Richness-biomass Relationships Research Articles

Water depth modulates the species richness–biomass relationship in submerged macrophytes

The effect of biodiversity on ecosystem productivity has been a controversial issue in ecological research. The species richness–productivity relationship is highly variable in natural ecosystems, with a positive relationship being one of the most commonly observed relationships. Previous regional studies from terrestrial ecosystems have demonstrated that environmental gradients can regulate the species richness–productivity relationship. However, how this relationship varies in freshwater ecosystems across spatial environment gradients remains unclear. In this study, we propose that the species richness–productivity relationship can be modulated by the water depth. Here, we surveyed the submerged macrophyte community structure by establishing 24 transects and 642 quadrats in Erhai Lake, Yunnan Plateau, China. Our findings highlight that the species richness–productivity relationship gradually changed from slightly positive to strongly positive as the environment became more light-limited with the increasing water depth, supporting the stress-gradient hypothesis. The results from this study provide new insights into the biodiversity–ecosystem functioning relationships and in managing lake macrophyte communities and productivity.

Richness–biomass relationships change with increasing acid rain intensity by shifting from positive to negative selection

The species interactions can be affected by environmental stress; however, how such change affects the plant species richness–biomass relationship is still unclear. Here, experimental plant communities with species richness levels of 1, 2, 4, and 8 were assembled and subjected to a simulated acid rain (SAR) intensity gradient (pH 7.0, 4.5 and 2.5). The species richness–biomass relationship was investigated and the absolute growth rate and survival rate were measured under each SAR intensity. With the increasing SAR intensity, the species richness–biomass relationships changed from positive to negative as a result of a shift in the biodiversity effects from positive to negative selection. Under a SAR intensity of pH 7.0, the absolute growth rate determined the biomass ratio of species in the mixtures. Mixtures that included Sedum lineare (with rapid growth) had a lower soil total nitrogen (TN), soil total phosphorus (TP), and greater aboveground biomass than mixtures that did not include the species, which led to a positive selection effect. Under a SAR intensity of pH 2.5, the survival rate determined the biomass ratio of species in the mixtures. Mixtures that included Sedum emarginatum and Phedimus spurius (with high survival rates) had less aboveground biomass than mixtures that did not include them, which led to a negative selection effect. Our results indicated that the mechanism by which a plant gains competitive superiority (i.e., a shift from rapid growth to a high survival rate) in response to environmental stress will affect the biodiversity effect. Considering future climate change scenarios, we suggest that changes in the competition mechanism should be integrated into future studies of the relationship between plant diversity and ecosystem functioning.

Hydropeaking impacts on riverine plants downstream from the world's largest hydropower dam, the Three Gorges Dam

Hydropeaking has become a global issue because of extensive hydropower dam construction worldwide. Yet, its ecological impacts on riverine ecosystems are not well studied. We explored the effects of hydropeaking on riverine plants, based on data from a ~300 km reach downstream of the world's largest hydropower dam, the Three Gorges Dam. We tested three hypotheses relating to hydropeaking impacts on species elevational distributions, assemblage structure and species-specific biomass patterns by generalized linear mixed modelling and joint species distribution modelling. We found that, first, hydropeaking greatly shaped species elevational ranges, leading to expansions of herbs to high elevations and shifting species dominance at low elevations. Secondly, we detected contrasting effects of hydropeaking on assemblage-level characteristics of herbs. The inundation induced by hydropeaking had strong effects on assemblage composition and biomass allocation, where more biomass was allocated to belowground part. Hydropeaking blurred the species richness-biomass relationship, although it had little effect on species richness or plot-level biomass. Thirdly, hydropeaking induced inundation was the most important covariate driving species biomass patterns of riverine plants, although complex species-specific effects were identified, and random effects were often large in fitted models. We concluded that hydropeaking likely acted as a major driver of plant community assembly in rivers with a hydropower dam. Conservation and restoration of riverine plants can benefit from the inclusion of water level management in operational schemes of hydropower dams, especially during the early life history stages.

