Differential survival among life stages contributes to co‐dominance of Abies mariesii and Abies veitchii in a sub‐alpine old‐growth forest

Questions: Are there interspecific differences in mortality and recruitment rates across life stages between two shade‐tolerant dominant trees in a sub‐alpine old‐growth forest? Do such differences in demography contribute to the coexistence and co‐dominance of the two species? Location: Sub‐alpine, old‐growth forest on Mt. Ontake, central Honshu, Japan. Methods: From 1980 to 2005, we recorded DBH and status (alive or dead) of all Abies mariesii and A. veitchii individuals (DBH ≥ 5 cm) in a 0.44‐ha plot. Based on this 25 year census, we quantified mortality and recruitment rates of the two species in three life stages (small tree, 5 cm ≤ DBH < 10 cm; subcanopy tree, 10 cm ≤ DBH < 20 cm; canopy tree, DBH ≥ 20 cm). Results: Significant interspecific differences in mortality and recruitment rates were observed in both the small tree and sub‐canopy tree stages. In this forest, saplings (< 5 cm DBH) are mostly buried by snow‐pack during winter. As a consequence, saplings of A. mariesii, which is snow and shade tolerant, show higher rates of recruitment into the small tree stage than do those of A. veitchii. Above the snow‐pack, trees must tolerate dry, cold temperatures. A. veitchii, which can more readily endure such climate conditions, showed lower mortality rate at the subcanopy stage and a higher recruitment rate into the canopy tree stage. This differential mortality and recruitment among life‐stages determines relative dominance of the two species in the canopy. Conclusion: Differential growth conditions along a vertical gradient in this old forest determine survival of the two species prior to reaching the canopy, and consequently allow co‐dominance at the canopy stage.     

Species turnover and diversity patterns along an evergreen broad-leaved forest coenocline

Direct gradient analysis was applied to the evergreen broad-leaved forest coenocline in the Tatera Forest Reserve, Japan. 10 quadrats of 0.1 -0.05 ha were laid out from 140 m to 560 m above sea level at intervals of 25–70 m. Gradient analysis revealed that distributions of many species terminated or started at ca. 400 m. Community similarity, calculated in Percentage Similarity (PS) and Community Coefficient (CC), changed abruptly below and above the 400 m contour, suggesting a change of vegetation structure at this altitude, which was also clear from population distributions. The spatial turnover rate of species along the altitudinal gradient was calculated in two ways: as the Average turnover rate along the whole range of the gradient, and as the Zone turnover rate at individual altitudes. The overall rates calculated for five categories of populations: DBH > 10 cm, DBH >3 cm, all woody species, herb-layer, and total vegetation, were- 0.0011 to- 0.0021 for PS, and - 0.0009 to- 0.0019 for CC. The calculated rates (PS basis) indicate that a 95% change in species composition is reached at 1120 to 620 m altitude. Similarly, the rates -0.0009 to - 0.0019 (CC) correspond to 1410 - 680 m. The altitudinal range expected here for a 95% change agrees with the actual elevation of forest zonation in northwestern Kyushu. The average rate of both PS and CC in the herb-layer population was 1.56 times higher than the rate in the woody species population, showing a more rapid change in herb-layer population than in the woody ones along the gradient. The Zone turnover rates were higher at the 370–440 m belt than those below and above the belt. This coincided with the interchanging pattern in population distributions and the abrupt change in similarity at about 400 m above sea level. This may be due to the change in environmental conditions such as physiography and air humidity. In the diversity measurements, the species density per 100 m² showed a gradual increase in the DBH >3 cm population but a constant level in the DBH >10 cm population along the whole range of the forest coenocline studied, while index values of S₍₁₀₀₎ and Shannon's H showed decreasing trends in the same gradient with a few exceptionally high and low values.     

