贵州百里杜鹃风景区旅游干扰对杜鹃群落特征的影响

为揭示旅游干扰对于百里杜鹃风景区杜鹃群落特征影响,选取杜鹃纯林和杜鹃混交林两种杜鹃群落,分析干扰对群落结构及物种多样性的影响。采用典型抽样的方法进行样地设置和调查,通过旅游影响系数分析样地旅游干扰等级,并分析对比了不同旅游干扰程度和干扰方式对群落特征的影响。研究表明：1）百里杜鹃景区共有植被67科102属130种,其中杜鹃纯林共有植被97种,以马缨杜鹃、箭竹和露珠杜鹃为优势物种,杜鹃混交林共有植被115种,以马缨杜鹃、露珠杜鹃和映山红为优势种;2）两种杜鹃群落均在中等干扰水平时具有最高的Berger-Parker丰富度指数和Shannon多样性指数,中度干扰一定程度上促进了杜鹃群落物种多样性增加,不同的是两种群落的Shannon指数变化趋势不同,在杜鹃纯林中表现为中度干扰>轻度干扰>重度干扰,而在杜鹃混交林中中度干扰>重度干扰>轻度干扰,相较于杜鹃纯林,杜鹃混交林物种更为丰富,在旅游干扰下生物多样性更为稳定,抗干扰能力更强,而杜鹃纯林受旅游干扰波动显著;3）垃圾指数、踩踏指数与杜鹃混交林物种多样性指数、群落生长结构无明显相关性,而垃圾指数与杜鹃纯林Shannon多样性指数、物种数以及草本均高呈显著负相关,踩踏指数与杜鹃纯林灌木层高度、盖度呈现极显著负相关,与草本均高呈显著正相关;4）各杜鹃群落对旅游干扰有不同响应,为保持杜鹃群落稳定性,应在花季适当分流,严格控制杜鹃纯林的重度干扰。     

Tree replacement in small canopy gaps of a Tsuga canadensis forest in the Southern Appalachians,Tennessee

Summary Tree species replacement was studied in 95 canopy gaps created by the fall of single trees in an undisturbed, old-growth forest in Great Smoky Mountains National Park, Tennessee. When large trees (dbh>70 cm) of the very shade tolerant species, Tsuga canadensis, die and fall, they are usually replaced by less tolerant species such as Betula alleghaniensis, Liriodendron tulipifera, and Magnolia fraseri. Species diversity of the replacement trees, measured by the index, 1/p_i ², was 5.77 compared to a diversity of 1.66 for the fallen trees.     

Mite (Acari) colonization of vegetated mine tailings near Sudbury,Ontario, Canada

INCO Ltd. near Sudbury, Ontario is rehabilitating nickel- and copper-mine tailings using vegetating techniques that have resulted in habitats of varying age and complexity. Mite (Acari) communities and soil quality characteristics were used to evaluate soil ecosystem development on four tailings sites, 0, 8, 20 and 40 years post rehabilitation in comparison with that on four control sites. Abundance, species richness, diversity (H) and community structure of soil mites were sensitive indicators of tailings rehabilitation and soil formation. Mite density on older and botanically diverse tailings sites was comparable to that on control sites; however, species richness of oribatids and mesostigmatics was lower than on control sites. Mite species richness and diversity on tailings were lower at less botanically diverse sites regardless of age. Similarity of tailings-mite communities to control-site communities generally increased with age; however, similarities were all less than 60% (Sorenson's quantitative index, C _N). Mite assemblages on tailings were dominated by a few colonizing species, whereas control sites had a diverse assemblage of species. Soil pH and organic matter (SOM) of rehabilitated tailings improved with age and degree of botanical complexity. Mite density and diversity was positively related to SOM particularily for the Oribatida. SOM and mites were mainly restricted to the 0–5-cm horizon.     

