Reverse J-shaped Distribution Research Articles

Liana abundance and diversity increase along a successional gradient, even with homogeneous closed canopy

One-half of the pantropical forests are regrowth that develop in certain stages along the succession gradient. As lianas can colonize rapidly in disturbed areas, they play a key role in forest succession and carbon sequestration. However, current knowledge remains limited and is from only a few sites in neotropical forests. Here we investigated liana succession in a chronosequence located in a Southeast Asian Forest. We determined liana abundance (stem density, basal area, prevalence) and diversity along the succession gradient with ages in the range 3–100 years. We also analyzed community composition, size structure, and the correlation with host tree size. We found that liana abundance and diversity increased non-linearly along the succession gradient, suggesting that the stem exclusion stage (35–41 years)—homogeneous closed canopy with low light penetration—did not inhibit liana colonization. Assuming the reverse J-shaped distribution, we fitted the size structure of each plot with the exponential distribution. The results demonstrated no differences among the fitted parameters of plots in the stem exclusion and the old-growth stage, suggesting the same capability of recruitment and colonization in both stages. Furthermore, we found a weak correlation between liana and host tree size (R2 ≤ 0.16, which varied among plots, implying that many lianas recruited after the establishment of large host trees in the past. The results regarding community composition perhaps suggested a stochastic process of liana colonization during the early stage (3–20 years) because of high spatial heterogeneity (a mosaic of open area alternating with closed canopy). In the stem exclusion and old-growth stages, we observed a predictable trajectory, with the composition of plots in the same stage being clustered. This implied that forest structure or unpredictable treefall gaps of old-growth forests have a limited impact on community dissimilarity. Collectively, these results suggested that (1) some liana species may be generalists or even shade-tolerant species, or (2) there was no seed dispersal limitation in the landscape. The contrary direction of the succession patterns reported here suggests a need for more studies across tropical forests including investigating life history trade-offs such as light tolerance.

Historical mixed-severity disturbances shape current diameter distributions of primary temperate Norway spruce mountain forests in Europe

Natural disturbances strongly influence forest structural dynamics, and subsequently stand structural heterogeneity, biomass, and forest functioning. The impact of disturbance legacies on current forest structure can greatly influence how we interpret drivers of forest dynamics. However, without clear insight into forest history, many studies default to coarse assumptions about forest structure, for example, whether forests are even or unevenly aged. The aim of this study was to analyze the effects of past disturbances on the current diameter distributions of Norway spruce (Picea abies (L.) Karst.)-dominated landscapes throughout the Carpathian Mountains. Our dendroecological dataset comprises tree cores from 339 plots (7,845 total tree cores), nested within 28 primary forest stands, known to vary greatly in the severity of historical disturbances. Our analyses revealed that historical disturbances had a strong and significant effect on the current diameter distribution shapes at the plot level. We demonstrated that mixed-severity disturbance regimes were more frequent and create a complex pattern of diameter distributions at the plot and stand scale. Here, we show that high severity disturbance was associated with unimodal diameter distributions, while low and moderate severity was associated with the reverse J-shaped distribution. This is a result of complex disturbance patterns, with structural biological legacies. Our results will have important management implication in the context of tree size heterogeneity, biomass storage, and productivity as influenced by natural disturbances. Lastly, these results demonstrate that structural changes may arise as consequences of changing disturbance regime associated with global change.

The long-term effects of thinning and mixing on species and structural diversity of Chinese fir plantations

Plantations are playing an increasingly important role in providing forest products and improving the ecological environment, but they also face many challenges, such as low biodiversity, severe pest and disease problems, reduced productivity, and diminished soil fertility. Reasonable management strategies are vital for their sustainability. In this study, we took a Chinese fir (Cunninghamia lanceolata (Lamb.) Hook.) plantation as an example to demonstrate the effects of thinning and mixing on the species diversity and structural diversity of plantations at the stand level over a rotation period (1993–2018). An intermediate thinning (26% of plant abundance) was conducted in a Chinese fir pure plantation in mid-age (2008), and a mixed forest stand of Chinese fir and Michelia macclurei Dandy was established directly. Thinning and mixing greatly increased the species diversity at the stand level, enhanced the mixture, transformed the pattern from regular to random distribution, and made the size differentiation of trees random. Thinning and mixing also greatly improved the mixture and dominance of Chinese fir. M. macclurei had an obvious advantage in tree size and maintained a high mixture proportion. Moreover, the diameter classes of the stands were bimodal. Chinese fir and M. macclurei showed a unimodal distribution of diameter, but other later-coming species with a larger number of individuals displayed a typical reverse J-shaped distribution. Our results suggest that both thinning and mixed planting may promote species diversity and structure over a long timescale, but thinning achieves these characteristics earlier because thinning directly manipulates structure in a way that accelerates stand development.

