Spatial association of Aspidosperma quebracho‐blanco juveniles with shrubs and conspecific adults in the Arid Chaco,Argentina

Abstract The survival of Aspidosperma quebracho‐blanco juveniles in the Arid Chaco is facilitated under the canopy of nurse plants. The possible effects of nurse plants were studied at intra‐ and interspecific levels by analysing the spatial distribution of juveniles and adults of A. quebracho‐blanco, of the main shrubs Larrea divaricata and Mimozyganthus carinatus, and of the group of deciduous and evergreen shrub species, and their pair associations. Data were analysed using the SADIE (Spatial Analysis by Distance Indices) software. A. quebracho‐blanco seedling abundance followed the distribution pattern of the main shade‐providing species: an aggregated spatial distribution pattern in most of the categories studied. The seedling bank of A. quebracho‐blanco also showed an aggregated pattern and was spatially associated with shrubs and adults of its own species. The intensity of the association depended on the functional types: deciduous Fabaceae, deciduous non‐Fabaceae, evergreen and conspecific adults, each of which provides a different canopy structure and therefore different amounts of shade. The spatial association was significant with the evergreen group, and less significant with the deciduous Fabaceae group. There was no positive association with deciduous non‐Fabaceae, or with gaps (open sky). The differences generated by canopy cover may influence the nurse effect, as observed in the intensity of association of A. quebracho‐blanco with shrubs and conspecific adults.     

Distribution patterns of tree species in a Malaysian tropical rain forest

Abstract. Spatial patterns of tree species were studied in a 50-ha tropical rain forest plot in the Pasoh forest, Malaysia. This forest is characterized by a high diversity and very high number of rare species. Out of the 745 species occurring with > five individuals, 80.4 % had an aggregated distribution, 19.5% were randomly distributed and one species had a regular distribution. The spatial patterns of rare vs. common species, juvenile vs. adult trees, and coarse vs. fine scales were compared. Rare species are generally less aggregated than common ones and most of the randomly distributed species are rare. Spatial patterns shift from high clumping to looser intensity or random distribution when moving from juveniles to adults for the same species. No adult tree species display a regular pattern, however. Regular distributions were rarely found; this is probably due to intraspecific competition at a local scale. There is a negative correlation between per capita death rate and population density. This study suggests that the Pasoh forest and its high diversity are subjected to multiple controlling factors, e.g., topography, spacing effect, density-dependent processes and species rarity. The importance of any factor changes across spatial and temporal scales.     

Distribution patterns of tree species in an evergreen broadleaved forest in eastern China

Ecological assembly rules in evergreen broad-leaved forest are far from clear understanding. Spatial dispersion of individuals in a species is central in ecological theory. We analyzed the spatial patterns as well as associations between adult and juvenile of each tree species in a 5-ha subtropical evergreen broad-leaved forest plot in eastern China. Out of the 74 species occurring with more than 10 individuals, 88.4% of these species are aggregated. Most of them are aggregated from small to large scales. Spatial distributions of some species corre-spond with topography. Many bad dispersed species in the Baishanzu exhibit a highly aggregated distribution at small scales. These suggest that environmental heterogeneity and/or dispersal limitation may be the most important mechanisms that control the distribution patterns of these species. Our observations of the aggregations of abundant species basically support the hypothesis that dispersal limitation decreases as the number of reproductive trees increases. The rest species are randomly distributed, with less than 10 individuals. For most common species, spatial aggregation is weaker in larger diameter classes, and the distance between adults is larger than that between juveniles and adults, suggesting that density-dependence works on loosing aggregation and excluding conspecific juveniles away from adult trees. However, the density-dependent effect is not strong enough to eliminate all seedlings near adult trees and to result in a regular distribution of trees; thus the density dependence is usually masked by the refuge effect.     

