considered were (1 and 2) natural (density unregulated) and managed (density regulated) upland black spruce ( Picea mariana (Mill.) B.S.P.) stands (denoted PIm UL(N) and PIm UL(M), respectively), (3 and 4) natural and managed jack pine ( Pinus banksiana Lamb.) stands (denoted PNb (N) and PNb (M), respectively), (5) natural black spruce–jack pine mixed stands (denoted PImPNb (N)), and (6) natural lowland black spruce stands (denoted PIm LL(N)). The full dataset, consisting of 26741 H– D measurements and associated stand-level variables ( N, G, R and H D) obtained from 985 sample plots situated throughout the central portion of the Canadian Boreal Forest Region, was randomly subdivided into calibration and validation subsets of approximately equal size by stand-type. Parameter estimates for each model were obtained using the calibration subsets in combination with nonlinear regression (Models 1–3) and multiple regression (Models 4 and 5) analyses. Employing the validation subsets, the calibrated models were evaluated using goodness-of-fit, lack-of-fit and prediction error indices at both the diameter class and stand levels. The results indicated that the best performing models were as follows: (1) Model 3 for PIm UL(N); (2) Model 5 for PIm UL(M); (3) Model 4 for PNb (N); (4) Model 5 for PNb (M); (5) Model 2 for PImPNb (N); and (6) Model 5 for PIm LL(N). Collectively, these results (1) reconfirms the utility of explicitly incorporating stand-level variables within the model specification when developing H– D models, (2) demonstrates the superiority of the newly introduced allometric-based H– D composite model which incorporates both stand density and developmental effects for four of the six stand-types assessed, and (3) provides a suite of calibrated functions and associated performance metrics for potential use in product recovery and value estimation, stand structural analyses, growth and yield projection systems, and carbon budgeting models. Furthermore, given the success of the allometric-based models derived from the multivariate expansion of the equation of simple allometry, suggests that this modeling approach may have wider applicability in the (1) development of prediction equations for other important dimensional relationships used in forest management (e.g., localizing stem taper, volume and biomass equations) and (2) study of allometry in general (e.g., provide analytical direction in the assessment of population-level effects on allometric scaling relationships).

Rehabilitating boreal forest structure and species composition in Finland through logging, dead wood creation and fire: The EVO experiment

This paper reviews an ongoing, large-scale multidisciplinary experiment designed to study the possibilities of rehabilitating forest structure and species composition through logging, dead wood creation and fire in managed Norway spruce ( Picea abies) forests in southern Finland. These forests have been utilized for several centuries with intensive management and clear-cut harvesting, which has been the dominant practice in Finland since World War II. During this era, the forest structure has become relatively even-aged, and the amount of dead wood has been reduced considerably. Simultaneously, due to an effective fire suppression policy, the role of fire in Finnish nature has been almost completely eliminated. One of the key species in biodiversity, aspen ( Populus tremula), has also been actively removed from the forests in the past. Forest restoration activities, such as the creation of dead wood and the reintroduction of fire to forest management, have been suggested in conservation and restoration programmes. So far we have studied the immediate effects of restorative actions on forest structure, regeneration, soil nutrient status, understorey and epixylic vegetation, lichens and beetles. In the larger Evo research area we have also studied the population structure of aspen in both protected and managed forests. Our early results show that it is possible, through active forest restoration, i.e. the creation of dead wood and prescribed burning, to rehabilitate boreal forest diversity, even when a significant part of the wood volume is harvested for commercial use. Despite the fact that the immediate effects of fire on many species groups were negative, the long-term effects are expected to be predominantly positive. There is currently a decline in aspen populations in Finnish forests. The absence of large aspens in managed forests and the absence of younger trees/cohorts in conservation areas, combined with high mortality, is a significant threat to aspen-dwelling species. We conclude that studies on active restoration treatments, together with long-term inventories of several species groups, are necessary in order to assess the impacts of varying restoration practices for cost-efficient large-scale applications.

