Spatial pattern of the threatened epiphytic bryophyte Neckera pennata at two scales in a fragmented boreal forest

The spatial pattern and occurrence of a threatened bryophyte, Neckera pennata. were studied in relation to the abundance and pattern of suitable substrate trees at two spatial scales: 1) in a 4 x 4 km fraction of fragmented, mostly managed southern boreal forest landscape, and 2) in an old-growth forest stand within this landscape, with abundant occurrence of suitable habitats. To explore in detail the spatial clustering of N. pennata at the forest stand scale, we applied a second order point process analysis based on the Ripley's K-function for binary point patterns, Neckera pennata proved to be a rare species in the studied landscape: it was found only on 31 Populus tremula trees. At the landscape scale, the distribution of the species was highly aggregated: the species occurred only within a 60 ha old-growth forest patch in the whole area. At the forest stand scale, N. pennata proved to be a widespread, randomly distributed species without any tendency towards aggregation. It was found on 19 Populus trees, which was only 1.5% of the total 1253 potential substrate trees within the inventory area. The species showed a statistically significant preference towards large trees. The future of the species in the study area is unclear due to 1) the very low population density and 2) the lack of regeneration of Populus within the protected old-growth forest area hosting the remaining population.     

Persistence of vascular plants in a Norwegian boreal coniferous forest

Persistence, the tendency of a species to remain in its original position and not to colonize new sites, is studied for the most abundant forest vascular plants (25 species in spruce forest and 7 in pine forest) in Solhomfjell, Gjerstad, S Norway Data sets included presence/absence in 199 meso plots (1 m²) and 3184 subplots (1/16 m²), analyzed over a 5 yr interval, and a subset of 50 meso plots and 800 subplots, analyzed for six consecutive years Relationships between species variables (seedling frequency and mobility rate compiled from the literature, and cover and abundance means in the study area) are studied, and related to species optima along ecologically interpreted DCA ordination axes Vascular plant mobility may increase towards nutrient-poor sites Dominance in the boreal forest floor is mostly by clonal species Persistence was calculated for different temporal (1-5 yr) and spatial (1/16 and I m²) scales Persistence patterns in the spruce and pine forests were similar, but persistence decreased towards the xeric pine forests One main component of variation in persistence was demonstrated by PCA analyses the absolute level of persistence, which is related to seedling recruitment vs clonal growth, and within clonal species to ramet longevity, abundance, mobility, growth pattern and mode of surviving the infavourable season Minor components of variation in persistence were related to spatial scale and temporal scale Persistence characteristics were species-specific and varied little between years Numerous species characteristics were relevant to interpretation of variation in persistence, indicating a continuous, multidimensional variation in life history characteristics     

Positive and negative effects of a dominant competitor on the settlement, growth, and survival of competing species in an epibenthic community

Because dominant competitors can monopolize resources, any positive effects they have on other species can have large community impacts. The solitary tunicate Ascidia ceratodes is a dominant competitor in the fouling community in Bodega Harbor, CA. This tunicate preempts primary substratum from competitors, but its thick tunic also allows other species to grow on its surface. The net effect of Ascidia on the community as a whole therefore depends on the balance between competitive and facilitative effects. In this study we evaluate the facilitative effects of Ascidia on different life stages of common competing species. We quantified larval settlement onto Ascidia compared to unoccupied space; we quantified the growth rate on Ascidia of small colonies of two common species; and we measured whether established colonies could escape overgrowth by Ascidia by growing onto its tunic. We found evidence for high rates of settlement on Ascidia, with some species showing higher and others lower settlement relative to that observed on free space. The growth rate of settlers was generally lower on Ascidia compared to primary substratum. We also found that colonial species established on primary space commonly escape overgrowth from Ascidia by growing onto Ascidia, as this occurs in about half of all encounters. This study indicates that the total effect of Ascidia on the community will depend on species-specific and life stage-specific effects, with likely long-term consequences for the diversity and composition of the community.     