中亚热带森林植物多样性增加导致细根生物量“超产”

细根在森林生态系统C分配和养分循环过程中发挥着重要作用, 但对地下细根与植物多样性之间关系的研究相对较少。该研究选择中亚热带从单一树种的杉木(Cunninghamia lanceolata)人工林到多树种的常绿阔叶林(青冈(Cyclobalanopsis glauca)-石栎(Lithocarpus glaber)林)的不同植物多样性梯度, 用根钻法采集细根并测定其生物量, 用Win-RHIZO 2005C根系分析系统测定细根形态参数, 以验证以下3个假设: 1)植物种类丰富度高的林分其细根生产存在“地下超产”现象; 2)根系空间生态位的分离水平是否随着植物多样性增多而增大? 3)细根是否通过形态可塑性对林木竞争做出响应?结果显示: 从单一树种的杉木人工林到植物种类较复杂的青冈-石栎常绿阔叶林, 0-30 cm土层的林分细根总生物量和活细根生物量均呈增加的趋势, 即细根总生物量为杉木林(305.20 g·m^-2) <马尾松(Pinus massoniana)林(374.25 g·m^-2) <南酸枣(Choerospondias axillaris)林(537.42 g·m^-2) <青冈林(579.33 g·m^-2), 活细根生物量为杉木林(268.74 g·m^-2) <马尾松林(299.15 g·m^-2) <南酸枣林(457.32 g·m^-2) <青冈林(508.47 g·m^-2), 各森林类型之间的细根总生物量差异显著(p < 0.05), 但活细根生物量差异不显著。土壤垂直剖面上, 除杉木林细根生物量随土层变化不显著外, 其他森林类型的活细根生物量和总细根生物量均随土层变化显著, 表层细根生物量随树种多样性的升高呈减小趋势, 据此推测树种间的生态位分离水平逐渐增大。植物多样性的不同对林分的细根形态及空间分布格局影响不显著, 细根形态可塑性对生物量变化响应不明显。     

Elevational changes in vascular plants richness,diversity, and distribution pattern in Abune Yosef mountain range,Northern Ethiopia

The aim of this research is to investigate the patterns of vascular plant species richness,diversity,and distribution along an elevation gradient in the Abune Yosef mountain range,Ethiopia.Preferential systematic sampling was employed to collect vegetation and environmental data along the elevation gradient.We found that plant species richness declines monotonically from low to high elevations.Specifically,vascular plant species richness and diversity were lower in the Afroalpine grassland(high elevation)than in the Dry evergreen Afromontane forest and Ericaceous forest(low elevations).In contrast,endemic vascular plant richness was significantly higher in the Afroalpine grassland than in the Dry evergreen Afromontane forest and Ericaceous forest.Elevation showed a significant impact on the richness,diversity,and endemism of vascular plants.According to Sorensen's coefficient,the similarity between Dry evergreen Afromontane forest and Ericaceous forest vegetation types is higher(32%)than the similarity between Ericaceous forest and Afroalpine grassland(18%).Only 5%similarity was recorded between the Dry evergreen Afromontane forest and Afroalpine grassland.Growth forms showed different elevationai richness patterns.Trees and liana increased monotonically up to 3300 m.Shrub and herb richness patterns followed a hump-shaped and inverted hump-shaped pattern along the elevation gradient.The elevation patterns of vascular plant species richness,diversity,and growth form in the present study may be attributed to differences in management intensity,spatial heterogeneity,microclimatic variations,and anthropogenic disturbances.     