C-band scattering simulation of a Scots pine shoot

Scots pine (Pinus sylvestris L.) has the widest distribution of any pine and is one of the most important timber trees in Europe and one of the main species of boreal forest, which have an important role in climate change studies. The leaf area index (LAI) is one of the key input parameters for the climate change models. Recently a relationship between C-band backscattering and the LAI has been detected for Scots pine. To understand the C-band microwave characteristics of Scots pine shoots the backscattering is simulated using the so-called discrete dipole approximation (DDA), which is the only possible, nearly exact method for this problem. The backscattering of the shoot is dominated by the needles. The VV/HH backscattering ratio of closely spaced parallel and perpendicular shoots averages to that of a single shoot. For a simulated whole Scots pine crown the VV/HH backscattering ratio is related to the total orientation distribution of the needles. The variation range of the VV/HH backscattering ratio was 0.95–1.25, which is close to empirical values.

Quality of growth substrates of post-disturbed lowland black spruce sites for black spruce (Picea mariana) seedling growth

Black spruce (Picea mariana (Mill.) BSP) is the most important commercial tree species in the eastern boreal forest of Canada. Only limited work has been conducted to assess the quality of the various substrates that are found on post-disturbed sites prone to paludification having an effect on black spruce seedling growth. The objectives of this study were (1) to use a pot test to assess black spruce seedling performance on substrates found at the soil surface, in the rooting zone of undisturbed soil, at depths that become available to spruce roots after soil disturbance by wildfire or through management; and (2) to determine the nutritional quality of these substrates when constraints of poor drainage are artificially removed. Black spruce growth was greatest with fibric Pleurozium in the rooting zone, and with burned fibric Pleurozium and living Sphagnum at the soil surface. Good seedling growth on different substrates found in the rooting zone was associated with higher N and P foliar concentrations. Based on these results, we recommend targeted planting of black spruce seedlings in substrates of Pleurozium origin and the development of management techniques that promote Pleurozium schreberi.

Phylogeography of the capercaillie in Eurasia: what is the conservation status in the Pyrenees and Cantabrian Mounts?

The Western capercaillie (Tetrao urogallus) is a keystone species of Palearctic boreal and altitude coniferous forests. With the increase of mountain leisure activities and habitat loss, populations are declining in most mountain ranges in Western Europe. Recent work has shown that the populations from the Pyrenees and Cantabrian Mountains survived a severe bottleneck during the 19th century, and are still considered as threatened due to habitat fragmentation and isolation with other populations. We present an extensive phylogeographic study based on mitochondrial DNA sequence (control region) extracted non-invasively from faeces collected throughout the species range (from western European mountains to central and eastern Europe, Fenno-Scandia, Russia and Siberia). We also compared our results with DNA sequences of closely related black-billed capercaillie (T. parvirostris). We found that populations from Pyrenees and Cantabrians are closely related but are different from all other capercaillie populations that form a homogenous clade. Therefore, we consider that these South-Western populations should be considered as forming an Evolutionary Significant Unit that needs an appropriate management at a local scale. We also discuss the possible locations of glacial refugia and subsequent colonisation routes in Eurasia, with a Western “aquitanus” lineage from Iberia and Balkans, and an Eastern “urogallus” lineage from Southern Asia. This work might have important implication for capercaillie conservation strategies to define important areas for conservation, and to prevent possible exchange or introductions of individuals originated from other lineages.

