Forest Tree Species Composition Research Articles

Effects of fire and selective logging on the tree species composition of lowland dipterocarp forest in East Kalimantan, Indonesia

Tree species composition (diameter at breast height (dbh) ≥ 10 cm) was studied in primary, selectively logged and heavily burnt forests in East Kalimantan, Indonesia. The number of trees, tree species, and the Fishers's-α diversity index were determined for the first 15 years (burnt forest) and 25 years (selectively logged forest) after disturbance. Additionally the population structure of six common and typical Macaranga pioneer tree species was compared through time between selectively logged, burnt and primary forest. Both selectively logged and burnt forest showed a significant reduction in number of trees and tree species per surface area directly after disturbance. Fire especially affected dominant tree species, while for selective logging the opposite was observed. In selectively logged forest the number of trees, tree species and the Fishers's-α index reached pre-disturbance levels within c. 15 years. For burnt forest, only the number of trees recovered to pre-disturbance levels. The number of tree species stayed constant after disturbance, while the Fishers's-α index decreased. The six studied Macaranga pioneer tree species seedlings were present in all forest types. Their density seems to be unrelated to light levels in the forest understorey but strongly related to the number of mature parent trees. Their sapling densities were strongly related to light levels in the forest understorey. The studied Macaranga species formed an important part of both under- and over-storey in burnt forest 15 years after disturbance, while they were almost absent in the understorey and only moderately common in the overstorey of selectively logged forest.

Influence of tree species composition on soil and soil solution properties in two mixed spruce-beech stands with contrasting history in Southern Germany

The properties of the soil and soil solution of two mixed spruce-beech forests in Southern Germany were investigated in order to identify non-additive effects of tree species compared to the monocultures. At five subplots in each of the two monocultures and at 10 subplots in each of the two mixed stands humus morphology, topsoil acidity as well as nitrate and sulphate concentrations in seepage water below the rooting zone were measured. At the Hoglwald site, an 8×8 m sampling grid was also installed. Tree species composition within a 10 m circle surrounding each sampling point was correlated with the soil properties and the soil solution properties using the method of breakpoint estimation as well as a linear and a cubic model. At both sites, thickness and acidity of the forest floor as well as sulphate and nitrate concentrations in seepage water were significantly higher in the spruce monocultures than in the beech monocultures. Non-linear patterns in the correlation between both the thickness and the acidity of the forest floor and tree species composition occurred at both sites. In addition, nitrate concentration in the seepage water showed a non-linear correlation pattern at the Hoglwald site. The correlation patterns were site specific and depended on stand history. While the influence of spruce at the Hoglwald site was greater than expected from spruce monocultures, the opposite was found at the Schongau site. Interaction effects on nitrate concentration were absent at the Schongau site. Interaction effects on sulphate concentrations were absent at both sites. Current knowledge about the complex processes and patterns in mixed species stands is still limited. At least for certain properties, mixed species stands cannot be treated as a summation of the corresponding monocultures.

Tropical Rain Forest Recovery from Cyclone Damage and Fire in Samoa1

ABSTRACTIn 1990 and 1991, Samoa was struck by two cyclones, Ofa and Val. In the Tafua Rain Forest Preserve on the island of Savai'i, one part of the forest also burned after the first cyclone. Here we report on patterns of regeneration and changes in tree species composition in the Tafua lowland rain forest after five years of recovery from cyclone and fire disturbance. In the unburned area, tree canopy cover increased from 27 percent after the last cyclone to 58 percent, and in the burned area from below 12 to 49 percent. Nine of the ten most common tree species decreased in relative abundance in the entire forest after the last cyclone. One fast growing pioneer species, Macaranga harveyana now makes up 42 percent of the total number of trees (>5 cm DBH) in the unburned area and 86 percent in the burned area. Large interspecific differences occur in size distribution and there are at least four distinguishable regeneration patterns, which may be related to shade tolerance. Mean number of species per plot was generally higher in the unburned area than in the burned area, while the Shannon evenness index was higher in the unburned than in the burned area only for trees above 1 cm DBH. Species with fruits known to be fed upon by birds and/or bats generally made up a larger proportion of all trees in the burned than in the unburned area. In contrast to other studies of post‐cyclone regeneration, in which recovery is often rapid due to resprouting of trees, recovery in the Tafua forest was a slow process with regeneration more dependent on vertebrate seed dispersal than on resprouting.

