卧龙自然保护区大熊猫栖息地植物群落多样性研究:丰富度、物种多样性指数和均匀度

根据64个植被样方调查资料,分析卧龙自然保护区大熊猫栖息地植物群落多样性特征.结果表明:卧龙自然保护区大熊猫栖息地不同植被类型的物种多样性指数值H'、D和均匀度指数Jsi基本表现出一致的变化趋势:常绿落叶阔叶林＞温性针阔混交林＞落叶阔叶林＞温性针叶林＞亚高山针叶林,而物种丰富度S变化为温性针叶林＞落叶阔叶林＞常绿落叶阔叶林＞亚高山针叶林＞温性针阔混交林.在不同的植物群落中,由于地形地势、坡度、土壤、水热条件等原因,其物种多样性指数不同,但其多样性测度指标除物种丰富度外均呈现出基本一致的变化趋势.随海拔的升高,大熊猫栖息地物种丰富度、多样性指数和均匀度变化先增加,然后下降,最后趋于平稳.坡度不是影响卧龙野生大熊猫栖息地生物多样性的关键因子.不同的坡向其物种丰富度S变化为西＞北＞东＞南,物种多样性指数H'、D呈现西＞南＞北＞东的递降格局,均匀度指数Jsi呈现南＞西＞东＞北的递降格局.在不同的群落中,物种丰富度变化表现为灌木层＞乔木层＞草本层,且42.9%群落中乔木层大于灌木层、64.3%群落中乔木层大于草本层、92.9%群落中灌木层大于草本层,落叶针叶林乔木层树种丰富度小于灌木层和草本层,但其灌木层物种丰富度大于草本层.在同一或不同生长型中,物种多样性指数和均匀度指数变化大体一致.     

不同森林类型物种多样性及影响因子研究

采用丰富度指数、多样性指数、均匀度指数对雾灵山不同森林类型灌木层和草本层的物种多样性进行了研究,并在此基础上用逐步回归方法研究影响森林物种多样性的主要因子。结果表明,在不同森林类型中灌木层和草本层物种多样性由高到低依次为:针阔混交林>落叶阔叶林>针叶林;多数森林类型草本层丰富度指数和多样性指数均高于灌木层,而均匀度指数则相反。影响灌木层物种多样性的主要因子包括林龄、郁闭度和坡向,影响草本层物种多样性的主要因子包括林分公顷株数、郁闭度和土层厚度。     

坡位和密度对桉树林生产力和林下植被多样性的影响

以广东省信宜市池洞镇和水口镇桉树人工林为研究对象,通过样地调查,统计和分析了不同坡 位（上坡位和下坡位）和不同密度（低密度 1 350~1 700 株 /ha、高密度 1 950~2 475 株 /ha）桉树林个体生 长量（树高、胸径、单株材积）、林分蓄积量及其林下植被物种多样性（Margale 丰富度指数、Simpson 优 势度指数、Shannon-Wiener 指数和 Pielou 均匀度指数）。结果表明：（1）坡位显著影响桉树林生产力和林 下植被多样性,下坡位桉树树高、胸径、单株材积和林分蓄积量和林下灌木层物种多样性明显高于上坡 位,但下坡位林下草本层物种多样性低于上坡位;（2）密度对胸径和单株材积有显著影响,但不影响树高 和林分蓄积量,高密度桉树林下灌木层和草本层物种多样性均明显低于低密度桉树林。总体而言,肥力条 件更好的下坡位更利于桉树生长,产量更高,坡位对林下灌木层和草本层物种多样性的影响有所不同;高 密度（1 950~2 475 株 /ha）造林时,增产效果不明显,但存在林下植被多样性下降的风险。     

Forest vegetation responses to climate and environmental change: A case study from Changbai Mountain, NE China