Species richness and composition of Curculionidae (Coleoptera) in a conifer plantation, secondary forest, and old-growth forest in the central mountainous region of Japan

Weevil (Curculionidae, Coleoptera) species richness and composition were investigated and compared among larch [Larix kaempferi (Lamb.) Carriére] plantations, secondary forests, and old-growth forests in the central mountainous region of Japan. In addition, to assess the effects of forest-management practices, namely thinning and long-rotation logging schedules (long rotation), the weevil assemblages of recently thinned middle-aged and long-rotated larch plantations were compared with those of middle-aged larch plantations. Malaise traps were set in 44 stands of these forest types, and weevils were separated and identified. Several environmental factors other than forest type were also examined. Weevil species richness and diversity indices [Shannon-Wiener diversity index (H) and Simpsons index of diversity (D)] were higher in the secondary forest than in the larch plantation. Because of its wide distribution and higher weevil species richness, the secondary forest contributed to maintaining weevil diversity in this region. Old-growth forest had higher diversity indices (H and D) than did the larch plantation. The secondary forest had the highest number of species in total. Though the number of individuals was the highest in larch plantation, species richness, H and D of the plantation were generally low. Weevil community structure and species composition differed among the three forest types, but the difference in weevil composition between the larch plantation and the other two forest types was the largest. Forest type is probably the most important factor for determining the differences in weevil assemblage, and further, both dominant tree type (coniferous trees versus broad-leaved trees) and the number of mature tree species seem to be important factors for weevil species composition. Among forest management practices, long rotation caused diversity indices (H and D) to increase while thinning appeared to cause only minor changes in the weevil assemblages. Because species richness and species composition of Curculionidae well reflected the differences in forest types and some other environmental factors investigated, this family seems suitable for diversity research in forests. Further research on biodiversity with the use of this family should, therefore, be expected.     

Species–area curve and distance–decay relationships indicate habitat thresholds of ectomycorrhizal fungi in an old‐growth Pseudotsuga menziesii landscape

Aim

Ectomycorrhizal fungi (EMF) are a diverse and essential biota of forests that are vulnerable to species loss through reductions in late‐seral habitat. We examined how the spatial ecology of this biota, particularly distance–decay and species–area relationships, could better inform habitat thresholds for EMF conservation planning.

Location

Southeast Vancouver Island near Victoria, British Columbia, Canada.

Methods

Using a stratified sampling design, 11 plots (0.15 ha in size) were established at 0.05–17.5 km apart across 2,800 ha of mesic old‐growth Pseudotsuga menziesii var. menziesii and Tsuga heterophylla forests. EMF communities were compiled through molecular analysis of root tips and sporocarps.

Results

The EMF community was comprised of many Cortinarius, Piloderma, Russula and Tricholoma species typical of mesotrophic habitat. A total of 238 EMF species were observed, of which 86 species were detected only once. The ratio of average species richness per plot (84 taxa) to total richness was low at 0.35, and inherent stochasticity of the EMF community was estimated to be 31% community dissimilarity for species incidence. Distance decay of EMF communities was nonlinear, with an estimated slope break at 2.6 km, followed by a largely unchanging trend in β‐diversity. Accumulated species–area curves were fitted best by the cumulative Weibull sigmoid model, and the asymptote (367 species) at approx. 50 ha was consistent with nonparametric estimates of γ‐diversity (342–362 spp.).

Main conclusions

Old‐growth forests host an impressive amount of EMF diversity, and many of the Ramaria, Inocybe and Russula species are likely to be endemic to the Pacific Northwest. Both niche‐ and neutral‐based processes influenced EMF community composition, resulting in a minimum threshold of 50 ha (1.8% of the sample area) for capturing γ‐diversity. These spatial patterns will help design and evaluate conservation efforts, such as retention forestry, to sustain fully diverse EMF communities over managed landscapes.

