Influence of light and soil moisture on Sierran mixed-conifer understory communities

Sierra Nevada forests have high understory species richness yet we do not know which site factors influence herb and shrub distribution or abundance. We examined the understory of an old-growth mixed-conifer Sierran forest and its distribution in relation to microsite conditions. The forest has high species richness (98 species sampled), most of which are herbs with sparse cover and relatively equal abundance. Shrub cover is highly concentrated in discrete patches. Using overstory tree cover and microsite environmental conditions, four habitats were identified; tree cluster, partial canopy, gap, and rock/shallow soil. Herb and shrub species were strongly linked with habitats. Soil moisture, litter depth and diffuse light were the most significant environmental gradients influencing understory plant distribution. Herb cover was most strongly influenced by soil moisture. Shrub cover is associated with more diffuse light, less direct light, and sites with lower soil moisture. Herb richness is most affected by conditions which influence soil moisture. Richness is positively correlated with litter depth, and negatively correlated with direct light and shrub cover. Disturbance or management practices which change forest floor conditions, shallow soil moisture and direct light are likely to have the strongest effect on Sierran understory abundance and richness.     

Upscaling hypotheses on herbivore damage in plants facing environmental stress: Variation among scales and plant enemies in a relict tree

The few existing analyses of broad-scale variation in plant–herbivore interactions are largely exploratory and not based on hypotheses on the effect of varying environmental conditions on the patterns of herbivore damage. However, there are two established hypotheses that relate herbivore damage and environmental stress mostly tested at the within-population level: the Plant Stress Hypothesis (PSH) and the Plant Vigor Hypothesis (PVH). To examine if support for the PSH holds true at broader scales, we tested it at the micro- (among individuals), meso- (between habitats) and macroscale (between geographical regions, Iberia and Macaronesia). We measured plant stress and leaf damage by different natural enemies (chewers, miners and pathogens) in 12 populations across the range of the relict tree Prunus lusitanica. Results regarding the proportion of leaves attacked by any enemy showed no support for the PSH at either micro or mesoscale, observing instead higher damage in less stressed individuals within populations and in high-quality habitats. However, the latter was true exclusively within the Macaronesian region, highlighting the important effect of the type of abiotic stress on plant susceptibility to herbivory. At the macroscale, alternatively, results showed support for the PSH: we observed a higher proportion of leaves attacked in Macaronesia than in Iberia, where plants unexpectedly exhibited greater stress symptoms. Among-scale inconsistencies may respond to the effect of distinct climatic factors governing both plant and herbivore dynamics at large scales, particularly in species with distributional ranges across contrasting climatic regions such as P. lusitanica. Finally, different plant enemies showed different patterns of damage, corroborating the need to study them separately to achieve consistent generalizations of these hypotheses.     

Stem and leaf hydraulics of congeneric tree species from adjacent tropical savanna and forest ecosystems

Leaf and stem functional traits related to plant water relations were studied for six congeneric species pairs, each composed of one tree species typical of savanna habitats and another typical of adjacent forest habitats, to determine whether there were intrinsic differences in plant hydraulics between these two functional types. Only individuals growing in savanna habitats were studied. Most stem traits, including wood density, the xylem water potential at 50% loss of hydraulic conductivity, sapwood area specific conductivity, and leaf area specific conductivity did not differ significantly between savanna and forest species. However, maximum leaf hydraulic conductance (K _leaf) and leaf capacitance tended to be higher in savanna species. Predawn leaf water potential and leaf mass per area were also higher in savanna species in all congeneric pairs. Hydraulic vulnerability curves of stems and leaves indicated that leaves were more vulnerable to drought-induced cavitation than terminal branches regardless of genus. The midday K _leaf values estimated from leaf vulnerability curves were very low implying that daily embolism repair may occur in leaves. An electric circuit analog model predicted that, compared to forest species, savanna species took longer for their leaf water potentials to drop from predawn values to values corresponding to 50% loss of K _leaf or to the turgor loss points, suggesting that savanna species were more buffered from changes in leaf water potential. The results of this study suggest that the relative success of savanna over forest species in savanna is related in part to their ability to cope with drought, which is determined more by leaf than by stem hydraulic traits. Variation among genera accounted for a large proportion of the total variance in most traits, which indicates that, despite different selective pressures in savanna and forest habitats, phylogeny has a stronger effect than habitat in determining most hydraulic traits.     

