Aims Beta diversity is the variation in species composition among sites in a geographic region. Beta diversity is a key concept for understanding the functioning of ecosystems, for the conservation of biodiversity and for ecosystem management. The present report describes how to analyse beta diversity from community composition and associated environmental and spatial data tables.
Methods Beta diversity can be studied by computing diversity indices for each site and testing hypotheses about the factors that may explain the variation among sites. Alternatively, one can carry out a direct analysis of the community composition data table over the study sites, as a function of sets of environmental and spatial variables. These analyses are carried out by the statistical method of partitioning the variation of the diversity indices or the community composition data table with respect to environmental and spatial variables. Variation partitioning is briefly described herein.
Important findings Variation partitioning is a method of choice for the interpretation of beta diversity using tables of environmental and spatial variables. Beta diversity is an interesting 'currency' for ecologists to compare either different sampling areas or different ecological communities co-occurring in an area. Partitioning must be based upon unbiased estimates of the variation of the community composition data table that is explained by the various tables of explanatory variables. The adjusted coefficient of determination provides such an unbiased estimate in both multiple regression and canonical redundancy analysis. After partitioning, one can test the significance of the fractions of interest and plot maps of the fitted values corresponding to these fractions.

Aims Mapping vegetation through remotely sensed images involves various considerations, processes and techniques. Increasing availability of remotely sensed images due to the rapid advancement of remote sensing technology expands the horizon of our choices of imagery sources. Various sources of imagery are known for their differences in spectral, spatial, radioactive and temporal characteristics and thus are suitable for different purposes of vegetation mapping. Generally, it needs to develop a vegetation classification at first for classifying and mapping vegetation cover from remote sensed images either at a community level or species level. Then, correlations of the vegetation types (communities or species) within this classification system with discernible spectral characteristics of remote sensed imagery have to be identified. These spectral classes of the imagery are finally translated into the vegetation types in the image interpretation process, which is also called image processing. This paper presents an overview of how to use remote sensing imagery to classify and map vegetation cover.
Methods Specifically, this paper focuses on the comparisons of popular remote sensing sensors, commonly adopted image processing methods and prevailing classification accuracy assessments.
Important findings The basic concepts, available imagery sources and classification techniques of remote sensing imagery related to vegetation mapping were introduced, analyzed and compared. The advantages and limitations of using remote sensing imagery for vegetation cover mapping were provided to iterate the importance of thorough understanding of the related concepts and careful design of the technical procedures, which can be utilized to study vegetation cover from remote sensed images.

Aims How growth of wild and crop species responds to global environmental perturbations has both ecological and agricultural significance in a changing world. The primary aim of this synthesis was to quantitatively assess the interactive effects of intraspecific competition and elevated CO₂ on biomass production in herbaceous species.
Methods Using meta-analytical techniques, we synthesized data from publications before 2006 that reported biomass responses to elevated CO₂ in 321 herbaceous species grown in isolation or in competition with con-specific individuals.
Important findings Intraspecific competition differentially modified biomass responses to elevated CO₂ in wild and crop species. For example, competition reduced CO₂ stimulation of total biomass (W_T) from 27 to 23% in wild species, but by a much greater magnitude, i.e., from 43 to 32% in crops. Competition had no effect on responses of either above- (W_AG) or below-ground (W_BG) biomass to elevated CO₂ in wild species, but significantly diminished CO₂ enhancement of W_AG, although not of W_BG, in crops. Considerable variations were found among functional groups in the modification of growth responses to elevated CO₂ by intraspecific competition, which exerted greater depression on CO₂ enhancement in C₃ than in C₄ species and in non-legumes than in legumes. Elevated CO₂ affected leaf and stem growth of individually grown C₃ graminoids and forbs similarly, but increased leaf growth only in C₄ graminoids and stem growth only in C₄ forbs. Results from this synthesis demonstrated that intraspecific competition differentially affected growth responses to elevated CO₂ in wild and crop species. The wild–crop species differences will have important implications for understanding primary production by herbaceous species in both natural and agricultural ecosystems in the future when atmospheric CO₂ is significantly higher than the current level.

Aims Many experiments have shown a positive effect of species richness on productivity in grassland plant communities. However, it is poorly understood how environmental conditions affect this relationship. We aimed to test whether deep soil and limiting nutrient conditions increase the complementarity effect (CE) of species richness due to enhanced potential for resource partitioning.
Methods We grew monocultures and mixtures of four common grassland species in pots on shallow and deep soil, factorially combined with two nutrient levels. Soil volume was kept constant to avoid confounding soil depth and volume. Using an additive partitioning method, we separated biodiversity effects on plant productivity into components due to species complementarity and dominance.
Important findings Net biodiversity and complementarity effects were consistently higher in shallow pots, which was unexpected, and at the low nutrient level. These two results suggest that although belowground partitioning of resources was important, especially under low nutrient conditions, it was not due to differences in rooting depths. We conclude that in our experiment (i) horizontal root segregation might have been more important than the partitioning of rooting depths and (ii) that the positive effects of deep soil found in other studies were due to the combination of deeper soil with larger soil volume.

