Patterns and gradients of diversity in South Patagonian ombrotrophic peat bogs

Many north‐hemispherical mires seemingly untouched by drainage and cultivation are influenced by a diffuse sum of man‐made environmental changes, such as atmospherical nitrogen deposition that mask general patterns in species richness and functional group responses along resource gradients. To obtain insights into natural diversity‐environment relationships, we studied the vegetation and the peat chemistry of pristine bog ecosystems in southern Patagonia along a west–east transect across the Andes. The studied bog ecosystems covered a floristic gradient from hyperoceanic blanket bogs dominated by cushion building vascular plants via a transitional mixed type to Sphagnum‐dominated raised bogs east of the mountain range. To test the influence of resource availability on diversity patterns, species richness and functional groups were related to environmental variables by calculating general regression models and generalized additive models. Species richness showed strong linear correlations to peat chemical features and the general regression model resulted in three major environmental variables (water level, total nitrogen, NH₄Cl soluble calcium), altogether explaining 76% of variance. Functional group response illustrated a clear separation along environmental gradients. Mosses dominated at the low end of a nitrogen gradient, whereas cushion plants had their optimum at intermediate levels, and graminoids dominated at high nitrogen contents. Further shifts were related to NH₄Cl soluble calcium and water level. The models documented partly non‐linear relationships between functional group response and trophical peat properties. Within the three bog types, the calculated models differed remarkably illustrating the scale‐dependency of the explanatory factors. Our findings confirmed several general patterns of species richness and functional shifts along resource gradients in a surprisingly clear way and underpin the significance of undisturbed peatlands as reference systems for testing of ecological theory and for conservation and ecological restoration in landscapes with strong human impact.     

Release of inorganic N,P and K in peat soils; effect of temperature,water chemistry and water level

In the Netherlands, fens that are fed by polluted river water are often eutrophic, whereas fens fed by calcium-rich groundwater often are mesotrophic. Differences in trophic status can not always be attributed to differences in the nutrient load of the water. In this paper we try to determine if the inflow of river water in fens, in fact, accelerates the soil nutrient release, thereby creating more eutrophic conditions (‘internal eutrophication’). For this purpose, we compared nutrient release rates (N, P and K) in soil cores fromSphagnum peat andCarex peat saturated with different media, that were artificially created to mimic the three basic water sources: polluted river water, unpolluted calcium-rich groundwater and rainwater. In addition, we studied the effect of temperature and water level on nutrient release rates. The experiments proved thatSphagnum peat released much more P and ammonium thanCarex peat. The strong site effect proved consistent throughout the water chemistry treatments, which indicates that soil quality may be the most important agent determining nutrient release rates. Nevertheless, it was established that water chemistry and water level are of significant influence on nutrient release rates in peat soils. In particular, river water stimulated P release by the peat, most notably in theSphagnum peat. P-release in both soils was only minor when the soils were incubated in clean Ca-rich groundwater. It is suggested that P release is strongly associated with soil chemical processes, and that high P release rates after incubation in river water are due to the high sulphate content of the water. The net release from the soil of ammonium, potassium and phosphate increased with increasing temperature. A freezing treatment significantly increased nutrient availability. The results of the experiments are examined in the context of hydrologic management strategies for the conservation of fens in agricultural landscapes.     

South Patagonian ombrotrophic bog vegetation reflects biogeochemical gradients at the landscape level

