Rate of compositional turnover along gradients and total gradient length

Abstract. A new measure of compositional turnover rate at any gradient point is proposed. The absolute values of the derivatives of estimated species response curves are used to estimate the instantaneous rate of change of the community. The total gradient length can be found by integrating the instantaneous turnover rates over the gradient span. Both the instantaneous rate and total gradient length have been known under the name of beta diversity. Our method is elaborated for the Gaussian response function. It is compared to Hill's SD measure, much used for estimating the gradient length in connection of Detrended Correspondence Analysis with nonlinear rescaling for axes. The turnover rate along a canopy cover gradient in forest vegetation in Finland was used as an example. Forest site type and stand age were used as subsidiary gradients. The two ways to compute Hill's scaling gave very different results and were not comparable with the new method. The turnover rate was dependent on the gradient position. However, the turnover rate along the gradient of interest and its total length were dependent on the subsidiary gradients.     

Large-scale terrestrial gastropod community composition patterns in the Great Lakes region of North America

Abstract: Previous ordination studies of land snail community composition have been limited to four or fewer habitat types from sites separated by no more than 300 km. To investigate the nature of large-scale patterns, North American land snail assemblages at 421 sites, representing 26 habitat types and covering a 1400 × 800 km area, were ordinated using global, nonmetric multi-dimensional scaling (NMDS). These data were then subjected to model-based cluster analysis and kmeans clustering to identify the main compositional groups and most important environmental covariables. Six primary compositional groups were identified. Three of these largely represent upland forest and rock outcrop sites, while the remaining largely represent either lowland forest, lowland grassland or upland grassland habitats. The geographical location and moisture level of sites also influences community composition. A strong compositional difference exists between sites having duff vs. turf soil surface layers. Only 8% of sites were improperly classified when soil surface architecture was used as the sole predictor variable. Fully 43% of taxa exhibited significant preferences towards one of these surface types, while only 15% of relatively common (10 + occurrence) taxa showed no preferences. Twelve groups of closely related taxa within the same genus had members that favoured different surface types, indicating that differential selection pressures have existed over evolutionary time scales. While turf faunas appeared unaffected by anthropogenic disturbance, duff faunas were strongly impacted, suggesting that their conservation will require protection of soil surface architecture.     

Closing the gap between plant ecology and Quaternary palaeoecology

Ecology and Quaternary palaeoecology have largely developed as parallel disciplines. Although both pursue related questions, information exchange is often hampered by particularities of the palaeoecological data and a communication gap has been perceived between the disciplines. Based on selected topics and developments mainly in Quaternary palaeoecology, we show that both disciplines have converged somewhat during recent years, while we still see untapped potential for closer interactions. Macroecology is probably the discipline that most easily combines different time scales and where co‐operations between palaeoecologists, geneticists and vegetation modellers have been inspiring. Quantitative vegetation reconstructions provide robust estimates of tree composition and land cover at different spatial scales, suitable for testing hypotheses about long‐term vegetation changes or as quantitative background data in studies on contemporary vegetation patterns. Palaeo data also hold yet unexplored potential to study the drivers of long‐term diversity, and aspects of functional diversity may facilitate comparisons between continents and over glacial–interglacial cycles.     

Scale dependence of the correlation between human population presence and vertebrate and plant species richness

Human presence is generally negatively related to species richness locally, but the relationship is positive at coarse scales. An increase in the strength of the latter correlation with increasing study resolution has been documented within studies, but it is not known whether such a scale dependence is present across different studies. We test this with data on the spatial co-occurrence of human beings and the species richness of plants and vertebrates from a continuum of scales. The correlation coefficient between human presence and species richness is positively related to study grain and extent. The correlation turns from positive to negative below a study grain of c. 1 km and below a study extent of c. 10 000 km². The broad-scale positive correlation between human presence and species richness suggests that people have preferentially settled and generally flourished in areas of high biodiversity and/or have contributed to it with species introductions and habitat diversification. The scale dependency of the correlation between people and biodiversity's presence emphasizes the importance of the preservation of green areas in densely populated regions.     