     

Tree diversity change in remaining primary mixed-broadleaved Korean pine forest under climate change and human activities

Studying biodiversity change in existing typical ecosystems of the world under possible global climate change and local human activities is important for diversity conservation. An adapted forest dynamics model is used to simulate tree diversity change of the remaining primary mixed-broadleaved Korean pine forest (RPMKPF) in northeast China under global climate change and local human activities for the next 50 years. Human activities include logging, which removes all big trees (DBH > 50 cm), removing all individuals of each single species and all species of each functional type (shade tolerant, shade intolerant and medium type tree species). As results for RPMKPF, the index of tree diversity decreases under climate change, but it increases significantly under a combination of climate change and logging. Removing all individuals of each single species significantly affects the tree diversity of the ecosystem. After the removal of shade tolerant species, both and _c indices of tree diversity experience a significant change. The index decreases significantly under climate change when shade intolerant or medium type tree species are removed, but the _c index does not change significantly. The results of this study have implications for tree diversity management in RPMKPF under climate change and human activities.     

Diversity of Peronosporomycete (Oomycete) Communities Associated with the Rhizosphere of Different Plant Species

Peronosporomycete (oomycete) communities inhabiting the rhizospheres of three plant species were characterized and compared to determine whether communities obtained by direct soil DNA extractions (soil communities) differ from those obtained using baiting techniques (bait communities). Using two sets of Peronosporomycete-specific primers, a portion of the 5′ region of the large subunit (28S) rRNA gene was amplified from DNA extracted either directly from rhizosphere soil or from hempseed baits floated for 48 h over rhizosphere soil. Amplicons were cloned, sequenced, and then subjected to phylogenetic and diversity analyses. Both soil and bait communities arising from DNA amplified with a Peronosporomycetidae-biased primer set (Oom1) were dominated by Pythium species. In contrast, communities arising from DNA amplified with a Saprolegniomycetidae-biased primer set (Sap2) were dominated by Aphanomyces species. Neighbor-joining analyses revealed the presence of additional taxa that could not be identified with known Peronosporomycete species represented in GenBank. Sequence diversity and mean sequence divergence ( ) within bait communities were lower than the diversity within soil communities. Furthermore, the composition of Peronosporomycete communities differed among the three fields sampled and between bait and soil communities based on F_st and parsimony tests. The results of our study represent a significant advance in the study of Peronosporomycetes in terrestrial habitats. Our work has shown the utility of culture-independent approaches using 28S rRNA genes to assess the diversity of Peronosporomycete communities in association with plants. It also reveals the presence of potentially new species of Peronosporomycetes in soils and plant rhizospheres.     

Plant species diversity in abandoned coppice forests in a temperate deciduous forest area of central Japan

We investigated plant species diversity as it related to stand structure and landscape parameters in abandoned coppice forests in a temperate, deciduous forest area of central Japan, where Fagus crenata was originally dominant. The species occurring in the study plots were classified into habitat types based on a statistical analysis of their occurrence bias in particular habitats (e.g., primary forest, coniferous plantation) in the landscape studied. The relationships between stand structure, which reflected the gradient of management, and forest floor plant species diversity (H and J) and richness (number of species per unit area) were not significant. However, these factors did influence the forest floor plant composition of the different types of habitat. According to the multiple regression analysis, species diversity and the richness of forest floor plants was affected by landscape parameters rather than by stand structure. For trees, species richness was mainly affected by the relative dominance of F. crenata, which is one of the stand structure parameters that decreases with intensive management. This is probably because many of the tree species that are characteristic of coppice forests increase after F. crenata have been eliminated by management; these species are not dominant in the original forest, where they are suppressed by F. crenata, the shade-tolerant dominant species. The species diversity (H and J) of trees was positively correlated with some landscape parameters, including the road density around the study plot, which may be associated with the intensity of management activity. The number of disturbance-tolerant species increased with increasing road density. Stand structure mainly affected disturbance-intolerant forest floor plant species and disturbance-tolerant tree species. Thus, the species diversity responses differed between forest floor plants and trees. The impact of forest management on species diversity was more prominent for forest floor plants.     

Effects of functional diversity and functional dominance on complementary light use depend on evenness

Questions

Does functional diversity play a more important role than species richness in complementary resource use? Is the effect of functional diversity on complementarity greater when species evenness is higher? Does functional dominance play an important role in resource use when species evenness is low?

