The tree species matrix,influence on the level of herbivore browsing in mixed forest stands in southwest Sweden†

Herbivory pressure on a forest stand and each plant individual may be affected by the spatial distribution of conspecific and allospecific plants on the site; whether the plants are standing in solitary or groupwise settings; or by the differences in the preference of plants in relation to each other. The study was conducted in southwest Sweden, where 120 plots (1508?m²) were visited and 1280 individual woody plants evaluated and measured. We tested the hypothesis that preferred woody plants can protect unpreferred conspecific and allospecific woody species against herbivory in a system with one dominant, generalist herbivore, the fallow deer (Dama L.), and that the effectiveness of this protection varies depending on the relative preference of the neighboring conspecific and allospecific woody species placed in conspecific groups or standing solitary. Our results support the hypothesis that preferred woody plants can protect unpreferred conspecific and allospecific woody species against herbivory in the case of Picea abies dominating stands.     

Could artificial reforestations provide as much production and diversity of fungal species as natural forest stands in marginal Mediterranean areas?

The aim of this work was to study and describe fungal communities in different habitats in dry Mediterranean areas. The objective was to determine whether artificial reforestations can develop fungal communities as productive and diverse as those found in natural stands. The results could provide ecological and economical implications for forest management in marginal areas, in order to recover the original forest dominated by Quercus, establishing as intermediate stage new forest stands dominated by Pinus which might play an essential role in restoring some type of degraded or marginal areas.     

Generalized height–diameter models—an application for major tree species in complex stands of interior British Columbia

Using permanent sample-plot data, selected tree height and diameter functions were evaluated for their predictive abilities for major tree species in complex (multiple age, size and species cohort) stands of interior British Columbia (BC), Canada. Two sets of models were evaluated. The first set included five models for estimating height as a function of individual tree diameter, the second set also included five models for estimating height as a function of individual tree diameter and other stand-level attributes. The inclusion of the BAL index (which simultaneously indicates the relative position of a tree and stand density) into the base height–diameter models increased the accuracy of prediction for all species. On average, by including stand level attributes, root mean square values were reduced by 30.0 cm. Based on the residual plots and fit statistics, these models can be recommended for estimating tree heights for major tree species in complex stands of interior BC. The model coefficients are documented for future use.     

The mean tree mass–stand density index relationship for forest stands in China

Most traditional studies of mean tree mass (MTM)– density relationships focus on crowded stands, without considering stands characterized with canopy gaps. We developed a model to estimate MTM of closed and unclosed forest stands based on stand density index (SDI). Data were obtained from eight forest stands in China to test the generality of this model. MTM was accurately expressed in terms of SDI by combining the equations for SDI and Yoda's model, and exponents of the MTM–SDI relationship ranged from –2.23 to 1.93. Compared with density, SDI is a better predictor of MTM, regardless of the degree of canopy closure in the stands.     

Dynamics of dominant tree species in a forest ecotone on the northern slop of Changbai Mountain

The competition and dynamics of dominant trees species in the forest ecotone between the broad-leaved/Korean pine （Pinus koraiensis） mixed forest and the spruce-fir forest （also known as dark conifer forest） in Changbai Mountain, Jilin Province in Northeast China were studied by using Lotka-Volterra model, based on the data from twenty-eight sample plots with area of 20 mx90 m for each one. Results showed that under natural condition, differentiation of communities followed two directions： one would be Spruce （Picea jezoensis and few P. koraiensis） and fir （Abies nephrolepis） co-dominant conifer forest, and at the equilibrium fir was absolutely preponderant （77.1% of relative dominance （RD））; the other would be the conifer and broad-leaved mixed forest, and at equilibrium, the broad-leaved tree species was 50% of RD in the broad-leaved/Korean pine mixed forest and 66% of RD in the broad-leaved and spruce-fir mixed forest. The study demonstrated that both broad-leaved/Korean pine mixed forest and dark conifer forest were climax community, the ecotone had transitional characteristics, and the diversification of the forest communities suggested that the direction of succession was affected by local habitat.     

