Úrtak Fyri at vita, hvar vøksturin í Føroyum skiftir frá at vera arktiskur til at vera tempereraður, kannaðu vit útbreiðsluna av lívshættum Raunkiærs niðan eftir fimm ymiskum fjalla síðum. Eisini kannaðu vit, hvønn týdning gróðrarlag ið, LOI (gløðitap) og árligur miðalhiti hava fyri útbreiðsluna av lívshættum við hæddini. Okkara niðurstøða var, at tíðleikin av hemikryptofytum minkaði linjurætt við hæddini, tíðleikin av therofytum og geofytum vaks linjurætt við hæddini, og rásin, sum vísir tíðleikanav charmaifytum sum funktión av hæddini hevur skap sum parabil, við lægsta tíðleikanum á 400-500 m hædd.Tíðleikin av hemikryptofytum samsvarar eins væl við lága gróðrarlagið sum við hæddina, men thero fytarnir samsvara best við lága gróðrarlagið. Chamae fytarnir samsvara best við tann árliga miðal hitan, men geo fytarnir samsvara best við LOI. Kanningin vísir, at lutfallið millum hemikryptofytar og cham ae fytar broytist við hæddini, sum vøksturin skiftir frá tempereraðum til arktiskt eyðkenni. Abstract To study the shift from temperate to arctic vegetation in the Faroe Islands, we quantitatively analysed the distribution of Raunkiær’s life-forms along five altitudinal gradients. We further tested the importance of the non-climatic parameters of altitude, total vegetation cover and LOI (loss on ignition), and the climate variable of annual mean temperature in describing the abundance variation of life-forms. We found that as altitude increased, the abundance of hemicryptophytes decreased linearly; the abundance of therophytes and geophytes increased linearly; and the abundance of chamaephytes varied parabolically, with the lowest abundance around 400-500 m. The abundance variation of hemicryptophytes seems to be as wellcorrelated with total vegetation cover as with altitude, while total vegetation cover was the best parameter to describe the variation in abundance of therophytes. Annual mean temperature was the most important parameter for describing the abundance variation of chamaephytes and LOI was the most important parameter describing the variation of geophytes. Weconcluded that the abundance rela tionship between hemicryptophytes and chamae phytes changed with altitude as the vegetation changed from temperate to arctic vegetation.

Bolderslev Skov (113 ha) is the largest contiguous ancient forest remnant in Denmark. The forest has been preserved since 1998 as a strict non-intervention forest reserve. We studied vegetation structure, floristic gradients, and diversity of the forest in 50 plots of 100 m2 placed according to a restricted random sampling design. Dominant tree species were Fagus sylvatica, Fraxinus excelsior, Tilia cordata and Quercus robur, which in most parts of the forest form a mixed canopy. Most stands appeared to be of moderate age, 55-80 years old, and large old trees were rare. pH in association with light and thickness of the litter layer were the most important factors in explaining floristic gradients in the forest. Soil moisture (dry to mesic) was not strongly correlated with DCA axes for neither tree nor field layer, but had a significant effect on the distribution of a number of herb species. Forest structure was not important in explaining species distributions. Field layer species richness showed a positive relationship with the pH-gradient. At the scale of 1m2 plots we also found a highly significant negative relationship between field layer species richness and the plot-wise Ellenberg indicator value for nitrogen availability. Structure of the tree layer had little effect on field layer species richness. The mixed composition, long continuity, and presence of a high proportion of the regional species pool assigns a high conservation value to Bolderslev Skov and makes it an important site for future studies of the dynamic properties, niche preferences, and inter-specific competition of temperate deciduous forest species.