How does herbivory affect individuals and populations of the perennial herb Paeonia officinalis?

In this study we quantified variability in foliage herbivory and pre-dispersal seed predation and its effects on plant performance and demography in populations of a rare and protected perennial herb, Paeonia officinalis. An individual-based survey was performed during four years in four populations, which contained plants in both open habitat and woodland. We detected marked spatial and temporal variation among and within populations in foliage herbivory (by insects) and pre-dispersal seed predation (by insects, rodents and Roe Deer). Foliage herbivory decreased with plant demographic stages in open habitats, from seedlings to reproductive individuals, but no significant trend was detected in woodland habitats. This may be due to different demographic origin of larger vegetative plants in this habitat. Depending on demographic stage, herbivory was higher in open habitats or not significantly different between habitats. This suggests differences in herbivore abundance in different habitats within sites. Pre-dispersal seed predation remained weak and did not depend on habitat. We did not detect any consequence of foliage herbivory on seedling mortality and individual growth in our study. Our results illustrate the need to investigate plant-herbivore interactions over several years in distinct populations in order to more accurately evaluate herbivore impact on plant population dynamics.     

Assessing habitat suitability for the translocation of Ochrosia tahitensis (Apocynaceae), a critically endangered endemic plant from the island of Tahiti (South Pacific)

Reintroduction or translocation of threatened plant species, as part of in situ conservation efforts, often failed because of the lack or the poor quality of remaining natural habitats due to human disturbances and invasion by alien species, especially in island ecosystems. We conducted a study on Ochrosia tahitensis (Apocynaceae), a critically endangered endemic small tree in the tropical high volcanic island of Tahiti (French Polynesia, South Pacific) to find the most suitable sites for future translocation. Distribution models were produced based on climate, topography, and plant community inventories (i.e. species composition and abundance, canopy height and openness, basal area of woody species) of the few remnant populations. Results show that this species, comprising 32 reproductive trees within 16 populations known in the wild, remains restricted to a few ecological refuges representing a very small part of its potential ecological range located on the northwest side of the island, and shares its current habitats with a set of more common native woody species found in mesic-wet forests. The use of native plant communities as a proxy for habitat suitability along with species distribution modelling can enhance translocation success in island ecosystems, but only if the major threats causing population decrease, mainly forest destruction and fragmentation and invasive alien species, are effectively managed.     

Physiological synecology of tree species in relation to geographic distribution and ecophysiological parameters at the Atlantic forest periphery in Brazil: an overview

This paper provides a synthesis of the three papers published in the series Ecophysiology of selected tree species in different plant communities at the periphery of the Atlantic forest of SE – Brazil (Trees, this issue). We reviewed data obtained for seven tree species, belonging to the legume family and the genus Clusia of the Clusiaceae. These groups were chosen because legumes are the most abundant tree species in the Atlantic forest complex (except in the open restingas), and the genus Clusia is reportedly of utmost ecological importance as nurse plants in several habitats of the complex. These species were surveyed along one or more of several forest and open habitats at the margin of the Atlantic rain forest (open restingas, restinga dry forest, inselberg, semideciduous dry forest) and indicated the following general patterns: (1) at the intraspecific level, ecophysiological performance often (but not always) varied largely in both time and space; (2) at the interspecific level, ecophysiological performance was often (but not always) related positively to species dominance in the community; and (3) at both levels, ecophysiological performance was not related to the geographic distribution patterns, i.e., generalists and specialists did not form groups of similarly behaving plants in regard to ecophysiology. We discuss the implications of these findings, compare them with earlier studies, and suggest that ecophysiological research in the Atlantic rain forest complex could enhance its explanatory power by increasing spatial and temporal scales of observation.     