Recolonization potential of bryophyte diaspore banks in harvested boreal mixed-wood forest

Bryophyte diaspore banks are a potential source of reproductive propagules that may be able to colonize newly available habitat after forest harvesting. However, their role and the factors influencing the successful establishment of species remain poorly understood. To investigate these aspects of diaspore banks, we obtained mineral soil samples from mixed and coniferous stands of boreal mixed-wood forest in northern Alberta, Canada, which had recently experienced a range of harvesting intensities. Samples were germinated in growth cabinets under two light regimes. The composition of germinated bryophyte species was compared among forest types, harvesting intensities, and light levels, and also related to edaphic conditions and geographic location of the sample site. Germinated species composition was not related to forest type or harvesting intensity, but was associated with measured edaphic variables and geographic space, indicating that similarity in species composition reflected similarity in edaphic conditions and spatial proximity. This was partly because of spatial dependence of edaphic variables. Light intensity had a significant influence on the development of species assemblages and individual species responses. Richness and cover of acrocarpous mosses (fugitive, colonist, and shuttle life-history strategies) were significantly reduced under low light conditions, but pleurocarpous mosses (perennial strategy) were not affected. Shannon diversity and the frequency of reproduction were significantly greater with high light. Pleurocarpous mosses that are characteristic of intact forests germinated frequently, suggesting that diaspore banks may influence their recovery after disturbance. Diaspore banks are a repository of species at sites affected by forest harvesting; however, diaspore germination and establishment will be constrained by the local environment, including edaphic conditions and light intensity.     

The bryophyte diaspore bank and its role after small-scale disturbance in a boreal forest

Abstract. The composition of the bryophyte diaspore bank in an old-growth Picea abies forest was studied before and after experimental disturbance of forest-floor patches. 40 species, both hepatics and mosses, emerged from spores, and probably also from gemmae and moss fragments, in greenhouse cultivations of soil samples. The three most abundant taxa were Pohlia nutans, Sphagnum spp. and Polytrichum commune/longisetum. Initially, the number of species from the diaspore bank in mineral soil, 9.9 species/sample, was higher than that in humus, 6.6. Four years after the disturbance took place, the reverse was found. Several species that are typical colonisers of disturbed soil were very common in the diaspore bank. By contrast, some of the most abundant forest floor species appeared to be absent. The diaspore bank of bryophytes appears to play a role similar to that of the seed bank in vascular plants: (1) it allows species to survive unfavourable periods (temporal dispersal); (2) it facilitates rapid colonisation after disturbance; (3) it influences the post-disturbance species composition and diversity. The results emphasise that the understanding of vegetation succession patterns is, to a large extent, dependent on quantitative data on the relative importance of spatial and temporal dispersal.     

Spatial patterns of association at local and regional scales in coastal sand dune communities

Questions: Are positive understorey‐dominant associations important in physically severe dune communities and does the strength of positive associations vary with disturbance at the local scale and with stress at the regional scale? Do associational patterns observed at the neighbourhood scale predict diversity at higher scales? Location: Coastal sand dunes, Aquitaine (France). Methods: Associational patterns with five dominant species were recorded along a local gradient of disturbance and a 240‐km long regional gradient. Density, richness, cover and variance ratio of understorey species were recorded in quadrats located in dominant and in open areas. Spatial pattern of dominant plant species was recorded using a distance‐based method. Results: Positive understorey‐dominant associations were most frequent at both regional and local scale, although negative associations with understorey species were observed for one of the five dominants. At the regional scale, there was a shift in the magnitude of spatial associations, with higher positive associations in the most stressful sites, whereas spatial associations where not affected by the local disturbance gradient. Positive associations were not related to the size of the dominants but rather influenced by the identity of the dominant species. Conclusions: Our study highlights the potential crucial role of facilitation together with the importance of turnover of the dominants in explaining large‐scale variation in diversity. However, because positive associations may also be attributed to environmental heterogeneity or co‐occurrence of microhabitat preferences of species, experiments are needed to fully assess the relative importance of facilitation versus other drivers of community diversity.     

