Content uploaded by Chris Wall
Author content
All content in this area was uploaded by Chris Wall on Jul 29, 2014
Content may be subject to copyright.
A preview of the PDF is not available
Assessing wetland mitigation efforts using standing vegetation and seed bank community structure in neighboring natural and compensatory wetlands in north-central Texas
Abstract and Figures
It is often presumed plant recruitment from the soil seed bank and nearby wetlands will be sufficient to establish a wetland plant community following the restoration or creation of wetland hydrology. This approach to wetland restoration was examined in four compensatory wetlands and a natural oxbow wetland (Oxbow) in a floodplain of the West Fork Trinity River in north-central Texas. We assessed: (1) similarities in vegetation and seed bank composition among natural and compensatory wet-lands, (2) within site similarity of vegetation relative to its seed bank community, and (3) the effects of hydrology (Wet vs. Drained soil) on the germination of seeds from the seed bank. Species richness of the standing vegetation was variable across sites and years, however when pooled across years (2008–2009) vegetation and seed banks showed similar species richness (66 vs. 70 species). Fewer wetland species (i.e., species occurring in wetlands[50 % of the time) were observed in the vegetation relative to the seed bank (25 vs. 41 species), and seed banks of compen-satory wetlands were more similar to the natural wetland than was the standing vegetation. In the seed bank study, location (i.e., site) significantly affected total species richness, wetland species richness, diversity, and germinated seeds m -2 , however no significant effect of hydrology was detected. These results suggest hydrology alone is not sufficient to establish a desired wetland plant community in a created wetland and the inclusion of seed bank surveys with field vegetation surveys provides a more com-plete assessment of wetland creation and restoration.
Figures - uploaded by Chris Wall
Author content
All figure content in this area was uploaded by Chris Wall
Content may be subject to copyright.
... The majority of seed bank studies carried out in grassland (Godefroid et al., 2018;Jacquemyn et al., 2011;Ma, Zhou & Du, 2010;Niknam et al., 2018) and forest ecosystems (Douh et al., 2018;Godefroid, Phartyal & Koedam, 2006;Jaroszewicz, 2013) usually investigated only the uppermost soil layers to a depth of 20 cm. However, the vertical distribution of the seed bank in wetland ecosystems has already been studied at greater depths (Burmeier et al., 2010;Dawson et al., 2019;Jauhiainen, 1998;McGraw, 1987;van der Valk & Davis, 1979;Wall & Stevens, 2015). According to the reviewed literature, these greatest depths were 45 cm (McGraw, 1987) and 50 cm (Burmeier et al., 2010;Jauhiainen, 1998), respectively. ...
Background: Soil seed banks play a central role in vegetation dynamics and may be an important source of ecological restoration. However, the vast majority of seed bank studies examined only the uppermost soil layers (0-10 cm); hence, our knowledge on the depth distribution of seed bank and the ecological significance of deeply buried seeds is limited. The aim of our study was to examine the fine-scale vertical distribution of soil seed bank to a depth of 80 cm, which is one of the largest studied depth gradients so far. Our model systems were alkaline grasslands in East-Hungary, characterised by harsh environmental conditions, due to Solonetz soil reference group with Vertic horizon. We asked the following questions: (1) How do the seedling density and species richness of soil seed bank change along a vertical gradient and to what depth can germinable seeds be detected? (2) What is the relationship between the depth distribution of the germinable seeds and the species traits? Methods: In each of the five study sites, four soil cores (4 cm diameter) of 80 cm depth were collected with an auger for soil seed bank analysis. Each sample was divided into sixteen 5-cm segments by depth (320 segments in total). Samples were concentrated by washing over sieves and then germinated in an unheated greenhouse. Soil penetration resistance was measured in situ next to each core location (0-80 cm depth, 1-cm resolution). We tested the number and species richness of seedlings observed in the soil segments (N = 320), using negative binomial generalized linear regression models, in which sampling layer and penetration resistance were the predictor variables. We ran the models for morphological groups (graminoids/forbs), ecological groups (grassland species/weeds) and life-form categories (short-lived/perennial). We also tested whether seed shape index, seed mass, water requirement or salt tolerance of the species influence the vertical distribution of their seed bank. Results: Germinable seed density and species richness in the seed bank decreased with increasing soil depth and penetration resistance. However, we detected nine germinable seeds of six species even in the deepest soil layer. Forbs, grassland species
and short-lived species occurred in large abundance in deep layers, from where
graminoids, weeds and perennial species were missing. Round-shaped seeds were
more abundant in deeper soil layers compared to elongated ones, but seed mass and
ecological indicator values did not influence the vertical seed bank distribution.