Effects of selection cutting on the forest structure and species diversity of evergreen broa-leaved forest in northern Fujian, southern China

The short-term effects of selection cutting of different intensities on the forest structure and species diversity of evergreen broad-leaved forest in northern Fujian Province were investigated and analyzed. The results showed that selection cutting of low and medium intensities caused little variation in the forest structure. After cutting, the dominant species retained their leading status in the community. However, the community structure changed significantly following selection cutting of high and extra-high intensities; the status of the dominant species of the community declined dramatically. Some tree species began to disappear from the sampling plots. Except for extra-high intensity cutting, the diversity of tree species did not change significantly for the other three cutting intensities. However, the evenness of the stands was very different among the four kinds of cutting plots. For low and medium intensity selection cutting, the evenness declined slightly. For extra-high intensity selection cutting, the evenness increased to some extent, which might be due to a more even distribution of tree species after cutting. Cutting operations resulted in some adverse reactions to development of arborous species diversity of evergreen broad-leaved forest, particularly serious damage to the forest canopy. But the rational selection cuttings, which may benefit the restoration and maintenance of species diversity over a long period and may come about from the variations in environmental factors such as sunlight, temperature and humidity.     

Relationships of climate change and tree ring of Betula ermanii tree line forest in Changbai Mountain

Based on the tree-ring growth characteristics of Erman＇s birch （Betula ermanii charm.） and the relationships between it and climatic ）＇actors at elevation of 1950m, the sensitivity of tree lines in Changbai Mountain to climatic factors was assessed. The results indicated tree line forest in Changbai Mountain had an obvious sensitivity to climate factors. However, difference from other study sits is that the main climatic control factor on tree-ring growth was not current growth season temperatures, as might be expected, but previous winter and current March temperature. Although the precipitation in the region was quite abundant, the tree-ring growth was still significantly correlated with the precipitation during previous winter and current spring. Additionally, climatic factors which influenced the Erman＇s birch growth were not the yearly variables, but seasonal and monthly variables. Therefore, the reported increase in yearly mean temperature and total yearly precipitation since 1980s was not responded by sustained increase in ring widths in recent decades.     

Relationship between diversity of forest plant species and environmental gradient in eastern mountainous area of Heilongjiang Province, China

Twenty-three secondary forest communities with different structure were selected in Mao＇er Mountain National Park of Heilongjiang Province, China to study the relationship between diversity of forest plant species and environmental gradient. The forest plant species diversity was analyzed by the diversity index, and the environmental factors was quantified by the method of Whittaker＇s quantification of environmental gradient. Meanwhile, β-diversity indexes of communities were calculated with similar measurements. The results showed that the Shannon-wiener diversity index of forest plant species increased with the increase of the environmental gradient, and the β-diversity indexes of communities showed a liner increase along with the change of environmental gradient.     

Patterns of species dominance,diversity and dispersion in ＇Khasi hill sal＇ forest ecosystem in northeast India

