Shifts in ecological behaviour of herbaceous forest species along a transect from northern central to North Europe

We investigated the ecological behaviour (the response to environmental factors in the field, synonymous to the term realized niche) of four closely related species pairs (Melica nutans, M. uniflora; Primula veris, P. elatior; Veronica chamaedrys, V. montana; Viola riviniana, V. reichenbachiana) across a transect from northern Central to North Europe. The second-mentioned species of each pair is confined in its geographical distribution to the southern parts of the studied transect. Sample plot data of deciduous forests were compiled from (1) Germany, S Niedersachsen, (2) Germany, northern Schleswig-Holstein, (3) Denmark, and (4) Boreo-nemoral Sweden. We compared the ecological optima and amplitudes of the response curves of species along the gradients for moisture, pH and nitrogen by means of phytosociological data, detrended correspondence analysis (DCA) and Ellenberg indicator values. pH measurements from Sweden were significantly correlated with the corresponding DCA sample plot scores and the plot averages of the Ellenberg values for reaction (pH). In accordance with our main hypothesis, the wide range species appeared to have broader ecological amplitudes on the northern margins of their distributional ranges, especially in Boreo-nemoral Sweden, than in the southern parts of the study area. Our findings are in contrast to theories claiming a reduced niche breadth of range-margin populations of species compared to range-centre populations. The shifts in ecological behaviour were particularly obvious with respect to soil acidity. We believe that these shifts are caused by changes in the competitive relationships between the species: in the north, the total pool of species in deciduous forests is comparatively small. The low species richness is likely to lead to reduced competition and to an expansion of the ecological amplitude, known as competitive release.     

Using species‐environmental amplitudes to predict pH values from vegetation

Question: Species optima or indicator values are frequently used to predict environmental variables from species composition. The present study focuses on the question whether predictions can be improved by using species environmental amplitudes instead of single values representing species optima. Location: Semi‐natural, deciduous hardwood forests of northwestern Germany. Methods: Based on a data set of 558 relevés, species responses (presence/absence) to pH were modelled with Huisman‐Olff‐Fresco (HOF) regression models. Species amplitudes were derived from response curves using three different methods. To predict the pH from vegetation, a maximum amplitude overlap method was applied. For comparison, predictions resulting from several established methods, i. e. maximum likelihood/present and absent species, maximum likelihood/present species only, mean weighted averages and mean Ellenberg indicator values were calculated. The predictive success (squared Pearson's r and root mean square error of prediction) was evaluated using an independent data set of 151 relevés. Results: Predictions based upon amplitudes defined by maximum Cohen's x probability threshold yield the best results of all amplitude definitions (R²= 0.75, RMSEP = 0.52). Provided there is an even distribution of the environmental variable, amplitudes defined by predicted probability exceeding prevalence are also suitable (R²= 0.76, RMSEP = 0.55). The prediction success is comparable to maximum likelihood (present species only) and – after rescaling – to mean weighted averages. Predicted values show a good linearity to observed pH values as opposed to a curvilinear relationship of mean Ellenberg indicator values. Transformation or rescaling of the predicted values is not required. Conclusions: Species amplitudes given by a minimum and maximum boundary for each species can be used to efficiently predict environmental variables from species composition. The predictive success is superior to mean Ellenberg indicator values and comparable to mean indicator values based on species weighted averages.     

Evaluating the ecological realism of plant species distribution models with ecological indicator values

