Early stages of Calluna vulgaris regeneration after burning of coastal heath in central Norway

Questions: How does Calluna vulgaris regenerate after burning wet and dry heaths of different age? Location: Central Norway. Methods: Patches of Calluna dominated old and young wet heath and old dry heath were burned. The mean temperatures reached in the categories of heath were measured. Cover, frequency, height and number of seedlings of Calluna were studied in plots. Results: The mean burning temperatures varied from 680 to 740°C, and were highest in wet heath that had not been burned for at least 50 years. Regeneration of Calluna was evident in the year of burning, but only from seeds. Even heath with a short burning interval lacked vegetative regeneration. Calluna cover increased yearly and exceeded 50 % three years after burning. Regeneration was evident in the year of burning, and was highest in heath with a short burning interval. The height increased regularly at all sites, but was most rapid in dry heath, probably because of better microclimatic conditions. There were more seedlings in the heath with a short burning interval. Conclusions: Calluna only regenerates from seeds afterburning in central Norway. The density of Calluna increased rapidly, which is positive for the conservation and management of coastal heaths in central Norway.     

Fire and regeneration: the role of seed banks in the dynamics of northern heathlands

Questions: How do species composition and abundance of soil seed bank and standing vegetation vary over the course of a post‐fire succession in northern heathlands? What is the role of seed banks – do they act as a refuge for early successional species or can they simply be seen as a spillover from the extant local vegetation? Location: Coastal Calluna heathlands, Western Norway. Methods: We analysed vegetation and seed bank along a 24‐year post‐fire chronosequence. Patterns in community composition, similarity and abundances were tested using multivariate analyses, Sørensen's index of similarity, vegetation cover (%) and seedling counts. Results: The total diversity of vegetation and seed bank were 60 and 54 vascular plant taxa, respectively, with 39 shared species, resulting in 68% similarity overall. Over 24 years, the heathland community progressed from open newly burned ground via species rich graminoid‐ and herb‐dominated vegetation to mature Calluna heath. Post‐fire succession was not reflected in the seed bank. The 10 most abundant species constituted 98% of the germinated seeds. The most abundant were Calluna vulgaris (49%; 12 018 seeds m^?2) and Erica tetralix (34%; 8 414 seeds m^?2). Calluna showed significantly higher germination the first 2 years following fire. Conclusions: Vegetation species richness, ranging from 23 to 46 species yr^?1, showed a unimodal pattern over the post‐fire succession. In contrast, the seed bank species richness, ranging from 21 to 31 species yr^?1, showed no trend. This suggests that the seed bank act as a refuge; providing a constant source of recruits for species that colonise newly burned areas. The traditional management regime has not depleted or destroyed the seed banks and continued management is needed to ensure sustainability of northern heathlands.     

The role of catastrophic death of Calluna in heathland dynamics

In the Breckland heaths of East Anglia large patches of Calluna are often killed by adverse climatic conditions or insect attack. This paper studies one site, Cavenham Heath, where large areas of Calluna were killed between 1976–1979, and shows that older stands were most affected, and recovery was slowest compared to either younger stands, or stands with an uneven-aged structure. Moreover, where Calluna death was most severe, directional succession to birch woodland was accelerated. At this site, although Calluna regeneration has been previously assumed to be initiated by endogenous factors (i.e. by the life cycle of the Calluna), it is also clearly interrupted by exogenous factors. The implications of these results for heathland conservation are discussed, and it is suggested that intervention management by cutting and burning, to maintain large areas of Calluna in the building phase, may be the most appropriate long term strategy.This work was funded in part by the Nature Conservancy Council as part of its research programme into nature conservation. I thank Mr D. Malins and Mrs D. Reynolds for assistance in both the field and the laboratory, Ms S. Ide and Mr J. Pattin-gale for preparing the figures, and Professor C. H. Gimigham, Dr J. Miles and Dr I. C. Prentice for helpful comments on earlier drafts of this paper.     