Beetle diversity in a matrix of old-growth boreal forest: influence of habitat heterogeneity at multiple scales

The relative contribution of compositional and structural heterogeneity on biodiversity is currently ambiguous because field studies generally integrate these two sources of habitat heterogeneity into a single index. We established the relationship between species richness of ground-dwelling and flying beetles and compositional and structural attributes of forest heterogeneity. The relationship was evaluated at two spatial scales: the scale of forest stand, corresponding to an 11.3  m radius, and the scale of landscape, corresponding to either a 400 or 800  m radius. Seventy stands were sampled in the matrix of old-growth boreal forest of the North Shore region of Québec, Canada, during the summers of 2004 and 2005. A total of 133 ground-dwelling beetle species (range: 4–42 species per site) were captured in the pitfall traps and 251 flying species (range 16–58 species per site) in flight-interception traps. We found that the most relevant type of heterogeneity to explain variations in species richness and the significance of landscape scale information varied between groups of beetles. Compositional heterogeneity (i.e. the number of species of forest trees and shrubs) at the stand scale best predicted species richness in ground-dwelling beetles. On the other hand, it was the combined influence of structural and compositional habitat heterogeneity at stand and landscape scales that best explained richness patterns in flying beetles. Our study outlines the significance of considering multiple types and spatial scales of habitat heterogeneity when describing patterns of species richness.     

Variation in invertebrate–bryophyte community structure at different spatial scales along altitudinal gradients

Aim This study assessed changes in diversity and assemblage composition in bryophytes and their associated invertebrates along altitudinal gradients in Australia and New Zealand. The importance of altitude in shaping these communities and for the diversity of both invertebrates and bryophytes was examined at different spatial scales, including local, altitudinal, regional and biogeographical. Location Samples were taken from four Australasian mountain ranges between 42° and 43°S: Mt Field and Mt Rufus, Tasmania, Australia, and Otira Valley and Seaward Kaikoura Mountains, South Island, New Zealand. Methods On both Tasmanian mountains, five altitudes were assessed (250, 500, 750, 1000 and 1250 m). At each location (mountain/altitude combination) two sites were chosen and six samples were taken. Six altitudes were assessed on New Zealand mountains (Otira: 250, 500, 750, 1000, 1250 and 1500 m; Kaikoura: 1130, 1225, 1325, 1425, 1525 and 2000 m). Bryophyte substrate was collected, and all samples were stored in 70% ethanol. Invertebrates were extracted from bryophytes using kerosene‐phase separation and all invertebrates were identified to family. At each location in Tasmania, all bryophyte species within six 25‐cm² grids per site were collected and identified to species. Bryophytes from New Zealand were identified to species from the invertebrate sample substrate because of sampling constraints. Results Altitude did have a significant effect on diversity, however, no general trend was found along the altitudinal gradient on the four mountains. There were distinct differences in diversity between biogeographical regions, mountains, altitudes and sites. In Tasmania, Mt Field had the highest diversity in invertebrates and bryophytes at 750 m. In contrast, Mt Rufus had consistent low invertebrate and bryophyte diversity along the entire altitudinal gradient. There were also distinctive differences between locations in the composition of invertebrate and bryophyte communities in Tasmania. Along the two altitudinal gradients in New Zealand, Otira had highest diversity for both invertebrates and bryophytes at low altitudes, whereas Kaikoura had highest invertebrate and lowest bryophyte diversity at the highest altitude. Main conclusions There was an effect of altitude, however, there were no consistent changes in diversity or composition on the four different mountains. There was considerable local and regional variation, and, despite a strong sampling design, no underlying altitudinal trends were detectable. This study demonstrates the importance of examining a range of spatial scales if patterns in community structure along altitudinal gradients are to be studied. The implications of this study are discussed with reference to survey design, taxonomic resolution, climate change and conservation of habitat.     