The distribution of plant species has always been altered by changing climatic conditions. Nonetheless, the potential for species’ range shift responses has recently become severely limited, as exceptionally fast temperature changes coincide with a high degree of anthropogenic habitat fragmentation. This study provides rare insights into the effects current temperature increases have on pristine temperate forest ecosystems, using the forests of Changbai Mountain, NE China, as a case study. On the northern slopes of the mountain at elevations between 750 and 2100 m, the composition of trees, shrubs and herbaceous species was recorded on 60 plots in 1963 and 2006/07. Multiple linear regression (MLR) and canonical correspondence analysis (CCA) were used to establish the response of plant diversity and plant distribution patterns to environmental conditions. Climatic factors proved important in explaining the spatio-temporal trends within the vegetation. The composition of dominant trees remained mostly unchanged over the last 43 years, reflecting a very slow response of the forest canopy to environmental change. The composition of young trees, shrubs and herb species showed varied changes in the different forest types. A homogeneous species composition in the cohort of regenerating trees indicates an increased future uniformity in the mixed broadleaved and coniferous forest. The understory vegetation of high elevation birch forests was invaded by floristic elements of the lower-elevation coniferous forests. Both these trends pose potential threats to forests plant diversity. Future research investigating climate change responses in forest canopy composition needs to be based on even longer timescales, while investigations in the near future need to pay particular attention to the changes in the distribution of rare and threatened herbaceous species.     

皆伐前后油松人工林下植物多样性变化及与土壤水分的关系

【目的】探讨油松人工林皆伐前后林下植物多样性的变化及与土壤水分的关系,为在油松林皆伐后植被恢复和发育阶段维持生物多样性、保持林分结构稳定、发挥更高生态效益等方面提供科学依据和经营措施建议。【方法】采用时序研究法,在河北平泉地区选择立地一致的不同林龄油松人工林(32年中龄林、40年近熟林、53年成熟林)和皆伐后不同时间(5、10、24 a)的天然更新林作为研究对象,分析不同生长发育阶段油松人工林下植物物种组成与多样性的变化规律及与土壤水分间的相关性。【结果】1)皆伐前后6种林分样地共出现灌木植物21种,草本植物65种,不同样地林下植物组成存在差异。胡枝子在各林分样地均有出现,且重要值均> 20%,在灌木层优势地位明显;草本层中菊科植物种类最多,有18种,其次是蔷薇科和禾本科,分别为6种和4种。2)不同林分样地林下植物多样性指数均表现为草本层>灌木层,皆伐前随着林龄增加林下植物多样性逐渐增加;皆伐后灌木层植物多样性表现为先下降后增加再下降,且变化幅度明显,伐后10 a灌木层Margalef丰富度指数、Simpson多样性指数、Shannon-Wiener多样性指数和Pielou均匀度指数最大,分别为1.40、0.61、1.24和0.74,与53年样地差异不显著。皆伐后不同时间的天然更新林草本层植物多样性均与伐前53年样地的差异不显著,皆伐对灌木层植物的影响较大。3)不同林地土壤水分变化规律较一致,表现为伐前随林龄增加而逐渐增加,伐后5~10 a仍保持较高水平,伐后24 a出现下降,经相关分析植物多样性指数与土壤水分之间有显著的正相关关系,与草本层的相关性达极显著水平。【结论】伐前林下植物多样性变化主要与林分密度降低、光照条件改善有关,伐后主要与油松天然更新及种间竞争有关。依靠油松天然更新恢复的林地保持了较高的生物多样性,但在皆伐10 a后出现下降的趋势,建议在此时对油松更新苗进行人工抚育、降低密度以维持植物多样性。土壤水分是影响植物多样性的关键生态因子,良好的土壤水分条件和林下植被的恢复和发展可以相互促进。     

湘中丘陵区3种林分林下植物多样性与土壤特性研究

在湘中丘陵区选取针叶林、针阔混交林和阔叶林为研究对象,研究三种林分林下植被多样性、土壤理化性质及其相关关系。结果表明:三种林分林下植物多样性总体表现为灌木层明显高于草本层,阔叶林、针阔混交林高于针叶林。土壤有机质、全N和全P含量基本表现为随土层加深而下降的规律。土壤含水率与各项多样性指标不相关,土壤容重、p H值与灌草层各多样性指数呈负相关关系,有机质、全N与灌木层均匀度指数呈负相关关系,有机质与草本层均匀度指数呈极显著正相关关系(P0.01),全P、全K与灌木层多样性指数呈显著正相关关系(P0.05)。     