A graphical null model for scaling biodiversity–ecosystem functioning relationships

AbstractGlobal biodiversity is declining at rates faster than at any other point in human history. Experimental manipulations at small spatial scales have demonstrated that communities with fewer species consistently produce less biomass than higher diversity communities. Understanding the consequences of the global extinction crisis for ecosystem functioning requires understanding how local experimental results are likely to change with increasing spatial and temporal scales and from experiments to naturally assembled systems.Scaling across time and space in a changing world requires baseline predictions. Here, we provide a graphical null model for area scaling of biodiversity–ecosystem functioning relationships using observed macroecological patterns: the species–area curve and the biomass–area curve. We use species–area and biomass–area curves to predict how species richness–biomass relationships are likely to change with increasing sampling extent. We then validate these predictions with data from two naturally assembled ecosystems: a Minnesota savanna and a Panamanian tropical dry forest.Our graphical null model predicts that biodiversity–ecosystem functioning relationships are scale‐dependent. However, we note two important caveats. First, our results indicate an apparent contradiction between predictions based on measurements in biodiversity–ecosystem functioning experiments and from scaling theory. When ecosystem functioning is measured as per unit area (e.g. biomass per m2), as is common in biodiversity–ecosystem functioning experiments, the slope of the biodiversity ecosystem functioning relationship should decrease with increasing scale. Alternatively, when ecosystem functioning is not measured per unit area (e.g. summed total biomass), as is common in scaling studies, the slope of the biodiversity–ecosystem functioning relationship should increase with increasing spatial scale. Second, the underlying macroecological patterns of biodiversity experiments are predictably different from some naturally assembled systems. These differences between the underlying patterns of experiments and naturally assembled systems may enable us to better understand when patterns from biodiversity–ecosystem functioning experiments will be valid in naturally assembled systems.Synthesis. This paper provides a simple graphical null model that can be extended to any relationship between biodiversity and any ecosystem functioning across space or time. Furthermore, these predictions provide crucial insights into how and when we may be able to extend results from small‐scale biodiversity experiments to naturally assembled regional and global ecosystems where biodiversity is changing.

Decadal dynamics of dry alpine meadows under nitrogen and phosphorus additions

Plants often exhibit positive responses to multiple nutrient additions, but generalities about the life form and traits of the most responsive species are few. Findings from long-term experiments in dry meadow alpine tundra in Colorado, USA, were used here to examine univariate and multivariate analyses of plant and plant trait responses. We found transient responses for community richness–biomass relationships, but a consistent increase in forb dominance in nitrogen (N) and phosphorus (P) addition plots. The response seen in the N + P plots was not affected by additions of micronutrients or potassium. Multivariate analyses corroborate transient responses in community shifts over shorter-time scales, and directional shifts in N + P over two decades. Using species-level aboveground trait data when available, we found N + P may favor species with resource-acquisitive traits, regardless of their lifeform, as well as relatively tall grasses, regardless of their resource strategy. In the absence of N and P limitation but with the environmental constraints found in dry alpine meadows, plant richness and community structure continued to exhibit transient states for decadal time frames.

Humped Relationship between Herbaceous Species Richness and Biomass Reveals a Potential for Increasing Productivity in a Temperate Desert in Central Asia

Species richness-biomass relationship has become a primary focus in plant community ecology. The most commonly reported pattern of species richness and biomass is the humped relationship with a peak in richness at moderate biomass, although negative, positive, or no relationships exited in some cases. However, the richness-biomass relationship in the temperate deserts of Central Asia, where herbaceous species with different life forms are abundant, remains unclear. In this study, 21–214 plots with herbaceous richness and aboveground biomass for each of four plot sizes (0.25, 25, 100, and 400 m2) were surveyed in early summer and early autumn in the Gurbantunggut Desert, China. Linear and quadratic regressions were employed to examine the richness-biomass relationship and the location of the richness peak. Significantly unimodal species richness-biomass relationships were observed in all plot sizes and seasons (except for 0.25 m2 plot in summer). In most cases (9/11), the biomass at the richness peak was higher than half of the biomass range. Meanwhile, the percent of sampling plots where the biomass was less than the peak was considerably greater than 50% (72.7 to 100%) in all cases, and nine of them were more than 95%, indicating strong interspecific coexistence and weak interspecific competition. In conclusion, under the background of increasing precipitation and nitrogen deposition, the humped richness-biomass relationship and the high percent of sampling plots with low biomass jointly revealed a huge potential for increasing productivity, which is crucial for the carbon fixation and ecosystem stability in deserts of Central Asia.