Long-term dynamics of vegetation and disturbance of a southern boreal spruce swamp forest

Abstract. Analysis of pollen, charcoal and loss-on-ignition in peat cores from a Picea aèies-dominated swamp forest in central Sweden show the vegetation changes and disturbance patterns over 9500 yr. Six major sequences of local vegetation development are identified: (A) Pinus period, ca. 9500–7000 cal. BP; (B) Open mire period (ca. 7000–4500 cal. BP; (C) Betula period, ca. 4500–2300 cal. BP; (D) Picea period (ca. 2300–1000 cal. BP; (E) Human impact period (ca. 1000–100 cal. BP); and (F) Period of human abandonment during the last ca. 100 yr. The swamp forest has been highly dynamic in response to various natural and anthropogenic disturbance agencies. Several fires have heavily influenced the vegetation development. During the last ca. 900 yr human influence has been important, initially from grazing and trampling by domesticated animals (ca. 1000–500 cal. BP), and subsequently small-scale cereal growing (ca. 400–100 BP). Cutting, burning and animal browsing influenced the structure and dynamics of the swamp forest by creating a more open stand and suppressing tree regeneration. Recent cessation of human impact has led to increased tree regeneration and a denser swamp forest stand. The present high biodiversity, and subsequent conservation interest does not result from long-term stability or absence of fire and human impact. However, in spite of repeated disturbances, a continuity of old and senescent trees produced a forest type with abundant dead wood. With the relatively minor importance of fire over long periods of time, the swamp forest developed a structure maintaining a high biological diversity. An important issue for maintaining long-term biodiversity in the boreal landscape must be to create a mosaic where different forest types are present, with a variety of structures, substrates and processes, to provide a certain degree of freedom for species to move around in the landscape.     

Modelling temporal variability in the carbon balance of a spruce/moss boreal forest

A model of the daily carbon balance of a black spruce/feathermoss boreal forest ecosystem was developed and results compared to preliminary data from the 1994 BOREAS field campaign in northem Manitoba, Canada. The model, driven by daily weather conditions, simulated daily soil climate status (temperature and moisture profiles), spruce photosynthesis and respiration, moss photosynthesis and respiration, and litter decomposition. Model agreement with preliminary field data was good for net ecosystem exchange (NEE), capturing both the asymmetrical seasonality and short-term variability. During the growing season simulated daily NEE ranged from -4 g C m^-2 d^-1 (carbon uptake by ecosystem) to + 2 g C m^-2 d^-1 (carbon flux to atmosphere), with fluctuations from day to day. In the early winter simulated NEE values were + 0.5 g C m^-2 d^-1, dropping to + 0.2 g C m^-2 d^-1 in mid-winter. Simulated soil respiration during the growing season (+ 1 to + 5 g C m^-2 d^-1) was dominated by metabolic respiration of the live moss, with litter decomposition usually contributing less than 30% and live spruce root respiration less than 10% of the total. Both spruce and moss net primary productivity (NPP) rates were higher in early summer than late summer. Simulated annual NEE for 1994 was -51 g C m^-2 y^-1, with 83% going into tree growth and 17% into the soil carbon accumulation. Moss NPP (58 g C m^-2 y^-1) was considered to be litter (i.e. soil carbon input; no net increase in live moss biomass). Ecosystem respiration during the snow-covered season (84 g C m^-2) was 58% of the growing season net carbon uptake. A simulation of the same site for 1968–1989 showed = 10–20% year-to-year variability in heterotrophic respiration (mean of + 113 g C m^-2 y^-1). Moss NPP ranged from 19 to 114 g C m^-2 y^-1; spruce NPP from 81 to 150 g C m^-2 y^-1; spruce growth (NPP minus litterfall) from 34 to 103 g C m^-2 y^-1; NEE ranged from +37 to -142 g C m^-2 y^-1. Values for these carbon balance terms in 1994 were slightly smaller than the 1969–89 means. Higher ecosystem productivity years (more negative NEE) generally had early springs and relatively wet summers; lower productivity years had late springs and relatively dry summers.     