Question: Which environmental variables affect the floristic composition of south Patagonian bog vegetation along a gradient of climate and biogeochemical changes with increasing distance from the Pacific ocean? Location: Trans‐Andean transect (53° S), southern Patagonia Material and Methods: Floristic composition, peat characteristics (water level, decomposition, pH, total nitrogen, total carbon, ash content and plant available P, K, Na, Ca, Mg, Fe, Mn, Zn, and Al) and climatic constraints of ombrotrophic peat‐lands were measured at 82 plots along a gradient of increasing distance from the Pacific Ocean. Results: Climatic constraints and biogeochemical peat characteristics significantly change with increasing distance from the Pacific. Peatland vegetation shifted from hyperoceanic blanket bogs dominated by cushion forming vascular plants to the west to Sphagnum bogs to the east. Climatic and biogeochemical variables explained a large proportion of the floristic variation along the first DCA axis. The second axis represented a water level gradient. When ‘distance to the Pacific’ was defined as a covariable in partial CCA, the proportion of variance explained declined for most other variables, especially in the case of annual precipitation and exchangeable base cations and related traits. The differences in biogeochemical characteristics related to peat were mainly attributed to the input of sea‐borne cations. Conclusions: While variation in vegetation composition along a longitudinal gradient crossing the southern Andes was attributed to climatic constraints as expected, vegetation composition was also strongly affected by the biogeochemical characteristics of peat. Sea spray was of high ecological importance to peat chemistry and, consequently, to floristic composition. Presumably, south Patagonian peat bogs represent a glimpse of pre‐industrial environments, so that these peat bogs may act as reference systems with respect to atmospheric inputs in mire ecology research.     

Assessing long‐term hydrological and ecological responses to drainage in a raised bog using paleoecology and a hydrosequence

Question: We studied vegetation succession after drainage in a bog, as an analogue for potential persistent water table drawdown due to climate change. We asked: (1) how does bog vegetation change following a long‐term water table lowering and (2) how are effects of drainage on hydrology and vegetation distributed temporally and spatially? Location: Mer Bleue peatland, Ontario, Canada (45.41°N, 75.48°W). Methods: Analyses of changes in vegetation and hydrology associated with drainage were examined spatially along a hydrosequence and temporally using paleoecological reconstructions from peat cores (testate amoebae, pollen) in a drained portion of a peatland untouched for 85 years following drainage. Relationships between modern vegetation and water table were assessed through clustering and ordination analyses of vegetation relevés. Results: Post‐drainage increases in tree cover, especially Betula and Larix, decreases in Sphagnum cover and shifts in species composition of dominant shrubs were observed. Present‐day vegetation patterns along the hydrosequence were primarily related to seasonal variability of water table depth. Paleoecological records reveal that where the present‐day vegetation has been impacted by drainage, persistent water table lowering occurred in response to drainage. However, in an area with relatively natural vegetation, a transient drop in water table depth occurred at the time of drainage. Conclusions: Temporal and spatial patterns revealed that the bog response to drainage was spatially and temporally heterogeneous, and probably mediated by feedbacks among vegetation, peat structure and hydrology. Spatial patterns along the hydrosequence were similar to those observed in paleoecological reconstructions, but the use of the two complementary techniques provides additional insights.     

Ecological studies on algal communities from Tierra del Fuego peat bogs

Microalgal communities from seven water hollows have been studied in six peat bogs located in the southwest of the Tierra del Fuego Province (Argentina). The evolution of these systems towards terrestrial conditions includes a gradual increase in conductivity and decrease in pH along a gradient from the open water to the drier surroundings. For the microalgae sampled along these gradients, these changes are reflected by the decrease in species richness and the rise in the relative frequencies of a few taxa well adapted to harsh conditions. Also, all sampling stations from the different water hollows were compared in terms of floristic composition and relative frequencies of the different taxa. Both cluster analysis and Principal Components Analysis revealed marked differences among water hollows for these features, which can be associated with morphometric and chemical parameters related to their evolutionary stage, rather than with their geographical distribution.     

