The impact of Acacia saligna invasion on Italian coastal dune EC habitats

Alien species can represent a threat to several ecosystems because they can alter species relationships and ecosystem function. In Italy, Acacia saligna is a major invader and it forms dense stands in coastal environments. We analyze the impact of A. saligna in Italian Mediterranean dune systems. We randomly sampled coastal dune vegetation and investigated its floristic composition with ordination techniques. We compared species richness in invaded and non-invaded plots with rarefaction curves and analyzed the frequency of focal and ruderal species. A. saligna invaded Mediterranean scrub (habitats 2250* and 2260) and coastal Pinus dune wood (habitat 2270*) and it is particularly prevalent in sunny areas of habitat 2270*. We observed an increase in ruderal species and a decrease in focal species in the invaded plots of habitat 2270*. We suggest that more open and disturbed areas are more prone to A. saligna invasion.     

Arundo donax L.: A non-food crop for bioenergy and bio-compound production

Arundo donax L., common name giant cane or giant reed, is a plant that grows spontaneously in different kinds of environments and that it is widespread in temperate and hot areas all over the world. Plant adaptability to different kinds of environment, soils and growing conditions, in combination with the high biomass production and the low input required for its cultivation, give to A. donax many advantages when compared to other energy crops. A. donax can be used in the production of biofuels/bioenergy not only by biological fermentation, i.e. biogas and bio-ethanol, but also, by direct biomass combustion. Both its industrial uses and the extraction of chemical compounds are largely proved, so that A. donax can be proposed as the feedstock to develop a bio-refinery.     

Tenacity and shell shape in six Patella species: Adaptive features

Measurements were made of te forces necessary to detach various South African Patella spp. These ranged from 5.18 to 1.95 kg/cm², with significant differences between the species. P. cochlear Born. had the highest value, followed in sequence by P. argenvillei Kr., longicosta Lam., P. granularis L., P. granatina L., and P. oculus Born. Adhesion is the only mechanism capable of providing forces of this magnitude.Differences between the species are related to differences in their morphology, high tenacity being associated with low mucus secretion, small number of mucocytes, and inflexibility of the foot. This is associated with a large area of muscle attachment on the shell and the size of basal haemocoelic spaces.Features favouring high tenacity conflict with those favouring mobility, and the limpets fall into two groups. P. granularis, P. oculus, and P. granatina occur on the upper shore and the last two usually occur in areas which are sheltered from strong wave action. They a rapid growth and high gonadal output, demanding extensive foraging and hence mobility at the cost of tenacity. P. cochlear and P. longicosta are territorial and together with P. argenvillei, remain low on the shore, grow slowly, and have a low reproductive output. Feeding is localized and mobility sacrificed for high tenacity which is essential in P. cochlear and P. argenvillei as they occur in areas of strong wave action.Shell height is not correlated with tenacity nor with the intensity of wave action normally experienced by each species, but P. cochlear, P. argenvillei and to a lesser extent P. granularis, are subjected to strong wave action and have proportionally narrower shells (increasing streamlining) and low coefficients of drag. The latter are low due to the rough but regular texture of the shells creating a turbulent boundary layer and hence reducing drag.     

Benthic foraminifera associated with the invasive ascidian, Didemnum sp. A

The invasive ascidian, Didemnum sp. A, first appeared in New England bays and harbors in the early 1990s, and in the waters around Cape Cod in 1993. While ship traffic was the likely vector introducing the species, its origin and precise date and location of its introduction are presently unknown. Colony surfaces of Didemnum sp. A appear very clean and not favorable substrates for epibiota settlement, but closer inspection revealed the presence of benthic foraminifera. During 2003 and 2004, 52 samples of Didemnum sp. A and other ascidians were collected to determine whether or not the foraminiferal assemblages might also be non-native and thus provide a potential clue to the place of origin of Didemnum sp. A. Sample locations included the New England coast from Connecticut to Maine (with a concentration in the Cape Cod area), northern California, Zeeland, The Netherlands, and Shakespeare Bay, New Zealand. From New England samples, 18 species of benthic foraminifera were identified. The most common species represented were Cornuspira involvens, C. planorbis, Elphidium galvestonense, E. margaritaceum, Glabratellina lauriei, Miliolinella subrotunda, Quinqueloculina bicornis, and Rosalina floridana. Foraminiferal assemblages on Didemnum sp. A from other regions sampled were composed of the same cosmopolitan species found in New England, plus other species which were indigenous to each region. Because no exotic foraminifera species were found it is concluded that Didemnum sp. A likely did not introduce non-native foraminifera originating from their native habitats into the New England region.     

