Dwarf Shrub Species Research Articles

Facilitative effects of top‐canopy plants on four dwarf shrub species in habitats severely disturbed by pollution

1 We hypothesized that the role of positive plant–plant interactions will increase with the environmental stress imposed by long-term pollution. We studied the effects of top-canopy plants on two deciduous (Vaccinium myrtillus, V. uliginosum) and two evergreen (V. vitis-idaea, Empetrum nigrum ssp. hermaphroditum) dwarf shrubs by comparing their growth and reproduction under trees and in gaps in industrial barrens and in unpolluted forests in the Kola Peninsula (NW Russia). 2 Interactions between habitat type and tree proximity on berry yield and reproductive effort were significant for four species combined. In forest habitats both berry yield and reproductive effort were higher in dwarf shrub patches growing in gaps than under tree canopies, but in barren habitats Vaccinium species reproduced better under tree canopies. 3 The interaction of habitat type and tree proximity was also significant for vegetative biomass, mostly due to evergreen species benefiting from neighbouring trees in barren habitats. 4 Overall, all four dwarf shrub species reproduced better in barren habitats than in forests, mostly due to increased reproduction observed under tree canopies in barren sites. 5 Values of the relative neighbour effect indicated that the impact of top-canopy plants on dwarf shrubs shifted from negative in forest habitats to generally positive in barren habitats.

Plants as seed traps: inter-specific interference with dispersal

Established plants may disrupt patterns of seed deposition by physically trapping dispersing seed. In this study we quantified seed trapping at very fine spatial scales, by measuring seed fall of two ericaceous dwarf shrub species at a range of distances from allospecific shrubs within a matrix of short grass vegetation. Next to allospecific bushes, seed deposition densities of Calluna vulgaris and Erica cinerea were between 7- and 20-fold higher than those in the short grass. This increase is comparable to deposition densities next to conspecific bushes, caused by local dispersal, which were 19–33-fold greater than the background seed rain. Seed densities decayed rapidly with distance from the allospecific bush, so that in general the bush’s influence on deposition extended <0.1 m. By causing localised, extreme peaks in seed density around established plants, seed trapping could have large effects on the fitness of plants dispersing seed and on the spatial pattern of recruitment across plant communities.

Postfire regeneration in Pinus pinea L. and Pinus pinaster aiton in Andalucia (Spain).

The objective of this study was to examine postfire regeneration of tree, shrub, and dwarf shrub species, in relation to levels of damage in four planted pine forests (Pinus pinea, Pinus pinaster) in Andalusia. A prefire vegetation map was used for detailing species composition, vertical structure, and density and another for detailing the extent and intensity of fire damage. Between 3 and 7 years after the fires, an inventory was made of the vegetation in each area, using the step-point method. The information thus obtained was used to determine the amount of cover in the dwarf/shrub and tree layers, the frequency of species in each of the layers, floristic richness, and diversity (Shannon index). The botanical composition of the dwarf and shrub layer was analyzed using TWINSPAN. Variables were poorly correlated with level of fire damage, which suggests that the forests in this study followed the autosuccession model. Because of the artificial origin or seminatural condition, regeneration of the dominant tree species is poor, and it seems unlikely that forests will recover to their prefire state. Therefore action is recommended to restore these ecosystems.

Ecological importance of ambient solar ultraviolet radiation to a sub-arctic heath community

