Pioneer Tree Species Research Articles

Positive association between Bromelia balansae (Bromeliaceae) and tree seedlings on rocky outcrops of Atlantic forest

Abstract:Plant facilitation can improve the diversity of plant communities in several ecosystems, especially in stressful environments. The establishment of tree species on rocky outcrops can be limited by several biotic and abiotic factors. The richness and abundance of forest trees species on rocky outcrops surrounded by a large forest remnant in south Brazil were correlated with the cover of Bromelia balansae, a spiny stoloniferous species commonly occurring at forest–grassland transitions. Sixty plots were established on three flat rocky outcrops (20 in each). In each plot the coverage of bromeliads was estimated into three classes (0%, 1–50% and 51–100%) and all seedlings (individuals 10–30 cm in height) were counted and identified. ANOVAs with randomization tests were performed to establish the effect of different bromeliad cover classes on the richness and abundance of seedlings. The cover of bromeliads was positively related to the richness and abundance of young pioneer tree species. Evidence suggests that B. balansae can act as a nurse plant for tree seedlings, but manipulative experiments are needed to confirm this.

Daily activity rhythm and habitat use of the semi-free European bison herd during the growing season / Denní aktivita a využití prostředí zubrem evropským (Bison bonasus) během vegetační sezóny

Abstract The European bison (Bison bonasus) became extinct in the wild in the 20th century. Due to successful reintroductions of captive individuals, the free-ranging bison population has been steadily increasing. However, the population consists of small and isolated herds whose survival depends on creating larger and connected populations. Detailed knowledge of movement and habitat use in human-dominated landscape is essential for further successful reintroductions of the European bison. Therefore, we studied daily activity and habitat use of the semi-free European bison herd in the hunting enclosure of Židlov from April to September 2014. The lead cow of the herd was fitted with a GPS collar equipped with GSM module. The average home range size of the herd was 29.5 km2 and the average daily utilisation area was 0.5 km2. Forested habitats were preferred during the day (Rayleigh test: Z = 107.31; p < 0. 0001) whereas idle lands (i.e. former shooting ranges now dominated by a mixture of pioneer tree species, hawthorn and grasslands) during the night (Rayleigh test: Z = 214.451; p < 0. 0001). The bison herd did not show any clear preference for a particular forest type (i.e. coniferous, deciduous, different age classes). Additional knowledge on year-long patterns of movement and habitat use is needed to ensure the success of reintroduction programmes

Ozone-induced responses in Croton floribundus Spreng. (Euphorbiaceae): metabolic cross-talk between volatile organic compounds and calcium oxalate crystal formation.

Here, we proposed that volatile organic compounds (VOC), specifically methyl salicylate (MeSA), mediate the formation of calcium oxalate crystals (COC) in the defence against ozone (O3) oxidative damage. We performed experiments using Croton floribundus, a pioneer tree species that is tolerant to O3 and widely distributed in the Brazilian forest. This species constitutively produces COC. We exposed plants to a controlled fumigation experiment and assessed biochemical, physiological, and morphological parameters. O3 induced a significant increase in the concentrations of constitutive oxygenated compounds, MeSA and terpenoids as well as in COC number. Our analysis supported the hypothesis that ozone-induced VOC (mainly MeSA) regulate ROS formation in a way that promotes the opening of calcium channels and the subsequent formation of COC in a fast and stable manner to stop the consequences of the reactive oxygen species in the tissue, indeed immobilising the excess calcium (caused by acute exposition to O3) that can be dangerous to the plant. To test this hypothesis, we performed an independent experiment spraying MeSA over C. floribundus plants and observed an increase in the number of COC, indicating that this compound has a potential to directly induce their formation. Thus, the tolerance of C. floribundus to O3 oxidative stress could be a consequence of a higher capacity for the production of VOC and COC rather than the modulation of antioxidant balance. We also present some insights into constitutive morphological features that may be related to the tolerance that this species exhibits to O3.

Linking belowground and aboveground phenology in two boreal forests in Northeast China.