Evidence for older carbon loss with lowered water tables and changing plant functional groups in peatlands

A small imbalance in plant productivity and decomposition accounts for the carbon (C) accumulation capacity of peatlands. As climate changes, the continuity of peatland net C storage relies on rising primary production to offset increasing ecosystem respiration (ER) along with the persistence of older C in waterlogged peat. A lowering in the water table position in peatlands often increases decomposition rates, but concurrent plant community shifts can interactively alter ER and plant productivity responses. The combined effects of water table variation and plant communities on older peat C loss are unknown. We used a full-factorial 1-m³ mesocosm array with vascular plant functional group manipulations (Unmanipulated Control, Sedge only, and Ericaceous only) and water table depth (natural and lowered) treatments to test the effects of plants and water depth on CO₂ fluxes, decomposition, and older C loss. We used Δ¹⁴C and δ¹³C of ecosystem CO₂ respiration, bulk peat, plants, and porewater dissolved inorganic C to construct mixing models partitioning ER among potential sources. We found that the lowered water table treatments were respiring C fixed before the bomb spike (1955) from deep waterlogged peat. Lowered water table Sedge treatments had the oldest dissolved inorganic ¹⁴C signature and the highest proportional peat contribution to ER. Decomposition assays corroborated sustained high rates of decomposition with lowered water tables down to 40 cm below the peat surface. Heterotrophic respiration exceeded plant respiration at the height of the growing season in lowered water table treatments. Rates of gross primary production were only impacted by vegetation, whereas ER was affected by vegetation and water table depth treatments. The decoupling of respiration and primary production with lowered water tables combined with older C losses suggests that climate and land-use-induced changes in peatland hydrology can increase the vulnerability of peatland C stores.     

Logged peat swamp forest supports greater macrofungal biodiversity than large‐scale oil palm plantations and smallholdings

Intensive land expansion of commercial oil palm agricultural lands results in reducing the size of peat swamp forests, particularly in Southeast Asia. The effect of this land conversion on macrofungal biodiversity is, however, understudied. We quantified macrofungal biodiversity by identifying mushroom sporocarps throughout four different habitats; logged peat swamp forest, large‐scale oil palm plantation, monoculture, and polyculture smallholdings. We recorded a total of 757 clusters of macrofungi belonging to 127 morphospecies and found that substrates for growing macrofungi were abundant in peat swamp forest; hence, morphospecies richness and macrofungal clusters were significantly greater in logged peat swamp forest than converted oil palm agriculture lands. Environmental factors that influence macrofungi in logged peat swamp forests such as air temperature, humidity, wind speed, soil pH, and soil moisture were different from those in oil palm plantations and smallholdings. We conclude that peat swamp forests are irreplaceable with respect to macrofungal biodiversity. They host much greater macrofungal biodiversity than any of the oil palm agricultural lands. It is imperative that further expansion of oil palm plantation into remaining peat swamp forests should be prohibited in palm oil producing countries. These results imply that macrofungal distribution reflects changes in microclimate between habitats and reduced macrofungal biodiversity may adversely affect decomposition in human‐modified landscapes.     

Physiological Changes in Rhizobia after Growth in Peat Extract May Be Related to Improved Desiccation Tolerance

Improved survival of peat-cultured rhizobia compared to survival of liquid-cultured cells has been attributed to cellular adaptations during solid-state fermentation in moist peat. We have observed improved desiccation tolerance of Rhizobium leguminosarum bv. trifolii TA1 and Bradyrhizobium japonicum CB1809 after aerobic growth in water extracts of peat. Survival of TA1 grown in crude peat extract was 18-fold greater than that of cells grown in a defined liquid medium but was diminished when cells were grown in different-sized colloidal fractions of peat extract. Survival of CB1809 was generally better when grown in crude peat extract than in the control but was not statistically significant (P > 0.05) and was strongly dependent on peat extract concentration. Accumulation of intracellular trehalose by both TA1 and CB1809 was higher after growth in peat extract than in the defined medium control. Cells grown in water extracts of peat exhibit morphological changes similar to those observed after growth in moist peat. Electron microscopy revealed thickened plasma membranes, with an electron-dense material occupying the periplasmic space in both TA1 and CB1809. Growth in peat extract also resulted in changes to polypeptide expression in both strains, and peptide analysis by liquid chromatography-mass spectrometry indicated increased expression of stress response proteins. Our results suggest that increased capacity for desiccation tolerance in rhizobia is multifactorial, involving the accumulation of trehalose together with increased expression of proteins involved in protection of the cell envelope, repair of DNA damage, oxidative stress responses, and maintenance of stability and integrity of proteins.     