Our research draws attention to the potential ecological importance of the deeply
buried seeds that may be a source of recovery after severe disturbance. As Vertisols
cover 335 million hectares worldwide, these findings can be relevant for many
regions and ecosystems globally. We highlight the need for similar studies in other
soil and habitat types to test whether the presence of deep buried seeds is specific to
soils with Vertic characteristics.
... Even if host plants are generalists and do not require specific mycorrhizal symbionts, not all symbionts provide equal benefits to their hosts (Kiers, Lovelock, Krueger, & Herre, 2000). Thus, when restoration efforts fail to reestablish focal plant species, it may often be owed to combinations of unamendable abiotic and biotic soil conditions (Heneghan et al., 2008;Wall & Stevens, 2014). ...
The negative effects of deforestation can potentially be ameliorated through ecological restoration. However, reforestation alone may not reassemble the same ecological communities or functions as primary forests. In part, this failure may be owed to forest ecosystems inherently involving complex interactions among guilds of organisms. Plants, which structure forest food webs, rely on intimate associations with symbiotic microbes such as root-inhabiting mycorrhizal fungi. Here, we leverage a large-scale reforestation project on Hawai'i Island underway for over three decades to assess whether arbuscular mycorrhizal (AM) fungal communities have concurrently been restored. The reference ecosystem for this restoration project is a remnant montane native Hawaiian forest that provides critical habitat for endangered birds. We sampled soils from 12 plots within remnant and restored forest patches and characterized AM fungal communities using high throughput Illumina MiSeq DNA sequencing. While some AM fungal community metrics were comparable between remnant and restored forest (e.g., species richness), other key characteristics were not. Specifically, community membership and the identity of AM fungal keystone species differed between the two habitat types, as well as the primary environmental factors influencing community composition. Remnant forest AM fungal communities were strongly associated with soil chemical properties, especially pH, while restored forest communities were influenced by the spatial proximity to remnant forests. We posit that combined, these differences in soil AM fungal communities could be negatively affecting the recruitment of native plant hosts and that future restoration efforts should consider plant-microbe interactions as an important facet of forest health.
... Furthermore, seed bank deposits and the emergence of vegetation vary greatly due to climate change (Wall & Stevens, 2015). ...
The Tibetan Plateau has undergone significant climate warming in recent decades, and precipitation has also become increasingly variable. Much research has explored the effects of climate change on vegetation on this plateau. As potential vegetation buried in the soil, the soil seed bank is an important resource for ecosystem restoration and resilience. However, almost no studies have explored the effects of climate change on seed banks and the mechanisms of these effects. We used an altitudinal gradient to represent a decrease in temperature and collected soil seed bank samples from 27 alpine meadows (3,158–4,002 m) along this gradient. A structural equation model was used to explore the direct effects of mean annual precipitation (MAP) and mean annual temperature (MAT) on the soil seed bank and their indirect effects through aboveground vegetation and soil environmental factors. The species richness and abundance of the aboveground vegetation varied little along the altitudinal gradient, while the species richness and density of the seed bank decreased. The similarity between the seed bank and aboveground vegetation decreased with altitude; specifically, it decreased with MAP but was not related to MAT. The increase in MAP with increasing altitude directly decreased the species richness and density of the seed bank, while the increase in MAP and decrease in MAT with increasing altitude indirectly increased and decreased the species richness of the seed bank, respectively, by directly increasing and decreasing the species richness of the plant community. The size of the soil seed bank declined with increasing altitude. Increases in precipitation directly decreased the species richness and density and indirectly decreased the species richness of the seed bank with increasing elevation. The role of the seed bank in aboveground plant community regeneration decreases with increasing altitude, and this process is controlled by precipitation but not temperature.