Effects of size,neighbors, and site condition on tree growth in a subtropical evergreen and deciduous broad‐leaved mixed forest,China

Successful growth of a tree is the result of combined effects of biotic and abiotic factors. It is important to understand how biotic and abiotic factors affect changes in forest structure and dynamics under environmental fluctuations. In this study, we explored the effects of initial size [diameter at breast height (DBH)], neighborhood competition, and site condition on tree growth, based on a 3‐year monitoring of tree growth rate in a permanent plot (120 × 80 m) of montane Fagus engleriana–Cyclobalanopsis multiervis mixed forest on Mt. Shennongjia, China. We measured DBH increments every 6 months from October 2011 to October 2014 by field‐made dendrometers and calculated the mean annual growth rate over the 3 years for each individual tree. We also measured and calculated twelve soil properties and five topographic variables for 384 grids of 5 × 5 m. We defined two distance‐dependent neighborhood competition indices with and without considerations of phylogenetic relatedness between trees and tested for significant differences in growth rates among functional groups. On average, trees in this mixed montane forest grew 0.07 cm year^?1 in DBH. Deciduous, canopy, and early‐successional species grew faster than evergreen, small‐statured, and late‐successional species, respectively. Growth rates increased with initial DBH, but were not significantly related to neighborhood competition and site condition for overall trees. Phylogenetic relatedness between trees did not influence the neighborhood competition. Different factors were found to influence tree growth rates of different functional groups: Initial DBH was the dominant factor for all tree groups; neighborhood competition within 5 m radius decreased growth rates of evergreen trees; and site condition tended to be more related to growth rates of fast‐growing trees (deciduous, canopy, pioneer, and early‐successional species) than the slow‐growing trees (evergreen, understory, and late‐successional species).     

鼎湖山南亚热带常绿阔叶林荷木种群动态变化

荷木(Schima superba)是鼎湖山南亚热带常绿阔叶林群落中的优势种,为了解南亚热带常绿阔叶林的群落构建机制,该研究分析了鼎湖山南亚热带常绿阔叶林20 hm2样地中荷木种群在2005—2017年间的动态变化,并从径级和生境两个方面分析了其死亡率的分布特征。结果表明:(1)荷木种群个体数量从2005—2017年呈现出减少的态势。(2)在径级方面,荷木的死亡率和相对生长率的变化在不同径级区间呈现出不同的变化规律。径级在1～10 cm范围的荷木相对生长率大并迅速下降,死亡率上升且维持在较高水平;径级在10～50 cm范围的荷木随着径级增大,相对生长率减缓,然后下降,而死亡率不断下降;在50 cm以上的径级范围内,荷木相对生长率小、死亡率大。(3)不同生境中,2010年各个生境死亡率相差不大,2015年高海拔生境(高坡、山脊、高谷)死亡率大于低海拔生境(低坡、低谷),2017年则为低海拔生境大于高海拔生境。(4)荷木的死亡率与土壤中酸碱度呈正相关关系,而与土壤有机质、总氮、总磷、有效钾、有效氮含量呈负相关关系。     

Regional‐scale directional changes in abundance of tree species along a temperature gradient in Japan

Climate changes are assumed to shift the ranges of tree species and forest biomes. Such range shifts result from changes in abundances of tree species or functional types. Owing to global warming, the abundance of a tree species or functional type is expected to increase near the colder edge of its range and decrease near the warmer edge. This study examined directional changes in abundance and demographic parameters of forest trees along a temperature gradient, as well as a successional gradient, in Japan. Changes in the relative abundance of each of four functional types (evergreen broad‐leaved, deciduous broad‐leaved, evergreen temperate conifer, and evergreen boreal conifer) and the demography of each species (recruitment rate, mortality, and population growth rate) were analyzed in 39 permanent forest plots across the Japanese archipelago. Directional changes in the relative abundance of functional types were detected along the temperature gradient. Relative abundance of evergreen broad‐leaved trees increased near their colder range boundaries, especially in secondary forests, coinciding with the decrease in deciduous broad‐leaved trees. Similarly, relative abundance of deciduous broad‐leaved trees increased near their colder range boundaries, coinciding with the decrease in boreal conifers. These functional‐type‐level changes were mainly due to higher recruitment rates and partly to the lower mortality of individual species at colder sites. This is the first report to show that tree species abundances in temperate forests are changing directionally along a temperature gradient, which might be due to current or past climate changes as well as recovery from past disturbances.     