Deciduous and deciduous—evergreen forests in Northeast China

Two types of forests in Northeast China is divided in this paper, that is, the deciduous forests in the northern part and the deciduous—evergreen forests in the eastern part. Both distributions of the two types of forests have also been presented. Meanwhile, the development and succession as well as components of forests have been studied in detail. In the end, the vertical distribution of the deciduous forests have been shown, in which, the near—temperate cold temperate deciduous coniferous forests are distributing in the low elevation area between 450m—600m from the north to the south, the typical Siberian cold temperate deciduous coniferous forests are widely distributing from 450m–820m in the north to 600m-1050m in the south, the humid cold temperate deciduous coniferous forests can only be found in high elevation area from 820m–1100m in the north to 1050m–1380m in the south, the cold temperate deciduous coniferous open forests can seldom appear at the top of a few peaks.     

DECIDUOUS AND DECIDUOUS-EVERGREEN FORESTS IN NORTHEAST CHINA

Two types of forests in Northeast China is divided in this paper,that is,the decidu-ous forests in the northern part and the deciduous-evergreen forests in the eastern part.Both distri-butions of the two types of forests have also been pre sented.Meanwhile,the development and suc-cession as well as components of forests have been studied in detail.in the end,the vertical distribu-tion of the deciduous forests have been shown,in which,the near-temperate cold temperate decidu-ous coniferous forests are distributing in the low elevation area between 450m—600m from the northto the south,the typical siberian cold temperate deciduous coniferous forests are widely distributingfrom 450m—820m in the north to 600m—1050m in the south, the humid cold temperate deciduousconiferous forests can only be found in high elevation area from 820m—1100m in the north to1050m—1380m in the south,the cold temperate deciduous coniferous open forests can seldom ap-pear at the top of a few peaks.     

Different response to environmental factors and spatial variables of two attributes (cover and diversity) of the understorey layers

We investigated the relationships among the vertical layers of a temperate forest and the power of environmental and spatial factors to explain the variation in two attributes of shrub and herbaceous layers: cover and diversity. In the study site, 102 square plots with sides of 20 m were established in a stratified random design. Among the environmental factors we studied overstorey related factors, soil attributes and topographic related variables. To use the space as an explanatory variable, we applied the Principal Coordinates of Neighbourhood Matrices method. Variation partitioning with regression analyses was used to discover which variables better explained variation in cover and diversity within the shrub and herbaceous layers. The spatial patterns displayed by cover and diversity in the shrub and herbaceous layer were more similar between both layers than within the same layer. Along the same lines, the amount of variance explained by all the environmental (overstorey, soil and topography) and spatial variables together was higher in the models of cover than in those of diversity. The differences in the explained variation were primarily due to the higher spatial fraction in the models of cover. In general, shrub and herbaceous cover was higher on southern slopes with a more diverse overstorey, high values of soil temperature and low values of litter cover. Otherwise, higher values of shrub and herbaceous diversity were found on steep slopes with low values of leaf litter cover. However, while higher values of shrub diversity were found on southern slopes, herbaceous values were more patchily distributed. The differences in the amount of variation explained by the spatial variables in both attributes (cover and diversity) indicate their different spatial arrangement at the scale which we considered. While values of cover were more continuous in space, those of diversity showed a patchy distribution of higher values. The presence of this spatial component could be interpreted as the importance of seed dispersal or unmeasured environmental variables. The results indicate that the lack of management in temperate forests allows species movement in a heterogeneous environment favouring higher values of cover and diversity in the understory layers.     

Understory plant diversity assessment of <Emphasis Type="Italic">Eucalyptus</Emphasis> plantations over three vegetation types in Yunnan,China