Impact of global warming on the tree species composition of boreal forests in Finland and effects on emissions of isoprenoids

AbstractThis study aims to identify how climate change may influence total emissions of monoterpene and isoprene from boreal forest canopies. The whole of Finland is assumed to experience an annual mean temperature (T) increase of 4 °C and a precipitation increase of 10% by the year 2100. This will increase forest resources throughout the country. At the same time, the proportions of Scots pine (Pinus sylvestris) and Norway spruce (Picea abies) in southern Finland (60°≤ latitude < 65°N) will be reduced from the current 40–50% to less than 10–20%, with increased dominance of birches (Betula pendula and Betula pubescens). In northern Finland (65°≤ latitude < 70°N), the proportions of Norway spruce and Scots pine will be balanced at a level of about 40% as the result of an increase in Norway spruce from the current 21% to 37% and a concurrent reduction in Scots pine from 63% to 40%. The proportion of birches is predicted to increase from the current 17% to 23%, but these will become the dominant species only on the most fertile sites.Total mean emissions of monoterpene by Scots pine will be reduced by 80% in southern Finland, but will increase by 62% in the north. Emissions from Norway spruce canopies will increase by 4% in the south but by 428% in the north, while those from birch canopies will increase by about 300% and 113%, respectively. Overall emissions of monoterpene over the whole country amount to about 950 kg km−2 y−1 under current temperature conditions and will increase by 17% to 1100 kg km−2 y−1 with elevated temperature and precipitation, mainly because of an increase at northern latitudes.Under current conditions, emissions of isoprene follow the spatial distribution of spruce canopies (the only isoprene‐emitting tree species that forms forests in Finland) with four times higher emissions in the south than in the north. The elevated temperature and the changes in the areal distribution of Norway spruce will result in increases in isoprene emissions of about 37% in southern Finland and 435% in northern Finland. Annual mean isoprene emissions from Norway spruce canopies over the whole country will increase by about 60% up to the year 2100.

Tree species composition in European pristine forests: Comparison of stand data to model predictions

The degree of general applicability across Europe currently achieved with several forest succession models is assessed, data needs and steps for further model development are identified and the role physiology based models can play in this process is evaluated. To this end, six forest succession models (DISCFORM, ForClim, FORSKA-M, GUESS, PICUS v1.2, SIERRA) are applied to simulate stand structure and species composition at 5 European pristine forest sites in different climatic regions. The models are initialized with site-specific soil information and driven with climate data from nearby weather stations. Predicted species composition and stand structure are compared to inventory data. Similarity and dissimilarity in the model results under current climatic conditions as well as the predicted responses to six climate change scenarios are discussed. All models produce good results in the prediction of the right tree functional types. In about half the cases, the dominating species are predicted correctly under the current climate. Where deviations occur, they often represent a shift of the species spectrum towards more drought tolerant species. Results for climate change scenarios indicate temperature driven changes in the alpine elevational vegetation belts at humid sites and a high sensitivity of forest composition and biomass of boreal and temperate deciduous forests to changes in precipitation as mediated by summer drought. Restricted generality of the models is found insofar as models originally developed for alpine conditions clearly perform better at alpine sites than at boreal sites, and vice versa. We conclude that both the models and the input data need to be improved before the models can be used for a robust evaluation of forest dynamics under climate change scenarios across Europe. Recommendations for model improvements, further model testing and the use of physiology based succession models are made.

