Article

Recovery Succession of Native Plant Communities at Big Meadow Bog After Disturbance and Eutrophication from Herring Gulls

Authors:
  • St. Francis Xavier
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Abstract

On Brier Island in eastern Canada, ditching of Big Meadow Bog resulted in predictable shifts in the plant community as shrubs and trees proliferated across the drained landscape. The attraction of nesting gulls to the ditched bog and their daily foraging at distant mink farms was not predictable. To better understand the impacts of the nesting gulls, we performed a retrospective analysis of plant community disruption and recovery succession. Areas of gull-bared peat within Big Meadow Bog were colonized in succession by exotic grasses (e.g. Holcus lanatus) and annuals; raspberry (Rubus spp.) canes and biotically-dispersed Rosaceae shrubs; and wind-dispersed Ericaceae, fern, and tree species. There was no evidence of a persisting bog-species seedbank in the soil to aid post-gull revegetation, nor was there evidence of an exotic-weed seedbank to interfere with plant-community regeneration. The exotic-weed seedbank (6 thousand seeds m⁻²) declined to zero after 33 years (half-life = 3.6 years). In contrast, a secondary, native (mainly Juncus spp.) seedbank of similar magnitude, persisted. The recovered plant communities had swamp features (i.e., trees, ferns, tall shrubs). Whether or not Big Meadow Bog regains ombrotrophy will depend upon whether blocked ditches and reinstated water tables deter nesting gulls.

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... The bog was historically ombrotrophic, and after ditching it dried. Thereafter, woody plants, including raspberries (Rubus spp.) and fireweed (Epilobium spp.) increased (Hill et al., 2019;Spooner et al., 2017). Due to these changes in hydrology and vegetation, herring and great black-backed gulls (Larus marinus) colonized the site in the 1980s (Environment and Change Canada, 2018;Hill et al., 2019). ...
... Thereafter, woody plants, including raspberries (Rubus spp.) and fireweed (Epilobium spp.) increased (Hill et al., 2019;Spooner et al., 2017). Due to these changes in hydrology and vegetation, herring and great black-backed gulls (Larus marinus) colonized the site in the 1980s (Environment and Change Canada, 2018;Hill et al., 2019). The population at this colony has increased since drying and recently was estimated to host 3200 nesting pairs (Toms, 2016). ...
... The reference bog for this study colony is located ~0.8 km northwest of Big Meadow Bog. The reference bog is ombrotrophic, conditions that likely characterise Big Meadow Bog before it was ditched, and has no nesting herring gulls (Hill et al., 2019). ...
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1. The effects of increased nitrogen or phosphorus supply on the productivity of Sphagnum-dominated ombrotrophic bogs in northern and southern Sweden were studied. Atmospheric nitrogen deposition in southern Sweden (high-N site) exceeds that in northern Sweden (low-N site) by about tenfold. 2. Vertical height growth of the Sphagnum carpet was measured by the cranked-wire method. Length growth of individuals was measured by autoradiography after labelling with 14CO2. The results of both methods were significantly correlated, but the cranked-wire data were systematically lower. 3. Productivity of Sphagnum at the low-N site increased almost fourfold after additional nitrogen supply (4 g N m-2 year-1), but no increase was found after additional phosphorus supply (0.4 g P m-2 year-1). At the high-N site, phosphorus supply caused an almost threefold productivity increase, but nitrogen supply did not result in any productivity increase. Thus, in an area with a high atmospheric nitrogen supply, plant productivity is P-limited instead of N-limited. 4. At an intermediate nitrogen supply (2 g N m-2 year-1) the recovery of the supplied nitrogen in the Sphagnum carpet was not different for both sites (60% and 69%, respectively). However, at a high nitrogen supply (4 g N m-2 year-1) nitrogen recovery at the low-N site significantly exceeded that at the high-N site (73% and 47%, respectively). At the low-N site, the supplied phosphorus was not recovered, but at the high-N site the phosphorus recovery was 85% (intermediate phosphorus supply) and 100% (high phosphorus supply), respectively. 5. It is suggested that a high atmospheric nitrogen supply may affect the carbon balance of ombrotrophic bogs, because productivity is under these circumstances not N-limited, but decomposition is probably increased by high loads of nitrogen. In the end, this may turn these C-accumulating systems into C-emitting systems.