Biodiversity in managed plantations has become an important issue for long-term sustainability of ecosystems. The environmental effects of plantations comprised of fast-growing introduced trees have been vigorously debated. On one hand, monocultures have been said to exhaust resources, resulting in decreased biodiversity. Conversely, it has been stated that monocultures may favor regeneration of undergrowth plants from surrounding forests, increasing biodiversity. In order to clarify the effects of planting Eucalyptus trees on species composition, diversity, and functional type of understory vegetation in Yunnan province, a field trial was implemented to compare Eucalyptus plantations (EPs) with two other local current vegetation types (secondary evergreen forests (SEs), and abandoned farmlands (AFs)). Each vegetation type was sampled in each of three elevational ranges (low = 1,000–1,400 meters above sea level (masl), medium = 1,400–1,800 masl, and high = 1,800–2,200 masl). Sample sites within each elevational range had similar environmental characteristics (slope, aspect, etc.). Thus, we sampled three vegetation types at each of three sites at each of three elevations for a total of 27 plots. We calculated relative abundance and importance value of species and diversity indexes to evaluate differences among local current vegetation types and elevational ranges, employing multivariate ordination analyses and other methods such as Analyses of Variance (ANOVA) and Indicator Species Analysis. We found that fast growing introduced Eucalyptus plantations led to reduced plant diversity in the study area, and that rare or threatened species were recorded almost exclusively in the SE plots, being essentially absent from the EP and AF plots. The understory plant diversity did not correlate with the altitude gradient significantly. Eucalyptus plantations (EPs) have a simpler community structure than that of either secondary evergreen forests (SEs; similar to natural state) or abandoned farmlands (AFs). No variable significantly explained variation of the understory shrub layer, but soil moisture-holding capacity and overstory coverage were significant in explaining variation of the understory herb layer, suggesting that the study of soil physical properties is necessary for better understanding of their importance in Eucalyptus plantations and other local current vegetation types.     

Biomass and production of fine roots in Japanese forests

To better understand the control of fine-root dynamics in Japanese forests, we reviewed studies conducted in Japan on fine-root biomass and production. Most of the data on fine-root biomass were obtained for conifer plantations in limited regions; the average fine-root biomass of dominant trees ranged from ∼50 g m₋₂ for Pinus species (n = 3) to ∼600 g m₋₂ for Cryptomeria japonica (n = 4) and Chamaecyparis obtusa (n = 3). These values are comparable with or less than those reported for other temperate forests mainly in North America or Europe. Information on fine-root production in Japanese forests remains limited. Fine-root production accounted for ∼30% of the net primary productivity in two deciduous forests, but similar data was not reported for coniferous forests in Japan. In Japanese forests, slope position is a key parameter controlling fine-root biomass that is greater on upper slopes than on lower slopes, probably because soil resource availability decreases upslope. Studies in manipulated soil environments (e.g., removing throughfall to simulate drought) also suggested that fine-root biomass and production were greatly affected by altered soil environments. Physiological control of fine-root dynamics was recently discussed via anatomical analyses of Chamaecyparis obtusa. Findings from Japanese studies generally support data on fine-root biomass and production obtained from other temperate regions. Further attempts to elucidate the influence of slope position (soil resource availability) on fine-root production would be useful to gain a more detailed understanding of the fine-root dynamics in Japanese forests.     

Exploring the “last biotic frontier”: Are temperate forest canopies special for saproxylic beetles?

Conserving saproxylic beetles in temperate forests will require a better understanding of habitat requirements. So far, quantitative community studies have rarely considered their vertical requirements. In comparison with the tropical forest canopy, it remains to be seen whether a comparably high level of beetle diversity exists in the temperate forest canopy.We compared saproxylic beetle assemblages at two vertical levels in three temperate French forests. Two datasets originated from emergence traps of pine and oak deadwood substrates (mid-canopy and forest floor branches) in lowland forests. The third compared flying beetle fauna at mid-canopy and understory levels using pairs of flight interception traps in beech-fir mountain forests.Our study provided contrasting results regarding the contribution of each stratum to biodiversity. Whereas higher abundance and species richness were apparent in understory samples in beech-fir stands and in oak branches, no difference for richness - or even the opposite pattern for abundance - was observed in pine branches. A significant inter-strata dissimilarity was revealed in all datasets. Each stratum harbored specialist taxa. Exclusive canopy species accounted for 20-40% of all species. In accordance with dissimilarity partitioning, arboreal saproxylic beetle communities were not just nested subsets of ground assemblages.It is likely that microhabitat requirements, food availability and other non-resource-based factors (microclimate preference, species interactions) drive the stratification of beetle assemblages.Our results lend support (i) to the recommendation of a multi-strata sampling strategy for forest insects and (ii) to management practices in favour of valuable canopy micro-habitats.     