Analysis of flotation rate distributions to assess erratic performances from size-by-size kinetic tests

This paper presents a size-by-size kinetic characterization for copper-lead separation from a complex ore. Batch tests are run under extended flotation times to obtain approximately steady recoveries (unscreened samples) at the end of the tests. The size-by-size time-recovery curves are fitted to the Gamma model to obtain estimates for the maximum recovery R∞ and the flotation rate distribution f(k). From reverse J-shaped distributions to normal probability density functions are representable from a Gamma f(k). Four size classes are studied: −20 μm, +20/−38 μm, +38/−75 μm and +75/−150 μm. The concave relationship between recovery and particle size is obtained up to a limiting flotation time; thereafter, a decreasing trend is observed for Pb and Cu. The finest (−20 μm) and coarsest (+75/−150 μm) classes present slower average rate constants. However, the different f(k) shapes (reverse J-shaped versus mound-shaped distributions) indicate that the use of average rate constants leads to limited conclusions in terms of mineral losses. Therefore, better kinetic interpretations can be obtained from the overall analysis of: the R∞ estimates, a location parameter of f(k) and the metal losses in a low f(k) percentile (e.g., 5%). From the proposed methodology, the poor performance of any erratic component can then be characterized as slow-rate-limited, R∞-limited or both together.

TEMPORAL AND SPATIAL VARIABILITY OF THE DIAMETER DISTRIBUTION IN A SECONDARY BRAZILIAN ATLANTIC FOREST SUGGESTS SITE-SPECIFIC MANAGEMENT PRACTICES

ABSTRACT The diameter distribution of a forest makes it possible to understand its ecological processes and to define actions related to forest management aiming at forest conservation, biodiversity increase, production, and carbon sequestration, among others. This study aimed to identify variation in the diameter distribution in a secondary Atlantic Forest, as a function of sites, over 24 years. The diameter at 1.3 m in height (dbh) was measured for each tree over 5.0 cm dbh, in ten sites, from 1992 to 2016. It was analyzed the quadratic mean diameter (Dq), the Dq annual periodic increment (APIDq), the Liocourt’s Quotient (q), and the diameter distribution with Meyer’s exponential model. The average APIDq over 24 years was 0.03 cm year-1, an average increase of 0.21%, with site variation ranging from 0.74% to -0.45%. The diameter distribution of the forest as a whole maintained the reverse J-shaped over 24-years. When the sites in each inventory year were analyzed, the variation in the diameter distribution was evident, and there were differences in the recovery capacity of the reverse J-shaped distribution from 1992 to 2016. The overall results indicate that, whenever possible, the management plan to recover the structure of the Atlantic Forest remnants should be site-specific, particularly in the mountainous region where the environmental conditions are quite diverse.

Species composition, structure and regeneration status of woody plant species in a dry Afromontane forest, Northwestern Ethiopia

