Seasonal wetlands on the Lake Wales Ridge, Florida: does a relict seed bank persist despite long term disturbance?

Wetlands maintain biodiversity and provide numerous ecosystem services, so the pressure to perform successful restoration consequently is high. However, restoration projects rarely include an in-depth assessment of wetland potential for recovery, and restoration techniques may not be tailored to site-specific concerns. This study examined the seed bank of disturbed wetlands slotted for hydrologic, but not vegetation, restoration to determine if a seed bank comparable to that of nearby undisturbed wetlands persisted despite long-term anthropogenic disturbance. We compared the aboveground vegetation and seed bank compositions under drained, drawdown, and flooded conditions between undisturbed and historically ditched (“disturbed”) wetlands. Disturbed and undisturbed wetlands shared fewer than 30 % of total aboveground species. While undisturbed wetlands were dominated by graminoids, disturbed wetlands had greater cover of forbs. The seed banks of disturbed wetlands had high species diversity, but their composition was dissimilar to that of nearby undisturbed wetlands. In total, the seed banks of both disturbance histories germinated 56 species; drained conditions had the fewest germinants while flooded conditions had the most. Germinant richness was significantly affected by disturbance, moisture, and their interaction; evenness was significantly affected by moisture, and Shannon diversity by disturbance. Because the seed bank of disturbed wetlands included many fast-growing wetland plants, passive vegetation restoration and active hydrologic restoration may result in wetlands overgrown with weedy species and with fewer conservative wetland plants. An understanding of the capacity for seed banks to re-vegetate wetlands post-restoration and approximate undisturbed wetlands is crucial to the overall success of restoration projects.     

How does the propagule bank contribute to cyclic vegetation change in a lakeshore marsh with seasonal drawdown?

Lakeshore marshes around Liangzi Lake, in the middle reach of the Yangtze River, China, experience annual changes of water level of c. 1.5 m. During the drawdown period, the vegetation is structured by helophytes and emergents; during the rainy season when the dams are closed (June–September) the marshes are flooded and their vegetation rapidly changes to be come dominated by submerged, floating-leaved and tall emergent species. The species composition and abundance of both the marsh seed bank and the vegetative propagule bank were compared with those of the drawdown and flooded vegetation types. These data provided a test of the predictive power of van der Valk's model of northern temperate seasonal vegetation change in a subtropical, freshwater wetland with cyclic vegetational change. The abundant species were detected in the propagule bank. The seed bank was found to determine the species richness of both types of the vegetation, whereas the vegetative propagule bank consisted of the dominants of the drawdown vegetation. Water depth conditions, and the composition of seed and vegetative propagules banks together determine the structure of the standing vegetation during drawdown and flooding. van der Valk's succession model was found to predict the seasonal vegetation change reasonably well. The Chi-square test showed no significant difference between predicted vegetation and actual vegetation in both drawdown and flooding periods.     

Flooding, soil seed bank dynamics and vegetation resilience of a hydrologically variable desert floodplain

1. This paper explores soil seed bank composition and its contribution to the vegetation dynamics of a hydrologically variable desert floodplain in central Australia: the Cooper Creek floodplain. We investigated patterns in soil seed bank composition both temporally, in response to flooding (and drying), and spatially, with relation to flood frequency. Correlations between extant vegetation and soil seed bank composition are explored with respect to flooding. 2. A large and diverse germinable soil seed bank was detected comprising predominantly annual monocot and annual forb species. Soil seed bank composition did not change significantly in response to a major flood event but some spatial patterns were detected along a broad flood frequency gradient. Soil seed bank samples from frequently flooded sites had higher total germinable seed abundance and a greater abundance of annual monocots than less frequently flooded sites. In contrast, germinable seeds of perennial species belonging to the Poaceae family were most abundant in soil seed bank samples from rarely flooded sites. 3. Similarity between the composition of the soil seed bank and extant vegetation increased following flooding and was greatest in more frequently flooded areas of the floodplain, reflecting the establishment of annual species. The results indicate that persistent soil seed banks enable vegetation in this arid floodplain to respond to unpredictable patterns of flooding and drying.     