The functional equilibrium between roots and shoots suggests an intrinsic linkage between belowground and aboveground phenology. However, much less understanding of belowground phenology hinders integrating belowground and aboveground phenology. We measured root respiration (Ra) as a surrogate for root phenology and integrated it with observed leaf phenology and radial growth in a birch (Betula platyphylla)-aspen (Populus davidiana) forest and an adjacent larch (Larix gmelinii) forest in Northeast China. A log-normal model successfully described the seasonal variations of Ra and indicated the initiation, termination and peak date of root phenology. Both root phenology and leaf phenology were highly specific, with a later onset, earlier termination, and shorter period of growing season for the pioneer tree species (birch and aspen) than the dominant tree species (larch). Root phenology showed later initiation, later peak and later termination dates than leaf phenology. An asynchronous correlation of Ra and radial growth was identified with a time lag of approximately 1 month, indicating aprioritization of shoot growth. Furthermore, we found that Ra was strongly correlated with soil temperature and air temperature, while radial growth was only significantly correlated with air temperature, implying a down-regulating effect of temperature. Our results indicate different phenologies between pioneer and dominant species and support a down-regulation hypothesis of plant phenology which can be helpful in understanding forest dynamics in the context of climate change.

Comparison of the growth traits of a commercial pioneer tree species, paper mulberry (Broussonetia papyrifera L. Vent.), with those of shade-tolerant tree species: investigation of the ecophysiological mechanisms underlying shade-intolerance

In rural areas of northern Laos, a commercially valuable pioneer tree species, paper mulberry (Broussonetia papyrifera L. Vent.) has been recommended for intercropping under plantations of commercial trees. However, less is understood about the growth of this pioneer tree species in the understorey and the mechanism underlying the shade intolerance. We measured growth characteristics for seedlings of paper mulberry under four light intensities. We compared the relative growth rates in aboveground biomass and standing leaf area (RGRmass and RGRleaf), light-capture efficiency, and seeding-level mass-based daily photosynthetic rates (A mass) with those of field-grown seedlings of eight shade-tolerant species to identify factors potentially responsible for shade-intolerance. Most growth traits of the paper mulberry seedlings did not differ consistently from those of the shade tolerant species. The ecophysiological–architectural model software showed higher A mass and RGRmass capacity in paper mulberry than in shade-tolerant species. Despite their higher RGRmass, paper mulberry seedlings had negative RGRleaf under shaded conditions due to short leaf lifespan. The linear RGRmass–RGRleaf relationship for paper mulberry had a high RGRmass intercept, indicating that a high RGRmass was required to provide positive RGRleaf. Progressive decreases in standing leaf area with time, and possibly photosynthesis, appear to be responsible for the shade-intolerance of paper mulberry. Although intercropping of paper mulberry has been suggested in the species’ native region, understorey cultivation of paper mulberry would only be possible with relatively open canopies.

Roles of birds and bats in early tropical-forest restoration.

Restoration of tropical forest depended in large part on seed dispersal by fruit-eating animals that transported seeds into planted forest patches. We tested effectiveness of dispersal agents as revealed by established recruits of tree and shrub species that bore seeds dispersed by birds, bats, or both. We documented restoration of dispersal processes over the first 76 months of experimental restoration in southern Mexico. Mixed-model repeated-measures randomized-block ANOVAs of seedlings recruited into experimental controls and mixed-species plantings from late-secondary and mature forest indicated that bats and birds played different roles in the first years of a restoration process. Bats dispersed pioneer tree and shrub species to slowly regenerating grassy areas, while birds mediated recruitment of later-successional species into planted stands of trees and to a lesser extent into controls. Of species of pioneer trees and shrubs established in plots, seven were primarily dispersed by birds, three by bats and four by both birds and bats. Of later-successional species recruited past the seedling stage, 13 were of species primarily dispersed by birds, and six were of species dispersed by both birds and bats. No later-successional species primarily dispersed by bats established in control or planted plots. Establishment of recruited seedlings was ten-fold higher under cover of planted trees than in grassy controls. Even pre-reproductive trees drew fruit-eating birds and the seeds that they carried from nearby forest, and provided conditions for establishment of shade-tolerant tree species. Overall, after 76 months of cattle exclusion, 94% of the recruited shrubs and trees in experimental plots were of species that we did not plant.