Proportional mixture of two rarefaction/extrapolation curves to forecast biodiversity changes under landscape transformation

Progressive habitat transformation causes global changes in landscape biodiversity patterns, but can be hard to quantify. Rarefaction/extrapolation approaches can quantify within‐habitat biodiversity, but may not be useful for cases in which one habitat type is progressively transformed into another habitat type. To quantify biodiversity patterns in such transformed landscapes, we use Hill numbers to analyse individual‐based species abundance data or replicated, sample‐based incidence data. Given biodiversity data from two distinct habitat types, when a specified proportion of original habitat is transformed, our approach utilises a proportional mixture of two within‐habitat rarefaction/extrapolation curves to analytically predict biodiversity changes, with bootstrap confidence intervals to assess sampling uncertainty. We also derive analytic formulas for assessing species composition (i.e. the numbers of shared and unique species) for any mixture of the two habitat types. Our analytical and numerical analyses revealed that species unique to each habitat type are the most important determinants of landscape biodiversity patterns.     

Macrophyte loss drives decadal change in benthic invertebrates in peatland drainage ditches

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Testate Amoebae Assemblages (Rhizopoda and Testacea) in the Peat Deposits of the Floodplain Terrace Swamp (the South of Forested Zone of Western Siberia)

Testate amoebae assemblages were investigated in the peat deposits of the floodplain terrace swamp located in the southern taiga subzone of Western Siberia. It was revealed that tests of amoebae were well preserved in the minerotrophic peat. Variations in the structure of assemblages show that these bioindicators are sensitive to changes in the environment. The dynamics of the water table depth in the swamp within an 8500-year period was determined according to the analysis of testate amoebae. It reflects the fluctuations of climate humidity during the Holocene.     

Organic matter sources and decay assessment in a <Emphasis Type="Italic">Sphagnum</Emphasis>-dominated peatland (Le Forbonnet,Jura Mountains,France): impact of moisture conditions

In a context of climate change peatlands may switch from a sink to a source of carbon (C). The induced positive feedbacks are closely linked to C dynamics, and thus to the fate of organic matter (OM) in the underlying peat. Our aims were to determine how moisture conditions in a Sphagnum-dominated peatland affect the dynamics of diagenetic sensitive OM which is thought to be the most reactive to warming effects. The approach was based on the identification of combined bulk and molecular bioindicators of OM sources and decay of peat profiles (up to 50 cm in depth) from two moisture conditions of the Le Forbonnet peatland (Jura Mountains, France). The (xylose + arabinose)/(galactose + rhamnose + mannose) ratio derived from the analysis of neutral monosaccharides was used to obtain indications on the botanical origin of the peat and tended to indicate a greater contribution of Cyperaceae in the deepest parts of the peat. Most bioindicators showed that OM decay increased with depth and was higher in the driest conditions. In these conditions, decay was shown by a loss of diagenetic sensitive oxygen-rich OM, probably leached by water table fluctuations. Decay intensity was also shown by the high ribose and lyxose contents at the peat surface, where microscopic observations also revealed relatively large quantities of fungal hyphae. The sugars could have arisen from microbial synthesis, primarily protozoan and fungal activity. These results suggest that water level changes preferentially impact biochemical changes in diagenetic sensitive OM, believed to be sensitive to drought events.     

