Undisturbed Bog Research Articles

Invertebrate abundance increases with vegetation productivity across natural and agricultural wader breeding habitats in Europe

Grassland breeding waders have been steadily declining across Europe. Recent studies indicating a dramatic decline in grassland invertebrates' abundance and biomass, the key food of most grassland wader chicks, suggest a likely driver of the demise of waders. While agricultural intensification is generally inferred as the main cause for arthropod decline there is surprisingly little information on the relationship between land use intensity and total arthropod abundance in grasslands. Here, we explored those relationships across several key wader breeding habitats by surveying ground-active, aerial and soil-dwelling invertebrate communities in five European countries that range from natural undisturbed bogs to intensively managed grasslands. Using maximum vegetation growth and soil moisture content we investigated how they shape the size of the invertebrate community within and across different countries. We found predominantly positive relationships between grassland invertebrate abundance, biomass and body weight with increasing vegetation growth and soil moisture. Maximum vegetation growth was strongly positively related to ground-active invertebrate abundance and biomass and abundance of soil dwelling invertebrates (mainly earthworms). Body weight of aerial invertebrates furthermore increased with increasing maximum vegetation growth. Our results provide little support for the hypothesis that agricultural practices associated with intensification of grassland management result in an abundance decline of invertebrate prey for wader chicks. Conservation practices aiming to enhance wader chick survival require a careful balancing act between maintaining habitat productivity to secure high prey abundance, and keeping productivity low enough to maintain open swards that do not need to be cut before chicks have fledged.

Vegetation Composition and Carbon Dioxide Fluxes on Rewetted Milled Peatlands — Comparison with Undisturbed Bogs

Vegetation Composition and Carbon Dioxide Fluxes on Rewetted Milled Peatlands — Comparison with Undisturbed Bogs

Steady and ebullitive methane fluxes from active, restored and unrestored horticultural peatlands

Peatlands used for horticultural peat extraction lose their ecological function of carbon accumulation. While their restoration has been shown to increase methane (CH4) flux compared to unrestored sites, the time required for CH4 balance to recover and the factors affecting the recovery remain unclear. We quantified CH4 emissions from restored sites with different time since restoration efforts began (5, 8 and 25 years prior to the study), an unrestored post-extraction (Unrestored) and actively extracted (Active) sites, and compared them to CH4 emission from a natural boreal bog (Natural). All study sites were located within one horticulture peatland complex in central Alberta, Canada. Both steady (diffusive and steady ebullitive) fluxes and abrupt ebullitive events were determined using manual chambers and a portable greenhouse gas analyzer. Methane emissions were greater at the restored sites than at the Natural, Unrestored, and Active sites. Abrupt ebullition occurred only at two restored sites that were flooded/water saturated, dominated by vascular plants, and had the highest steady fluxes. Ebullition accounted for 7% of total CH4 emission at the site restored in 1991 (25–26 years post-restoration), and 6% at the site restored in 2012 (4–5 years post-restoration). Despite shallow water table and dense sedge cover, the third restored site (7–8 years post-restoration), showed no abrupt ebullition and mean steady flux lower than at the Natural site, likely caused by peat geochemistry. At sites where it occurred, ebullition was significantly positively but weakly correlated with CH4 flux, concentration of CH4 in pore water, soil temperature, water table (WT), gross ecosystem production , and percentage cover of moss. Steady CH4 fluxes were higher when soil temperature at 20 cm depth was higher, WT shallow, and with greater plant productivity and cover of graminoids, but lower with higher shrub cover. Peat chemical characteristics can supersede these environmental factors and suppress CH4 emission even in restored, wet, and sedge-dominated sites. Restored sites with more fen-like conditions (wet and sedge-dominated) are likely to have abrupt ebullition events and higher CH4 fluxes than undisturbed bogs, with local controls seemingly more important than time since restoration on resulting CH4 emission.

