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The study central goal was to analyze secondary succession in a degraded peatland: (1) Sphagnum distribution trends and (2) successional patterns. Main study sites were adjacent abandoned pastures, where grazing was carried out in former peatland and where degradation had occurred, hereafter referred as degraded peatland. (1) Degraded peatland was mapped in 2006 (while it was still a pasture, grazed for over 30 years), and throughout the study period in 2013 (2 years post-abandonment) and 2015 (4 years post-abandonment). The baseline assessment of 2006 revealed that Sphagnum spp. were present in 7% of the area, which pointed at the resilience of the peat ecosystem. After the grazing ceased, Sphagnum cover increased to 17% and 39%, in the next 2 and 4 years respectively post animal removal. (2) To gain a general comprehension of flora and vegetation changes along the regenerative sucession, 48 permanent plots were established in the degraded peatland. In two other study sites, a further twenty plots were established, ten plots in a semi-natural peatland area where grazing ceased 30 years ago and ten others in a natural peatland. These were monitored between July 2012 and July 2015 (triannual). After 4 years, the formerly degraded peatland showed considerable recovery with a growth of Sphagnum spp. cover as well as other species like Calluna vulgaris, tending to become more similar to semi-natural and natural peatlands. Grazing cessation induced the regenerative succession that could lead to self-recovery, which, in optimal conditions, could be an alternative to active restoration in Azores.

1 Facilitation between neighbouring plants can promote species survival and regulate community composition. However, the role of facilitation varies along environmental severity gradients. It is important to understand the shape of this relationship to improve our ability to predict the impact of a changing environment on biodiversity. 2 We used Scots pine saplings growing within heather to examine the shape of the relationship between facilitative interactions (protection from browsing) and the severity of the environment (deer browsing intensity). We also investigated whether protection from browsing translated into a biomass response of saplings. 3 In the first winter following planting heather had a facilitative effect on saplings by reducing the probability of browsing. This effect was strongest at intermediate deer browsing intensities, thus producing a hump-backed relationship between facilitative effects and the severity of the environment. 4 Protection from browsing did not lead to longer-term biomass gains for the saplings. The competitive effects of heather on sapling growth therefore outweighed the beneficial effects of protection from browsing. 5 These results provide much-needed information on the shape of the severity-interactions relationship with respect to a key natural disturbance phenomenon (herbivory), and demonstrate that an observable interaction relationship does not necessarily translate into a biomass response. 6 This illustrates the complex and potentially transient nature of plant-plant interactions, and the potential difficulty that would be associated with using shelter effects of heather as a management tool to promote Scots pine regeneration.

(1) Increased atmospheric nitrogen deposition has shifted plant dominance from ericaceous plants to grass species. To elucidate the reduced competitiveness of heather, we tested the hypothesis that additions of nitrogen reduce the concentrations of phenolics and condensed tannins in ericaceous leaves and retard mycorrhizal colonisation in ericaceous plants. We also tested the negative effects of reduced light intensity on carbon-based secondary compounds and mycorrhizal colonisation in ericaceous plants. (2) We performed a field inventory at three heathland sites in the Netherlands varying in nutrient supply and light intensity. Leaves of ericaceous plants and grasses were collected and analysed for concentrations of tannins, phenolics and nutrients. Similarly, we took root samples to record mycorrhizal colonisation and soil samples to measure the soil mineralisation. In addition, we conducted two-factorial experiments with Calluna vulgaris plants, in which we varied fertiliser and shade levels under greenhouse and field conditions. (3) The field inventory revealed that nitrogen addition and shading both negatively affected the concentration of total phenolics. The total phenolics and condensed tannin concentrations were positively correlated (P < 0.001), but in the field experiment, the condensed tannins were not significantly affected by the treatments. Our results provide the first evidence that the carbon nutrient balance can be used to predict the amount of total phenolics in the dwarf shrub C. vulgaris. (4) In the field experiments, shading of plants resulted in significantly less mycorrhizal colonisation. Only in the greenhouse experiment did addition of nitrogen negatively affect mycorrhizal colonisation. (5) Our results imply that increased atmospheric nitrogen deposition can depress the tannin concentrations in ericaceous plants and the mycorrhizal colonisation in roots, thereby reducing the plants' competitiveness with respect to grasses. Additionally, if ericaceous plants are shaded by grasses that have become dominant due to increased nitrogen supply, these effects will be intensified and competitive replacement will be accelerated.