Community dynamics in relation to management of heathland vegetation in Scotland

The paper describes studies of post-fire succession in heathland vegetation in N.E. Scotland, dominated by Calluna vulgaris. A preliminary model (Legg, 1978) suggested good agreement between simulation of succession on the basis of a Markov chain and observations of stands at different stages of development after burning, at least in the earlier stages. Vegetation transitions are currently being recorded in permanent plots on burnt areas. First results confirm the view that (a) the post-fire succession has the properties of a Markov process, (b) this type of model remains valid when constructed from records of actual transitions, rather than data obtained by inference from evidence of transition. Comparing successional events in stands where, at the time of burning, the Calluna population was in pioneer-, building-, mature-and degenerate phases, shows that transition matrices generally agree with the Markov hypothesis, but not in the case of stands where Calluna was degenerate when burnt. The composition of establishing vegetation 1 year after fire is not confined to species normally associated with the early stages of succession, but reflects the composition of the stand before burning. Redevelopment after fire is described in terms of an initial floristic composition of species with strategies permitting early re-establishment, selected by the recurrence of the fire factor. Subsequent transitions represent changes in their relative abundance due to differing growth properties and competitive interactions. This interpretation applies only under conditions of recurrent incidence of fire (normally once in 10–15 yr). If fire does not recur, Calluna stands pass into the degenerate phase, where changes in the nature of relay floristics may come into play (e.g. with tree colonization).Nomenelature follows Clapham, Tutin & Warburg (1962) for vascular plants; Smith (1978) for bryophytes.     

Early regeneration of Calluna heathland under various fertilization treatments

Summary A sod-cutting and fertilization experiment was performed on a Calluna-dominated heathland in The Netherlands to determine appropriate management regimes for Calluna regeneration, and to further understand the nutrient responses of heathland species. Replicated permanent plots were analysed by multivariate techniques. Sod-cutting alone caused Calluna regeneration from its soil seed bank. A single fertilization at the start of the experiment caused initial vegetation differences which disappeared after a few years as the nutrients were lost from the system, except that one application of nitrogen enhanced the rate of Calluna regeneration. Repeated fertilization caused large differences in the vegetation: repeated nitrogen enhanced several bryophyte species while greatly inhibiting Calluna, repeated phosphate partly inhibited Calluna while greatly favouring several lichen species, and the most striking result of repeated calcium was also an increase in bryophytes, but the species were different from those favoured by nitrogen. Treatments which inhibited Calluna tended to increase species diversity because of the lessened Calluna dominance.     

The effect of traditional management burning on lichen diversity

Question: How does regular management burning of a northern, Calluna vulgaris‐dominated heathland affect the lichen diversity at the patch and landscape scale? Location: Mar Lodge Estate, Scottish Highlands, United Kingdom. Methods: 26 fire sites of different ages and 11 long‐term unburnt stands were surveyed to create a chronosequence of changing lichen diversity following burning. Data were analysed graphically, with a GLM and using a CCA. Results: Though the immediate effect of fire was to significantly reduce lichen diversity, it generally recovered within 20 years. There was a significant difference in the population dynamics between wet and dry moorland areas with terricolous lichens in the former site being replaced by pleurocarpous mosses. Older stands, unburnt for 25 years or more, generally had lower diversity than stands 10 to 15 years old. Changes in lichen diversity and community composition can be attributed to the development of Calluna stand structure following burning. Conclusions: Fire can be seen to play an important role in maintaining the diversity of lichens in heathland areas by providing a variety of stand‐structures and ages across the landscape that favours the development of greater beta‐diversity.     