Background： The ＇Khasi hill sal＇ forest ecosystem in Meghalaya, India represents the easternmost limit of sal distribution. We tested if tree diversity and compositional heterogeneity of this ecosystem was higher than other sal-dominated forests due to moister environment. Methods： Vegetation was sampled in 11 transects of 10 m width and up to 500 m length covering 5.2 ha area. All stems ≥10 cm girth at breast height were enumerated. Results： We found a pattern of mixed dominance of Shored robusta （sal） and Schima wollichii and co-dominance of Pinus kesiyo and Careya arborea. The Shannon＇s diversity index （H＇） was 3.395 nats. This value is remarkably high and competitive to that of moist sal forests of eastern Himalayan foothills and sal-dominated forests of Tripura. A high value of H＇ was manifested by： a） high species richness （S = 123）, b） good equitability （70.6%）, c） ＇fair＇ resource apportionment, and d） abundance of rare species （84% species with less than one per cent of total individuals, 67% species with two or less individuals ha-1 and 59% species with one or less individuals ha-1）. The compositional heterogeneity was ＇fair＇ （Whittaker＇sβw = 3.15）. The presence of Fagaceae with six species commanding 4.3% of importance value （IVl） and of a pine （P. kesiya） in sal forest was remarkable. As many as 58 species showed ＇low density （〈 10 individuals ha-1）, uniform dispersion＇, five species achieved ＇higher density （〉 10 individuals ha-l）, uniform dispersion＇ and six of the top 10 species were ＇clumped＇. The forest showed an exponential demographic curve illustrating ＇good＇ regeneration of an expanding community. Vertical stratification was simple with a poor canopy and fair subcanopy, which together with low basal area （15.65 m2 . ha-1 for individuals ≥ 10 cm gbh） indicated logging of mature sal trees in the past. Conclusions： The ＇Khasi hill sal＇ forest ecosystem is richer in alpha and beta diversi     

Growth response of coniferous stands to whole‐tree harvesting in early thinnings

A series of 15 field experiments was established to quantify the growth response of first‐thinning stands of Scots pine (Pinus sylvestris L.) and Norway spruce (Picea abies (L.) Karst) to whole‐tree harvesting and to estimate the need for nutrient compensation. The experiments were undertaken in Finland, Norway and Sweden and represent a wide range of site conditions. The site index (H ₁₀₀) of Scots pine stands varied from 19 to 29 m, and that of Norway spruce stands from 28 to 36 m. Total amounts of biomass and nutrients removed were calculated based on data obtained from felled sample trees. During the first 5‐yr period the growth response to the removal of logging residues varied considerably in both pine and spruce stands. Regression analyses did not reveal any functions that explained the variation in results satisfactorily. In cases where whole‐tree harvesting influenced tree growth negatively, this effect was counteracted by compensatory fertilization. It was concluded that to determine the response of remaining trees to harvesting intensity reliably, the post‐harvest period analysed must be longer than 5 yrs.     

Patterns of tree growth in a single tree selection silver fir–European beech forest

The basal area and height growth of trees and saplings in silver fir–European beech single stem selection forest were studied with regard to their social status and crown parameters of size, coverage, shading and vitality. On 24 permanent research plots (20 m × 20 m each) all trees [diameter at breast height (dbh) ≥10 cm] and saplings (≥1.3 m tall and dbh <10 cm) were surveyed. Repeated measurements of dbh (N = 1,608) and height (N = 1,135) 10 years apart enabled the calculation of annual basal area increment (BAI) of trees and saplings, and annual height (HI) increment of saplings. To obtain the growth characteristics for individual trees and saplings, their social status and crown parameters were assessed by rank. In the multivariate general linear model for BAI, social status, crown size and crown coverage of individuals as the predictors, and dbh² as the covariate, explained 70% of total variability. Similarly, social status, crown size, crown coverage and crown shading had a significant impact on the HI of saplings, explaining 70% of total variability. Among the observed variables, social status determined according to the individual’s position in vertical stand structure was, in addition to dbh, the most important predictor for both BAI and HI. Significant differences were observed between the BAI and HI models for the main tree species (European beech and silver fir), indicating their different growth characteristics. The applied method could be used as a supplement to the more widely used approaches for studying basal area and height growth of individual trees in selection forest stands.     

Determination of number of stems in coniferous forest stands by means of aerial photo‐interpretation

Two models for determination of the number of stems per hectare in forest stands (N) from attributes derived by aerial photo‐interpretation were developed. The models relied on the assumption that N could be determined by dividing the total stand volume per hectare with the volume of the “average tree”; defined by stand mean height and the diameter corresponding to mean basal area of a stand. Input variables of the models were stand mean height, crown closure and site quality. Additionally, model II required input of average stand volume per hectare and average mean diameter derived from stratified field sample plot inventories. Material for 143 coniferous stands was used for the testing of the models. The stands were recorded by intensive field measurements. Aerial photographs at the approximate scale of 1:15 000 were used for photo‐interpretation. The N value was underestimated in model I by 5.4–47.0%. The standard deviation for the differences was 15.2–26.2% for mature stands and 41.4–44.2% for young thinning phase stands. For model II, the mean difference between the predicted and observed N value was in the range ‐16.1% to 12.2%.     