Пигментный состав Sphagnum fuscum заболоченных территорий в условиях техногенного воздействия

Oligotrophic bogs prevail among wetlands in the mainland of the North of Russia. The study of the moss cover response to the increase in anthropogenic load makes it possible to reveal a shift in the ecological balance of bog ecosystems. The goаl of the research is to reveal changes in the pigment apparatus of the moss cover under drainage, road construction and mining operation as in the case of the Arkhangelsk region. Sphagnum fuscum (Schimp.) H. Klinggr. was used as the main object for studying the pigment composition of the photosynthetic apparatus. A change in the pigment composition during the drainage of bogs was found when comparing the pigments of S. fuscum moss on the undisturbed Ilas bog massif and the drained bog massif “Ovechye”; the content of carotenoids decreases and the content of chlorophyll a increases. The influence of the traffic load was studied in an open wetland of the Mezen district, where there is no tree-shrub layer. Succession of dominant species is observed in the moss-lichen layer of the bog in the immediate vicinity of the road (34 m); the projective cover of sphagnum mosses decreases to less than 10 %, and brie mosses emerge as dominants. The content of all analyzed pigments in moss samples increases with the distance from unpaved roads, especially the content of chlorophylls (>5 times at a distance of 100 m and more). As an example of the anthropogenic impact of a mining enter prise, we used terricones of the Lomonosov Mining and Processing Plant, PJSC Severalmaz, from which aeolian transport of dust particles of rocks containing saponite occurs. Near the pollution source, the content of total moss pigments is noticeably lower than in the area protected by a forest belt. A decrease in the proportion of chlorophylls a and b with a slight increase in the content of carotenoids was found in the pigment complex. The changes are due to the transfer of saponite; a clay mineral that actively absorbs water. The increased moisture provides favorable conditions for the moss vegetation, which mitigates the negative effect of pollutants on the pigment apparatus of plants. Overall, pigments content change represents plants adaptation to the adverse impacts and anthropogenic pressing.

Comparison of energy fluxes between an undisturbed bog and an adjacent abandoned peatland pasture

This study compared the energy budget components of latent heat flux (LE), sensible heat flux (H), net radiation (Rn) and ground heat flux (G) between an undisturbed bog and an adjacent abandoned peatland pasture within the same peatland complex in western Newfoundland, Canada. The analysis was based on the period of April 2014 to August 2015 when measurements were concurrent at both sites, thus encompassing two growing seasons. The overall objective was to identify the impact of agricultural management and abandonment on peatland energy flux and partitioning. LE and H showed strong seasonal patterns for both sites. LE, which was higher at the pasture, peaked near the middle of the growing season. H at the bog was smaller than that at the pasture during the early growing season, but became larger during the middle and late growing seasons, with the maximum H occurring during the early growing season. G was the smallest flux in the energy budget at both sites, and it showed no obvious temporal pattern at either site. The variation in daytime average evapotranspiration (ET) was related to net radiation and vapor pressure deficit (VPD) at both sites. However, it was more strongly related to Rn. ET at the pasture site exhibited greater sensitivity to changes in Rn and VPD. Daytime ET increased and decreased with water table depth (WTD) when WTD was above and below a threshold of -0.24 m at the bog and -0.46 m at the pasture. The between-site differences in growing season H and LE (∆H and ∆LE) were mainly caused by their different vegetation conditions, and ∆H and ∆LE were negatively and positively related to ∆EVI (difference in enhanced vegetation index), respectively.

The impact of a black spruce (Picea mariana) plantation on carbon exchange in a cutover peatland in Western Canada

Northern peatlands are sinks for atmospheric carbon (C), but peat extraction converts these ecosystems to C sources. Due to a dry regional climate, undisturbed bog peatlands in western Canada often have a tree cover of Picea mariana (Mill.) B.S.P. Thus, a coniferous forest plantation may be an appropriate land use for cutover peatlands. This study determined the effect of a 7-year-old P. mariana plantation on C balance of a cutover peatland. We measured C stored in P. mariana biomass and carbon dioxide (CO2) and methane (CH4) fluxes from bare peat at each of four fertilizer doses. Carbon stored in biomass of Betula papyrifera (Marsh.) that had spontaneously colonized the postfertilized site was also determined. Given that the water table remained very deep and that the sphagnum moss – ericaceous shrub peat-accumulating vegetation was not present, the site remained a source of C when only the planted P. mariana trees were considered, primarily in the form of CO2 emissions by soil respiration. However, C accumulation in trees, including B. papyrifera biomass, resulted in a net C sink in fertilized plots. Results from this study indicate that tree plantations on cutover peatland may be a suitable land-management strategy on sites difficult to effectively rewet.