... Artemisia selengensis still grew and other auxiliary species like Conyza canadensis thrived due to the luxurious seed bank available in the Poyang Lake wetland (Wall & Stevens, 2015;Yu & Yu, 2011). In accordance with our second hypothesis, 10 cm groundwater level was more beneficial for C. cinerascens growth compared to 20 cm groundwater level. ...
Groundwater level is crucial for wetland plant growth and reproduction, but the extent of its effect on plant growth can vary along with changed precipitation and temperature at different seasons. In this context, we investigated the effect of two groundwater levels (10 cm vs. 20 cm depth) on growth and reproductive parameters of Carex cinerascens, a dominant plant species in the Poyang Lake wetland, during three seasons (spring, summer, and autumn) and during two consecutive years (2015 and 2016). Carex cinerascens showed low stem number, height, and individual and population biomass in summer compared to spring and autumn. 10 cm groundwater level was overall more suitable for plant growth resulting in higher stem height and biomass. However, the interactive effect between groundwater level and season clearly demonstrated that the effect of groundwater level on plant growth occurred mainly in autumn. After the withering of the plant population in summer, we observed that C. cinerascens growth recovered in autumn to similar values observed in spring only with 10 cm groundwater level. Consequently, we could deduce that lowering groundwater level in the studied Poyang Lake wetland will negatively impact C. cinerascens regeneration and growth particularly during the second growth cycle occurring in autumn. Additionally, our results showed that, independently of the season and groundwater level, population biomass of C. cinerascens was lower during drier year. Altogether, our findings suggest that water limitation due to both reduction in precipitation and decreased groundwater level during the year can strongly impact plant communities. We investigated the effect of groundwater level on growth and reproductive parameters of Carex cinerascens, a dominant plant species in the Poyang Lake wetland, during two consecutive years. We clearly demonstrated that the effects of groundwater level on plant growth occur mainly in autumn.
... Given this similarity throughout the wetland, it is possible that hydrology and salinity do not play a role in structuring the soil seed bank composition for this CFW; however, there may be some role in seed viability and germination success, as has been found in tidal marshes in North America (Baldwin et al. 1996;Peterson and Baldwin 2004). Such homogeneity in wetland soil seed banks is likely due to widespread dispersal of propagules via wind and water (Baldwin et al. 1996;Capon 2003Capon , 2007Wall and Stevens 2015). The lack of substantial variation in the soil seed bank also suggests that compositional differences in the extant vegetation are due to effects of drivers such as hydrology and salinity on plant establishment and growth, rather than spatial differentiation in the availability of propagules (e.g. ...
Coastal freshwater wetlands are amongst the world’s most modified but poorly researched ecosystems and some of the most vulnerable to climate change. Here, we examine vegetation resilience in coastal wetlands of subtropical Australia to altered salinity and flooding regimes likely to occur with climate change. We conducted field surveys and glasshouse experiments to examine plant diversity and regeneration responses of understorey and canopy species across four habitats. Vegetation composition, but not richness, varied between seaward and inland habitats while soil seed bank diversity was greatest in more inland sites. Experimental salinity and flooding treatments strongly influenced emergence from seed banks with most species germinating under fresh, waterlogged conditions and very few in saline treatments. Composition of emerging seedling assemblages was similar across habitats and treatments but differed considerably from the extant vegetation, indicating a relatively minor role of soil seed banks in sustaining current vegetation structure in this wetland. An exception to this was Sporobolus virginicus (marine couch) which was common in both the vegetation and seed banks suggesting a high capacity for this species to re-establish following disturbances. Seedlings of dominant canopy species also reacted strongly to increased salinity treatments with decreased survivorship recorded. Overall, our findings suggest a high probability of constrained vegetation regeneration in this wetland in response to key projected climate change disturbances with implications for vegetation diversity at a landscape scale including declines in the extent and diversity of more landward vegetation communities and expansion of salt-tolerant marshes dominated by Sporobolus virginicus.
