Dinoflagellate resting cysts as factors in phytoplankton ecology of the North Sea

The occurrence and distribution of dinoflagellate resting cysts were investigated at 11 locations in the south-eastern part of the North Sea. Twenty-six known cyst species and 7 unknown cyst types, which may act as seed population for planktonic dinoflagellate blooms, have been recorded for the first time in the area. The most common cysts in recent sediments were those ofScrippsiella trochoidea, Zygabikodinium lenticulatum, Peridinium dalei, Scrippsiella lachrymosa, Protoceratium reticulatum, Protoperidinium denticulatum, andP. conicum. At all stations,S. trochoidea dominated the cyst assemblages with a maximal abundance of 1303 living cysts/cm³ in the uppermost half centimetre. Cysts of the potentially toxic dinoflagellatesAlexandrium cf.excavatum andA. cf.tamarense were scarce. In the upper 2-cm layer of sediment, dinoflagellate cysts were found in concentrations of 1.8 up to 682 living cysts/cm³. Empty cysts constituted 22–56% of total cyst abundance. The comparative distribution of the cysts showed a general increase in abundance from inshore sites to the offshore area, whereby sandy stations exhibited the lowest cyst abundance and diversity. The wide distribution of living and empty cysts ofScrippsiella lachrymosa suggests that its motile form, which has not been officially recorded in the area until now, is a common plankton organism in German coastal waters. The relatively high abundance of cysts in recent sediments demonstrates the potential importance of benthic resting stages for the initiation of dinoflagellate blooms in the study area.     

Subtidal and intertidal mussel beds (Mytilus edulis L.) in the Wadden Sea: diversity differences of associated epifauna

In 1997 and 1998, surveys were performed to compare species composition, abundance and diversity of non-attached epifauna (>1 mm) in low intertidal and adjacent shallow subtidal zones of three mussel beds (Mytilus edulis L.) near the island of Sylt in the North Sea. The community structure was similar when compared within tidal zones: no significant differences in species numbers and abundances were recorded between locations and between years. A comparison between tidal zones, however, revealed higher diversity, species densities and total species numbers in the subtidal (per 1,000 cm²: H ′=2.0±0.16; 12 ±1 species density; 22 species) than the intertidal zone (per 1,000 cm²: H ′=0.7±0.27; 6±2 species density; 19 species). Abundances significantly dropped with increasing submergence from 2,052 (±468) m^–2 to 1,184 (±475) m^–2. This was mainly due to significantly higher densities of both juvenile periwinkles, Littorina littorea, and crabs, Carcinus maenas, in intertidal mussel beds. However, many less dominant species were significantly more abundant in subtidal mussel beds. This study revealed that in the non-attached epifaunal community of mussel beds the tidal level effect within metres was strong, whilst the spatial variability in a much wider (kilometre) range but the same tidal level was negligible. The high epifaunal diversity in the subtidal zone suggests that the protective measures for mussel beds against the effects of mussel fishery should be extended from the intertidal to the subtidal zone, if the integrity of the mussel bed community in the Wadden Sea National Park is to be maintained. Electronic Publication     

Meiofaunal (re)colonization of the Arctic intertidal (Hornsund,Spitsbergen) after ice melting: role of wrack deposition

Intertidal meiobenthos of Hornsund—the southernmost fjord of Spitsbergen—was investigated between July and September 2005. Mean total meiofaunal densities ranged between 4.3 and 328 ind. 10 cm⁻². Nematode assemblages were impoverished in terms of the number of genera when compared with those from the western Spitsbergen coast (11 vs. 25–28 genera in total, respectively). It is suggested that severe environmental conditions in the southern part of Spitsbergen overcome the adaptation skills of many nematode species and hamper the establishment of a diverse community. Comparatively high nematode numbers on a beach subject to heavy macroalgal wrack input contrast sharply with numerically poor communities in sparse-wrack beaches (up to 315 vs. 31 ind. 10 cm⁻², respectively). It is suggested that the wrack input to the Arctic beach may substantially influence the richness and composition of the intertidal meiobenthic community. Nematode assemblages were dominated by extreme colonizers: Geomonhystera disjuncta and rhabditids. Their relatively high densities in beach sediments recorded at the beginning of July indicate their ability to recover rapidly after the winter period and to effective (re)colonization of the intertidal habitat just after the ice melt. Average concentration of rhabditids and monhysterids associated with macroalgal wrack deposited on the upper shore was as high as 52 × 10³ individuals per gram of the substrate. It is hypothesized that nematodes can play a substantial role in the wrack decomposition in the Arctic intertidal.     