古田山24 ha森林动态监测样地常绿阔叶林群落结构和组成动态: 探讨2008年冰雪灾害的影响

常绿阔叶林是我国亚热带地区的地带性植被, 其中最为典型而且分布最广泛的是中亚热带常绿阔叶林。为探讨2008年初我国南方发生的冰雪灾害对中亚热带常绿阔叶林的影响, 以浙江省古田山国家级自然保护区24 ha森林动态监测样地内的中亚热带常绿阔叶林为例, 研究了该森林在冰雪灾害前后(2005-2010年)的群落结构及物种组成动态。结果表明, 群落径级结构变化较小, 但群落整体补员不足且死亡率较高; 多个粒度上的群落动态显示出一致的衰退特征, 但不同生境间的群落动态存在差异; 物种多度和胸高截面积多呈减小趋势, 但频度和重要值变化不明显。同时, 物种的多度、胸高截面积、频度和重要值等次序均无明显变化。这说明2008年发生的冰雪灾害对古田山中亚热带常绿阔叶林群落的短期动态产生了较大的负面影响, 且其影响程度与植物胸径和地形等因素密切相关; 同时也反映了古田山中亚热带常绿阔叶林群落结构对冰雪灾害干扰具有一定的抵抗力。     

猫儿山不同海拔植物群落树木构型差异及其影响因子

通过对猫儿山海拔梯度上常绿阔叶林(低海拔,1100 m)、常绿落叶阔叶混交林(中海拔,1500 m)和常绿针阔叶混交林(高海拔,1900 m)3种典型植物群落中乔木层植物构型性状以及环境因子的测定,分析乔木层植物构型性状在3个群落间的变异规律及其影响因素.结果表明:随海拔升高,乔木层树冠面积、45 cm基径、胸径和叶片聚集度持续增加,树高、枝下高和树冠厚度先增加后减小;枝条伸展方向表现为在低海拔群落中水平枝条比例最大,高海拔群落次之,中海拔群落最小;中海拔群落中乔木层植物构型性状之间的相关性更强.冗余分析表明,土壤有机质和总辐射是乔木层植物构型性状变异的主要环境影响因素,它们分别解释了构型性状39.6%和23.9%的变异.土壤有机质对树冠面积和枝下高影响较大,总辐射对胸径和45 cm基径影响较大,且都呈正相关.猫儿山乔木层植物在不同海拔群落间存在构型分异,影响乔木层植物构型变化的主要环境驱动力是土壤有机质和总辐射.     

中国东北森林生长演替模拟模型及其在全球变化研究中的应用

 NEWCOP模型是一个新的适于模拟东北森林的种类组成动态的林窗类计算机模拟模型,它通过模拟在每一个林分斑块上的每株树木的更新、生长和死亡的全过程来反映森林群落的中长期生长和演替动态。由于 NEWCOP模型是一个由气候变量驱动的生态系统模型,故可用于评价气候变化对东北森林生长和演替的影响。在东北大兴安岭、小兴安岭和长白山地区对NEWCOP模型进行了验证和校准。沿环境梯度对NEWCOP模型的数字模拟实验表明：它能准确地再现顶极森林中树种组成及其在东北地区的垂直分布规律和水平分布规律;能准确地再现大兴安岭、小兴安岭和长白山的主要类型森林的生长和演替规律;在一定的场合NEWCOP还可反映林分的径级结构;NEWCOP模型还具有对现有森林的跟踪模拟能力。应用NEWCOP模型评估了东北森林生态系统对可能气候变化的敏感性。在GFDL 2×CO2和GISS 2×CO2气候变化情景下,东北森林的种类组成将发生很大变化,落叶阔叶树将取代目前长白山、小兴安岭的红松(Pinus koraiensis)和大兴安岭的兴安落叶松(Larix gmelinii)成为东北森林主要树种,而针叶树将在地带性森林中占很小的比重,阔叶树中蒙古栎(Quercus mongolica)将是最重要的树种,它将成为小兴安岭和大兴安岭最主要树种;东北地区适于森林生长的区域将大幅度减少,这些变化主要发生在气候变化过渡期。东北森林对不同的气候变化情景有不同响应。但是,总的趋势是未来东北森林中落叶阔叶树的比重将大幅度增加。这些结论对在全球气候变化背景下,我国东北合理地选择造林树种和制定现有森林的保护经营策略具有一定参考价值。     