Location

An arable field in Linhai City, Zhejiang Province, China.

Methods

We assembled experimental plant communities with different species richness (one, two, four, eight and 12 species) and evenness (low and high). In each community, we quantified light interception efficiency (LIE ) and light complementarity index (LC ) to reflect light use. We measured four functional traits related to light capture to quantify functional diversity and functional dominance. We then tested effects of observed species richness, functional diversity and functional dominance on LIE , LC and above‐ground biomass in the low and high evenness communities.

Results

Functional diversity was positively related to LIE , LC and above‐ground biomass in the high evenness communities, but not in the low evenness communities. In contrast, functional dominance was positively related to LIE and negatively related to LC in the low evenness communities, but not in the high evenness communities. Moreover, functional dominance had a larger promotion to above‐ground biomass in the low evenness communities. Observed species richness and evenness had a significant interactive effect on LIE and LC . LIE of a species mixture of the low evenness communities was positively correlated with LIE of the monoculture consisting of the species with the highest initial abundance in the species mixture, while LC of a species mixture of the low evenness communities was negatively correlated with it.

Conclusions

Functional diversity and functional dominance play a crucial role in light complementary use of plant communities, and their effects on light complementarity are mediated by species evenness. Thus, interactions of functional traits and evenness may greatly affect ecosystem functioning.

     

Genetic diversity in the threatened insular endemic plantAster asa-grayi (Asteraceae)

Genetic diversity in an insular endemic plantAster asa-grayi was examined using enzyme electrophoresis. Distribution ofA. asa-grayi is restricted to only four subtropical islands of Japan, and this species is listed as vulnerable to extinction in the Red Data Book of Japanese wild plants. A total of 161 individuals were sampled from five populations on four islands. Genetic diversity values at the population level were very low, compared to other plant species with a similar life history. Genetic variability at the species level is comparable to the mean value of endemic species. Genetic differentiation among populations is extremely high (G_ST= 0.71), indicating that the gene flow among populations is highly impeded, and pollen and seed dispersal is limited due to the pollinators and the seed morphology. This is because the four islands are geographically isolated. Fixation indices suggested that most populations do not randomly cross. To conserve the genetic diversity of the species, artificial crossings among different island populations are necessary.     

A phytosociological analysis of woody species in forest communities of a part of Kumaun Himalaya

This paper reports on a detailed phytosociological analysis of forests in the NW catchment of the Gola River in Kumaun Himalaya, 29°19–29°27N and 79°32–79°42E. Fourteen sites and 56 stands at elevations ranging from 1200 to 2523 m and covering the following five forest types were investigated: Pinus roxburghii, mixed, Quercus leucotrichophora, Q. lanuginosa, and Q. floribunda. The basal cover of the forests differed according to slope position and aspect. The three oak forests had more basal cover than the other two, and Q. lanuginosa had the most. The performance of individual tree and shrub species and the number of saplings and seedlings differed according to slope position and aspect. The mixed forest had the greatest tree diversity, and among the others diversity increased with increasing basal cover. The diversity of trees, saplings, and herb layer was greatest on aspects with intermediate temperature and moisture conditions; whereas that of shrubs and seedlings increased towards the cooler (and wetter) and warmer (and drier) exposures. There was a positive relation between the diversity of shrubs plus seedlings and trees plus saplings in P. roxburghii and mixed forests; whereas this relationship was inverse in the three oak forests. In general, the dominance-diversity curves for the tree layer followed a geometric series conforming to the niche pre-emption situation in communities of low diversity. Among the forests, the regeneration was best in Q. lanuginosa and worst in Q. leucotrichophora.Nomenclature follows: Osmaston (1926).Finacial support from the Council of Scientific and Industrial Research, New Delhi and the Indian Space Research Organisation, Banglore is gratefully acknowledged.     