The reproductive potential and importance of key management aspects for successful Calluna vulgaris rejuvenation on abandoned Continental heaths

The abandonment of traditional pastoralism as well as the use of heath areas for military purposes has had a major impact on dry heaths in the Continental biogeographical region of Europe, causing severe degradation of its key species Calluna vulgaris (L.) HULL. The reproductive potential of this species in a Continental climate is assumed to be low, although there is yet no observational or experimental evidence for this. More knowledge is also needed about cost‐effective and sustainable measures to restore abandoned dry heaths in this biogeographical region, because traditional management options are often too expensive (e.g., sod‐cutting) or restricted due to environmental laws and the danger of unexploded ammunition (e.g., burning). Using as an example an 800 ha Continental heathland in Germany that has been abandoned for about two decades, we studied the reproductive potential (seed production, soil seed bank, and germination ability) of degenerate C. vulgaris stands. In addition, we conducted a comprehensive field experiment to test the effects of low‐intensity, year‐round grazing by Heck cattle and Konik horses as well as one‐time mowing and patchy exposure of bare soil on the generative rejuvenation (i.e., recruitment and survival) of degenerate C. vulgaris stands over 3 years. We used generalized linear mixed models for statistical analyses. Seed production of degenerate C. vulgaris stands was high as well as the germination ability of their seeds, being similar to Atlantic heathlands. However, soil seed‐bank densities were lower than those found in managed or abandoned Atlantic heaths. Overall seedling recruitment in the field was considerably lower in comparison with Atlantic heaths. Low‐intensity grazing or one‐time mowing did not induce a substantial increase in C. vulgaris recruitment, whereas an additional one‐time creation of bare soil patches or the one‐time creation of bare soil without subsequent management significantly facilitated seedling recruitment and survival in the first year. However, from the second year on, the positive effect of the creation of bare soil without subsequent management was no longer present. In the third year, survival of juveniles was significantly supported by low‐intensity grazing in combination with shallow soil disturbances as well as in combination with one‐time mowing and shallow soil disturbances, whereas mowing alone resulted in marginally significant lower survival. The extremely low seedling recruitment requires a careful choice of suitable management measures to promote the survival of sufficient numbers of Calluna individuals. Therefore, we recommend low‐intensity grazing with free‐ranging robust breeds and the combination of this with one‐time mowing as an effective means of supporting generative rejuvenation of C. vulgaris in degraded heaths. However, at the beginning of the restoration process, the creation of bare soil patches for seedling recruitment is crucial. For implementation into practice, we present different strategies to enhance the proportion of bare soil after long‐term abandonment of heaths when traditional management options are no longer feasible.     

Germination and establishment of seedlings in different phases of theCalluna life cycle in a Scottish heathland

Previous authors have suggested that cyclical succession takes place inCalluna-dominated heathland, and is determined by the different growth phases of the dominant. Characteristic species are said to invade at different stages of the life cycle ofCalluna, particularly in the initial and pioneer phases and in the degenerate phase. In the last phase, gaps are formed due to separation and dying of the oldest frame branches.This paper aims to analyze in which microhabitat and in which phase of theCalluna life cycle seedling emergence and establishment is possible.More seedlings appear in pioneerCalluna than in matureCalluna stands in experimentally manipulated micro-sites. In pioneerCalluna establishment is affected only by application of litter, in matureCalluna by increased illumination. The differences between treatments disappeared after three years, but not the difference in establishment between stands.Seedling emergence from species sown experimentally was different in the successive phases ofCalluna. Highest emergence was in the pioneer stand.In a seedling survey also most seedlings appeared and established in the pioneer phase. The number of recently germinated seeds was high in all phases. However, seedling survival was very low, except in the pioneer stands. This study does not of itself show evidence for cyclical succession inCalluna-dominated heath vegetation. Colonization of gaps by seedlings ofCalluna in mature or degenerate phases is possible, but must be an infrequent occurrence.Nomenclauture follows Clapham, Tutin & Warburg (1962).We wish to thank Dr G. R. Miller for stimulating discussions during the start of the experiments. E. de Hullu wishes to thank the Botany Department in Aberdeen for their hospitality during the research period.     

Does prescribed burning result in biotic homogenization of coastal heathlands?