Tropical Rain Forest Recovery from Cyclone Damage and Fire in Samoa1

In 1990 and 1991, Samoa was struck by two cyclones, Ofa and Val. In the Tafua Rain Forest Preserve on the island of Savai'i, one part of the forest also burned after the first cyclone. Here we report on patterns of regeneration and changes in tree species composition in the Tafua lowland rain forest after five years of recovery from cyclone and fire disturbance. In the unburned area, tree canopy cover increased from 27 percent after the last cyclone to 58 percent, and in the burned area from below 12 to 49 percent. Nine of the ten most common tree species decreased in relative abundance in the entire forest after the last cyclone. One fast growing pioneer species, Macaranga harveyana, now makes up 42 percent of the total number of trees (>5 cm DBH) in the unburned area and 86 percent in the burned area. Large interspecific differences occur in size distribution and there are at least four distinguishable regeneration patterns, which may be related to shade tolerance. Mean number of species per plot was generally higher in the unburned area than in the burned area, while the Shannon evenness index was higher in the unburned than in the burned area only for trees above 1 cm DBH. Species with fruits known to be fed upon by birds and/or bats generally made up a larger proportion of all trees in the burned than in the unburned area. In contrast to other studies of post-cyclone regeneration, in which recovery is often rapid due to resprouting of trees, recovery in the Tafua forest was a slow process with regeneration more dependent on vertebrate seed dispersal than on resprouting.

Impacts of interannual climate variability on past and future forest composition

Numerous analyses of the possible impacts of future climatic changes on tree species composition have been published for both lowland and high-elevation forests. Most of these studies were based on the application of forest "gap" models, and the vast majority of them considered only changes in the average of climatic parameters over time. In this study, we use a unique data set on reconstructed past climatic variations to analyse forest dynamics simulated by the forest gap model ForClim. This analysis forms the basis for a systematic exploration of the ecological effects of changing means vs. changing variability of climate on central European forests. A reconstruction of historical climate covering the last 470 years in the Swiss lowlands (ClimIndex) is extrapolated to a transect across the alpine (cold) treeline and used to simulate the influence of climate variations on the time scale of decades on forest biomass and tree species composition at both sites. While the simulation at the low-elevation site shows little sensitivity to climate variations, the results from upper subalpine forests suggest that two major dieback events would have occurred at elevations above the current but below the climatic tree line, induced by clusters of exceptionally cold summers. The results are in agreement with available dendrochronological data and with documentary evidence on massive negative impacts on flora and fauna at high elevations during these periods. We conclude that ForClim is capable of capturing the effects on tree population dynamics of climate variability at these sites as reconstructed from the ClimIndex record. A factorial design is used to address the sensitivity of ForClim to changes of the long-term averages vs. changes of the variability of monthly temperature and precipitation data. To this end, the simulated tree species composition of near-natural forests is examined along a climate gradient in Europe. The results indicate that there are three types of forest response: (1) little sensitivity to both kinds of change, (2) strong sensitivity to changes in the means, but little sensitivity to changing variability, and (3) strong sensitivity to changing variability at least in parts of the examined climate space. Half of the cases investigated fall under the third category, suggesting that emphasis should be placed on also assessing the sensitivity of ecosystems to future changes in climate variability rather than on changes of average values alone.

Nature conservation and timber production in areas with fragmented ownership patterns