Quantifying components of risk for European woody species under climate change

AbstractEstimates of species extinction risk under climate change are generally based on differences in present and future climatically suitable areas. However, the locations of potentially suitable future environments (affecting establishment success), and the degree of climatic suitability in already occupied and new locations (affecting population viability) may be equally important determinants of risk. A species considered to be at low risk because its future distribution is predicted to be large, may actually be at high risk if these areas are out of reach, given the species' dispersal and migration rates or if all future suitable locations are only marginally suitable and the species is unlikely to build viable populations in competition with other species. Using bioclimatic models of 17 representative European woody species, we expand on current ways of risk assessment and suggest additional measures based on (a) the distance between presently occupied areas and areas predicted to be climatically suitable in the future and (b) the degree of change in climatic suitability in presently occupied and unoccupied locations. Species of boreal and temperate deciduous forests are predicted to face higher risk from loss of climatically suitable area than species from warmer and drier parts of Europe by 2095 using both the moderate B1 and the severe A1FI emission scenario. However, the average distance from currently occupied locations to areas predicted suitable in the future is generally shorter for boreal species than for southern species. Areas currently occupied will become more suitable for boreal and temperate species than for Mediterranean species whereas new suitable areas outside a species' current range are expected to show greater increases in suitability for Mediterranean species than for boreal and temperate species. Such additional risk measures can be easily derived and should give a more comprehensive picture of the risk species are likely to face under climate change.

Phylogenetic relationships, host affinity, and geographic structure of boreal and arctic endophytes from three major plant lineages

Although associated with all plants, fungal endophytes (microfungi that live within healthy plant tissues) represent an unknown proportion of fungal diversity. While there is a growing appreciation of their ecological importance and human uses, little is known about their host specificity, geographic structure, or phylogenetic relationships. We surveyed endophytic Ascomycota from healthy photosynthetic tissues of three plant species ( Huperzia selago, Picea mariana, and Dryas integrifolia, representing lycophytes, conifers, and angiosperms, respectively) in northern and southern boreal forest (Québec, Canada) and arctic tundra (Nunavut, Canada). Endophytes were recovered from all plant species surveyed, and were present in <1–41% of 2 mm 2 tissue segments examined per host species. Sequence data from the nuclear ribosomal internal transcribed spacer region (ITS) were obtained for 280 of 558 isolates. Species-accumulation curves based on ITS genotypes remained non-asymptotic, and bootstrap analyses indicated that a large number of genotypes remain to be found. The majority of genotypes were recovered from only a single host species, and only 6% of genotypes were shared between boreal and arctic communities. Two independent Bayesian analyses and a neighbor-joining bootstrapping analysis of combined data from the nuclear large and small ribosomal subunits (LSUrDNA, SSUrDNA; 2.4 kb) showed that boreal and arctic endophytes represent Dothideomycetes, Sordariomycetes, Chaetothyriomycetidae, Leotiomycetes, and Pezizomycetes. Many well-supported phylotypes contained only endophytes despite exhaustive sampling of available sequences of Ascomycota. Together, these data demonstrate greater than expected diversity of endophytes at high-latitude sites and provide a framework for assessing the evolution of these poorly known but ubiquitous symbionts of living plants.

Identification of two genera of N2-fixing cyanobacteria growing on three feather moss species in boreal forests of Quebec, Canada

The recent discovery that N2fixation rates by the feather moss carpet of boreal Scandinavian forests increases with stand maturity has put into question the paradigm that N2fixation is negligible in mature boreal forest. The N2fixation was attributed to a previously unknown association between Nostoc sp., a N2-fixing cyanobacteium and Pleurozium schreberi (Brid.) Mitt., a feather moss that is abundant worldwide in the boreal forest. Here we report for the first time that this association also exists in the Canadian boreal forest. We discovered, however, that Nostoc was found growing not only on Pleurozium but also on two other moss species ( Hylocomnium splendens (Hedw.) Br. Eur. and Ptillium crista-castrensis (Hedw.) De Not.). In addition, the N2-fixing cyanobacterium Stigonema sp. was observed on the three moss species mentioned above, indicating the existence of six different associations. At least one of the six associations was found at 9 of 13 sites that are representative of a large area of the Quebec boreal forest. These findings suggest possibilities for further research, aimed at measuring the unaccounted for N2-fixing potential of the feather moss carpet in Canadian boreal forests.