Climatic humidity mediates the strength of the species richness–biomass relationship on the Mongolian Plateau steppe

The relationships between biodiversity and ecosystem functioning (BEF) have been extensively studied over past decades. However, the environmental factors affecting their relationships, and how their relationships vary under the influence of environmental factors, remain controversial. Studying the BEF relationships in natural/wild environments is of great significance for devising strategies in biodiversity conservation and ecosystem functioning. Using the data from 75 sites on the Mongolian Plateau steppe, we analyzed the relationship between species richness and biomass with general linear models (GLMs) and linear mixed models (LMMs), and analyzed the variation in the species richness–biomass relationships under environmental conditions by the partial least square path modeling (PLSPM). The results showed that de Martonne aridity index affected both species richness and community biomass in parallel, and that hydrothermal coupling conditions were more important direct impact factors for aboveground biomass. However, the significant species richness–biomass relationships became weaker when the effects of environmental factors (i.e. climate and soil properties) were present. Climate humidity was the most important factor in mediating the relationship between species richness and community biomass. Our research suggested that species richness–biomass relationships are weak in the natural grasslands of the Mongolian Plateau, and that this may be due to the differences in the regional-scale environment and changes in species interactions. We recommend that a more comprehensive understanding of the relationship between diversity and biomass requires further research within broader environmental gradients.

A general biodiversity–function relationship is mediated by trophic level

Species diversity affects the functioning of ecosystems, including the efficiency by which communities capture limited resources, produce biomass, recycle and retain biologically essential nutrients. These ecological functions ultimately support the ecosystem services upon which humanity depends. Despite hundreds of experimental tests of the effect of biodiversity on ecosystem function (BEF), it remains unclear whether diversity effects are sufficiently general that we can use a single relationship to quantitatively predict how changes in species richness alter an ecosystem function across trophic levels, ecosystems and ecological conditions. Our objective here is to determine whether a general relationship exists between biodiversity and standing biomass. We used hierarchical mixed effects models, based on a power function between species richness and biomass production (Y = a × Sb), and a database of 374 published experiments to estimate the BEF relationship (the change in biomass with the addition of species), and its associated uncertainty, in the context of environmental factors. We found that the mean relationship (b = 0.26, 95% CI: 0.16, 0.37) characterized the vast majority of observations, was robust to differences in experimental design, and was independent of the range of species richness levels considered. However, the richness–biomass relationship varied by trophic level and among ecosystems; in aquatic systems b was nearly twice as large for consumers (herbivores and detritivores) compared to primary producers; in terrestrial ecosystems, b for detritivores was negative but depended on few studies. We estimated changes in biomass expected for a range of changes in species richness, highlighting that species loss has greater implications than species gains, skewing a distribution of biomass change relative to observed species richness change. When biomass provides a good proxy for processes that underpin ecosystem services, this relationship could be used as a step in modeling the production of ecosystem services and their dependence on biodiversity.

Consistent Richness-Biomass Relationship across Environmental Gradients in a Marine Macroalgal-Dominated Subtidal Community on the Western Antarctic Peninsula.

Biodiversity loss has spurred the biodiversity-ecosystem functioning research over a range of ecosystems. In Antarctica, however, the relationship of taxonomic and functional diversity with ecosystem properties (e.g., community biomass) has received less attention, despite the presence of sharp and dynamic environmental stress gradients that might modulate these properties. Here, we investigated whether the richness-biomass relationship in macrobenthic subtidal communities is still apparent after accounting for environmental stress gradients in Fildes Bay, King George Island, Antarctica. Measurements of biomass of mobile and sessile macrobenthic taxa were conducted in the austral summer 2013/4 across two environmental stress gradients: distance from nearest glaciers and subtidal depth (from 5 to 30 m). In general, community biomass increased with distance from glaciers and water depth. However, generalised additive models showed that distance from glaciers and depth accounted for negligible proportions of variation in the number of functional groups (i.e., functional richness) and community biomass when compared to taxonomic richness. Functional richness and community biomass were positive and saturating functions of taxonomic richness. Large endemic, canopy-forming brown algae of the order Desmarestiales dominated the community biomass across both gradients. Accordingly, differences in the composition of taxa accounted for a significant and large proportion (51%) of variation in community biomass in comparison with functional richness (10%). Our results suggest that the environmental factors here analysed may be less important than biodiversity in shaping mesoscale (several km) biomass patterns in this Antarctic system. We suggest that further manipulative, hypothesis-driven research should address the role of biodiversity and species’ functional traits in the responses of Antarctic subtidal communities to environmental variation.