Understorey gaps influence regeneration dynamics in subtropical coastal dune forest

Dominant understorey species influence forest dynamics by preventing tree regeneration at the seedling stage. We examined factors driving the spatial distribution of the monocarpic species Isoglossa woodii, a dominant understorey herb in coastal dune forests, and the effect that its cover has on forest regeneration. We used line transects to quantify the area of the forest understorey with I. woodii cover and with gaps in the cover. Paired experimental plots were established in semi-permanent understorey gaps with I. woodii naturally absent and in adjacent areas with I. woodii present to compare plant community composition, soil, and light availability between the two habitats. Isoglossa woodii was widespread, covering 65–95% of the understorey, while gaps covered the remaining 5–35% of the area. The spatial distribution of this species was strongly related to tree canopy structure, with I.␣woodii excluded from sites with dense tree cover. Seedling establishment was inhibited by low light availability (<1% of PAR) beneath I.␣woodii. When present, I. woodii reduced the density and species richness of tree seedlings. The tree seedling community beneath I. woodii represented a subset of the seedling community in gaps. Some species that were found in gaps did not occur beneath I. woodii at all. There were no significant differences between the sapling and canopy tree communities in areas with I. woodii gaps and cover. In the coastal dune forest system, seedling survival under I. woodii is dependent on a species’ shade tolerance, its ability to grow quickly during I. woodii dieback, and/or the capacity to regenerate by re-sprouting and multi-stemming. We propose a general conceptual model of forest regeneration dynamics in which the abundant understorey species, I. woodii, limits local tree seedling establishment and survival but gaps in the understorey maintain tree species diversity on a landscape scale.     

Conservation value of degraded habitats for forest birds in southern Peninsular Malaysia

Clearance of tropical forest for agricultural purposes is generally assumed to seriously threaten the survival of forest species. In this study, we quantified the conservation value, for forest bird species, of three degraded habitat types in Peninsular Malaysia, namely rubber tree plantations, oil palm plantations, and open areas. We surveyed these degraded habitats using point counts to estimate their forest bird species richness and abundance. We assessed whether richness, abundance, and activities of different avian dietary groups (i.e. insectivores and frugivores) varied among the habitats. We identified the critical habitat elements that accounted for the distribution of forest avifauna in these degraded habitats. Our results showed that these habitats harboured a moderate fraction of forest avifauna (approximately 46–76 species) and their functions were complementary (i.e. rubber tree plantations for moving; open habitats for perching; shrubs in oil palm plantations for foraging). In terms of species richness and abundance, rubber tree plantations were more important than oil palm plantations and open habitats. The relatively high species richness of this agricultural landscape was partly due to the contiguity of our study areas with extensive forest areas. Forecasts of forest-species presence under various canopy cover scenarios suggest that leaving isolated trees among non-arboreal crops could greatly attract relatively tolerant species that require tree canopy. The conservation value of degraded habitats in agricultural landscapes seems to depend on factors such as the type of crops planted and distance to primary forest remnants.     

Vegetation and plant food reconstruction of lowermost Bed II, Olduvai Gorge, using modern analogs