Species distribution models (SDMs) are routinely applied to assess current as well as future species distributions, for example to assess impacts of future environmental change on biodiversity or to underpin conservation planning. It has been repeatedly emphasized that SDMs should be evaluated based not only on their goodness of fit to the data, but also on the realism of the modeled ecological responses. However, possibilities for the latter are hampered by limited knowledge on the true responses as well as a lack of quantitative evaluation methods. Here we compared modeled niche optima obtained from European-scale SDMs of 1476 terrestrial vascular plant species with empirical ecological indicator values indicating the preferences of plant species for key environmental conditions. For each plant species we first fitted an ensemble SDM including three modeling techniques (GLM, GAM and BRT) and extracted niche optima for climate, soil, land use and nitrogen deposition variables with a large explanatory power for the occurrence of that species. We then compared these SDM-derived niche optima with the ecological indicator values by means of bivariate correlation analysis. We found weak to moderate correlations in the expected direction between the SDM-derived niche optima and ecological indicator values. The strongest correlation occurred between the modeled optima for growing degree days and the ecological indicator values for temperature. Correlations were weaker for SDM-derived niche optima with a more distal relationship to ecological indicator values (notably precipitation and soil moisture). Further, correlations were consistently highest for BRT, followed by GLM and GAM. Our method gives insight into the ecological realism of modeled niche optima and projected core habitats and can be used to improve SDMs by making a more informed selection of environmental variables and modeling techniques.     

Prediction of occurrence of vascular plants in deciduous forests of South Sweden by means of Ellenberg indicator values

Abstract. In this study we present a new method for predicting the occurrences of species using data from deciduous forests in South Sweden. Complete species lists of vascular plants were compiled from 101 stands and from representative sample plots inside the stands. Soil samples from each stand were collected for determination of pH and nitrogen mineralization. Presence-absence data for species were fitted to the values of four environmental variables - soil moisture, soil reaction (pH), soil nitrogen and light - by means of Linear (Multiple) Logistic Regression (LLR), and Gaussian (Multiple) Logistic Regression (GLR). First, these values were estimated by calculating the weighted averages of Ellenberg indicator values. Second, the estimates for reaction and nitrogen were substituted by the real measurements of pH and mineralized NH₄⁺, keeping the Ellenberg estimates for light and moisture. The models were validated by an independent test data set. In general, the models had high predictive abilities. GLR fitted the species occurrences better to the environmental variables than LLR, but had a lower accuracy of prediction of species occurrence in the stands. The use of soil measurements instead of Ellenberg indicator values did not improve the predictive abilities of the models. The environmental conditions in the stand test set were successfully estimated by using species data from the plots. When using the species lists of the stands instead of plot data, a slightly better predictive ability was obtained. The collection of plot data, however, is easier and less time-consuming. The accuracy of prediction differed considerably between species.     

Acidification and eutrophication of deciduous forests in northwestern Germany demonstrated by indicator species analysis

Abstract. A new method of indicator species analysis is suggested that can be used to demonstrate changes in the species composition of forests resulting from atmospheric deposition of acidifying substances and nitrogen. The method is not dependent on an exact re-localization of sites. 2162 published relevés of Fagus sylvatica and Quercus robur-Carpinus betulus forests from two study areas in Germany (S Niedersachsen and Nordrhein-Westfalen) were compiled and divided into relevés from before 1975 and more recent relevés. Weighted averages of Ellenberg indicator values for light (L), moisture (M), reaction (R), and nitrogen (N) were calculated and for each of the four data sets - mesic and dry sites in two areas - N was regressed on R to give a predicted value (N_pred) for any given R. The differences between observed values N_obs and N_pred were calculated separately for old and new relevés (Ndev-old and Ndev-new). The same analysis was applied to model data including 16 different scenarios of acidification and/or eutrophication. The model runs resulted in six different types of regression plots for Ndev and R. All models had in common that the regression lines for Ndev-new lay, completely or largely, above the zero line ofno change and above the lines for N_dev-old. Also, in the four data sets, N_dev-new was generally larger than N_dev-old, and particularly so in Nordrhein-Westfalen. The values of L_dev-old and L_dev-new indicate that the differences in N_dev are unlikely to be caused by altered forest management, but must result from atmospheric pollution.     

