Bamboo dieback and tree regeneration responses in a subtropical forest of South America

Bamboos’ vegetative growth are frequently associated to negative effects on tree recruitment and survival and despite this process, the effects of bamboo dieback after flowering events are poorly understood due the rarity of these events. 2 years after the massive flowering of the woody bamboo Merostachys multiramea in a southern South America subtropical forest, we compared changes in environmental conditions; tree species regeneration and production of new culms in canopy gaps resulted from bamboo dieback and areas of continuous canopy allowed by sparse bamboo cover. We observed sharp differences in environment conditions mainly resulted from differences in canopy openness and a NPMANOVA revealed differences among the stands regeneration directions (species composition and density). Average density, number of culms per sapling and total height of M. multiramea did not differ between stands, although slight differences were detected with increasing values toward opened sites.     

Twenty-three years of stand dynamics in an old-growth Chamaecyparis forest in central Japan

Structures and dynamics of old-growth coniferous stands are affected by several types of disturbances including typhoons. We report the forest dynamics of four old-growth Chamaecyparis stands in central Japan that differ in the disturbance history of typhoons over a period of 23 years. The stem number, basal area and mortality were examined. In a predominant stand of C. obtusa (Sieb. et Zucc.) Endl., 24 % of the C. obtusa canopy trees died, mainly as a result of the severe damage of a strong typhoon that caused a single tree-fall gap and the following gap enlargements. In this stand, the total basal area decreased to 76.5 % of the initial value, although the mortality declined in recent years. In contrast, the other three stands decreased only slightly in the stem numbers (0.0–5.6 %) and increased in the basal areas of C. obtusa canopy trees. It is confirmed that the stand-level ingrowths of 300-year-old C. obtusa canopy trees could contribute to the increase in the stock of each stand. Our results support an idea that the dynamics of old-growth Chamaecyparis forests were greatly affected by typhoons. The stand structures will be gradually changed (with the processes of gap dynamics) and C. obtusa will continue to be dominant, potentially over hundreds of years.     

Temporal and spatial dynamics of an old-growth beech forest in western Japan

Dendrochronological approaches enable us to understand forest stand dynamics by estimation of disturbance history and age structure. The present study was conducted in an old-growth beech forest in a forest reserve in western Japan. Increment cores were taken for tree ring analysis from all canopy trees in a 50 m × 130 m study plot. Radial growth release criteria were developed to identify significant growth releases in each tree ring series and to characterize the disturbance history of the study site. The age structure of the forest was indicative of continuous establishment by Fagus crenata and simultaneous establishment by Magnolia obovata. A variety of low-intensity disturbances were identified in each decade, especially after the 1900s, but the occurrence of high-intensity catastrophic disturbance was rare, and likely played an important role in maintaining species diversity in the existing forest canopy. The results also suggest that F. crenata regenerates gradually before and after both large- and small-scale disturbances, whereas M. obovata and Betula grossa regenerate only after large-scale catastrophic disturbances.     

Recovery of forest structure and composition to harvesting in different strata of mixed even-aged central Appalachian hardwoods

Context

Implementing nature-based silviculture requires understanding the structural and compositional changes that occur in forested stands under known disturbance types and intensities.

Aims

The objectives were to assess the (a) resistance of hardwood forests to change, (b) their trajectory of recovery following disturbance, and (c) how closely resulting forests resemble original forests.

Methods

We characterized tree structure and composition at three points in time (pre-disturbance, 1-year post-disturbance, and ～15 years following disturbance) along a harvesting disturbance gradient created by removing trees in different forest canopy strata.

Results

Significant differences to pre-disturbance conditions were noted immediately post-harvest for tree basal area, density, species richness, and tree species composition; treatment differences were observed for all parameters except diversity. Plots exposed to the least extreme harvesting disturbances (cutting small and intermediate trees) had returned to pre-disturbance conditions for most parameters after 15 years, while the most extreme harvesting disturbance (cutting large trees) had not yet recovered.