Characterization of phosphorus fractions in the sediments of a tropical intertidal mangrove ecosystem

Solid phases of phosphorus fractions in the surface and core sediments were studied to understand the biogeochemical cycling and bioavailability of phosphorus in the Pichavaram intertidal mangrove sediments of India. Total P in surface and core sediments ranged between 451–552 and 459–736 μg g⁻¹ respectively and Fe bound P was the dominant fraction. Low levels of Fe bound P in the mangrove zone than the two estuarine zones may be because of high salinity inhibition of phosphate adsorption onto the Fe-oxides/hydroxides. Post-depositional reorganization of P was observed in surface sediments, converting organic P and Fe bound P into the authigenic P. High levels of organic P in the mangrove zone is primarily due to intensive cycling and degradation of organic matter and adsorption of phosphate on the organic molecules. The burial rates and regeneration efficiency of P in the intertidal mangrove ecosystem ranged from 5.41 to 7.27 μmol P cm⁻² year⁻¹ and 0.122 to 0.233 μmol P cm⁻² year⁻¹, respectively. High burial efficiency (≈99%) of P proves the earlier observation of limiting nature of P for the biological productivity. Further, bioavailable P (exchangeable P + Fe bound P + organic P) constituted a considerable proportion of sedimentary P pool of which an average accounted for 55 and 50% in surface and core sediments respectively. The results indicate that significant amount of P is locked in sediments in the form of authigenic P and detrital P which makes P as a limiting nutrient for the biological productivity.     

Resting eggs of conchostracans and their adaptive possibilities

The dimensional specifications and morphology of the resting eggs of ten conchostracan species (Cyzicus tetracerus, Eocyzicus orientalis, Caenestheria davidi, C. perrieri, Leptestheria dahalacensis, Eoleptestheria ticinensis, Limnadia lenticularis, Imnadia yeyetta, Lynceus brachyurus, and L. dauricus) have been studied. The data are presented on the number of eggs produced by females. Unlike other crustaceans, no correlation between the eggs size and their quantity was found. Although the number of eggs can vary one to two times, their size is relatively stable (variation coefficient <5%). The wet (1.5–5.4 μg) and dry (0.41–0.93 μg) weights of eggs and the share of clutch (11.4–21.6%) in the female’s wet weight were determined for eight species. The polyfunctionality of the external envelope of the egg was considered under anhydrobiosis conditions.     

Evaluation of ammonium and phosphate release from intertidal and subtidal sediments of a shallow coastal lagoon (Ria Formosa – Portugal): a modelling approach