Habitat selection of two gobies (Microgobius gulosus, Gobiosoma robustum): influence of structural complexity, competitive interactions, and presence of a predator

Herein I compare the relative importance of preference for structurally complex habitat against avoidance of competitors and predators in two benthic fishes common in the Gulf of Mexico. The code goby Gobiosoma robustum Ginsburg and clown goby Microgobius gulosus (Girard) are common, ecologically similar fishes found throughout the Gulf of Mexico and in the southeastern Atlantic Ocean. In Florida Bay, these fishes exhibit habitat partitioning: G. robustum is most abundant in seagrass-dominated areas while M. gulosus is most abundant in sparsely vegetated habitats. In a small-scale field survey, I documented the microhabitat use of these species where their distributions overlap. In a series of laboratory experiments, I presented each species with structured (artificial seagrass) versus nonstructured (bare sand) habitats and measured their frequency of choosing either habitat type. I then examined the use of structured versus nonstructured habitats when the two species were placed together in a mixed group. Finally, I placed a predator (Opsanus beta) in the experimental aquaria to determine how its presence influenced habitat selection. In the field, G. robustum was more abundant in seagrass and M. gulosus was more abundant in bare mud. In the laboratory, both species selected grass over sand in allopatry. However, in sympatry, M. gulosus occupied sand more often when paired with G. robustum than when alone. G. robustum appears to directly influence the habitat choice of M. gulosus: It seems that M. gulosus is pushed out of the structured habitat that is the preferred habitat of G. robustum. Thus, competition appears to modify the habitat selection of these species when they occur in sympatry. Additionally, the presence of the toadfish was a sufficient stimulus to provoke both M. gulosus and G. robustum to increase their selection for sand (compared to single-species treatments). Distribution patterns of M. gulosus and G. robustum likely result from a synthesis of various biotic and abiotic filters, including physiological tolerances to environmental factors, dispersal ability of larvae, and availability of food. Selection for structural complexity, competition, and presence of predators may further define the resulting pattern of distribution observed in the field.     

Competition and facilitation between the alien mussel Mytilus galloprovincialis and indigenous species: Moderation by wave action

As the alien species that most dominates space along the South African coast, the Mediterranean mussel Mytilus galloprovincialis has radically altered community composition on invaded shores. We experimentally assessed interspecific interactions between this invasive species and dominant indigenous species in conjunction with considering how wave action moderates such interactions. The density of both M. galloprovincialis and the limpet Scutellastra granularis increased with wave action. Conversely, the tube-building polycheate Gunnarea capensis was negatively affected by wave exposure, being most abundant on sheltered shores. The influence of wave action on the indigenous mussel Aulacomya ater, however, remains unclear. M. galloprovincialis outcompeted both G. capensis and A. ater at moderate to high exposure levels, whereas it had both positive and negative effects on S. granularis. It outcompeted adult limpets on primary rock space on semi-exposed and exposed shores, reducing densities of this portion of the population. However, recruitment of S. granularis was facilitated by M. galloprovincialis, as greater numbers recruited to the secondary substratum offered by mussel shells. Again this interaction intensified with wave action. Due to the extremely high density of recruits on secondary space, the net effect of M. galloprovincialis on S. granularis was positive. Thus, wave action not only influences the abundance of individual species, but also mediates both positive and negative interspecific interactions in rocky shore communities, including the impact of alien species such as M. galloprovincialis.     