Disentangling tree species identity and richness effects on the herb layer: first results from a German tree diversity experiment

AbstractQuestionsThe forest herb layer provides a multitude of ecosystem services as a result of its species‐rich character. Herb layer diversity and biomass are both influenced by tree layer composition and species richness through species‐specific influences on environmental conditions. The results of observational studies on richness–biomass relationships between tree and herb layer have not been unequivocal. We examined tree species identity and richness effects on herb layer species richness, composition, biomass and nutrient concentrations in young experimental tree plantations.LocationBIOTREE tree diversity experiment, Kaltenborn, Germany.MethodsSixteen plots were planted in 2004, using a pool of four tree species (beech, oak, Douglas‐fir, Norway spruce) and four richness levels, comprised of all possible species combinations. In this way, complete dilution was avoided, allowing separation of tree species identity and richness effects. Mixed plots consisted of a matrix of monospecific patches. One permanent vegetation quadrat of 1 m2was established in the centre of four patches per plot. The herb layer was monitored in 2004 and 2010; in 2010 light measurements were performed in each quadrat, and in 2011 above‐ground biomass was sampled on 0.25 m2within the quadrat.ResultsCommunity composition shifted markedly between 2004 and 2010. Tree species identity did not yet influence temporal compositional turnover or herb layer species richness in 2004 and 2010. Ellenberg N indicated a temporal shift towards lower soil fertility under all tree species, whereas Ellenberg R indicated decreasing soil acidity under beech and Douglas‐fir. Ellenberg L and F showed no shift from 2004 to 2010. Apart from the significantly lower Ellenberg N for beech, none of the Ellenberg indicators indicated interspecific differences. Douglas‐fir, and especially Norway spruce, negatively influenced total above‐ground herb layer biomass. Douglas‐fir also induced lower relative light availability, higher potassium, magnesium and nitrogen concentrations and lower carbon:nitrogen ratios in the total biomass. Higher tree species richness positively affected graminoid and total biomass and also slightly increased plot‐level herb layer species richness.ConclusionsDespite the young age of the experiment, tree species identity and richness effects on the herb layer could be discerned. We expect these relations to become stronger with time.

The relationship between species richness and biomass changes from boreal to subtropical forests in China

Diversity‐manipulation experiments suggest a positive effect of biodiversity on ecosystem properties (EPs), but variable relationships between species richness and EPs have been reported in natural communities. An explanation for this discrepancy is that observed richness–EPs relationships in natural communities change with environment and species functional identities. But how the relationships change along broad‐scale climatic gradients has rarely been examined. In this paper, we sampled 848 plots of 20 × 30 m2 from boreal to tropical forests across China. We examined plot biomass with respect to environmental factors, tree species richness and functional group identity (FGI, i.e. evergreen vs deciduous, and coniferous vs broadleaf). Variation partitioning was used to evaluate the relative effects of the three classes of factors. We found that, most of the ‘effects’ (percentage of variation explained) of richness and FGI on forest biomass were shared with environmental factors, but species richness and FGI still revealed significant effects in addition to environment for plots across China. Richness and FGI explained biomass mainly through their shared effects instead of independent effects, suggesting that the positive biodiversity effect is closely associated with a sampling effect. The relative effects of richness, FGI and environment varied latitudinally: the independent effects of environment and richness decreased from boreal to subtropical forests, whereas the total effect of FGI increased. We also found that the slope of richness–biomass relationship decreased monotonically from boreal to subtropical forests, possibly because of decreasing complementarity and increasing competition with increasing productivity. Our results suggest that while species richness does have significant effects on forest biomass it is less important than environmental gradients and other biotic factors in shaping large‐scale biomass patterns. We suggest that understanding how and why the diversity–EPs relationships change along climatic gradient would be helpful for a better understanding of real biodiversity effects in natural communities.