Late‐glacial and Holocene palaeovegetation zonal reconstruction for central and north‐central North America

AbstractAim The purpose of this study is to develop palaeovegetation zonation models for central and north‐central North America, based on late‐Quaternary and Holocene pollen stratigraphic data (n = 246 sites). A secondary purpose was to evaluate an hypothesis (Strong &amp; Hills, 2003) to explain the disjunct distribution of species in western Alberta.Location Hudson Bay‐Lake Michigan to the Rocky Mountains region, north of 36° N to the Arctic Ocean (c. 70° N).Methods Pollen profiles spanning 40 years of palaeoecological research in North America were extracted from published and unpublished archival sources. Individual profiles were subdivided into 1000‐year increments based on the assumption of a constant sedimentation rate between stratigraphic dates (e.g. surface sediments, radiocarbon 14C dates, tephra layers). The pollen composition among profiles was standardized to 54 commonly recognized taxa, with percentage composition within each stratigraphic sample prorated to 100% prior to analysis. Near‐surface sediments from these profiles were included as analogues of modern vegetation. Cluster analysis was used as a guide to the classification of 2356 temporal stratigraphic samples, which resulted in the recognition of 16 pollen groups. These groups were summarized in terms of their pollen composition, mapped, and used in combination with terrain information and an ecological knowledge of the study area to construct six physiognomically‐based palaeovegetation zonation models at 2000‐year intervals from 14,000 to 4000 yr bp (radiocarbon years before present).Results The 14,000 yr bp model placed Boreal and Cordilleran Forests proximal to the southern glacial front, whereas Arctic tundra dominated the Yukon Territory–Alaska ice‐free zone. Pollen and macrofossil evidence suggests that this Boreal Forest zone contained a mixture of coniferous and deciduous tree species. Grassland was postulated immediately south of the forest zone, with its northern extreme near 49° N latitude in the Alberta–Montana border area. Separation of the Laurentide and Cordilleran glacial fronts about 12,000 yr bp initiated the northward advance of Boreal Forests into western Canada. By the end of the Hypsithermal at about 6000 yr bp, Boreal Forests occurred near the Arctic Ocean, and Grassland and Aspen Parkland zones may have extended to 54° N and 59° N latitude in Alberta, respectively. Between 6000 and 4000 yr bp, a 5° and 1° latitudinal southward shift of the northern Boreal Forest and Grassland/Aspen Parkland boundaries occurred, respectively, near their contemporary positions with corresponding expansions of the Subarctic and Arctic zones. Modern Canadian Cordilleran Forests along the eastern slopes of the Rocky Mountains were interpreted as originating from the north‐central Montana–south‐western Alberta area. Jack pine (Pinus banksiana Lamb.), a common Boreal Forest species, appears to have entered central Canada via the north side of Lake Superior after 11,000 yr bp.Main conclusions Modern vegetation in central Canada evolved from biomes located in the northern USA during the late‐Quaternary. The Boreal Forest biome contained the same arboreal taxa as the modern vegetation, except it lacked jack pine. The proposed regional palaeovegetation models support the hypothesis of Strong &amp; Hills (2003), but new independent palaeoecological data will be needed for a proper evaluation.