... It is important to know the regeneration ecology of mangrove species (Pascual, 2016) because successful regeneration determines the establishment of a wetland mangrove plant community (Wall & Stevens, 2015). Hoque et al. (1999) studied the effect of salinity on the germination of Sonneratia apetala Buch.-Ham. ...
Adaptive phenotypic plasticity of Avicennia officinalis across the salinity gradient in the Sundarbans of Bangladesh was studied. Propagule morphology was compared through use of a completely randomized design. Propagule growth initiation traits across the salinity gradient (from 0 to 35 ppt at 5 ppt interval) were studied by means of a randomized block design. Propagules showed variability in length, width, and weight across the salinity gradient in the Sundarbans. Propagule growth initiation time, mean growth initiation time, growth initiation index, and propagule growth initiation percentage of A. officinalis varied significantly with the increasing salinity and among low, medium, and high saline zones. However, propagules originating from the high and medium saline zones started their growth initiation more rapidly and vigorously at high salinities compared to those from the low saline zone. Therefore, A. officinalis exhibited adaptive phenotypic plasticity in terms of variability in propagule size and weight as well as physiologically adaptive plastic responses during propagule growth initiation across the salinity gradient in the Sundarbans. A. officinalis in high and medium saline zones of Sundarbans is the most salt-adapted phenotype, and a good knowledge about this will be widely useful for successful regeneration, coastal afforestation, and conservation of this species in increasing saline environments in the future.
... The importance of the structure and dynamics of seed banks has been broadly recognized in plant community ecology (Grubb, 1977;Adondakis and Venable, 2004;Fenner and Thompson, 2005;P€ artel, 2014), but unfortunately there is a lack of knowledge about the processes that regulate soil seed banks. Several studies have described the seed bank structure and composition of target communities (Caballero et al., 2003(Caballero et al., , 2008aWhite et al., 2012;Wall and Stevens 2015;Wu et al., 2015), but our understanding of the processes involved in their formation and dynamics (Olano et al., 2012), as well as their connection with the standing vegetation, is still limited (e.g. primary and secondary dispersion, predation, soil penetration and persistence). ...
Background and aims:
Many studies have analysed the mechanisms that determine plant coexistence in standing vegetation, but the determinants of soil seed bank species assemblies have rarely been studied. In gypsum soil communities, aerial vegetation and seed banks are tightly connected in space and time, but the mechanisms involved in their organization may differ. The aim of this study is to understand the relative importance of biotic and abiotic factors controlling soil seed bank composition and structure.
Methods:
Persistent and complete (i.e. persistent plus transient) soil seed banks were investigated at two spatial scales in a very species-rich semi-arid community dominated by annuals. A water addition treatment equivalent to 50 % annual increase in average precipitation (abiotic factor) was applied for two consecutive years, and the relationships of the soil seed bank to the biological soil crust (BSC), above-ground vegetation and the presence ofStipa tenacissimatussocks (biotic factors) were simultaneously evaluated.
Key results:
As expected, the standing vegetation was tightly related to seed abundance, species richness and composition in both seed banks. Remarkably, BSC cover was linked to a decrease in seed abundance and species richness in the persistent seed bank, and it even determined complete seed bank composition at the fine spatial scale. However, this effect disappeared at coarser scales, probably because of the high spatial heterogeneity induced by BSCs. In contrast to findings on standing vegetation,Stipaand the irrigation treatment for two consecutive years had no effect on soil seed banks.