While there is considerable knowledge of the effects of enhanced levelsof ultraviolet radiation (UV) on plant species, much less is known of theimportance of ambient levels of solar UV, particularly on natural plantcommunities. Effects of ambient solar UV radiation on a natural sub-Arcticheathcommunity were investigated in a three year UV exclusion experiment in northernSweden (68° N). UV transparent and UV opaque (excluding< 400 nm) plexiglas screens were placed over vegetation forthree years to determine ambient solar UV effects on growth, reproduction andphenology of the three dominant dwarf shrub species, Vacciniumuliginosum, V. vitis-idaea andEmpetrum hermaphroditum. Additionally, effects of ambientsolar UV radiation on leaf protection from UV-B were assessed throughmeasurements of leaf UV-B absorbing compounds. Flowering and berry productionbyV. uliginosum were greatly increased (by five and 15 fold)in plots receiving ambient solar UV compared to those where solar UV had beenexcluded for three years. However, solar UV had no effect on stem growth,senescence and cover of the dwarf shrub species studied. It was thereforeconcluded that sub-Arctic dwarf shrubs are generally tolerant of ambient solarUV. Counterintuitively, ambient solar UV radiation reduced the levels of UV-Babsorbing compounds in both Vaccinium species suggesting areduction in protection provided. This indicates that measurements of leaf UV-Babsorbing compounds do not necessarily provide a good indicator of planttolerance to UV.

Leaf photosynthetic characteristics and net primary production of the polar willow (Salix polaris) in a high arctic polar semi-desert, Ny-Ålesund, Svalbard

Photosynthetic characteristics and their leaf-age dependence were examined to estimate ecophysiological effects on net primary production (NPP) of a polar willow (Salix polaris), a dominant dwarf shrub species in a polar semi-desert area of Ny-Ålesund, Svalbard. Leaves of S. polaris emerged just after snowmelt in early July in 2000; flowers were initiated within 1 week, and fruits in late July. Light-saturated rate of photosynthesis and stomatal conductance to water vapor increased rapidly to their maximum values within 1 week after leaf emergence and then decreased gradually. Depending on the leaf age, photosynthetic rates saturated at photosynthetically active photon flux density (PPFD) of 200–400 µmol·m–2·s–1, which is the light level usually available in the natural habitat. Optimum leaf temperature of photosynthesis ranged from 10 to 18°C, while air temperature in the habitat ranged from 8 to 20°C. These light and temperature responses of photosynthesis of S. polaris would be suitable for efficient carbon gain in the natural habitat characterized by highly variable light and temperature conditions. Using the photosynthetic and respiratory characteristics, biomass distribution, and meteorological data, NPP of S. polaris in the current year was estimated to be 26.1 g C·m–2. A model simulation of rising temperature conditions predicted a reduction of NPP because of a large increase in respiration. It was suggested that temperature condition and leaf phenological aspects strongly influence the carbon fixation by plants in the high arctic area studied.Key words: arctic semi-desert, climate change, net ecosystem production (NEP), net primary production (NPP), Salix polaris, photosynthesis.

How do nutrients and warming impact on plant communities and their insect herbivores? A 9‐year study from a sub‐Arctic heath

Summary 1 Responses of a Scandinavian sub-Arctic dwarf shrub heath community to 9 years of nutrient and temperature treatments were examined. Our objective was to assess the responses of plant and insect herbivore communities to these treatments, and to determine how vegetation responses scale-up to those of a second trophic group. 2 There were strong effects of nutrient addition on the above-ground biomass of both dominant (dwarf shrubs) and subordinate (grasses and mosses) plant functional groups, with responses by the latter being of greater magnitude. Responses to temperature were less frequent and of a smaller magnitude. 3 There were marked changes in the abundance of insect herbivores in response to the treatments. Changes in the above-ground biomass of subordinate plant species had a greater impact on the composition of the insect herbivore community than the smaller responses of dominant dwarf shrubs. For example, the abundance of a moss-feeding Heteropteran in fertilized plots was as little as 6% that of controls, while Homoptera specializing on grasses were over 400% more abundant. In addition, gramnivorous taxa (the Delphacidae) were present only in those plots that received nutrients. 4 Despite some species-specific effects of the perturbations on the quality of dwarf shrub annual shoots (defined as the concentrations of nitrogen and phenolic compounds), little change in leaf herbivory was observed. Insect herbivores removed less than 1% of annual biomass from dominant dwarf shrub species. 5 It is proposed that insect community change was driven by subordinate plant groups and not by the dominant dwarf shrub species, suggesting a wider importance of subordinate species for community structure.