Calibration of Ellenberg indicator values for the Faroe Islands

Abstract. Elenberg's bio‐indication system for soil moisture (F), soil nitrogen (N) and soil reaction (R) was examined, based on 559 vegetation samples and environmental characteristics (vegetation cover, soil depth, soil moisture, chemical soil properties) from four Faroe islands. The original indicator values from central Europe were used for the calculation of weighted community indicator values of F, N and R. These were regressed with respect to environmental data, applying standard curvilinear regression and generalized linear modelling (GLM) and new predicted values of community indicator values were obtained from the best model. Faroe species optima values of 162 taxa for one or more of the three EUenberg scales were derived from fitting Huisman‐Olff‐Fresco (HOF) models of species abundance with respect to predicted community indicator values and are proposed as new EUenberg species indicator values to be used in the Faroe Islands. F was best correlated with a GLM model containing soil moisture, organic soil fraction, soil depth and total vegetation cover, R with a GLM model containing pH and calcium in % organic soil fraction, N with total phosphorus in % organic soil fraction. The calibrated species indicator scales are much truncated, as compared with the original values, resulting in significantly different overall distributions of the original and new species indicator values. The recalculated community indicator values are much better correlated to environmental measurements. Several species do not have clear optima, but linear or monotone relationships to the examined indicator scales. This probably indicates that the occurrence of some species in the Faroe Islands are either determined by factors other than moisture, pH or soil nutrient status or, given the young age and environmental instability of the islands, are governed by stochastic mechanisms. Extension of Ellenberg indicator values outside central Europe should always be carefully calibrated by means of adequate environmental data and adequate statistical models, such as HOF models, should be applied.     

Effects of Nitrogen Deposition: Results of a Temporal-Spatial Analysis of Deciduous Forests in South Sweden

Abstract: We studied permanent plots in deciduous forests in two provinces of South Sweden, Skåne (127 plots) and Småland (116 plots). Vegetation data were sampled in 1983 and 1993 and used to calculate weighted averages of Ellenberg indicator values for light, reaction (pH) and nitrogen. Soil samples were collected from all plots in 1993 for determination of pH, organic matter content and potential net nitrogen mineralization (minN). Data on minN were also available for 66 plots in Skåne from 1983. Nitrogen deposition is considerably higher in Skåne than in Småland. The same holds true for total minN, minNH₄⁺, minNO₃^-_-, and the proportion of total minN due to nitrate (nitrification ratio). According to the comparison of average Ellenberg indicator values between 1983 and 1993, the stands had become darker (not in the heavily managed plots), more acid and nitrogen rich, except at the most acid sites where only minor changes could be observed. The nitrification ratio was significantly higher in 1993 than in 1983. Mean soil nitrification ratios were determined for the most common species in both regions. The means were higher in Skåne than in Småland. It is likely that nitrogen deposition causes an increase in nitrification rate and nitrification ratio. This ratio is a significant determinant of the species composition in deciduous forests.     

Foliar macronutrient concentrations of forest understorey species in relation to Ellenberg's indices and potential relative growth rate

In order to investigate broad patterns of variation of the foliar mineral nutrient concentrations of herbaceous plant communities in the ground layer of W Europe forests, correlations were examined between Ellenberg's indices (N-index: mineral nitrogen availability, R-index: pH, F-index: soil moisture and L-index: light intensity) and literature values of macronutrient concentrations for 84 forbs and 39 graminoid species. Significant, positive correlations were found between the R-index and the plants' concentration of Ca and K (forbs only) and between the N-index and the plants' concentration of K, P (forbs only) and N (forbs and graminoids). Multiple regressions showed that the N-index was the best predictor of the plants' concentration of N (forbs and graminoids), P (forbs) and Ca (graminoids) and the R-index of the plants' concentration of Ca and K (forbs). The mineral nutrient concentrations of graminoids were lower and less strongly correlated with Ellenberg's indices than those of forbs. It is argued that the mineral nutrient concentrations in the plants match the availability of mineral nutrients in the soil for N, P (N-index) and Ca (R-index), but not for K and Mg. Significant, positive correlations were found between potential relative growth rate and the concentration of some elements (N, P, K and Ca in forbs, Ca and Mg in graminoids). This suggests that the increase in the concentration of these elements in plants along fertility gradients is due, at least partly, to genetically controlled alterations of leaf anatomy associated with increasing potential relative growth rate.     