Conclusions

Although not initially resistant, Central Appalachian eastern hardwoods are fairly resilient to the removal of trees in the subcanopy or a mixture of the subcanopy and canopy; only the removal of solely canopy trees (i.e., high grading) and complete removal (i.e., clearcutting) appear to impose harvesting disturbances to which these forests may not be resilient.     

Aboveground biomass increment and stand dynamics in tropical evergreen broadleaved forest

Forest ecosystems can modify the atmospheric CO₂ through biomass accumulation mostly in tree stems with diameter at breast height (DBH) ≥ 10 cm. Aboveground biomass increment (ΔAGB), and changes in stand AGB, no. stems and basal area (BA) were calculated from mortality, recruitment, and growth data of tree stems in tropical evergreen broadleaved forest, Central Highland Vietnam. Data were derived from ten 1-ha permanent plots established in 2004, where all stems with DBH ≥ 10 cm were tagged, identified to species, and measured for DBH in 2004 and 2012. In an 8-year duration, the increment was 53 ± 10 stems ha^–1, 7.8 ± 0.3 m² ha^–1 for BA and 86.0 ± 4.6 Mg ha^–1 for AGB. The stem mortality rate was 0.9% year^–1 and the stem recruitment rate was 2.2% year^–1. Annual ΔAGB was 10.8 Mg ha^–1 year^–1, equaling to 5.4 Mg C ha^–1 year^–1. Of which, tree stems of 35–80 cm DBH classes accounted for 65%. The results indicated that the forest is in stage of carbon sequestration. Any disturbances causing death of 35–80 cm DBH tree stems will much reduce carbon sequestration capacity and it will take a long time for AGB to return to pre-disturbance stage.     

Forest self-regeneration following clear-felling of dieback-affected Fraxinus excelsior: focus on ash

Due to the dieback caused by invasive fungus Hymenoscyphus pseudoalbidus, ash is threatened in many regions of Europe. In order to predict the situation with ash ecosystems, it is important to examine forest regeneration in areas formerly dominated by ash with long disease history and known management. The main aim of the present study was, therefore, to evaluate forest self-regeneration following clear-felling of ash dieback-devastated stands, focusing on ash. In Lithuania, during 2011, a forest regeneration inventory was performed on twenty clear-cuts, initially dominated by stands of ash, but severely damaged by the dieback caused by H. pseudoalbidus and clear-felled 1–10 years previously. In subsequent forest regeneration, grey alder and birch dominated. Ash regeneration was scarce, and its proportion decreased from 40–100 % in pre-dieback stands to 0–21 % in current stands. Of all observed ash trees (n = 775), 53.9 % were diseased, 16.8 % were dead, and only 29.3 % were visually healthy. Moreover, ash was among the slowest growing species, while grey alder, aspen and birch were the fastest. The regeneration and health condition of ash in forests, where previous to the dieback ash was dominant, demonstrated a sharp decrease in occurrence of this species and a clear shift in species composition towards grey alder and birch.     

Contributions of root and stump sprouts to natural regeneration of a logged tropical dry forest in Bolivia