The influence of agricultural system,stand structural complexity and landscape context on foraging birds in oil palm landscapes

Functional diversity, an important element of avian biodiversity, can be examined by quantifying foraging guild composition. Understanding the ecological processes that underpin functional diversity of birds in oil palm Elaeis guineensis landscapes is important because different foraging guilds are likely to be influenced in different ways by land use practices. We surveyed birds at 55 sites within oil palm landscapes and at 20 sites within logged peat swamp forest, recording 208 species belonging to 19 foraging guilds. Oil palm landscapes supported a lower abundance of insectivorous, granivorous and omnivorous birds than did logged peat swamp forest despite the latter being severely degraded due to intensive timber extraction. However, abundances of other groups of foraging birds, such as raptors and wetland taxa, were higher in oil palm landscapes than logged peat swamp forest. Frugivorous species were more abundant in smallholdings than plantation estates, probably because of the presence of native trees. Foraging guild diversity was explained by stand‐level attributes such as stand age, vegetation cover, epiphyte persistence and canopy cover. However, each foraging guild exhibited unique responses to different oil palm management regimes and stand‐level attributes. Only arboreal omnivores and terrestrial frugivores were affected by the proximity of nearby natural forest. This diversity of responses implies that the occurrence of particular avian foraging guilds may not be a suitable ecological indicator of best‐practice palm oil production. Our study also suggests that multiple conservation measures will be needed in oil palm landscapes irrespective of management regimes, including: (1) the maintenance of ground layer vegetation cover; (2) the pruning of oil palm canopy to permit light penetration to the ground layer; (3) re‐vegetation of parts of oil palm landscapes with native trees; and (4) retention of natural and/or secondary forest patches within the boundaries of plantations.     

Climate change effects on carbon and nitrogen mineralization in peatlands through changes in soil quality

Climate change will directly affect carbon and nitrogen mineralization through changes in temperature and soil moisture, but it may also indirectly affect mineralization rates through changes in soil quality. We used an experimental mesocosm system to examine the effects of 6‐year manipulations of infrared loading (warming) and water‐table level on the potential anaerobic nitrogen and carbon (as carbon dioxide (CO₂) and methane (CH₄) production) mineralization potentials of bog and fen peat over 11 weeks under uniform anaerobic conditions. To investigate the response of the dominant methanogenic pathways, we also analyzed the stable isotope composition of CH₄ produced in the samples. Bog peat from the highest water‐table treatment produced more CO₂ than bog peat from drier mesocosms. Fen peat from the highest water‐table treatment produced the most CH₄. Cumulative nitrogen mineralization was lowest in bog peat from the warmest treatment and lowest in the fen peat from the highest water‐table treatment. As all samples were incubated under constant conditions, observed differences in mineralization patterns reflect changes in soil quality in response to climate treatments. The largest treatment effects on carbon mineralization as CO₂ occurred early in the incubations and were ameliorated over time, suggesting that the climate treatments changed the size and/or quality of a small labile carbon pool. CH₄ from the fen peat appeared to be predominately from the acetoclastic pathway, while in the bog peat a strong CH₄ oxidation signal was present despite the anaerobic conditions of our incubations. There was no evidence that changes in soil quality have lead to differences in the dominant methanogenic pathways in these systems. Overall, our results suggest that even relatively short‐term changes in climate can alter the quality of peat in bogs and fens, which could alter the response of peatland carbon and nitrogen mineralization to future climate change.     

Comparative assessment of chelated spent mushroom substrates as casing material for the production of Agaricus bisporus

Spent mushroom substrate (SMS) leached with water or treated with chelating agents to remove metal cations, pasteurised to remove any harmful micro-organisms and mixed with peat has potential as a casing material for mushroom production. The microbial and chemical changes in SMS after treatment with citric acid, ethylene diaminetetraacetic acid (EDTA) and water were compared; treatment with the chelating agents resulted in lower ash content, conductivity and minerals, higher fibre fractions, carbon, hydrogen and nitrogen. The microbial and chemical changes in the materials after treatment with the two chelators and water were compared. Blending peat with the heat-treated materials at a ratio of 1:1 resulted in improved physical properties. The casings prepared from the test materials and the control, consisting of 100% peat, were compared after neutralising with lime for their productivity in a mushroom yield trial. As expected, the compost bags cased with the control were the most productive compared to the other casings. Of the three treated materials, casing prepared from SMS treated with EDTA blended with peat was the most productive. Dry matter of harvested mushrooms from chelated-SMS casings was significantly higher than the control casing. Comparison of the main components of peat and chelated SMS revealed that the major differences were in the proportions of ash, lipid, lignin and fibre fractions. The stability of some of these components, when complexed with metal cations present in lime may play an important role in determining the composition of the cell wall in fruiting bodies leading to high dry matter content. Received: 19 November 1998 / Received revision: 29 March 1999 / Accepted: 6 April 1999     

