Question: Will a non-indigenous, invasive, understorey shrub, such as Lonicera maackii (Amur honeysuckle) have an impact on the productivity of overstorey trees in hardwood forests?

Location: Trees from 12 invaded and four non-invaded sites were sampled in hardwood forests of southwestern Ohio, US.

Methods: Changes in radial and basal area tree growth in the ten years prior to L. maackii invasion vs. ten years after invasion were examined using dendrochronological techniques. Intervention analysis was used to detect growth changes 25 years prior to and 25 years following invasion, and estimates of load impacts for L. maackii population and biomass were also calculated.

Results: We found that the rate of radial and basal area growth of overstorey trees was reduced significantly in eleven out of twelve invaded sites. Non-invaded sites did not exhibit this consistent pattern of reduced growth. For invaded vs. non-invaded sites, the mean basal area growth was reduced by 15.8%, and the overall rate of basal area growth was reduced by 53.1%. Intervention analysis revealed that the first significant growth reductions were 6.25 ± 1.24 (mean ± SE) years after invasion with the greatest frequency of negative growth changes occurring 20 years after invasion. In invaded stands, 41% of trees experienced negative growth changes. In terms of invasive load estimates per 1000 L. maackii individuals, radial tree growth was reduced by 0.56 mm·a⁻¹, and basal area growth was reduced by 0.74 cm²·a⁻¹. Given these findings, significant economic losses could occur in hardwood forests of Ohio.

Conclusions: To our knowledge, this is the first study using dendrochronological techniques to investigate the impact of a non-indigenous, understorey plant on overstorey tree growth. Active management will likely be needed to maintain forest productivity in L. maackii impacted landscapes.

Nomenclature: Gleason & Cronquist (1991) for vascular plants.

Abbreviations: MANOVA = Multivariate Analysis of Variance; RANOVA = Repeated Measures Analysis of Variance; PCQ = Point-Centered Quarter; RI = Radial Increment; BAI = Basal Area Increment

Question: How useful are Ellenberg N-values for predicting the herbage yield of Central European grasslands in comparison to approaches based on ordination scores of plant species composition or on soil parameters?

Location: Central Germany (11°00′-11°37′ E, 50°21′-50°34′ N, 500 - 840 m a.s.l.).

Methods: Based on data from a field survey in 2001, the following models were constructed for predicting herbage yield in montane Central European grasslands: (1) Linear regression of mean Ellenberg N-, R- and F-values; (2) Linear regression of ordination scores derived from Non-metric Multidimensional Scaling (NMDS) of vegetation data; and (3) Multiple linear regression (MLR) of soil variables. Models were evaluated by cross-validation and validation with additional data collected in 2002.

Results: Best predictions were obtained with models based on species composition. Ellenberg N-values and NMDS scores performed equally well and better than models based on Ellenberg R- or F-values. Predictions based on soil variables were least accurate. When tested with data from 2002, models based on Ellenberg N-values or on NMDS scores accurately predicted productivity rank order of sites, but not the actual herbage yield of particular sites.

Conclusions: Mean Ellenberg N-values, which are easy to calculate, are as accurate as ordination scores in predicting herbage yield from plant species composition. In contrast, models based on soil variables may be useful for generating hypotheses about the factors limiting herbage yield, but not for prediction. We support the view that Ellenberg N-values should be called productivity values rather than nitrogen values.

Nomenclature: Wisskirchen & Haeupler (1998).

Abbreviations: CV = Coefficient of variation; ICP-AES = Inductively coupled plasma-atomic emission spectrometry; MLR = Multiple linear regression; NMDS = Non-metric Multidimensional Scaling

Question: Arctophila fulva var. pendulina, Primula nutans var. jokelae and Puccinellia phryganodes are threatened early successional species growing in the seashore meadows of the northern Baltic Sea. Patches formed by these species are destined to be replaced by other species during primary succession and in order to persist in the area they have to continuously colonize new areas. We studied whether the displacement of the species could be slowed down and their sexual and/or vegetative reproduction enhanced by management targeted to surrounding vegetation.

Location: Bothnian Bay, Baltic Sea, W Finland.

Methods: Vegetation surrounding patches of all study species was mown in four successional growing seasons. Moreover, the impact of additional soil turning on creating new favourable growing sites was tested for A. fulva.

Results: Deterioration of suitable habitats of A. fulva and P. nutans was markedly slowed down by management and the vegetative and/or sexual reproduction of these species was enhanced. In the case of P. phryganodes, however, no positive response to management was obtained.