Forestry has transformed the tree species composition and structure of Swedish forests. The fragmented ownership pattern in areas with non-industrial private forest ownership (NIPF), in combination with these forestry practices, have created fragmented forests with relatively low proportions of habitat types important to many species. Ecological landscape planning has been suggested and tested as a mean for integrating nature conservation and timber production in Sweden. However, ecological landscape planning concepts have been developed for areas with homogenous ownership patterns and not for areas with fragmented ownership. In this study, stands that are voluntarily set aside by individual forest owners were examined in terms of nature conservation value, and compared to randomly selected stands obtained by Monte Carlo simulation. In order to obtain rather detailed data about the set-aside stands, semi-standardized interviews were carried out directly with forest owners in three landscape areas dominated by NIPF. The interviews showed that 26 out of 29 forest owners could locate some stands where they did not have high requirements for timber yield. These stands had higher than average local and spatial nature conservation value as a result of stand structure, composition and location in the landscape. The stands did not have a random location or size, being found closer to key habitats as well as forming equally large or larger patches than other stands. These stands are suggested to form a basis for ecological landscape planning as forest owners seem to have some kind of ‘common view’ of which stands to set aside. This common view could be used to coordinate the contribution made by individual forest owners to nature conservation in areas with fragmented ownership patterns.

Patch Structure within Brazilian Atlantic Forest Fragments and Implications for Conservation1

Forest structure and tree species composition were studied in four Atlantic seasonal forest fragments ranging from 0.7 to 220 ha, isolated for more than a century in southeastern Brazil. Four physiognomic units were recognized within these fragments: (1) low forest, (2) bamboo forest, (3) high forest, and (4) mature forest. Tree density, basal area, and species diversity (Shannon-Wiener index) increased from low forest to bamboo forest to high forest to mature forest. Liana cover was highest in low forest. Gap-opportunistic species were the dominant ecological group in low forest, bamboo forest, and high forest, while shade tolerant canopy species formed the dominant group in mature forest. These structural and compositional features formed a gradient of forest development from the least developed low and bamboo forests to the most developed mature forest. Low forest is hypothesized to be in a stage of arrested succession and high forest a stage of degraded forest. A conceptual model is suggested to explain how these physiognomic units may be related to one another. Although these fragments were covered mainly by high and low forests and thus had a degraded structure, species diversity remained high in all of them. Fragments thus may undergo degradation long after isolation, even when they have been protected from human disturbance for a considerable period. Nonetheless, they also preserve important samples of local and regional floristic diversity for a long time after isolation.

Minireviews: Neighborhood Effects, Disturbance Severity, and Community Stability in Forests

A theoretical framework and conceptual model for temporal stability of forest tree-species composition was developed based on a synthesis of existing studies. The model pertains primarily to time periods of several tree lifetimes (several hundred to a few thousand years) at the neighborhood and stand spatial scales (0.01–10 ha), although a few extensions to the landscape scale are also made. The cusp catastrophe was chosen to illustrate compositional dynamics at the stand level for jack pine, northern hardwood, and white pine forests in the Great Lakes Region of the United States and for tropical rainforests in the northern Amazon basin. The models feature a response surface (degree of dominance by late-successional species) that depends on two variables: type of neighborhood effects of the dominant tree species and severity of disturbances. Neighborhood effects are processes that affect the chance of a species replacing itself at the time of disturbance (they can be positive, neutral, or negative) and are of two types: overstory–undestory effects, such as the presence of advanced reproduction; and disturbance-activated effects, such as serotinous seed rain. Disturbance severity is the proportion of trees killed during a disturbance. Interactions between neighborhood effects and disturbance severity can lead to either punctuated stability (dramatic but infrequent change in composition, in those forests dominated by species with positive neighborhood effects) or succession (continuous change, in those forests dominated by species with neutral-negative neighborhood effects). We propose that neighborhood effects are a major organizing factor in forest dynamics that provide a link across spatial scales between individual trees and disturbance/patch dynamics at the stand and landscape scales.