Management of the margins in cutover bogs: ecological conditions and effects of afforestation

Several studies contributed to the development of restoration techniques for open Sphagnum-dominated habitats on peat-extracted bogs. Yet, in exception to some afforestation efforts, connectivity between restored sites and surrounding landscapes has received little attention. The general goal of this study is to ameliorate management of very shallow peat fields (<30 cm) located within the margins of peat-extracted bogs. Firstly, to assist decision making in peatland management, baseline ecological conditions, peat physicochemistry and spontaneous vegetation recolonization were assessed for 18 of these fields. This first study revealed that (1) concentrations of several macro-nutrients are almost one order of magnitude lower for unrestored fields than previously characterized natural lagg habitats of the same region, and (2) there is little spontaneous colonization. In a second study, peat chemistry and soil/air microclimate were evaluated in plantations established on shallow residual peat (a 21-year-old Larix laricina plantation and an 18-year-old Picea mariana plantation) and compared to adjacent unrestored shallow bare-peat fields. This second study showed that afforested peat fields are characterized by (1) a soil enriched in nutrients, notably in N, P, and K, and (2) a more humid and cooler microclimate at the soil/air interface, with less daily humidity and temperature fluctuations. These results indicate that afforestation is an appropriate approach to start an ecological recovery. Yet, the absence of natural recolonization by herbs and mosses in the understory of afforested peat fields suggests that reintroduction of appropriate understory species should also be considered if the goal is to restore a fully functional ecosystem.     

Evolution of a multidimensional architectural landscape under urban regeneration: A case study of Jinan,China

Urban regeneration is a key to achieving the main goals of China's urbanisation plan. How to analyse the urban landscape of the rapid development in order to meet the challenges of urban planning and build liveable cities is a concern for both government and society. This analysis is based on a case study on downtown Jinan, China, covering the period 2001–2011. It explores urban architectural changes in the horizontal and vertical landscapes after a decade of urban regeneration, focusing on two aspects: construction purpose and number of floors. The study uses the land use transfer matrix method, along with landscape indexes and spatial autocorrelation analysis, based on cadastral data. Results show that the horizontal architectural landscape changed at the city's edges, with no apparent change in the city centre. With changes in urban functions, horizontal landscapes became broken, but patch shapes did not manifest obvious changes. Residential, commercial, and industrial landscapes were the dominant types. Most converted areas became residential landscapes. Vertical landscapes tended to feature upward development. Patch shapes became more complex and broken, landscape richness increased, and building types became less densely aggregated. The dominant landscape type changed from bungalows to multi-layer and low-layer buildings. Vertical space utilisation became increasingly intensive. Urban regeneration was carried out locally. Respective areas marked by horizontal or vertical architectural renewal showed significant positive spatial correlation, implying increasing spatial centralisation. Vertical landscape patches largely changed in line with the horizontal types, but not the other way round. Ramshackle areas and shantytowns were transformed. Urban land use developed intensively, forming vertically dense landscapes. These results will serve as reference source for urban planning, regeneration, land resources management, urban architectural design and layout, optimisation of the ecological environment, and construction of liveable cities.     