Article
We grew four perennial grass species (Poa pratensis, Agropyron repens, Agrostis scabra, and Schizachyrium scoparium) for 5 yr in monocultures and in pairwise competition plots on an experimental nitrogen gradient. The gradient contained plots ranging from 100% sand to 100% black soil, plus plots that received additional N fertilizer. To examine the impact of initial conditions on the long-term outcome of interspecific competition, three competitive situations were created: seed vs. seed competition (both species planned simultaneously), seed invasions (each species added as seed to year-old monocultures of the other), and vegetative invasions (dividers separating adjacent monocultures of two species removed after 1 yr). Extractable soil NO"3^- and NH"4^+ were measured to test if species differences in the concentration of available soil N in monoculture (i.e., R* for N, Tilman 1982) could predict the long-term outcome of competition. By year 5, Schizachyrium displaced or greatly reduced the biomass of both Poa and Agropyron on the soil mixture gradient (the mixed soils but not the added-N plots) independent of the wide range of starting conditions. On these soils, Schizachyrium monocultures had significantly lower soil concentrations of both NO"3^- and NH"4^+ than either Poa or Agropyron monocultures. Similarly, Agropyron displaced or greatly reduced the biomass of Agrostis by year 5. Agropyron monocultures had significantly lower concentrations of NO"3^- and NO"3^- + NH"4^+, but not NH"4^+, than Agrostis monocultures. In contrast, no competitive displacement occurred in competition between Poa and Agropyron, and initial differences persisted over 5 yr. Monocultures of these two species did not differ in NO"3^- concentration, but did differ for NH"4^+ and NO"3^- + NH"4^+. Thus, species differences in ability to deplete soil NO"3^- successfully predicted the outcome of competition for all four species pairs on the soil mixture gradient. If resource preemption or asymmetric competition had been the mechanism of competition, initial conditions would have affected the long-term outcome of competition. Rather, these results support the R* (i.e., resource reduction) model for competition for soil N. In the added-N fertilizer plots, Schizachyrium had decreased biomass in competition with both Poa and Agropyron. However, neither Agropyron nor Poa appeared to have an advantage when they competed with each other in the added-N plots. For these three species pairs, the 5-yr results of competition in the added-N plots, which had greatly reduced light availability because of increased production and litter accumulation, depended on initial conditions. In the fourth pair, Agrostis was displaced by Agropyron in all competition treatments in the added-N plots. Thus, we cannot reject the hypothesis that resource preemption (i.e., asymmetric competition) is important in light competition.
Article
This article presents a reconstruction of the development of the ombrotrophic Ga˛zwa peatland based on a high-resolution macrofossil analysis and AMS dating. Successional changes in the plant assemblages dominated by Sphagnum were influenced mainly by climate changes. Local fires occurred in the peatland, but did not have a substantial impact on the Sphagnum succession. The disappearance of the first stage of the ombrotrophic peatland, which was dominated by Sphagnum magellanicum and Sphagnum angustifolium, resulted from a decrease in the water level that was also recorded at a number of sites in Europe in approximately 3750 BC. The development of Sphagnum fuscum/rubellum assemblages in approximately 350 BC corresponds with a climate cooling that resulted from low solar activity. The reappearance of Sphagnum magellanicum in approximately AD 1650 corresponds with the Maunder Minimum of the Little Ice Age. The recent dominance of Sphagnum fallax is a result of the drainage of the peatland and of changes in the nearby vegetation. The paleoecology of Sphagnum contortum is also discussed. In the Ga˛zwa peatland, S. contortum occurred during two periods, 3700–3300 BC and 2850–2000 BC. The fossil occurrence of S. contortum in the Ga˛zwa peatland corresponds with its modern ecological requirements in the northern hemisphere. S. contortum occurred in the rich fen phase with Carex lasiocarpa, Comarum palustre, Menyanthes trifoliata and Meesia triquetra. The disappearance of S. contortum is assumed to have been caused by a trophic shift and the succession of a more acidophilic species, Sphagnum obtusum.
