An Analysis of Vegetation Restoration on Opencast Oil Shale Mines in Estonia

We compared four types of 30‐year‐old forest stands growing on spoil of opencast oil shale mines in Estonia. The stand types were: (1) natural stands formed by spontaneous succession, and plantations of (2) Pinus sylvestris (Scots pine), (3) Betula pendula (silver birch), and (4) Alnus glutinosa (European black alder). In all stands we measured properties of the tree layer (species richness, stand density, and volume of growing stock), understory (density and species richness of shrubs and tree saplings), and ground vegetation (aboveground biomass, species richness, and species diversity). The tree layer was most diverse though sparse in the natural stands. Understory species richness per 100‐m² plot was highest in the natural stand, but total stand richness was equal in the natural and alder stands, which were higher than the birch and pine stands. The understory sapling density was lower than 50 saplings/100 m² in the plantations, while it varied between 50 and 180 saplings/100 m² in the natural stands. Growing stock volume was the least in natural stands and greatest in birch stands. The aboveground biomass of ground vegetation was highest in alder stands and lowest in the pine stands. We can conclude that spontaneous succession promotes establishment of diverse vegetation. In plantations the establishment of diverse ground vegetation depends on planted tree species.     

The competitive status of trees determines their responsiveness to increasing atmospheric humidity – a climate trend predicted for northern latitudes

The interactive effects of climate variables and tree–tree competition are still insufficiently understood drivers of forest response to global climate change. Precipitation and air humidity are predicted to rise concurrently at high latitudes of the Northern Hemisphere. We investigated whether the growth response of deciduous trees to elevated air humidity varies with their competitive status. The study was conducted in seed‐originated silver birch and monoclonal hybrid aspen stands grown at the free air humidity manipulation (FAHM) experimental site in Estonia, in which manipulated stands (n = 3 for both species) are exposed to artificially elevated relative air humidity (6–7% over the ambient level). The study period included three growing seasons during which the stands had reached the competitive stage (trees were 7 years old in the final year). A significant ‘treatment×competitive status’ interactive effect on growth was detected in all years in birch (P < 0.01) and in one year in aspen stands (P = 0.015). Competitively advantaged trees were always more strongly affected by elevated humidity. Initially the growth of advantaged and neutral trees of both species remained significantly suppressed in humidified stands. In the following years, dominance and elevated humidity had a synergistic positive effect on the growth of birches. Aspens with different competitive status recovered more uniformly, attaining similar relative growth rates in manipulated and control stands, but preserved a significantly lower total growth yield due to severe initial growth stress. Disadvantaged trees of both species were never significantly affected by elevated humidity. Our results suggest that air humidity affects trees indirectly depending on their social status. Therefore, the response of northern temperate and boreal forests to a more humid climate in future will likely be modified by competitive relationships among trees, which may potentially affect species composition and cause a need to change forestry practices.     

Sexual and Asexual Reproduction in Natural Stands of Populus nigra

The balance between sexual and asexual propagation in the establishment of natural stands of Populus nigra was assessed from the genotypes of trees sampled in different natural stands. One site was completely sampled and genotyping proceeded using STS and RAPD markers. Among 118 trees, only four were vegetative copies of other trees of the site. Isozymes were used in four stands, and a method to detect the presence of vegetative copies in a sample is proposed for these markers. No vegetative copies were found in two cases, and a low number of copies was detected in the other two. Observations are reported for seedlings as well as for different modes of vegetative propagation in natural stands. We conclude that sexual and asexual propagation play complementary roles in the dynamics of this species, and that in most cases the adults originate from seedlings.     