Conclusions: In order to improve the long-term persistence of these three species successional vegetation changes should be slowed down and their dispersal and colonization success improved by continuous management of the populations. We further suggest that the colonization of new areas should be aided by transplantations to the non-vegetated islets, which have recently risen from the sea and cannot be reached by means of dispersal.

Nomenclature: Hämet-Ahti et al. (1998).

Question: Is the expansion of Hippophaë rhamnoides in coastal dunes associated with a decline in plant species richness, and is this decline best described by a hump-backed relationship between species number and shrub cover?

Location: Grey and yellow dunes on the East Frisian islands Spiekeroog and Norderney.

Methods: Total plant species richness as well as the number of herbaceous and cryptogam species were determined in 2001 using plots of 16 m² size. We compared shrubland plots with varying cover of Hippophaë with neighbouring dune grassland plots without shrubs as reference sites. Soil samples were collected to determine the values of some important edaphic variables (pH, organic matter, nitrogen).

Results: The shrubland plots with Hippophaë had or tended to have lower soil pH and C/N ratios and higher contents of organic matter and nitrogen than the grassland plots. Total species richness was marginally significantly related to the cover of Hippophaë in a hump-backed manner on both islands. The pattern was more pronounced for mosses and lichens than for herbaceous species. For all species groups on Spiekeroog and for the herbaceous species on Norderney, the hump-backed relationship was much improved when using the difference in species number between shrubland and grassland plot as a dependent variable. Relationships could be improved by including the soil parameters as co-variables. Species richness was highest at moderate levels of shrub expansion, while it was much reduced in very dense shrubland. The decrease in species number is caused by the decline in grassland species typical of the open dunes, including some rare taxa.

Conclusions: The expansion of Hippophaë rhamnoides is a serious threat to the plant species richness of open coastal dunes, and needs to be counteracted by management measures.

Nomenclature: Wisskirchen & Haeupler (1998).

Abbreviations: Nor = Norderney; Spi = Spiekeroog

Questions: Does the diversity of heathland vegetation change when subjected to experimental disturbances such as cutting and nitrogen fertilization? Do changes in the vegetation structure negatively affect the regeneration of the dominant species Calluna vulgaris? Is cutting an alternative method of conserving the diversity and maintaining the structure of heathlands in the Cantabrian Mountains?

Location: Calluna vulgaris heathlands on the southern slopes of the Cantabrian Mountain range, NW Spain.

Methods: A total of 60 plots were treated with different combinations of cutting and twice the estimated atmospheric deposition of nitrogen (56 kg-N·ha⁻¹·yr⁻¹). The changes in the cover values of the species present were monitored over a five year study period. The cover values were used to calculate abundance and species richness.

Results: Fertilizing with nitrogen allows biodiversity to increase over time. However, the greatest biodiversity is associated with the cutting plus fertilization treatment, since cutting allows gaps to be opened that are easily colonized by pioneer annual species, while fertilization mainly favours an increase in the mean number of perennial herbs (graminoids and forbs). Increased perennial herb richness also corresponds to a rise in their cover values. The recovery of the dominant woody species in these communities, Calluna vulgaris, is not impeded by the increase in perennial herbs species' cover values.

Conclusions: In the Calluna vulgaris heathlands studied, cutting plus fertilization allowed an increase in biodiversity over time. No displacement of the dominant woody species, Calluna vulgaris, is observed due to the presence of the perennial herbs. Cutting patches of heathland is recommended as a mechanism for maintaining high vegetation diversity, when grazing is not possible.

Nomenclature: Tutin et al. (1964–1980).

Question: Can fire be used to maintain Yellow pine (Pinus subgenus Diploxylon) stands disturbed by periodic outbreaks of southern pine beetle?

Location: Southern Appalachian Mountains, USA.

Methods: We used LANDIS to model vegetation disturbance and succession on four grids representative of xeric landscapes in the southern Appalachians. Forest dynamics of each landscape were simulated under three disturbance scenarios: southern pine beetle, fire, and southern pine beetle and fire, as well as a no disturbance scenario. We compared trends in the abundance of pine and hardwood functional types as well as individual species.

Results: Yellow pine abundance and open woodland conditions were best maintained by a combination of fire and southern pine beetle disturbance on both low elevation sites as well as mid-elevation ridges & peaks. On mid-elevation SE-W facing slopes, pine woodlands were best maintained by fire alone.