Properties of soil organic matter in Podzols under mountain dwarf pine (Pinus mugo Turra.) and Norway spruce (Picea abies (L.) Karst.) in various stages of dieback in the East Sudety Mountains, Poland

Dieback of forests because of industrial air pollution was observed in the East Sudety Mountain, Poland. The properties of soil organic matter in Podzols in the subalpine region under mountain dwarf pine and Norway spruce in various stages of dieback (without degradation, with about 50% brown needles and dead trees) were investigated. The content of carbon, nitrogen, humic substances and characteristics of humic acids (HA) from organic and mineral horizons were analyzed. Forest dieback influenced HA properties depending on the species. Under pine, it led to an increase in alkyl and carboxyl C, while an increase in aromatic C and O- alkyl C was found at spruce sites. Humic acids under Picea abies were characterized by more aliphatic structures, whereas HA under Pinus mugo were more aromatic in nature. HA created in soils under pine stands in the investigated area showed lower solubility, higher stability and a lower tendency to translocate to deeper parts of the soil profile, compared to those under Norway spruce. Organic matter under spruce monoculture can be more susceptible to oxidation and may have less impact on the stability of soil aggregates, than those under pine ecosystems. Conversion of spruce monocultures to mixed forest – more resistant to biotic and abiotic disturbances – or introduction of the pioneer tree species in Norway spruce stands may be an effective tool to prevent forest decline and ensuring the stability of forest ecosystems.

Demographic history of a common pioneer tree, Zanthoxylum ailanthoides, reconstructed using isolation-with-migration model

The Japanese prickly ash, Zanthoxylum ailanthoides Siebold & Zucc. (Rutaceae), is one of the most common pioneer tree species that grow in disturbed areas, such as canopy gaps, in Japanese warm-temperate evergreen oak forests. The strong genetic structure of its current population might suggest long-term isolation of subpopulations by demographic events, in addition to ecological features of this species. Analyses of genome-wide nucleotide variation using model-based approaches are necessary to achieve a good understanding of the demographic history of a species. In this study, we analyzed the nucleotide variation in natural populations of Z. ailanthoides using a computer program that applied the isolation-with-migration model to quantitatively infer the demographic history. Nucleotide variations at 10 or 26 nuclear loci in six populations from a wide range of the species distribution were analyzed. The maximum likelihood estimate of the divergence time between the current populations in the two hypothetical refugia of Z. ailanthoides was approximately 24,000 years. Unexpectedly, the estimated size of the ancestral population was larger than the sizes of the two current populations. The results suggested a relatively recent divergence of these two populations and rapid formation of strong genetic structure among subpopulations. The large ancestral population may indicate a more complex demographic history during or after the last glacial period than the simple isolation-with-migration model implies.

Aluminum toxicity to tropical montane forest tree seedlings in southern Ecuador: response of biomass and plant morphology to elevated Al concentrations

AimsIn acid tropical forest soils (pH <5.5) increased mobility of aluminum might limit aboveground productivity. Therefore, we evaluated Al phytotoxicity of three native tree species of tropical montane forests in southern Ecuador.MethodsAn hydroponic dose-response experiment was conducted. Seedlings of Cedrela odorata L., Heliocarpus americanus L., and Tabebuia chrysantha (Jacq.) G. Nicholson were treated with 0, 300, 600, 1200, and 2400 μ M Al and an organic layer leachate. Dose-response curves were generated for root and shoot morphologic properties to determine effective concentrations (EC).ResultsShoot biomass and healthy leaf area decreased by 44 % to 83 % at 2400 μ M Al, root biomass did not respond (C. odorata), declined by 51 % (H. americanus), or was stimulated at low Al concentrations of 300 μ M (T. chrysantha). EC10 (i.e. reduction by 10 %) values of Al for total biomass were 315 μ M (C. odorata), 219 μ M (H. americanus), and 368 μ M (T. chrysantha). Helicarpus americanus, a fast growing pioneer tree species, was most sensitive to Al toxicity. Negative effects were strongest if plants grew in organic layer leachate, indicating limitation of plant growth by nutrient scarcity rather than Al toxicity.ConclusionsAl toxicity occurred at Al concentrations far above those in native organic layer leachate.