Patterns of bryophyte diversity and rarity at a regional scale

Information on bryophyte diversity and rarity were combined withinformation on soil conditions and land use for Walloon Brabant (centralBelgium, 1091 km²) in order to investigate whichlandscape features sustain the most rare and diverse species assemblages.Presence–absence of 325 bryophyte species was recorded in 87 grid-squaresof 4 × 4 km. Species diversity was significantly correlatedwith forest cover (r = 0.71, P <0.001), sandy soils (r = 0.61, P <0.001), loamy soils, (r = –0.68,P < 0.001), and agricultural fields(r = –0.49, P < 0.001). Themost diverse grid-squares possessed up to 182 species and were characterized byat least 10% forest cover and the presence of unique micro-habitats.Grid-squares with forest cover reaching at least 10% but lacking uniquemicro-habitats contained between 90 and 130 species. Below 10% forest cover,diversity ranged between 55 and 110 species per grid-square. However, even theleast diverse cultivated areas included a significant amount of the regionallyrare species. A number of the latter are characteristic in other areas forspecific primary habitats lacking in Walloon Brabant but display an unexpectedability to disperse throughout hostile areas and colonize secondary habitats.The tendency of such species to occur in man-made habitats decreased our abilityto predict species richness and rarity from landscape features and soilconditions.     

Patterns of occurrence of myxomycetes in a spruce forest in South Sweden

A 4-yr field study was carried out on selected species of myxomycetes. Reticularia jurana, Symphytocarpus flaecidus, Amaurochaete atra , and A. tubulina occur predominantly in May–June. Ceratiomyxa fruticulosa, Stemonitis axifera, S. fusca, S. hyperopta , and Fuligo septica in June–August, and Colloderma oculatum, Trichia botrytis, T. decipiens , and Fuligo muscorum in September–October. Lycogala epidendrum may occur from May to October. Whereas several species seem to be restricted to late autumn, those appearing in spring and early summer are occasionally found also later in the season. Many species with large plasmodia are rare under arid conditions. Complex factors probably influence spore germination, and it is often impossible to explain a sudden abundance of a species merely from temperature and precipitation. Several species show clear substrate preferences. Plasmodia may develop in cavities in wood and then move out to the surface to fructify. Insects are probably important for the dispersal of several species. Invertebrates, among them snails, are predators on plasmodia as well as on fructifications.     

Diversity of coleoptera of the bracket fungus Fomitopsis pinicola in a Norwegian spruce forest

The beetle fauna of 299 sporocarps of the bracket fungus Fomitopsis pinicola in a 200 ha spruce forest in southeastern Norway was investigated in relation to sporocarp, tree and forest variables. The sporocarps contained 36 species of beetles, of which six species are on the Norwegian Red List. Of 12,373 individual beetles collected, 91% were Cis glabratus. Plots of species accumulation curves suggested that there may be more than 60 beetle species present in F. pinicola in the area, but that probably all the specialist Ciidae were found. The major factor influencing beetle diversity turned out to be the level of dead wood at and in the vicinity of the sampling site, with a higher number of species per unit volume of sporocarps in areas with high levels of dead wood. There were also significantly more red-listed species in those areas. Analysing the species occurrence with stepwise logistic regression, we show preferential habitat selection of the six most abundant species of Ciidae. Conservation of beetles associated with bracket fungi using amount of dead wood as a surrogate measurement is discussed.     