Conclusions:
Soil seed bank assemblies in our semi-arid plant community were the result of above-ground vegetation dynamics and of the direct filtering processes on seed fate operated by the spatially heterogeneous BSCs. Cover of BSCs was negatively correlated with seed abundance and species richness, and affected seed species composition in the soil. Changes in species composition and enrichment when the BSC cover is low suggest that BSCs promote a fine scale niche differentiation in the soil seed bank and thereby potentially enhance species coexistence and high species diversity in these communities.
The U.S. Clean Water Act requires that development projects causing negative impacts to wetlands must provide compensation for wetland losses through the wetland mitigation process. Compensation can be achieved through the purchase of credits from wetland mitigation banks, which are large wetland restoration projects constructed by third-party bank sponsors. To evaluate how effectively wetland mitigation banks have achieved the goal of “no net loss” of wetland resources, we compared mitigation banks to natural wetlands in the Chicago (Illinois, USA) region. We surveyed vegetation plots in 20 mitigation banks to compare vegetation metrics and composition between banks and 114 natural wetlands, representing a gradient of ecological quality, in northern Illinois. Based on metrics of species richness and floristic quality, mitigation banks possessed wetland plant communities of greater conservation value than the lowest quality, degraded, natural wetlands, but banks were not close to reaching equivalence with high-quality, reference, natural wetlands. Overall, the plant communities in banks were distinct from those of natural wetlands, a condition that appears to be driven by the abundance of the non-native species Typha angustifolia and Phragmites australis in mitigation banks. We found some evidence that dominance by native species may be lower in older banks, but otherwise did not find evidence for a relationship between vegetation metrics and bank age. These results will help those involved with wetland mitigation and similar offsetting programs assess whether compensation sites meet no-net-loss goals, informing goal setting, monitoring, and offsetting policies.
The construction of the Three Gorges Dam has resulted in the occurrence of reverse seasonal water level fluctuations. The species composition and quantity of riparian soil seed banks collected from four hydro‐fluctuation belts were assessed by simulating different submersion cycles to determine the effects of reverse seasonal water level fluctuations on the germination and persistence of soil seed banks in the Three Gorges Reservoir Region. Results showed the number of species that germinated from the soil seed bank decreased with submersion. The number of germinated seeds in soil seed banks after submersion for seven months in Xingshan, Zigui, Wanzhou, and Zhongxian decreased by 60%, 53%, 57%, and 57%, respectively, relative to the control. The species diversity index and seed density of germinated seeds in soil seed banks also significantly decreased with prolongation of submersion time. Seed density decreased by 93%, 83%, 76%, and 72%, respectively, after seven months of submersion. Species composition and dominance within the soil seed bank changed over time due to submersion. In general, reverse seasonal submersion negatively impacts the germination and persistence of soil seed banks. The response of soil seed bank germination and persistence to reverse seasonal submersion became the key factor determining the heterogeneity in the spatial distribution of the soil seed bank in hydro‐fluctuation belts due to the large differences in submersion time between areas at various elevations.
Selection of sites for wetland restoration requires analysis of probable success at recreating diverse natural vegetation. We studied the seed banks and the remnant vegetation at restoration sites to determine their degree of similarity to the vegetation that developed following restoration of wetland hydrology. The study sites had been used for forage crops and pasture following long-term drainage. The seed bank was a very poor predictor of plant species abundances following restoration. Similarity between remnant vegetation and restored vegetation was consistently higher than similarity values using seed banks at both restored and natural wetlands. Our results suggest that seed-bank analysis is an inefficient technique for predicting restored vegetation in sites with prolonged disturbance, and that analysis of remnant vegetation on the sites is probably more useful. However, results would probably differ at sites with tile drainage that have limited remnant vegetation or created wetlands with bare soil where seed germination would play a greater role in revegetation. In addition, seed-bank studies are important to determine if aggressive invasive species are present at potential restoration sites.