A drought assessment model for Karoo rangeland

The KAROO drought assessment model simplifies veld growth responses to rainfall variability by simulation of the growth and dieback of a hypothetical plant species. Soil water content is treated as a simple weighting factor which determines the plant's growth rate as a weighted average of two basic growth rates, viz. those under well- watered and dry soil conditions. Multiple growth stages of variable extent are postulated on the basis of evolutionary forcing by Karoo rainfall patterns. The model was fitted to growth data of a Karoo dwarf shrub species, assuming three growth stages which are initiated when the annual growth equals 0 (on day 1), 3 and 50% of that of an equivalent, well-watered plant. The averaging of basic growth rates needs further investigation in order to better simulate compensatory growth after drought.

Light-use properties in two sun-adapted shrubs with contrasting canopy structures

We investigated the impact of high solar irradiance and elevated temperature on carbon gain by two, co-occurring, sun-adapted, dwarf shrub species, Planchonella obovata var. dubia (Koidz.) Hatusima and Hibiscus glaber Matsumura, growing on sun-exposed ridges in the Bonin Islands, in the subtropical Pacific Ocean. Planchonella had steeply inclined, longer lived, sclerophyllous leaves, whereas Hibiscus has thinner, more horizontally oriented, and shorter lived leaves. We tested the hypothesis that leaf physiological tolerance to high light is lower in Planchonella than in Hibiscus. Under relatively high irradiances (photosynthetic photon flux density, PPFD, > 500 micromol m(-2) s(-1)), net photosynthetic rate (P(n)) was about 8.0 and 0.4 micromol m(-2) s(-1) in mature and young leaves of Planchonella, and about 12.4 and 10.3 micromol m(-2) s(-1) in mature and young leaves of Hibiscus, respectively. Both P(n) and photosystem II (PSII) quantum yield at a given PPFD were lower in Planchonella than in Hibiscus, whereas non-photochemical quenching (NPQ) at a given PPFD was higher in Planchonella. When leaf discs were exposed to high light (1900 micromol m(-2) s(-1) PPFD) at 37, 40 or 43 degrees C for 3 h, the recovery of PSII quantum yield (F(v)/F(m)) in the following 60-min dark period was slower in Planchonella than in Hibiscus, indicating that the ability of PSII to tolerate high light and high temperature was less in Planchonella than in Hibiscus. We postulate that there is a linkage between leaf display and leaf photochemical ability in sun-adapted shrub species.

Viability and germination of seeds of Carmichaelia (Fabaceae) after prolonged storage

Eleven species of Curmichuelia retained high seed viability for up to 24 years, linked with sustained impermeability of the seed testa. Viable seeds germinated rapidly after scarification and showed no specific light requirements. Shrub and dwarf shrub species retain high viability after prolonged storage, whereas seeds of tree species had reduced viability in older seeds. Long‐term seed storage would be a suitable ex situ conservation tool for shrub and dwarf shrub species.

Characterisation of the differential interference effects of two boreal dwarf shrub species.

Our purpose was to characterize the relative competitive and phytotoxic potential of two closely related dwarf-shrub species, Empetrum nigrum and E. hermaphroditum, which form clones in a mosaic pattern in post-fire successions of the boreal forest of northern Sweden. We determined morphological and growth parameters of both species, performed bioassays and chemical analysis, and established field experiments to explore possible differing interference effects on trees by the two species. Both Empetrum species had very similar morphological and growth characteristics. E. hermaphroditum exerted considerably greater negative effects than E. nigrum against Pinus sylvestris and Populus tremula seed and seedlings. These negative effects were related to the different substitution of a bibenzyl in the two species. The effect on seed germination of the two bibenzyls isolated from E. nigrum and E. hermaphroditum was compared with that of other simple phenolics; the latter were found to be inactive, indicating a specific phytotoxic component in the bibenzyls. P. sylvestris seeds planted into clones of both species in the field revealed that E. hermaphroditum had much stronger inhibitory effects than did E. nigrum and the addition of activated carbon partially reversed these effects. Seed germination, biomass and survival of P. sylvestris after four seasons were significantly lower in E. hermaphroditum- than in E. nigrum-dominated plots. We conclude that while both Empetrum species are superficially very similar morphologically, they have vastly different effects on tree seed germination, seedling establishment and growth. These effects appear to be due, at least in part, to the different chemical profile of the two species.