ABSTRACTAim To identify the effect of climate change on selected plant species representative of the main vegetation types in the Faroe Islands. Due to a possible weakening of the North Atlantic Current, it is difficult to predict whether the climate in the Faroe Islands will be warmer or colder as a result of global warming. Therefore, two scenarios are proposed. The first scenario assumes an increase in summer and winter temperature of 2 °C, and the second a decrease in summer and winter temperature of 2 °C.Location Temperate, low alpine and alpine areas in the northern and central part of the Faroe Islands.Methods The responses of 12 different plant species in the Faroe Islands were tested against measured soil temperature, expressed as Tmin, Tmax, snow cover and growing degree days (GDD), using generalised linear modelling (GLM).Results The tolerance to changes in winter soil temperature (0.3–0.8 °C) was found to be lower than the tolerance to changing summer soil temperature (0.7–1.0 °C), and in both cases lower than the predicted climate changes.Conclusions The species most affected by a warming scenario are those that are found with a limited distribution restricted to the uppermost parts of the mountains, especially Salix herbacea, Racomitrium fasciculare, and Bistorta vivipara. For other species, the effect will mainly be a general upward migration. The most vulnerable species are those with a low tolerance, especially Calluna vulgaris, and also Empetrum nigrum, and Nardus stricta. If the climate in the Faroe Islands should become colder, the most vulnerable species are those at low altitudes. A significantly lower temperature would be expected to produce a serious reduction in the extent of Vaccinium myrtillus and Galium saxatilis. Species like Empetrum nigrum, Nardus stricta, and Calluna vulgaris may also be vulnerable. In any case, these species can be expected to migrate downwards.

For the first time, a tentative overview of described plant communities in Denmark is presented according to the phytosociological Braun-Blanquet approach. An attempt was made to compile all available names of syntaxa at the association level, which have appeared in the literature, mostly as defined from vascular plants and the Charetea. In total 173 associations belonging to 38 classes have been registered in Denmark. The listed associations are characterized by a brief description of their ecology, Danish distribution and rarity. Basic literature sources for each syntaxon are provided. The current knowledge of Danish plant communities is discussed. It is concluded that the number of known syntaxa from Denmark is probably underestimated.

Tilia species are important constituents of natural broadleaved, deciduous forests of Europe, but have vanished from many forest during the past millennium. In this chapter, a survey of Tilia in Danish forest is presented and compared with forest management, age and structure. Tilia cordata and T. platyphyllos are mostly found in natural, ancient forests, and appear to be convenient indicators of forest management and forest age. Most populations are very small, but a few remarkable stands of both species with thousands of individuals are still surviving. The results point to the urgent need for installing active conservation and management measures, together with monitoring, in order to stabilize the most threatened populations of endangered woody species in Danish forests in general, and of Tilia species in particular.

Species distribution depends on the physiological and ecological niche where a species can exist and regenerate in resource competition with other species (niche limitation). The realized niche is influenced by local biotic processes that influence species behaviour and the shape of the response curves relative to environmental gradients. Processes on larger scales also influence the species niche through source-sink mechanisms (dispersal limitation) and the species richness of an area (pool limitation). Despite the growing evidence of skewed or irregular species response curves along gradients, many ecologists still assume symmetric, unimodal response curves along gradients in ecological interpretation. Ellenberg’s indicator system is probably the most common example. However, the assumption is not ecologically or statistically valid, due to the many different processes affecting the distribution of plant species. Here I present the results of Huisman-Olff-Fresco (HOF) regressions for 209 Danish forest species. HOF modelling is chosen to avoid the classical drawbacks of assuming symmetric, unimodal response patterns. I calculate the optima for all species with unimodal responses to soil pH and compare these with the Ellenberg indicator values for reaction (R), which are often used as a substitute for soil pH measurements. I demonstrate that the assumption of symmetric, unimodal species behaviour is violated in 54% of the cases and that pH optima and R indicator values for species are not always compatible. Ellenberg reaction scale has been used byEwald (Folia Geobot. 38: 357–366, 2003) as an indicator of which species are calcicole, i.e., whether they can grow and reproduce on calcareous soils. Such affinities of species, however, are related to both local niche properties and processes on large scales and cannot be generalized from a single empirical variable such as pH, nor from Ellenberg semi-ordinal indicator scale. I conclude that while the determination of whether species are calcicole or calcifuge requires more research, it is evident that Denmark contains a fairly balanced number of calciphytic and acidophytic species. This is probably due to the nearly equal areas with acidic and alkaline soils in Denmark, which also contribute to the high species richness of more than 500 vascular plant species in Danish forests.

Ellenberg'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 Ellenberg 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 Ellenberg 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.