Dynamics of phytomass and production on reclaimed mesotrophic mire during repeated water-logging process in the Lower Amur region

Проведено сравнение результатов изучения динамики фитомассы и продукции безлесного кустарничково-травяно-сфагнового болотного сообщества, сформировавшегося на чеке мелиоративной системы через 20 лет после осушения и сообщества ненарушенного мезотрофного кустарничково-сфагнового лиственничника (без учета древесного яруса) на Среднеамурской низменности. Сравнение показало, что произошла перестройка структуры фитомассы и увеличение продукции сфагновых мхов и травянистых растений с одновременным снижением продукции психрофильных кустарничков в ходе вторичного заболачивания в результате изменения гидрологического режима. Запасы живой фитомассы составили 1106 г/м2 на ненарушенном болоте и 1640 г/м2 на вторично заболоченном. Запасы мортмассы в надземной части и деятельном горизонте на нем увеличены до 3561 г/м2 с 2272 г/м2 на ненарушенном. Чистая первичная продукция вторично заболоченного участка колеблется в пределах 627-863 г/м2 год и превышает NPP ненарушенного фитоценоза, которая колеблется с 538 до 662 г/м2 год.

Using functional diversity as an indicator of restoration success of a cut-over bog

A trait-based approach was used to evaluate the restoration success of a moss layer transfer technique on the herbaceous community of a cut-over bog. In order to understand the herbaceous dynamics following restoration, the bog was monitored prior to restoration and biannually over ten subsequent years, in two initial drainage conditions (dry peat fields and wet ditches), and compared to seven undisturbed bogs. Herbaceous community found prior to and in the early stage after restoration were characterized by species associated to mesic soil conditions with a fen-like pH, ruderal or wetland species, species with mycorrhiza or exotic species. These species did not persist in the latter stage after restoration and were replaced by species that are carnivorous, are associated to variable water availability and show mostly sexual reproduction. The extent of changes in traits composition of the herbaceous community between the early and latter stages after restoration showed the importance of multiple-year monitoring to evaluate restoration projects. The trait composition found in the latter stage after restoration appeared to converge toward the reference ecosystem where the community was characterized by species with large seeds, associated to humid soil conditions and a forest or peatland habitat. Lower trait diversity was found in the latter stage after restoration than in the reference ecosystem, especially in peat fields. In addition, species and functional diversity pattern varied with the initial drainage conditions, decreasing in peat fields while remaining stable in ditches. This suggests that different initial topography for restoration might help increase species and functional diversity of a managed ecosystem. Finally, our results outline measures to improve the moss layer transfer technique: sowing herbaceous species with large seeds in the latter stage after restoration, applying the restoration technique as soon as exploitation has terminated or removing all vegetation (including seeds and rhizomes) from the site to be restored.

Sampling the invertebrate community associated with a threatened wetland plant, Sporadanthus ferrugineus, using a new design of emergence trap