Partitioning sources of soil respiration in boreal black spruce forest using radiocarbon

Separating ecosystem and soil respiration into autotrophic and heterotrophic component sources is necessary for understanding how the net ecosystem exchange of carbon (C) will respond to current and future changes in climate and vegetation. Here, we use an isotope mass balance method based on radiocarbon to partition respiration sources in three mature black spruce forest stands in Alaska. Radiocarbon (Δ¹⁴C) signatures of respired C reflect the age of substrate C and can be used to differentiate source pools within ecosystems. Recently‐fixed C that fuels plant or microbial metabolism has Δ¹⁴C values close to that of current atmospheric CO₂, while C respired from litter and soil organic matter decomposition will reflect the longer residence time of C in plant and soil C pools. Contrary to our expectations, the Δ¹⁴C of C respired by recently excised black spruce roots averaged 14‰ greater than expected for recently fixed photosynthetic products, indicating that some portion of the C fueling root metabolism was derived from C storage pools with turnover times of at least several years. The Δ¹⁴C values of C respired by heterotrophs in laboratory incubations of soil organic matter averaged 60‰ higher than the contemporary atmosphere Δ¹⁴CO₂, indicating that the major contributors to decomposition are derived from a combination of sources consistent with a mean residence time of up to a decade. Comparing autotrophic and heterotrophic Δ¹⁴C end members with measurements of the Δ¹⁴C of total soil respiration, we calculated that 47–63% of soil CO₂ emissions were derived from heterotrophic respiration across all three sites. Our limited temporal sampling also observed no significant differences in the partitioning of soil respiration in the early season compared with the late season. Future work is needed to address the reasons for high Δ¹⁴C values in root respiration and issues of whether this method fully captures the contribution of rhizosphere respiration.     

东北林区不同尺度森林的含碳率

准确估算森林生态系统碳储量对整个陆地生态系统碳循环及全球变化研究具有至关重要的作用.本研究利用2007、2008年东北林区(大兴安岭林区、小兴安岭林区、张广才岭和长白山林区)标准地调查数据及同一时期的一类样地清查数据,采用地面乔、灌、草生物量模型及实验室Multi N/C 3000分析仪测定的林木含碳率,计算不同尺度上森林生物量及碳储量,分析不同尺度森林含碳率的变化及稳定性.结果表明: 东北林区林木不同器官的含碳率差异明显,其平均含碳率为树叶(0.4448)＞树枝(0.4422)＞树皮(0.4398)＞树干(0.4351).张广才岭和长白山林区针叶林的含碳率高于阔叶林,而大、小兴安岭林区阔叶林的含碳率高于针叶林.研究区域森林的含碳率相对稳定,东北林区森林总含碳率为0.44.     

Liana habitat associations and community structure in a Bornean lowland tropical forest

Lianas (woody vines) contribute substantially to the diversity and structure of most tropical forests, yet little is known about the importance of habitat specialization in maintaining tropical liana diversity and the causes of variation among forests in liana abundance and species composition. We examined habitat associations, species diversity, species composition, and community structure of lianas at Sepilok Forest Reserve, Sabah, Malaysia in northeastern Borneo among three soil types that give rise to three distinct forest types of lowland tropical rain forest: alluvial, sandstone hill, and kerangas (heath) forest. Alluvial soils are more nutrient rich and have higher soil moisture than sandstone soils, whereas kerangas soils are the most nutrient poor and drought prone. Lianas ≥0.5-cm in diameter were measured, tagged, and identified to species in three square 0.25-ha plots in each forest type. The number of lianas ≥0.5 cm did not differ significantly among forest types and averaged 1348 lianas ha⁻¹, but mean liana stem diameter, basal area, estimated biomass, species richness, and Fisher’s diversity index were all greater for plots in alluvial than sandstone or kerangas forests. Liana species composition also differed greatly among the three habitats, with 71% of species showing significant positive or negative habitat associations. Sandstone forests were intermediate to alluvial and kerangas forests in most aspects of liana community structure and composition, and fewer species showed significant habitat associations with this forest type. Ranking of forest types with respect to liana density, biomass, and diversity matches the ranking in soil fertility and water availability (alluvial > sandstone hill > kerangas). These results suggest that edaphic factors play an important role in maintaining liana species diversity and structuring liana communities.     