Changes in structure and composition of evergreen forests on an altitudinal gradient in the Venezuelan Guayana shield

There have been several ecological studies in forests of the Guayana Shield, but so far none had examined the changes in structure and composition of evergreen forests with altitude. This study describes and analyzes the structure, species composition and soil characteristics of forest stands at different altitudinal zones in Southeastern Venezuelan Guayana, in order to explain the patterns and the main factors that determine the structure and composition of evergreen forests along the altitudinal gradient. Inventories of 3 948 big (>10cm DBH) and 1 328 small (5-10cm DBH) woody stems were carried out in eleven plots, ranging from 0.1 to 1.0ha, along a 188km long transect with elevations between 290 and 1 395masl. It has been found that 1) hemiepihytes become more dominant and lianas reduce their dominance with increasing altitude and 2) the forest structure in the study area is size-dependent. Five families and 12 genera represented only 9% of the total number of families and genera, respectively, recorded troughout the gradient, but the two groups of taxa comprised more than 50% of the Importance Value (the sum of the relative density and the relative dominance) of all measured stems. Moreover, the results suggest that low species richness seems to be associated with the dominance of one or few species. Stand-level wood density (WD) of trees decreased significantly with increasing elevation. WD is an indicator of trees'life history strategy. Its decline suggests a change in the functional composition of the forest with increasing altitude. The Canonical Correspondence Analysis (CCA) indicated a distinction of the studied forests on the basis of their altitudinal levels and geographic location, and revealed different ecological responses by the forests, to environmental variables along the altitudinal gradient. The variation in species composition, in terms of basal area among stands, was controlled primarily by elevation and secondarily by rainfall and soil conditions. There are other interacting factors not considered in this study like disturbance regime, biological interactions, productivity, and dispersal history, which could affect the structure and composition of the forests in the altitudinal gradient. In conclusion, it appears that the structural and floristic variability observed in the studied transect is produced by a combination of different climates and randomly expressed local processes interacting across a complex physical landscape.     

Forest community survey and the structural characteristics of forests in China

Most of the world’s terrestrial biome types can be found in China. To systematically investigate species composition and structure of China’s forest communities, we launched a long‐term project consisting forest vegetation surveys across China’s mountains in the mid 1990s. Over the study period, we have conducted vegetation surveys for 65 mountains and collected vegetation data from about 1500 forest plots, using consistent sampling protocols. In this paper we first introduce the aims, protocols, and major research themes of the project, and then describe the major characteristics of forest communities and their geographic patterns and climatic controls. As latitude increased, diameter at breast height (DBH) and height of trees increased, while individual density of trees and woody species richness decreased. Total basal area (TBA) of trees and species richness of herbs did not vary with latitude. Contemporary climate seems to drive these patterns: temperature was the leading factor for DBH, precipitation was most important for tree height and individual density, actual evapotranspiration (a surrogate of productivity) determined woody (trees and shrubs) species richness, and rainfall was the major controller of the herb species richness. The species–abundance relationship showed that species dominance (measured by the number of individuals per species) declined significantly from boreal forests to evergreen broadleaf forests from north to south. Our results are in line with the idea that productivity drives woody species richness. Similarly, we find that biomass (measured as TBA) is invariant along the environmental gradients. However, individual density varies dramatically, in contrast to the assumptions underlying the metabolic theory of ecology.     