During an annual cycle, overlying water and sediment cores were collected simultaneously at three sites (Tavira, Culatra and Ramalhete) of Ria Formosa’s intertidal muddy and subtidal sandy sediments to determine ammonium, nitrates plus nitrites and phosphate. Organic carbon, nitrogen and phosphorus were also determined in superficial sediments. Ammonium and phosphate dissolved in porewater were positively correlated with temperature (P < 0.01) in muddy and sandy sediments, while the nitrogen-oxidized forms had a negative correlation (P < 0.02) in muddy sediments probably because mineralization and nitrification/denitrification processes vary seasonally. Porewater ammonium profiles evidenced a peak in the top-most muddy sediment (380 μM) suggesting higher mineralization rate when oxygen is more available, while maximum phosphate concentration (113 μM) occurred in the sub-oxic layer probably due to phosphorus desorption under reduced conditions. In organically poor subtidal sandy sediments, nutrient porewater concentrations were always lower than in intertidal muddy sediments, ranging annually from 20 μM to 100 μM for ammonium and from 0.05 μM to 16 μM for phosphate. Nutrient diffusive fluxes predicted by a mathematical model were higher during summer, in both muddy (104 nmol cm⁻² d⁻¹––NH₄⁺; 8 nmol cm⁻² d⁻¹––HPO₄⁻²) and sandy sediments (26 nmol cm⁻² d⁻¹––NH₄⁺; 1 nmol cm⁻² d⁻¹––HPO₄⁻²), while during lower temperature periods these fluxes were 3–4 times lower. Based on simulated nutrient effluxes, the estimated annual amount of ammonium and phosphate exported from intertidal areas was three times higher than that released from subtidal areas (22 ton year⁻¹––NH₄⁺; 2 ton year⁻¹––HPO₄⁻²), emphasizing the importance of tidal flats to maintain the high productivity of the lagoon. Global warming scenarios simulated with the model, revealed that an increase in lagoon water temperature only produces significant variations (P < 0.05) for NH₄⁺ in porewater and consequent diffusive fluxes, what will probably affect the system productivity due to a N/P ratio unbalance.     

Benthos structure on tropical tidal flats of Australia

General features of benthos communities of tropical tidal flats are defined from northeast Australia, based on surveys from 1988 to 1991 in Hinchinbrook Channel and in the Haughton River estuary. A zonation of benthic communities is described. Total abundances for macrofauna averaged 31 individuals 200 cm⁻², mesofauna (defined as infauna smaller than 0.5 mm and retained on a 0.25 mm sieve) averaged 16 individuals 10 cm⁻² and meiofauna averaged 231 individuals 5 cm⁻². The two study sites were similar in their abundance structures, but species due to a higher diversity of polychaeta in the Channel (120 species, H′=3.80 vs. 29 species and H′=1.78 in the Haughton estuary). Species densities were comparable at both sites and rather low (6 species 177 cm⁻², 2–7 species 10 cm⁻² and 5 meiobenthic Plathelminth species 5 cm⁻²). Over 50% of the species encountered were represented by less than three individuals. Deposit feeders, dominated the assemblages both in terms of individuals as well as species numbers. Tropical tidal flats are compared with their temperate counterparts and approaches for future research in tropical benthos communities are recommended.     

Leaf and bud demography and shoot growth in evergreen and deciduous trees of central Himalaya, India

Leaf and bud demography and shoot growth were studied in 10 evergreen (ES) and 15 deciduous (DS) tree species occurring between 600 and 2200 m elevation in the central Himalayan mountains in India. Results were analyzed to help explain why ES prevail in the vegetation of this region, even though the number of ES is no greater than for DS. Although each species had its own pattern with regard to leaf and bud demography and seasonality of shoot extension and radial growth, it was possible to group the species on the basis of shoot growth phenology. In most species, leaves emerged during March-April, at the onset of warm and dry summer season. The ES recruit leaves in shoots more rapidly than the DS. Across all species, peak number of leaves per shoot (5.8–20.7), peak leaf area per shoot (116.2–1559.2 cm²), peak number of vegetative buds per shoot (1.9–14.5), bud survival per shoot (23–84%), shoot extension growth (6.4–40.8 cm) and shoot extension period (13–30 weeks) varied considerably. The peak leaf area per shoot (587.7 vs. 246.7 cm²) and shoot extension growth (19.3 vs. 11.2 cm) were significantly greater for DS than for ES, and these two functional groups of species were clearly separable with regard to shoot growth characteristics.Results indicate that rapid recruitment of leaf crop in the shoots, longer leaf life-span, and access to ground water due to deep roots were some of the advantages, the ES had over the DS, that may have likely enable them to maintain growth for a longer period in this region of warm winters and longer winter day length as compared to temperate climates. In the shallow rooted DS, shoot growth seems to be much affected by a seasonal drought in winter and they are likely to be affected more in the event of failure of monsoon rains in this region.     