Organic matter accumulation in western boreal saline wetlands: A comparison of undisturbed and oil sands wetlands

Reconstructing landscapes after open pit mining of the Canadian oil sands presents enormous challenges. Freshwater peatlands dominate the pre-disturbance landscape; however, elevated salinity in the post-disturbance landscape will exclude the use of many freshwater vegetation species for reclamation. Successful reclamation will require plants to grow and accumulate peat despite elevated salinity. We evaluated the potential of salt-tolerant plants to accumulate peat by integrating plant production and decomposition rates in natural and oil sands wetlands across a salinity gradient. These wetlands were dominated by marsh-like vegetation with relatively rapid decomposition, especially of the belowground plant material. Aboveground production was high enough to compensate for rapid decomposition, resulting in mean annual organic matter accumulation of 307 g m^?2. Thus, both natural wetlands (which despite the elevated salinity had peat deposits >35 cm) and the oil sands wetlands accumulated organic matter during the study. There is potential for peat to accumulate in future oil sands wetlands, although long-term accumulation rates may be slower than in undisturbed freshwater fens and bogs. A reliable water supply and a host of other factors will be required for wetlands to accumulate organic matter, and eventually peat, in the post-mining landscape.     

Plant recolonization of reclamation areas from patches of salvaged forest floor material

Question

Understorey development is a great challenge in the restoration of many forest sites, particularly when sources of vegetation propagules are scarce. Can placement of propagule‐rich soil patches within reclaimed landscapes otherwise covered with propagule‐poor material promote the dispersal of vegetation from the patches into the surrounding areas?

Location

Large reclamation site in the Canadian (Alberta) boreal forest.

Method

Patches of propagule‐rich forest floor material were placed within a matrix of propagule‐poor peat material. Vegetation assessments (cover estimates, seed rain) were done surrounding these patches in the third and fourth growing seasons.

Results

There was significant egress of species from the patches into the peat after four growing seasons, and overall species associated with the patches had higher cover in the peat than species that were associated with the peat itself. While wind‐dispersed herbaceous species from the patches were found at the leading edge of the egressing community, most species used vegetative propagation, resulting in short egress distances. Several patch‐associated species were found in seed rain collected on the peat areas but were not observed in this material, suggesting seedbed limitations.

Conclusion

Despite the relatively short distance of egress, this experiment suggests that placement of propagule‐rich soil material within reclaimed landscapes will promote egress into adjacent propagule‐poor soil material.     

In search of a hydrological explanation for vegetation changes along a fen gradient in the Biebrza Upper Basin (Poland)

The understanding of succession from rich fen to poorer fen types requires knowledge of changes in hydrology, water composition, peat chemistry and peat accumulation in the successional process. Water flow patterns, water levels and water chemistry, mineralisation rates and nutrient concentrations in above-ground vegetation were studied along a extreme-rich fen-moderate-rich fen gradient at Biebrza (Poland). The extreme-rich fen was a temporary groundwater discharge area, while in the moderate-rich fen groundwater flows laterally towards the river. The moderate-rich fen has a rainwater lens in spring and significant lower concentrations of calcium and higher concentrations of phosphate in the surface water. Mineralisation rates for N, P and K were higher in the moderate-rich fen. Phosphorus concentrations in plant material of the moderate-rich fen were higher than in the extreme-rich fen, but concentrations of N and K in plant material did not differ between both fen types. Water level dynamics and macro-remains of superficial peat deposits were similar in both fen types.We concluded that the differences observed in the moderate-rich and the extreme-rich fens were caused by subtile differences in the proportion of water sources at the peat surface (rainwater and calcareous groundwater, respectively). Development of an extreme-rich fen into a moderate-rich fen was ascribed to recent changes in river hydrology possibly associated with a change in management practices. The observed differences in P-availability between the fen types did not result in significantly different biomass. Moreover, biomass production in both fen types was primarily N-limited although P-availability was restricted too in the extreme-rich fen. Aulacomnium palustre, the dominant moss in the moderate-rich fen, might be favoured in competition because of its broad nutrient tolerance and its quick establishment after disturbance. It might outcompete low productive rich fen species which were shown to be N-limited in both fens. We present a conceptual model of successional pathways of rich fen vegetation in the Biebrza region.