Response of dwarf shrubs to neighbour removal and nutrient addition and their influence on community structure in a subalpine heath

Summary 1 A 3‐year experiment involving nutrient addition and removal of one of two coexisting dwarf shrub species was conducted in two community types in a subalpine heathland on the northern Apennines (Italy). Vaccinium uliginosum occurred at all sites but was associated with the deciduous Vaccinium myrtillus at more sheltered nutrient‐rich sites (HV community), and with the evergreen Empetrum hermaphroditum where the habitat was poorer and more exposed (EV community). Length of current‐year shoots and fruit production of each species were determined in each of the 3 years, and standing crop at the beginning and end of the experiment. 2 The length of current‐year shoots of both deciduous species, but not of the evergreen, varied considerably between years, presumably due to varying temperatures at the beginning of the three growing seasons. Fruit production also varied. 3 Fertilization promoted an increase in the length of V. uliginosum shoots at the HV community but not at the EV community. The removal of V. uliginosum enhanced shoot elongation in V. myrtillus (HV community) but reduced shoot elongation in E. hermaphroditum (EV community). Neighbour removal did not affect shoot length of V. uliginosum at either community. There were few treatment effects on fruiting of these clonal species. 4 The standing crop in untreated stands did not change during the experimental period. Changes in shoot length resulting from environmental manipulations were not accompanied by consistent variation in the standing crop of any species. Standing crop increased only for V. myrtillus after removing V. uliginosum at the HV community (same direction as shoot length). The standing crop of E. hermaphroditum did not change after removing V. uliginosum at the EV community, although shoot length was significantly reduced. The standing crop of V. uliginosum was unaffected by neighbour removal and was decreased by nutrient addition at both communities. 5 None of the shrubs appeared able to utilize more abundant resources to increase above‐ground biomass. However, increased shoot length in nutrient‐rich habitats gave V. uliginosum a superior ability to capture light compared with V. myrtillus, the latter being more successful when the coexisting competitively superior species was removed. This would support Grime’s theory, indicating that competition becomes more important as soil resource levels increase. Positive interactions appeared to play a role in the more extreme habitat, where E. hermaphroditum normally benefited from the shelter of the V. uliginosum canopy but was able to adapt its architecture when exposed.

The effects of controlled sheep grazing on the dynamics of upland Agrostis–Festuca grassland

Summary 1. Agrostis capillaris–Festuca ovina‐dominated communities are widespread in the uplands of Great Britain. They are agriculturally productive but little is known about how to manage this community for specific goals. Vegetation trajectories were examined in this plant community under different sheep grazing management regimes at two sites in Scotland. One site had a substantial presence of moorland species, the other was characterized by a more productive vegetation. Management consisted of maintaining sward heights of 3, 4·5 or 6 cm during the growing season, or complete exclusion of grazing stock. 2. Changes in species composition were small over the 7 years of the experiment. Few species invaded or were lost during the course of the study. The observed changes were largely as a result of shifts in abundance of the dominant species. 3. Maintenance of sward height at low levels (3 or 4·5 cm) during the growing season resulted in the spread of Nardus stricta where present. Where N. stricta was absent, the sward developed a higher content of mosses, specifically Hypnum jutlandicum and Rhytidiadelphus squarrosus. 4. Removal of grazing resulted in an increase of cover of grazing‐intolerant species, such as Deschampsia flexuosa and Molinia caerulea, and in the cover of dwarf shrub species where present. 5. The two sites differed in the treatment that resulted in the smallest change in species composition. At the more productive site, maintenance of the sward at 4·5 cm resulted in the smallest overall change in species composition. At the less productive site, grazing the sward to 6 cm resulted in the smallest shift in vegetation composition. Grazing at this height appeared to prevent the spread of both M. caerulea and N. stricta. 6. The study demonstrates that sustainable grazing regimes for upland Agrostis–Festuca grasslands need to take into account both the initial composition of the vegetation, specifically the presence of species capable of replacing A. capillaris and F. ovina and of achieving dominance, and the overall productivity of the site.