Competitive interactions among raptors in boreal forests

We examined inter-specific interactions among goshawks ( Accipiter gentilis), common buzzards (Buteo buteo) and honey buzzards (Pernis apivorus) in western Finland in 1983-1996. Because goshawks are among the largest birds of prey species in boreal forests they may take over the nest of smaller and less-competitive forest-dwelling raptors when searching for suitable places for breeding. Accordingly, more than half of newly established goshawk territories were found on the territories previously occupied by the common buzzard and the honey buzzard. Otherwise, territory sharing between these species was rare. Fledgling production of honey buzzards was not associated with the presence of goshawks, probably owing to the almost 2 months later onset of breeding. This probably decreases competitive interactions between these two species. An intensive interference competition, instead, seemed to be evident between common buzzards and goshawks, because the fledgling production of common buzzards was decreased by 20% as a result of failures during incubation and nestling period in the vicinity (<1 km) of occupied goshawk nests. Similarly, territory occupancy of common buzzards till the next breeding season was significantly reduced in the presence of goshawks. Relatively high proportions of occupied buzzard territories (17%) in the study area were shared by breeding goshawks on the same territory. This suggests that although their diets are dissimilar they inhabit similar habitats and might compete for the available prime nesting habitats within forest landscapes. In addition, goshawks benefit from taking over the complete nests of other raptors, imposing upon the original owners of the nest, because building a large stick nest is probably energetically costly. As a large raptor, the goshawk apparently has a competitive advantage over smaller ones, and may have an ever-increasing impact on smaller birds of prey, if there is a lack of sheltered forests inducing competition for the available nest sites.

Long-term persistence of aspen – a key host for many threatened species – is endangered in old-growth conservation areas in Finland

Large, dead and dying European aspens ( Populus tremula L.) host many threatened species in Fennoscandian boreal forests. Large aspen trees have mostly disappeared and are being harvested from the managed forests that cover 95% of the forest area in Finland. Due to the small area protected (4.1%), the aspen-associated species may encounter major difficulties in the protected areas if aspen trees disappear due to natural forest succession. The availability of aspens was assessed in the old-growth conservation area network in eastern Finland. We mapped all the living and dead aspens in 15 protected old-growth forests. The total number of counted trees was 32 903 individuals. Current amounts of living (2.7 m 3/ha) and especially dead aspens (2.8 m 3/ha) in the protected areas were higher than in the surrounding managed forests (1.1 and 0.1 m 3/ha for living and dead trees, respectively). However, while saplings (dbh<5 cm) occur in most of the areas (12 individuals/ha on average) they survive poorly and young aspen cohorts (5 cm <dbh<15 cm) are lacking or are very rare. The most likely reason for the poor sapling survival is high browsing pressure by the mammalian herbivores, especially the moose. The moose population has increased many times in Finland during the past decades. The poor regeneration of aspens implies that the value of the old-growth conservation areas for aspen-associated species will face a serious bottleneck within a few decades when the currently middle-aged tree cohorts disappear. If the current high browsing pressure and lack of natural disturbances continue the obligatory aspen-associated species may disappear both locally and regionally from the network of the protected areas.

Carbon dioxide and water vapour exchange from understory species in boreal forest

Although recent eddy covariance measurements in boreal forests provide CO 2 and energy exchange data for the whole ecosystem, very little is known about the role of the understory vegetation. We conducted chamber flux measurements in an Alaskan black spruce forest in order to compare CO 2 and water vapour exchange among patches of understory vegetation dominated by feathermoss ( Hylocomium), peatmoss ( Sphagnum), vascular plants (mainly low shrubs), or lichens. We found large differences among understory vegetation types with respect to midday net CO 2 exchange and its seasonal pattern of variation. Sphagnum and vascular-plant plots showed net CO 2 uptake, with most uptake on days of high light availability. In contrast, Hylocomium and lichen plots lost CO 2 during the middle of the growing season, but showed net uptake at the end of the season when the soil had cooled down. Spatial variation in net CO 2 exchange was related more to biotic variables like soil organic matter than to environmental variables. The differences among vegetation types with respect to water vapour fluxes were smaller, because evapotranspiration was more constrained by climatic variables like solar radiation. Net CO 2 uptake in Hylocomium plots was negatively related to evapotranspiration, because Hylocomium photosynthesis was very sensitive to evaporative stress, whereas evapotranspiration and net CO 2 uptake in Sphagnum were not limited by moisture conditions. These differences suggest that species composition of the understory should be taken into account when discussing understory contributions to CO 2 and water vapour exchange.