Vegetation and plant foods for hominins of lowermost Bed II, Olduvai Gorge were modeled by examining vegetation in modern habitats in northern Tanzania (Lake Manyara, Ngorongoro, Serengeti) that are analogous to the paleolandscape in terms of climate, land forms, and soil types, as indicated by previous paleoenvironmental studies of Olduvai. Plant species in the modern habitats were identified in a series of sample plots, and those known to be eaten by modern humans, chimpanzees, or baboons were considered potentially edible for early hominins. Within the 50-80 kyr deposition of lowermost Bed II, periods of drier climate were characterized by low lake stands and a broad eastern lacustrine plain containing a mosaic of springs, marsh, woodland, and edaphic grassland. Based on results of this study, plant food diversity in each of those habitats was relatively low, but the mosaic nature of the area meant that hominins could reach several different habitat types within short distances, with access to potential plant foods including marsh plants, grass grains, roots, shrub fruits, edible parts from palms, leafy herbaceous plants, and Acacia pods, flowers, and gum. Based on Manyara analogs, a greater variety of plant foods, such as tree fruits (e.g., Ficus, Trichilia) and the roots and fruits of shrubs (e.g., Cordia, Salvadora) would be expected further east along the rivers in the lacustrine terrace and alluvial fans. Interfluves of the alluvial fans were probably less wooded and offered relatively fewer varieties of plant foods, but there is sparse paleoenvironmental evidence for the character of Olduvai's alluvial fans, making the choice of appropriate modern analogs difficult. In the western side of the basin, based on modern analogs in the Serengeti, riverine habitats provided the greatest variety of edible plant food species (e.g., Acacia, Grewia, Justicia). If the interfluves were grassland, then a large variety of potentially edible grasses and forbs were present seasonally. Periods of wetter climate resulted in a much expanded paleolake and a shrinking of the eastern lacustrine plain mosaic into a narrow zone. The dominant landscape features were then forest-lined rivers in the eastern alluvial fans, and rivers in the western side of the paleo-Olduvai basin were also better watered at these times, supporting denser woody vegetation with large varieties of edible fruits, leaves, and underground parts.     

Vegetation diversity, composition and structure in a cattle agro-landscape of Matiguás, Nicaragua

The diversity, composition and structure of vegetation in a cattle landscape in Matiguás, Nicaragua was characterized, and the floristic and structural differences of six types of habitats (secondary forests, riparian forests, charrales, live fences and pastures with high and low tree cover) were compared. A total of 3 949 trees of 180 species and 52 families were recorded. Forty six percent of the total trees reported for the landscape were represented by Guazuma ulmifolia (18.5%), Bursera simaruha (13.2%), Tabebuia rosea (6.3%), Enterolobium cyclocarpum (4.2%) and Albizia saman (3.4%). Many of the dominant species in the landscape were typical of open and disturbed areas. There were significant differences between the different habitats in the patterns of tree species richness, abundance, diversity, structure and floristic composition. The riparian forests had greater tree richness (p=0.0001) and diversity (p=0.0009) than other habitats. The floristic composition varied across habitats. with pairs of habitats sharing between 18.4 and 51.6% of the same tree species, and with clear differences in composition between the forested (riparian and secondary forests) and agricultural habitats. Of the habitats studied, the riparian forests and secondary forests seem to have greatest value for the conservation of the flora in the agropaisaje because they have the greatest species richness, and maintain small populations of endangered species. On the basis of the study, we recommend including agricultural landscapes in strategies to conserve tree diversity and suggest measures to ensure the maintenance of tree diversity in the Matiguas landscape.     

喀斯特常绿落叶阔叶林死亡个体空间分布格局及生境关联

树木死亡在森林动态中发挥着重要作用, 环境因子是影响树木死亡的重要因素。为了阐明喀斯特常绿落叶阔叶林死亡个体空间分布格局及其与环境的相关性, 本研究以木论25 ha森林动态监测样地的两次木本植物调查数据为基础, 分析了死亡个体的物种组成、径级结构、分布格局及其与生境的关联。结果表明, 样地内共有死亡个体17,306株, 隶属57科130属194种; 其中, 死亡率排名前三的科和属分别为八角枫科、蔷薇科、大风子科以及山麻杆属(Alchornea)、火棘属(Pyracantha)、八角枫属(Alangium); 在物种水平上, 山麻杆(Alchornea trewioides)、毛桐(Mallotus barbatus)、野桐(Mallotus japonicus)等死亡率较高。样地内死亡个体的平均胸径为3.83 cm, 最大47.11 cm; 径级分布呈倒“J”型。从分布格局来看, 样地内大部分死亡个体在0-50 m的尺度上呈聚集分布, 部分大径级树木死亡个体趋向于随机分布。生境关联分析发现, 个体死亡率与山顶、陡坡、缓坡、洼地呈正关联的物种数分别为41种、13种、41种和38种, 呈负关联的物种数分别为38种、67种、33种和10种, 与各生境无关联的物种数分别为4种、3种、9种和35种; 多度排名前20的物种其个体死亡率均与4种生境类型呈现出正关联或者负关联; 不同径级个体死亡率都与山顶生境呈正关联, 与缓坡生境呈负关联, 其中5 cm ≤ DBH < 10 cm和10 cm ≤ DBH < 15 cm个体死亡率均与洼地生境呈正关联; DBH ≥ 15 cm个体死亡率与陡坡生境呈正关联, 与洼地生境呈负关联。在喀斯特亚热带常绿落叶阔叶林中, 死亡个体空间分布格局总体表现为聚集分布, 树木死亡受生境作用的影响较大。     