Seasonal patterns of fine root demography in a cool-temperate deciduous forest in central Japan

In forest ecosystems, fine roots have a considerable role in carbon cycling. To investigate the seasonal pattern of fine root demography, we observed the fine root production and decomposition processes using a minirhizotron system in a Betula-dominated forest with understory evergreen dwarf bamboo. The length density of fine roots decreased with increasing soil depth. The seasonal patterns of each fine root demographic parameter (length density of visible roots, rates of stand-total fine root production and decomposition) were almost the same at different soil depths. The peak seasons of the fine root demographic parameters were observed in the order: stand-total fine root production rate (late summer) > length density of the visible roots (early autumn) > stand-total fine root decomposition rate (autumn, and a second small peak in spring). The fine root production rate was high in the latter part of the plant growing season. Fine root production peaked in late summer and remained high until the end of the tree defoliation season. The higher stand-total fine root production rate in autumn suggests the effect of understory evergreen bamboo on the stand-total fine root demography. The stand-total fine root decomposition rate was high in late autumn. In the snow-cover period, the rates of both fine root production and decomposition were low. The fine root demographic parameters appeared to show seasonal patterns. The fine root production rate had a clearer seasonality than the fine root decomposition rate. The seasonal pattern of stand-total fine root production rate could be explained by both overstory and understory above-ground productivities.     

Plant morphometric traits and climate gradients in northern China: a meta-analysis using quadrat and flora data

Background and Aims

The collection of field data on plant traits is time consuming and this makes it difficult to examine changing patterns of traits along large-scale climate gradients. The present study tests whether trait information derived from regional floras can be used in conjunction with pre-existing quadrat data on species presence to derive meaningful relationships between specific morphometric traits and climate.

Methods

Quadrat records were obtained for 867 species in 404 sites from northern China (38–49°N, 82–132°E) together with information on the presence/absence of key traits from floras. Bioclimate parameters for each site were calculated using the BIOME3 model. Principal component analysis and correlation analysis were conducted to determine the most important climate factors. The Akaike Information Criterion was used to select the best relationship between each trait and climate. Canonical correspondence analysis was used to explore the relationships between climate and trait occurrence.

Key Results

The changing abundance of life form, leaf type, phenology, photosynthetic pathway, leaf size and several other morphometric traits are determined by gradients in plant-available moisture (as measured by the ratio of actual to potential evapotranspiration: α), growing-season temperature (as measured by growing degree-days on a 0 ° base: GDD₀) or a combination of these. Different plant functional types (PFTs, as defined by life form, leaf type and phenology) reach maximum abundance in distinct areas of this climate space: for example, evergreen trees occur in the coldest, wettest environments (GDD₀ < 2500 °Cd, α > 0·38), and deciduous scale-leaved trees occur in drier, warmer environments than deciduous broad-leaved trees. Most leaf-level traits show similar relationships with climate independently of PFT: for example, leaf size in all PFTs increases as the environment becomes wetter and cooler. However, some traits (e.g. petiole length) display different relationships with climate in different PFTs.

Conclusions

Based on presence/absence species data and flora-based trait assignments, the present study demonstrates ecologically plausible trends in the occurrence of key plant traits along climate gradients in northern China. Life form, leaf type, phenology, photosynthetic pathway, leaf size and other key traits reflect climate. The success of these analyses opens the possibility of using quadrat- and flora-based trait analyses to examine climate–trait relationships in other regions of the world.     

A climate change‐induced threat to the ecological resilience of a subtropical monsoon evergreen broad‐leaved forest in Southern China