Distribution patterns of tree species in an evergreen broadleaved forest in eastern China

Ecological assembly rules in evergreen broad-leaved forest are far from clear understanding. Spatial dispersion of individuals in a species is central in ecological theory. We analyzed the spatial patterns as well as associations between adult and juvenile of each tree species in a 5-ha subtropical evergreen broad-leaved forest plot in eastern China. Out of the 74 species occurring with more than 10 individuals, 88.4% of these species are aggregated. Most of them are aggregated from small to large scales. Spatial distributions of some species correspond with topography. Many bad dispersed species in the Baishanzu exhibit a highly aggregated distribution at small scales. These suggest that environmental heterogeneity and/or dispersal limitation may be the most important mechanisms that control the distribution patterns of these species. Our observations of the aggregations of abundant species basically support the hypothesis that dispersal limitation decreases as the number of reproductive trees increases. The rest species are randomly distributed, with less than 10 individuals. For most common species, spatial aggregation is weaker in larger diameter classes, and the distance between adults is larger than that between juveniles and adults, suggesting that density-dependence works on loosing aggregation and excluding conspecific juveniles away from adult trees. However, the density-dependent effect is not strong enough to eliminate all seedlings near adult trees and to result in a regular distribution of trees; thus the density dependence is usually masked by the refuge effect.     

Changes in stand composition and structure between 1981 and 1996 in four Front Range plant communities in Colorado

We measured leaf distribution, crown shape, and biomass allocation patterns in open-grown saplings of three tree species (Cedrela odorata, Cordia alliodora, and Hyeronima alchorneoides) that differed in above-ground architecture and successional status. The objectives were to: (1) analyze the relationship between crown structure and biomass allocation in free-growing juveniles and (2) assess whether predictions that relate crown structure and biomass distribution of adult individuals can be applied to noncompeting saplings. Significant differences in crown structure and biomass allocation were found among the three species. Mean dry biomass was 990 g in Cedrela, 665 g, in Cordia, and 1281 g in Hyeronima. Cedrela allocated a greater proportion of biomass into roots than the other two species. We observed no distinct pattern of foliage angle, and no evidence of decrease in crown construction efficiency with tree size. Predictions stated by other authors for mature individuals partially explained the relationships between biomass allocation and morphological variables of non-competing saplings. We proposed two alternative biomass allocation patterns: (1) in open conditions saplings of early successional species exhibit structural characteristics more adapted for high light levels than gap-dependent species, and (2) early successional species have lower cost-benefit ratio for biomass construction and higher foliar efficiency than late successional ones. In general, crown morphometric characteristics and biomass distribution patterns of the three species studied corresponded with the two proposed patterns.     

广西大青山次生林的群落特征及主要乔木种群的空间分布格局

本文依托广西友谊关森林生态系统国家定位观测研究站在大青山设置的1 ha长期监测样地, 分析了森林群落的物种组成、区系特征及乔木种群的径级结构, 并用点格局分析方法的O-ring统计对主要乔木植物种群的空间分布格局及其空间关联性进行了研究, 旨在深入探讨该区域次生林的物种多样性特点及其维持机制, 分析影响优势树种空间分布格局的可能因素。大青山次生林共调查到植物109种, 其中乔木58种、灌木29种、草本22种, 樟科为样地内物种最丰富的科, 区系组成以泛热带成分为主; 乔木树种的径级结构接近倒“J”形, 主要种群的个体集中分布于中小径级范围(1-5 cm), 林分结构合理, 更新良好。从物种多度、胸高断面积和重要值来看, 大叶栎(Quercus griffithii)和锈毛梭子果(Eberhardtia aurata)是群落中的共优种, 其个体数占总个体数的30.8%, 鸭公树(Neolitsea chuii)、广东琼楠(Beilschmiedia fordii)和尖连蕊茶(Camellia cuspidata)为群落的主要伴生树种。用完全随机模型不排除生境异质性的条件下, 主要种群多数呈聚集分布; 用异质性随机模型排除生境异质性的条件下, 主要种群的聚集程度显著下降, 仅在小尺度上呈聚集分布; 主要树种均在一定尺度上表现为两两间正相关, 且在0-50 m的大部分尺度上显示出相互独立的特点, 没有表现出负相关。     

Microsite specialization and spatial distribution of <Emphasis Type="Italic">Geonoma brevispatha</Emphasis>, a clonal palm in south-eastern Brazil