Does insect herbivory on oak depend on the diversity of tree stands?

Studies on the effects of plant diversity on insect herbivory have produced conflicting results. Plant diversity has been reported to cause positive and negative responses of herbivores. Explanations for these conflicting responses include not only various population-level processes but also changes in plant quality that lead to changes in herbivore performance. In a tree diversity experiment, we investigated the effects of tree diversity on insect herbivory on oak in general and whether the effects of tree diversity on herbivore damage are reflected by the performance (leaf consumption, growth) of the generalist herbivore Lymantria dispar. Our study showed that the feeding damage caused by naturally occurring herbivores on oak trees decreased with increasing diversity of tree stands. The performance of L. dispar on oak leaves was not affected by tree diversity, neither in field nor laboratory experiments. Our results can be explained by the various processes behind the hypothesis of associational resistance.     

古尔班通古特沙漠三种生境下梭梭种群的生殖分配特征

对古尔班通古特沙漠梭梭种群进行样地调查,从各构件生物量分配特征、开花和结果特征、不同发育阶段的生殖分配、同化枝与生殖生物量之间关系等方面研究了3种生境下梭梭种群的生殖分配特征。结果表明:3种生境中各构件生物量分配格局均具有显著差异,且变化趋势不一致,梭梭平均生殖分配在0.64%～1.5%;3种生境下,梭梭开花和结果特征均具有显著差异,表现出砾石生境>沙质生境>土质生境。不同生境梭梭生殖分配均随径级的增加变化不同,砾石生境和沙质生境样地随着径级的增加而降低,而土质生境样地随着径级的增加而增加;不同生境类型下梭梭同化枝、生殖生物量与径级的关系不同;梭梭的生殖分配和同化枝生物量之间呈线性或多项式正相关。     

森林次生演替优势种苗木的光可塑性比较研究

本文从研究苗木的叶绿素含量和ＲｕＢＰ羧化酶活性随着光环境的变化而发生改变的规律出发,来探讨森林次生演替优势种苗木的光可塑性大小和对弱光环境的适应能力。各种苗木的叶绿素含量都随着光强度变弱而增加,但如果较长时间生长在弱光环境中,由于叶绿素的合成小于分解,其含量也会逐渐变小。不同的演替阶段优势种苗木的叶绿素含量的增加或减少在量上有一定的区别。以叶绿素含量随着光环境变化的测定值为指标,用模糊数学分析的结果表明,苗木的耐荫性大小顺序是演替后期种（黄果厚壳桂Ｃｒｙｐｔｏｃａｒｙａｃｏｎｃｉｎｎａ）＞演替过渡种（藜蒴Ｃａｓｔａｎｏｐｓｉｓｆｉｓａ）＞演替过渡种（荷木Ｓｃｈｉｍａｓｕｐｅｒｂａ）＞演替先锋树种（马尾松Ｐｉｎｕｓｍａｓｏｎｉａｎａ）;且藜蒴和荷木很接近,稍靠近黄果厚壳桂。马尾松和荷木的ＲｕＢＰ羧化酶活性随着生长环境的光强度的增加,其活性有所增加;但黄果厚壳桂的相应值是在每日直照光１ｈ的光环境中最高。除马尾松外,演替过渡种和后期种的苗木都是在每日直照光１ｈ的光环境中生长最好,这和每日短期照光提高ＲｕＢＰ羧化酶活性的（与没有直照光的环境相比较）同时又不分解叶绿素、不降低其含量有密切的关系。     