Intra- and interspecific competition differently influence growth and stem quality of young oaks (Quercus robur L. and Quercus petraea (Mattuschka) Liebl.)

Cluster planting has become a conventional establishment method for oaks in Central Europe, where the spacing of seedlings within clusters varies between ‘nests’ (0.2 × 0.2 m) and ‘groups’ (1 × 1 m). Although the space between clusters is expected to fill with voluntary regeneration, its competitive effect on oak growth and quality had not been studied yet. The aim of the study was to analyse the effects of inter- and intraspecific interactions on growth and quality of oaks grown in cluster plantings by quantifying the influence of neighbouring trees. In addition, we analysed whether the spatial position of oaks within groups (inner section or periphery) influenced their quality development. Using Hegyi’s competition index, the influence of competition from intra- and interspecific trees from early, mid- and late-successional species, on diameter, height, slenderness and quality (length of branch-free bole) of 10- to 26-year-old oaks grown in cluster planting stands was quantified at seven sites in Baden-Württemberg and Hessen, Germany. In general, mid- and late-successional trees exerted a stronger competitive influence on growth of target oaks in clusters than the conspecific oaks and pioneer tree species. Oak quality development benefited from intraspecific competition, but self-pruning was not further promoted through additional interspecific competition. Within groups, inner oaks had a higher probability of developing into potential future crop trees than outer oaks. Our study showed that intra- and interspecific competition had different effects on target oak trees and that these effect differed between nest and group plantings. The development of naturally regenerated and planted trainer trees in group plantings should be monitored carefully and if necessary be controlled through thinning or pollarding.

Forest trees in human modified landscapes: ecological and genetic drivers of recruitment failure in Dysoxylum malabaricum (Meliaceae).

Tropical agro-forest landscapes are global priority areas for biodiversity conservation. Little is known about the ability of these landscapes to sustain large late successional forest trees upon which much forest biodiversity depends. These landscapes are subject to fragmentation and additional habitat degradation which may limit tree recruitment and thus compromise numerous ecosystem services including carbon storage and timber production. Dysoxylum malabaricum is a large canopy tree species in the Meliaceae, a family including many important tropical timber trees. This species is found in highly fragmented forest patches within a complex agro-forest landscape of the Western Ghats biodiversity hot spot, South India. In this paper we combined a molecular assessment of inbreeding with ecological and demographic data to explore the multiple threats to recruitment of this tree species. An evaluation of inbreeding, using eleven microsatellite loci in 297 nursery-reared seedlings collected form low and high density forest patches embedded in an agro-forest matrix, shows that mating between related individuals in low density patches leads to reduced seedling performance. By quantifying habitat degradation and tree recruitment within these forest patches we show that increasing canopy openness and the increased abundance of pioneer tree species lead to a general decline in the suitability of forest patches for the recruitment of D. malabaricum. We conclude that elevated inbreeding due to reduced adult tree density coupled with increased degradation of forest patches, limit the recruitment of this rare late successional tree species. Management strategies which maintain canopy cover and enhance local densities of adult trees in agro-forest mosaics will be required to ensure D. malabaricum persists in these landscapes. Our study highlights the need for a holistic understanding of the incipient processes that threaten populations of many important and rare tropical tree species in human dominated agro-forest landscapes.

Differences in Survival and Growth Among Tropical Rain Forest Pioneer Tree Seedlings in Relation to Canopy Openness and Herbivory

AbstractAlthough differences in canopy openness, herbivory and their interaction may promote species coexistence, how these factors affect pioneer tree species and potentially limit growth, and survival has been poorly studied, particularly in tropical South Asia. We monitored the effect of canopy openness and herbivore damage on seedling survival and growth of 960 individuals of six pioneer tree species: Dillenia triquetra, Macaranga indica, Macaranga peltata, Schumacheria castaneifolia, Trema orientalis, and Wendlandia bicuspidata. Seedlings were placed in four gap‐understory positions—center, outer gap edge, inner forest edge, and understory—in four large, natural gaps within the Sinharaja World Heritage Reserve, Sri Lanka. Canopy openness positively affected survival probability beyond the 550‐d experiment, while herbivory decreased survival and was highest in understory conditions. The relative order of species survival stayed fairly consistent between gap‐understory positions and followed their known shade tolerance rankings. When averaged across all experimental conditions, T. orientalis had the lowest survival probability estimate beyond the 550‐d experiment (0.05), but the greatest capacity for growth where it successfully established, while the species with highest averaged survival probability (0.79), D. triquetra, showed the lowest growth. One species, W. bicuspidata, responded positively to herbivory by re‐sprouting. Coexistence of D. triquetra, T. orientalis, and W. bicuspidata can be explained by a trade‐off among species in survival, growth, and response to herbivory. In addition to variation in canopy light environment, herbivory may be important in determining pioneer species distribution through fine‐scale niche partitioning and should be carefully considered in reforestation efforts.