Plant Richness-Biomass Relationships in Restored Northern Great Plains Grasslands (USA)

We investigated plant richness-biomass relationships in tall grass (Field 1, 12 years) and mixed grass (Field 2, 5 years) restoration experiments located in the northern Great Plains grasslands (USA). They were organized as randomized factorial experiments with fertilization rates (N or P) and number of species as factors. Results were as follows: (1) above ground biomass (AGB) increased and year-to-year variability declined with plant species and functional form richness. (2) AGB was higher when the species had various combinations: (a) high relative growth rates, root density, root surface area, N or P uptake rates, and N use efficiency; (b) low root-to-shoot ratio and root plasticity. (3) Biomass stability was positively related to high root surface area in Field 1 and N use efficiency and P uptake rates in Field 2. (4) Invasion of nonseeded species declined with plant species and functional form richness.

Spatial Structure Alters the Shape of the Unimodal Species Richness-Biomass Relationship in a Neutral Model

Variation in individual density may explain the unimodal richness-biomass relationship in which species richness peaks at an intermediate level of total biomass. However, it is unclear how individual density is regulated by community thinning (i.e., mortality due to competition with neighbors) as total above-ground biomass increases. We developed a simulation model which demonstrates that the spatial structure of a population can influence the initiation and rate of community thinning and thus the shape of the richness-biomass relationship. Specifically, we found that more clustered populations resulted in a more abrupt initiation and rapid rate of thinning and thus a sharper unimodal richness-biomass relationship. Our simulation also demonstrated that a wide diversity of richness-biomass relationships can be produced by community-thinning.

Relationships between herbaceous diversity and biomass in two habitats in arid Mediterranean rangeland

Plant diversity patterns vary across the landscape. This study was conducted to answer the question: what is the pattern of species diversity ( α and β) along an abstract productivity/cover gradient at two topographical positions (Wadi (a depression with overland flow) and hilltop) of a Mediterranean herbaceous plant community in Jordan? Results indicated that the less productive hilltop localities exhibited higher species richness than the more productive Wadi localities. Species richness exhibited a unimodal relationship with aboveground biomass within Wadis whereas a positive linear relationship was revealed for hilltops. Within Wadis, abundant species did not show a significant relationship with productivity while common and rare species showed a unimodal relationship. Within hilltops, abundant, common, and rare species showed a linear relationship with biomass. β-diversity, measured as species dissimilarity, showed significant negative relationship to biomass within hilltops, whereas a positive relationship was observed within Wadis. Wilson–Shmida index ( β T) had a unimodal function with increased differences in productivity whereas Morisita–Horn index ( C mh) showed a reverse unimodal relationship. Examination of the species richness–biomass relationship among species groups (abundant, common, and rare) suggested that abundant species maybe more important on low productivity sites whereas common and rare species maybe more important on high productivity sites.

Relationship between species richness and biomass on environmental gradient in natural forest communities on Mt. Xiaolongshan, northwest China

We analyzed the relationship between species richness and biomass in natural forest communities at two similar sites on Mt. Xiaolongshan, northwest China. At both sites, a wide range of tree layer biomass levels was available by local biomass estimation models. In order to identify underlying mechanism of the species richness-biomass relationship, we included different water resource levels and number of individuals in each plot in our analysis. We sampled 15 and 20 plots (20 m × 20 m), respectively, at both two sites. These plots were sampled equally on the sunny slope and the shady slope. Species richness, number of individuals of each species and diameter at breast height (DBH) as a substitute of biomass of tree layer were recorded in each sample. At one site, the relationship between species richness and biomass was significant on the sunny slope, and this relationship disappeared on the shady slope due to more environmental factors. The relations between species richness and number of individuals and between number of individuals and biomass paralleled the species richness-biomass relation on both slopes. The difference in number of individuals-biomass relationships on the sunny slope and the shady slope revealed “interspecific competitive exclusion” even though the species richness-biomass relationships were not hump-shaped. At the other site, species richness was not related to biomass or to number of individuals. Our study demonstrated the importance of environmental stress and succession of community in the understanding of species diversity-productivity patterns.