Resurvey studies of terricolous bryophytes and lichens indicate a widespread nutrient enrichment in German forests

Questions

Vegetation resurveys, both single studies and meta-analyses, have predominantly been based on vascular plant data while bryophytes and lichens have largely been neglected. Our study aims to fill this gap and addresses the following research questions: has the overall species richness of terricolous bryophytes and lichens in forests changed over time? Which are the winners and losers among single species and ecological species groups? Do the results give a signal of the impact of nutrient enrichment, of changes in the light regime and of climate change?

Location

Deciduous and coniferous forests in Germany.

Methods

We compiled 35 single resurvey data sets, including 1096 plots in total (each sampled twice). The time interval between initial surveys and resurveys ranged from 10 to 65 years. The differences between old and new plots were analysed with respect to the frequency of single species, total species richness, and the absolute and relative numbers of taxa in the species groups. Trend scores of species were related to ecological indicator values to identify the main environmental drivers behind the observed changes.

Results

Total species richness did not systematically change, while pleurocarpous mosses had increased at the expense of acrocarpous mosses and, in coniferous forests, of lichens. Weak changes were generally observed in deciduous forests on base-rich soils. In coniferous forests and in deciduous forests on acid soils, species with high nitrogen demand and high shade tolerance had increased, whereas those being typical for more infertile and open forest sites had decreased. There were trends towards a larger share of taxa with a more oceanic distribution.

Conclusions

The changes in the vegetation of terricolous bryophytes and lichens in the studied forests indicate nutrient enrichment and increasingly shady conditions in forests on acid soils, likely caused by nitrogen deposition and shrub layer closure.     

What makes a plant species specialist in mixed broad-leaved deciduous forests?

Knowledge about relationships between specialization degree of species, i.e. the width of their realized niche and functional traits, may have important implications for the assessment of future population developments under environmental change. In this study, we used a recently introduced method to calculate ecological niche widths of plant species in mixed broad-leaved deciduous forests and to investigate the dependence between niche widths of plants and their functional traits and Ellenberg indicator values. The research is based on a dataset of 4556 phytosociological relevés of mixed broad-leaved deciduous forests in Slovenia. We calculated theta indices for 326 species, which ranks them along a continuous gradient of habitat specialization. For 272 species, we compiled 26 functional traits and Ellenberg indicator values. We found some significant correlations between theta indices of species and their functional traits and Ellenberg indicator values; habitat specialists thrive primarily on the highest altitudes, on colder, dry sites and achieve the age of first flowering later than generalists. They also have smaller seed diameter, lower leaf dry matter content, lower mean canopy height and bigger specific leaf area than generalists. Two species groups, chamaephytes and spring green species, are particularly characterized as specialist species. The added value of our work is in complementing the knowledge about the niche differentiating along different environmental gradients and species coexistence in mixed broad-leaved deciduous forests.     

Vegetation of beech forests in the Rychlebské Mountains,Czech Republic,re-inspected after 60 years with assessment of environmental changes

From 1941–;1944 nearly 30 phytosociological relevés were completed by F. K. Hartmann in the Rychlebské Mountains, a typical mountainous area in northeastern Czech Republic. Of the original plots still covered with adult grown beech (Fagus sylvatica) forest, 22 were resampled in 1998 and 1999. In order to describe the recent vegetation variability of the sites 57 relevés were recorded. Changes in vegetation were estimated using relative changes in species density and ordinations (PCA, RDA). Environmental changes were assessed using Ellenberg indicator values when no direct measurements were available. A decline in species diversity has been documented, particularly, many species occurring frequently in deciduous forests with nutrient and moisture well-supplied soils around neutral have decreased. In contrast, several light-demanding, acid- and soil desiccation-tolerant species have increased. Natural succession, quantified as forest age, contributed slightly to these changes. In Ellenberg indicator values, a decline in F (soil moisture), R (soil calcium) and N (ecosystem productivity), and an increase in L (understorey light) were shown. This is interpreted as the influence of modified forestry management and of airborne pollutants. Intensified logging caused the canopy to open and soil conditions to worsen. The latter is most likely also due to acid leaching of soil cations (Ca, K, Na). This caused a decline in soil productivity, thus the effect of nitrification could not be detected. The original relevés may have differed in size influencing the results. This revised version was published online in August 2006 with corrections to the Cover Date.     