A major impediment to the sustainable management of tropical dry forests in Bolivia is the scarcity of natural regeneration of commercial timber tree species. Where regeneration is present, true seedlings of many species are outnumbered by vegetative sprouts from roots, broken stems, and the stumps of felled trees. This study evaluates the importance of resprouts promoted by logging operations for the regeneration of commercially important canopy tree species. The objectives of the study were: (1) to characterize stump and root sprouting behaviors of canopy tree species harvested for timber; (2) to quantify the effect of logging on relative abundances and growth rates of stump sprouts, root sprouts, and true seedlings; (3) to relate the species-specific probabilities of stump sprouting to stump diameter and stump height; and (4) to explore how sprouting varies with the ecological requirements of canopy tree species. The study was carried out 1–5 years after logging of a privately owned land in a Bolivian tropical dry forest. Twenty-seven of the 31 species monitored resprouted at least occasionally, among which Centrolobium microchaete (Leguminosae-Fabaceae) and Zeyheria tuberculosa (Bignoniaceae) were the most frequent stump sprouters, and Acosmium cardenasii (Leguminosae-Fabaceae) and C. microchaete were the most frequent root sprouters. In all species the number of sprouts declined with increasing stump diameter and stump height. The probability of stump resprouting differed among species but did not vary consistently with stump diameter, except in Z. tuberculosa in which it declined. Approximately 45% of juveniles <2 m tall of canopy tree species originated from root or stem sprouts. Light-demanding species tended to regenerate more from seeds and root sprouts than from stumps. Seedling densities were higher in microsites opened by logging, while root and stem sprouts were equally common across microsites. Given their abundance and the fact that root and stem sprouts at least initially grew faster than true seedlings, we conclude that vegetative regeneration in this tropical dry forest is an important mode of post-logging regeneration especially for species that regenerate poorly from seed. Resprout management should be considered as a potentially effective strategy for the procurement of regeneration following logging, especially for species that do not readily recruit from seed.     

Regeneration patterns of Eastern white pine (Pinus strobus L.) in hardwood-dominated forests in Virginia, USA

Eastern white pine (Pinus strobus L.) is a moderately shade-tolerant species that co-occurs with hardwood tree species in many forests of the eastern United States, as well as in pure stands. The species is valued for its timber, as well as for wildlife and recreation. Regeneration of this species is somewhat unpredictable and often occurs in patches of similarly-aged cohorts. We described the regeneration patterns of this species and examined their relation to environmental variables within hardwood forests of southwestern Virginia, USA. An average of 5.3 white pine patches per ha were observed in this study. The majority of patches consisted of saplings (85%), with 9% of patches in pole size classes, and 6% in seedling size classes. The average density of patches was 43.5 stems with an average age of 20 years. The size of patches averaged 80.6 m². The total density of seedlings and the number of regeneration patches of all sizes of regeneration (seedlings, saplings, and poles) in plots was related to the surrounding density of large white pine trees (potential seed trees). The density of seedlings or patches was not significantly related to current vegetation cover or soil surface cover variables, but more than half of regeneration patches were located in or adjacent to old canopy gaps, most of which were old logging gaps. While seedling regeneration may occur within the understory of these forests near seed trees, advancement to the sapling and pole stage appears to be associated with canopy gap formation.     

Earthworm population and microbial activity temporal dynamics in a Caspian Hyrcanian mixed forest

Few studies have analyzed how tree species within a mixed natural forest affect the dynamics of soil chemical properties and soil biological activity. This study examines seasonal changes in earthworm populations and microbial respiration under several forest species (Carpinus betulus, Ulmus minor, Pterocarya fraxinifolia, Alnus glutinosa, Populus caspica and Quercus castaneifolia) in a temperate mixed forest situated in northern Iran. Soil samplings were taken under six individual tree species (n = 5) in April, June, August and October (a total of 30 trees each month) to examine seasonal variability in soil chemical properties and soil biological activity. Earthworm density/biomass varied seasonally but not significantly between tree species. Maximum values were found in spring (10.04 m^?2/16.06 mg m^?2) and autumn (9.7 m^?2/16.98 mg m^?2) and minimum in the summer (0.43 m^?2/1.26 mg m^?2). Soil microbial respiration did not differ between tree species and showed similar temporal trends in all soils under different tree species. In contrast to earthworm activity, maximum microbial activity was measured in summer (0.44 mg CO₂–C g soil^?1 day^?1) and minimum in winter (0.24 mg CO₂–C g soil^?1 day^?1). This study shows that although tree species affected soil chemical properties (pH, organic C, total N content of mineral soils), earthworm density/biomass and microbial respiration are not affected by tree species but are controlled by tree activity and climate with strong seasonal dynamics in this temperate forest.     