GREEN-TREE RETENTION: CONSEQUENCES FOR TIMBER PRODUCTION IN FORESTS OF THE WESTERN CASCADES, OREGON

National Forest management in the Pacific Northwest is adopting ecosystem management, in which the entire forest ecosystem is considered, as well as commodity production. Silvicultural prescriptions in ecosystem management often include retention of some live trees following timber harvest (green-tree retention) with the primary goal of maintaining biodiversity. How green-tree retention will affect growth and tree species composition of future forests is an important question. We took a retrospective approach to this question by using past disturbance as an analogue to green-tree retention following timber harvest. We used United States Department of Agriculture (USDA) Forest Service timber inventory plot data from the Cascade Mountains of Oregon and southwest Wash- ington (western hemlock zone). We selected 132 unmanaged stands with a tree cohort of 70-110 yr old (regeneration) or a tree cohort of 70-110 yr old with an overstory of large trees 200+ yr old (remnants), representing clearcuts and stands harvested with green-tree retention, respectively. Regeneration basal area (BA) across species and for Pseudotsuga menziesii tended to decline with increasing remnant density (R 2 = 0.51 and 0.60, respec- tively). but only after remnant densities reached 15 trees/ha; the relationships were roughly sigmoidal. Part of the effect of remnants on regeneration results from remnants' occupation of space, making it unavailable to the regeneration. After adjusting regeneration BA to account for remnants' space occupation, the relationship between regeneration BA and remnant density weakened by about half, implying that remnant effects resulted from both space occupancy and other factors associated with remnants. Total-stand BA was relatively constant across remnant densities. Remnant density was not related to tree-species diversity in the regeneration.

Green-Tree Retention: Consequences for Timber Production in Forests of the Western Cascades, Oregon

National Forest management in the Pacific Northwest is adopting ecosystem management, in which the entire forest ecosystem is considered, as well as commodity production. Silvicultural prescriptions in ecosystem management often include retention of some live trees following timber harvest (green-tree retention) with the primary goal of maintaining biodiversity. How green-tree retention will affect growth and tree species composition of future forests is an important question. We took a retrospective approach to this question by using past disturbance as an analogue to green-tree retention following timber harvest. We used United States Department of Agriculture (USDA) Forest Service timber inventory plot data from the Cascade Mountains of Oregon and southwest Washington (western hemlock zone). We selected 132 unmanaged stands with a tree cohort of 70–110 yr old (regeneration) or a tree cohort of 70–110 yr old with an overstory of large trees 200+ yr old (remnants), representing clearcuts and stands harvested with green-tree retention, respectively. Regeneration basal area (BA) across species and for Pseudotsuga menziesii tended to decline with increasing remnant density (R2 = 0.51 and 0.60, respectively), but only after remnant densities reached ≈15 trees/ha; the relationships were roughly sigmoidal. Part of the effect of remnants on regeneration results from remnants’ occupation of space, making it unavailable to the regeneration. After adjusting regeneration BA to account for remnants’ space occupation, the relationship between regeneration BA and remnant density weakened by about half, implying that remnant effects resulted from both space occupancy and other factors associated with remnants. Total-stand BA was relatively constant across remnant densities. Remnant density was not related to tree-species diversity in the regeneration.

Diversity, size composition and spatial aggregation among trees on a 1-ha rain forest plot at La R�union

Because lowland rain forests of oceanic islands have almost always been destroyed soon after human colonization, there exist few quantitative descriptions of tree species composition and diversity in such forests. For this reason, the diversity and structure of a lowland tropical rain forest were studied on a 1-ha permanent plot on the oceanic island of La Rrunion. A total of 1270 individuals of gbh ~ 25 cm (girth at breast height), including at least 43 species, were mapped, measured and identified. Several species were represented only by large individuals. Ten species among the 23 common enough to test are randomly distributed over the hectare, while 13 show aggregated spatial distributions. The tree species diversity, size structure and spatial distribution observed in this island plot are discussed in light of patterns occurring in continental lowland tropical rain forests. In the study area, the high density of trees and the tendency of conspecific individuals to be clumped may be linked to several factors: hurricane disturbance, lack of seed dispersers and patchy seed rain.