In this paper we investigate whether Ellenberg's Climate Quotient (EQ, defined as the mean temperature of the warmest month divided by annual precipitation, multiplied by IOOO), can be used to predict the distribution of Carpinus betulus in Denmark. It has been suggested that the competitive relationship between the two tree species Fagus sylvatica and C.betulus is related to EQ in central Europe. Areas with low EQ have dominance of E. sylvatica, whereas higher EQs are associated with dryer and warmer climates that favour C.betulus. To determine if this holds true, also in northern Europe, we investigate the present distribution of C.betulus in Denmark, based on a comprehensive dataset with presence‐absence information of the species. We relate the distribution of C.betulus to 12 climate parameters and indices (including EQ), analyse it in a geographical information system and compare the ecology of C.betulus and E sylvatica in four Danish forests, located in different climatic and floristic regions. The highest density of C.betulus was found in eastern Denmark where EQ is high, i.e. summer temperature is relatively high and precipitation low. In the western and south‐western parts of the country, where the climate is slightly more wet and more oceanic, there are fewer populations of C.betulus. Based on present climatic data it seems that the climate of Denmark does not limit the occurrence of C.betulus, except perhaps for a small area in western Jutland. We believe that climate changes in the late Holocene cannot alone account for the changes in the distribution of C.befulus in Denmark. And future climate change is likely to affect the distribution of C.betulus with generally better conditions.

Floristic and structural data of oak dune forests in western Jutland (Kaergard and Blabjerg) were collected in 1998 and compared with previous studies of Danish oligotrophic oak forests.A hierarchical divisive clustering resulted in four main clusters, containing two coastal oak vegetation types. Quercus robur-Carex arenaria and Q. robur-Pleurozium schreberi communities, both restricted to the oak dune forest areas in western Jutland, and two more widespread oak forest types. Q. robur-Vaccinium myrtillus and Q. robur-Holcus mollis communities.The low-growing Q. robur-C. arenaria shrub and forest vegetation occurs primarily in the outer dunes, with the tallest trees on the leeward sides of the dunes, while a Q. robur-P schreberi community is found in the inner parts of the dune system. The similarity to a considerable number of the acidophilous vascular plant species closely relates the Danish oak dune forest communities to the Pinus sylvestris or P. sylvestris-Q. robur vegetation described in neighbouring countries, suggesting that R sylvestris probably had a prominent role in the Danish oak dune forests before human exploitation caused its extinction in the 18th century.The low-growing oak shrub in the outer dunes. aged between 52 and 85 years, generally seems to have remained unchanged in floristic composition and structure since 1964 when the previous study on the shrub was performed.In the dune valleys, oak stand-level dieback is widespread and was latest recorded in 1985. Such retrogressive processes are probably due to a combination of low winter temperatures and other adverse climatic conditions. In the central parts of the oak dune forest, the oak trees, aged between 55 and 73 years, grow to a higher stature, but also here stand-level dieback is widespread leading to retrogression. Only in the innermost parts, a regular forest cover seems to prevail with trees of 68-104 years of age and the development of the field vegetation cover progresses into a typical forest community. This is exemplified by the decrease of light-demanding species and the establishment of true forest species like Oxalis acetosella and Dryopteris dilatata.The structure and poor-species diversity make the oak dune forest unique both in Denmark and on an international scale. We recommend further studies of the remnants of the original. and in the past probably more widespread dune forests in Denmark. and drawing up of a detailed management and conservation plan. The possibility of permitting the native and now reintroduced P. sylvestris to re-colonise the oak dune forest area and be part of the natural vegetation succession processes should be seriously considered. (C) 2002 Elsevier Science B.V. All rights reserved.

Patterns of vascular plant diversity in Denmark are examined, based on the most recently published Danish Flora. The highest diversity is found on the major isles of Sjælland, Møn, Falster and Bornholm, but many rare taxa occur in Jylland. Two different cluster analyses suggest a division of Denmark into six phytogeographical regions, which only partly supports earlier, more subjective divisions of Denmark. Our results suggest that north- and northwestern Jylland and the isles of Læsø and Anholt belong to the boreo-nemoral phytogeographical region, due to their high number of northern taxa, which clearly differentiate them from the rest of Denmark, despite the lack of typical boreo-nemoral tree species, such as Pinus sylvestris.