Biotic homogenization due to replacement of native biodiversity by widespread generalist species has been demonstrated in a number of ecosystems and taxonomic groups worldwide, causing growing conservation concern. Human disturbance is a key driver of biotic homogenization, suggesting potential conservation challenges in seminatural ecosystems, where anthropogenic disturbances such as grazing and burning are necessary for maintaining ecological dynamics and functioning. We test whether prescribed burning results in biotic homogenization in the coastal heathlands of north‐western Europe, a seminatural landscape where extensive grazing and burning has constituted the traditional land‐use practice over the past 6000 years. We compare the beta‐diversity before and after fire at three ecological scales: within local vegetation patches, between wet and dry heathland patches within landscapes, and along a 470 km bioclimatic gradient. Within local patches, we found no evidence of homogenization after fire; species richness increased, and the species that entered the burnt Calluna stands were not widespread specialists but native grasses and herbs characteristic of the heathland system. At the landscapes scale, we saw a weak homogenization as wet and dry heathland patches become more compositionally similar after fire. This was because of a decrease in habitat‐specific species unique to either wet or dry habitats and postfire colonization by a set of heathland specialists that established in both habitat types. Along the bioclimatic gradient, species that increased after fire generally had more specific environmental requirements and narrower geographical distributions than the prefire flora, resulting in a biotic ‘heterogenisation’ after fire. Our study demonstrates that human disturbance does not necessarily cause biotic homogenization, but that continuation of traditional land‐use practices can instead be crucial for the maintenance of the diversity and ecological function of a seminatural ecosystem. The species that established after prescribed burning were heathland specialists with relatively narrow geographical ranges.     

Seed-shedding in heather (Calluna vulgaris (L.) Hull

Abstract

Background: Accumulating evidence, mainly from small-scale experiments, suggests that species diversity helps stabilise ecological communities; however, this relationship needs testing at larger scales in a wider range of natural communities.

Aims: In experimentally burnt ericaceous shrub stands, we aimed to determine whether more diverse stands had more stable vegetation cover.

Methods: Using two prescribed fire management experiments – one on heathland and one in forest – at scales of 100–700 m², we compared pre-disturbance vegetation characteristics (measures of diversity, traits and composition) with resistance (degree of perturbation on disturbance), resilience (here defined as post-disturbance recovery rate) and stability (the inverse of temporal variability).

Results: Responses to disturbance were usually best explained by a measure of dominance: Simpson's index. High dominance was associated with high resilience, but low resistance and low stability. Within the forest, the shrub community had lower dominance and higher stability than it did on heathland. Dominance and diversity were strongly linked as opposite poles of a principal axis of vegetation variation; therefore, more diverse vegetation was more stable.

Conclusions: Ericaceous shrub cover is known to support important ecosystem services, such as soil protection, carbon sequestration, flood prevention and livestock grazing. Our results suggest that high shrub diversity would support stable provision of these services. Land managers who prioritise this aim in British heathlands and pinewoods should consider a wider range of management approaches than those of typical current practice.     

Conservation of Calluno-Vaccinietum heathland in the Belgian Ardennes,an experimental approach

It is now difficult to manage the semi-natural groupings of heathland because of the tendency for succession towards forest stages.Several experiments were conducted in the Hautes Fagnes region (Belgium). After the vegetation was mapped, plots were treated by mowing, burn-beating, and burning.The changing floristic composition was followed from 1972 to 1980 in permanent quadrats. Burn-beating is an excellent method of management for old heath, because it reestablishes the properties of the heath ecosystem.Nomenclature follows de Langhe et al., 1978. Nouvelle flore de la Belgique, du Grand-Duché de Luxembourg, du Nord de la France et des Régions voisines, 2e éd.     