Article
Riparian wetlands are under heavy pressure from hydrological changes produced by dam construction and water diversion projects. There has been ample documentation of the relationship between the extent of flooding and the composition of shoreline plant communities, yet we have few models that allow us to predict the impact of altered flooding regimes on riparian wetlands. In the humid temperate zone, river regulation commonly affects the distribution of two major vegetation types: wooded wetland and herbaceous wetland. The practice of reducing peak floods and augmenting minimum river flows is often followed by the succession of herbaceous to wooded wetland. We used logistic regression models to describe the distribution of wooded wetland as a function of all possible combinations of seven hydrological variables. The variables were chosen to reflect the depth, duration, and time of flooding and were calculated for four different time intervals (3, 7, 12, and 18 growing seasons). Our best model was a combination of two variables: the last day of the first flood and the time of the second flood. For three of the four time intervals, the vegetation type was correctly identified as herbaceous or wooded for > 80% of the sample points. Our results suggest that models based on a few key environmental variables can be valuable tools in the conservation management of the vegetation of temperate and boreal zone wetlands.
Article
It is suggested that evolution in plants may be associated with the emergence of three primary strategies, each of which may be identified by reference to a number of characteristics including morphological features, resource allocation, phenology, and response to stress. The competitive strategy prevails in productive, relatively undisturbed vegetation, the stress-tolerant strategy is associated with continuously unproductive conditions, and the ruderal strategy is characteristic of severely disturbed but potentially productive habitats. A triangular model based upon the three strategies may be reconciled with the theory of r- and K-selection, provides an insight into the processes of vegetation succession and dominance, and appears to be capable of extension to fungi and to animals.
Article
The effects of nesting colonies of the Ring-billed Gull (Larus delawarensis Ord.) on vegetation and soil nutrients were monitored over a 4-year period on Barrier Island and other islands in Georgian Bay and Lake Huron, in the Great Lakes region of Canada. Nesting had a profound effect on the vegetation and species composition. Two distinct communities of annual alien species dominated the nesting sites, one flowering in May and June and the other from late August to October. Native species were rare in the nesting sites, in contrast to adjacent areas, where perennial native grasses were dominant. Factors favouring the replacement of indigenous vegetation by annual aliens include physical disturbance by gulls during nesting and deposition of guano, which caused dramatic increases in the levels of soil nutrients. Plant succession in nesting sites that had been abandoned for 3 and 4 years was characterized by a rapid decline in the abundance of annual aliens and their replacement by perennials. After the 2nd year native perennial grasses were dominant. Nutrient levels in the soil rapidly returned to near normal, except for phosphorus, which persisted at high levels. Herring Gull (Larus argentatus Pontoppidan) nests were also studied. Their density was much lower, and hence their effects were less pronounced. However, they supported a similar annual alien flora. Herring Gulls frequently nested on unvegetated cobble or gravel shores where the humus from the nests permitted the establishment of a permanent vegetation.
Article
Seedling emergence from organic and mineral soil layers was measured for nine study sites at the Acadia Forest Experiment Station near Fredericton, New Brunswick. The number of viable seeds showed a decrease from deciduous-dominated forest, to conifer-dominated forest, to organic soil study sites. Viable seed number varied from 3400/m2 for a deciduous-dominated forest study site to zero for a bog study site. Most seeds germinated from the upper organic soil layers of all study sites and were predominantly Rubus strigosus Michx. After the germination experiment, ungerminated seeds, which showed no viability by the tetrazolium test, were separated from the soil. These seeds were almost entirely Betula spp. and seed numbers were as high as 4200–9400/m2 for a deciduous-dominated forest. The applicability of the results to differing types of postdisturbance revegetation is discussed.