Genetic variation and reproduction strategy of Gentiana pannonica in different habitats

Gentiana pannonicascop. (Gentianaceae) is a long-lived perennial mountain species. It is a typical east−Alpine element. The centre of its distribution is situated in the eastern Alps, where the species occurs in alpine and subalpine areas. Besides the Alps, G. pannonica occurs also in the Bohemian Forest, Czech Republic. The reproduction strategy and genetic variation of this species endangered in the Czech Republic were studied. Genetic variation within and among six populations of G. pannonica in the Bohemian Forest and two populations in the Alps was studied using random amplified polymorphic DNAs (RAPD) markers. The variation found between populations from primary habitats and populations situated in the secondary mountain meadows accounted for 5% of the total genetic variation, whereas no significant genetic diversity was found between two different regions (Bohemian Forest, the Alps). Most of the variation is distributed among individuals within populations in the primary habitats, specifically 77% in the Bohemian Forest and 79% in the Alps. The pattern of among-population variation was substantially different between primary and secondary habitats. While among-population variation in primary habitats was low in both of the regions (21–23%), the proportion of RAPD variation among populations in secondary habitats was distinctly higher (65%). Within-population genetic variation was higher in primary habitats than in the secondary ones. This may be a consequence of processes such as genetic drift or bottleneck, and founder effects caused by changes in their distribution during the Holocene period. The differences of vegetation composition, seedlings recruitment and seed set were investigated in the field. Vegetation composition differed between primary and secondary habitats of G. pannonica and seedlings recruitment was recorded only in primary habitats. The reproduction output of the species under study is probably influenced by the availability of pollinators.     

外来植物紫茎泽兰入侵对土壤理化性质及丛枝菌根真菌(AMF)群落的影响

为了揭示外来植物紫茎泽兰入侵对入侵地土壤丛枝菌根真菌(AMF)群落及相关肥力的影响,比较测定了紫茎泽兰不同入侵程度土壤理化性质、AMF侵染率及AMF群落的差异。结果表明,紫茎泽兰入侵降低了土壤pH,使土壤中有机碳、全氮和速效钾含量分别增加83.0%,106.9%和111.0%;尽管对全磷含量没有显著影响,但有机磷含量呈升高的趋势,而速效磷呈降低的趋势。紫茎泽兰入侵降低了本地植物的AMF侵染率;随着入侵程度的加深,土壤中以膨胀无梗囊霉(Acauospora dilatata)为优势种的AMF群落结构逐渐转变为以近明球囊霉(Glomus claroideum )为优势种的结构,紫茎泽兰可在其根周选择培育近明球囊霉,而对其它AMF种,特别是对膨胀无梗囊霉则存在抑制作用;基于各AMF种多度的聚类分析表明,形成紫茎泽兰单优群落土壤中各AMF种多度与未入侵的本地植物群落及入侵程度较轻的紫茎泽兰与本地植物群落之间存在明显分歧。综合分析推断认为,紫茎法兰入侵改变了入侵地土壤理化性状,抑制AMF对土著植物的侵染,改变AMF群落,并在其根周选择培育近明球囊霉,这可能是紫茎泽兰入侵及扩张的重要途径之一。     

Vegetative reproduction in the octocoral Briareumasbestinum (Pallas)

Briareum asbestinum (Pallas), a common octocoral of Caribbean reefs, produces runner-like branches which are capable of attaching to the substratum and establishing new colonies. The subsequent death of the intervening runner leaves groups of genetically identical but physiologically distinct colonies. The origin of these colonies can be deduced by the presence or absence of runners. Analysis of colonies at Marsarkantupo in the San Blas Islands, Panama and at Carrie Bow Cay, Belize indicate that 23–56% and 18–67%, respectively, of the colonies at these sites originate from vegetative runners. In both areas the distribution of colonies of larval origin is not uniform. Colonies originating from larvae are patchily distributed within habitats and are over-represented in shallow habitats. The ability of B. asbestinum to reproduce vegetatively results in the spread and development of large populations of this species in many habitats where it might otherwise be rare.     

Positive interactions of the smooth cordgrass Spartina alterniflora on the mud snail Heleobia australis, in South Western Atlantic salt marshes

The role of positive interactions is often crucial in communities with intense abiotic stress such as intertidal environments. Grasses acting as ecosystem engineers, for example, may ameliorate intertidal harsh physical conditions and modify the community structure. The mud snails Heleobia australis d'Orbigny frequently inhabit the SW Atlantic marshes, mainly associated to intertidal marsh plants (mainly the smooth cordgrass Spartina alterniflora Loisel) probably due to the plant indirect effects. The purpose of this work was to investigate the magnitude of these association and the processes that generate the pattern. Samples of the snail abundance in six SW Atlantic coastal marshes show that H. australis is associated to coastal areas of low energy and low or none freshwater input. This result is important because this species is being used as bioindicator of coastal estuarine systems during the Holocene. Thus the paleontological interpretation based on this species should be revised. Within the studied areas, snails are associated to intertidal marsh plants. However, stable isotope analysis shows that neither plant nor their epiphytes are their main food sources. Field experiments show that snails actively select areas with plants, although tethering experiments show that plants do not provide shelter from predators. However, plants do buffer physical stress factors such as temperature, which generate important mortality outside plants covered areas. These positive interactions have large effects on H. australis distributions in marsh communities; increasing the habitats available for colonization and affecting their local distribution.     