Contrasting changes in vegetation structure and diversity with time since fire in two Australian Mediterranean‐climate plant communities

Mallee‐heath and mallee communities occur in a mosaic across large areas of south‐western Australia, in topographically subdued and fire‐prone landscapes. Consequently, it could be expected that these communities would have historically experienced similar fire regimes, and would respond similarly to variation in aspects of the fire regime. We studied the response of mallee‐heath and mallee to time since the last fire, measuring species density, species–area relationships, diversity indices and vegetation structure. Floristic responses to time since fire accorded with the initial floristic composition model of plant succession, with declining species density and Shannon diversity with age in mallee‐heath. Mallee‐heath exhibited structural senescence when > approximately 45–55 years since fire, with increasing standing dead vegetation, bare ground and stagnating or declining size in sprouting Eucalyptus spp. Mallee showed no such evidence of senescence, and indeed continued to increase in stature beyond the mean fire interval but without the compositional change required to provide support for the relay floristic model of plant succession. These results indicate that mallee‐heath is a fire maintained community and as such is reliant upon periodic burning to maintain diversity and vigour. Mallee, in contrast, is modified but not maintained by fire (at least over the period of time since fire examined) and hence is less susceptible to fire interval effects. Indeed, structural attributes likely to be significant for fauna habitat and carbon sequestration continue to develop in mallee unburnt for 55 years or more. Different responses to time since fire will create challenges for management, particularly in fragmented landscapes where fire potentially interacts with other threatening processes.     

The Holocene vegetation history of northern West Jutland, Denmark

Holocene sediments of three closed Danish lake basins (Solsø, Skånsø, Kragsø) were used for the inference of post-glacial vegetational dynamics in former heathland areas in northern West Jutland, Denmark. The sites were selected to represent the major geomorphological units of West Jutland. The Holocene history of each lake basin was investigated by mapping of sediment distribution, analysis of loss-on-ignition, coarse inorganic matter, humus content, mineral magnetics, δ¹³C, pollen and selected other microfossils. These techniques were supplemented by plant macrofossil analysis at one site. Holocene terrestrial vegetational development was inferred at each site from analyses of pollen and microscopical charred particles. Chronologies were provided by numerous ¹⁴C dates. Stratigraphies of wet ground and terrestrial pollen and spore types were zooned by stratigraphically constrained cluster analysis. Based on the resultant site pollen asemblage zones (site PAZ), regional PAZ were proposed. Using modern analogues, Holocene floristic richness was estimated from pollen richness in the microfossil assemblages. The results support the hypothesis that disturbance is one of the most important mechanisms behind the maintenance of floristic richness. In particular, the response of estimated floristic richness to the intensity of vegetational fires followed the predictions of the Intermediate Disturbance Hypothesis. A period of elevated palynological richness and inferred vegetational disturbance was identified at all sites between 6000 and 5200 BC (calendar years). Using correspondence analysis (CA), the major gradient in the terrestrial pollen sequences was identified as a light-shade gradient, and CA first axis sample scores were used as a supplement to standard AP/NAP pollen ratios as an indicator of the shade-tolerance/light-demand of Holocene terrestrial plant communities. In spite of different vegetational developments since 4000 BC, the timing of major changes towards more light-demanding vegetation types were broadly synchronous at the three sites. Using chord distance as a dissimilarity index, rates of palynological change suggest that the interval between 8000 and 7500 BC (calendar years) was the period of most rapid vegetational change during the Holocene, both in terrestrial as well as lacustrine ecosystems. While climatic forcing of the rapid events around 8000 BC is hypothesised, the synchronous timing of relatively rapid inferred change in lake and terrestrial vegetation around AD 600 may reflect changes in climate as well as in land-use. Reducdancy analysis was used to develop a model between fire intensity (inferred from microscopical charred particles) and vegetational response, as reflected by pollen assemblages. Formulated at one site and tested at the two other sites, the model explains regional Calluna-heathland expansions as a result of vegetational burning. Similarly, declines in heathland cover are explained by lack of maintenance by fire. Regional vegetational development in northern West Jutland is reconstructed and special consideration is given to heathland history. The Holocene heathland development is interpreted as resulting from its importance for grazing. It is hypothesized that on poor soils, Calluna-dominated heathland was a better grazing resource than grass-dominated pasture, due to the winter-grazing offered by Calluna and the low palatibility of dominant grasses on poor soils. This hypothesis is relevant for the explanation of the variation in timing of heathland expansions on the different soil types represented by the study sites.     