Article
Question: Does the seed density of invasive species affect establishment by native species in a bare ground context (following invasive species control efforts), and is it possible to promote transition to a native species dominated state by manipulating sowing density of the native community? Location: Experimental wetland basin in Chanhassen, Minnesota, USA. Methods: A mesocosm experiment investigated the influence of Phalaris arundinacea (invasive species) propagule pressure on establishment of native wet meadow species in the context of a newly restored wetland. Mesocosms were sown with P. arundinacea (0, 10, 50, 100, or 500 seeds/m2) and a mix of native species (3000 or 15000 seeds/m2). Results: When planted at densities > 100 seeds/m2, P. arundinacea increased suppression of native species. Also, high native seed density suppressed P. arundinacea biomass production. This effect was more pronounced when P. arundinacea seed density was high (> 100 seeds/m2), but high native seed density (15000 seeds/m2) did not suppress recruitment of P. arundinacea from seed. Conclusions: The transition from post-control bare ground (a common result of efforts to control invasive species) to native species establishment depends on both native species and invader seed density. These results suggest that a threshold of P. arundinacea propagule pressure exists, beyond which transition to a native community is less likely without management intervention. P. arundinacea can establish in the presence of a newly developing native plant community, even at very low densities of P. arundinacea seed. Invader control (following initial site clearing efforts) is essential to native species establishment.
Article
Freshly-collected seeds of twenty species of annual weeds were uniformly mixed with 2.5, 7.5 or 15 cm of soil confined in cylinders sunk in the ground outdoors. The soil was either cultivated four times a year or left undisturbed, seedling emergence was recorded, and after 5 years the numbers of viable seeds remaining were determined.Total seedling emergence from seeds incorporated to 2·5, 7·5 and 15 cm amounted to 75, 65 and 54% respectively of those added when the soil was cultivated, and 58, 36 and 21% where it was left undisturbed. The corresponding numbers of viable seeds remaining after 5 years were 2·3, 4·0 and 7·7% respectively for cultivated soil, and 6·8, 16·5 and 31·6% of the seeds initially added and then not disturbed. Individual species varied in their responses to increasing depth of incorporation and to cultivation; these differences are discussed in relation to the dormancy characteritics of the seeds.Devenir des semences de quelques mauvaises herbes annuelles à différentes profondeur dans un sol cultivé et non cultivéRésumé. Des semences récoltées récemmeni sur vingt espèces de mauvaises herbes an-nuelles furent uniformément mélangées avec 2,5; 7,5 ou 15 cm de sol contenu dans des cylindres stockés dans le sol en dehors du laboratoire. Le sol fut travaillé quatre fois dans l'année, ou au contraire laissé sans facon culturale, la levée dts plantules fut enregistrée, et, après 5 ans, les semences viables restantes furent dénombrées.La levée totale des semences incorporées a 2,5; 7,5 et 15 cm fut respectivement de 75, 65 et 54% pour les semences ajoutées au sol travaillé et de 58, 36, et 21 % pour les semences en sol non travaillé. Les nombres correspondants de semences restées viables aprés 5 années représentèrent respectivement 2,3; 4,0 et 7,7% du nombre initial dans le sol travaillé et 6,8; 16,5 et 31,6% dans le sol non travaillé, Les espèces, considérées individuellement, présentèrent des réactions variées à l'accroissement de la profondeur d'enfouissement et au travail du sol; ces différences sont examinées en relation avec les caractératiques des dormances des semences.Verhalten von Samen einiger annueller Unkräauter in versckiedenen Tiefen eines bearbeiteten und nicht bearbeiteten BodensZusammenfassung. Frisrh gesammelte Samen von zwanzig Arten annueller Unkräuter wurden mit Boden gleichiormig gemischt und In Zylindern in 2,5; 7,5 oder 15 cm Tiefe draussen im Boden gclagert. Der Boden wurde entweder viermal im