Conclusions: Our simulations suggest that fire can help maintain open pine woodlands in stands affected by southern pine beetle outbreaks.

Abbreviations: BDA = Biological disturbance agent; SPB = Southern pine beetle; SRD = Site resource dominance; SRDm = Modified site resource dominance; SV = Site vulnerability

Questions: 1. What is the scale and extent of spatial variability in factors affecting Betula invasion of heaths? 2. How much effect does each factor have on within-patch patterns of invasion? 3. How can this understanding aid in managing Betula invasions?

Location: Lowland heath of southern England.

Methods: Determinants of Betula (both B. pubescens and B. pendula) invasion: biomass density, necromass density, mean vegetation height, P-availability, soil water content and total Betula seed bank density, were measured at two sites on a 5-ha sampling grid. Spatial pattern was assessed using geostatistics. Contributions of each determinant to within-site heterogeneity in predicted Betula seedling densities were estimated by varying variables over their full and interquartile ranges in a statistical model derived from experimental data.

Results: Salient spatial trends were revealed: strong autocorrelation over distances of < 50 m for soil factors and more extensive autocorrelation (0 to >150 m) in vegetation variables and Betula seed bank densities. The latter resulted in single across-site gradients, the former small, distinct patches. All patterns were overlain with variance that was present at distances of < 17.6 m. Variables displaying spatial pattern also accounted for within-site heterogeneity in predicted Betula seedling densities but their relative contribution to this varied between sites.

Conclusions: Identifiable spatial autocorrelation in factors controlling patch-scale invasion patterns allows managers to target invasion prone patches, potentially reducing management intensities. Furthermore, management effort may be optimised by spatially de-coupling Betula seed from safe-sites. This plan may adaptable to the management of other weeds and openland ecosystems.

Nomenclature: Anon. (2005).

Abbreviations: P = Phosphorus

Question: To establish a habitat classification based on functional group co-occurrence that may help the drawing up of conservation plans.

Location: Riverine forest fragments in the Grand-duché de Luxembourg, Europe.

Methods: Forest fragments were surveyed for their abundance of vascular plants. These were clustered into emergent groups according to 14 life-traits related to plant dispersal, establishment and persistence. Forest fragments were classified according to similar distribution of the identified emergent groups. Environmental factors were related to the emergent group richness in each forest type using generalized linear models.

Results: Contrary to former species centred classifications, only two groups of forests, each with clearly different emergent group composition and conservation requirements, were detected: (1) swamp forests characterized by anemogamous perennials, annuals and hydrochorous perennials and (2) moist forests characterized by barochorous perennials, small geophytes and zoochorous phanerophytes. From a conservation point of view, priority should be given to large swamp forest with intact flooding regimes. This is in accordance with the high wind and water dispersal capacities of their typical emergent groups. For the moist forests, conservation priorities should be high forest connectivity and historical continuity since dispersal and establishment of their characteristic emergent groups are highly limited.

Conclusions: The described methodology, situated at an intermediate integration level between the individual species and whole community descriptors, takes advantage of both conservation plans built for single species and the synthetic power of broad ecological measures.

Nomenclature: Lambinon et al. (2004).

Abbreviations: EG = Emergent group; EU = European Union; GLM = Generalized Linear Model

Question: Is the diverse mosaic of forest/grassland (Campos) vegetation on the hills in the Porto Alegre region natural or of anthropogenic origin? What are the best approaches to management and conservation of forest/grassland mosaics in southern Brazil?

Location: 280 m a.s.l., Rio Grande do Sul State (30°04′32″S; 51°06′05″W, southern Brazil.

Methods: A 50-cm long radiocarbon dated sediment core from a swamp on Morro Santana was analysed for pollen and charcoal, and multivariate data analysis was used to reconstruct past vegetation and fire dynamics.

Results: The formation of swamp deposits is related to a change to wetter climatic conditions since 1230 cal yr BP. The diverse forest/grassland mosaic existed already at that time and can be seen as natural in origin as it has been also shown from other studies in southern Brazil. Since 580 cal yr BP, forests expanded continuously. The marked higher occurrence of the pioneer Myrsine during the last 70 years, indicates a change in the disturbance regime. In the past, vegetation has been influenced by mostly anthropogenic fire, set first by Amerindians and later by European settlers.