Influence of terrestrial runoff on phytoplankton species richness-biomass relationships: A double stress hypothesis

The relationship between biomass and species richness (SR) was studied along productivity gradients in coastal phytoplankton assemblages under the influence of terrestrial runoff. In particular, the investigation focused on (a) whether phytoplankton blooms affect the shape of the relationship, (b) whether the relationship is taxon specific (between dinoflagellates and diatoms), and (c) the potential mechanisms regulating the shape of the relationship. Analysis was based on phytoplankton and physicochemical data from six coastal areas in the Aegean Sea, Eastern Mediterranean, covering the whole range from oligotrophy to eutrophication. A SR-biomass relationship was not observed for the more oligotrophic areas, whereas hump-shaped curves were found in areas yielding higher maximum biomass values, corresponding to bloom events occurring mainly during winter. Furthermore, the observed hump-shaped relationships were taxon specific since they were more pronounced in the case of diatoms than dinoflagellates. It is hypothesized that SR at the leftmost part of the hump-shape is nutrient regulated, whereas at the rightmost part is limited by extreme abiotic stress occurring during the formation of blooms in coastal ecosystems. The results of this study suggest that a double stress mechanism related to abiotic factors may be responsible for the hump-shaped SR-biomass relationships occurring in coastal phytoplankton communities at various levels of productivity.

Spatiotemporal segregation regulates species richness along biomass gradients in estuarine fish assemblages

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 342:217-226 (2007) - doi:10.3354/meps342217 Spatiotemporal segregation regulates species richness along biomass gradients in estuarine fish assemblages Atahualpa Sosa-Lopez1, David Mouillot2,* 1Centro EPOMEX, Universidad Autónoma de Campeche, Av. Agustín Melgar s/n, Campeche, CP 24030, Campeche, Mexico 2UMR CNRS-UM2 5119 Ecosystèmes Lagunaires, Université Montpellier 2, CC 093, 34095 Montpellier Cedex 5, France *Corresponding author. Email: mouillot@univ-montp2.fr ABSTRACT: The number of fish species in subtropical and tropical estuaries is much greater than in temperate regions and is greater in large estuaries than in small ones. Thus, large estuaries of the tropics are of primary interest for biodiversity conservation, and the processes underpinning the distribution of fish diversity in these ecosystems deserve attention. Factors controlling biodiversity patterns have been the focus of numerous recent investigations and include species interactions, speciation, environmental gradients and heterogeneity, with all of these operating differently at each observation scale. Today, the question is no longer whether particular biodiversity patterns occur, but why they occur and whether they are consistent across scales and organisms under study. In this study we combined the results of 2 classical ecological patterns, namely diversity–biomass relationships and species co-occurrences, into a common framework. Fish sampling was carried out in the coastal Terminos Lagoon (southern Gulf of Mexico) during 2 periods (1980–1981 and 1998–1999) using 408 tows. A total of 22834 individuals representing 106 fish species were collected. Our study revealed that both diversity–biomass relationships and species co-occurrences show inconsistent patterns across years, seasons and zones. However, taken together, our results show that C-score values, which measure spatiotemporal segregation among species, were closely related to the shape of observed richness–biomass relationships. When fish assemblages showed positive C-score values (species segregation), the relationship between species richness and fish biomass was either hump-shaped or non-significant. Conversely, negative C-score values (species aggregation) were associated with an increase in fish species richness along the total biomass gradient. Our results support the idea that species segregation due to competition or spatiotemporal partitioning can be an important determinant of biodiversity patterns in species-rich tropical fish assemblages, but only during some periods and for some spatial strata. KEY WORDS: Terminos Lagoon · Co-occurrence · C-score index · Randomization · Species segregation Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 342. Online publication date: July 24, 2007 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2007 Inter-Research.