Applying age-based mortality analysis to a natural forest stand in Japan

Mortality analysis of tree populations is widely applied to forest science studies. When mortality analysis is applied to forest inventories, the use of the variable of tree age is not common due to the difficulty of measuring age data censored in successive observations. The purpose of this study is to apply age-based mortality analysis, i.e., survival analysis, to the individual tree populations in a natural forest. The study site was the secondary natural stand of 0.26 ha dominated by fir (Abies firma), hemlock (Tsuga sieboldii), and oak (Quercus serrata) in the Boso peninsula, Japan. First, we measured the ages of the trees with diameter at breast height greater than or equal to 5 cm using a RESISTOGRAPH. Then, tree mortality probabilities of both non-parametric Kaplan–Meier estimates and parametric probability distributions of Gamma and Weibull were estimated by applying survival analysis techniques to the tree age data. The results implied that the survival analyses could be implemented not only by the non-parametric estimates in any cases but also by the common parametric distributions of Gamma and Weibull in cases in which the tree mortality probability distribution had a monotonously decreasing shape as observed in the immature natural stand in the study site.     

Aerial photo-interpretation using Z/I DMC images for estimation of forest variables

Abstract

Interpretation and tree height measurements in aerial photographs using photogrammetric workstations are frequently performed in standwise forest inventory. Images acquired by digital aerial cameras are now replacing the traditional film-based aerial photographs. In this study, digital images from the airborne Z/I DMC system for standwise estimation of stem volume, tree height and tree species composition were investigated at a 1200 ha forest area located in southern Sweden (58°30′N, 13°40′E). The 56 selected stands were dominated by Norway spruce [Picea abies (L.) Karst.] and Scots pine (Pinus sylvestris L.) with stem volume in the range of 30–630 m³ ha^?1 (average 300 m³ ha^?1) and tree height in the range of 6–28 m (average 20 m). The large-format pansharpened colour infrared images were captured at a flight altitude of 4800 m above ground level corresponding to a pixel size of 0.48 m. The photo-interpretation was conducted by four professional interpreters, independently. In particular, two different base-to-height ratios (i.e. the ratio between the ground distance between image centres at the time of exposure and the flight altitude above ground level) of 0.26 and 0.39 were evaluated, but no significant difference in the estimation accuracy for stem volume and tree height was found. The accuracy for stem volume estimation in terms of relative root mean square error, corrected for systematic errors, was on average 24% (in the range of 17–39%). The corresponding accuracy for tree height estimation was on average 1.4 m (in the range of 0.9–1.6 m). The tree species composition accuracy assessment using a fuzzy set evaluation procedure showed that 95% of the stands were correctly classified. The estimation accuracies are in agreement with previous results using conventional film-based aerial panchromatic photographs.     

Temporal development of ash dieback symptoms and spatial distribution of collar rots in a provenance trial of Fraxinus excelsior

European ash (Fraxinus excelsior) is threatened by Hymenoscyphus pseudoalbidus, the agent of ash dieback disease. Beside ordinary ash dieback symptoms, collar rots have been reported on declining ashes as an additional problem of increasing severity. Since 2009, ash dieback has been surveyed annually in a provenance trial on four different sites in southwest Germany (Metzler et al. in Ger J For Res 183:168–180, 2012). The trial was established in 2005. Data of tree growth, ash dieback symptoms and collar rot prevalence were collected by surveying the trial in summer 2012 and compared with previously published data of the trial. Evaluations revealed a continuous and considerable increase in dieback severity since 2009. The results suggest that the infection process has not come to a standstill yet. Up to 2012, 6 % of the trees remained symptomless, whereas mortality added up to 9 %. There were significant differences in ash dieback severity between the investigated provenances. Collar rot prevalence ranged from 19 to 59 % between study sites. Moreover, high spatial dependency of collar rot prevalence could be detected within sites. Collar rots were more abundant on trees of severe ash dieback intensity, but could also be detected on 15 % of otherwise healthy trees. Mycelium from collar rots could be identified by means of RFLP analyses and sequencing of the ITS region as most likely belonging to Armillaria gallica. The possible roles of Armillaria spp. and H. pseudoalbidus in collar rot formation are discussed.     