Genetic biogeography among insular populations of the amphidromous fish Plecoglossus altivelis assessed from mitochondrial DNA analysis

Ayu, Plecoglossus altivelis, is an amphidromous fish which isdistributed over the Japanese Archipelago including peripheralislands, some of which harbor endangered populations. Weanalyzed nucleotide sequences of the mitochondrial DNA controlregion to clarify the factors affecting the genetic variabilityof mainland and insular populations. As inferred from nucleotidediversity , the overall low genetic variability in insularpopulations suggests their vulnerability to extinction, althoughthere were still significant genetic differences betweenpopulations. Patterns of genetic variability were explained bygene flow with the mainland population as inferred from pairwisefixation index F _ST and the rate of loss of haplotypes assessedfrom haplotype diversity h, in turn, these two factors arefunctions of the geographical distance from the mainland andpopulation size, respectively. We conclude that the geneticvariability observed on each island is brought about by its owndynamic equilibrium maintained by continuous immigration andlocal extinction, depending on the geographical location of theisland relative to the mainland together with the size of theisland. Conservation measures for insular populations arerecommended to take this uniqueness into account.     

The role of recruitment and dispersal limitation in tree community assembly in Amazonian forests

Background: Species composition of plant communities is shaped by the interplay between dispersal limitation, environmental filters and stochastic events.

Aims: The aim of this work was to investigate the effects of dispersal limitation and environmental filtering on tree recruitment. To accomplish this, we employed the unified neutral theory of biodiversity and biogeography to examine migration within the metacommunity, defined as a set of interacting local communities linked by the dispersal of multiple potentially interacting species.

Methods: We sampled 12,975 individuals with dbh ≥ 1 cm in 26 1-ha permanent plots, including habitats of terra firme, transitional forests, várzea and campinarana, on the upper Madeira River, Brazilian Amazon.

Results: Campinarana drew individuals from outside the metacommunity species pool at a mean probability of recruitment of 0.06, a much lower probability than terra firme (0.31), transitional (0.21) and várzea forests (0.22). Environmental variables, such as water table depth, soil texture and fertility, were related to differences in community assembly.

Conclusions: Species abundance distribution and diversity patterns of plant assemblages in a large river landscape in the Amazon highlight the importance of environmental heterogeneity that conditions beta-diversity. The high variation in recruitment probabilities from the metacommunity species pool to local communities suggests high habitat variability in the process of maintaining patterns of local diversity.     

Responses of the soil fungal communities to the co‐invasion of two invasive species with different cover classes

• Soil fungal communities play an important role in the successful invasion of non‐native species. It is common for two or more invasive plant species to co‐occur in invaded ecosystems.
• This study aimed to determine the effects of co‐invasion of two invasive species (Erigeron annuus and Solidago canadensis) with different cover classes on soil fungal communities using high‐throughput sequencing.
• Invasion of E. annuus and/or S. canadensis had positive effects on the sequence number, operational taxonomic unit (OTU) richness, Shannon diversity, abundance‐based cover estimator (ACE index) and Chao1 index of soil fungal communities, but negative effects on the Simpson index. Thus, invasion of E. annuus and/or S. canadensis could increase diversity and richness of soil fungal communities but decrease dominance of some members of these communities, in part to facilitate plant further invasion, because high soil microbial diversity could increase soil functions and plant nutrient acquisition. Some soil fungal species grow well, whereas others tend to extinction after non‐native plant invasion with increasing invasion degree and presumably time. The sequence number, OTU richness, Shannon diversity, ACE index and Chao1 index of soil fungal communities were higher under co‐invasion of E. annuus and S. canadensis than under independent invasion of either individual species.
• The co‐invasion of the two invasive species had a positive synergistic effect on diversity and abundance of soil fungal communities, partly to build a soil microenvironment to enhance competitiveness of the invaders. The changed diversity and community under co‐invasion could modify resource availability and niche differentiation within the soil fungal communities, mediated by differences in leaf litter quality and quantity, which can support different fungal/microbial species in the soil.