Energetic implications of floodplain wetland restoration strategies for waterfowl

Modifications of the Illinois River and associated tributaries have resulted in altered hydrologic cycles and persistent river‐floodplain connections during the growing season that frequently impede the establishment of hydrophytic vegetation and have reduced value for migratory waterfowl and other waterbirds. To help guide floodplain restoration, we compared energetic carrying capacity for waterfowl in two wetland complexes along the Illinois River under different management regimes during 2012–2015. The south pool of Chautauqua National Wildlife Refuge (CNWR) was seasonally flooded due to a partial river connection and managed for moist‐soil vegetation. Emiquon Preserve was hydrologically isolated from the Illinois River by a high‐elevation levee and managed as a semipermanently flooded emergent marsh. Semipermanent emergent marsh management at Emiquon Preserve produced 5,495 energetic use‐days (EUD)/ha for waterfowl and other waterbirds across wetland cover types and years, and seasonal moist‐soil management at CNWR produced 6,199 EUD/ha in one of 4 years. At Emiquon Preserve, the aquatic bed cover type produced 9,660 EUD/ha, followed by 5,261 EUD/ha in moist‐soil, 1,398 EUD/ha in persistent emergent, 1,185 EUD/ha in hemi‐marsh, and 12 EUD/ha in open water cover types. At CNWR, the annual grass and sedge cover type produced 7,031 EUD/ha, followed by 5,618 EUD/ha in annual broadleaf and 1,305 EUD/ha in perennial grass cover types. Restoration of floodplain wetlands in isolation from frequent flood pulses during the growing season can produce hemi‐marsh and aquatic bed vegetation communities that provide high‐quality habitat for waterfowl and which have been mostly eliminated from large river systems in the Midwest, U.S.A.     

Testing a Passive Revegetation Approach for Restoring Coastal Plain Depression Wetlands

Restoration of coastal plain depressions, a biologically significant and threatened wetland type of the southeastern United States, has received little systematic research. Within the context of an experimental project designed to evaluate several restoration approaches, we tested whether successful revegetation can be achieved by passive methods (recruitment from seed banks or seed dispersal) that allow for wetland "self-design" in response to hydrologic recovery. For 16 forested depressions that historically had been drained and altered, drainage ditches were plugged to reestablish natural ponding regimes, and the successional forest was harvested to open the sites and promote establishment of emergent wetland vegetation. We sampled seed bank and vegetation composition 1 year before restoration and monitored vegetation response for 3 years after. Following forest removal and ditch plugging, the restored wetlands quickly developed a dense cover of herbaceous plant species, of which roughly half were wetland species. Seed banks were a major source of wetland species for early revegetation. However, hydrologic recovery was slowed by a prolonged drought, which allowed nonwetland plant species to establish from seed banks and dispersal or to regrow after site harvest. Some nonwetland species were later suppressed by ponded conditions in the third year, but resprouting woody plants persisted and could alter the future trajectory of revegetation. Some characteristic wetland species were largely absent in the restored sites, indicating that passive methods may not fully replicate the composition of reference systems. Passive revegetation was partially successful, but regional droughts present inherent challenges to restoring depressional wetlands whose hydrologic regimes are strongly controlled by rainfall variability.     

三江平原恢复湿地土壤种子库特征及其与植被的关系

通过幼苗萌发法和样方调查相结合的方法对三江平原不同演替恢复阶段的种子库特征及其与植被的关系进行了研究。将开垦湿地、不同演替恢复阶段湿地以及天然湿地不同土壤层次(0-5、5-10 cm和根茎)的种子库在两种水分条件下(湿润、淹水10 cm)进行萌发处理。结果表明: 随着演替恢复阶段的进行, 种子库的结构和规模逐渐扩大, 地表群落表现出由旱生物种占优势的群落逐渐演变成以小叶章(Calamagrostis angustifolia)占优势的湿生群落的演替趋势。恢复7年湿地、恢复14年湿地、天然湿地土壤种子库萌发物种数分别为24种、29种、39种, 植被物种数为21种、25种、14种。湿地类型、水分条件和土壤层次均显著影响种子库萌发的物种数及幼苗数(p < 0.01)。种子库具有明显的分层现象, 天然湿地0-5 cm土层种子库种子萌发密度是5-10 cm土层的4倍左右, 而恢复湿地仅1.3倍左右, 且土层间萌发物种相似性系数较低。湿润条件下的萌发物种数显著高于淹水条件, 且两种水分条件下萌发物种的生活型不同。由于恢复时间较短, 不同演替恢复阶段的种子库与植被相似性维持在30%以下。湿地中根茎分蘖出大量的湿地物种, 对于小叶章等优势物种的繁殖具有重要作用。研究表明, 在开垦湿地退耕后的次生演替阶段, 种子库能够保持大量的湿地物种, 通过对湿地种子库与植被的关系研究, 能够为三江平原湿地群落演替与湿地恢复提供策略指导。     