We tested the hypotheses that: (i) reproductive Geonoma brevispatha, an understorey clonal palm endemic to South American swamps, is most abundant in more brightly lit microsites but the abundance of juveniles is not responsive to light availability, (ii) the species is restricted to the transitional zones between flooded and well-drained microsites, (iii) if hypotheses (i) and/or (ii) are accepted, the microhabitat specialization they represent should be reflected in the spatial distribution of the individuals at distinct scales. The study was carried out in a swamp forest in south-eastern Brazil. Soil moisture was autocorrelated at distances up to approximately 1m, reflecting a fine-scale microtopographic pattern of flooded pits and channels delimited by drier mounds. The first hypothesis was rejected, but the second hypothesis was accepted. No genets occurred on flooded microsites. A juvenile emergence experiment showed that seeds were unable to develop into juveniles under flooded conditions, but canopy openness did not influence the number of juveniles emerging. The third hypothesis was accepted. Individual genets were randomly distributed at scales corresponding to soil moisture patches, but were aggregated at larger scales. Juvenile genets were positively associated with reproducer genets. Our results indicate that palms may specialize on narrow parts of moisture gradients in swamp forests, and that this specialization can exclude them from even subtly distinct microhabitats.     

无人机调查白鹤种群数量和越冬分布

白鹤(Leucogeranus Leucogeranus)是国家Ⅰ级重点保护野生动物,唯一一种极度濒危(CR)鹤类,分布和种群数量是评估其濒危程度的重要参数。无人机调查作为目前生态学研究的一个重要调查方法,为查明白鹤的越冬分布、种群数量及幼鸟比例,于2022年1月使用地面监测结合无人机调查的方法在江西、山东、安徽、湖南、湖北等地的湖泊和农田中开展越冬白鹤调查。野外调查共记录白鹤5607只,网络信息检索在调查区域外的8个地点记录白鹤9只,合计记录越冬白鹤5616只。其中江西鄱阳湖记录到越冬白鹤4813只,占总数的85.7%,主要分布在康山垦殖场、五星垦殖场和成新垦殖场;山东黄河三角洲记录到越冬白鹤625只,占总数的11.1%。安徽、湖南、湖北分别记录到越冬白鹤34,63和72只。对部分群体的白鹤幼鸟数量进行统计,4680只白鹤中,记录到幼鸟674只,幼鸟比例为14.4%,其中湖南越冬白鹤幼鸟比例最高,达28.6%,山东越冬白鹤幼鸟比例最低,为11.5%。调查刷新了白鹤种群数量,证实了山东黄河三角洲是目前除江西鄱阳湖外最重要的白鹤越冬地,缓解了白鹤越冬期过度集中的压力。基于本研究结果,我们...     

Gonad Morphology, Colony Demography and Evidence for Hermaphroditism in Gobiodon Okinawae (Teleostei, Gobiidae)

Gobiodon okinawae is a small-sized, obligate coral-dwelling goby. The majority of species in this Indo-Pacific genus exhibit an obligatory association with branching live corals and a number have been shown to be bi-directional hermaphrodites in which adults have the capacity to shift between male and female function. Gonadal histology in G. okinawae demonstrated that all individuals had either an ovotestis or an ovary. Some females had an ovary with vitellogenic oocytes, indicating adult female function. Hermaphrodites having an ovotestis were either functionally male, as evidenced by the presence of spermatozoa or, in one instance, functionally female so judged by the presence of vitellogenic oocytes. No individuals were found to have mature gametes of both sexes, although a number of hermaphrodites had an inactive ovotestis with no mature gametes of either sex. Based on size ranges for fish having different gonad morphologies, individuals in this species appear to develop first as a female. They then either mature and function solely as a female, or become hermaphroditic. Findings based on experimentally maintained individuals suggests that adult hermaphrodites can shift sexual function in either direction. Accessory gonadal structures (AGS) were found in both sexes. These consisted of two fully differentiated pairs of lobes, each compartmentalized internally by lumina and containing PAS+secretions. The secretions of the dorsally located AGS were colloidal while those of the ventrally located AGS were fibrillar and granular in nature. The presence of two sets of AGS among males appears to be characteristic of both Gobiodon and its putative sister genus, Paragobiodon. However, the occurrence of fully developed AGS in both females and males has not previously been reported and may be unique to G. okinawae.     