Understory plant communities of boreal mixedwood forests in western Canada: Natural patterns and response to variable-retention harvesting

We examined patterns of variation in richness, diversity, and composition of understory vascular plant communities in mixedwood boreal forests of varying composition (broadleaf, mixedwood, conifer) in Alberta, Canada, before and for 2 years following variable-retention harvesting (clearcut, 20 and 75% dispersed green tree retention, control). Broadleaf-dominated forests differed from mixedwood or conifer-dominated forests in that they had greater canopy cover, litter depth, soil nitrogen, warmer soils, as well as greater shrub cover, herb and shrub richness and diversity (plot scale). In contrast, conifer, and to a lesser extent mixedwood, forest had greater β diversity than broadleaf forest. Overall, mixedwood and conifer forests were similar to one another, both differed from broadleaf forest. Several species were found to be significant indicators of broadleaf forest but most of these also occurred in the other forest types. Understory composition was related to canopy composition and edaphic conditions. Variable-retention harvesting had little effect on understory cover, richness, or diversity but resulted in reduced richness and β diversity at a larger scale. The clearcut and 20% treatments affected composition in all forest types. Early successional species and those common in disturbed sites were indicators of harvesting while evergreen, shade-tolerant understory herbs were indicators of the control forest and 75% retention harvest. We conclude that it is important to maintain a range of variation in canopy composition of mixedwood forests in order to conserve the associated understory communities. The presence of conifers in these forests has a particularly important influence on understory communities. The threshold for a lifeboat effect of variable-retention harvesting is between 20 and 75% retention. Examination of richness and β diversity at a variety of scales can provide interesting information on effects of harvesting on spatial reorganization and homogenization of understory plant communities.     

Effect of abiotic factors on understory community structures in moist deciduous forests of northern India

Understory vegetation controls, in a significant way, the regeneration of overstory trees, carbon sequestration and nutrient retention in tropical forests. Development and organization of understory vegetation depend 3n climate, edaphic and biotic factors which are not well correlated with plant community structures. This study aimed to ~xplore the relationships between understory vegetation and abiotic factors in natural and planted forest ecosystems. A non-metric multidimensional scaling （NMS） ordination technique was applied to represent forest understory vegetation among five forest communities, i.e., a dry miscellaneous forest （DMF）, a sal mixed forest （SMF）, a teak plantation （TP）, a low-land miscellaneous forest （LMF） and a savanna area （SAV） of the Katerniaghat Wildlife Sanctuary, located in northern India. Microclimatic variables, such as photosynthetically active radiation （PAR）, air temperature （AT）, soil Lemperature （ST）, ambient atmospheric CO2 concentration, absolute air humidity （AH）, physical and chemical soil ~roperties as well as biological properties were measured. Understory species were assessed via 100 random quadrats （5 m x 5 m） in each of the five forests in which a total of 75 species were recorded encompassing 67 genera from 37 families, consisting of 32 shrubs and 43 plant saplings. DMF was the most dense forest with 34,068 understory individuals per ha of different species, whereas the lowest understory population （13,900 per ha） was observed in the savanna. Ordination and correlation revealed that microclimate factors are most important in their effect compared to ~daphic factors, on the development of understory vegetation in the various forest communities in the north of India.     

Comparison of tree growth and undergrowth development in aerially seeded and planted Pinus tabulaeformis forests