Impact of severe forest dieback caused by Phytophthoracinnamomi on macrofungal diversity in the northern jarrah forest of Western Australia

The relative diversity and abundance of different functional groups of macrofungi were investigated in the northern jarrah forest, a mediterranean climate sclerophyllous forest dominated by eucalyptus trees in Western Australia. We sampled paired sites that were either severely affected by dieback, a disease caused by Phytophthora cinnamomi which causes selective plant mortality, or unaffected by this type of forest decline. Macrofungi were sampled 3 times during the growing season along six 100 m × 2 m transects in these sites. Dieback-unaffected sites were found to have significantly different macrofungal floras than unaffected sites. Macrofungal abundance and diversity were approximately 1.5 times and 1.8 times greater respectively in dieback-unaffected sites than in severely affected sites. Dieback-affected sites had a similar diversity of saprotrophic and ectomycorrhizal fungi, whereas more fungal taxa on dieback-unaffected sites were mycorrhizal (>60%). Dung fungi were the most common saprophytes, especially in dieback-affected sites, but abundance data greatly overestimated the importance of these relatively small fungi. We concluded that vegetation changes linked to dieback had a negative effect on fungal community structure and biodiversity in the northern jarrah forest, in a similar manner to other forms of severe disturbance. Conversely, high tree mortality increased the abundance of wood decay fungi, at least in the short term. We expect that reductions in macrofungal species richness were indirectly linked to impacts on mycorrhizal host plants and saprotrophic substrates. Our data show that changes in vegetation composition had the greatest effect on ectomycorrhizal fungi, presumably due to their obligate symbiotic associations.     

Canopy transpiration of a Pinus canariensis forest at the tree line: implications for its distribution under predicted climate warming

Canopy transpiration (E _c) of a 50-year-old Pinus canariensis Chr. Sm. Ex DC. stand at tree line in Tenerife, Canary Islands, was estimated continuously throughout a year from March 1, 2008, to February 28, 2009, by means of xylem sap flow measurements. E _c varied markedly throughout the entire year generally following the seasonal trends in soil water availability and varied between 0.89 mm day^?1 under the conditions of non-limiting soil water availability and close to zero under soil drought. This is because canopy conductance declined significantly with increasing evaporative demand and thus significantly reduced tree water loss, and this decrease was more pronounced during the soil drought. Total annual E _c was 79.6 mm, which is significantly below the values estimated for other Mediterranean forest ecosystems and even 70 % lower than the value estimated for a P. canariensis forest at 1,650 m a.s.l. where the soil water content was higher than at the tree line site. Therefore, these results highlighted the importance of drought stress in tree line ecotone and should be taken more into account in semiarid tree lines.     

An assessment of Hawaiian dry forest condition with fine resolution remote sensing

Remote sensing offers the potential to spatially map forest cover quickly and reliably for inventory purposes. We developed a new image analysis approach using an integrated methodology of “object-based” image classification techniques and field-based measurements to quantify forest cover in a degraded dry forest ecosystem on the leeward side of the Island of Hawaii. This new approach explicitly recognized the transitional areas between tree crowns and tree shades (tree shadows) as a unique class and fully utilized them for the quantification of canopy cover. Object-oriented classification of Ikonos-2 satellite images allowed delineation of tree shades and crowns and the transitional areas between them from objects with similar reflectance and size that were surrounding the trees. These included patches of fountain (Pennisetum setaceum) and kikuyu (Pennisetum clandestinum) grass, lava outcrops and lava–grass mixtures. Crown-shade transitions were clearly differentiated in spite of their wide range of spectral values and reflectance similarities with areas of lava–grass mixture. Segments representing tree shades and dark lava outcrops were also classified into their respective classes even if they were contiguous. The image estimates of canopy cover using the tree shade plus transition classes were linearly related with field estimates of canopy cover (R² = 0.86 and slope = 0.976). Based on this relationship, dry forest cover throughout the 2627-ha area was estimated at 7.7 ± 1.9%. An immediate application of this new approach is to select and delineate areas with higher canopy cover in order to concentrate ecological restoration and conservation efforts.     