Dry evergreen Afromontane forests are the most threatened in Ethiopia due to agricultural land expansion as they are exposed to high population pressure and thus, conservation measures should be based on scientific evidence since resources for nature conservation are limited. We evaluated the species composition, structure and regeneration status of woody plant species at Gelawoldie community forest. This was analyzed from 32 quadrats laid down in belt transect, each with 400 m2 and 25 m2 for trees and shrubs, and seedlings and saplings, respectively using systematic sampling method. Diversity was analysed using Shannon-Wiener diversity index. A total of 59 woody plant species in 49 genera and 38 families were identified. Of these, 35.5%, 50.8% and 13.5% were trees, shrubs and climbers, respectively. The diversity and evenness of the forest were 3.8 and 0.9, respectively. Moreover, the forest had total mean stand density of 2016 stems ha−1 and basal area of 93.8 m2ha−1. More than 61% of the woody plant species had lower than 5% importance value index (IVI), while the remaining 39% had ≥ 5%. The overall results of the present study revealed higher number of individuals at the lowest diameter (2.5–10 cm) and height classes and progressively declined numbers in higher classes yielding reverse J-shaped distribution pattern. This shows that the forest had healthy regeneration. However, analysis from individual woody plant structure, and count of seedlings and saplings showed that about 17.7% and 5.3% of the species including the endemic have fair and poor regeneration, respectively. Thus, there is a strong need for conservation measures that have to start by identifying the major drivers of low regeneration and the subsequent loss.Species composition, structure and regeneration status of woody plant species in a dry Afromontane forest, Northwestern EthiopiaAll authorsGetie Mucheye & Getahun Yemata | https://doi.org/10.1080/23311932.2020.1823607Published online:25 September 2020Display full size

Assessing Forest Structure and Composition along the Altitudinal Gradient in the State of Sikkim, Eastern Himalayas, India

Understanding the structure and composition of native forests is a prerequisite in developing an adaptive forest management plan for Himalayan forest ecosystems where climate change is rapid. However, basic information on forest structure and composition are still limited in many places of the Eastern Himalayas. In this study, we aimed to understand the diversity, structure, and composition of forests and their variations along an altitudinal gradient in Himalayan forests. The study was conducted in the Indian federal state of Sikkim, Eastern Himalayas. We carried out a comprehensive and comparative evaluation of species diversity, stand basal area, and stem density along the altitudinal gradient from 900 m a.s.l. to 3200 m a.s.l. We used stratified random sampling to survey eighty-three plots each 0.1 ha in forest communities that occurred along the altitudinal gradient: (a) lower (900–1700 m) altitude forest (N = 24), (b) mid (1700–2500 m) altitude forests (N = 37), and (c) higher (2500–3200 m)altitude forests (N = 22). We measured and identified all living trees with a >3 cm diameter at breast height in each plot. We counted 10,344 individual plants, representing 114 woody species belonging to 42 families and 75 genera. The family Fagaceae and its species Lithocarpus pachyphyllus (Kurz) Rehder. were reported as the most dominant forest trees with the highest Importance Value Index. The Shannon diversity index was recorded as being the highest for the low-altitude forests, whereas measures of structural diversity varied among forests along with altitude: the mid-altitude forests recorded the highest stem density and the high-altitude forests showed the highest mean stem DBH (diameter at 1.3 m height). One significant finding of our study was the disparity of the size class distribution among forests along the altitudinal gradient. Overall, we found a reverse J-shape distribution of tree diameter signifying the uneven-agedness. However, we showed, for the first time, a complete lack of large trees (>93 cm DBH) in the lower altitude forests. Our study highlights conservation concerns for the low-altitude forests that record high species diversity, although lacked large-diameter trees. We anticipate that our study will provide a comprehensive understanding of forest diversity, composition, and structure along the altitudinal gradient to design conservation and sustainable management strategies

Population structure and regeneration status of rhododendrons in temperate mixed broad-leaved forests of western Arunachal Pradesh, India

ABSTRACTThis study was conducted to investigate the population structure and regeneration status of Rhododendron tree species in temperate mixed broad-leaved forests in Tawang and West Kameng districts of western Arunachal Pradesh, India. Population structure was determined through densities of seedlings, saplings and adults from the sampling quadrats. Based on density of individuals at the seedling, sapling and adult, the regeneration status of the species was determined. Density and basal area of the selected rhododendrons ranged from 16 individuals ha−1 to 1422 individuals ha−1 and 0.24 m2 ha−1 to 131.30 m2 ha−1, respectively. Rhododendron species (viz. R. arboreum, R. arboreum ssp. delavayi var. delavayi, R. barbatum and R. kesangiae) exhibited reverse J-shaped distribution with the density of sapling less than seedling and adult population. Density of selected Rhododendron species is found to be higher between the girth classes 10-30 cm to 130-150 cm and decreased with the increase of girth in all the study stands. About, 90% degrees of disturbances recorded due to cooking and space heating purposes. Among the regenerating species, 77% of the species exhibited fair regeneration, 8% species showed good regeneration while 15% of the species exhibited no regeneration. However, 90% of the tree species showed fair regeneration in disturbed stands than the undisturbed stands. Selected Rhododendron species exhibited fair regeneration in their respective stands. Inadequate regeneration status and population structure of tree species, including rhododendrons, are observed as the density of sapling less than seedling and adult population. Anthropogenic disturbances resulted to be declined in populations of Rhododendron and may lead many species to endangered, rare and threatened categories. Therefore, proper conservation and management initiatives with active involvement of local people are urgent need to protect this keystone plant species in their habitat particularly in western Arunachal Himalaya.