Phenotypic plasticity for skeletal growth,density and calcification of <Emphasis Type="Italic">Porites lobata</Emphasis> in response to habitat type

A reciprocal transplant experiment (RTE) of the reef-building coral Porites lobata between shallow (1.5 m at low tide) back reef and forereef habitats on Ofu and Olosega Islands, American Samoa, resulted in phenotypic plasticity for skeletal characteristics. Transplants from each source population (back reef and forereef) had higher skeletal growth rates, lower bulk densities, and higher calcification rates on the back reef than on the forereef. Mean annual skeletal extension rates, mean bulk densities, and mean annual calcification rates of RTE groups were 2.6–9.8 mm year⁻¹, 1.41–1.44 g cm⁻³, and 0.37–1.39 g cm⁻² year⁻¹ on the back reef, and 1.2–4.2 mm year⁻¹, 1.49–1.53 g cm⁻³, and 0.19–0.63 g cm⁻² year⁻¹ on the forereef, respectively. Bulk densities were especially responsive to habitat type, with densities of transplants increasing on the high energy forereef, and decreasing on the low energy back reef. Skeletal growth and calcification rates were also influenced by source population, even though zooxanthella genotype of source colonies did not vary between sites, and there was a transplant site x source population interaction for upward linear extension. Genetic differentiation may explain the source population effects, or the experiment may have been too brief for phenotypic plasticity of all skeletal characteristics to be fully expressed. Phenotypic plasticity for skeletal characteristics likely enables P. lobata colonies to assume the most suitable shape and density for a wide range of coral reef habitats.     

Effect of density on spatial distribution,pit formation and pit diameter of Myrmeleon acer Walker, (Neuroptera: Myrmeleontidae): patterns and processes

The effect of increasing population density on the formation of pits, their size and spatial distribution, and on levels of mortality was examined in the antlion Myrmeleon acer Walker. Antlions were kept at densities ranging from 0.4 to 12.8 individuals per 100 cm². The distribution of pits was regular or uniform across all densities, but antlions constructed proportionally fewer and smaller pits as density increased. Mortality through cannibalism was very low and only occurred at densities greater than five individuals per 100 cm². Antlions in artificially crowded situations frequently relocated their pits and when more space became available, individuals became more dispersed with time. Redistribution of this species results from active avoidance of other antlions and sand throwing associated with pit construction and maintenance, rather than any attempt to optimise prey capture per se.     

Seasonal, altitudinal and host plant-related variation in the abundance of aphids (Insecta, Hemiptera) on sub-Antarctic Marion Island

Although aphids are the most species-rich group of invasive alien insects across the Southern Ocean Islands, their biology on the islands is poorly known. In this study, host plant-related, seasonal and altitudinal variation in the abundance of the three aphid species (Macrosiphum euphorbiae, Myzus ascalonicus, Rhopalosiphum padi) found on sub-Antarctic Marion Island is examined. Myzus ascalonicus is the most abundant of the species, reaching densities of c. 2,400 individuals per 1,200 cm² on the indigenous Acaena magellanica (Rosaceae) and 479 individuals per 1,200 cm² on the indigenous Cotula plumosa (Asteraceae), with lower numbers at elevations up to 300 m and a pronounced seasonal peak in December-February. Macrosiphum euphorbiae occurs on the same plant species in densities of between c. 11 individuals per 1,200 cm² on C. plumosa and c. 200 individuals per 1,200 cm² on A. magellanica, and with a pronounced summer peak in December. In both species, small numbers of winged forms are found (c. 1–5%), although they are permanently parthenogenetic on the island. Rhopalosiphum padi is also permanently parthenogenetic on the island and likewise shows a December peak in abundance. The current data suggest that low ambient temperatures, which are close to the lower development threshold of R. padi, and other temperate aphid species, limit development in winter, thus leading to a decline in abundance.     