Geomorphic principles of terrain organization and vegetation gradients

Abstract. Moisture and nutrient gradients consistently explain much of the variation in plant species composition and abundance, but these gradients are not spatially explicit and only reveal species responses to resource levels. This study links these abstract gradients to quantitative, spatial models of hill‐slope assembly. A gradient analysis in the mixed‐wood boreal forest demonstrates that patterns of upland vegetation distribution are correlated to soil moisture and nutrient gradients. Variation in species abundance with time since the last fire is removed from the gradient analysis in order to avoid confounding the physical environment gradients. The physical‐environment gradients are related to qualitative positions on the hill slope i.e. crest, mid‐slope, bottom‐slope. However, hill‐slope shape can be quantitatively described and compared by fitting allometric equations to the slope profiles. Using these equations, we show that hill‐slope profiles on similar surficial materials have similar parameters, despite coming from widely separated locations. We then quantitatively link the moisture and nutrient gradients to the equations. Moisture and nutrients significantly increase as distance down‐slope from the ridgeline increases. Corresponding vegetation composition changes too. These relationships characterize the general pattern of vegetation change down most hill slopes in the area. Since hill slopes are a universal feature of all landscapes, these principles may characterize landscape scale spatial patterns of vegetation in many environments.     

The relationship between the seed bank and species composition of plant communities in two British salt marshes

The composition of the seed bank was compared with that of the above-ground vegetation in two British salt marshes. Vegetation and seed banks were sampled in autumn and spring. There was a relatively low correlation between seed bank and vegetation in most perennial-dominated zones. Percentage annual plant cover was significantly positively correlated to percentage similarity value between vegetation and seed bank. Cluster analysis indicated that the zones dominated by annuals and by Suaeda vera on the ungrazed Nod Marsh in Norfolk formed groups between seed bank and vegetation, whereas on the Llanrhidian Marsh in Wales the seed bank of four of the six zones formed a group.     

Spatial segregation of pines and oaks under different fire regimes in the Sierra Madre Occidental

Surface fire can modify spatial patterns and self-thinning in pine-oak ecosystems. Spatial pattern analyses were used to compare pattern development and interspecific spatial interactions in trees and seedlings in five Madrean pine-oak stands with different recent fire histories. Interspecific and intraspecific patterns were compared in small (< 15 cm dbh) and large (< 15 cm dbh) diameter classes of the pines (Pinus durangensis, P. teocote, and P. leiophylla) and oaks (Quercus sideroxylla, Q. crassifolia, and Q. laeta) that collectively dominated the five stands. Numbers of juvenile trees in 2.5 × 2.5 m subplots were correlated with cumulative distances to adult trees. Small pine and oak trees were intraspecifically clustered at all scales, irrespective of fire regime. Large pines were strongly clustered only in stands with longer fire-free intervals, and patterns of large versus small pine trees were regular or random in frequent fire stands. These patterns were consistent with fire-induced mortality of maturing trees under frequent fire. Large and small pines were segregated from small oaks at short and long distances in one stand with a 32-year fire-free interval, implying that two or more dynamic factors had produced regular patterns at different scales. Such regular spatial patterns at short distances were not seen in other stands. Therefore, there was little evidence for direct competition between oaks and pines. The results reported here are consistent with studies from other pine-oak ecosystems showing that different fire regime and site factors interact to influence stand development processes and relative dominance of pines and oaks. In some stands, the continued absence of fire could foster increasing tree densities and an intensification of local neighborhood effects, producing segregation of pine and oak species at longer distances. This revised version was published online in August 2006 with corrections to the Cover Date.     

Examining the strength and possible causes of the relationship between fire history and Sudden Oak Death

Fire can be a dominant process in the ecology of forest vegetation and can also affect forest disease dynamics. Little is known about the relationship between fire and an emerging disease epidemic called Sudden Oak Death, which is caused by a new pathogen, Phytophthora ramorum. This disease has spread across a large, fire-prone portion of California, killing great numbers of oaks and tanoaks and infecting most associated woody plants. Suitable hosts cover a much broader geographic range, raising concern over where the disease may spread. To understand the strength and potential sensitivities of a fire–disease relationship, we examined geographic patterns of confirmed P. ramorum infections in relation to past fire history. We found these infections to be extremely rare within the perimeter of any area burned since 1950. This finding is not caused by spatial bias in sampling for the disease, and is robust to variation in host abundance scenarios and to aggregation of closely spaced sampling locations. We therefore investigated known fire-related factors that could result in significantly lower incidence of the disease in relatively recently burned landscapes. Chemical trends in post-fire environments can influence the success of pathogens like P. ramorum, either by increasing plant nutrient stress or by reducing the occurrence of chemicals antagonistic to Phytophthoras. Succession in the absence of fire leads to greater abundance of host species, which will provide increased habitat for P. ramorum; this will also increase intraspecific competition where these trees are abundant, and other density-dependent effects (e.g. shading) can reduce resource allocation to defenses. Despite these findings about a fire–disease relationship, a much deeper understanding is necessary before fire can be actively used as a tool in slowing the epidemic.     