Molecular phylogeny of the paper wasp subgenus Polistes (Polistella) Ashmead, 1904 (Hymenoptera: Vespidae: Polistinae) from Vietnam

This study provides the first molecular phylogeny of the social wasp subgenus Polistella (Hymenoptera: Vespidae: Polistes) from Vietnam. Fragments of the mitochondrial COI and 16S rRNA genes were used to reconstruct the phylogenetic trees among 38 Polistes species plus two out-group species (Vespa soror du Buysson and Ropalidia fasciata (Fabricius)). Our results support the existence of several species-groups, including two that are congruent with the previous stigma and Stenopolistes groups defined on the basis of morphology. Moreover, we recovered a clade including the stigma group and the two species P. humilis and P. variabilis that was sister to all other species of Polistella. However, the results also challenged the definition of other groups of Polistella based on morphological data, as well as the definition of two species: P. brunus and P. affinis. This first study calls for further analyses including morphological characters to clarify the taxonomy and the classification of the group.     

西门岛人工秋茄林恢复对大型底栖生物的影响

选择乐清湾西门岛海域相同高程断面不同造林时间的人工红树林(秋茄林)、光滩和互花米草丛,采用空间代替时间的方法,分析我国分布最北界人工红树林造林过程对大型底栖生物的影响.大型底栖动物生活型分布基本表现为幼林(1、4、8a秋茄林)以底上附着型为主,而在光滩、50a秋茄林和互花米草中底下生活类群相对增加.并且穴居型动物只出现在发育成熟的生态系统内.各项指标显示50a老林群落生态稳定性较好,光滩和互花米草丛次之,但优于发育中的秋茄幼林.与以往研究结果不同,50a老林的大型底栖动物生物种类的丰度及群落的物种多样性最高,并不与红树林的发育状况呈负相关,也不比邻近光滩低.结合50a林下滩涂底泥情况,西门岛50a红树林林下滩涂的底质发育要落后于国内天然红树林土壤.这可能与当地红树林造林规模小以及强潮差海域有关.此外,红树林恢复过程中,大型底栖动物生物多样性与生态稳定性之间的线性关系,其适用的系统面积和演替时间的尺度范围有必要做更加深入的探讨.     

Energy transfer dynamics in a red-shifted violaxanthin-chlorophyll a light-harvesting complex

Photosynthetic eukaryotes whose cells harbor plastids originating from secondary endosymbiosis of a red alga include species of major ecological and economic importance. Since utilization of solar energy relies on the efficient light-harvesting, one of the critical factors for the success of the red lineage in a range of environments is to be found in the adaptability of the light-harvesting machinery, formed by the proteins of the light-harvesting complex (LHC) family. A number of species are known to employ mainly a unique class of LHC containing red-shifted chlorophyll a (Chl a) forms absorbing above 690?nm. This appears to be an adaptation to shaded habitats. Here we present a detailed investigation of excitation energy flow in the red-shifted light-harvesting antenna of eustigmatophyte Trachydiscus minutus using time-resolved fluorescence and ultrafast transient absorption measurements. The main carotenoid in the complex is violaxanthin, hence this LHC is labeled the red-violaxanthin-Chl a protein, rVCP. Both the carotenoid-to-Chl a energy transfer and excitation dynamics within the Chl a manifold were studied and compared to the related antenna complex, VCP, that lacks the red-Chl a. Two spectrally defined carotenoid pools were identified in the red antenna, contributing to energy transfer to Chl a, mostly via S₂ and hot S₁ states. Also, Chl a triplet quenching by carotenoids is documented. Two separate pools of red-shifted Chl a were resolved, one is likely formed by excitonically coupled Chl a molecules. The structural implications of these observations are discussed.     