     

Urban rotifers: structure and densities of rotifer communities in water bodies of the Poznań agglomeration area (western Poland)

The rotifer fauna of 19 mostly small water bodies (natural and artificial ponds, clay-pits and pools) in Pozna was studied on four occasions during 1996–98 to determine the suitability of urban areas for rotifer habitats. Rotifers were present in all the water bodies studied, with 114 species in 39 genera found, representing ca. 25% of all rotifers recorded from Poland. Mean diversity was 10 spp (range 1–36). Most common were: Brachionus angularis and Keratella cochlearis (spring), Colurella uncinata, Lecane closterocercaand Lepadella patella (summer) and L. closterocerca and K. cochlearis (autumn). Rotifer densities (1-1503 ind l^–1), Shannon's diversity (H 0.00-3.71) and dominant species differed in different water-bodies. The index of percentage similarity of community showed strong differences in qualitative structure of rotifer assemblages. The different types of water habitats, both the existing or the newly created in towns, may explain the relatively high diversity of rotifer communities observed in the urban areas studied.     

Comparison of landscape diversity in forests of the upper Rhine and the middle Loire floodplains (France)

Traditional measures of biotic indices (, , ) from phytosociological relevés are used to compare diversity at three scale-levels in the upper Rhine valley (Alsace, northeastern region) and the middle Loire (Bourgogne, central region), France. Both study areas included a tributary. The Ill, which is the Rhine tributary in this sector, has no forest communities in common with the main river because of opposite hydrological and edaphic characteristics. This is not the case in the Loire valley, in which the fluvial characteristics are close to those of its tributary, the Allier.Nearly all forest communities (12/14) were shown to be species-rich, due to the role of natural disturbances. Species richness peaks in late-successional forests of the Rhine valley (for example, up to 50 woody species in Querco-Ulmetum). Sixty per cent of the forest-communities are comon to the two floodplains, which explains why 85% of the families, 65% of the genera and 55% of the species are in common. Compared to the Loire valley, the Rhine valleys shows higher biotic diversity. This was related first to its geographical situation, and second to higher landscape heterogeneity. Human disturbance through river management is responsible for changes in species composition as shown by floristic comparison of flooded and unflooded sites. Insularity of natural forests among man-made landscapes is involved in species diversity. In order to preserve the natural diversity of such rich landscapes, floodable areas should be recreated and the attitudes of foresters should evolve accordingly.     

A comparison of fungal endophytic community diversity in tree leaves of rural and urban temperate forests of Kanto district,eastern Japan

To clarify the effects of forest fragmentation and a change in tree species composition following urbanization on endophytic fungal communities, we isolated fungal endophytes from the foliage of nine tree species in suburban (Kashiwa City, Chiba) and rural (Mt. Wagakuni, Ibaraki; Mt. Takao, Tokyo) forests and compared the fungal communities between sites and host tree species. Host specificity was evaluated using the index of host specificity (Si), and the number of isolated species, total isolation frequency, and the diversity index were calculated. From just one to several host-specific species were recognized in all host tree species at all sites. The total isolation frequency of all fungal species on Quercus myrsinaefolia, Quercus serrata, and Chamaecyparis obtusa and the total isolation frequency of host-specific species on Q. myrsinaefolia, Q. serrata, and Eurya japonica were significantly lower in Kashiwa than in the rural forests. The similarity indices (nonmetric multidimensional scaling (NMS) and C_MH) of endophytic communities among different tree species were higher in Kashiwa, as many tree species shared the same fungal species in the suburban forest. Endophytic fungi with a broad host range were grouped into four clusters suggesting their preference for conifer/broadleaves and evergreen/deciduous trees. Forest fragmentation and isolation by urbanization have been shown to cause the decline of host-specific fungal species and a decrease in β diversity of endophytic communities, i.e., endophytic communities associated with tree leaves in suburban forests were found to be depauperate.     