Disturbance history, species diversity, and structural complexity of a temperate deciduous forest

Stand structural complexity enhancement is an increasingly popular management objective, especially on public lands. Complex stand structures are hypothesized to support a relatively high degree of native forest diversity and be more resistant and resilient to disturbances. Complex structures are characterized by the presence of deadwood and heterogeneity of tree-size classes and tree architecture. Relatively little is known about how discrete disturbance events affect structural complexity and compositional diversity in Quercus-dominated stands at fine spatial scales (i.e. neighborhoods). We established 20 0.05 ha fixed-radius plots on the Sipsey Wilderness of William B. Bankhead National Forest in northern Alabama to quantify woody plant species composition and structure. Trees were mapped on each plot to quantify overstory structural complexity and compositional diversity. We extracted two cores from all canopy Quercus spp. ≥ 5 cm diameter at breast height to quantify age, recruitment pulses, and reconstruct canopy disturbance history. Shannon species diversity in the sampled area was 1.75 for trees, 2.08 for saplings, and 1.69 for seedlings. Quercus alba had the greatest basal area, and Ostrya virginiana had the highest density. The stand exhibited a reverse J-shaped distribution with a q-factor of 1.72. The oldest Quercus dated to 1795, and the largest recruitment pulse occurred in the 1870s. The mean return interval for intermediate-severity disturbance was 38 years. Although we documented no relationships between disturbance frequency and compositional diversity at the neighborhood scale (0.05 ha), less frequent disturbance was associated with higher structural complexity (r2 = 0.258, p = 0.026) at the neighborhood scale. We suggest that localized disturbance increases species diversity and structural complexity, but these processes are manifest at the stand level and not at the neighborhood scale. We conclude that the spatial variability (i.e. size, shape, orientation, microsite conditions) is likely more influential on diversity and complexity than the temporal variation (frequency) of these processes at the neighborhood scale.

Maternal age and offspring developmental vulnerability at age five: A population-based cohort study of Australian children

BackgroundIn recent decades, there has been a shift to later childbearing in high-income countries. There is limited large-scale evidence of the relationship between maternal age and child outcomes beyond the perinatal period. The objective of this study is to quantify a child’s risk of developmental vulnerability at age five, according to their mother’s age at childbirth.Methods and findingsLinkage of population-level perinatal, hospital, and birth registration datasets to data from the Australian Early Development Census (AEDC) and school enrolments in Australia’s most populous state, New South Wales (NSW), enabled us to follow a cohort of 99,530 children from birth to their first year of school in 2009 or 2012. The study outcome was teacher-reported child development on five domains measured by the AEDC, including physical health and well-being, emotional maturity, social competence, language and cognitive skills, and communication skills and general knowledge. Developmental vulnerability was defined as domain scores below the 2009 AEDC 10th percentile cut point.The mean maternal age at childbirth was 29.6 years (standard deviation [SD], 5.7), with 4,382 children (4.4%) born to mothers aged <20 years and 20,026 children (20.1%) born to mothers aged ≥35 years. The proportion vulnerable on ≥1 domains was 21% overall and followed a reverse J-shaped distribution according to maternal age: it was highest in children born to mothers aged ≤15 years, at 40% (95% CI, 32–49), and was lowest in children born to mothers aged between 30 years and ≤35 years, at 17%–18%. For maternal ages 36 years to ≥45 years, the proportion vulnerable on ≥1 domains increased to 17%–24%. Adjustment for sociodemographic characteristics significantly attenuated vulnerability risk in children born to younger mothers, while adjustment for potentially modifiable factors, such as antenatal visits, had little additional impact across all ages. Although the multi-agency linkage yielded a broad range of sociodemographic, perinatal, health, and developmental variables at the child’s birth and school entry, the study was necessarily limited to variables available in the source data, which were mostly recorded for administrative purposes.ConclusionsIncreasing maternal age was associated with a lesser risk of developmental vulnerability for children born to mothers aged 15 years to about 30 years. In contrast, increasing maternal age beyond 35 years was generally associated with increasing vulnerability, broadly equivalent to the risk for children born to mothers in their early twenties, which is highly relevant in the international context of later childbearing. That socioeconomic disadvantage explained approximately half of the increased risk of developmental vulnerability associated with younger motherhood suggests there may be scope to improve population-level child development through policies and programs that support disadvantaged mothers and children.