A reappraisal of cyclical processes in Calluna heath

Small-scale, short-term cycles constitute an important aspect of vegetation dynamics. It has been widely accepted that such cycles are characteristic of unmanaged heath communities where the dominant, Calluna vulgaris, undergoes an age-related series of changes in its growth and morphology. This is thought to give rise to a repetitive sequence of changes in the occupancy of gaps which form in the Calluna canopy and are first colonized by other species, with Calluna re-establishing later. Recently, doubts have been cast as to whether the changes are in fact often repetitive. A new study has shown much greater variability than was previously suspected in the transitions occurring in gaps. There is evidence that, in some instances though by no means all, Calluna can re-establish and thereby initiate a genuine cycle. It seems, however, that such re-entry is seldom by means of seedling establishment, but more frequently by development of adventitious shoots and roots on stems which have come to lie across the gap and have been covered by moss, moist litter or humus.     

Long‐term nitrogen additions increase likelihood of climate stress and affect recovery from wildfire in a lowland heath

Increases in the emissions and associated atmospheric deposition of nitrogen (N) have the potential to cause significant changes to the structure and function of N‐limited ecosystems. Here, we present the results of a long‐term (13 year) experiment assessing the impacts of N addition (30 kg ha^?1 yr^?1) on a UK lowland heathland under a wide range of environmental conditions, including the occurrence of prolonged natural drought episodes and a severe summer fire. Our findings indicate that elevated N deposition results in large, persistent effects on Calluna growth, phenology and chemistry, severe suppression of understorey lichen flora and changes in soil biogeochemistry. Growing season rainfall was found to be a strong driver of inter‐annual variation in Calluna growth and, although interactions between N and rainfall for shoot growth were not significant until the later phase of the experiment, N addition exacerbated the extent of drought injury to Calluna shoots following naturally occurring droughts in 2003 and 2009. Following a severe wildfire at the experimental site in 2006, heathland regeneration dynamics were significantly affected by N, with a greater abundance of pioneering moss species and suppression of the lichen flora in plots receiving N additions. Significant interactions between climate and N were also apparent post fire, with the characteristic stimulation in Calluna growth in +N plots suppressed during dry years. Carbon (C) and N budgets demonstrate large increases in both above‐ and below‐ground stocks of these elements in N‐treated plots prior to the fire, despite higher levels of soil microbial activity and organic matter turnover. Although much of the organic material was removed during the fire, pre‐existing treatment differences were still evident following the burn. Post fire accumulation of below‐ground C and N stocks was increased rapidly in N‐treated plots, highlighting the role of N deposition in ecosystem C sequestration.     

Markov models and initial floristic composition in heathland vegetation dynamics

A simple Markov model is used to test the hypothesis that the floristic composition of vegetation colonizing bare ground immediately after burning is the major factor influencing post-fire development in heathland vegetation. Data are taken from stands of different ages at time of burning in a species-rich Calluna-Arctostaphylos heath in NE Scotland. It is shown that variation in the initial floristic composition of the stands is not, in itself, sufficient to produce model simulations which match observed trends, although altering the probabilities of transition from bare ground to other states allows more successful simulations. The model supports the hypothesis that stand age before burning influences the post-fire development through the process of colonization of bare ground. After a very severe fire post-fire development may initially depend on the formation of a moss cover, although this requires further study. It is concluded that simple Markov models can provide the basis for examining successional processes when used in a comparative way.Nomenclature follows Tutin et al. (1964–80) for vascular plants and Smith (1978) for mosses.We thank Prof. C. H. Gimingham for comments on the draft, and J. M. M. Humphrey, P. Marren and the Nature Conservancy Council for permission to work on the Muir of Dinnet.     