Pattern and mortality in Colorado Desert plants

Summary We tested for intraspecific interference among Colorado Desert shrubs using an integrated analysis of spatial pattern and juvenile mortality. The data set included 7,000 woody perennials of 24 species in a mapped hectare of Joshua Tree National Monument, California. The site is dominated by Ambrosia dumosa (62.0% of the stems), with Larre tridentata a conspicuous secondary species (2.3% of the stems). Analyses of static pattern for common species showed: (1) aggregated adults and juveniles for Ambrosia dumosa, Erigonum fasciculatum, Mirabilis bigelovii, and Sphaeralcea ambigua, with more aggregation among juveniles than adults; (2) randomly distributed adults and juveniles for Krameria grayi, Opuntia rasmosissima, Simondsia chinensis, and Yucca schidigera. The summed volumes and distances between nearest conspecific neighbors were positively correlated for Ambrosia dumosa and Larrea tridentata, but not significantly correlated for eight remaining species with 100 individuals. Static pattern suggests only weak evidence for negative interactions in Ambrosia and Larrea, and little evidence for other species. Alternative mechanisms other than negative interaction that could give rise to these static patterns are discussed. Juvenile mortality was documented for four common species (Ambrosia dumosa, Eriogonum fasciculatum, Mirabilis bigelovii, and Sphaeralcea ambigua) that experienced substantial mortality. Analyses show: (1) the proportion of individuals that died was independent of the initial density of conspecifics; (2) distance to conspecific adults did not differ for juveniles that died versus those that survived; and (3) death was no more likely for juveniles that contacted other plants than for those that were isolated. The exception was a vine, Mirabilis bigelovii, whose juveniles survived better in contact with other plants. In sum, neither spatial pattern nor patterns of mortality showed clear evidence of negative intraspecific interference.     

Frenulate siboglinids at high Arctic methane seeps and insight into high latitude frenulate distribution

Frenulate species were identified from a high Arctic methane seep area on Vestnesa Ridge, western Svalbard margin (79°N, Fram Strait) based on mitochondrial cytochrome oxidase subunit I (mtCOI). Two species were found: Oligobrachia haakonmosbiensis, and a new, distinct, and undescribed Oligobrachia species. The new species adds to the cryptic Oligobrachia species complex found at high latitude methane seeps in the north Atlantic and the Arctic. However, this species displays a curled tube morphology and light brown coloration that could serve to distinguish it from other members of the complex. A number of single tentacle individuals were recovered which were initially thought to be members of the only unitentaculate genus, Siboglinum. However, sequencing revealed them to be the new species and the single tentacle morphology, in addition to thin, colorless, and ringless tubes indicate that they are juveniles. This is the first known report of juveniles of northern Oligobrachia. Since the juveniles all appeared to be at about the same developmental stage, it is possible that reproduction is either synchronized within the species, or that despite continuous reproduction, settlement, and growth in the sediment only takes place at specific periods. The new find of the well‐known species O. haakonmosbiensis extends its range from the Norwegian Sea to high latitudes of the Arctic in the Fram Strait. We suggest bottom currents serve as the main distribution mechanism for high latitude Oligobrachia species and that water depth constitutes a major dispersal barrier. This explains the lack of overlap between the distributions of northern Oligobrachia species despite exposure to similar current regimes. Our results point toward a single speciation event within the Oligobrachia clade, and we suggest that this occurred in the late Neogene, when topographical changes occurred and exchanges between Arctic and North Atlantic water masses and subsequent thermohaline circulation intensified.     

Microdistribution within a population ofAcrocnida brachiata (Montagu), (Echinodermata: Ophiuroidea) in Little Killary, west coast of Ireland

Acrocnida brachiata (Montagu), like many other infaunal ophiuroids, has a penchant for gregariousness. In Little Killary, a small embayment on the west coast of Ireland, it colonises an extensive tract of sandy inshore ground (ca 7 m depth), at densities of 150–200 individuals/m². In the course of a two-year study, variation in regular suction-sampling returns prompted a detailed study of the species distribution pattern. Towards this end, 256 contiguous and stratified core samples were taken along a line of transect, in May 1995. These showed randomness with respect to the population at large, but exposed an aggregated distribution for juveniles and adults separately, at different levels within the sediment. Juveniles formed wide, ‘loose’ patches in the surficial deposit, while adults formed smaller, denseer patches deeper within the sediment. It remains to be seen what this approach may expose, when applied in different seasons, or during different phases of the species life cycle.     