Sources of variation in the incidence of ant–aphid mutualism in boreal forests

• 1 The mutualism between wood ants of the Formica rufa group and aphids living in the canopy of trees is a widespread phenomenon in boreal forests, and it can affect tree growth. However, not all trees in the forest are involved in this interaction.
• 2 To assess the incidence of host trees involved in this ant–aphid mutualism and its spatial distribution in boreal forests, we inventoried sample plots with a radius of 10–15 m around wood ant mounds in 12 forest stands of two age classes (5–12‐year‐old sapling stands and 30–45‐year‐old pole stands) and two dominant tree species (Scots pine and silver birch) in Eastern Finland from 2007 to 2009.
• 3 The proportion of trees visited by ants out of all trees on the individual study plots were in the range 4–62%, and 1.5–39% of the trees on the plots were consistently visited by ants during all 3 years. The percentage of host trees increased with the ant mound base area on the plots. Trees visited by ants were larger and closer to the mound than trees not visited by ants. Within the group of visited trees, more ants were found on bigger trees and on trees close to the ant mounds.
• 4 Extrapolated from plot to stand level, we estimated that 0.5–6.6% of the trees were host trees in at least one of the three study years, and that only 0.01–2.3% of all the trees were consistently visited by ants during all 3 years. It is concluded that ant–aphid mutualism is a minor occurrence at the stand level.

     

Estimating bark thickness in natural stands of Eucalyptus

Information on bark thickness at various heights is sought to predict damage to trees by forest fires. A procedure which for natural stands of some smooth bark eucalyptus species enables the estimation of bark thickness at different heights from a single girth measurement at one metre height is discussed. The method utilizes the relationships of average girth, average bark thickness, and the regression coefficients of girth and bark thickness at given height positions, with height at one metre. The height positions are determined on a calibrating sample of about thirty trees of different sizes. Furthermore it is shown how the above information can be used to estimate bark volume, and hence bole volume, for Eucalyptus species of some commercial importance such as E. viminalis. Four species are considered: E. viminalis, E. pauciflora, E. mannifera and E. radiata.     

Maximum yield and the C-D effects in natural white birch stands

The competition-density effect for natural Japanese white bitch (Betula platyphylla var.japonica) stands, located in the northern part of Hokkaido Island, was examined for various growth stages to establish mean tree weight-density relationships over a considerable extent of stand growth of white birch. Aboveground yields of investigated stands ranged from 16.0 to 161.7 t·ha⁻¹, and it was recognized that maximum aboveground yield of this species was about 160 t·ha⁻¹. ConstantsA andB of the reciprocal equation of the C-D effect, 1/w=AN+B (w, mean tree weight; N, tree density), were related to mean height classes of birch stands. ConstantB was related to the entire mean height classes as the allometric relationship. On the other hand, constantA had an allometric relationship to mean height classes under 16 m, but became fixed over the 16 m class. White birch stands can come up to the maximum yield approximately at the stage of the 16 m class. The asymptotic tendency seemed to be appropriate for constantA-mean height class relationship. The maximum yield of white birch stands was predicted by the asymptotic value ofA. The trend of mean tree weight-density relationships with stand growth also changed with constantA. It was considered that maximum yield was an important characteristic for practical applications of the C-D effect to agriculture and forestry.     

Genetic features of root fungus-resistant scotch pine trees in artificial stands in the steppe zone of Ukraine

A comparative analysis of the allozyme variation in 18 loci of three steppe natural populations of Pinus sylvestris L. and a sample of 36 resistant trees from artificial stands at locations affected by root fungus (Heterobasidion annosum (Fr.) Bref.) is conducted. The resistant trees are characterized by lowest percentages of polymorphic allozyme loci, a fewer number of alleles, and number of genotypes close to the mean-population number, as well as a level of observed and expected heterogeny. In terms of composition and frequencies of multi-loci genotypes (Dia-1, Lap-1, Acp) that are responsible for the greatest contribution to the partitioning of the stands studied, the sample of resistant trees differs markedly from the natural populations.     