Jahr bearbeitet oder blieb unbcarbeitet. Das Auflaufen der Samen wurde ermittelt, und nach 5 Jahren wurde die Zahl der lebensfähig gebliebenen Samen bestimmt.Der gesamte Auflauf der Samen, die in 2,5; 7,5 und 15 cm Tiefe eingebracht worden waren, belief sich bei dem bearbeiteten Boden auf 75; 65 und 54% der untergemischten Samen. Im nicht bearbeiteten Boden waren cs 58; 36 und 21%. Die entsprechende Anzahl der nach 5 Jahren noch lebensfäAhig gebliebenen Samen belief sich im bearbeiteten Boden auf 2,3; 4,0 und 7,7% und im nicht bearbeiteten Boden auf 6,8; 16,5 und 31,6% der ausgcbrachten Samen. Vcrsrhiedene Arten zeigten in ihrer Reaktion aufdie zunehmende Tiefe ihrer Aussaat und aufdie Bearbeitung ein abweichendes Verhalten. Diese Unterschiede werden in Bczug zu den Dormanzcharaktc Hstika der Samen diskutiert.
Article
1. Characterization of the seed bank is one of the most important demographic assessments that can be undertaken for a plant community. Overlapping generations, evidence of past above-ground vegetation and histories of invasion and disturbance are recorded in the seed bank. 2. Two broad approaches have been used to elucidate seed bank components – sifting-sorting techniques and germinability assays. The utility of these approaches varies with community type and habitat although a common theme among studies has been the quest for an efficacious method. Here, we compare the two approaches for semi-arid ephemeral wetlands: seed extraction through flotation and seedling emergence. 3. Species composition of the soil seed bank differed dramatically depending on the technique, with only 19 species common to both methods and a total of 66 species detected using both procedures. 4. Both techniques provided similar estimates of seed density and species richness of the seed bank in the top 5 cm of soil. However, samples collected from 5 cm to 20 cm had lower seed densities using the flotation technique than with the seedling emergence technique. 5. Differences in seed detectability between the two approaches may be related to seed size, seed dormancy and specific germination requirements. 6. The community composition of soil seed banks for ephemeral wetlands depends on the choice of technique.
Article
The interference between vascular plants and peat mosses with respect to nitrogen and phosphorus was studied in a fertilization experiment and with respect to competition for light in a removal experiment in poor fens with either soligenous or topogenous hydrology using Nartheciumossifragum (L.) Huds. and three species of Sphagnum sect. Sphagnum as targets. Adding fertilizer either on the moss surface or below it confirmed the hypotheses of an asymmetric competition for nutrients, viz. that the Sphagnum mosses relied on the atmospheric supply while Narthecium depended on mineralization in the peat. The results of the removal experiments and the negatively correlated growth of Narthecium and Sphagnum mosses demonstrated a symmetric competition for light. The intensity of the competition for light increased as the availability of N and P increased. The nutrient resources in the total biomass decreased with decreasing standing crop of Narthecium. Only with a considerable amount of mineral nutrients in the biomass has Narthecium the capacity to grow ahead of Sphagnum, because the asymmetric competition for N and P gives Sphagnum the capacity to reduce the performance of vascular plants. The mosses are more efficient in their use of nutrients and produce a decay-resistant litter inducing low mineralization and increasing the peat accumulation rate, and that withdraws N and P from the rhizosphere. The Sphagnum mosses thus act as ecological engineers structuring the plant community and determining the carbon balance of the system. The development of ombrotrophic conditions through peat accumulation seems less probable on soligenous than on topogenous mires owing to the higher mineralization rate there supporting the growth of the vascular plants. Correspondingly, disturbances of the Sphagnum cover, such as through airborne pollutants, increase the productivity of the vascular plants and decrease the capacity for carbon accumulation.