岷江冷杉林皆伐后次生群落结构和物种多样性的演替动态

PDF HTML阅读 XML下载 导出引用 引用提醒 岷江冷杉林皆伐后次生群落结构和物种多样性的演替动态 DOI: 10.5846/stxb201211151605 作者: 作者单位: 四川大学生命科学学院生物资源与生态环境教育部重点实验室,阿坝州川西林业局,中国林业科学研究院森林生态环境与保护研究所 国家林业局森林生态环境重点实验室,四川省林业科学研究院 作者简介: 通讯作者: 中图分类号: 基金项目: 国家“十二五”科技支撑计划专题（2012BAD22B0102）；国家自然科学基金项目（31200477）资助 Successional dynamics of community structure and species diversity after clear-cutting of faxon fir (Abies faxoniana) forest stands Author: Affiliation: Key Laboratory of Bioresource and Eco-environment of Ministry of Education,College of Life Sciences,Sichuan University,Aba State Western Sichuan Forestry Bureau,Li county,Key Laboratory on Forest Ecology and Environmental Sciences of State Forestry Administration,Institute of Forest Ecology,Environment and Protection,Chinese Academy of Forestry, Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:为阐明岷江冷杉林皆伐后次生群落的演替过程，采用空间代替时间的方法，在川西米亚罗林区海拔3100-3600 m的阴坡选择岷江冷杉林皆伐后次生演替10、20、30、40和50a阶段的次生群落作为研究对象，对其群落结构和物种多样性的动态进行了研究。不同演替阶段的树木均呈显著聚集分布。按群落中优势种的重要值将该演替序列划分为3个类型：悬钩子-蔷薇灌丛、白桦阔叶林和桦木-岷江冷杉针阔混交林。随次生演替，乔木和灌木种的物种丰富度趋于增加，而草本种的物种丰富度趋于减少；乔木和灌木种的Shannon-Wiener多样性指数趋于增大，而草本的Shannon-Wiener多样性指数趋于减小；乔木、灌木和草本层的Pielou均匀度指数均趋于增大；乔木层的Simpson优势度指数趋于减小，灌木和草本层的Simpson优势度指数在演替0-40年阶段趋于增大，而在演替50a阶段趋于减小。在该演替序列中，乔木、灌木和草本层的物种组成均呈耐荫种替代非耐荫种的趋势。 Abstract:In the early 1950s, the subalpine forests in western Sichuan province were dominated by old growth Abies faxoniana forests, large scale logging occurred between 1954 and 1965 and clear-cut was used as the predominant harvest method. Up to 1965 timber yield dropped dramatically for a little of harvestable forest stands and timber harvest operation stopped completely in 1998 when the Natural Forest Protection Program began in the region. In order to clarify the recovery processes of the forests region in western Sichuan Province, China, we studied the dynamics of community structure and species diversity over the first 60 year period of secondary successional stages in the Miyaluo forest area. We observed successional changes in the secondary forest community by adopting the concept of space as a substitute for time. We established 34 20 m × 20 m plots at study sites located at altitudes between 3100-3600 m on shady slopes the Miyaluo forest area. Our study showed that the secondary forests were characterized by Betula albo-sinensis, Betula platyphylla, and A. faxonniana. The vascular plants recorded in the plots included 107 species of 79 genera from 38 families (x herb species, y shrub species, and z tree species). Tree density increased over the first 40 years of successional stages, but then declined by the 50 year stage of secondary succession. Size-classes of trees in 20 to 50 year stages of succession, which were mainly small-sized and medium-sized, all showed reverse J-shaped distributions. Tree species, along with shrub and herb species, all showed significantly aggregated distributions at different successional stages. The successional series was classified into three stages according to the importance value of the dominant species: first, the Rubus and Rosa shrub; second, the Betula broad-leaved forest; and third, the Abies and Betula conifer and broadleaf mixed forest. Betula species still were the dominant species in the third stage, but regeneration of A. faxoniana, which is the dominant tree of old growth in the Miyaluo forest area, was increasingly abundant and widespread. As the successional stages shifted from one to three, herb species richness decreased, while tree and shrub species richness increased. Following changes in successional series from 10 years to 50 years at 10 year intervals, the overall species richness in secondary communities was 54, 49, 33, 54, and 59, respectively. The overall species richness decreased over the first three intervals from 10 to 30 year, and then increased over the next two intervals (40 and 50 years). The Shannon-Wiener diversity indices of tree and shrub layer species increased throughout over the intervals from 10 to 50 years, while the indices of herb layer species decreased continuously over the same successional series. The Pielou Evenness indices of all three layers of species increased with the successional time. Simpson Dominance indices of tree layer species decreased over the successional time, while the dominance indices of the shrub and herb layer species increased up through the 40 year interval of the successional stages and then decreased at the 50 year interval. The species composition also varied over the different time intervals of the successional stages. Light-demanding pioneer tree species such as B. albo-sinensis, which regenerated rapidly after logging was being replaced at later successional stages by the effects of increasing canopy closure and competitive advantages of shade tolerant tree species such as A. faxoniana, which was becoming the dominant tree species in an increasingly species diverse plant community as the Miyaluo forest was returning to the old growth forest of its past. 参考文献 相似文献 引证文献