Escape in space from enemies: a comparison between stands with and without enhanced densities of the spruce bark beetle

1 Populations of the spruce bark beetle, Ips typographus (L.), are known to grow rapidly in storm‐disturbed stands as a result of relaxation from intraspecific competition. In the present study, it was tested whether a second mechanism, escape in space from natural enemies, also contributes to the rapid population increase. 2 The experiment was conducted during the initiation phase of five local outbreaks of I. typographus triggered by a storm‐disturbance in November 1995 in southern Sweden. 3 The impact of natural enemies on the ratio of increase (number of daughters per mother) of I. typographus was compared pairwise between disturbed stands with high numbers of storm‐felled trees and undisturbed stands without wind‐felled trees. 4 Enemy impact was assessed by comparing the ratio of increase in uncaged (exposed to enemies) and caged (protected from enemies) bolts colonized by I. typographus prior to being placed in the stands. The experiment was conducted in the second and third summers after the storm‐felling. 5 Enemy impact was about twice as high in stands without wind‐felled trees compared with in stands with wind‐felled trees in the second summer whereas there was no significant difference between the stand types in the third summer. 6 The result demonstrates that spatial escape from enemies contributes to the rapid population growth of I. typographus after storm‐disturbances.     

Winter home range and habitat use by porcupines in Alaska

Habitat selection results from trade-offs between availability and use of resources under constraints of predation, competition, or other threats, which can vary spatially and temporally. For northern herbivores, winter food availability and quality can limit population size and may drive habitat preference. North American porcupines (Erethizon dorsatum) are widespread generalist herbivores that range from Mexico to the northern reaches of Alaska. During the long Alaskan winter, porcupines deal with high energetic demands resulting from low ambient temperatures while subsisting on low quality forage. We tracked free-ranging porcupines over 3 winters in southcentral Alaska to determine habitat selection and home range size in relation to diet. Porcupines maintained larger than expected home ranges, and selected for conifer-hardwood forests at the home range level. Individual variation among porcupines was too large to determine a pattern of microhabitat selection among trees. Regardless, direct observations revealed that porcupines used only white spruce and paper birch trees for foraging. White spruce may provide some nutritional and thermoregulatory advantage over paper birch; however, porcupines did feed on paper birch cambium, suggesting some nutritional requirement is met by eating paper birch. Porcupines most likely feed on paper birch cambium when detoxification pathways used to process plant toxins in white spruce needles are saturated. Maintaining mixed conifer-hardwood forests in southcentral Alaska would provide suitable winter habitat for porcupines and may alleviate damage to single species stands of conifers or hardwoods that are preferred by commercial forestry operations. © 2012 The Wildlife Society.     

Additive and non‐additive effects of birch genotypic diversity on arthropod herbivory in a long‐term field experiment

Herbivores are important drivers of plant population dynamics and community composition in natural and managed systems. Intraspecific genetic diversity of long‐lived plants like trees might shape patterns of herbivory by different guilds of herbivores that trees experience through time. However, previous studies on plant genetic diversity effects on herbivores have been largely short‐term. We investigated how tree genotypic variation and diversity influence herbivory of silver birch Betula pendula in a long‐term field experiment. Using clones of eight genotypes, we constructed experimental plots consisting of one, two, four or eight genotypes, and measured damage by five guilds of arthropod herbivores twice a year over three different years (four, six and nine years after the experiment was established). Genotypes varied significantly for most types of herbivore damage, but genotype resistance rankings often shifted over time, and none of the clones was more resistant than all others to all types of herbivores. At the plot level, birch genotypic diversity had significant positive additive effect on leaf rollers and negative non‐additive effects on chewing herbivores and gall makers. In contrast, leaf‐mining and leaf‐tying damage was not influenced by birch genotypic diversity. Within diverse plots, the direction of genotypic diversity effects varied depending on birch genotype, some having lower and some having higher herbivory in mixed stands. This research highlights the importance of long‐term studies including different feeding guilds of herbivores to understand the effects of plant genetic diversity on arthropod communities. Different responses of various feeding guilds to genotypic diversity and shifts in resistance of individual genotypes over time indicate that genotypic mixtures are unlikely to result in overall reduction in herbivory over time.     