Causes of pattern in plant communities where environmental change is rapid and species longevity is short

Questions : To what extent can spatial structure and its causes be determined in a highly disturbed environment? What are the main determinants of pattern and are these species‐specific? How much do spatial patterns change over generations? Location : Wimmera region of southern Australia. Methods : Broad‐leaved weeds were counted in 225 000 contiguous 20‐cm square quadrats. A substantial number of these quadrats were recorded again after two and four years. An hierarchical ‘adaptive analysis’ approach was used to select spatial analytical methods to examine specific aspects of pattern and variation in pattern from year to year. Results : Patterns varied among species and included both dense and sparse patches surrounded by areas of zero density, diffuse gradations of density and clear anisotropy. Patterns in Erodium botrys and Oxalis pes‐caprae persisted over years, whereas patterns in Arctotheca calendula were less pronounced and varied over time. Edaphic factors appeared to have only a minor influence over the spatial distribution of the weed community as a whole. In Oxalis pes‐caprae, whose patches were hypothesized to have been shaped by cultivation, there was no spread in four years, despite further tillage. Outlying plants of O. pes‐caprae failed to establish new patches, even in the year of greatest population increase. Little evidence of localised recruitment events was found. Conclusions : Despite repeated annual disturbances by natural and anthropogenic mechanisms, clear and interpretable spatial structure develops in annual weeds over a range of spatial resolutions. Adaptive analysis is a useful approach to the characterization of such patterns.     

Overstory vegetation and successional trends of Land Between The Lakes,USA

133 stands from the uplands of Land Between The Lakes (LBL) were sampled. Stand data were ordinated to identify clinal patterns in the overstory vegetation. A coeno-cline, accounting for 52% of the species variance, was developed from the first ordination axis. Classification of stands identified nine dominance types: Pinus echinata-Quercus spp., Q. prinus, Q. prinus-Q. alba, Q. stellata-Q. alba, Q. velutina-Q. alba, Q. alba, Q. alba-Q. rubra, Acer saccharum-Q. alba-Fagus grandifolia sadF. grandifolia-A. saccharum. Compositionally-stable (climax) and unstable (successional) stands were analyzed separately. Trajectories of unstable stands include the succession of P. echinata to Quercus-dominated communities on xeric sites and of Quercus types to more mesophytic communities (e.g. A. saccharum and F. grandifolia) onmesic sites. These shifts indicate the nature of the future climax overstory composition at LBL. The first axis DCCA ordination for climax stands accounted for 45% of the vegetation variance. Factor Analysis identified two significant suites of variables related to vegetation: soil chemistry/soil moisture and soil texture. Specific variables related to variation in the climax vegetation include soil pH, calcium and magnesium, effective soil depth, available water capacity, percent rock in the soil, slope position, aspect, elevation and distance to the opposing slope. Modal positions of species along the direct gradient ordination were similar in rank order to those derived from the indirect gradient ordination of all stands. The latter ordination represents the present forest vegetation pattern at LBL. Climax stands showed a shift in modes of Quercus spp. toward the xeric end of the gradient and increases in habitat width of mesophytic species. Following a reduction in disturbance, species appear to adjust to changes in competition and available habitat. That is, the dimensions of realized niches (i.e. habitat widths) change with succession. The climax vegetation at LBL appears to show centrifugal organization.     

Diversity and succession of epiphytic macrolichen communities in low‐elevation managed conifer forests in Western Oregon

Abstract. We examined epiphytic macrolichen communities in Pseudotsuga menziesii (Douglas‐fir) forests across the western Oregon landscape for relationships to environmental gradients, stand age and structure, and commercial thinning. We used a retrospective, blocked design through the Coast and the western Cascade ranges of Oregon. Each of our 17 blocks consisted of a young, unthinned stand (age 50–110 yr); an adjacent, thinned stand of equivalent age; and an old‐growth stand (age > 200 yr). We found 110 epiphytic macrolichen taxa in the stands. Forage‐providing alectorioid lichens and the nitrogen‐fixing cyanolichen Lobaria oregana associated strongly with old‐growth stands and remnant old trees in younger stands (unthinned + thinned). Relative to unthinned stands, thinned stands had a slightly higher abundance of alectorioid lichens and a greater presence of Hypogymnia imshaugii. However, thinned stands hosted a lower landscape‐level (γ) diversity, lacking many species that occurred infrequently in the unthinned stands. Patterns in the lichen community composition correlated strongly with climatic gradients; the greatest variation in composition was between the Coast and Cascade ranges. The difference in communities between mountain ranges was greatest among stands 70–110 yr old, suggesting a difference in lichen successional dynamics between the ranges.     