Cytogenetics and characterization of microsatellite loci for a South American pioneer tree species, Croton floribundus

Despite the recent advances in plant population genetic studies, the lack of information regarding pedigree, ploidy level, or mode of inheritance for many polyploids can compromise the analysis of the molecular data produced. The aim of this study was to examine both microsatellite and cytogenetic characteristics of the pioneer tree Croton floribundus Spreng. (Euphorbiaceae) to test for the occurrence of polyploidy in the species and to evaluate its implications for the appropriate use of SSR markers. Seven microsatellite markers were developed and screened for 62 individuals from a semi-deciduous tropical forest in Brazil. Chromosome number, meiotic behavior, and pollen viability were evaluated from male flower buds. All SSR loci were highly polymorphic. The number of bivalents observed in meiosis n = 56 (2n = 8× = 112) and the maximum number of alleles per individual (Ni = 8) demonstrated the occurrence of polyploidy in C. floribundus. The normal meiotic pairing and the high pollen viability suggested that C. floribundus is a regular and stable polyploid, most likely an allopolyploid. The combined SSR and cytogenetic data provided new evidence on the origin and evolution of the species as well as assured the accurate use of SSR loci for population genetic studies of the polyploid pioneer species.

High gene flow in two thrips-pollinated South-East Asian pioneer trees: genetic diversity and population structure ofMacaranga hypoleucaandM. beccariana(Euphorbiaceae)

As a result of intensive exploitation, disturbed forests now dominate large areas of lowland tropical rainforest in South-East Asia. The genus Macaranga comprises some of the most important pioneer tree species of the region, among them M. beccariana and M. hypoleuca, two closely related obligate ant-plants pollinated by thrips. We used nuclear and plastid DNA markers to address questions of genetic diversity and population structure. Twelve plastid haplotypes were detected among 281 samples, three of which were shared between the two study species. Hybrids between the two species appear to be rare. Overall, genetic diversity in both species was moderate to high, with low levels of population differentiation, consistent with other tropical pioneer trees. Genetic structure was generally more pronounced in plastid than in nuclear data, indicating that gene flow via pollen may be more efficient than via seeds. Thrips apparently also serve as efficient pollinators over long distances, perhaps through a combination of passive dispersal by wind and active search for inflorescences in the target area. Our results indicate that M. beccariana and M. hypoleuca populations from recently disturbed habitats do not yet suffer from reduced genetic diversity or increased inbreeding.