Estimation of canopy density and irradiance in 20- to 40-year-old birch stands (Betula pubescens Ehrh. andBetula pendula Roth)

Three different experiments in birch (Betula pubescens Ehrh. andBetula pendula Roth) stands were conducted during summer 1991: an evaluation of the accuracy of the vertical tube method measuring crown free projection (CFP) in four birch stands; a study of relative irradiance (RI; photosynthetically active radiation, PAR), in birch stands differing in stem density and basal area; and an estimation of the CFP in different types of birch stands and the correlation between RI and CFP. The results indicate that the number of observation points well distributed over an area of 0.1 ha can vary between 50 and 200 to achieve sufficient accuracy. There were no significant differences in the CFP estimates made on the same plot by different observers including an untrained observer. CFP was related to basal area, stem number and diameter sum in a non-linear regression, CFP = A^*e^-BX. The correlations between RI and basal area, density and diameter sum, respectively, were 0.54, 0.57 and 0.67 for PAR. The coefficients of determination for RI (PAR) and CFP were high (0.86).     

Changes in the chemical content of birch (<Emphasis Type="Italic">Betula pendula </Emphasis>Roth) leaves in the air polluted Krusne hory mountains

Analyses of birch leaves (Betula pendula Roth) sampled from trees in the air polluted Krusne hory mountains and Decin sandstone highlands were performed in 1995 and 1998. The results revealed a connection between reduction of air pollutants and overall decrease in sulphur and nitrogen content of the leaves. Simultaneously, in many stands an increase in calcium content and a decrease in contents of phosphorus, magnesium and potassium occurred. The content of microelements and non-nutrient elements did not change.     

Dynamics in Central European near‐natural Abies‐Fagus forests: Does the mosaic‐cycle approach provide an appropriate model?

Question: The mosaic‐cycle concept of forest dynamics dominates in Central Europe. According to this concept intermediate‐scale disturbances only accelerate the forest break‐up under existing cycles of forest development. Is such an approach correct, or should new developmental cycles be elaborated for intermediate‐scale disturbances? Location: Near‐natural Abies alba ‐ Fagus sylvatica forests in the ?wiétokrzyski National Park in Central Poland. In these forests intermediate‐scale disturbances occurred between 1970 and 1990. Methods: Data were collected twice in areas surrounding 212 permanent sample points (in 1994 and 2004). Two increment cores were taken from 259 sample Abies trees. The effect of intermediate‐scale disturbances on radial increment of Abies was assessed. Probabilities of stand transition during a 10‐year period between individual stages and phases of development of the mixed forest were calculated. The development stages and phases were arranged into hypothetical succession series of successive changes. Results: In 1994 70 stands and in 2004, 47 stands representing stages and phases containing the older generation formed by trees > 100–150 years were found. Also, in 1994 142 and in 2004, 165 stands representing stages and phases containing the younger generations only, formed by trees < 100‐150 years, were recorded. Stages and phases containing only younger generations do not occur in the existing forest development cycle which does not consider the influence of intermediate‐scale disturbances separately. Two developmental cycles, which take into account the presence of the older generation and the younger generations only (under conditions of the occurrence of intermediate‐scale disturbances), are proposed. Conclusion: The mosaic‐cycle concept of forest dynamics can be used to analyse the dynamics of Central European near‐natural mixed‐species forests, but new developmental cycles should be elaborated for intermediate‐scale disturbances.     