The Holocene vegetation history of northern West Jutland, Denmark

Holocene sediments of three closed Danish lake basins (Solsø, Skånsø, Kragsø) were used for the inference of post-glacial vegetational dynamics in former heathland areas in northern West Jutland, Denmark. The sites were selected to represent the major geomorphological units of West Jutland. The Holocene history of each lake basin was investigated by mapping of sediment distribution, analysis of loss-on-ignition, coarse inorganic matter, humus content, mineral magnetics, δ¹³C, pollen and selected other microfossils. These techniques were supplemented by plant macrofossil analysis at one site. Holocene terrestrial vegetational development was inferred at each site from analyses of pollen and microscopical charred particles. Chronologies were provided by numerous ¹⁴C dates. Stratigraphies of wet ground and terrestrial pollen and spore types were zooned by stratigraphically constrained cluster analysis. Based on the resultant site pollen asemblage zones (site PAZ), regional PAZ were proposed. Using modern analogues, Holocene floristic richness was estimated from pollen richness in the microfossil assemblages. The results support the hypothesis that disturbance is one of the most important mechanisms behind the maintenance of floristic richness. In particular, the response of estimated floristic richness to the intensity of vegetational fires followed the predictions of the Intermediate Disturbance Hypothesis. A period of elevated palynological richness and inferred vegetational disturbance was identified at all sites between 6000 and 5200 BC (calendar years). Using correspondence analysis (CA), the major gradient in the terrestrial pollen sequences was identified as a light-shade gradient, and CA first axis sample scores were used as a supplement to standard AP/NAP pollen ratios as an indicator of the shade-tolerance/light-demand of Holocene terrestrial plant communities. In spite of different vegetational developments since 4000 BC, the timing of major changes towards more light-demanding vegetation types were broadly synchronous at the three sites. Using chord distance as a dissimilarity index, rales of palynological change suggest that the interval between 8000 and 7500 BC (calendar years) was the period of most rapid vegetational change during the Holocene, both in terrestrial as well as lacustrine ecosystems. While climatic forcing of the rapid events around 8000 BC is hypothesised, the synchronous timing of relatively rapid inferred change in lake and terrestrial vegetation around AD 600 may reflect changes in climate as well as in land-use. Reducdancy analysis was used to develop a model between fire intensity (inferred from microscopical charred particles) and vegetational response, as reflected by pollen assemblages. Formulated at one site and tested at the two other sites, the model explains regional Colluna-heathland expansions as a result of vegetational burning. Similarly, declines in heathland cover are explained by lack of maintenance by fire. Regional vegetational development in northern West Jutland is reconstructed and special consideration is given to heathland history. The Holocene heathland development is interpreted as resulting from its importance for grazing. It is hypothesized that on poor soils, Calluna-dominated heathland was a better grazing resource than grass-dominated pasture, due to the winter-grazing offered by Calluna and the low palatibility of dominant grasses on poor soils. This hypothesis is relevant for the explanation of the variation in timing of heathland expansions on the different soil types represented by the study sites.     

Fungal associations of Danish Calluna vulgaris roots with special reference to ericoid mycorrhiza

Fungi were isolated from young, serial-washed roots of Calluna sampled from a Danish heathland, Hjelm Hede. Of the 626 isolates, those that were dark, sterile and septate were divided into 13 morphological groups based on their appearance in culture on malt agar. Mycorrhizal synthesis in vitro showed that several groups formed typical ericoid mycorrhiza with seedlings of Calluna; these ericoid mycorrhizal fungi were morphologically similar to Hymenoscyphus ericae. The identities of the other dark, septate fungi are uncertain. Oidiodendron spp. were isolated in a very low frequency; these fungi also formed typical ericoid mycorrhiza. The Calluna root system on Hjelm Hede demonstrated a high morphological diversity among the associated dark, septate fungi suggesting that more than one fungus could coexist in the same host root system.