Effect of increased Populus cover on Abies regeneration in the Picea–feathermoss boreal forest

Question: Does the increase in Populus tremuloides cover within the Picea mariana–feathermoss domain enhance establishment and growth conditions for Abies balsamea regeneration? Location: Boreal forest of northwest Quebec, Canada. Method: To document the effect of Populus tremuloides on A. balsamea regeneration, mixed stands with a heterogeneous presence of P. tremuloides adjacent to Picea mariana‐dominated stands were selected. Abies balsamea regeneration, understorey environment and canopy composition were characterized from 531 sampling units distributed along transects covering the mixed–coniferous gradient. Abundance of understorey A. balsamea regeneration was described using three height groups: seedling (<30 cm), small sapling (30 to <100 cm) and tall sapling (100 to 300 cm). Growth characteristics were measured from 251 selected individuals of A. balsamea (<3 m). Results: Results showed that A. balsamea regeneration was generally more abundant when P. tremuloides was present in the canopy. Differences between seedling and sapling abundance along the mixed–coniferous gradient suggest that while establishment probably occurs over a wide range of substrates, the better growth conditions found under mixed stands ensure a higher survival rate for A. balsamea seedlings. Conclusions: The abundant A. balsamea regeneration observed within mixed stands of the Picea mariana–feathermoss domain suggests that the increase in P. tremuloides cover, favoured by intensive management practices and climatic change, could contribute to acceleration of the northward expansion of the A. balsamea–Betula papyrifera domain into the northern boreal forest dominated by Picea mariana.     

Red spruce forest regeneration dynamics across a gradient from Acadian forest to old field in Greenwich,Prince Edward Island National Park,Canada

Red spruce forests have declined considerably throughout their range in the past decades. As agricultural fields are abandoned and land becomes available for reforestation, the possibility arises for red spruce forests to expand onto them. This study addresses the potential for red spruce forests to expand onto adjacent old fields in Greenwich, Prince Edward Island National Park, Canada. We examined red spruce distribution and abundance, plant species diversity and changes in community composition along a gradient from the interior of red spruce forests out towards the centre of adjacent old fields. Examining the patterns of red spruce distribution and abundance revealed that, where cultivation and logging have been abandoned recently in the fields and forests, regeneration is limited to the forest stands, but in the sites with older fields and forests, regeneration extends into and is more vigorous in the fields. Although species diversity varied from forest to field only for the tree and shrub layers, important changes occurred in the ground species composition. There is no evidence yet that the herbaceous species present in the forest stands will colonise the old fields. The results suggest that both environmental differences among sites and length of time since the fields were abandoned explain red spruce regeneration patterns. In order to more accurately assess the potential for red spruce regeneration in old fields, long-term monitoring of the production, dispersal and viability of red spruce seeds from adjacent forests and of the constraints to seedling establishment and survival in old fields will be needed.     

Patterns of diversity in the strata of boreal montane forest in British Columbia

Abstract. Patterns of diversity were analyzed in a boreal coniferous forest and its strata (tree, shrub, herb and bryophyte layers): number of species per community — α-diversity, total species richness — γ-diversity, mean similarity — β-diversity, and mosaic diversity, a measure of complexity. These four measures of diversity consistently decreased from lower to upper vegetation layers. To study the effect of juveniles of larger life forms on diversity of lower layers, they were removed from the data and the measures of diversity reanalyzed. Number of species per community and mosaic diversity decreased substantially, but β-diversity did not change. So, the effect of juveniles on γ-diversity is due to the greater number of species per community. Multiple regression models revealed that the relationships between α-diversity and the environmental variables were the same for the whole forest and for the herb layer. Elevation and soil pH were the major variables explaining α-diversity in the whole community. Climate was the only environmental gradient related to species richness in all individual strata. Tree and herb richness values were negatively related to soil drainage and acidity, respectively. Species richness of the plant community was affected by environmental variability mostly through the herb layer. Various explanations of the observed diversity patterns included: environmental constraints, resource competition, generation time, and colonization processes.