Gerald Jurasinski

Inventory, differentiation, and proportional diversity: a consistent terminology for quantifying species diversity

Almost half a century after Whittaker (Ecol Monogr 30:279–338, 1960) proposed his influential diversity concept, it is time for a critical reappraisal. Although the terms alpha, beta and gamma diversity introduced by Whittaker have become general textbook knowledge, the concept suffers from several drawbacks. First, alpha and gamma diversity share the same characteristics and are differentiated only by the scale at which they are applied. However, as scale is relative––depending on the organism(s) or ecosystems investigated––this is not a meaningful ecological criterion. Alpha and gamma diversity can instead be grouped together under the term “inventory diversity.” Out of the three levels proposed by Whittaker, beta diversity is the one which receives the most contradictory comments regarding its usefulness (“key concept” vs. “abstruse concept”). Obviously beta diversity means different things to different people. Apart from the large variety of methods used to investigate it, the main reason for this may be different underlying data characteristics. A literature review reveals that the multitude of measures used to assess beta diversity can be sorted into two conceptually different groups. The first group directly takes species distinction into account and compares the similarity of sites (similarity indices, slope of the distance decay relationship, length of the ordination axis, and sum of squares of a species matrix). The second group relates species richness (or other summary diversity measures) of two (or more) different scales to each other (additive and multiplicative partitioning). Due to that important distinction, we suggest that beta diversity should be split into two levels, “differentiation diversity” (first group) and “proportional diversity” (second group). Thus, we propose to use the terms “inventory diversity” for within-sample diversity, “differentiation diversity” for compositional similarity between samples, and “proportional diversity” for the comparison of inventory diversity across spatial and temporal scales.

Commentary: do we have a consistent terminology for species diversity? We are on the way

A consistent terminology for species diversity is subject of an ongoing debate. Recently Tuomisto (Oecologia 164:853–860, 2010) stated that a consistent terminology for diversity already exists. The paper comments on recent papers by ourselves (Jurasinski et al. Oecologia 159:15–26, 2009) and by Moreno and Rodriguez (Oecologia 163:279–282, 2010). Both started from Whittaker’s diversity concept to discuss the ambiguities of the terminology and propose a new, more consistent terminology that is based on the different approaches to diversity analysis. In contrast, Tuomisto adheres to a strict school of thinking and derives a diversity framework in the sense of Whittaker (alpha, beta, gamma) from the conceptual definition of diversity itself. A third group of papers discusses appropriate methods for the analysis of the variation in species composition. Here, we support the idea that alpha, beta and gamma diversity should be used in a strict sense that is based only on the conceptual definition of diversity. We accordingly extend and modify our terminological concept for species diversity. All approaches to the analysis and quantification of species composition and diversity can be assigned to three abstraction levels (species composition, variation in species composition,and variation in variation in species composition) and two scale levels (sample scale, aggregation scale). All methods that investigate the variation in species composition across scale levels evaluate beta relation with beta diversity being just one form of beta relation, which is calculated by dividing gamma diversity of order q by the appropriate alpha diversity of the same order. In contrast, differentiation refers to a pairwise calculation of resemblance in species composition. It is restricted to sample scale and is therefore most often only an intermediate step of analysis. Many ecological questions can be addressed either by direct analysis of the variation in species composition using raw data approaches or by further analysis of differentiation datasets on aggregation scale with or without respect to an external gradient.

Resurveying historical vegetation data – opportunities and challenges

Background Resurveying historical vegetation plots has become more and more popular in recent years as it provides a unique opportunity to estimate vegetation and environmental changes over the past decades. Most historical plots, however, are not permanently marked and uncertainty in plot location, in addition to observer bias and seasonal bias, may add significant error to temporal change. These errors may have major implications for the reliability of studies on long-term environmental change and deserve closer attention of vegetation ecologists. Material & Methods Vegetation data obtained from the resurveying of non-permanently marked plots are assessed for their potential to study environmental-change effects on plant communities and the challenges the use of such data have to meet. We describe the properties of vegetation resurveys distinguishing basic types of plots according to relocation error, and we highlight the potential of such data types for studying vegetation dynamics and their drivers. Finally, we summarise the challenges and limitations of resurveying non-permanently marked vegetation plots for different purposes in environmental change research. Results and Conclusions Resampling error is caused by three main independent sources of error: error caused by plot relocation, observer bias, and seasonality bias. For relocation error, vegetation plots can be divided into permanent and non-permanent plots, while the latter are further divided into quasi-permanent (with approximate relocation) and non-traceable (with random relocation within a sampled area) plots. To reduce the inherent sources of error in resurvey data, the following precautions should be followed: (i) resurvey historical vegetation plots whose approximate plot location within a study area is known; (ii) consider all information available from historical studies in order to keep plot relocation errors low; (iii) resurvey at times of the year when vegetation development is comparable to the historical survey to control for seasonal variability in vegetation; (iv) keep a high level of experience of the observers to keep observer bias low; and (v) edit and standardise datasets before analyses.