Origins and genetic conservation of tropical trees in agroforestry systems: a case study from the Peruvian Amazon

Hundreds of native tree species are currently found in extensive agroforestry ecosystems in the Peruvian Amazon, forming an important reservoir of biodiversity. To further promote conservation, farmers are encouraged to supplement intra-specific genetic diversity in these populations with seed collected from local forests. For some tree species, however, this approach may be inappropriate, as stands of these taxa already found on-farm may not be of local origin. Despite this issue being of importance for conservation, little information is available on the history of cultivated trees in the region, a situation that we here rectify for the important fruit tree Inga edulis. Based on nuclear SSR and chloroplast DHPLC analyses of closely geographically matched natural and planted stands at five sites, it appears that cultivated material of I. edulis is primarily of non-local origin, indicating that conservation based on new wide-scale infusions from local wild stands into farms may be inappropriate in the region. Although nuclear and chloroplast diversity were both lower in planted stands, values were still relatively high (∼80 and 70% of natural stands, respectively), indicating that when farmers plant trees, good collection practice of seed from already cultivated I. edulis should be an effective means for ensuring long-term conservation on farms.     

Birch family and environmental conditions affect endophytic fungi in leaves

We investigated whether variation in foliar endophyte frequency among mountain birch trees from different maternal families was due in part to genetic differences among trees. The effect of different environmental conditions on the susceptibility of these mountain birch families to foliar endophytes was tested. The 3-year study was conducted in two tree gardens (altitudinal difference 180 m) with ten families of mountain birch. The frequency of the commonest endophytic fungus in mountain birch leaves, Fusicladium sp., was significantly affected by mountain birch family, with the ranking of families relative to Fusicladium sp. frequency being consistent from environment to environment. Variation in the frequency of Melanconium sp. was difficult to interpret because of significant family × garden × year interaction. Fusicladium sp. and Melanconium sp. endophytes were most frequent in different tree individuals, families and gardens. We conclude that mountain birch trees show heritable variation in their foliar endophyte frequency, and thus one of the conditions necessary for foliar endophytes of mountain birch trees to be able to affect the evolution of their host plant is fulfilled. However, the effect of mountain birch family on the frequency of endophytic fungi varies depending on the endophytic genera in question and partially also on environmental conditions. Received: 28 March 1998 / Accepted: 14 October 1998     

Structure of Anogeissus leiocarpa Guill., Perr. natural stands in relation to anthropogenic pressure within Wari‐Maro Forest Reserve in Benin

The present study focused on the analysis of the structure of the Anogeissus leiocarpa dominated natural stands in the Wari‐Maro forest reserve which are under high and minimal anthropogenic pressures. These stands were considered for forest inventories after carrying out a random sampling scheme of 40 sample units of 30 m × 50 m. In each level pressure stand, the dbh and tree‐height of identified tree‐species were measured in each plot. Data analyses were based on the computation of structural parameters, establishment of diameter and height distributions and the floristic composition of the two types of stands. Results obtained showed higher values for the overall basal area (9.78 m² ha^?1), mean height (22.37 m) and mean diameter (36.92 cm) for A. leiocarpa in low‐pressure stands. In high‐pressure stands, some species like Afzelia africana had lower Importance Value Index and the frequency of A. leiocarpa trees in the successive diameter classes dropped rapidly and the value of the logarithmic slope of the height–diameter relationship was lower (9.77) indicating a lanky shape. Results obtained suggest that effective conservation is needed for A. leiocarpa stands under high pressure by limiting human interference and developing appropriate strategy for restoration purposes.     

Environmental conditions and host genotype direct genetic diversity of Venturia ditricha,a fungal endophyte of birch trees

We investigated whether genetic variation of a common foliar endophyte of birch trees, Venturia ditricha, is affected by environmental conditions or host genotype. Fungal samples were collected from 10 half-sibling families of mountain birch (Betula pubescens ssp. czerepanovii) grown in two environmental conditions with different daily average temperatures: a forested river valley and an adjacent open tundra (altitudinal difference 180 m). Genetic analysis of V. ditricha isolates was done using random amplified microsatellite polymerase chain reaction. We found that host genotypes, along with prevailing environmental conditions, influence the probability of infection by particular endophyte genotypes. The most susceptible host genotypes were highly infected with genetically similar endophyte genotypes, whereas the most resistant trees were poorly infected and they were infected by genetically dissimilar endophytes. Our results also showed environment-host genotype interactions, suggesting that the susceptibility of the host to a particular endophyte genotype may change in natural environments when environmental conditions are changed. It appears that a particular endophyte genotype needs to find the right host genotype for a successful infection. There are many host genotypes in natural stands; this means, from the point of view of the fungus, the environment is heterogeneous. Thus, under the influence of birch tree genotypes, genetically differentiated subgroups of the endophytic fungus may be formed in different environments.     