A novel design of emergence trap was used to examine the invertebrate fauna associated with Sporadanthus ferrugineus, a threatened wetland plant. Potted S. ferrugineus plants were placed in sealed emergence traps after 6, 12 and 18 weeks exposure to invertebrates in an undisturbed peat bog at Torehape, North Island, New Zealand. A total of 1,137 individuals from 42 species in seven invertebrate Orders colonized 30 S. ferrugineus plants and were captured within the emergence traps. The invertebrate densities did not change signifi cantly during the short duration of the experiment, or with increasing distance into the undisturbed peat bog. In contrast, total species richness caught in each emergence trap increased signifi cantly during the course of the experiment. The most common species captured was the aphid Rhopalosiphum rufiabdominalis (Aphididae: Homoptera), accounting for 24% of total abundance. Other common species caught included the spider Anateropsis hilaris (Lycosidae: Araneae), an unidentified species of Agromyzidae (Diptera), and the beetle Selenopalpus cyaneus (Oedemeridae: Coleoptera). The trap was effective at capturing Houdinia flexilissima (Lepidoptera), a strictly monophagous species specialized to feed in the narrow stems of S. ferrugineus. The advantages of this trap design are the relatively low construction cost, and ease of installation and transportation. Its potential for use in control programmes and other ecological studies is discussed.

Carbon dioxide and methane production potentials of peats from natural, harvested and restored sites, eastern Québec, Canada

Drainage, vegetation removal and harvesting, and vegetation restoration have a profound effect on carbon cycling in peatlands. Through laboratory incubations of 114 peat samples collected from the surface layer and just above and just below the water table at 13 sites, we examined the potential for carbon dioxide (CO2) production under aerobic and anaerobic conditions and methane (CH4) production under anaerobic conditions. CO2 production rates ranged from 0.04 to 1.05 mg g 21 d 21 under aerobic conditions and 0.01 to 0.29 mg g 21 d 21 under anaerobic conditions. Rates of CO2 production were generally smallest in the lower parts of the profiles and at the recently restored sites where deep peat was exposed at the surface; they were largest in the freshly-formed surface peat at the undisturbed bog and older restoration sites where a strong cover of vegetation had developed. The CO2 production potentials were negatively correlated with the Von Post Index of decomposition, and aerobic:anaerobic production ratios averaged 4.3: 1. Largest rates of anaerobic CH4 production occurred in samples close to the soil surface with fresh peat accumulation and a high water table, and smallest rates were in samples from the subsurface of sites with a low water table. Anaerobic CH4 production was significantly positively correlated with aerobic and anaer- obic CO2 production. These production potentials show that drainage, harvesting, and restoration change the ability of the peat profile to produce and emit CO 2 and CH4.

Vegetation ofSphagnumbogs in highly disturbed landscapes: relative influence of abiotic and anthropogenic factors

AbstractQuestion:Has the vegetation ofSphagnumbogs been affected by more than 200 years of human activities?Location:Bas‐Saint‐Laurent region, southeastern Québec, Canada.Methods:Data (species assemblages, abiotic and spatio‐historical variables) were collected in 16 bogs ranging from 2 to 189 ha, and incorporated in a geographical information system. Major gradients in vegetation composition were identified using DCA. CCA was used to relate vegetation gradients to abiotic and spatio‐historical variables.Results:A clear segregation of species assemblages was observed, from open and undisturbed bogs to forested and highly disturbed sites. Among abiotic factors, tree basal area, water table level and peat thickness had a significant influence on plant species composition. Among spatio‐historical factors, disturbance level, area loss and fire were the most influential factors. Variance partitioning between these groups of factors suggests that spatio‐historical factors had a major influence on peatlands, representing 22% of the variation observed in the plant species assemblages while abiotic factors represent only 17% of the variation.Conclusions:The results highlight the influence of agricultural and other anthropogenic activities on plant assemblages and suggest that even wetlands apparently resistant to disturbances, such as peatlands, can be severely affected by anthropogenic factors. Plant species assemblages of ombrotrophic peatlands of the Bas‐Saint‐Laurent region were, and still are, largely influenced by human activities.