Are kelp holdfasts islands on the ocean floor? – indication for temporarily closed aggregations of peracarid crustaceans

During the colonisation process of islands, newly immigrating species often arrive as single individuals. Islands that have received single colonisers may subsequently harbour large populations of a species, while other islands may completely lack this species. Exchange between islands is limited, thereby strongly affecting evolutionary processes. While this concept is widely used in the context of oceanic islands or habitat patches on the mainland, it is rarely used to explain and examine the distribution patterns of marine invertebrates. Benthic marine organisms inhabiting patches with island-like features may also be restricted in their movements between patches. Once established in a patch, it may be more favourable to remain there rather than moving to another patch. Juveniles of species with direct development may recruit to the island patch of their parents. Herein, we examined the peracarid fauna in patches that have island-like features, i.e. kelp holdfasts. The number of peracarid species within an individual holdfast increased with its size. Similarly, the number of individuals per holdfast increased with holdfast size. However, several peracarid species showed a strongly aggregated distribution pattern, being highly abundant in some holdfasts and almost completely absent in others. Our results suggest that these aggregations of conspecifics may be a consequence of the peracarid reproductive biology: fully developed juveniles emerge from the female's marsupium and recruit to the immediate vicinity of their mother, showing little or no tendency to emigrate towards other patches. At present, while it is not known how long peracarid aggregations within kelp holdfasts persist, our data suggest that some juveniles may remain with the natal holdfast and possibly reproduce therein. It is concluded that, during certain time periods, reproduction rates of peracarids in a holdfast may exceed their migration rates between holdfasts.     

Spatial pattern of downed logs and wood‐decaying fungi in an old‐growth Picea abies forest

Abstract. Since many wood‐living forest species are influenced by the dynamics of coarse woody debris (CWD), information about the spatial pattern of CWD under natural conditions is essential to understand species distributions. In this study we examined the spatial pattern of downed logs and wood‐decaying fungi in an old‐growth boreal Picea abies forest in northwestern Sweden that is governed by gap‐phase dynamics. The spatial pattern of wood‐decaying fungi was studied to draw conclusions about species dispersal abilities. A total of 684 logs with a diameter > 10 cm were mapped and analysed with Ripley's K‐function. The distribution of all logs taken together displayed a significant aggregated pattern up to 45 m. The different decay stages also deviated from random expectations. Fairly fresh logs and logs in the middle decay stage were clumped up to about 25 and 35 m respectively, and late decayed logs aggregated up to 95 m. Logs with diameters from 10–29 cm were aggregated up to 25 m, whereas logs ≥30 cm diameter were randomly distributed. The result suggests that gap‐dynamics do have an impact on the spatial pattern of the CWD, creating fine‐scale clumping. The random distribution of large logs may result from the slightly regular spacing of large living trees. The spatial patterns of 16 species (n > 20) of wood‐decaying fungi were analysed with Ripley's K‐function. Three patterns were aggregated, for Gloeophyllum sepiarium, Coniophora olivacea and Vesiculomyces citrinus. These results indicate that the distribution of most species at the stand level is generally not influenced by dispersal limitations.     

Fish distribution and ontogenetic habitat preferences in non-estuarine lagoons and adjacent reefs

We surveyed fish distribution in three lagoons and adjacent forereefs in the British Virgin Islands recording about 28,000 fish from 40 families and 118 species. Canonical correspondence indicated that rock, sand, fleshy algae, gorgonians, mangroves and live hard coral were the most important habitat types influencing fish assemblage composition. About 47% of fishes occurring at more than 10 stations displayed evidence of ontogenetic partitioning between reefs and lagoons but post-settlement ontogenetic life history strategies were quite varied depending on the species. For example Chaetodon striatus juveniles occurred exclusively in lagoons and all sexually mature adults were found on reefs. Some differences were less pronounced as seen in Halichoeres bivittatus where individuals of all sizes occurred on reefs and lagoons, but when analysed it was found that reefs had larger individuals than lagoons. Some species, such as Acanthurus bahianus, were primarily reef species whose juveniles also used lagoon habitats while others, such as Gerres cinereus, were generally lagoon species whose adults occasionally moved onto reefs. Even with all this variation in life-history strategies, all the species that exhibited bay-reef partitioning used the lagoons as juveniles then moved onto reefs as adults and not vice versa, supporting the hypothesis that bays are important nursery areas for reef-dwelling fishes. These results show that a detailed review of the natural life-history strategies and habitat requirements are required before making further generalisations about the role of near-shore habitat types as nurseries for reef fishes. This is especially important given the rapid changes in tropical near-shore habitats around the world.     