The effect of biomass harvesting on greenhouse gas emissions from a rewetted temperate fen

The growing demand for bioenergy increases pressure on peatlands. The novel strategy of wet peatlands agriculture (paludiculture) may permit the production of bioenergy from biomass while avoiding large greenhouse gas emissions as occur during conventional crop cultivation on drained peat soils. Herein, we present the first greenhouse gas balances of a simulated paludiculture to assess its suitability as a biomass source from a climatic perspective. In a rewetted peatland, we performed closed‐chamber measurements of carbon dioxide, methane, and nitrous oxide exchange in stands of the potential crops Phragmites australis, Typha latifolia, and Carex acutiformis for two consecutive years. To simulate harvest, the biomass of half of the measurement spots was removed once per year. Carbon dioxide exchange was close to neutral in all tested stands. The effect of biomass harvest on the carbon dioxide exchange differed between the 2 years. During the first and second year, methane emissions were 13–63 g m−2 a−1 and 2–5 g m−2 a−1, respectively. Nitrous oxide emissions lay below our detection limit. Net greenhouse gas balances in the study plots were close to being climate neutral during both years except for the Carex stand, which was a source of greenhouse gases in the first year (in CO2‐equivalents: 18 t ha−1 a−1). Fifteen years after rewetting the net greenhouse gas balance of the study site was similar to those of pristine fens. In addition, we did not find a significant short‐term effect of biomass harvest on net greenhouse gas balances. In our ecosystem, ~17 t ha−1 a−1 of CO2‐equivalent emissions are saved by rewetting compared to a drained state. Applying this figure to the fen area in northern Germany, emission savings of 2.8–8.5 Mt a−1 CO2‐equivalents could possibly be achieved by rewetting; this excludes additional savings by fossil fuel replacement.

Winter warming pulses affect the development of planted temperate grassland and dwarf-shrub heath communities

Background: Winter conditions are changing considerably due to climate change. Resulting alterations in the frequency of soil freeze–thaw cycles (FTCs) are ecologically important. Aim: We quantified the impact of winter soil-warming pulses on the community structure of temperate plant communities. Methods: The cover of vascular plant species in two vegetation types, each at three diversity levels, was recorded 1 year before to 3 years after an FTC-manipulation that added five additional FTCs. Changes in species abundance patterns (Bray–Curtis similarity) were analysed by linear mixed effect models. Results: Communities exposed to additional FTCs showed less change in their species abundance patterns than the reference plots. Community development in the grassland differed between the FTC-manipulation and the reference plots in the first growing season after the FTC-manipulation, but such effects disappeared over time, whereas the divergence from the reference plots in the dwarf-shrub heath started in the second year after the FTC-manipulation and effects grew over time. Responses to FTCs were related to growth forms: some grasses increased after the FTC-manipulation, whereas the cover of dwarf shrubs was reduced. There was less change in species abundance distributions in the more diverse communities with legumes present. Conclusions: Winter climate change is a critical driver of temperate ecosystems. Short-term climatic events can have long-term implications on the structure of ecosystems. Community composition regulates alterations in the development and competitive balance of plant communities caused by soil warming pulses.

Four decades of vegetation development in a percolation mire complex following intensive drainage and abandonment

Background: Many minerotrophic fens in Central Europe have undergone similar sequences of land-use transformation. Drained and used as meadows or pastures for decades in the twentieth century, they were abandoned in the 1990s due to changes in agricultural economics. This sequence of land-use change has a severe impact on vegetation and is likely to initiate secondary succession and is possibly leading to an impoverishment in species diversity and to taxonomic homogenisation. Aims: We assess the impact of agricultural use and subsequent abandonment on vegetation composition in a percolation fen in north Germany and characterise successional changes and changes in abiotic site conditions. Methods: In 2010, we resampled 77 plots of a phytosociological survey from 1967–1970 in a lowland percolation mire complex in the lower Recknitz valley, north-east Germany. These included three characteristic vegetation types of percolation fens. To investigate and quantify vegetation changes we used dissimilarity measures, diversity metrics and ecological species indicator values. Results: Overall species richness declined only slightly while there was a more pronounced decrease in species richness at the plot level in all recorded vegetation types, resulting in increased beta diversity. Generalist and nitrophilous species increased in abundance, indicating ongoing succession. Conclusions: Drainage for agricultural use and subsequent abandonment has long-lasting effects. Altered hydrological and nutrient status of the fen soil has initiated secondary succession. There is indication of an extinction debt that in the future may lead to an impoverishment of species diversity in the area. Conservation of open mesotrophic fen species may thus only be achieved if moderate use is continued and hydrologic conservation measures are applied on wide contiguous areas.