Constructed wetland soil samples contained many more species with densities > 100 seeds / m2 than reference marsh ones (102 vs. 28); constructed wetland densities for many species were considerably higher and richness (species / sample) were > 2X greater than the reference marsh. Of the total 218 seed bank species, 60 were common to both and 34 occurred only in reference marsh samples. Numbers of cover species were similar, but composition differed. Invasive species, notably Lythrum salicaria, Phalaris arundinacea, and Phragmites australis, were more important in constructed wetland soil samples and vegetation. Non-native species comprised 9 % and 13 % of the reference marsh and constructed wetland seed bank species and 8 % and 12 % of the cover species, respectively. Variable dispersal patterns and in situ seed production contributed to these differences. Over the entire study area (wetlands and adjacent terrestrial areas) we recorded 875 species, representing 141 families, more than doubling the number observed in a 1988 report. The families having the most species were Asteraceae (103 species), Poaceae (100), and Cyperaceae (83). The largest genera were Carex (46) and Polygonum (19); seven other genera also had ≥ 10 species. Nine species were pseudo-viviparous, producing plantlets on inflorescences. Non-native species comprised 27 % of the total flora. Overall there were 37 NJ rare / endangered species for the entire area; 11 occurred only in the constructed wetland with constructed wetland soil samples containing more than the reference marsh samples (8 vs. 1). Available lists from 1824, 1887, and 1964/65 and five species known only from herbarium specimens indicate that several species have been extirpated since the 19th C. Anthropogenic influences continue to have impact on diversity.
Thousands of wetland restorations have been done in the glaciated midcontinent of the United States. Wetlands in this region revegetate by natural recolonization after hydrology is restored. The floristic composition of the vegetation and seed banks of 10 restored wetlands in northern Iowa were compared to those of 10 adjacent natural wetlands to test the hypothesis that communities rapidly develop through natural recolonization. Restoration programs in the prairie pothole region assume that the efficient-community hypothesis is true: all plant species that can become established and survive under the environmental conditions found at a site will eventually be found growing there and/or will be found in its seed bank. Three years after restoration, natural wetlands had a mean of 46 species compared to 27 species for restored wetlands. Some guilds of species have significantly fewer (e.g., sedge meadow) or more (e.g., submersed aquatics) species in restored than natural wetlands. The distribution and abundance of most species at different elevations were significantly different in natural and restored wetlands. The seed banks of restored wetlands contained fewer species and fewer seeds than those of natural wetlands. There were, however, some similarities between the vegetation of restored and natural wetlands. Emergent species richness in restored wetlands was generally similar to that in natural wetlands, although there were fewer shallow emergent species in restored wetlands. The seed banks of restored wetlands, however, were not similar to those of natural wetlands in composition, mean species richness, or mean total seed density. Submersed aquatic, wet prairie, and sedge meadow species were not present in the seed banks of restored wetlands. These patterns of recolonization seem related to dispersal ability, indicating the efficient-community hypothesis cannot be completely accepted as a basis for restorations in the prairie pothole region.