Conclusions: Management for conservation of forest/grassland mosaics should take into account, first, that grasslands are remnants of earlier drier Holocene periods and not a result of deforestation and, second, the history of disturbance by grazing and fire. Suppression of grazing and burning has likely resulted in a trend towards more woody vegetation under modern wet climatic conditions. If management for conservation excludes fire, the present grassland patches will tend to disappear due to forest expansion under the modern humid climate. Maintaining or reintroducing cattle grazing in conservation areas could be an alternative to fire.

Abbreviations AD = Anno Domini; AMS = Accelerator mass spectrometry; Cal yr BP = calibrated years before 1950; PCoA= Principal Coordinates Analysis

Question: Understanding functional change in vegetation and how it might impact on vegetation change and ecosystem function entails measuring plant traits and attributes in situ. However, it is not realistically possible to sample every species for every trait, hence we need to address the consequences of not sampling all species.

Location: Nine arable and grassland sites from the machair of the Western Isles, UK and twenty grassland and woodland sites from Nynäs Nature Reserve, southern Sweden.

Methods: The effects of progressively reducing the proportion of species used to estimate the weighted mean of a range of continuous and qualitative traits were assessed.

Results: Relative abundance and species traits were related, and hence there is a cost in accuracy in reducing the number of species sampled in estimating the weighted mean for the vegetation. This cost was higher for qualitative traits than quantitative ones.

Conclusion: The analysis suggested that for the quantitative traits a minimum of those species that make up at least 80% of the vegetation should be sampled if traits do not vary greatly between species. If this variability is high and the trait is likely to be correlated to abundance then greater effort in sampling species for traits is required. Qualitative information on the rarer species should still be entered into the analysis if it can be accessed in any way, even if quantitative information for that species is unavailable.

Abbreviations: RMSE = Root mean square error; SLA = Specific leaf area

Questions: How is succession on ex-arable land affected by sowing high and low diversity mixtures of grassland species as compared to natural succession? How long do effects persist?

Location: Experimental plots installed in the Czech Republic, The Netherlands, Spain, Sweden and the United Kingdom.

Methods: The experiment was established on ex-arable land, with five blocks, each containing three 10 m × 10 m experimental plots: natural colonization, a low- (four species) and high-diversity (15 species) seed mixture. Species composition and biomass was followed for eight years.

Results: The sown plants considerably affected the whole successional pathway and the effects persisted during the whole eight year period. Whilst the proportion of sown species (characterized by their cover) increased during the study period, the number of sown species started to decrease from the third season onwards. Sowing caused suppression of natural colonizing species, and the sown plots had more biomass. These effects were on average larger in the high diversity mixtures. However, the low diversity replicate sown with the mixture that produced the largest biomass or largest suppression of natural colonizers fell within the range recorded at the five replicates of the high diversity plots. The natural colonization plots usually had the highest total species richness and lowest productivity at the end of the observation period.

Conclusions: The effect of sowing demonstrated dispersal limitation as a factor controlling the rate of early secondary succession. Diversity was important primarily for its ‘insurance effect’: the high diversity mixtures were always able to compensate for the failure of some species.

Abbreviations; ED = Euclidian distance; HD = High diversity; LD = Low diversity; NC = Natural colonization

Question: Is Rhynchostegium megapolitanum an expanding species?

Location: Viennese Basin (120–220 m a.s.l.), Austria.

Methods: 121 dry grasslands, were investigated for the occurrence of R. megapolitanum. Nineteen environmental variables at 50 randomly selected sites, species composition at sites with and without R. megapolitanum and the spatial patterns of distribution of the species at the landscape scale were analysed. We compared actual distribution data of three rare species (Didymodon acutus, Pleurochaete squarrosa R. megapolitanum) and a common one (Brachythecium rutabulum) with the distribution obtained by vouchers that were collected between 1860 and 1940 in the investigated area. We calculated a GIS based model pattern and compared it with the actual distribution.

Results: R. megapolitanum was detected in 28 of these sites, almost 50 % of its populations produced sporophytes. We found significant differences between sites with and without R. megapolitanum with regard to grassland size, the percentage of silt and of sand in the soil. There were fewer occurrences of historic herbarium vouchers of R. megapolitanum than our current field survey discovered. The GIS based analyses of distribution patterns at the landscape scale showed a clustering of sites in which R. megapolitanum was present or absent. Simulations with a spatially realistic expansion model showed high similarities to the actual distribution of the species.

Conclusions: All these analyses suggest that R. megapolitanum has been expanding in the investigated area. A significant increase in temperature and nitrogen deposition within the last hundred years might be the underlying cause for the species' spread.

Nomenclatural reference: For bryophyte species Corley et al. (1981); for vascular plants Adler et al. (1994).