We investigated whether partial self-sterility inCalluna vulgarisresults from abortion of selfed offspring owing to inbreeding depression or a late-acting self-incompatibility mechanism, and whether self-pollen interferes with normal functioning of cross-pollen. Self-pollination resulted in 75% less seed set than cross-pollination. Self-pollen tubes reached ovaries and penetrated ovules as often as those of cross-pollen. Following self-pollination, examination of the size of undeveloped seeds showed that at least 70% resulted from ovule fertilization and arrest of development occurred at various stages. All self-pollinated plants produced seeds and self-fertility varied among plants. These results indicate that the reduced seed set observed in self-pollination is more likely the result of inbreeding depression rather than a late-acting self-incompatibility system. The fecundity component of inbreeding depression was high (0.762). Seed set was reduced by an average of 40% when self-pollen was mixed with cross-pollen, compared to pure cross-pollination. Using genetic markers, we found about 20% of seeds resulted from self-pollination in mixed-pollinated fruits.C. vulgarisis likely to experience self-pollination in nature and our data suggest this will reduce the number of ovules that might otherwise mature after cross-pollination.

Techniques for encouraging natural tree regeneration are of increasing interest to managers of Scots pine Pinus sylvestris forests. We tested prescribed fire at a management scale, with deer present or excluded, as a means of increasing rates of Scots pine forest expansion on heathland. At a semi-natural pinewood in Scotland, ten experimental blocks were established, within range of pine seed-fall. Each block comprised four, 100 m² plots. Two plots at each site were burnt and two fenced, allowing the effects of burning on pine regeneration to be measured at two levels of deer abundance. We monitored pine seedlings, seed-fall, deer dung and vegetation for 5 years following treatment. Differences in seedling detection rates between treatments were quantified using dummy seedlings, and analyses corrected accordingly. Mean new pine seedling establishment was 9.8 times higher on burnt ground than unburnt ground (confidence intervals 3.2-30). Differences were even more pronounced in a year of high seed-fall, and following fires with low rates of spread. Establishment rates varied strongly between experimental blocks. Exclusion of deer increased establishment rates, but only in the first 2 years after fire. There was evidence that both seedling survival, and cumulative recruitment of older (over 12 months) seedlings, were improved by prescribed burning. Our results support the use of prescribed fire as a tool to promote increased Scots pine seedling establishment. This technique is likely to give strong fine-scale variation in seedling densities, and so would most suit areas where a variable spatial pattern of regeneration is sought, for landscape or naturalness reasons.

• The relationship is examined here between Nardus stricta root length colonized (RLC) by arbuscular mycorrhizal (AM) fungi (% RLC) and vegetation composition in a heathland community. • Two approaches were taken: a field survey of AM colonization of Nardus at two contrasting locations (Glen Clunie and Glen Shee, UK) in relation to vegetation composition; and an 11-month bioassay of AM inoculum potential in Calluna vulgaris and Nardus swards using uncolonized Nardus transplants. • In the field survey,% RLC of Nardus was positively related to Nardus density. This relationship was strongest in Glen Clunie, probably because overall colonization levels were lower at the more fertile Glen Shee site. In the bioassay, Nardus transplants within Calluna swards developed little or no AM colonization, whereas those within Nardus swards had a mean RLC of 23%. • This is the first report that degree of AM colonization is related to host density in the field. Isolated Nardus plants in Calluna swards might be disadvantaged compared with Nardus plants in Nardus swards because of lower of AM colonization.

We investigated whether partial self-sterility in Calluna vulgaris results from abortion of selfed offspring owing to inbreeding depression or a late-acting self-incompatibility mechanism, and whether self-pollen interferes with normal functioning of cross-pollen. Self-pollination resulted in 75% less seed set than cross-pollination. Self-pollen tubes reached ovaries and penetrated ovules as often as those of cross-pollen. Following self-pollination, examination of the size of undeveloped seeds showed that at least 70% resulted from ovule fertilization and arrest of development occurred at various stages. All self-pollinated plants produced seeds and self-fertility varied among plants. These results indicate that the reduced seed set observed in self-pollination is more likely the result of inbreeding depression rather than a late-acting self-incompatibility system. The fecundity component of inbreeding depression was high (0.762). Seed set was reduced by an average of 40% when self-pollen was mixed with cross-pollen, compared to pure cross-pollination. Using genetic markers, we found about 20% of seeds resulted from self-pollination in mixed-pollinated fruits. C. vulgaris is likely to experience self-pollination in nature and our data suggest this will reduce the number of ovules that might otherwise mature after cross-pollination.