A novel empirical approach for determining the extension of forest development stages in temperate old-growth forests

In the analysis of old-growth forest dynamics, the continuous process of tree aging and forest structural change is split up into several distinct forest development stages. The criteria for distinguishing the stages vary among the different approaches. In most of them, vertical canopy heterogeneity is only coarsely addressed and horizontal forest structure is quantified at spatial scales far exceeding the size of conventional forest inventory plots. In order to describe and analyze the complex mosaic structure of temperate old-growth forests with objective and quantitative measures in the context of forest inventories, we propose the Development Stage Index I _DS . It employs two easily measured stand structural parameters (stem density and basal area) for quantifying the abundance of trees in three conventionally recognized tree diameter classes (premature ?<?40 cm; mature 40–70 cm; and over-mature?≥?70 cm) in plots of 500 m² size, systematically distributed in the forest. This allows quantifying the spatial extension of the Initial, Optimum and Terminal stages of forest development at plot, stand and landscape levels. Based on thorough stand structural analyses in three virgin beech (Fagus sylvatica) forests in Slovakia, we demonstrate that I _DS is a promising tool for (1) quantifying the proportion of the three stages on different scales, (2) visualizing the complex mixing of stages, and (3) analyzing dynamic changes in old-growth forest structure. We conclude that the Development Stage Index has the potential to improve the empirical foundation of forest dynamics research and to allow this discipline to proceed to more rigorous hypothesis testing.     

Enrichment planting of native species for biodiversity conservation in a logged tree plantation in Vietnam

Decades of deforestation and over logging have created large expanses of degraded lands in many countries including Vietnam. Reforestation may offer one means of mitigating these processes of degradation while sustaining biodiversity conservation. However a lack of information regarding trees, in particular threatened tree species has been identified as an important limitation in being able to reforest for biodiversity conservation. In the current study, conducted in the Tan Phu “protection forest”, the investigation surrounds the feasibility of biodiversity restoration in a fast-growing plantation after logging. Twelve threatened and native species mainly belonging to the Dipterocarpaceae and Fabaceae families have been considered. Seedlings grown in a local nursery have been planted under the canopy of a 50 ha pioneer forest, with a distance of 5 m between plants and between rows. The experimental design consists of blocks, each one with a replication of a 16-tree plot for each species. Four years after plantation, the survival rate of seedlings is high (>70 %), except for Dipterocarpus costatus (<10 %). Growth shows possible inhibitions under a closed canopy but the mean annual increment is generally satisfactory. The early performance of the seedlings is promising to make this plantation a good example of biodiversity restoration. These results could enhance the reforestation efforts of forest managers and encourage them to use native tree species including threatened ones in order to restore a high level of biodiversity in tropical degraded forests.     

Differences in transpiration between a forest and an agroforestry tree species in the Sudanian belt

Average population growth in the African Sudanian belt is 3 % per year. This leads to a significant increase in cultivated areas at the expense of fallows and forests. For centuries, rural populations have been practicing agroforestry dominated by Vitellaria paradoxa parklands. We wanted to know whether agroforestry can improve local rainfall recycling as well as forest. We compared transpiration and its seasonal variations between Vitellaria paradoxa, the dominant species in fallows, and Isoberlinia doka, the dominant species in dry forests in the Sudanian belt. The fallow and dry forest we studied are located in northwestern Benin, where average annual rainfall is 1200 mm. Sap flow density (SFD) was measured by transient thermal dissipation, from which tree transpiration was deduced. Transpiration of five trees per species was estimated by taking into account the radial profile of SFD. The effect of the species and of the season on transpiration was tested with a generalized linear mixed model. Over the three-year study period, daily transpiration of the agroforestry trees, V. paradoxa (diameters 8–38 cm) ranged between 4.4 and 26.8 L day^?1 while that of the forest trees, I. doka, (diameters 20–38 cm) ranged from 9.8 to 92.6 L day^?1. Daily transpiration of V. paradoxa was significantly lower (15 %) in the dry season than in the rainy season, whereas daily transpiration by I. doka was significantly higher (13 %) in the dry season than in the rainy season. Our results indicate that the woody cover of agroforestry systems is less efficient in recycling local rainfall than forest cover, not only due to lower tree density but also to species composition.     