Response patterns of Vaccinium myrtillus and V. vitis‐idaea along nutrient gradients in boreal forest

Abstract. The relationships between biomass of dwarf shrub species and nutrient gradients of forest soils was studied under field conditions in boreal forests. The biomass‐response curves of Vaccinium myrtillus and V. vitis‐idaea were fitted against soil nutrient gradients using Generalized Linear Models (GLM). Ecological niches of Vaccinium myrtillus and V. vitis‐idaea were evaluated, and effects of nitrogen addition (manipulation of the nutrient gradient) on response function were tested.The Vaccinium species showed statistically significant Gaussian responses along soil nitrogen, phosphorus and calcium gradients, but not along other gradients (K and Mg). Furthermore, manipulation of the nitrogen gradient seemed to have a minor effect on response functions, i.e. addition of nitrogen did not change ecological niches of these species. Ecological optima of V. myrtillus and V. vitis‐idaea on the nutrient gradients were about the same. This study suggests that differences in dominance between Vaccinium myrtillus and V. vitis‐idaea in boreal forest is not determined by nutrient gradients, but may rather be explained by light conditions and/or moisture availability.

Andromeda polifoliaL.

A low, glabrous, evergreen shrub, (5)-10-25-(40) cm tall. The flowering stems are decumbent to erect, sparingly branched, arising from a creeping, woody rhizome (Warming 1908; Fl. Eur. 3; Fl. Br. Isl.; Hegi Fl. 1, ed. 3; Ramneau et al. 1993; Stace 1997). The leaves are narrow, alternate, subsessile, coriaceous, oblong to linear, dark green above, silvery-glaucous beneath, 10-40 x 2-8 mm (Barvaux 1958; Fl. Eur. 3; Fl. Br. Isl.; Rameau et al. 1993; Stace 1997). They are mucronulate (Anderson 1961) or acute to apiculate (Fl. Eur. 3); their margins are usually revolute (Fl. Br. Isl.; Rameau et nl. 1993). The flowers are pentamerous (Barvaux 1958; Anderson 1961; Hegi Fl. 1, ed. 3), in very short, umbellike terminal racemes of 2-7-(12) (Warming 1908; Fl. Eur. 3; Rameau etal. 1993). However, Warming (1908) reported 4-merous flowers in Finnmark and in Greenland. The pedicels are pinkish, 2-4 times as long as the corolla (Barvaux 1958; Fl. Br. Isl.; Hegi Fl. 1, ed. 3); they are 7-15 mm long and slender (Fl. Eur. 3). The sepals are persistent, triangular, reddish, acute, about 1 .5 mm long (Anderson 1961; Fl. Eur. 3) and connate at base (Fl. Eur. 3). Two bracteoles lie at the extreme base of the pedicel, concealed by a bract (Fl. Eur. 3). Corolla globose-urceolate with 5 recurved teeth; drooping (Webb 1967), inclined or pendent (Fl. Eur. 3), bright pink at first, fading almost to white. It reaches 5-8 mm long (Warmzing 1908; Barvaux 1958; Anderson 1961; Fl. Br. Isl.; Hegi Fl. 1, ed. 3; Rameau et cal. 1993) and it continues to grow during flowering (Warming 1908). The interior of the corolla is covered with erect, usually somewhat upturned, hairs that extend to the margin of the limb (Warming 1908). The stigma lies just at or imnediately within the throat of the corolla, and the 10 anthers, which are at the level of the middle of the pistil and the corolla, bend inwards towards the style (Warming 1908; Barvaux 1958; Hegi Fl. 1, ed. 3; Rameau etal. 1993). The filaments are strongly swollen just above their slender short bases and are covered with fairly long hairs along the greater part of their length (Warming 1908; Anderson 1961). The anthers are covered with small protuberances; they open at the apex by two pores of irregular shape (Warming 1908; Hegi Fl. 1, ed. 3). The two apical appendages are as long as the anthers, glabrous and slightly curved (Warming 1908; And-