Possible interactions between environmental factors in determining species optima

Questions: 1. Indicator values, such as those of Ellenberg, for different environmental factors are seen as independent. We tested for the presence of interactions between environmental factors (soil moisture and reaction) to see if this assumption is simplistic. 2. How close are Ellenberg indicator values (IV s) related to the observed optima of species response curves in an area peripheral to those where they have been previously employed and 3. Can the inclusion of bryophytes add to the utility of IVs? Location: South Uist, Outer Hebrides, Scotland, UK. Methods: Two grids (ca. 2000 m × 2000 m) were sampled at 50‐m intervals across the transition from machair to upland communities covering an orthogonal gradient of both soil pH (reaction) and soil moisture content. Percentage cover data for vascular plants, bryophytes and lichens were recorded, along with pH and moisture content of the underlying sand/soil/ peat. Reaction optima, derived from species response curves calculated using HOF models, were compared between wet and dry sites, and moisture optima between acidic and basic samples. Optima for the whole data set were compared to Ellenberg IVs to assess their performance in this area, with and without the inclusion of bryophytes. Results: A number of species showed substantially different pH optima at high and low soil moisture contents (18% of those tested) and different soil moisture optima at high and low pH (49%). For a number of species the IVs were poor predictors of their actual distribution across the sampled area. Bryophytes were poor at explaining local variation in the environmental factors and also their inclusion with vascular plants negatively affected the strength of relationships. Conclusions: A substantial number of species showed an interaction between soil moisture and reaction in determining their optima on the two respective gradients. It should be borne in mind that IVs such as Ellenberg's may not be independent of one another.     

ORIGINAL ARTICLE: Can Ellenberg's indicator values for Mediterranean plants be used outside their region of definition?

Aim The aims of this study are: (1) to explore the relationships between the Ellenberg indicator values (light, temperature and moisture) recently developed for two Mediterranean regions (Italy and Greece); and (2) to evaluate the possibility of using these values in other Mediterranean areas. Location Southern Greece and the Mediterranean part of Italy. Methods A global matrix containing 966 items of information (161 species × 3 indicator variables × 2 values assigned in each study, one in Italy and one in Greece) was constructed. A test of the accuracy of the values in predicting actual environmental conditions was provided using a detrended correspondence analysis (DCA) on published vegetation relevés from the Mediterranean region. The gamma statistic was used to express relationships of ecological indicator values between the two regions, and pairs of indicator values calculated for each species were compared using Wilcoxon matched pairs tests. Results The results showed that indices developed for Greece and Italy were not similarly correlated to sample scores along DCA axis 1. Species’ indicator values for Italy and for Greece were highly significantly correlated for light and moisture and significantly correlated for temperature, but the correlations were weak (0.20 ≤ gamma ≤ 0.31). Pairwise testing gave significantly different indicator values for the two regions. Discrepancies below or equal to 2 units on 9‐point scales (12 points for moisture) were found for 88%, 70% and 54% of the species respectively for light, temperature and moisture indices. A substantial number of species showed higher discrepancies, from 3 up to 6 units. Main conclusions In the light of the present work, it seems clear that the indicator values developed for Italy and for Greece should not be used outside the region for which they were defined. This constitutes additional evidence that indicator values can be influenced by the identity of potential competitors. It also underlines the need to use standardized methods for calibrating indicator values against measured variables in such a way that indicator systems can serve as general reference systems.     

Invasive behaviour of Lactuca serriola (Asteraceae) in the Netherlands: Spatial distribution and ecological amplitude

Species invasions have been a central theme in ecology over the past decades, with a focus on invasions of non-indigenous European species in the New World. However, within Europe, native species may also become invasive. Such species rapidly increase their geographic range and may at the same time broaden their ecological amplitude. We report on Lactuca serriola L., which has shown a rapid range expansion in many parts of Europe. We reconstructed its geographical spread through The Netherlands; furthermore, we tested for changes in its ecological amplitude.