Seasonal changes in the relationship between plant species richness and community biomass in early succession

We analysed the relationship between plant species richness and productivity on first-year-old fields at two similar sites in central Europe. At both sites, a wide range of productivity levels was available resulting from different long-term fertilisation. In order to identify underlying mechanisms of the species richness–productivity relationship we included the seasonal dynamics and the number of individuals of each species in our analysis. We sampled 10 and 21 plots, respectively, at the two sites in May, June and July by harvesting all aboveground parts of vascular plants in 0.25 m2 subplots. Species richness, number of individuals of each species and community biomass as a surrogate of productivity were recorded in each sample. At one site, the relationship between species richness and biomass was significantly positive in the May and June harvest. This relationship disappeared in the July harvest due to a reduction in species richness at high productivity levels. The relations between species richness and number of individuals and between number of individuals and biomass paralleled the species richness–productivity relation but the individual number–biomass relationship remained positive until the last harvest. Between-species differences in individual number–community biomass relationships and their seasonal dynamics revealed “interspecific competitive exclusion” even though the species richness–biomass relationships were not negative or hump-shaped. At the second site, species richness was not related to productivity or to number of individuals. Our study demonstrated the importance of temporal dynamics and regional processes in understanding species richness–productivity patterns. Die Beziehung zwischen pflanzlicher Artenvielfalt und Produktivität wurde in einjährigen Brachen an zwei ähnlichen Standorten in Mitteleuropa untersucht. Innerhalb beider Standorte hatte eine langjährig unterschiedliche Düngung zu grossen Differenzen in der Produktivität geführt. Um die der Artenvielfalt-Produktivitäts Beziehung zugrundeliegenden Mechanismen heraus zu arbeiten, wurden die zeitliche Dynamik und die Individuenzahl jeder einzelnen Art in die Analyse einbezogen. Im Mai, Juni und Juli wurden an beiden Standorten die oberirdischen Teile aller Gefässpflanzen in 10 bzw. 21 Teilflächen von je 0.25 m2 abgeerntet. Für jede Probe wurden die Artenzahl, die Individuenzahl pro Art sowie die Biomasse als Maß für die Produktivität bestimmt. An einem der beiden Standorte war die Beziehung zwischen Artenvielfalt und Biomasse in der Mai- und Juni-Ernte signifikant positiv. Aufgrund einer Verringerung der Artenvielfalt bei hoher Produktivität verschwand dieser positive Zusammenhang jedoch in der Juli-Ernte. Die Beziehungen zwischen Artenvielfalt und Individuenzahl sowie zwischen Individuenzahl und Biomasse verliefen parallel zu der Beziehung zwischen Artenvielfalt und Biomasse, die Individuenzahl–Biomasse–Beziehung blieb allerdings bis zur letzten Ernte positiv. Zwischen den Arten traten große Unterschiede in der Beziehung zwischen Individenzahl und Biomasse pro Teilfläche auf. Auch wenn keine negativen oder unimodalen Beziehungen zwischen Artenvielfalt und Biomasse beobachtet wurden, stellen diese artspezifischen Unterschiede und vor allem ihr zeitlicher Verlauf einen Beleg für den Ausschluss von Arten durch interspezifische Konkurrenz dar. Am zweiten Standort war die Artenvielfalt zu keinem Zeitpunkt mit der Biomasse und der Individuenzahl korreliert. Die vorliegende Arbeit veranschaulicht die große Bedeutung von zeitlicher Dynamik und standörtlichen Unterschieden für das Verständnis der Beziehung zwischen Artenvielfalt und Produktivität.

Temporal species richness-biomass relationships along successional gradients

Diversity-biomass relationships are frequently re- ported to be hump-shaped over space at a given time. How- ever, it is not yet clear how diversity and biomass change simultaneously and how they are related to each other over time (e.g. in succession) at one locality. This study develops a temporal model based on the projected changes of various community variables in a generalized terrestrial environ- ment after fire and uses post-fire succession data on Santa Monica Mountains of southern California and other pub- lished succession data to examine the temporal diversity- biomass relationships. The results indicate that in the early stages of succession, both diversity and biomass increase and a positive relationship appears, while in the late stages of succession, biomass continued to increase but diversity usu- ally declines; thus a negative relationship may be observed. When the scales of measurement become sufficiently large so that the measured diversity and biomass cross various stages of succession, a 'hump-shaped' relationship can emerge. The diversity-biomass relationship appears to be concordant in space and time when appropriate scales are used. Formerly proposed explanations for spatial patterns may well apply to the temporal patterns (particularly colonization, facilitation and competitive exclusion).

Lichen richness-biomass relationship in terricolous lichen vegetation on non-calcareous substrates

Lichen richness-biomass relationship in terricolous lichen vegetation on non-calcareous substrates