Methane Exchange in a Coastal Fen in the First Year after Flooding - A Systems Shift

Background Peatland restoration can have several objectives, for example re-establishing the natural habitat, supporting unique biodiversity attributes or re-initiating key biogeochemical processes, which can ultimately lead to a reduction in greenhouse gas (GHG) emissions. Every restoration measure, however, is itself a disturbance to the ecosystem. Methods Here, we examine an ecosystem shift in a coastal fen at the southern Baltic Sea which was rewetted by flooding. The analyses are based on one year of bi-weekly closed chamber measurements of methane fluxes gathered at spots located in different vegetation stands. During measurement campaigns, we recorded data on water levels, peat temperatures, and chemical properties of peat water. In addition we analyzed the first 20 cm of peat before and after flooding for dry bulk density (DBD), content of organic matter and total amounts of carbon (C), nitrogen (N), sulfur (S), and other nutrients. Results Rewetting turned the site from a summer dry fen into a shallow lake with water levels up to 0.60 m. We observed a substantial die-back of vegetation, especially in stands of sedges (Carex acutiformis Ehrh). Concentrations of total organic carbon and nitrogen in the peat water, as well as dry bulk density and concentrations of C, N and S in the peat increased. In the first year after rewetting, the average annual exchange of methane amounted to 0.26 ± 0.06 kg m-2. This is equivalent to a 190-times increase in methane compared to pre-flooding conditions. Highest methane fluxes occurred in sedge stands which suffered from the heaviest die-back. None of the recorded environmental variables showed consistent relationships with the amounts of methane exchanged. Conclusions Our results suggest that rewetting projects should be monitored not only with regard to vegetation development but also with respect to biogeochemical conditions. Further, high methane emissions that likely occur directly after rewetting by flooding should be considered when forecasting the overall effect of rewetting on GHG exchange.

Scale-dependent temporal variation in determining the methane balance of a temperate fen

Methane emissions from peatlands vary considerably over time which complicates the determination of methane balances. In this study, the relative magnitude of methane flux variation over different time scales (years, seasons, days) is evaluated using data from two years of manual chamber estimation. Closed-chamber estimations were conducted on three vegetation stands in a fen in northeastern Germany. During the first investigation year, emissions were considerably higher than during the second year. Clear seasonal patterns were only present during the first year. In both years emissions varied among vegetation stands. The parameters year and month together explained more than half of the variation in methane fluxes. In contrast, the parameter time of day was not significant in explaining variation in methane fluxes. The impact of methane emission patterns on the resulting balances decreases with a decreasing time scale. The results suggest that methane balances might be significantly biased if they rely on data from one or two years only. Consequently, if there is interest in whole balances, resources should be allocated primarily towards acquiring long-term data series. This might involve a reduction of measurement frequency to monthly or bimonthly methane flux determination.

Impact of adjacent land use on coastal wetland sediments.

Coastal wetlands link terrestrial with marine ecosystems and are influenced from both land and sea. Therefore, they are ecotones with strong biogeochemical gradients. We analyzed sediment characteristics including macronutrients (C, N, P, K, Mg, Ca, S) and heavy metals (Mn, Fe, Cu, Zn, Al, Co, Cr, Ni) of two coastal wetlands dominated by Phragmites australis at the Darss-Zingst Bodden Chain, a lagoon system at the Southern Baltic Sea, to identify the impact of adjacent land use and to distinguish between influences from land or sea. In the wetland directly adjacent to cropland (study site Dabitz) heavy metal concentrations were significantly elevated. Fertilizer application led to heavy metal accumulation in the sediments of the adjacent wetland zones. In contrast, at the other study site (Michaelsdorf), where the hinterland has been used as pasture, heavy metal concentrations were low. While the amount of macronutrients was also influenced by vegetation characteristics (e.g. carbon) or water chemistry (e.g. sulfate), the accumulation of heavy metals is regarded as purely anthropogenic influence. A principal component analysis (PCA) based on the sediment data showed that the wetland fringes of the two study sites are not distinguishable, neither in their macronutrient status nor in their concentrations of heavy metals, whereas the interior zones exhibit large differences in terms of heavy metal concentrations. This suggests that seaside influences are minor compared to influences from land. Altogether, heavy metal concentrations were still below national precautionary and action values. However, if we regard the macronutrient and heavy metal concentrations in the wetland fringes as the natural background values, an accumulation of trace elements from agricultural production in the hinterland is apparent. Thus, coastal wetlands bordering croplands may function as effective pollutant buffers today, but the future development has to be monitored closely to avoid breakthroughs due to exceeded carrying capacities.

Opaque closed chambers underestimate methane fluxes of Phragmites australis (Cav.) Trin. ex Steud.

Closed chamber measurements for methane emission estimation are often carried out with opaque chambers to avoid heating of the headspace. However, mainly in wetlands, some plants possess an internal convective gas transport which quickly responds to changes in irradiation. These plants have also been found to often channel a large part of the released methane in temperate fens. We compare methane fluxes derived from transparent versus opaque chambers on Carex-, Phragmites-, and Typha-dominated stands of a temperate fen. Transparent chamber fluxes almost doubled opaque chamber fluxes in the convective transporting Phragmites stand. In Typha, a trend of higher fluxes determined with the transparent chambers was detectable, whereas in Carex, transparent and opaque chamber fluxes did not differ significantly. Thus, opaque chambers bias the outcome of methane measurements, depending on dominant vegetation. We recommend the use of transparent chambers when determining emissions of convective plants or extrapolating fluxes to larger scales.