Temporal Variability of Phenolics and Batatasin-III in Empetrum hermaphroditum Leaves over an Eight-Year Period: Interpretations of Ecological Function

Although many plant species produce high levels of secondary metabolites, comparatively little is known about the temporal variability of the production and concentrations of these compounds, either in terms of quantitative or qualitative aspects. In the Swedish boreal forest the dwarf-shrub species Empetrum hermaphroditum produces high levels of phenolics which are important agents of allelopathy, regulators of herbivory and determinants of plant litter decomposition. We performed quantitative analyses of total phenolics and monitored the phytotoxic activity (defined as the ability of the extracts to retard germination of Populus tremula seeds) of aqueous leaf extracts from three age classes of leaves, collected from the field approximately every two weeks for every growing season from 1988 to 1995. The concentrations of the dihydrostilbene batatasin-III, an E. hermaphrodium metabolite with a documented phytotoxic effect, were determined in both extracts and entire leaves for material collected in 1988 and 1994. We also studied leaf gland variation of first-year leaves in relation to phenolic concentration and phytotoxic activity. Large differences existed between sampling times within years, with first-year shoots producing high levels of phenolics; these levels were maintained for second-year shoots but phenolic concentrations declined for third-year shoots, i.e. prior to leaf senescence. Phytotoxic activity was low immediately after leaf emergence, and was not consistently correlated to total phenolicconcentrations of the leaves. However, more detailed analyses showed that much of the phytotoxic activity of E. hermaphrodium extracts is due to the production of batatasin-III, which reaches its maximum concentration not until September of the first year. We believe that batatasin-III is critical in determining the phytotoxic effects of E. hermaphrodium and that this compound may have additional benefits for E. hermaphrodium other than deterring herbivory. Leaf glands were present on newly formed leaves, and were produced continuously over the growing season. However, correlation analyses between the number of leaf glands and either the release of phenolics or phytotoxic activity did not reveal any significant relationships. There were also important differences in both leaf phenolic concentrations and phytotoxicity between years, although we were unable to relate this to inter-year macroclimatic parameters collected from the same site. We conclude that temporal variability of the production of phenolic compounds by E. hermaphrodium is considerable and is almost certainly of importance in introducing a degree of temporal variability into the biotic interactions that E. hermaphrodium participates in.

Effects of the Length of the Snow-Free Period on Leaf Longevity in Alpine Shrubs: A Cost-Benefit Model

Leaf longevities of three woody dwarf-shrub species were investigated in relation to the length of the snow-free period in a mountain area in Hokkaido, northern Japan. Leaf longevity of a deciduous species, Sieversia pentapetala, slightly increased with increasing length of the snow free period. In contrast, the leaf life-span of two evergreen species, Phyllodoce aleutica and Rhododendron aureum, decreased with increasing snow-free period. These trends are consistent with a cost-benefit model for leaf longevity as a function of the changing length of the yearly period favorable for photosynthesis. Hence the plastic changes in leaf longevity with varying snow-free periods were concluded to be adaptive traits for maximizing photosynthetic gain for the plants

Growth and Reproduction of Dwarf Shrubs in a Subarctic Plant Community: Annual Variation and Above-Ground Interactions with Neighbours

1 The effects of coexisting shrub species on the growth, branching, survival and berry production of three dominant dwarf shrubs (Empetrum nigrum, Vaccinium vitis-idaea and V. uliginosum) were examined in northern Finland in a six year experiment. The measurements covered both natural, unmanipulated plots as well as plots from which ramets of one of five dwarf shrub species had been removed. 2 Annual patterns of growth and reproduction of ramets of the three species were different, suggesting that the plants were affected by different combinations of environmental factors and internal patterns of ramet growth. Neither cumulative summer temperature nor summer precipitation accounted for the variations in annual growth of any dwarf shrub species; however, ramet age contributed significantly to the observed variation in growth of shoots of V. vitis-idaea and V. uliginosum. 3 The growth of ramets of E. nigrum in unmanipulated plots was positively correlated with the cover of V. myrtillus and total cover of dwarf shrubs; the growth of V. uliginosum was similarly correlated with the cover of V. myrtillus in undisturbed plots. Furthermore, the growth of both E. nigrum and V. uliginosum was reduced by the removal of V. uliginosum and V. myrtillus, respectively. These observations probably indicate some kind of positive relationship between these species. By contrast, the shoot growth of V. vitis-idaea was less and mortality greater in unmanipulated plots where V. uliginosum was abundant, while both branching and reproduction of V. vitis-idaea were increased by the removal of other dwarf shrubs. These results indicate that interspecific competition may limit the growth and reproduction of V. vitis-idaea.