Before 1950, L. serriola was rare in The Netherlands, recorded from only 80 grid-cells (of 5×5 km²). Subsequently, its distribution increased from 219 grid-cells (1980), to 546 cells (990) and 998 grid cells (2000). It currently occupies at least 60% of The Netherlands. Analyses of relevées demonstrate, using detrended correspondence analysis (DCA), that the variance in the assemblage of species co-occurring with L. serriola increased significantly since 1940, indicating that the species currently occurs in a broader range of vegetation types. Correlating averages of Ellenberg's indicator values per vegetation relevée with time, we found correlations for continentality (+), acidity (−) and (soil) humidity (+). Moreover, the proportion of phanerophytes in the relevées increased over time. These findings suggest that in addition to its original ruderal habitat, L. serriola also currently occurs in more closed vegetation types. Based on analyses of two other co-occurring Asteraceae species, we showed that these patterns were specific for L. serriola only. We conclude that L. serriola has broadened its ecological amplitude and discuss four mutually non-exclusive explanations for the recent invasiveness of L. serriola: (i) Effects of a changed environment: global warming and ruderalisation; (ii) metapopulation dynamics and increased diaspore pressure; (iii) microevolution; (iv) genetic reinforcement due to hybridisation with conspecific (crop) species.     

An application case of ecological indicator values (Zeigerwerte) calculated with a simple algorithmic approach

Abstract

The vegetation of the study site near Rome (Castelporziano Estate), where different woodland types occur, was analysed on the basis of ecological indicator values (Zeigerwerte) for light, temperature, continentality of climate, soil moisture, soil pH and nitrogen. Indicator values were estimated with Hill's reprediction algorithm for the flora of Central-Southern Italy relying on a database of 4,207 original relevés representing a balanced survey of the vegetation of this and surrounding areas. It was possible to obtain indicator values for an important fraction of the Italian Mediterranean flora. Results are ecologically reasonable, and it was possible to find strong correlation between the recalculated values and a few environmental variables. These correlations were not significant in an analogous test with subjectively derived scores of Ellenberg indicator values.     

Species richness in deciduous forests: Effects of species pools and environmental variables

Abstract. The study was conducted in deciduous forests of two Swedish regions, Öland and Uppland. It had two objectives: to (1) test the species pool hypothesis by examining if differences in small‐scale species richness are related to differences in large‐scale species richness and the size of the regional species pool, and (2) to examine the relationship between species richness and productivity and its scale‐dependence. The first data set comprised 36 sites of moderate to high productivity. In each site, we recorded the presence of vascular plant species in nested plots ranging from 0.001 to 1000 m² and measured several environmental variables. Soil pH and Ellenberg site indicator scores for nitrogen were used as estimators of productivity. The second data set included 24 transects (each with 20 1‐m² plots) on Öland in sites with low to high productivity. Species number, soil pH and relative light intensity were determined in each plot. The forest sites on Öland were more species‐rich than the Uppland sites on all spatial scales, although environmental conditions were similar. Small‐scale and large‐scale species richness were positively correlated. The results present evidence in favour of the species pool hypothesis. In the nested‐plots data set, species number was negatively correlated with pH and nitrogen indicator scores, whereas a unimodal relationship between species number and pH was found for the transect data set. These results, as well as previously published data, support the hump‐shaped relationship between species richness and productivity in Swedish deciduous forests. Two explanations for the higher species richness of the sites with moderate productivity are given: first, these sites have a higher environmental heterogeneity and second, they have a larger ‘habitat‐specific’ species pool.     

Specific leaf area as a superior predictor of changes in field layer abundance during forest succession

Question : How accurately can a suite of suggested functional traits predict plant species response to succession from semi‐open woodland to closed deciduous canopy forest? Location : Southeastern Sweden. Methods : Abundance of 46 field‐layer plant species in a temperate deciduous forest, measured as frequency of occupied plots, was estimated in 1961, 1970 and 2003. Abundance change over time across species was tested for correlations with functional traits and literature information on habitat preference. Results : Increase in abundance was positively correlated with specific leaf area (SLA), weakly negatively correlated with seed mass and not significantly correlated with plant height or start, peak and length of the flowering period. Change in abundance was correlated with the Ellenberg light indicator value, whereas no correlations were found with Ellenberg values for nitrogen, calcium and moisture, or forest preference according to the literature. Conclusions : SLA was a better predictor of how field layer plants responded to succession from semi‐open woodland to closed canopy forest than empirically‐derived measures of habitat preference. The same holds for SLA in relation to seed size, indicating that interactions in the established life‐cycle phase are more important than the recruitment phase for species response to succession.     