Genetic diversity, population genetic structure and gene flow in Calluna vulgaris (L.) Hull were assessed by means of seven allozyme loci scored in 18 populations from the South-Western area of the species' range. Genetic diversity was lower (HT=0·20) than reported for long-lived widespread species but was characterized by a high number of alleles per locus (5·60 at the species level) of which more than 70% were rare. More than 95% of genetic variation was found at the intrapopulation level (GST=0·047). High levels of past gene flow were inferred, based on the allozyme data (Nm=5·2 from GST, Nm=10·2 from the ‘private allele’ method). Calluna vulgaris exhibited several geographic patterns of genetic variation. Both cluster analysis, constructed with various genetic distances and principal components analysis showed that Spanish and Pyrenean populations were clearly different from those collected in the Massif Central and Belgium. Also, a trend for decreasing genetic diversity towards Northern populations was detected. These patterns might be related to the post-glacial history of Calluna. In addition, it is shown that isolation by distance has played a role in the geographic shaping of genetic variation in this species.

Calluna vulgaris L. (Hull) is not one of the usual hosts of the winter moth, Operophtera brumata L., but outbreaks have caused extensive damage to heather moorland in Scotland in recent years. This study investigated the potential role of environmental change in such outbreaks by rearing O. brumata larvae on C. vulgaris plants grown in open-top chambers for 20 months with enriched CO2 (600 ppm) and nitrogen supply (average 52·5 kg N ha−1 yr−1) in factorial combination. This prolonged exposure to elevated CO2 caused no change in shoot growth, photosynthesis or foliar C[ratio ]N ratio of C. vulgaris, even with increased N supply, indicating that the absence of response was not due to N limitation. Increased N supply itself resulted in increased shoot growth and a decrease in tissue C[ratio ]N ratio. Phenolic content did not change in response to either CO2 or N enrichment, contrary to the predictions of the carbon/nutrient balance hypothesis. In line with the absence of plant response, there was no effect of CO2 on the development of Operophtera brumata on C. vulgaris, and so continued increase in atmospheric CO2 concentration is unlikely to affect directly O. brumata outbreaks on heather moorland. Operophtera brumata showed increased larval development, growth rate and pupal weight on N-treated plants, correlated both to the decrease in foliar C[ratio ]N ratio, and to the increase in shoot extension which was predictive of survivorship. Thus, increased atmospheric N deposition, or increased rates of mineralization in a warmer environment, might increase the severity of O. brumata outbreaks on C. vulgaris. Since the combination of high N availability and disturbance of heather canopy by herbivory is known to result in increased dominance of grasses, it is suggested that this could lead to further degradation of moorland in upland Britain.

Short-term uptake of137Cs by heather (Calluna vulgaris L.) was measured using radiolabelled liquid media and plants grown from shoot cuttings. Uptake by mycorrhizal plants was compared with uptake by non-mycorrhizal plants, and the effects of different external Cs and K concentrations were determined. At each time point during the 3 h experimental period the content (and hence also the apparent influx) of the mycorrhizal plants in each treatment was found to be lower than that of the non-mycorrhizal plants. An increase of 100-fold in the total external Cs concentration (from 5 to 500 μM) gave between a 35-fold and 96-fold increase in initial influx of Cs. A similar change in external K concentration, however, had little effect on Cs influx. Root-shoot transfer of Cs over the 3 h uptake period was slight; in most cases more than 90% of the radiocaesium remained in the root. The final shoot:root Cs ratio was higher in mycorrhizal than in nonmycorrhizal plants, suggesting that in mycorrhizal plants, despite their lower overall accumulation during the first 3 h, a higher proportion of the Cs taken up is translocated to the shoot.