An individual tree height increment model for mixed white spruce–aspen stands in Alberta,Canada

Individual tree-height increment models were developed for white spruce (Picea glauca (Moench) Voss) and aspen (Populus tremuloides Michx.) growing in the boreal mixed-species in Alberta. The models were formulated based on a selected base function (the Box–Lucas function), and the method of parameter prediction. Height increment was modeled as a nonlinear function of tree height, tree diameter, diameter increment, stand density, relative competitiveness of the tree in the stand, site productivity, and species composition. Since the data from permanent sample plots used in this study were time-dependent and cross-sectional, diagnostic techniques were applied to identify the models' error structure. Appropriate fits based on the identified error structure were accomplished using the nonlinear least squares procedures with a first-order autoregressive process. The models were also validated on independent testing data sets representing the population on which the models are to be used. Results showed that the average prediction biases were not significantly different from zero at α = 0.05, suggesting that the fitted models appropriately described the data and performed well when predictions were made. Biological implications of the variables that affect height increment in mixed-species stands were discussed.     

Does the effect of forest roads extend a few meters or more into the adjacent forest? A study on understory plant diversity in managed oak stands

Roads are recognised as having different ecological roles such as barrier, corridor or habitat, but the spatial extent of road effects on plant communities in forests remains unclear. We studied the effect of forest road distance on plant understory diversity at 20 sites in young and adult oak stands in a French lowland forest with a long history of management and road construction. All vascular and bryophyte species were collected at five distances ranging from the road verge to 100 m into the adjacent forest stand. We analysed species composition, individual species response, a priori life-history traits response – life form, habitat preference and dispersal mode – and environmental indicator values in relation to road distance and stand age. Plant composition strongly differed between road verge and forest interior habitats. The main road effect extended less than 5 m into the forest stand. A third habitat was detected at the forest-road edge resulting from the road effect on light and soil conditions, and from edge-specific topography. Non-forest species were almost absent from the forest interior. In contrast, many bryophytes and several vascular plants kept away from the road. We identified a posteriori six species groups that better explained the variability of plant response profiles than a priori life-history traits. Plant response to road distance was also dependent on stand age: some species colonised from the road into the forest interior in young stands following regeneration cutting, while other species displayed the reverse pattern in adult stands once canopy closed above the forest road. Even if the depth of forest road effect measured in lowland managed stands was narrow, building of a new forest road has non-negligible effects on plant population dynamics. Forest managers should take into account the impacts of roads on biodiversity, since the expected intensification of silviculture in response to global changes is set to accentuate the effect of forest roads. We recommend further study on the role of dispersal by vehicles (i.e. agestochory) in road effects.     

Plant β-diversity in human-altered forest ecosystems: the importance of the structural,spatial, and topographical characteristics of stands in patterning plant species assemblages

An understanding of spatial patterns of plant species diversity and the factors that drive those patterns is critical for the development of appropriate biodiversity management in forest ecosystems. We studied the spatial organization of plant species in human-modified and managed oak forests (primarily, Quercus faginea) in the Central Pre-Pyrenees, Spain. To test whether plant community assemblages varied non-randomly across the spatial scales, we used multiplicative diversity partitioning based on a nested hierarchical design of three increasingly coarser spatial scales (transect, stand, region). To quantify the importance of the structural, spatial, and topographical characteristics of stands in patterning plant species assemblages and identify the determinants of plant diversity patterns, we used canonical ordination. We observed a high contribution of β-diversity to total γ-diversity and found β-diversity to be higher and α-diversity to be lower than expected by random distributions of individuals at different spatial scales. Results, however, partly depended on the weighting of rare and abundant species. Variables expressing the historical management intensities of the stand such as mean stand age, the abundance of the dominant tree species (Q. faginea), age structure of the stand, and stand size were the main factors that explained the compositional variation in plant communities. The results indicate that (1) the structural, spatial, and topographical characteristics of the forest stands have the greatest effect on diversity patterns, (2) forests in landscapes that have different land use histories are environmentally heterogeneous and, therefore, can experience high levels of compositional differentiation, even at local scales (e.g., within the same stand). Maintaining habitat heterogeneity at multiple spatial scales should be considered in the development of management plans for enhancing plant diversity and related functions in human-altered forests.     