Article
It is notable that Themeda reduced soil nitrate at Windermere even though other native perennial grasses already dominated these plots. This could reflect the small overall increase in native perennials on these plots by autumn 2004 (Fig. 4), or Themeda may have a greater effect than other native grasses on soil nitrate. The latter is supported by evidence for consistently lower nitrate levels beneath Themeda swards than beneath other native grass swards (Prober, Thiele & Lunt 2002) and evidence that perennial grass species can differ greatly in their effects on soil nitrate (Tilman & Wedin 1990). Studies comparing effects of relevant native perennial grasses on soil nutrients are thus needed to guide selection of species for restoring ecosystem function in temperate Australian woodland. Of particular interest is the influence of Poa, once codominant with Themeda in woodland understoreys; this cool-season C3 perennial may influence soil nitrogen during winter and early spring, when Themeda is dormant and exotic annuals are active. The contribution of subsidiary forbs and grasses to this process also requires assessment.
Article
Most of North America’s northern Great Plains have been cultivated for crop production, leaving remnants of natural mixed-grass prairie fragmented and threatened by alien plant invasions. The region’s most widespread alien perennial forage crop, crested wheatgrass (Agropyron cristatum sensu amplo), has invaded native grassland and raised concerns regarding its ecological impact. To evaluate impacts at multiple scales of organization, adjacent invaded and uninvaded mixed-grass prairie were sampled at eight widely separated locations. At the population level, native C3 mid-grasses and forbs were less abundant in invaded grasslands, while native C3 and C4 short-grass abundance was not different. At community and landscape levels, diversity was lower in invaded grasslands largely because of lower forb species richness and cover, and crested wheatgrass dominance of both cover (14% basal cover) and seedbank (404 seeds m−2). At the ecosystem level, both vegetation and litter biomass were greater in invaded grasslands, however, below ground organic matter (roots and litter), soil organic carbon, total nitrogen and phosphorus were not different. Crested wheatgrass invasion of mixed-grass prairie was associated with lower diversity within and among plant communities, and appears to simplify the composition of mixed-grass prairie landscapes. Hypotheses for crested wheatgrass dominance and persistence following invasion are suggested.
Article
Bogs and fens are rare communities in the southern Appalachians of the USA. Many have been degraded, and little ecological information beyond cursory floral inventories is available to help guide conservation and restoration efforts. The seedling emergence technique was used to examine the soil seed banks of open and closed canopy regions of a southern mountain fen in North Carolina. We also examined the seed bank of an adjoining portion of the floodplain, which had been drained and cleared for a golf fairway and is now slated for restoration. A total of 32 taxa emerged, with graminoids (particularlyJuncus spp.) dominating all three seed banks. Seedlings were assigned to one of five plant types: woody, rush, sedge, grass, or forb. Significantly more woody seedlings emerged in soils from the closed canopy fen than in soils from the other two areas. Most rush seedlings emerged in open canopy fen soils, more sedge and forb seedlings emerged in floodplain soils, and more grass seedlings emerged in floodplain soils than in closed canopy fen soils. A discriminant function analysis separated the open canopy fen from the closed canopy fen and floodplain by seedlings of woody plants and rushes. The floodplain was separated from the open and closed regions of the fen by sedge and grass seedlings. These patterns in seed bank composition bore little similarity to the standing vegetation in the three areas. Restoration activities planned for the floodplain are intended to restore its hydrology and microtopography, which will strongly influence recruitment from the seed bank and surrounding seed sources.