More species germinated in the moist soil treatment (24) than in the submerged treatment (12). Typha spp. and Scirpus acutus sites had the greatest number of species germinate and S. acutus sites also had the highest seedling density. Open water sites had few species and low seedling densities. Scirpus spp. seedlings were found primarily in Scirpus spp. seed bank samples whereas Typha seedlings were found in high densities in all emergent vegetation types (Scirpus spp., Typha spp. and Phragmites australis). Mud- flat species (eg Chenopodium rubrum) were found at higher densities in Scirpus acutus sites. Shoot densities in the field and seedling densities in greenhouse tests of samples from the same vegetation types were not similar during marsh drawdown. Frequency of marsh plant species shifted as the water table fell (drawdown) with emergent plant species decreasing and mud-flat species increasing. Rather than a complete drawdown for establishment of marsh plants in the area studied, maintenance of a few centimeters water depth will keep salinities low, allow germination of at least 12 species, and prevent establishment of Tamarix pentandra.-from Authors Typha Scirpus acutus Phragmites australis Chenopodium rubrum Tamarix pentandra
A qualitative model of succession in freshwater wetlands is proposed, based on the life history features of the species involved. Three key life history traits can be used to characterize wetland species: life-span, propagule longevity, and propagule establishment requirements. By combining these three life history traits, 12 basic wetland life history types are recognized. For each life history type, the future state (presence only in the form of propagules in the seed bank, presence as adult plants, or complete absence) of each species type in a wetland can be predicted if environmental conditions change. Most of the information needed to apply this model to a particular wetland can be obtained by an examination of a wetland's seed bank. Several examples of succesion in North American and African wetlands are presented to illustrate the application of the model.
(1) Measurements have been made of seasonal variation in the density and composition of the reservoir of germinable seeds present in surface (0-3 cm) soil samples collected at 6-weekly intervals from ten ecologically-contrasted sites in the Sheffield region. (2) The procedure was not designed to provide a complete assessment of the seed flora, and the methods were found to be ineffective in recovering germinable seeds of those species (e.g. Endymion non-scriptus, Viola riviniana, several Umbelliferae) in which there is only a brief interval between fulfilment of a chilling requirement and the onset of germination. (3) The techniques adopted were particularly suitable for the detection of persistent seed banks (i.e. those in which some of the component seeds are at least 1 year old), and also allowed recognition of species in which there is a transient accumulation of detached germinable seeds during the summer. (4) Comparison of the results obtained for populations of the same species in different types of habitat suggests that seasonal variation in seed number is a function of the species rather than of the environment. (5) It is concluded that the major evolutionary force determining the nature of the seed bank is the selective advantage derived from mechanisms of seed dormancy and germination which allow seedlings to evade the potentially-dominating effects of established plants. (6) From the data collected in this study, four types of seed bank (Types I-IV) have been recognized, and an attempt has been made to assess their ecological significance. (7) The transient seed banks (Types I and II) are adapted to exploit the gaps created by seasonally-predictable damage and mortality in the vegetation, whilst the persistent seed bank (Type IV) confers the potential for regeneration in circumstances where disturbance of the established vegetation is temporally and/or spatially unpredictable. A second type of persistent seed bank (Type III) has characteristics intermediate between those of Types I and IV, and contains some seeds which germinate soon after release and others which are more persistent in the soil. (8) A feature of the results was the lack of a general correspondence between the species-composition of the seed flora and that of the associated vegetation. At certain sites, substantial persistent seed banks were detected for species which were either extremely scarce or did not occur at all in the established vegetation. (9) Both transient and persistent types of seed banks were represented at each of the ten sites; this is consistent with the hypothesis that complementary mechanisms of regeneration are involved in the maintenance of floristic diversity.
All vegetation change can be reduced to one of three basic phenomena, succession, maturation, and fluctuation, or some combination of these. Each of these phenomena is a result of a change in some attribute of one or more of the plant populations comprising the vegetation of an area. Succession ocurs when different populations are present from time to time. Maturation is an increase in the biomass of an area which is the result of a change in the age/size structure of the populations with time. Fluctuations result from changes in the number of individuals or ramets in the populations of an area from year to year.
The contribution of succession, maturation, and fluctuation to the vegetation dynamics of Eagle Lake, a prairie glacial marsh in Iowa, is examined. In those areas where changing water levels and extensive musk-rat damage occur, succession is the most important phenomenon. A knowledge of the life-history characteristics of each species, particularly its establishment requirements, the presence or absence of its seeds in the seed bank, and its life-span, enables successional sequences to be predicted in this marsh. There are short periods where maturation is the major phenomenon causing vegetation change. Fluctuations also occur both in the emergent vegetation and the submerged vegetation.