Mycorrhizal mushroom diversity and productivity—an indicator of forest health?

• Introduction   

Fruit-body production of mushrooms is not well understood to date as many factors interact with mushroom growth in nature. Weather conditions play a key role, but they do not completely explain the growth and productivity of wild mushrooms. Mycorrhizal fungi depend on photosynthetically fixed carbon produced by their associated trees, and the physiological state of host trees may well drive the growth of these fungi. We raise the question of whether mycorrhizal fungi can be used as indicators for tree health.     

Response of seedlings of different tree species to elevated C02 in Changbai Mountain

Eco-physiological responses of seedlings of eight species,Pinus koraiensis, Picea koraiensis, Larix olgensis, Populus ussuriensis, Betula platyphylla, Tilia amurensis, Traxinus mandshurica andAcer mono from broadleaved/Korean pine forest, to elevated CO₂ were studied by using open-top chambers under natural sunlight in Changbai Mountain, China in two growing seasons (1998–1999). Two concentrations of CO₂ were designed: elevated CO₂ (700 μmol·mol⁻¹) and ambient CO₂ (400 μmol·mol⁻¹). The study results showed that the height growth of the tree seedlings grown at elevated CO₂ increased by about 10%–40% compared to those grown at ambient CO₂. And the water using efficiency of seedlings also followed the same tendency. However, the responses of seedlings in transpiration and chlorophyll content to elevated CO₂ varied with tree species. The broad-leaf tree species were more sensitive to the elevated CO₂ than conifer tree species. All seedlings showed a photosynthetic acclimation to long-term elevated CO₂. Foundation item: The project was supported by National Key Basic Development of China (G1999043400) and the grant KZCX 406-4, KZCX1 SW-01 of the Chinese Academy of Sciences Biography: WANG Miao (1964-), maie, associate professor in Institute of applied Ecology, Chinese Academy of Sciences, Shenyang 110016, P. R. China. Responsible editor: Song Funan     

The use of species–stem curves in sampling the development of the Zambian miombo woodland species in charcoal production and slash-and-burn regrowth stands

The use of fixed-area plot methods was considered unsuitable to compare the responses and recovery over time of different miombo woodland species to different land-use practices (i.e. charcoal production and slash-and-burn agriculture). Young regrowth stages have many stems and the older more advanced stages have fewer stems. Different land-use practices in miombo woodland impact on the recovery potential of the woodlands. Timber harvesting does not result in significant change in stocking of the woodland compared to changes in regrowth after vegetation clearing for either charcoal production or slash-and-burn agriculture. After such clearing the woodland regrowth changes from an initial high stocking to a much lower stocking over time. This study in Zambian Copperbelt miombo woodland assessed the feasibility to use species–stem curves to determine the optimum number of stems or plants to record at a sampling point in order to compare species recovery over time in regrowth stands 2–15 years after ending the slash-and-burn and charcoal production activities. The results show that 34 and 31 stems or plants for slash-and-burn and charcoal production regrowth stands, respectively, would adequately capture the representative number of species to describe the plant community of these regrowth stands. The research has also revealed that the use of fixed-area methods would result in the measuring of too many plants in one category (younger stands) with too few in the other category (advanced stands). Therefore, the study explains why, and concludes that, variable plot size is an appropriate method for sampling species recovery in regrowth stands.