Keystone Species, Forest and Landscape: A Model to Select Protected Areas.

The selection of forest fragments for conservation is usually based on spatial parameters as forest size and canopy integrity. This strategy assumes that chosen fragments present high conservation status, ensuring biodiversity and ecological functions. We argue that a well-preserved forest fragment that remains connected by the landscape structure, does not necessarily hold attributes that ensure the presence of keystone species. We also discuss that the presence of keystone species does not always mean that it has the best conditions for its occurrence and maintenance. We developed a model to select areas in forest landscapes to be prioritized for protection based on suitability curves that unify and compare spatial indicators of three categories: forest fragment quality, landscape quality, and environmental conditions for the occurrence of a keystone species. We use a case study to compare different suitability degrees for Euterpe edulis presence, considered an important functional element in Atlantic Forest (São Paulo, Brazil) landscapes and a forest resource for local people. The results show that the identification of medium or advanced stage fragments as singular indicator of forest quality does not guarantee the existence or maintenance of this keystone species. Even in some well-preserved forest fragments, connected to others and with palm presence, the reverse J-shaped distribution of the population size structure is not sustained and these forests continue to be threatened due to human disturbances.

Size class structure, growth rates, and orientation of the central Andean cushion Azorella compacta.

Azorella compacta (llareta; Apiaceae) forms dense, woody, cushions and characterizes the high elevation rocky slopes of the central Andean Altiplano. Field studies of an elevational gradient of A. compacta within Lauca National Park in northern Chile found a reverse J-shape distribution of size classes of individuals with abundant small plants at all elevations. A new elevational limit for A. compacta was established at 5,250 m. A series of cushions marked 14 years earlier showed either slight shrinkage or small degrees of growth up to 2.2 cm yr−1. Despite their irregularity in growth, cushions of A. compacta show a strong orientation, centered on a north-facing aspect and angle of about 20° from horizontal. This exposure to maximize solar irradiance closely matches previous observations of a population favoring north-facing slopes at a similar angle. Populations of A. compacta appear to be stable, or even expanding, with young plants abundant.