Vegetation of Sphagnum bogs in highly disturbed landscapes: relative influence of abiotic and anthropogenic factors

Question: Has the vegetation of Sphagnum bogs been affected by more than 200 years of human activities? Location: Bas-Saint-Laurent region, southeastern Quebec, Canada. Methods: Data (species assemblages, abiotic and spatio-historical variables) were collected in 16 bogs ranging from 2 to 189 ha, and incorporated in a geographical information system. Major gradients in vegetation composition were identified using DCA. CCA was used to relate vegetation gradients to abiotic and spatio-historical variables. Results: A clear segregation of species assemblages was observed, from open and undisturbed bogs to forested and highly disturbed sites. Among abiotic factors, tree basal area, water table level and peat thickness had a significant influence on plant species composition. Among spatio-historical factors, disturbance level, area loss and fire were the most influential factors. Variance partitioning between these groups of factors suggests that spatio-historical factors had a major influence on peatlands, representing 22% of the variation observed in the plant species assemblages while abiotic factors represent only 17% of the variation. Conclusions: The results highlight the influence of agricultural and other anthropogenic activities on plant assemblages and suggest that even wetlands apparently resistant to disturbances, such as peatlands, can be severely affected by anthropogenic factors. Plant species assemblages of ombrotrophic peatlands of the Bas-Saint-Laurent region were, and still are, largely influenced by human activities.

Role and character of seasonal peat soil deformation on the hydrology of undisturbed and cutover peatlands

This paper describes the nature and magnitude of peat soil volume changes and its relation to seasonal changes in water table at an undisturbed bog peatland and on two cutover sections of the same peatland and its effect on hydraulic conductivity. In the latter two sites, operations had ceased 2 and 7 years prior to this study, respectively. The water table dropped to a maximum depth of 40, 50, and 68 cm, respectively, at the undisturbed, 2‐year, and 7‐year abandoned sites and a resulted in subsidence of 0.96, 3.84, and 2.65 cm m−1, respectively. At the undisturbed site, surface elevation changes did not always correspond to water table changes, but peat underwent a period of swelling even as the water table fell, probably due to the accumulation of methane in soil pores. At all sites most volume change occurred in the upper 50 cm layer, with maximum strain of 5, 15, and 5% at the undisturbed, 2‐year, and 7‐year abandoned sites, respectively, and was strongly related to water table decline. A model of peat deformation in the zone of saturation (100 cm depth), based on changes in saturated soil moisture (6%), grossly overestimated strain (1%) in the saturated zone, and again methane accumulation was the suspected cause of the soil moisture decrease. Peat compression (and perhaps methane accumulation) caused hydraulic conductivity to decrease over two orders of magnitude at 75, 125, and 170 cm depth. The decrease in hydraulic conductivity as a peatland dries may be an important self‐preservation mechanism (i.e., against further water loss).

Germination and seedling growth of bog plants in relation to the recolonization of milled peatlands

Two controlled experiments were conducted to evaluate the potential for vascular plants to germinate and establish in milled peatlands and to assess whether easily measured plant traits can be used to predict their probable success. Study species included twenty species of perennial herbs, shrubs and trees occurring frequently in undisturbed bogs or abandoned milled bogs in Quebec, Canada. First, a glasshouse experiment was performed to test the effect of burial under peat on germination and seedling emergence. Second, a growth chamber experiment was conducted to measure relative growth rate and other growth parameters of seedlings between 1 and 3 weeks of age. In the burial experiment, seedling emergence decreased exponentially with peat depth for most species examined. The slope of the exponential decline varied between species and was strongly correlated to seed mass. Seeds less than 0.1 mg in mass were most sensitive to burial. In the seedling growth experiments, Betula species had the highest absolute and relative growth rates, which may help to explain their prevalence in milled bogs. Relative growth rate (RGR) was not correlated with seed mass, however it was strongly correlated with leaf area ratio (LAR) and especially specific leaf area (SLA) of seedlings, except for species with seed mass less than 0.01 mg. Screening of species for seed mass and SLA should help predict their germination and establishment success or failure in milled peatlands and allow more directed interventions to favour the establishment of desirable species in milled bogs.