Tuning of electron delocalization in polynuclear mixed-valence clusters by super-exchange and double exchange

 Values for the exchange-coupling constant J and the double-exchange parameter B have been estimated for dimeric and hexameric mixed-valence iron clusters. For sulfur-bridged species the range of J values is 300–450 cm^–1, and B values vary between 320 and 400 cm^–1. For an OH-bridged diiron cluster B is as large as 1300 cm^–1. Received and accepted: 23 January 1996     

田间不同植物上烟粉虱种群密度

对廊坊地区田间81种植物上烟粉虱的发生情况进行了系统调查。结果表明,烟粉虱可为害其中44种植物,且在不同的寄主植物上烟粉虱的种群密度有显著差异;而玉米、高粱和小米等37种植物上无烟粉虱为害。烟粉虱在香水薄荷、荆芥、甘草、薄荷、藿香、益母草、猪屎豆、白晶菊、牛膝、待宵草、蓝蓟、紫花苜蓿、极香罗勒上的虫口密度最高,危害级别达到4级(每100 cm2叶片虫口密度大于50头)。在蜀葵、向日葵和烟草上每100 cm2叶片烟粉虱虫口密度较低,但单株虫口密度较高。鉴于向日葵、玉米、高粱在中国北方棉花产区广泛种植,玉米和高粱的植株高大,且烟粉虱为害对向日葵产量影响极小,可考虑选用向日葵作为田间诱集植物,玉米和高粱作为屏障植物辅助控制棉田烟粉虱。     

The current state of the Demoiselle crane population in the Transural steppe

The Demoiselle crane population was studied in the southern Chelyabinsk region (52°12′N; 60°21′E) during 1988–2008. Counts of nesting pairs were annually conducted over an area of 100–130 km² in May. The number of breeding pairs varied from 6.5 to 9.5 per 100 km²; on average, there were 8 pairs per 100 km² during 1989–1991. In 2000–2008, the population density increased from 7.5 to 12 pairs per 100 km², on average, 9.3 pairs per 100 km2. Demoiselle crane nesting in steppe pastures and perennial grass fields has been rarely observed for the last decade. Now the main nesting biotopes of the species are stubble fields accounting for up to 70% of all nidification cases documented. The decline in agricultural production in recent decades has resulted in the appearance of long-fallow lands, in which 17 to 35% crane pairs nest.     

Ecology and management of moorland pools: balancing acidification and eutrophication

Moorland pools originally are shallow, often hydrologically isolated, soft-water bodies, with a low productivity. Some thousands of moorland pools originated from the late Pleistocene onwards in the heathland landscape in The Netherlands and adjacent areas, where soils have a poor buffering capacity. As the pools are largely fed by atmospheric precipitation, they are very vulnerable to changes in the environment, e.g. eutrophication and acidification. Moorland pools are exposed to very high rates of wet atmospheric deposition: 44–50 mmol m⁻² yr⁻¹ sulphate and 84–103 mmol m ⁻² yr⁻¹ ammonium. Mass budgets indicate that 20–70% of the input of sulphate by precipitation is reduced, 40–100% of the ammonium input escapes to the air or sediments, apparently due to nitrification, and 90–100% of incoming nitrate disappears. The production of alkalinity ranges from 12 to 52 meq m⁻² yr⁻¹. The efficiency of these processes augments with pH-values of surface water increasing from 4.1 to 5.4. The accumulation of reduced sulphur compounds in the sediments is a threat in extremely dry summers, when desiccation causes oxydation of these compounds, resulting in very low pH-values (≤ 3.7). Acidification by acid atmospheric deposition and eutrophication by agricultural acidification are the main threats to the moorland pool ecosystems and affect the species composition of assemblages of aquatic macrophytes, desmids, diatoms, macrofauna, fishes and amphibians, as has been shown by comparison of old and recent records on their distribution and paleolimnological methods. Afforestation exacerbates acidification and also reduces wind dynamics. Particularly the decrease of isoetids and desmids by both processes indicate the biological impoverishment of the pools. Reductions of (potential) acid atmospheric deposition to less than 40 mmol m⁻² yr and of ammonia to less than 30 mmol m⁻² yr are necessary for recovery of the moorland pools. Methods for the addition of buffering material to a number of moorland pools, to counteract acidification until these deposition rates have lowered sufficiently, are given, as well as other methods for restoring the biological quality of moorland pools.     