Effects of planting design on planted seedlings and spontaneous vegetation 16 years after establishment of forest edges

In afforestation, studies of forest edges seldom span the effects of planting design and the self-designing capacities of spontaneous vegetation. This study revisited experimental forest edge sections 16 years after their establishment to assess the impact of five design elements on (1) horizontal and vertical edge structure, (2) growth of planted species and species groups, and (3) spontaneous establishment of woody vegetation. The design elements were: exposure to direct solar radiation; edge typology (shrub mixture, mixture of trees and shrubs, no edge planting); width of edge planting (5 or 10 m); species mixture principle (intimate mixtures or single species grouping); and planting row position from outermost to interior planting row (max. 6 rows). The results demonstrate that edge plantings support significantly more spontaneous woody vegetation than stand boundaries without such edge plantings. This result was consistent across the different design elements. Position across the planting rows from the outermost to innermost row was the most influential design element for the development of planted seedlings. Planted tree and shrub species of similar shade tolerance had contradicting development, where light-demanding pioneer tree species had obtained dominant positions while shade-tolerant shrub species had outgrown more light-demanding species. These results demonstrate that important successional processes can be activated by establishing the initial components and structures of forest edges. When designing such edges, species should preferably be allocated to different row cohorts reflecting their growth form and shade tolerance.

Variações espaço-temporais no estoque de sementes do solo na floresta amazônica

A dispersão eficiente, a longevidade e a capacidade das sementes de permanecer em estado latente a espera de condições adequadas de germinação no banco de sementes do solo da floresta garantem a presença de espécies arbóreas pioneiras nas áreas perturbadas. As variações estacionais e espaciais na densidade e na composição florística do banco de sementes em Florestas Tropicais Úmidas são assuntos ainda pouco compreendidos. Este trabalho verificou a existência de modificações espaço-temporais do banco de sementes presente em áreas de Floresta Tropical úmida localizadas próximas a Manaus, AM. Em cada uma das seis áreas estudadas, foram coletadas 40 amostras circulares de solo superficial (10 cm de diâmetro e 2 cm de profundidade) ao acaso. Essas amostras foram coletadas a cada dois meses, entre agosto/2004 e junho/2005,. As amostras de solo foram distribuídas em bandejas em casa de vegetação e a emergência das sementes presentes no solo foi acompanhada por 4 meses. Houve uma redução significativa (H: 14,09, p &lt; 0,05) na densidade média de sementes no solo em junho (início da estação seca) em relação a fevereiro (meio da estação chuvosa). Houve também diferença significativa (H: 188,72, p &lt; 0,05) na densidade média de sementes do solo presente nas diferentes áreas amostradas. Assim como para outras áreas de florestas tropicais, o banco de sementes permanente da floresta foi dominado por espécies pioneiras, principalmente da família Melastomataceae, enquanto as espécies típicas da Floresta Tropical madura foram raras no solo florestal.

Photosynthetic response of early and late leaves of white birch (Betula platyphylla var. japonica) grown under free-air ozone exposure

Betula platyphylla var. japonica (white birch) has heterophyllous leaves (i.e., early and late leaves) and is a typical pioneer tree species in northern Japan. Seedlings of white birch were exposed to ozone during two growing seasons, and measurements were carried out in the second year. Early leaves did not show an ozone-induced reduction in photosynthesis because of lower stomatal conductance resulting in higher avoidance capacity for ozone-induced stress. Also, an ozone-related increase in leaf nitrogen content may partly contribute to maintain the photosynthetic capacity in early leaves under elevated ozone in autumn. On the other hand, late leaves showed an ozone-induced decline of photosynthesis and early defoliation of leaves occurred. Also, smaller leaf size and higher stomatal density in late leaves were observed under elevated ozone. Differences in stress resistance to ozone may be related to differing functional roles of early and late leaves for birch species.