Near anoxia and sulfide as possible factors influencing the spatial distribution of Acartia tonsa and Acartia clausi: Comparative evaluation of egg tolerance

In many coastal and estuarine areas the planktonic copepods Acartia tonsa and Acartia clausi show a spatial separation with A. tonsa restricted to brackish waters and confined environments and A. clausi inhabiting areas more influenced by sea water. The hatching and viability of A. tonsa and A. clausi eggs exposed to anoxia and anoxia/sulfide (conditions that are frequent in bottom waters of the most confined areas) was evaluated to determine if these stress factors play a role in the distribution of these species. Subitaneous eggs, spawned by laboratory reared organisms, were incubated in near anoxia (< 7.59 × 10^− 3 mmol O₂ L^− 1) or anoxia/sulfide (∼ 1 mmol L^− 1) for different periods (1, 4, 8 and 15 days), then transferred to normoxic conditions. The exposure of the eggs to near anoxia and sulfide appears to induce the same response (quiescence) in both species. Exposure times ≤ 8 days to near anoxia or anoxia/sulfide did not affect egg viability, while 15 day exposure caused significant declines in hatching success of both species. A significant difference between the effects of near anoxia and anoxia/sulfide was observed when incubation lasted 15 days; hatching of eggs exposed to sulfide being higher than that of eggs exposed to near anoxia for both species. No significant differences were observed between the two species in hatching success of eggs exposed to both near anoxia and anoxia/sulfide (with the exception of eggs incubated in near anoxia for 4 days). The results indicate that the impact of anoxia and sulfide on the eggs of the two Acartia species cannot be a factor explaining the spatial distribution in coastal and brackish environments of these copepods.Feeding experiments on A. clausi were also performed. Suitability of different algal species to rear this copepod was evaluated and the results were compared with data previously obtained for A. tonsa. Differences in feeding needs between A. clausi and A. tonsa are discussed.     

The effect of habitat and human disturbance on the spatiotemporal activity of two urban carnivores: The results of an intensive camera trap study

With rising urbanization, the presence of urban wildlife is becoming more common, increasing the need for wildlife‐friendly spaces in urban planning. Despite this, understanding is limited to how wildlife exploits urban environments and interacts with human populations, and this is vital to our ability to manage and conserve wildlife in urban habitats. Here, we investigate how two urban mammal species, the red fox (Vulpes vulpes) and the European badger (Meles meles), exploit urban environments. Using intensive camera trap surveys, we assessed how habitat and human disturbance influenced the spatiotemporal activity of these species across south‐west London. Firstly, we found elevated activity levels of both species at boundaries and within built‐up areas, suggesting movement paths follow anthropogenic features. However, badgers were most active in woodland, indicating the importance of high cover habitats suitable for setts and foraging. Secondly, we found badger activity levels were negatively affected by human activity, whilst foxes were unaffected. Further investigation suggested foxes may adapt their activity patterns to avoid human disturbance, with badger activity patterns less plastic. Whilst the results of this study are useful for both the conservation and management of urban wildlife populations, these results also show potential factors which either facilitate or limit wildlife from fully exploiting urban environments.     

Unusual iridoid glycosides in Veronica sects. Hebe and Labiatoides

In a chemosystematic investigation of three Southern hemisphere species of Veronica, namely the Australian Veronica derwentiana Andrews and Veronica perfoliata R.Br. (formerly Derwentia species), and the New Zealand Veronica catarractae G. Forster (formerly a species of Parahebe), the water-soluble constituents were isolated and identified by spectroscopic methods. Apart from other iridoid glucosides common to the genus, three unusual substituted benzoyl esters of aucubin (derwentiosides A–C) were obtained from V. derwentiana and a chlorinated iridoid glycoside (catarractoside) from V. catarractae in addition to other iridoids common to the genus. The chemical profile of V. perfoliata is similar to that of Northern hemisphere species of Veronica because of the presence of characteristic 6-O-catalpol esters. The profile of V. derwentiana is unique, since 6-O-esters of aucubin rather than of catalpol dominate, however, the acyl groups are the same as those present in catalpol esters found in some other Veronica sections. V. catarractae also contains one of the catalpol esters characteristic of Veronica, but in addition three 6-O-rhamnopyranosyl substituted iridoid glycosides, one of which is 6-O-rhamnopyranosylcatalpol. Esters of the latter compound are previously only known from the more derived species in recent phylogenetic trees of sect. Hebe to which V. catarractae now also belongs, but as a more basal member.     