Reaction of winter oilseed rape callus to different concentrations of elicitors: pectinase or chitosan

The aim of the presented methodical experiments was 1) the evaluation if callus of winter oilseed rape (Brassica napus var. oleifera L.) initiates a defence reaction to fungal elicitors: pectinase (polygalacturonase) or chitosan, and 2) the choice of the elicitor doses, which evoke the strongest tissue reaction. The results obtained will be used in the next experiments relating the studies of pathogenesis mechanisms proceeding in rape plants infected by necrotrophic fungi. The defence response was estimated on the basis of changes in electrolyte leakage from cells, metabolic efficiency, phenolic content and catalase activity. In the experiment pectinase was used at concentration of 3, 8, 16, 133 and 166 μl per 1 cm³ of culture medium while chitosan at: 25, 50, 75 and 100 μg·cm⁻³. Both elicitors increased cell membrane permeability: pectinase at the doses equal or greater to 16 μl·cm⁻³ while chitosan of 25 μg·cm⁻³. The greatest metabolic inefficiency was observed in calli elicited with 16 μl·cm⁻³ pectinase and with chitosan of 100 μg·cm⁻³. The decrease in phenolic content was noted under influence of most doses of both elicitors. The highest catalase activity was evoked by pectinase of 8 μl·cm⁻³ and chitosan of 75 and 100 μg·cm⁻³. The results indicated that 8–16 μl·cm⁻³ of pectinase and 100 μg·cm⁻³ of chitosan caused the strongest defence reaction of oilseed rape tissue.     

Gymnodinium catenatum Graham (Dinophyceae)in Europe: a growing problem?

The microreticulate resting cyst of the potentially toxic, chain-forming,unarmoured neritic dinoflagellate Gymnodinium catenalum Graham1943. the planktonic stage of which is not known from NorthEuropean waters, is reported for the first time from recentGerman coastal sediments of the North Sea and Baltic Sea. Insandy mud sediments of the German Bight, a maximum of 8 5 livingcysts cm^–3 were found. In Kiel Bight sediments G.catenalumwas found in maximum concentrations of 17.0 living cysts cm^–3.In surface waters of the German Bight resuspended G catenatumcysts were observed at concentrations of up to 3.6 cysts l^–1.Successful germination experiments conducted with natural seawatershow that the occurrence of a vegetative form of G.catenatumin northern Europe is very likely. The present study highlightsthat cyst surveys provide an important tool for the evaluationof areas with potential toxicity problems, as they may indicatethe presence of hitherto overlooked species in the water column.     

Influences of sedimentation and hydrodynamics on the spatial distribution of Alexandrium catenella/tamarense resting cysts in a shellfish farming lagoon impacted by toxic blooms

Since resting cysts are a potential seeding source for blooms, the presence of these cysts in sediments is a marker of an established population for a number of harmful algal species. The spatial patterns of cyst density in relation to sediment characteristics and hydrodynamics are still largely misunderstood. This study investigated the spatial distribution of resting cysts belonging to the Alexandrium tamarense species complex (Dinophyceae) in sediments of a Mediterranean coastal lagoon (Thau Lagoon, France). This lagoon, hosting shellfish farming, is regularly impacted by toxic Alexandrium catenella blooms. The average cyst density across the whole lagoon was rather low, <20 cysts g⁻¹ of dry sediment (DS). However, densities varied widely among sampled stations, with the highest density (∼440 cysts g⁻¹ DS) recorded in a shallow cove named Crique-de-l’Angle, which is the only area where dense blooms of A. catenella and A. tamarense have been recorded in the years preceding this survey. An analysis using spatial autoregressive models demonstrated that cyst densities were highly spatially autocorrelated (indicating that close stations tended to have more similar cyst densities) with accumulation sites. With respect to sediment characteristics (5 granulometric fractions <2 mm and biochemical components), the highest densities were found in silty sediments containing high proportions of water and organic matter. Nevertheless, the linkage between cyst density and sediment structure was not always verified; this reflected the influence of hydrodynamics on the sedimentation of cysts and sediment particles, and on the dispersal of cysts away from the bloom area by wind-induced currents, suggesting that hydrodynamics was responsible for the spatially autocorrelated distribution of cyst densities.     