CHANGES IN VEGETATION AND SOIL CHARACTERISTICS OF REGENERATING FOREST AT RANDENIGALA

Victoria, Randenigala, Rantambe(VRR) sanctuary is the largest sanctuary in Sri Lanka. Certainareas in the Rantambe catchment was disturbed for the construction of Randenigala dam in 1987with no planned rehabilitation programme. This study was initiated to assess the changingpattern of vegetation and its influence on soil physical and chemical properties of disturbedforestland near Randenigala dam, relative to the surrc:unding undisturbed natural forest.The site was located 1 km North of the Randenigala Dam in a hilly slope in the intermediatezone and was surrounded by relatively undisturbed natural vegetation of dry mixed evergreenforest. In the sampling site (about 100 ha) the vegetation and soil has been removed down toparental material for dam construction. Three rectangular transacts measuring 5mxlOOmweremarked in each natural and regenerating forest sites .AlI plants were identified, height anddiameter at breast height (dbh) over &gt;2cm of woody plants were measured. Soil pits were cut inboth disturbed and undisturbed forest sites and profiles were described. Soil samples wereremoved from each horizons for the analysis of soil physical and chemical properties. In thedegraded sites, soil pits were cut in the open area (6m), in the canopy edge (3m), and 0.5m fromthe tree base of dominant pioneer tree species to observe the soil improvement.Plant density of the undisturbed forest was three times higher than the disturbed forest andconsists of 17 trees, six shrubs, and four woody climber species. Five trees, six shrubs, onewoody climber, two grasses, and three creepy herbaceous species were found in the regeneratingforest. Common families present were Euphorbiaceae (38%), Sterculaceae (24%) and Rubaceae(12%) in the undisturbed forest and Hipocraraceae (40%), Leguminosae (26%) andApocynaceae (18%)in the disturbed forest.Five and two major soil horizons were identified in the undisturbed and disturbed forest sites,respectively. Soil N, P, K and organic matter contents and hydraulic conductivity were greaterand the bulk density was lower in the undisturbed site. The mean weight diameter (MWD) of thesoil aggregate was greater in the soil horizons of undisturbed site (1.6-2.7mm) compared to thedegraded site (1.1 mm). Similar trends were also observed for wet aggregate stability in theundisturbed (90% remaining) and disturbed (71% remaining) in forest soils. However, MWD(1.5mm) and wet aggregate stability (83% remaining) gradually improved towards the tree baseof pioneer tree species. (i.e. under Bouhinia racemosat in the regenerating disturbed forest site.Increase in soil organic matter content stabilizes the soil aggregates and makes soil moreresistant to erosion by wind and water under the canopy of pioneer species. The retention of soilunder these trees contributes to the development of the soil profile, improvement of soil fertilityand subsequently, the vegetation diversity of degraded sites.

SIFAT FISIK DAN MEKANIK TIGA JENIS POHON PIONIR

This research was conducted were to determine physical and mechanical characteristics of three pioneer tree species namely : Macaranga hosei, Macaranga hypoleuca and Endospermum diadenum; to determine the effect of species differences on the physical and mechanical characteristic of the woods. the result showed that : Maximum water content and dry weight of the species were Endospermum diadenum (115,627 %; 12,15 %), Macaranga hosei (156,534 %; 12,49 %) and Macaranga hypoleuca (171,510 % and 12,49 %), respectively, Average bulk density in wet volume, dry volume and tenure dry volume were Endospermum diadenum (0,323 (Vb); 0,346 (Vku); 0,378 (Vkt), Macaranga hosei (0,261 (Vb); 0,278 (Vku); 0,300 (Vkt) and Macaranga hypoleuca (0,296 (Vb); 0,315 (Vku); 0,338 (Vkt), respectively, The shrinking dry weight-tenure weight were Endospermum diadenum (6,91 %; 14,47 %), Macaranga hosei (6,43 %; 12,87 %), and Macaranga hypoleuca (6,40 % and 12,33 %), respectively, The statical elasticity strength were Endospermum diadenum (372,220 kg/cm 2 ), Macaranga hosei (282,490 kg/cm 2 ) and Macaranga hypoleuca (261,490 kg/cm 2 ), respectively, Fiber strength were Endospermum diadenum (63,360 kg/cm2), Macaranga hosei (40,800 kg/cm 2 ), Macaranga hypoleuca (34,618 kg/cm 2 ). Kata kunci : physical, mechanical, pioneer woo d