Aims Large hurricanes have profound impacts on temperate forests, but owing to their infrequent nature these effects have rarely been examined in detail. In 1996, Hurricane Fran significantly damaged many long-term tree census plots in the Duke Forest on the North Carolina Piedmont, thereby providing an exceptional opportunity to examine pre- and post-hurricane forest compositional trajectories. Our goal was to examine immediate, short-term (0–4 years) and longer term (~5 year) hurricane-induced structural, spatial and compositional changes in the tree population (stem d.b.h> 1 cm) in the context of our detailed, long-term knowledge of the dynamics of these forests.
Methods We surveyed stem damage and tree mortality in 34 long-term permanent plots (ca. 70-year record; 404–1?012 m 2) and 7 large mapped tree stands (ca. 20-year record; 5?250–65?000 m 2) representing both transition-phase, even-aged pine stands and uneven-aged upland hardwood forests. We employed three types of damage measures to quantify stand-level damage severity: percentage of stems damaged, percentage of basal area lost and a 'stand-level damage index'. Second-order spatial analysis (Ripley's K -function) was used to investigate patterns in tree mortality.
Important findings Our study found hurricane effects on the structural attributes of Piedmont forests to be variable and patchy. Changes in tree species composition, however, were modest. Uprooting was the major damage type for the overstory trees [diameter at breast height (d.b.h.)>10 cm] apparently due to the exposure of the crowns to high wind combined with heavy rainfall prior to and during the storm. Saplings, juvenile trees and small trees (1–10 cm d.b.h.) of the understory and midstory were mainly damaged by being pinned or bent by their damaged large neighbors. Hurricane-induced tree mortality varied weakly among species, was positively correlated with pre-hurricane tree size and remained up to 2-fold higher than pre-hurricane background mortality 5 years after the hurricane. Spatial point pattern analysis revealed a patchy distribution of tree mortality during the hurricane sampling interval. Hurricane Fran resulted in a dramatic increase in average gap size from ca. 400 m 2 pre-hurricane to ca 1100 m 2 after the hurricane, whereas maximum gap sizes reached 18–34 times larger than the pre-hurricane levels.

Aims The mechanism by which species richness affects variation in ecosystem functioning both within and among ecosystems remains a key question at the interface of community and ecosystem ecology. Statistical averaging (the smoothing of average system performance via consideration of additional components) and the insurance effect (reduced variation in system performance by inclusion of asynchronously varying components) predict that more diverse communities should vary less both between replicates and internally. We experimentally tested these theories in small plant assemblages.
Methods We constructed plant assemblages modeled after old-field plant communities. We varied species richness, species composition and initial densities while holding functional group richness constant in replicate assemblages under glasshouse conditions.
Important findings The inverse of the coefficient of variation of aboveground biomass production, a proxy measure of reliability, increased with higher diversity when examined at the level of the assemblage (i.e. among-replicate assemblages) but not at the levels of functional group or species. These stabilizing processes were weakest in low-diversity, low-density assemblages. This experiment demonstrates the utility of hierarchical analysis of ecosystem reliability at the assemblage, functional group and species level.

Aims Free-surface flow-constructed wetland is a powerful means for the reduction of contaminants from agricultural runoff. Wetlands dominated by submerged aquatic vegetations (SAVs) may take up nutrients, particularly phosphorus (P), from surface flow with high efficiency. The objective of this study was to assess P removal performance by the SAV community under high and low P concentrations.
Methods Weekly or biweekly inflow and outflow water samples were collected from four small constructed wetlands (test cells) planted with SAV in South Florida, USA, between September 1999 and September 2001. These test cells were divided into two groups, with the north test cells receiving a higher inflow total phosphorus (TP) concentration (average = 75 μg l^-1) than the south test cells receiving a lower TP concentration (average = 23 μg l^-1). Limerock (LR) berms were installed in two of these test cells to allow an evaluation of the efficiency of this physical barrier to enhance wetland performance.
Important findings North test cells displayed high TP removal of ~60% while the removal efficiency of the south test cells was only ~20%. Soluble reactive phosphorus concentrations in both north and south test cells were sequestered down to near-detection limit. High removal efficiencies for particulate phosphorus were also observed in the north test cells. The LR berms at the two test cells were found to be associated with decreases of an average TP removal of 2 μg l^-1. Outflow TP concentration did not increase with inflow TP concentration, but increased with nominal hydraulic loading rates. Findings from this study demonstrated high P removal from inflow water containing high TP concentration by the SAV wetland and the importance of hydraulic regime to wetland performance.