Long-Term Growth and Succession in Restored and Natural Mangrove Forests in Southwestern Florida

We compared colonization, growth and succession from 1989 to 2000 in a restored mangrove site and in gap and closed canopy sites in a natural mangrove forest. The restored site was created in 1982 and planted with Rhizophora mangle (≈2 m⁻²) propagules. By 1989, Laguncularia racemosa, with densities up to 12.9 tree m⁻², was a dominant in all plots, although densities were greater at edge plots relative to inner plots, and near open water (west plots) relative to further inland (east plots), and in tall mangrove plots relative to scrub plots. Rhizophora mangle (1989 tree densities about 2 m⁻²) was a codominant in inner and scrub plots, while Avicennia germinans had the lowest densities (<1 tree m⁻²) in all plots. From 1989 to 2000 L. racemosa experienced reduced recruitment and apparent density-dependent mortality of canopy individuals in plots with high initial densities. Scrub plots experienced high rates of colonization by R. mangle and L. racemosa, rapid growth in height of all species (1989–1996), followed by a dieoff of L. racemosa in later years (1997–2000) as the canopy came to resemble that of tall mangrove plots. Colonization and growth rates were lower in gap and closed canopy regions of the natural forest relative to rates in the restored site. After 11 years, densities of L. racemosa were 10–20× lower and R. mangle slightly less in the gap relative to densities in tall mangrove plots in the restored site at the same age. Although the restored stand had converged with the natural forest by 2000 in terms of some factors such as species richness, vegetation cover, litterfall, and light penetration, trees were still much smaller and stem densities much higher. Full development of mature structure and ecological function will likely require decades more development.     

Vegetation heterogeneity and ditches create spatial variability in methane fluxes from peatlands drained for forestry

Drainage of peatlands for forestry starts a succession of ground vegetation in which mire species are gradually replaced by forest species. Some mire plant communities vanish quickly following the water-level drawdown; some may prevail longer in the moister patches of peatland. Drainage ditches, as a new kind of surface, introduce another component of spatial variation in drained peatlands. These variations were hypothesized to affect methane (CH₄) fluxes from drained peatlands. Methane fluxes from different plant communities and unvegetated surfaces, including ditches, were measured at the drained part of Lakkasuo mire, Central Finland. The fluxes were found to be related to peatland site type, plant community, water-table position and soil temperature. At nutrient-rich fen sites fluxes between plant communities differed only a little: almost all plots acted as CH₄ sinks (−0.9 to −0.4 mg CH₄ m⁻² d⁻¹), with the exception of Eriophorum angustifolium Honck. communities, which emitted 0.9 g CH₄ m⁻² d⁻¹. At nutrient-poor bog site the differences between plant communities were clearer. The highest emissions were measured from Eriophorum vaginatum L. communities (29.7 mg CH₄ m⁻² d⁻¹), with a decreasing trend to Sphagna (10.0 mg CH₄ m⁻² d⁻¹) and forest moss communities (2.6 mg CH₄ m⁻² d⁻¹). CH₄ emissions from different kinds of ditches were highly variable, and extremely high emissions (summertime averages 182–600 mg CH₄ m⁻² d⁻¹) were measured from continuously water-covered ditches at the drained fen. Variability in the emissions was caused by differences in the origin and movement of water in the ditches, as well as differences in vegetation communities in the ditches. While drainage on average greatly decreases CH₄ emissions from peatlands, a great spatial variability in fluxes is emerged. Emissions from ditches constantly covered with water, may in some cases have a great impact on the overall CH₄ emissions from drained peatlands.