Direct seeding is a less expensive practice than planting and has the potential to become a viable alternative to transplanting for afforestation and regeneration purposes. As an effective and a less costly regeneration method, aerial seeding has been applied with several tree species. As early as 1956, Chinese people engaged in aerial seeding and stands with a total of 2.97×10⁷ hm² have been developed up to 2004. Our study tested whether the growth of planted Chinese pine (Pinus tabulaeformis Carr.) seedlings and its undergrowth development in northwest aspects differ from that of aerially sown seedlings on the northern and northwestern aspects of slopes. In 2007, we collected data such as height, diameter at breast height (DBH), clear bole height and canopy widths of trees, abundance, coverage, and frequency of shrubs and herbs from 21-year-old planted Chinese pine stands on a northwestern aspect (PNW), aerially sown stands in a northwest aspect (ANW) and aerially sown stands in a northern aspect (AN). Results showed that the relation of crown area and mean DBH was best fitted by a double inverse model for the ANW and AN forests and by a quadratic model for the PNW forest. There was no difference in the growth between ANW and AN forests, while growth was significantly higher in the PNW forest than in the ANW and AN forests. That was consistent with the Sorenson diversity indices in the shrub and herb layers, indicating that there was a large number of the same species in both aerially seeded stands, although their locations were different. Both the number of species in the undergrowth and the Shannon-Wiener index in the shrub layer were higher in the PNW stands than in the ANW and AN stands. Dominant families for all three stands were Rosaceae and Compositae in the shrub and herb layer, respectively. The dominant species for all three stands was Spiraea pubescens in the shrub layer, while the dominant species was different from each other in the three stands. The discrepancy in diversity and composition of species in the herb layer show that herbs are sensitive to shrubs in the three forests. High mortality and skewed diameter distributions reflect severe competition and too high a density in the aerially seeded forests. Thus, aerial seeding is a viable and effective regeneration technique, but management practices, such as thinning, should be applied to these forests.     

Influence of tree species on understory vegetation diversity and mechanisms involved—A critical review for temperate and boreal forests

Tree species composition is a primary attribute of forest ecosystems, and is often manipulated by silvicultural practices. Forest management to diversify tree species is now being promoted to favor biodiversity. To assess the soundness of this policy we reviewed and analyzed the literature on the relationship between tree species composition and floristic diversity, including the mechanisms involved therein. Coniferous forests generally provide less diversified vascular understories than broadleaved forests. At the tree species scale, there are not enough reports to draw firm conclusions on the effect of any particular species. Mixing of deciduous and coniferous tree species generally affects understory diversity, but in almost all cases maximum diversity is observed in one of the pure stands, not in mixed stands. Understory vegetation is influenced by overstory composition and structure through modifications of resource availability (light, water and soil nutrients) and other effects, such as physical characteristics of the litter layer. Overstory light transmittance and diverse properties of forest litter are factors that have been most fully studied to date, but other factors such as throughfall water quantity and chemistry may also play a role. While the relative importance of mechanisms that account for the effect of overstory on understory biodiversity has often been discussed, these mechanisms have rarely been the subject of formal experiments. Overall, varying management practices and site attributes make it difficult to generalize results. They combine with the effects of tree species in influencing understory vegetation diversity, but they have been rarely considered. Future research is needed to gain a better understanding of the relationship between overstory and understory diversity and establish general laws.     

The potential of hinoki (Chamaecyparis obtusa [Sieb. et Zucc.] Endlicher) plantation forests for the restoration of the original plant community in Japan

We estimated the potential of plantation forests for the restoration of the original plant community. We compared the understory vegetation in hinoki (Chamaecyparis obtusa [Sieb. et Zucc.] Endlicher) plantations at the understory re-initiation stage and in adjacent natural forests. To estimate the effect of the original natural forests on the understory species composition of plantation forests, we established study sites in five types of natural forests (mature evergreen broadleaf, mature deciduous broadleaf, mature evergreen coniferous, immature deciduous broadleaf warm-temperate, and immature deciduous broadleaf cool-temperate) and nearby plantation forests. The understory vegetation of the plantation forests had a higher species richness, a higher proportion of early-seral species, and a higher proportion of herb or fern species than the natural forests. The differences between natural and plantation forests varied according to the species composition of the natural forests. The composition of the understory vegetation of the plantations at the understory re-initiation stage was similar to that of the immature deciduous forests. The characteristics of immature, disturbed forests remained in the understory vegetation of the hinoki forests. No great loss of species was observed. Our findings suggest that most of the original forest species still survive in the understory of the plantation forests. These forests have the potential to follow the successional pathway to broadleaf or mixed forests via thinning or clear-cutting without planting.     