Canopy tree development and undergrowth bamboo dynamics in old-growth Abies–Betula forests in southwestern China: a 12-year study

Interactions between forest canopy characteristics and plants in the forest understory are important determinants of forest community structure and dynamics. In the highlands of southwestern, China the dwarf bamboo Bashania fangiana Yi is an understory dominant beneath a mixed canopy of the evergreen Abies faxoniana (Rheder & Wilson) and the deciduous Betula utilis (D. Don). The goal of this study was to better understand the role of bamboo dominance, canopy characteristics, and periodic bamboo dieback on forest development. To achieve this goal, we measured tree seedling, tree saplings, and trees, forest canopy characteristics, and bamboo cover in permanent forest (n = 4) and gap plots (n = 31) in a mixed A. faxoniana and B. utilis forest in Sichuan, China. Dwarf bamboos died off in 1983 in the gap plots, and in three of the four forest plots. Forest development was assessed for the period 1984–1996. The seedling bank in forest and gap plots increased after bamboo die-off. A. faxoniana seedlings increased more than B. utilis in forest plots; the opposite pattern characterized gap plots. The proportion of seedlings on raised micro-sites on the forest floor also changed and new seedling were more abundant on the forest floor. By 1996, bamboo seedling cover and biomass had recovered to ca. 45% or their pre-flowering values. Rates of bamboo seedling recovery were faster beneath canopy gaps and deciduous trees than beneath forest or evergreen trees. Tree mortality exceeded recruitment in plots with dense bamboo; the opposite pattern was found in the plot with little bamboo. The mortality rate for B. utilis trees (2.4% year⁻¹) was higher than that for A. faxoniana (0.8% year⁻¹) and forests with dense bamboos became more open over the census period. Tree mortality was size-dependent and intermediate sized trees had the lowest rates of mortality. Stand basal area increased mainly due to greater basal area gain than loss for A. faxoniana. Interactions between tree species life history, canopy type, and bamboo life-cycles create heterogeneous conditions that influence tree and bamboo regeneration and contribute to the coexistence of A. faxoniana and B. utilis in old-growth forests in southwestern China.     

Stand characteristics of mixed oriental beech (<Emphasis Type="Italic">Fagus orientalis</Emphasis> Lipsky) stands in the stem exclusion phase,northern Iran

The structure of forest stands changes through developmental phases. This study is carried out in the unmanaged, oriental beech (Fagus orientalis Lipsky) stands in the north of Iran. The aim of this research was to quantify structural characteristics of stands in the stem exclusion phase using common structural indices, which include mingling, tree–tree distance, stem diameter, and tree height differentiation. According to our measurements from three stands, naturally regenerated stands tend to be mixed in species composition have slightly heterogeneous diameter distributions and uniform tree height. The average distance between trees was 3.3 m. Stocking volume of the stands had an average of 540 m³ ha^?1 and 412 stem ha^?1. Dead wood volume was 24 m³ ha^?1, and as a standing volume, the most frequent species in dead wood pool was oriental beech (F. orientalis) (48 %). The common form of dead trees was snag (41 %). The mean value of mingling and tree-to-tree interval indices revealed that beech was mixed intensively with hornbeam and appears to be a more successful competitor for space and light compared with hornbeam; moreover, we found relatively high evidence of inter-species competition in this phase. A better understanding of stand characteristics in the stem exclusion phase as a critical part of the natural dynamics of forest ecosystems could facilitate predictions about the future changes within the stand.