Delayed induced changes in the biochemical composition of host plant leaves during an insect outbreak

In birch, Betula pubescens, herbivore-induced delayed induced resistance (DIR) of defoliated trees may cause a strong reduction in the potential fecundity of a geometrid folivore Epirrita autumnata. In this study, we examined the biochemical basis of DIR in birch leaves during a natural outbreak of E. autumnata. A set of experimental trees was defoliated at four sites by wild larvae in the peak year of the outbreak, whereas control trees were protected from defoliation by spraying with an insecticide. The biochemical composition of leaves was analysed in the following year and, although the DIR response was weak during this outbreak, causing less than a 20% reduction in the potential fecundity of E. autumnata, some consistent relationships between defoliation, biochemistry and pupal mass of E. autumnata suggested a general biochemical basis for the defoliation-induced responses in birch leaves. Total concentrations of nitrogen, sugars and acetone-insoluble residue (e.g. cell wall polysaccharides, cell-wall-bound phenolics, protein, starch, lignin and hemicellulose) were consistently lower, and total concentrations of phenolics, especially of gallotannins and soluble proanthocyanidins, were higher in the leaves of trees defoliated in the previous year than in those protected from defoliation. The capacity of tannins to precipitate proteins correlated with contents of gallotannins, and was highest in defoliated trees. The pupal mass of E. autumnata showed a strong, positive correlation with concentrations of nitrogen and sugars, and a negative correlation with the acetone-insoluble residue and gallotannins in foliage. Correlations with other measured biochemical traits were weak. The correlation coefficients between biochemical traits and pupal mass consistently had similar signs for both defoliated and insecticide–sprayed trees, suggesting that variation in leaf quality due to defoliation in the previous year was based on similar biochemical traits as variation for other reasons. We suggest that DIR is associated with reduced growth activity of leaves, and may be seen as a delay in the biochemical maturation of leaves in defoliated trees. This explains the high concentration of gallotannins in defoliated trees, a characteristic feature of young leaves. However, the lower content of nitrogen and the higher content of soluble proanthocyanidins in defoliated trees are traits usually characterising mature, not young, leaves, indicating defoliation-induced changes in chemistry in addition to modified leaf age. Our results emphasise the importance of understanding the natural changes in chemistry during leaf maturation when interpreting defoliation-induced changes in leaf biochemistry. Received: 26 January 1998 / Accepted: 10 April 1998     

Foliar oxidases as mediators of the rapidly induced resistance of mountain birch against <Emphasis Type="Italic">Epirrita autumnata</Emphasis>

Induced resistance of the mountain birch against its main defoliator Epirrita autumnata is a well-characterized phenomenon. The causal mechanism for this induced deterioration, however, has not been unequivocally explained, and no individual compound or group of traditional defensive compounds has been shown to explain the phenomenon. Phenolic compounds are the main secondary metabolites in mountain birch leaves, and the biological activity of phenolics usually depends on their oxidation. In this study, we found that the activity of polyphenoloxidases (PPOs), enzymes that oxidize o-diphenols to o-diquinones, was induced in trees with introduced larvae, and bioassays showed that both growth and consumption rates of larvae were reduced in damaged trees. PPO activity was negatively associated with both larval growth and consumption rates in trees with bagged larvae, but not in control trees. Our results suggest that the oxidation of phenolics by PPOs may be a causal explanation for the rapidly induced resistance of mountain birch against E. autumnata. This finding also helps to explain why correlations between insect performance and phenolics (without measuring indices explaining their oxidation) may not produce consistent results.