백두대간 조침령-신배령 구간 소나무림과 신갈나무림의 군락구조

백두대간 조침령-신배령 구간 소나무림과 신갈나무림을 대상으로 2012년 4월부터 2013년 8월까지 영구조사구(<TEX>$100m{\times}100m$</TEX>) 설치하여 조사하였다. 총 50개소의 산림식생조사 자료를 토대로 Z-M식물사회학적 방법에 의해 식생유형 분류를 수행하였던바, 최상위 수준에서 신갈나무군락군이 분류되었으며, 군락단위에서는 물푸레나무군락과 까치박달군락으로 세분되었다. 물푸레나무군락은 군단위에서 소나무군과 가래나무군으로 나누어지며, 소나무군은 다시 회나무소군과 머루소군으로 분류되었고, 까치박달군락은 시닥나무군과 사스래나무군으로 각각 세분되어, 총 5개의 식생단위로 분류되었다. 식생단위별 중요치를 분석한 결과 소나무림에서 소나무와 신갈나무의 중요치가 20%이상으로 높게 나타났으나 소나무가 신갈나무보다 상대피도가 50%이상으로 가장 높게 나타났다. 종간연관 분석결과 크게 4개의 유형으로 구분되었고, 이는 식생단위의 식별종 및 표징종과 일치하는 경향이었다. 또한 소나무림의 흉고직경급별 개체 분포에서 중간직경급에서 개체수가 가장 많은 정규분포를 나타낸 소나무와 이를 제외한 다른 수종은 직경이 커질수록 개체수가 감소하는 역 J자형의 분포유형을 나타내어 소나무림에서 신갈나무림으로 교체될 가능성이 크다 판단된다. 반면 신갈나무림에서는 신갈나무를 포함한 다른 수종 모두 역 J자형의 분포유형을 나타내어 신갈나무림은 당분간 안정된 상태로 지속될 것으로 판단되었다. The study was carried out to analyze vegetation structure of Pinus densiflora and Quercus mongolica forests located in Jochimryeong to Shinbaeryeong of the Baekdudaegan mountain range. The survey for 50 plots was conducted from April 2012 to August 2013 in the permanent plots (<TEX>$100m{\times}100m$</TEX>) using phytosociological analysis. As a result, the vegetations were classified into five vegetation units. In species composition, they were classified into Q. mongolica community group divided into 2 community such as Fraxinus rhynchophylla community and Carpinus cordata community, F. rhynchophylla community was subdivided Pinus densiflor group (into Euonymus sachalinensis subgroup, Vitis coignetiae subgroup) and Juglans mandshurica group. C. cordata community was subdivided Acer komarovii group and Betula ermanii group. In terms of importance value, P. densiflora and Q. mongolica were more than 20% respectively. P. densiflora was found to have the highest relative coverage. Analysis of interspecific association showed four types which were coincident with differential species and character species on the constancy table. Based on the diameter class distribution, P. densiflora forest presented a normal distribution pattern except for other species which showed a reverse Jshaped distribution pattern, therefore P. densiflora forest would likely be replaced by Q. mongolica forests. While in Q. mongolica forest, diameter class distribution of all species population presented a reverse J-shaped distribution pattern, therefore Q. mongolica forest could likely remain in the future.

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

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This study assessed the diversity and distribution of trees and shrubs in a 16 ha disturbed plot in the Takamanda Rainforest. Linear transects (8) were laid in the field which radiated from the centre of the plot. The girth of the trees and shrubs were measured and species identified. A total of 99 species (72 trees and 27 shrubs) belonging to 87 genera and 34 families were recorded. Caesalpinaceae was the most represented tree family (9 species) while Rubiaceae was the most represented among shrubs (9 species). Baphia nitida recorded the highest tree density (143.75 individual’s ha-1) and lowest tree density (1.56 individual’s ha-1) was recorded for Khaya anthotera. The highest shrub density (192.19ha-1) was recorded for Angylocalyx pynatii while the lowest was (1.56 ha-1) was recorded for Voacanga africana. The girth class distribution showed a reverse J-shape distribution, with the highest densities in the lower girth (15-30 and 30-45 cm) classes. This decreases in density with the larger girth (> 75) class. The Importance Value Index (IVI) of trees was highest for Baphia nitida (20.06) while the lowest was recorded for Millettia sanagana (0.51). For shrubs, Chytranthus macrobotrys had highest IVI of 45.05 while the lowest was observed in V. Africana (1.24). Diversity index of trees and shrubs were 3.87 and 2.88, respectively. A dominance index of trees was 0.03 and that of shrubs was 0.08. The species evenness for trees (0.90) and shrubs (0.87) showed a slight variation in distribution. Abundance/ frequency ratio (A/F) for tree and shrub was >0.05 and showed a clumped pattern of distribution. Sustainable management of the forest would continue to provide goods and services for communities around the rainforest. Key words: Diversity index, distribution, abundance/frequency ratio’ contagious, importance value index, evenness index.

Diversity, Population Structure and Regeneration Status of Woody Species in Dry Woodlands Adjacent to &amp;lt;i&amp;gt;Molapo&amp;lt;/i&amp;gt; Farms in Northern Botswana