中国壳斗科植物属的空间多样性格局及其指标研究

通过植物专业网站及已发表的论文论著,查找每一种壳斗科植物在中国的具体分布地点(县),并采用地理信息系统技术,以县为空间数据的基本单元,以壳斗科植物为研究对象,从空间上获取多样性格局指标,定量研究中国壳斗科植物的属、类型的空间多样性格局。结果表明:(1)中国壳斗科植物中青冈属、栎属、锥属、柯属的斑块丰富度、多样性指数、斑块总数、总形状指数明显高于三棱栎属、栗属、水青冈属,而三棱栎属因只有一个斑块,属与种的空间多样性格局相同,与其他属明显不同。(2)中国壳斗科植物中属的空间多样性格局指标之间有一定的相关性,斑块丰富度、多样性指数、斑块总数、总形状指数相互之间、总面积与斑块总数、多样性指数、总形状指数之间呈显著正相关关系,总的最大斑块指数与均度指数之间呈显著负相关关系。(3)除三棱栎属外,其他属的斑块类型所占面积、占属面积的比例、斑块数目、最大斑块指数、形状指数各指标,基本上均随所在属斑块类型值的增加其相应指标依次降低,斑块类型与其他指标呈显著负相关关系。(4)中国壳斗科植物在青冈属、栎属、锥属、柯属中,每一个属种数为1~7的斑块类型所占面积之和、斑块数目之和分别占其属对应总指标的值均高于80%,表明种数较少的斑块类型构成了属的主要分布区,而种数较多的斑块类型,其各指标值均较低,分布范围很狭窄,但物种多样性高。     

Quantitative and qualitative seasonal changes in the microbial community from the phyllosphere of sugar beet (Beta vulgaris)

Bacteria, yeasts and filamentous fungi colonizing immature, mature and senescing primary leaves of field grown Beta vulgaris (sugar beet) were analysed over a complete growing season. Greatest microbial numbers were detected on senescing primary leaves and these numbers increased over most of the season. The number of colonizers detected on mature leaves was found to be stable over most of the study.Filamentous fungi and yeasts were identified to the genus level and the communities found to have greatest diversity during the summer months. There was no consistent pattern of diversity according to leaf type. Two genera of filamentous fungi, Cladosporium and Alternaria and two yeast genera, Cryptococcus and Sporobolomyces were the most numerous fungal populations isolated. Only 8 filamentous fungi and 3 yeast genera were commonly isolated on PDA (potato dextrose agar).Bacterial strains (1236) were isolated on Tryptic Soy Broth (TSB) agar and identified to species, or in some cases sub-species level, by analysis of their fatty acid methyl ester (FAME) profiles. Isolated bacteria were grouped into 78 named and 37 unnamed species clusters. Greatest number of bacterial species were isolated from young plants and leaves, sampled during the autumn months. Bacterial community diversity was lowest in mid-summer and winter months. Pseudomonas was the most commonly isolated genus and Erwinia herbicola the most common species. P. aureofaciens was the only species isolated from soil that was also isolated from the phyllosphere of B. vulgaris throughout the season.     