Relationships between environment and mountain riparian plant communities associated with two rare tertiary-relict tree species, Euptelea pleiospermum (Eupteleaceae) and Cercidiphyllum japonicum (Cercidiphyllaceae)

Euptelea pleiospermum and Cercidiphyllum japonicum are dominant relictual tree species of the riparian plant communities in the subtropical region of Shennongjia Mountains, central China. Community survey and multivariate analysis were carried out to characterize their ecological ranges and regeneration characteristics, and further to explore the factors determining their present distribution boundaries and the barriers restricting their range expansion. We recorded 303 woody species, among which there were 14 relictual, rare and/or endemic woody species. Results obtained from cluster analysis corroborated the results from non-metric multidimensional scaling (NMS) ordination, classifying the 42 plots into three well-defined associations. Correlation analysis revealed that variation in species composition among associations was partly explained by some physical (altitude, slope, soil temperature) and chemical (available K, NH₄, pH) properties. Multiple regression analyses with data of adults and seedlings with physical and chemical variables revealed contrasting patterns of the two dominant relictual species. Both taxa have a high resprouting rate that keeps the stands stable irrespective of scarcity of seedlings. However, expansion of the distribution range is difficult in such a situation. E. pleiospermum prefers riparian habitats with poor nutrients in the south-facing slope of the Shennongjia Mountains, which may indicate that this species is light-demanding at some life stages and well adapted to a nutrient-poor habitat where competition from other species is limited. The Cercidiphyllum japonicum population was more scattered and fragmented, and preferred riparian habitats on gentle slopes. Both species are favored by the mild and moist microclimate, but the current conditions in these subtropical mountain riparian habitats probably do not really provide optimal ecological conditions for the two relictual species.     

Multi‐scale effects of habitat structure and landscape context on a vertebrate with limited dispersal ability (the brown‐throated sloth,Bradypus variegatus)

As human population, food consumption, and demand for forest products continue to rise over the next century, the pressures of land‐use change on biodiversity are projected to intensify. In tropical regions, countryside habitats that retain abundant tree cover and structurally complex canopies may complement protected areas by providing suitable habitats and landscape connectivity for a significant portion of the native biota. Species with low dispersal capabilities are among the most at risk of extinction as a consequence of land‐use change. We assessed how the spatial distribution of the brown‐throated sloth (Bradypus variegatus), a model species for a vertebrate with limited dispersal ability, is shaped by differences in habitat structure and landscape patterns of countryside habitats in north‐central Costa Rica using a multi‐scale framework. We quantified the influence of local habitat characteristics and landscape context on sloth occurrence using mixed‐effects logistic regression models. We recorded 27 sloths within countryside habitats and found that both local and landscape factors significantly influenced their spatial distribution. Locally, sloths favored structurally complex habitats, with greater canopy cover and variation in tree height and basal area. At the landscape scale, sloths demonstrated a preference for habitats with high proportions of forest and nearby large tracts of forest. Although mixed‐use areas and tree plantations are not substitutes for protected forests, our results suggest they provide important supplemental habitats for sloths. To promote the conservation and long‐term viability of sloth populations in the tropical countryside, we recommend that land managers retain structurally complex vegetation and large patches of native habitat.     

Effects of natural and seminatural elements on the composition and dispersion of carabid beetles inhabiting an agroecosystem in Northern Italy