Long-term influence of deforestation on tree species composition and litter dynamics of a tropical rain forest in Puerto Rico

Understanding the long-term impact of deforestation on ecosystem structure and function of tropical forests may aid in designing future conservation programs to preserve biodiversity and sustain ecosystem productivity. We examined forest structure, tree species composition, litterfall rate, and leaf litter decomposition in a mid-successional forest (MSF) and an adjacent mature tabonuco forest (MTF) in the Luquillo Experimental Forest of Puerto Rico. Whereas the MTF site received limited human disturbance, the MSF site had been cleared for timber production by the beginning of this century and was abandoned after hurricanes struck the Luquillo Mountains in the 1920s and 1930s. We found that the MSF was dominated by successional tree species 50 years after secondary succession, and did not differ in tree basal area and litterfall rate from the MTF. Leaf decomposition rate in the MSF was higher than in the MTF, but this difference was small. Our results show that deforestation has long-term (over 50 years) influence on tree species composition and that recovery of leaf decomposition processes in secondary forest is relatively faster than that of tree species composition.

Changes in tree species composition, structure and growth in a bald cypress-water tupelo swamp forest, 1980–1990

Changes in forest vegetation during a 10 year period in a second growth bald cypress-water tupelo swamp were analyzed. The vegetation composition of this swamp forest is characteristic for deep-water alluvial river swamps in the southeastern United States. Bald cypress ( Taxodium distichum) dominates the lowest elevation sites, while water tupelo ( Nyssa aquatica) increases in importance with increasing elevation. Species composition and diameter at breast height (DBH) of the trees in the swamp forest were measured in permanent plots established in 1980 and growth rates were estimated from the change in DBH between 1984 and 1990. Repeated measures analyses indicated that forest canopy opening had no significant effect on density, basal area, or relative importance of the three dominant tree species. In the 10 years of the study, the densities of bald cypress and water tupelo have stayed relatively constant, while red maple ( Acer rubrum) and ash ( Fraxinus spp.) densities are declining rapidly. For all four tree species, mortality exceeded recruitment between 1984 and 1990. Since this 65–100 year old second growth forest has a closed canopy, low recruitment was expected. However, saplings of all species, except ash, were observed in all plots. The most important change in species composition in the study area was the large decrease in the number of red maple trees. Water tupelo growth rates were the highest at 9.8 ± 3.4 cm 2 year −1, followed by bald cypress at 7.0 ± 1.5 cm 2 year −1, and red maple at 1.4 ± 0.2 cm 2 year −1. Bald cypress growth rate was significantly correlated with site elevation. Variation in growth rates of the three dominant tree species was not explained by total tree density or total basal area.

Effect of Size Structure, Forest Floor Type and Disturbance Regime on Tree Species Composition in a Coniferous Forest in Japan

Effect of Size Structure, Forest Floor Type and Disturbance Regime on Tree Species Composition in a Coniferous Forest in Japan

Bivråkens Pernis apivorus boplatsval

At 30 Honey Buzzard nests in southwest Uppland (59°45'N) data were collected concerning different parameters of the forest (tree species composition, age, density, site quality class, silviculture, history etc.). These data were compared with the same parameters collected from a random sample of 32 spots in forests from the same area. The results show that the Honey Buzzard Pernis apivorus preferred to nest in diversified forest with high site quality class, and the preferred forests were often neglected concerning forestry measures and were also often affected by earlier wood pasturage. Old forests with a high proportion of deciduous trees and with a high mixture of tree species were preferred, while no nests were found in pine forest despite this forest type being the most common in the study area. The nests of Honey Buzzard were not randomly situated in the landscape but tended to be congregated along lakes, where also the highest site quality class forests were found.