The diversity, population structure and regeneration status of woody species were studied at Xobe and Shorobe Villages in northern Botswana. A total of 130 and 111 quadrats of 20 × 20 m size were laid down at 50 m intervals along parallel line transects at Xobe and Shorobe, respectively. A total of 46 woody species, 27 from Xobe and 41 from Shorobe were recorded. Of the 46 woody species, only 22 were recorded at both sites. Ten genera and six families were found only in Shorobe while one genus and one family were found only in Xobe. The diversity and evenness of woody species were 1.5 and 0.5 in Xobe, respectively, and 2.18 and 0.6 in Shorobe, respectively. The similarities of woody species in terms of richness of species, genera and families at the two sites were about 50%, 54% and 56%, respectively. The mean densities of woody species were 2745.7 ± 1.35 and 4269.7 ± 36 individuals ha-1 at Xobe and Shorobe, respectively. Despite differences in absolute numbers, the total mean densities of woody species at both sites did not exhibit significant (P = 0.35) differences. At both sites, woody species were dominated by individuals of only a few species, which also exhibited the highest values of important value index. The population structure patterns of the woody species were categorized into five groups. The species in the first group exhibited reverse J-shaped distribution, which indicates stable population structures. The species in the second group showed relatively good recruitment but the regeneration is negatively affected. The species in the other three groups exhibited hampered regeneration as a result of disturbances caused by humans, domestic animals and annual fires. The parameters assessed indicate the need for attention and appropriate management interventions by the relevant national authorities at various levels.

High Dominance of &lt;i&gt;Shorea robusta&lt;/i&gt; Gaertn. in Alluvial Plain Kamrup Sal Forest of Assam, N. E. India

The study emphasizes on the community characteristics of naturally regenerated sal forest of Kamrup district, Assam, India. Sal is one of the most important timber y ield ing plants and also good source of aromatic gum and non- tim- ber forest product. These forests are exposed to over-exploitation, deforestation, encroachment and alterat ion in land use and land cover and in return being replaced by secondary regenerated sal forest. Altogether, 71 p lant species were recorded fro m the selected sal forest. Herbaceous layer of the fo rest was most species rich (30 species) layer fo llo wed by tree and shrub species. Leguminosae and Asteraceae were among the most dominant families in the forest while large nu mber of families was monospecious. Shorea robusta has contributed about 90% of the total stand density (2559 individual ha -1 ) of the forest, while species like Erythrina suberosa, Delonix regia and Pterospermum acerifolium were represented by single stem. Similar to that of stand density, sal have contributed to the maximu m basal area o f the forest. The g irth class distribu- tion confirmed a reverse J-shaped distribution, with h igher density in lo wer girth classes and sharp decline thereafter. Total density of shrubs and herbs was recorded 2 individuals m -2 and 63 individuals m -2 , respectively. Based on the dominance, Shorea robusta showed highest dominance followed by Zizyphus rugosus. Diversity index fo r tree, shrub and herb species was recorded 1.43, 2.30 and 3.28, respectively. Do minance index showed reverse trend to that of d iversity index. About 84% of the plant species showed contagious distribution, however none of the species exhib ited regular distribution. The forest is heterogenous in composition with h igh dominance of Shorea and is under regenerating stage. Therefore, for sustainabili- ty of the forest it requires effective conservation measures for sal and its associate plant species.

Scale-specific determinants of a mixed beech and oak seedling–sapling bank under different environmental and biotic conditions

The persistence of seedlings in the forest understorey is of major importance for the maintenance and regeneration of canopy trees in several forested ecosystems. In the present study, we examine the small-scale spatial pattern of a mixed beech and oak seedling–sapling bank in two areas of an unmanaged temperate deciduous forest with different environmental conditions. We used environmental, biotic and spatial variables to establish the main factors that explain the spatial pattern of these seedling–sapling banks at different scales. The stand structure in both areas was similar, but while in plot A beech dominated the canopy, plot B was dominated by oaks. In both areas, established beech individuals showed a clear reverse J-shaped distribution, whereas established oaks showed a unimodal distribution with only a few young individuals. Seedlings of beech and oak were distributed in aggregates, whereas beech saplings had a random distribution. At broader scales, the abundance of seedlings and saplings is affected by the environment as well as by inter-species competition, while at finer scales the spatial pattern is mainly influenced by stochastic processes, probably related to seed predation and establishment. The structure of the seedling–sapling bank indicates an advantage of beech over oak as far as regeneration is concerned. Beech seedlings and saplings tolerate the stress induced by the canopy and the understorey and persist for many years, while oak seedlings decline in a few years. Therefore, if current conditions persist, after canopy opening beech seedlings and saplings can grow rapidly into the canopy and the stands will move towards beech dominance.