Effects of fire and selective logging on the tree species composition of lowland dipterocarp forest in East Kalimantan, Indonesia

Tree species composition (diameter at breast height (dbh) 10 cm) was studied in primary, selectively logged and heavily burnt forests in East Kalimantan, Indonesia. The number of trees, tree species, and the Fishers's- diversity index were determined for the first 15 years (burnt forest) and 25 years (selectively logged forest) after disturbance. Additionally the population structure of six common and typical Macaranga pioneer tree species was compared through time between selectively logged, burnt and primary forest. Both selectively logged and burnt forest showed a significant reduction in number of trees and tree species per surface area directly after disturbance. Fire especially affected dominant tree species, while for selective logging the opposite was observed. In selectively logged forest the number of trees, tree species and the Fishers's- index reached pre-disturbance levels within c. 15 years. For burnt forest, only the number of trees recovered to pre-disturbance levels. The number of tree species stayed constant after disturbance, while the Fishers's- index decreased. The six studied Macaranga pioneer tree species seedlings were present in all forest types. Their density seems to be unrelated to light levels in the forest understorey but strongly related to the number of mature parent trees. Their sapling densities were strongly related to light levels in the forest understorey. The studied Macaranga species formed an important part of both under- and over-storey in burnt forest 15 years after disturbance, while they were almost absent in the understorey and only moderately common in the overstorey of selectively logged forest.     

Scale-dependent relationships between the spatial distribution of a limiting resource and plant species diversity in an African grassland ecosystem

One cornerstone of ecological theory is that nutrient availability limits the number of species that can inhabit a community. However, the relationship between the spatial distribution of limiting nutrients and species diversity is not well established because there is no single scale appropriate for measuring variation in resource distribution. Instead, the correct scale for analyzing resource variation depends on the range of species sizes within the community. To quantify the relationship between nutrient distribution and plant species diversity, we measured NO₃^- distribution and plant species diversity in 16 paired, modified Whittaker grassland plots in Serengeti National Park, Tanzania. Semivariograms were used to quantify the spatial structure of NO₃^- from scales of 0.4–26 m. Plant species diversity (Shannon-Weiner diversity index; H ) was quantified in 1-m² plots, while plant species richness was measured at multiple spatial scales between 1 and 1,000 m². Small-scale variation in NO₃^- (<0.4 m) was positively correlated with 1-m² H , while 1,000-m² species richness was a log-normal function of average NO₃^- patch size. Nine of the 16 grassland plots had a fractal (self-similar across scales) NO₃^- spatial distribution; of the nine fractal plots, five were adjacent to plots that had a non-fractal distribution of NO₃^-. This finding offered the unique opportunity to test predictions of Ritchie and Olff (1999): when the spatial distribution of limiting resources is fractal, communities should display a left-skewed log-size distribution and a log-normal relationship between net primary production and species richness. These predictions were supported by comparisons of plant size distributions and biomass-richness relationships in paired plots, one with a fractal and one with a non-fractal distribution of NO₃^-. In addition, fractal plots had greater large-scale richness than paired non-fractal plots (1,0–1000 m²), but neither species diversity (H ) nor richness was significantly different at small scales (1 m²). This result is most likely explained by differences in the scale of resource variation among plots: fractal and non-fractal plots had equivalent NO₃^- variation at small scales but differed in NO₃^- variation at large scales (as measured by the fractal dimension). We propose that small-scale variation in NO₃^- is largely due to the direct effects of plants on soil, while patterns of species richness at large scales is controlled by the patch size and fractal dimension of NO₃^- in the landscape. This study provides an important empirical step in understanding the relationship between the spatial distribution of resources and patterns of species diversity across multiple spatial scales.     

Allozymic and morphological relationships amongAndrocymbium gramineum,A. europaeum,andA. psammophilum (Colchicaceae)

Levels of allozymic and morphological diversity amongAndrocymbium gramineum, A. europaeum, andA. psammophilum have been assessed using data on 17 allozyme loci and 18 morphological characters. No apparent pattern of geographic or ecological variation was found. Our results also suggest thatA. gramineum andA. europaeum should be considered members of a single species and that the insular speciesA. psammophilum can no longer be thought of as the result of a founder effect fromA. gramineum. Intrapopulational variability was greater than inter-populational variability at both levels studied, which is of strategic interest for the ex-situ conservation of these threatened endemic species.