Effect of flooding regime and understorey bamboos on the physiognomy and tree species composition of a tropical semideciduous forest in Southeastern Brazil

The interrelationship between river flooding regime, topography, soil properties and the distribution of tree and bamboo species was analysed in an area of tropical semideciduous forest on the margins of the Rio Grande, in Madre de Deus de Minas, Southeastern Brazil. A survey was carried out in a single forest plot (1.597 ha, 71 adjacent 225 m2 quadrats) located in the inner side of a river bend and extending from the point bar to the top of the slope. All trees (≥5 cm diameter at the base of the trunk) and bamboo culms were registered. Soil samples were collected and analysed for their properties and the river level was monitored during a two year period. In the point bar the forest was dominated by only two tree species, Salix humboldtiana and Inga affinis, that tended to occur in distinct areas. Differences in soil properties between these areas suggest variation in sedimentation dynamics. In the sloping part of the plot, a canonical correspondence analysis (CCA) indicated that the floristic composition was significantly correlated with three topographic sectors and their corresponding flood regimes. The Lower Slope corresponds to the sharp transition to the point bar forest, endures partial and annual floods and shows a very distinct flora that includes many light-demanding species. The Middle Slope is only occasionally reached by exceptional river floods and is characterised by a high density of the bamboo Merostachys neesii. The comparatively low density and basal area of trees, particularly for the smaller ones, provide evidence that the bamboos are problably interfering with the trees by restricting their recruitment. The Ridgetop lies entirely above the highest flooding level registered. The density of bamboos is lower and the understorey trees abundant.

Simulation of tree species composition and organic matter accumulation in Finnish boreal forests under changing climatic conditions

A model simulating the regeneration, growth and death of trees and the consequent carbon and nitrogen dynamics of the forest ecosystem was applied to determine the effect of expected temperature rise on tree species composition and the accumulation of organic matter in the boreal forest ecosystem in Finland (between latitudes 60°–70° N). In the southern and middle boreal zones a temperature rise of 2–3° C (temperature for 2 x CO2) over a period of one hundred years increased the competitive capacity of Scots pine (Pinus sylvestris) and birch species (Betula pendula and B. pubescens), and slowed down the invasion by Norway spruce (Picea abies). In the northern boreal zone a corresponding rise in temperature promoted the invasion of sites by Norway spruce. The accumulation of organic matter was promoted only slightly compared to that taking place in the current climatic conditions. A further doubling of temperature (temperature for 4 x CO2) over an additional period of two hundred years led to the replacement of coniferous stands with deciduous onesin the southern and middle boreal zones. In the northern boreal zone an admixture of coniferous and deciduous species replaced pure coniferous stands with the latter taking over sites formerly classified as tundra woodland. In the southern and middle boreal zones the replacement of coniferous species induced a substantial decrease in the amount of organic matter; this returned to its former level following the establishment of deciduous species. In the northern boreal zone there was no major change in the amount of organic matter such as occurred in the case of the tundra woodland where the amount of organic matter accumulated was nearly as high as in the northern boreal zone.

Tree population dynamics, stand structure and species composition in the montane virgin forest of Vallibäcken, northern Sweden

The population dynamics of Betula pubescens and Picea abies in a boreal forest near Kvikkjokk, northern Sweden, are governed by a process of storm gap regeneration similar to the gap regeneration described for boreo-nemoral forests. Cumulative age distribution curves, interpreted as static survivorship curves, lead to a simple theory of differential survival based on properties of the species, i.e. shade tolerance and relative growth rate. The theory is sustained by diameter and height distributions and by the spatial distributions of logs and of trees in different life-phases. Species of the field and ground layers respond differentially to gap formation and the ensuing successional stages. Browsing by moose (Alces alces) may prevent tree species, mainly Sorbus aucuparia, Betula pubescens and Pinus sylvestris, from developing into a tree layer. The regeneration ability for tree species growing in a stand at 460 m a.s.l. is limited compared with the regeneration at 330 m a.s.l., and typical storm gap formation involving more than one tree seems to occur rarely if at all, while overthrown trees with exposed rootplates are uncommon. Spruce at 460 m a.s.l. shows also a lower growth rate and a lower height/diameter ratio compared to the lower situated stands.