The natural and seminatural components of agricultural landscapes play a key role in maintaining a high level of biodiversity. Being the Po Valley one of the most human‐dominated and intensively cultivated landscapes in Europe, we investigated the effect of no‐crop habitats on carabid richness and composition and evaluated the role of tree row as corridor for forest carabid dispersion. Carabids were sampled with 70 pitfall traps arranged in 35 sampling plots along three parallel transects (80, 100, and 140 m long) and encompassing five different habitats: tree row, tree row edge, grassland, forest edge, and forest. We found 5,615 individuals belonging to 55 species. Despite the similarity in species richness, all the habitats investigated showed a peculiar and distinct species assemblage. The main distinction was between the "open habitat" cluster composed of grassland and tree row edge and the “forest" cluster composed of forest, tree row, and forest edge. We found that forest species are able to penetrate the grassland matrix up to 30 m from the forest edge and that a distance of no more than 60 m between tree row and forest can allow the passage of up to 50% of the forest species. Beyond this distance, the grassland matrix becomes a barrier, preventing them from reaching other suitable habitats. Our findings confirm the importance of maintaining different types of natural habitats to significantly increase biodiversity in an intensively cultivated agroecosystem and demonstrated the role of linear elements as a corridor and “stepping stones” for many forest species.     

Scale dependent diversity patterns in arboreal and terrestrial oribatid mite (Acari: Oribatida) communities

In naturally fragmented, isolated, or patchily distributed habitats that contain non‐vagile organisms, we expect dispersal to be limited, and patterns of diversity to differ from similar, yet continuous habitats. We explored the alpha‐beta‐gamma relationship and community composition of oribatid mites (Acari: Oribatida) inhabiting spatially discrete canopy suspended soils, and compared the patterns of diversity with the continuous forest floor soils over two years. We explored dispersal limitation for oribatid mites in the canopy by using additive partitioning of species richness at multiple spatial scales. ANOSIM was used to demonstrate differences in oribatid mite community composition between the canopy and forest floor habitats over different sampling periods. Community composition of oribatid mites differed significantly between canopy and forest floor habitats, by season and yearly sampling period. Oribatid mite richness and abundance were positively correlated with substrate moisture content, particularly in the canopy. Richness and abundance of ground oribatid mites was greater in September than in June, a trend that is reversed in the canopy, suggesting canopy oribatid mite species may have altered life histories to take advantage of earlier moisture conditions. Alpha diversity of oribatid mites in the canopy was lower than the ground at all sampling levels, and not significantly different from a random distribution in either habitat. Beta diversity was greater than expected from a random distribution at the patch‐ and tree‐level in the canopy suggesting dispersal limitation associated with physical tree‐to‐tree dispersal barriers, and limited dispersal among patches within a tree. Beta diversity at the tree‐level was the largest contribution to overall species richness in both canopy and ground habitats, and was also greater than expected on the ground. These results suggest that factors other than physical dispersal barriers, such as aggregation, habitat availability, and environmental factors (moisture), may limit the distribution of species in both habitats.     

哈尔滨市区灰喜鹊巢址选择研究

2010年6月至9月在哈尔滨市园林科学研究所实验基地采用样方法对灰喜鹊的巢址选择特征进行研究,并且利用主成分分析法对灰喜鹊巢址样方生境因子进行检验.结果表明,灰喜鹊主要选择针叶树筑巢;在同一生境中巢间距变化小,呈均匀分布;灰喜鹊巢址选择的主要因子包括营巢树高、距最近巢距离、样方内树均高、巢树胸径、距干扰源距离、距最近树距离.这说明灰喜鹊在巢址选择过程中选择巢树和其周围的小生境.     

黑石顶自然保护区森林次生演替过程中群落主要种的种间协变分析

采用2×2列联表,通过Pearson积矩相关系数和Speaman秩相关系数对黑石顶森林次生演替过程中各阶段群落优势种的种间协变进行了定量分析。结果表明,在演替初期的裸地恢复阶段,显著种间协变的种对较多,有14对(正协变9对负协变5对),在针阔混交林阶段,显著种间协变的种对较少,仅有5种。全为正协变,表现为主要种间对群落环境的相同要求,并形成了主要种间的竞争格局,在阳生性常绿阔叶林阶段。显著种间协变的种对最少,只有4对,其中3对为负协变,这是主要种之间对群落环境相同要求的激烈竞争结果,在中生性常绿阔叶林阶段,显著种间协变的种对最多有20对,19对为正协变,主要表现为群落上层种和中下层种间形成了大量的正协变,但群落上层主要种间无显著的种间协变。