Establishment and growth characteristics of inshore populations of Ligusticum scoticum (Apiaceae)

Two inshore and four shore localitites of Ligusticum scoticum in C Norway were studied regarding the growth and reproductive characteristics of the L. scoticum individuals, and the vegetation and ecology of the sites. L. scoticum showed a similar growth and reproductive characteristics at the inshore and the shore localities. The inshore localities were judged as relatively persistent on their basis of growth and reproductive characteristics and population size, and one of the inshore localities has with certainty maintained itself for at least 20 years. We suggest the inshore populations have established from seeds dispersed from the shore by birds. There were large differences in vegetation and ecological variables and cover between the inshore and the shore localities. At the inshore localities vegetation contained a large number of dwarf shrub and moss species which were almost entirely absent from the shore. Due to various physiological properties L. scoticum has a relatively better competitive ability and is better adapted to grow on inshore localities in the northern part of its distribution area. At the inshore localities L. scoticum occurred at two types of localitites: summits and rocky walls. The absence of inshore localitites in areas where conditions for further dispersal would appear to be ideal, indicate that specific conditions are required for successful establishment of L. scoticum at inshore localities. We suggest that the occurrence of L. scoticum at the summits depends to some extent promoted by the influence of birds, e.g. by nutrients in the excrements. However in the case of rocky walls this is an unlikely explanation, because individuals are often scattered over many hundreds of metres.

The significance of the dormant viable seed bank in the restoration of heathlands

The dormant viable seed bank of heathland dwarf shrub species was investigated in several different heather moorland soils. Soil was incubated in a warm, moist environment for periods of up to twelve months. Generally there was a high density of viable seeds of Calluna vulgaris, Erica cinerea and Erica tetralix and several other heathland species. At all sites, a substantial portion of the seed bank (usually more than 90%) of all the species occurred in the upper 40 mm of the soil. This upper soil layer also contains a ‘bud bank’ of certain species (e.g. Molinia caerulea and Vaccinium myrtillus), which is equally important for subsequent regeneration of these species. When heathland is disturbed by mineral extraction, construction operations and installation of pipelines, it is essential that the seed-rich topsoil is carefully conserved to enable subsequent restoration to be successfully achieved. Since the seed bank is concentrated in a relatively shallow upper soil layer, it is important that only the upper 40–50 mm is removed. A greater depth of soil removal only dilutes the seed bank and reduces the usefulness of the separately stripped topsoil as a source of plant propagules.

Niche differentiation with respect to light utilization among coexisting dwarf shrubs in a subarctic woodland

Canopy structure, shoot design, and photosynthetic light recruitment were used to compare four coexisting dwarf shrub species with respect to light utilization. All four species showed different shoot designs which probably result in different light interception properties. Leaves of Vaccinium uliginosum showed the highest levels of photosynthetic light saturation but in situ the shoots of this species reached their maximum photosynthetic rate at the lowest photon flux densities. No consistent differences with respect to photosynthetic light responses were found between deciduous and evergreen species. At sites dominated by one of the deciduous species (Vaccinium uliginosum or V. myrtillus), the two evergreen species studied (V. vitis-idaea and Empetrum hermaphroditum) occurred in the understory, i.e., with their leaf distribution slightly below that of the deciduous species. Sites dominated by one of the evergreen species showed less vertical differentiation in leaf distribution between species.