Effect of brousse tigrée on the dynamics of nurse–protégé interactions of a cactus in the Chihuahuan Desert

A nurse–protégé relationship is a frequent facilitation interaction in deserts that allows the recruitment of new individuals of many species. Our aim was to evaluate the relationship of Echinocereus enneacanthus during its life cycle and its nurse plants in the brousse tigrée (tiger bush) vegetation of the Chihuahuan Desert. The population structure of the cactus is skewed toward adult stages, which are commonly found in the bare areas of the brousse tigrée, whereas juveniles are located in the vegetated bands. The vegetation structure and the nurse–protégé relationship were determined using censuses of 19 permanent plots monitored between 2008 and 2019. The differential association of E. enneacanthus with potential nurse plants was evaluated using an interaction network, under the hypothesis of strict association of the seedlings and juveniles with nurse species. In addition, χ² tests and standardized residuals were fitted among likely nurse species, weighted by the cover of the nurse and of the areas without vegetation. The study species, as well as the nurse plants, had an aggregated distribution pattern. The interaction network showed that the frequency of the association with nurse plants decreased as the size of the protégé individuals increased. At the same time, there were differences in the establishment of E. enneacanthus under particular nurse plants; Prosopis glandulosa and Hilaria mutica were the most important. The nurse–protégé relationship for seeds and seedlings is integral to the vegetation bands of the brousse tigrée.     

藏东南急尖长苞冷杉群落空间点格局分析及其时空动态

为探究藏东南色季拉山急尖长苞冷杉（Abies georgei var.smithii）群落的空间分布格局及其时空动态,在急尖长苞冷杉纯林中设置1个1 hm²的固定样地,记录样地内所有高度>2 m的急尖长苞冷杉的年龄、胸径、冠幅和坐标等指标。根据径级分布分析种群的径级结构,采用点格局分析方法对种群的空间格局进行分析。结果显示：（1）急尖长苞冷杉的径级分布为倒"J"型,结构稳定,自然更新良好。（2）成树在各个时期和不同尺度上都呈随机分布;幼树在1891年之后的各个时期在小尺度（2 m）上呈聚集分布,1981-2012年在1-41 m尺度上陆续出现聚集分布;幼苗在1861-1920年在小尺度（1-2 m）上呈聚集分布,1951-1980年出现聚集分布的尺度范围最大（1-35 m、41 m和48 m）。（3）在不同时期中,不同年龄组树木之间几乎都呈正关联或无关联;成树和幼树随时间推移从无关联到在各个尺度上陆续出现正关联的变化;成树和幼苗随时间呈无关联、中大尺度（32-35 m、44 m和49 m）正关联和无关联的变化;幼苗和幼树呈现从无关联转变为小尺度（8 m）正关联和小、中尺度（1-30 m）正关联的变化。研究结果表明：成树在小尺度上对幼龄树存在一定的抑制,但在较大尺度是促进的。1951-1980年样地中的幼苗数量大量增加,随后30年幼树的数量因幼苗长大也有增加,这在一定程度上增大了竞争。但总体来看急尖长苞冷杉群落在演替过程中具有种内促进作用。     

红松存在/不存在数据的多尺度空间分布格局

红松属小兴安岭地区地带性植被优势种,该地区也是其分布的北缘。在景观尺度上开展红松的分布格局研究有利于进一步了解红松分布机理、未来迁移过程等问题,对其经营和保护有重要意义。将景观指数法与点格局分析法结合,设定8个空间尺度,利用红松存在/不存在数据,通过计算各空间尺度上红松聚集程度和景观指数,分析小兴安岭地区红松种群在多尺度上的分布格局。研究结果表明,小尺度上红松聚集分布明显,随机分布区多处于其聚集分布区的边缘,均匀分布区则散布在其聚集分布区内。景观指数研究表明,通过景观指数可判断红松聚集分布格局趋势,而不能判断均匀分布、随机分布格局趋势,因为它们在多尺度下景观指数波动大,不能用景观指数来描述分布格局。研究得出如下结论:1)红松主要分布在其分布区的核心区域内,在分布区边缘和过渡带上呈随机分布,2)存在/不存在数据能够用来分析种群的多尺度空间分布格局,3)空间尺度的变化会引起树种分布格局的变化,随机分布随尺度增加,边缘化程度加强,4)单一尺度上,景观格局指数不能完全描述种群分布格局;而在多尺度上,变化趋势稳定的景观指数表明聚集分布存在,而波动剧烈的景观指数常与随机分布和均匀分布联系在一起,5)地形因子中,红松对坡度和海拔两个因子变化敏感。