福州大叶榕隐头果内的小蜂群落结构与多样性

对福州2个样地10株大叶榕果内小蜂群落组成和物种多样性进行研究。全年在两个样地267个隐头果内共收集到小蜂13458只。发现大叶榕隐头果内有7种小蜂,隶属小蜂总科Chalcidoidae中的榕小蜂科Agaonidae、金小蜂科Pteromalidae的隐针榕小蜂亚科Epichrysomallinae、锥尾榕小蜂亚科Otitesellinae和延腹榕小蜂亚科Sycoryctinae;广肩小蜂科Eurytomidae、刻腹小蜂科Ormyridae、姬小蜂科Eulophidae,其中榕小蜂科的Platyscapa coronata是大叶榕唯一的传粉者,传粉方式为主动传粉;非传粉榕小蜂的雄性多型现象普遍。传粉与非传粉小蜂的性比明显具有偏雌现象。传粉小蜂性比为0.19±0.07,非传粉小蜂中Camarothorax bismasculinus小蜂性比为0.36±0.10;Walkerella sp.小蜂性比为0.36±0.22,Sycoscapter sp.小蜂性比为0.31±0.22,Sycophila sp.小蜂性比为0.35±0.13。雄性多型现象可能是导致非传粉小蜂性比提高的原因之一。根据各种榕小蜂发生数量及连续性,可将大叶榕隐头果中的榕小蜂分为常见种和偶见种,Platyscapa coronata、Camarothorax bismasculinus、Walkerella sp.、Sycoscapter sp.和Sycophila sp.为常见种,Omyrus sp.和Aprostocetus sp.为偶见种。偶见种的存在对常见种的数量几乎没有影响,偶见种利用的是榕果内未饱和的一部分资源,也可能是榕果为偶见种的发生预留了空间和资源。首次发现姬小蜂科的昆虫寄生在榕果内,且有一定的种群数量,为姬小蜂科昆虫分类及其生物学、生态学特性研究提供了基础资料。在大叶榕小蜂群落结构中,传粉小蜂和非传粉小蜂的种类和数量呈现明显的季节性。冬-春季(12-翌年5月)榕果内小蜂的种类和数量较多,传粉榕小蜂是优势种,其重要值达到0.42,榕果种子结实率高;夏-秋季(6-11月间)小蜂种类和数量略少,Camarothorax bismasculinus和Sycophila sp.是优势种,其重要值分别为0.56和0.28,而传粉小蜂的重要值仅为0.025,此期大叶榕榕果中几乎找不到传粉小蜂,榕果结实率极低,对大叶榕的繁殖利益有较大的负面影响。雨水和高温等不良气候,可能是导致夏-秋季雄花期榕果内的传粉小蜂数量骤减的主要原因。两个实验样地的小蜂群落结构组成没有明显差异,年变化趋势相似。研究结果为城市绿化和热带雨林生物多样性保护提供科学依据。     

Community Structure of Coastal Fishes in Relation to Heavily Impacted Human Modified Habitats

Diversity and community structure of coastal fishes were compared between reforested mangrove and reclaimed sandy habitats at Pasir Ris, in the eastern part of Singapore. Both habitats supported a total of 91 species, but a single species, Ambassis kopsii dominated in abundance. Mean fish density was significantly higher at the reclaimed sandy shore than the reforested mangrove, but the reforested mangrove habitat yielded higher diversity. Apart from A. kopsii, abundant species in the mangroves included Ambassis interrupta, Thryssa hamiltonii, Acentrogobius sp., Scatophagus argus and Arius sagor. Anodontostoma chacunda, Acentrogobius sp., Leiognathus decorus, Sillago sihama and Stolephorus sp. were abundant in the reclaimed sandy habitat. Both habitats exhibited a higher mean density and average species richness during high tide. Several species from the family Gobiidae dominated the catch during low tide while pelagic fishes were most abundant during high tide. Diel variation showed significantly higher density during the day than at night, a result that contrasts to similar studies elsewhere. However, species richness showed no significant variation between day and night catches. Interaction between combined factors of time of the day and tidal height on fish density and average species richness was significantly different. The results indicated both habitat types to be important fish nurseries.     

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.