A comparison of biological characteristics and distribution between Swedish threatened and non-threatened forest vascular plants

Threatened (n = 59) and non-threatened (n = 308) Swedish forest vascular plant taxa were compared with regard to a number of variables, including distribution, site factors taxonomy, morphology and flowering time A majority of the threatened taxa occur in the southern deciduous woodlands, which only constitute c 0.5% of the total forested area in Sweden There are considerably more threatened taxa in southern than in northern Sweden, a consequence of the successively higher number of forest vascular plants from the north towards the south Threatened taxa grow in forests with significantly higher soil fertility than non-threatened taxa Significant differences were also revealed regarding light conditions, soil water conditions and month of flowering Threatened taxa grow on soils with significantly higher pH and also with slightly more available nitrogen than non-threatened taxa, as measured with Ellenberg indicator values Forest stands on fertile soils are uncommon in Sweden and they are also very species-rich Soil-type rarity in combination with high species diversity in these soil types thus partly explain why taxa are included in the Swedish Red data list     

Species richness correlations among primary producers in boreal forests

Close correlations in species numbers may make it possible to indirectly assess the species richness of difficult taxonomic groups by investigating indicator groups, for which data are more easily collected. We asked if species numbers correlate among the four dominating groups of primary producers in boreal forests (liverworts, macrolichens, mosses, and vascular plants) and if substrate affiliation of species (ground vs. other substrates), sample plot size (0.01–1000 m²), and stand age (young vs. old) influence correlation strength. We used three sets of study plots from northern Sweden each including wide ranges of species richness. Although there are large differences in the ecophysiology and substrate use of vascular plants and the two bryophyte groups (mosses and liverworts), we found strong positive correlations among them not previously reported from boreal forests. In contrast, no correlation in total species richness was found between macrolichens and the two bryophyte groups, despite large overlaps in their ecology. We suggest that the positive correlations among land plants (liverworts, mosses, and vascular plants) are linked to positive relationships between site moisture and species number for all three groups. In contrast, total species number of macrolichens has not been shown to be strongly associated with moisture. However, ground‐living lichens and mosses correlated negatively in old forests. This may relate to the inability of macrolichens to exploit shaded and wet old forest ground, a habitat that is used by many moss species. Furthermore, lichens and mosses of ‘other substrates’ correlated positively in old forests, probably because the amount of boulders was positively related to species richness in both groups. Generally, correlations became stronger with increasing plot size, whereas stand age had relatively little influence. We conclude that vascular plants could be used as an indicator group for species richness of mosses and liverworts in boreal landscapes.     

Small-scale species patterns and associations in an alvar limestone grassland on Öland, Sweden

This paper reports on the results of a transect analysis carried out in order to detect small-scale patterns ofAvenetum species in a limestone grassland on the Great Alvar on the Baltic island of Öland, Sweden. Three transects consisting of 500 10×10 cm quadrats were used. The cover and number of flowering stalks (if any) of the 21 most common species were recorded. In addition the total cover of vascular plants, cover of mosses and lichens, cover of cow dung and soil depth in each quadrat were recorded. Ellenberg indicator values for light, moisture, reaction and nitrogen were calculated for each quadrat as weighted averages of the values for the species included in the analysis. Patch size frequency analysis, PASFRAN, a new method for detecting patches and their sizes, revealed that 42% of all significant species patches detected had mean patch sizes (diameter) in the range of 26–50 cm, which matched the size of dung patches—49 cm in transect 1 and 30 cm in transect 2. Results of association analysis revealed correlations for several species pairs and between species and environmental factors with similar patch sizes. Combination of PASFRAN and association analysis is recommended as an effective method for pattern detection.