Tree morphology responds to neighbourhood competition and slope in species-rich forests of subtropical China

Trees are able to respond to their local biotic and abiotic environment with morphological adjustments which improve resource acquisition and, thus, growth. In forests, light is broadly recognised as one of the major factors determining growth, and morphological responses comprise changes in crown architecture and stem stature. On sloping terrain, the interplay of phototropism and gravitropism may further affect morphological growth characteristics. However, different tree species are expected to show species-specific responses. In this study, we analysed three growth characteristics of tree individuals belonging to four species of two functional groups (evergreen: Schima superba, Castanopsis eyrei, deciduous: Quercus serrata var. brevipetiolata, Castanea henryi) in a species-rich Chinese subtropical forest. Crown projection area, relative crown displacement and stem inclination were related to biotic (local species richness, functional richness, competition, stand age) and abiotic (slope aspect and inclination, soil depth) variables in the local neighbourhood of the tree individuals. We hypothesised that (i) there are species-specific differences in the morphological response of crown architecture and stem stature and (ii) that crown size and asymmetry as well as stem inclination are influenced by both, biotic and abiotic factors. In contrast to our expectations we were unable to reveal any species-specific differences in any of the three growth characteristics. The results of mixed effects models showed that crown area was mainly affected by the target tree's dbh and biotic variables related to neighbours (competition, functional diversity), whereas stem inclination was mainly influenced by slope. Relative crown displacement was influenced by both, biotic and abiotic variables. We conclude that growth responses resulting in crown displacement and stem inclination seem to be an important mechanism to ameliorate foraging for light in our study area, but that these responses appear to be species-independent. The interplay of stem inclination and crown displacement allows for a plastic response of tree individuals in biotically and abiotically heterogeneous environments. Our results indicate that forest management in this region should focus on functionally diverse stands which are promoting crown area positively resulting in increased growth rates of individual trees.     

岷江上游干旱河谷区植被多样性与环境因子的相关性研究

对岷江上游干旱河谷区植被多样性与环境因子相关研究表明：1）阴、阳坡灌、草丛植物群落物种α多样性指标均随海拔升高表现出明显的增加趋势,阳坡呈现出中间低两头高的海拔梯度格局;阴坡总体呈现直线上升的趋势。2）该区土壤肥力总体水平高低表现为：中上部〉中部〉下部〉中下部、阴坡〉阳坡。低海拔地区土壤破碎,土壤含水量和土壤肥力极低,高海拔地区的土壤水分含量和土壤肥力都相对较高,立地条件也较适宜植物的生长。3）植被多样性与环境因子的相关分析表明,海拔、坡向、坡度、土壤含水量、速效N、速效K、有机质、全N、全K与灌丛群落多样性和生物量均呈正相关关系,而pH值、速效P、全P、全Ca与多样性和生物量呈负相关关系。通过逐步回归分析和主成分分析筛选出环境主导因子为全N、速效P、土壤含水量和速效N。     

Selective harvesting at rational intervals promotes carbon sequestration in temperate coniferous and broad-leaved mixed forests in China

Evidence-based selective cutting at prescribed intervals as part of good forest management can enhance the carbon sequestration capacity of the forest. The effect of forest management on carbon sequestration has, however,not been quantified. Thus, carbon content of various organs was measured for 323 tree species, 247 shrub species, and233 herb species in seven temperate coniferous and broadleaved mixed forests that were subjected to selective cutting with restoration durations of 100, 55, 45, 36, 25, 14, and6 years to explore dynamic changes in carbon storage. The results showed that biomass carbon allocation in different organs followed a pattern: trunk root branch leaf for all forests. With longer restoration durations, more carbon accumulated in different organs and in soils. Interestingly,when the restoration duration exceeded 50 years, carbon storage in ecosystem was larger than that in primary forests with 100-year cutting intervals, suggesting that a reasonable selective cutting interval can increase forest carbon sequestration. Mean diameter at breast height(DBH) and forest carbon storage were significantly positively correlated, and carbon storage of selectively cut forests exceeded that of primary forests when the stand mean DBH exceeded 15.66 cm. Therefore, mean DBH of forests can be an indicator for combining sustainable forest management and forest carbon sequestration. Additionally, the classic coefficients of 0.45 and 0.50 used to estimate carbon sequestration underestimated values by 2.65% and overestimated by 8.16%, respectively, in comparison with the measured carbon content from different plant organs.