Recent studies have suggested that tropical forests may not be resilient against climate change in the long term, primarily owing to predicted reductions in rainfall and forest productivity, increased tree mortality, and declining forest biomass carbon sinks. These changes will be caused by drought‐induced water stress and ecosystem disturbances. Several recent studies have reported that climate change has increased tree mortality in temperate and boreal forests, or both mortality and recruitment rates in tropical forests. However, no study has yet examined these changes in the subtropical forests that account for the majority of China's forested land. In this study, we describe how the monsoon evergreen broad‐leaved forest has responded to global warming and drought stress using 32 years of data from forest observation plots. Due to an imbalance in mortality and recruitment, and changes in diameter growth rates between larger and smaller trees and among different functional groups, the average DBH of trees and forest biomass have decreased. Sap flow measurements also showed that larger trees were more stressed than smaller trees by the warming and drying environment. As a result, the monsoon evergreen broad‐leaved forest community is undergoing a transition from a forest dominated by a cohort of fewer and larger individuals to a forest dominated by a cohort of more and smaller individuals, with a different species composition, suggesting that subtropical forests are threatened by their lack of resilience against long‐term climate change.     

Variation in tree growth,mortality and recruitment among topographic positions in a warm temperate forest

Questions: Do the population dynamics of trees differ among topographic positions and, if so, how does topographic position affect the population dynamics of species that are distributed in a topography‐specific manner? Which is the most important life stage in determining vegetation patterns? Location: Primary and secondary warm temperate evergreen broad‐leaved forest (40 ‐ 280 m a.s.l.) on the western part of Yakushima Island, Japan. Methods: Mortality, recruitment, DBH growth and distribution of stems (= 5 cm DBH) in a 2.62‐ha plot were surveyed in 1992 and 2002 to determine the relationships between population parameters and (1) topography and (2) distribution patterns of 17 common tree species. Results: Common species (n = 17) were classified into three distribution pattern groups: group A, distributed mainly on convex slopes; group B, on concave slopes, and group C, not aggregated with respect to topographic position. Stem mortality, recruitment and DBH growth were greater in group A than in group B within each topographic class. The hierarchy of stem mortality among topographic classes for groups A and B was convex > planar > concave. Stem recruitment density was relatively high on the convex and concave slopes, respectively, for groups A and B. Conclusions The topographical positions of adult trees were not always most suited for adult survival and growth. For group A, the distribution pattern of adults was determined in the juvenile stage, while this was not the case for group B. Studies of juvenile stages are important for understanding the demographic basis of vegetation distribution patterns.     

毛竹扩张对次生常绿阔叶林物种组成、结构与多样性的影响

毛竹(Phyllostachys edulis)向邻近次生常绿阔叶林扩张现象明显, 极大地影响了常绿阔叶林的生态功能, 但关于其扩张对常绿阔叶林的群落结构与生物多样性影响的后效研究较少。本文采用时空替代法, 在江西井冈山国家级自然保护区沿毛竹扩张方向, 依次设置毛竹林、竹阔混交林和常绿阔叶林样地, 比较分析了扩张前后群落物种相似性、群落结构和多样性指数等特征。结果表明: (1)毛竹林与常绿阔叶林乔木层、灌木层和草本层的Bray-Curtis相似性指数很小, 分别为0.003、0.046和0.030。(2)毛竹林的垂直结构呈“>”型, 高度12-14 m区间的多度百分比达33.3%, 径级结构集中分布于5-10 cm区间, 达总数的90.0%; 常绿阔叶林的垂直结构为“L”型, 高度2-4 m的物种数占54.3%, 径级分布范围较广, 4个较大径级区间的平均百分比为10.3%。(3)乔木层的Shannon-Wiener指数由常绿阔叶林的2.56降至毛竹林的0.06, 降幅高达98%; 灌木层也由2.58降至2.03, 降幅21%。以上结果说明, 毛竹扩张会导致次生常绿阔叶林群落组成和结构简化、物种多样性下降, 对森林生态系统功能产生负面影响。     