Ankle Brachial Index Combined With Framingham Risk Score to Predict Cardiovascular Events and Mortality

Prediction models to identify healthy individuals at high risk of cardiovascular disease have limited accuracy. A low ankle brachial index (ABI) is an indicator of atherosclerosis and has the potential to improve prediction. To determine if the ABI provides information on the risk of cardiovascular events and mortality independently of the Framingham risk score (FRS) and can improve risk prediction. Relevant studies were identified. A search of MEDLINE (1950 to February 2008) and EMBASE (1980 to February 2008) was conducted using common text words for the term ankle brachial index combined with text words and Medical Subject Headings to capture prospective cohort designs. Review of reference lists and conference proceedings, and correspondence with experts was conducted to identify additional published and unpublished studies. Studies were included if participants were derived from a general population, ABI was measured at baseline, and individuals were followed up to detect total and cardiovascular mortality. Prespecified data on individuals in each selected study were extracted into a combined data set and an individual participant data meta-analysis was conducted on individuals who had no previous history of coronary heart disease. Sixteen population cohort studies fulfilling the inclusion criteria were included. During 480,325 person-years of follow-up of 24,955 men and 23,339 women, the risk of death by ABI had a reverse J-shaped distribution with a normal (low risk) ABI of 1.11 to 1.40. The 10-year cardiovascular mortality in men with a low ABI (< or = 0.90) was 18.7% (95% confidence interval [CI], 13.3%-24.1%) and with normal ABI (1.11-1.40) was 4.4% (95% CI, 3.2%-5.7%) (hazard ratio [HR], 4.2; 95% CI, 3.3-5.4). Corresponding mortalities in women were 12.6% (95% CI, 6.2%-19.0%) and 4.1% (95% CI, 2.2%-6.1%) (HR, 3.5; 95% CI, 2.4-5.1). The HRs remained elevated after adjusting for FRS (2.9 [95% CI, 2.3-3.7] for men vs 3.0 [95% CI, 2.0-4.4] for women). A low ABI (< or = 0.90) was associated with approximately twice the 10-year total mortality, cardiovascular mortality, and major coronary event rate compared with the overall rate in each FRS category. Inclusion of the ABI in cardiovascular risk stratification using the FRS would result in reclassification of the risk category and modification of treatment recommendations in approximately 19% of men and 36% of women. Measurement of the ABI may improve the accuracy of cardiovascular risk prediction beyond the FRS.

THE INFLUENCE OF SUCCESSIONAL PROCESSES AND DISTURBANCE ON THE STRUCTURE OF TSUGA CANADENSIS FORESTS

Old-growth forests are valuable sources of ecological, conservation, and management information, yet these ecosystems have received little study in New England, due in large part to their regional scarcity. To increase our understanding of the structures and processes common in these rare forests, we studied the abundance of downed coarse woody debris (CWD) and snags and live-tree size-class distributions in 16 old-growth hemlock forests in western Massachusetts. Old-growth stands were compared with eight adjacent second-growth hemlock forests to gain a better understanding of the structural differences between these two classes of forests resulting from contrasting histories. In addition, we used stand-level dendroecological reconstructions to investigate the linkages between disturbance history and old-growth forest structure using an information-theoretic model selection framework. Old-growth stands exhibit a much higher degree of structural complexity than second-growth forests. In particular, old-growth stands had larger overstory trees and greater volumes of downed coarse woody debris (135.2 vs. 33.2 m3/ha) and snags (21.2 vs. 10.7 m3/ha). Second-growth stands were characterized by either skewed unimodal or reverse-J shaped diameter distributions, while old-growth forests contained bell-shaped, skewed unimodal, rotated sigmoid, and reverse J-shaped distributions. The variation in structural attributes among old-growth stands, particularly the abundance of downed CWD, was closely related to disturbance history. In particular, old-growth stands experiencing moderate levels of canopy disturbance during the last century (1930s and 1980s) had greater accumulations of CWD, highlighting the importance of gap-scale disturbances in shaping the long-term development and structural characteristics of old-growth forests. These findings are important for the development of natural disturbance-based silvicultural systems that may be used to restore important forest characteristics lacking in New England second-growth stands by integrating structural legacies of disturbance (e.g., downed CWD) and resultant tree-size distribution patterns. This silvicultural approach would emulate the often episodic nature of CWD recruitment within old-growth forests.