Article
We examined the natural colonization by vascular plants of 11 created wetlands in southeastern Wisconsin. The wetlands studied were small depressional wetlands that were isolated from other wetland sites. Wetlands were sampled over a two-year period, providing samples of wetlands aged one to three years. The development of wetland vegetation in these 11 naturally colonized sites was compared to that in five wetlands to which we introduced 22 species of native wetland plants. We identified 142 species of vascular plants in the naturally colonized wetlands. Of these, 82 (58%) were native, obligate or facultative wetland plants. The diversity and richness of native wetland plants and the proportion of total plant cover that was comprised of native wetland species increased from one-to three-year-old wetlands. The diversity and richness of native wetland species increased with wetland age, wetland size, and with proximity to the nearest established wetland. Distance to the nearest seed source had a particularly strong effect on the number of native wetland species present. Cattail (Typha spp.) accounted for 15% of the cover of native wetland species in one-year-old wetlands; this increased to 55% in three-year-old wetlands. We predict that the naturally colonized wetlands will develop into near monocultures of cattail with a fringe of willows (Salix spp.) and cottonwood (Populus deltoides) at the wetland/upland margin. Wetlands seeded with native wetland species had much higher diversity and richness of native wetland species than unseeded wetlands after two years. Seventeen of the 22 seeded species became established in at least two wetlands after simple introduction of seed to the sites. Cattail cover after two years was lower in seeded sites, both as an absolute cover and as a proportion of native wetland plant cover. Early introduction of a diversity of wetland plants may enhance the long-term diversity of vegetation in created wetlands.
Article
Nutrient loading is a subtle, yet serious threat to the preservation of high diversity wetlands such as peatlands. Pathways of nutrient loading and impacts on plant diversity in a small peatland in New York State, USA were determined by collecting and analyzing a suite of hydrogeological, hydro-chemical, soil, and vegetation data. Piezometer clusters within an intensive network constituted hydro-chemical sampling points and focal points for randomly selected vegetation quadrats and soil-coring locations. Hydrogeological data and nutrient analyses showed that P and K loading occurred chiefly by means of overland flow from an adjacent farm field, whereas N loading occurred predominantly through ground-water flow from the farm field. Redundancy analysis and polynomial regression showed that nutrients, particularly total P in peat, total K in peat, extractable NH4-N, and NO3-N flux in ground water, were strongly negatively correlated with plant diversity measures at the site. No other environmental variables except vegetation measures associated with eutrophication demonstrated such a strong relationship with plant diversity. Nitrate loading over 4 mg m−2 day−1 was associated with low plant diversity, and Ca fluxes between 80 and 130 mg m−2 day−1 were associated with high plant diversity. Areas in the site with particularly low vascular plant and bryophyte species richness and Shannon-Wiener diversity (H′) occurred adjacent to the farm field and near a hillside spring. High H′ and species richness of vascular plants and bryophytes occurred in areas that were further removed from agriculture, contained no highly dominant vegetation, and were situated directly along the ground-water flow paths of springs. These areas were characterized by relatively constant water levels and consistent, yet moderate fluxes of base cations and nutrients. Overall, this study demonstrates that knowledge of site hydrogeology is crucial for determining potential pathways of nutrient loading and for developing relationships between nutrient inflows and wetland plant diversity.
Article
A three year fertilization experiment was conducted in which nitrogen (N series: 20 g N m–2 yr–1), phosphorus (P series: 4 g P m–2 yr–1) and potassium (K series: 20 g K m–2 yr–1) were added to a mixed vegetation of Erica tetralix and Molinia caerulea. At the end of each growing season the percentage cover of each species was determined. At the end of the experiment percentage cover of each species was found to be positively correlated with the harvested biomass. In the unfertilized control series the cover of Erica and Molinia did not change significantly during the experiment. In all fertilized series however, especially in the P series, cover of Erica decreased significantly. The cover of Molinia increased significantly in the P series only.In the fertilized series the biomass of Erica and total biomass per plot did not change significantly compared with the control series. In the P series the biomass of Molinia increased significantly.It is suggested that with increasing phosphorus or nitrogen availability Molinia outcompetes Erica because the former invests more biomass in leaves which in turn permits more carbon to be allocated to the root system, which thereupon leads to a higher nutrient uptake.