Water budget and surface‐layer water storage in a Sphagnum bog in central Sweden

AbstractA water budget was established for the open, undisturbed bog Stormossen, central Sweden, for the growing seasons of 1996 and 1997 as a part of the NOPEX project. The water budget was complemented with data on the spatial variation of groundwater levels and water contents in different microrelief elements (ridge, hollow and ridge margin). The seasonal (24 May to 4 October) rainfall, evaporation and runoff were 200, 256, and 43 mm in 1996, respectively, and 310, 286 and 74 mm in 1997, giving negative budgets of −99 mm in 1996 and −50 mm in 1997. Approximately 60% of the total budget was caused by storage changes in the upper 40 cm of the bog and 40% by swelling/shrinking in the layers below. This ‘mire breathing’ must be incorporated in future models of mire‐water dynamics. The water content varied diversely among the different microrelief elements, much depending on the properties of moss and peat together with distance to water table. There also was a strong hysteresis in the relationships between groundwater level and measured volumetric water content, depending partly on pore‐throat effects and partly on swelling/shrinking of the peat matrix. A seasonal variation of volumetric water content in a layer beneath water table was found to be larger than what could be justified by compression alone. We think that probable causes could be methane gas expansion together with temperature effects. The main conclusions of this study were: (i) water‐transport and storage characteristics are distinctly different among hummocks, ridges and hollows, (ii) mire wetness cannot be deduced from groundwater levels only, and (iii) an important part of the total water storage was caused by swelling/shrinking of the peat, not by changes in unsaturated water content. Copyright © 2002 John Wiley & Sons, Ltd.

Artificial nest predation in bogs: Does peat harvest increase risk?

Bogs in southern Québec are facing significant and growing industrial pressure. Peat moss harvesting results in bog fragmentation and in edge increase between harvested areas and remaining natural patches. The objective of our study was to assess the effects of harvesting on nesting success of songbirds in adjacent undisturbed sites. We determined whether exposure of nests to predators was edge-dependent in harvested bogs and compared the risk of nest predation in harvested and undisturbed bogs. Over three summers, we placed a total of 480 artificial nests at various distances (£ 450 m) from edges in five harvested and nine unharvested bogs. Mean nest predation rate was significantly higher (62.7%) and more variable in harvested bogs, compared to unharvested bogs (8.6%). However, we found no relation between nest fate and distance to exploitation edge in harvested bogs. We suggest factors associated with harvesting that may attract nest predators to remaining unharvested sites, thereby increasing risk of nest predation and ultimately lowering reproductive success.

Species diversity, niche metrics and species associations in harvested and undisturbed bogs

Abstract. Competition is considered an important force in structuring plant communities and in governing niche relations, but communities recovering from disturbance, may be less governed by species interactions and less orderly organized. To address this issue, we studied species richness, abundance and patterns of association between plant species at three spatial scales (1 m2, 1/25 m2, 1/625 m2) in two ombrotrophic mires in east‐central Sweden. One was at a secondary successional stage following peat extraction 50 yr ago and the other was undisturbed. Peat extraction leads to a change in hydrology which is slowly restored by the formation of new peat. Niche breadth and niche overlap along the gradient of height above the water table were calculated for the five common Sphagnum species occurring at both mires in an attempt to better understand differences in species co‐occurrence at each mire.Species cover differed between the mires, and the number of species per plot was higher in the undisturbed community at all scales, suggesting that the degree of species intermingling was greater than at the harvested site. At all scales, the number of non‐random associations was higher, and niche overlap lower among ecologically similar species (e.g. hollow Sphagnum species) in the undisturbed mire. These differences indicate that random events are important in colonization, and that biotic interactions between neighbours later result in a higher degree of non‐randomness.In addition, we surveyed a number of abandoned peat pit sites to test the effect of disturbance for species composition at a regional scale. Ombrotrophic peat pits contained several Sphagnum species normally associated with minerotrophic mires, and species of wooded mires occurred frequently in peat pits, making them more species‐rich than undisturbed bogs. There were also Sphagnum species new to, or rare in, this part of Sweden which indicates effective long‐distance dispersal. Even 50 yr after peat extraction had ceased, the vegetation had not recovered to its original composition.