Phytogeographical and community similarities of alpine tundras of Changbaishan Summit,China, and Indian Peaks,USA

Abstract. We compared the diversity, phytogeography, and plant communities in two mid-latitude alpine tundras with comparable aerial and elevational extents: Changbaishan Summit in eastern Asia and Indian Peaks in western North America. Despite wide separation, the two areas shared 72 species. In all, 43% of the species on Changbaishan Summit are also distributed in the alpine zones of western North America, while 22% of the species on Indian Peaks are also distributed in the alpine zones of eastern Asia. Almost all the shared species also occur in the Beringian region. Phytogeographical profiles of species and genera showed that 69% of species and over 90% of genera in both alpine tundras belong to the three phytogeographical categories: cosmopolitan, circumpolar, and Asian-North American. We attributed the current floristic relationship between these widely separated areas to the periodic past land connection between the two continents during the Tertiary and Pleistocene. Indian Peaks has a closer floristic relationship with the Arctic tundra than does Changbaishan Summit. Indian Peaks also has 45% higher species richness and lower vegetation cover than Changbaishan Summit. Plant communities from the two areas were completely separated in the two-way indicator species analysis and non-metric multidimensional scaling on floristic data at both species and generic levels, whereas ordination of communities by soil data produced a greater overlap. The plant communities on Changbaishan Summit in general have lower alpha diversity, higher beta diversity (lower between-community floristic similarity), and more rare species than does Indian Peaks. Mosaic diversity does not differ in the two alpine tundras, although the analysis suggests that Changbaishan Summit communities are more widely spaced on gradients than the Indian Peaks communities.     

Natural disturbance and tree species coexistence in an old-growth beech - dwarf bamboo forest,southwestern Japan

Abstract. The structure and composition of a cool-temperate old-growth beech (Fagus crenata) - dwarf bamboo (Sasa spp.) forest, partially affected by landslide disturbance, in the Daisen Forest Reserve of southwestern Japan, were investigated in relation to forest floor and canopy conditions. All stems ≥ 4 cm DBH were mapped on a 4-ha plot and analyses were made of population structure, spatial distribution and spatial association of major tree species. The dominant species, F. crenata, which had the maximum DBH among the species present, had the highest stem density. However, for other species, larger-sized species had lower stem density with few smaller stems or saplings, while smaller-sized species had higher stem density with many smaller stems or saplings. Canopy trees of F. crenata were distributed randomly in the plot, while its stems in the other layers and all other species were distributed patchily. Small patches represent gap-phase regeneration. Larger patches correlate with landslide disturbance, difference in soil age, or the presence/absence of Sasa. Cluster analysis for spatial associations among species and stems in the different layers revealed that the forest community consists of several groups. One main group was formed on sites not covered with Sasa. This group contained a successional subgroup (from Betula grossa to Acer mono and/or F. crenata) initiated by landslide disturbance and a subgroup of tree species that avoid Sasa. Another group was formed on sites with mature soils covered largely with Sasa. This contained associations of canopy trees of F. crenata and smaller-sized tree species such as Acanthopanax sciadophylloides and Acer japonicum. It is found that the community of this old-growth beech forest is largely organized by natural disturbance and heterogeneous conditions of the forest floor (difference in soil age and presence/absence of Sasa). The existence of these different factors and the different responses of species to them largely contribute to the maintenance of tree species diversity in this forest.; Keywords: Cluster analysis; Fagus crenata; Forest dynamics; Gap; Landslide; Spatial pattern.     

Dimensionality Reduction and Visualization of the Environmental Impacts of Domestic Appliances

There is an increasing worldwide concern about the problem of dealing with the waste electrical and electronic equipment (WEEE), given the high volume of appliances that are disposed of every day. In this article, an environmental evaluation of WEEE is performed that combines life cycle assessment (LCA) methodology and multivariate statistical techniques. Because LCA handles a large number of data in its different phases, when one is trying to uncover the structure of large multidimensional data sets, multivariate statistical techniques can provide useful information. In particular, principal‐component analysis and multidimensional scaling are two important dimension‐reducing tools that have been shown to be of help in understanding this type of complex multivariate data set. In this article, we use a variable selection method that reduces the number of categories for which the environmental impacts have to be computed; this step is especially useful when the number of impact categories or the number of products or processes to benchmark increases. We provide a detailed illustration showing how we have used the proposed approach to analyze and interpret the environmental impacts of different domestic appliances.     