Abbreviations AFLP = Amplified Fragment Length Polymorphism; GIS = Geographic information system; NHM = Natural History Museum Vienna; ZAMG = Central Institute of Meteorology and Geodynamics

Question: What is the impact of the presence of Rhinanthus minor on forb abundance in newly established swards?

Location: Wetherby, West Yorkshire, UK (53°55′ N, 1°22′ W).

Method: A standard meadow mix containing six forbs and six grasses was sown on an ex-arable field and immediately over-sown using a randomised plot design with three densities of Rhinanthus minor (0, 600, and 1000 seeds per m²). Above-ground biomass was analysed over a period of three years, while detailed assessments of sward composition were performed during the first two years.

Results: Values of grass biomass were reduced in the presence of Rhinanthus, especially at the higher sowing density. The ratio of grass:forb biomass was also lower in association with Rhinanthus, but only at the higher sowing density. The presence of Rhinanthus had no effect on species number or diversity, which decreased between years regardless of treatment.

Conclusions: Although not tested in a multi-site experiment, the benefit of introducing Rhinanthus into newly established swards to promote forb abundance was determined. The efficacy of Rhinanthus presence is likely to depend on whether species not susceptible to the effects of parasitism are present.

Nomenclature: Stace (1997).

Question: Can the seed bank play a significant role in the restoration of plant communities of dry acidic dune grassland where fire has destroyed Ulex europaeus scrub?

Location: Northern French Atlantic coast.

Methods: One year after the fire, the seed bank and vegetation were sampled in 1 m ×1 m plots along three transects from the oldest scrub vegetation towards the grassland. Differences in species richness, seed density and contribution of ecological groups in the seed bank and vegetation along the transects were analysed.

Results: Seed density and species richness in the seed bank decreased significantly from the grassland towards the centre of the scrub vegetation; 50% of the seed bank consisted of core species of the target plant community, such as Carex arenaria, Aira praecox, Rumex acetosella and Agrostis capillaris. Seeds of these species were also found in the deeper soil layers beneath the oldest scrub vegetation, indicating that they can be considered to be long-term persistent. Beneath the youngest scrub vegetation, seeds of rare satellite target species also occurred. However, no target species were established on the burned site after one year, resulting in a large discrepancy between seed bank and vegetation.

Conclusions: Although the seeds present in the soil indicate that restoration of the acidic grassland based on the seed bank is possible, additional management actions such as mowing and soil disturbance may be necessary to restrict resprouting of Ulex and to stimulate the germination of seeds of target species in the deeper soil layers.

Nomenclature: Lambinon et al. (1998).

Abbreviations; DCA = Detrended Correspondence Analysis

Questions: The formerly overgrazed Inner Mongolia steppe was subject to retrogressive succession. Today, Artemisia frigida and Potentilla acaulis are two dominant species in different phases of successive degradation. To investigate the impact of grazing intensity on spatial community structure, we investigated the small-scale spatial association between A. frigida and P. acaulis at zero, light, medium and heavy sheep grazing, and proposed factors involved in the spatial associations between these two species along a grazing intensity gradient.

Location: The Inner Mongolia Grassland Ecosystem Research Station of the Chinese Academy of Sciences.

Methods: Four grazing intensities were selected: zero, light (1.33 sheep/ha), medium (4.0 sheep/ha) and heavy (6.7 sheep/ha). After 13 years of grazing three 2 m × 2 m quadrats with 100 × 100 cells of size 2 cm × 2 cm were randomly selected in each treatment in July and August 2002. The presence of A. frigida and P. acaulis in each cell was recorded and the positions of the individuals were mapped using Cartesian coordinates in each quadrat. The small-scale spatial associations between A. frigida or P. acaulis were quantified with the L₁₂(d), J₁₂(d) functions (both derived from K₁₂(d), the former indicating the type of the spatial association, the latter indicating the strength of the spatial association), using Monte Carlo simulations.

Results: A. frigida was negatively associated with P. acaulis at short distances (0 - 100 cm) under zero and light grazing, and negatively or independently under medium and heavy grazing. Increasing grazing intensities suppressed the peak negative associations. More intense grazing enhanced the tendency towards independent distribution of these two species.

Conclusions: The small-scale spatial associations between A. frigida and P. acaulis were significantly different at four different intensities of sheep grazing. Grazing disturbance, clonal growth habit of species, and interspecific competition are the main factors leading to a difference of spatial associations between these two species at different grazing intensities.