Climatic and anthropogenic influences on radial growth of scots pine at hanvedsmossen, a raised peat bog, in south central sweden

Past studies of the climatic influence on tree growth at peat bogs in northern latitudes have shown weak correlation between annual tree‐ring widths and climatic parameters during the growing season. At Hanvedsmossen, a raised peat bog in south central Sweden, tree‐ring width chronologies from one drained and one undrained growth site, as well as one dry site outside the bog, were compared to meteorological records. Low temperatures, which means less evaporation, as well as high precipitation appear to be inhibiting pine growth at the undisturbed bog site as the trees are sensitive to changes in the local water table. Drainage causes an instant increase in annual tree growth for approximately 10 years. If draining is maintained, the response to climate of the pines resembles that of pines growing on mineral soils. The variance in annual tree‐ring growth explained by temperature/precipitation or both was low for the entire lengths of all chronologies, but high for some analysed subperiods; the significant months changed with time. The reason for this seems to be that pines at Hanvedsmossen are growing in a region where precipitation and temperature are less limiting to tree growth than at higher and lower latitudes.

Avian recolonization of eastern Canadian bogs after peat mining

To evaluate the potential of bog ecosystems to recover following peat mining, we compared bird species richness,abundance, and assemblages and vegetation among naturally revegetated and undisturbed bog sites in southeastern Quebec.Based on mining history, we selected 28 sites (12 natural, 9 abandoned after blockcut extraction, and 7 abandoned after vacuumextraction) in 15 bogs. We estimated percent cover for six vegetation strata in 106 plots with 100 m radius, on which bird pointcounts were conducted in 1993 and 1996. Vegetation structure differed significantly between natural, post-blockcut andpost-vacuum sites. While vegetation cover was almost complete in natural sites, abandoned sites, especially post vacuum, wereless vegetated, even after 20 years. Bird species richness and abundance were similar in natural and post-blockcut sites andboth were higher than in post-vacuum sites. Ten of the 28 species studied in detail responded to site perturbation. Among them,the Palm Warbler was most closely associated with natural sites. Bird communities were closely associated with vegetationstructure. Communities of post-blockcut sites were more similar to those of natural bogs than were bird communities ofpost-vacuum sites. Since the blockcut method of peat mining is no longer economically feasible, we conclude that bog habitatrestoration should be accompanied by a preservation “safety net” area to counteract the lasting effect of vacuum peat mining onbird species assemblages.

Environmental change during the medieval reclamation of the raised-bog area Waterland (The Netherlands): a palaeophytosociological approach

A report is given of a palaeoecological study based on the analysis of pollen, non-pollen palynomorphs and macrofossils of an excavated medieval house site and its underlying peat deposit at Poppendam, Waterland (The Netherlands). The house site represents one of the first human occupations in this former raised-bog area. The analysis includes a raised-bog sequence with cultural layers on top of it. A detailed reconstruction of the changing vegetation from natural raised-bog to cultural landscape is given. The main phases of the deposit comprise: a natural, undisturbed bog (from mid-Subboreal to the 8th century AD); a disturbed raised-bog with eutraphentic taxa prior to the first occupation (between the 8th century and the first half of the 10th century AD); an anthropogenic accumulation layer of mixed former bog material, eutraphentic taxa and cultural indicators (from the first half of the 10th century AD onwards). Seeds and pollen of cultivated plants and vegetation of the Lolio-Potentillion anserinae alliance indicates a mixed agricultural economy in which domesticated animals played an important role. This is confirmed by the simultaneous occurrence of large numbers of ascospores of coprophilous Sordariaceae. Inundations of Lake Almere, as evident from the occurrence of brackish/salt elements, suggest that the lake had already become brackish/salt around the 8–9th century. Two methods for the reconstruction of palaeophytosociological communities containing halophytic plant species are presented. The Lolio-Potentillion anserinae alliance as an indication for inundations, lowering of the original bog surface and the occurrence of grazed, brackish grasslands is discussed.