In situ quantitation of the spatial scale of calling distances and population density-independent N-acylhomoserine lactone-mediated communication by rhizobacteria colonized on plant roots

We used computer-assisted microscopy at single cell resolution to quantify the in situ spatial scale of N-acylhomoserine lactone (AHL)-mediated cell-to-cell communication of Pseudomonas putida colonized on tomato and wheat root surfaces. The results of this in situ quantification study on close-to-natural surfaces challenge the conventional view of a quorum group requirement of high cell densities for this type of bacterial communication. In situ image analysis indicated that the effective 'calling distance' on root surfaces was most frequent at 4-5 microm, extended to 37 microm in the root tip/elongation zone and further out to 78 microm in the root hair zone. The spatial scale of these calling distances is very long-range in proportion to the size of individual bacteria. Geostatistical modeling analysis implicated the importance of AHL-gradients mediating effective communication between remote cells. We conclude that AHL-mediated cell-to-cell communication occurs not only within dense populations, but also in very small groups and over long ranges between individual bacteria, and therefore this cellular activity is more commonplace and effective than hitherto predicted. We propose that this cell-to-cell communication is governed more by the in situ spatial proximity of cells within AHL-gradients than the requirement for a quorum group of high population density.     

Response patterns of Vaccinium myrtillus and V. vitis-idaea along nutrient gradients in boreal forest

Abstract. The relationships between biomass of dwarf shrub species and nutrient gradients of forest soils was studied under field conditions in boreal forests. The biomass-response curves of Vaccinium myrtillus and V. vitis-idaea were fitted against soil nutrient gradients using Generalized Linear Models (GLM). Ecological niches of Vaccinium myrtillus and V. vitis-idaea were evaluated, and effects of nitrogen addition (manipulation of the nutrient gradient) on response function were tested. The Vaccinium species showed statistically significant Gaussian responses along soil nitrogen, phosphorus and calcium gradients, but not along other gradients (K and Mg). Furthermore, manipulation of the nitrogen gradient seemed to have a minor effect on response functions, i.e. addition of nitrogen did not change ecological niches of these species. Ecological optima of V. myrtillus and V. vitis-idaea on the nutrient gradients were about the same. This study suggests that differences in dominance between Vaccinium myrtillus and V. vitis-idaea in boreal forest is not determined by nutrient gradients, but may rather be explained by light conditions and/or moisture availability.     

Linear relationships between aboveground biomass and plant cover in low open herbaceous vegetation

Abstract. Four herbaceous plant species of a sand dune area and several herb species of an open early‐successional patch were investigated for the occurrence of a simple relationship between aboveground biomass and plant cover. Without exception linear regressions of aboveground biomass on plant cover were found with slope factors depending on the growth form of the species. These results suggest that (early) growth of herbaceous plants in low and (temporarily) open vegetation is not affected by possible constraints caused by a decreasing ratio of plant cover to aboveground biomass. The obtained linear relationships could be used for rapid non‐destructive determination of aboveground biomass by image‐analysis of cover data.     

Nutrient limitation in boreal plant communities and species influenced by scything

Abstract. The nutrient status was studied in permanent plots of four plant communities, two rich-fen communities and two wooded grassland communities, all formerly used for haymaking. The concentrations of N, P and K in plant material of dominant and subdominant species (above- and below-ground) were measured in plots experimentally scythed annually or biennially for two decades, and in plots unscythed for four decades. Three of the communities had an N:P ratio of 14 or less, indicating N-limitation; the most fertile grassland community had particularly low values for the N:P ratio (6–12), as did a majority of the species, including all tall-herb species. A species-rich community of fen-margin vegetation in the lowest productive rich fen, had an N: P ratio of 17–19 in the above-ground biomass, which indicates P-limitation of nutrients. Molinia caerulea and Thalictrum alpinum were found to be the vascular plants with the highest N:P ratio, indicating P-limitation of nutrients. Calculations of N:K and K:P ratios indicated possible K-limitation in the rich-fen communities, especially for Thalictrum alpinum, the species with the highest N:K value. No expected change from N- to P-limited growth was found; in contrast, a reduction in the N:P ratio was found in the annually scythed plots of the rich fens, suggesting that reduced biomass production is mainly a result of disturbance by scything. As expected, a reduction in the concentration of K was detected in the scythed plots.     

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.