贵州赤水常绿阔叶林不同层次树木空间分布格局和竞争的关系

在贵州赤水桫椤国家级自然保护区的亚热带常绿阔叶林中设置0.96 hm~2的固定样地进行调查,将2299株乔木按树高分级(林木下层、中层、上层),进行空间定位并记录胸径和冠幅等个体指标。采用基于个体间距离的对数相关函数(Paircorrelation functions,PCF)和基于个体胸径、冠幅的标记点格局分析(Marked correlation functions,MCF)空间统计方法检测不同高度层内和层间的空间分布格局和潜在的竞争,结果表明:(1)样地内上层树种呈现随机分布,中下层树种在0—6 m的小尺度内呈聚集分布,在层间关系上表现为0—1 m尺度下显著的正相关关系。(2)在群落内上层个体中没有检测到显著的层内竞争,也未发现其与中、下层树种存在层间竞争关系。(3)群落中、下层树种的层内和层间竞争对两者间空间分布格局和个体大小均产生了一定影响,其相邻个体的胸径和冠幅呈现显著负相关关系。这说明在贵州赤水地区常绿阔叶林中群落中不同层次个体处于不同演替阶段,群落内层内和层间竞争对个体较大的林木上层物种的影响已经非常微弱,而主要发生在中、下层树种内,导致了个体较小的中下层更新树种在层间和层内都出现了小尺度下聚集分布格局,这解释了研究地内不同高度级别树种间竞争关系与共存策略,也验证了标记点格局分析方法在检测植物群落竞争中的敏感性。     

三峡大老岭山地常绿落叶阔叶混交林林隙干扰研究II.林隙干扰的地形格局

 根据对三峡大老岭地区山地常绿落叶阔叶林林隙的调查结果,运用多种方法定量分析和检验了5种地形要素对林隙和3类林隙形成木(GM)各方面特征的空间格局的影响。结果反映了地形对林隙时空格局的影响,和不同类型林隙形成木的响应特征：1）林隙干扰随海拔上升、坡度增大、坡位从山脊到沟谷、坡形由凸到凹而加剧;坡向影响的规律不明显。林隙特征对各地形因素梯度有显著的响应,其中扩展林隙面积、林隙高度、GM数量、种数以及平均胸径是反映地形影响的敏感指标。2）GM的平均胸径、最大胸径和扩展林隙面积与海拔显著正相关;GM平均胸径还与坡位正相关;GM数量沿N→S的坡向梯度减少,而随坡度增大及坡形由凹转凸而增加;GM种类沿坡度和坡形梯度有相同的变化趋势。林隙高度（亦即植被高度）随海拔和坡度增大而减小,但随坡位上升而增大。地形要素对林隙高度和GM平均胸径的空间格局的贡献最大,分别达到75.9%和67.0%。3）折干特征的空间格局受海拔和坡位的显著影响;枯立木的分布特征主要受小地形的坡位和坡形控制;影响翻倒木的最根本地形因素是坡度。     

三峡大老岭山地常绿落叶阔叶混交林林隙干扰研究II.林隙干扰的地形格局

根据对三峡大老岭地区山地常绿落叶阔叶林林隙的调查结果,运用多种方法定量分析和检验了5种地形要素对林隙和3类林隙形成木(GM)各方面特征的空间格局的影响。结果反映了地形对林隙时空格局的影响,和不同类型林隙形成木的响应特征：1）林隙干扰随海拔上升、坡度增大、坡位从山脊到沟谷、坡形由凸到凹而加剧;坡向影响的规律不明显。林隙特征对各地形因素梯度有显著的响应,其中扩展林隙面积、林隙高度、GM数量、种数以及平均胸径是反映地形影响的敏感指标。2）GM的平均胸径、最大胸径和扩展林隙面积与海拔显著正相关;GM平均胸径还与坡位正相关;GM数量沿N→S的坡向梯度减少,而随坡度增大及坡形由凹转凸而增加;GM种类沿坡度和坡形梯度有相同的变化趋势。林隙高度（亦即植被高度）随海拔和坡度增大而减小,但随坡位上升而增大。地形要素对林隙高度和GM平均胸径的空间格局的贡献最大,分别达到75.9%和67.0%。3）折干特征的空间格局受海拔和坡位的显著影响;枯立木的分布特征主要受小地形的坡位和坡形控制;影响翻倒木的最根本地形因素是坡度。