A main floristic coenocline is extracted from a Danish forest vegetation data set with Detrended Correspondence Analysis. Huisman-Olff-Fresco (HOF) modelling of 262 species occurrences relative to site scores along the coenocline is compared with Gaussian and Generalized Linear Modelling. HOF models allow for responses of variously skewed forms, which may result from interspecific interactions. Most species have symmetric (60%) or skewed (29%), and only few species have flat or monotone response curves. This provides evidence for the generality of unimodal plant species response curves, provided the gradient in question comprises a sufficient amount of compositional turnover. The Gaussian niche width is correlated with density of optima and probability of occurrence of the species. Detailed analysis of HOF estimates for 28 woody species indicates that early succession species such as Pinus sylvestris and Populus tremula have wider niches than middle to late successional canopy species such as Alnus glutinosa, Carpinus betulus, Fagus sylvatica, Fraxinus excelsior, Quercus robur and Tilia cordata. A marked overlap in niche range along the coenocline is interpreted in terms of species competition. Rubus idaeus intrudes into the niches of all other shrub species. Several canopy tree species, such as Fagus sylvatica, Fraxinus excelsior and Quercus robur overlap more than 60% of the ranges of all other species, while their internal overlaps are fairly equal, presenting evidence for their likely co-existence given more natural forest conditions. The combined analysis of coenoclines with HOF modelling of species behaviour is the most robust among the compared methods for estimating model parameters and niche characteristics of plant species. It is recommended for future ecological studies.

A Danish beech (Fagus sylvatica) forest was studied during a period of five years, to reveal temporal and spatial patterns in the ground vegetation within a year and between years. In 1994, twenty stations were established in commercially managed forests south of Aarhus, and the frequency of the vascular plants was recorded in 40 stratified random Raunkiier circles (0.1m2). The sampling was repeated in 1995, 1997 and 1998. The seasonal variation in species frequencies was furthermore studied in nine of the permanent stations. The findings were summarised in terms of species richness and averaged Ellenberg ecological values, and analysed with clustering analysis and ordination. We applied Steinhaus similarity index and detrended correspondence analysis to detect fluctuation and succession. To test for significant vegetation changes, a non‐parametric Mantel test was used. The species richness and Ellenberg's indicator values were unchanged during the five years. The classification results, however, differed between the years. In particular, changes in the quantitative similarity between years were high (12–23%), and this was supported by ordination. We conclude that the vegetation in the study area, at least in the studied 5‐years period, did not how signs of clear successional trends, but merely changes in species abundance, which we associate with short‐term fluctuation. Further studies, on different time scales, of vegetation dynamics in forests should be initiated, in order to make better descriptions of plant communities, and to detect possible successional trends. We suggest that such studies also include long term monitoring of environmental parameters in a nested, permanent sampling design.

A Danish managed forest of 325 hectares was sampled for plant species richness in a regular 100 × 100 m grid using four nested quadrates of 2, 4, 25, and 200 m2, respectively, at each sample point. The survey resulted in total counts of 161, 171, 224, and 289 species depending on size of quadrates. A list of more than 370 species, however, was accumulated for the forest based on the present study, the literature, and additional personal observations. It was shown that species richness estimators and especially the log‐log estimator resulted in improved estimates of species richness. It was also shown that a search strategy in which plots with high habitat diversity in the immediate neighbourhood or plots close to forest roads were chosen first was more effective than a random search strategy. The random strategy, on the other hand, was more efficient than emphasising core areas of major habitat types in the beginning of the search. The study has clearly demonstrated that a managed forest ecosystem with its mixture of open areas and different stands can harbour a very high plant species diversity (in this case ca. 25% of the total Danish flora in only 325 hectare). It is also shown, however, how difficult and time consuming it is to count all species in a heterogeneous ecosystem.

Rydin, H., Snoeijs, P. & Diekmann, M. (eds.) 1999. Swedish plant geography ‐ Dedicated to Eddy van der Maarel on his 65th birthday. 233 pp. Opulus Press, Uppsala. ISBN 91–7210–084–2 (paperback), 91–7210–484–8 (cloth). Price: USD 56.‐ (paperback); xx USD (cloth). Joost: graag even checken