Managing plant species diversity under fluctuating wetland conditions: the case of temporarily flooded depressions

Temporarily flooded depressions in arable fields support populations of specialised plant species that are affected by flooding and agricultural management. Depending on the degree of flooding, different proportions of wetland and arable species contribute to the seed bank. This is reflected by high inter-annual variations in plant communities with a high conservation value. Due to ongoing agricultural intensification, the biodiversity of temporarily flooded depressions has declined, and several plant species have become regionally extinct. Because seed banks harbour persistent seeds over long periods, they play a crucial role in the conservation and restoration of temporary wetland vegetation. This study focuses on the effects of different flooding regimes on plant species emerging from seed banks of temporarily flooded depressions in arable fields in northeast Germany. We cultivated soil samples from upper and lower wetland zones under short, intermediate and long-term flooding (5, 15 and 40 cm above soil surface) in a common garden experiment over 2 years. We observed significant changes in species composition depending on the flooding duration. Species richness declined and evenness increased with increasing flooding duration. Upper and lower zones showed similar species richness and evenness, but species compositions differed. Red List species emerged from all treatments although the species differed, indicating that all communities emerging under different flooding regimes have a high conservation value. Seed banks under fluctuating site conditions can constitute a series of alternating plant communities. This could be used to develop management strategies that benefit different communities with high conservation values.     

Hydrologic Regime Controls Soil Phosphorus Fluxes in Restoration and Undisturbed Wetlands

Many wetland restoration projects occur on former agricultural soils that have a history of disturbance and fertilization, making them prone to phosphorus (P) release upon flooding. To study the relationship between P release and hydrologic regime, we collected soil cores from three restoration wetlands and three undisturbed wetlands around Upper Klamath Lake in southern Oregon, U.S.A. Soil cores were subjected to one of three hydrologic regimes—flooded, moist, and dry—for 7.5 weeks, and P fluxes were measured upon reflooding. Soils from restoration wetlands released P upon reflooding regardless of the hydrologic regime, with the greatest releases coming from soils that had been flooded or dried. Undisturbed wetland soils released P only after drying. Patterns in P release can be explained by a combination of physical and biological processes, including the release of iron‐bound P due to anoxia in the flooded treatment and the mineralization of organic P under aerobic conditions in the dry treatment. Higher rates of soil P release from restoration wetland soils, particularly under flooded conditions, were associated with higher total P concentrations compared with undisturbed wetland soils. We conclude that maintaining moist soil is the means to minimize P release from recently flooded wetland soils. Alternatively, prolonged flooding provides a means of liberating excess labile P from former agricultural soils while minimizing continued organic P mineralization and soil subsidence.     

Seed bank potential of moist-soil managed wetlands in east-central Texas

Proper management techniques on moist-soil wetlands provide methods for enhancement of established wetlands, restoration of former wetlands, and creation of new wetland habitat. These techniques also create suitable wetland habitat for non-breeding waterfowl and other wetland dependent species during winter. To understand moist-soil managed wetland vegetative patterns, aspects such as plant species distribution, reproductive strategy, seed bank composition and viability should be thoroughly characterized. We investigated soil seed bank potential of moist-soil managed wetlands on Richland Creek Wildlife Management Area, Texas to determine which treatment (i.e., drawdown or flooded) produced the most desirable moist-soil plants. A total of 27 species germinated, producing 3,731 and 3,031 seedlings in drawdown and flooded treatments, respectively. There were also differences in stem densities between treatments of desirable and non-desirable species. Drawdown treatments had more seedlings germinate than flooded treatments, validating the notion that drawdown treatments provide favorable conditions for seed germination. Drawdown and flooding techniques, when properly timed, will allow managers to drive and directly influence managed wetland plant communities based on seed bank composition and response to presence or absence of water during the germination period.     

Soil propagule banks of ectomycorrhizal fungi share many common species along an elevation gradient

We conducted bioassay experiments to investigate the soil propagule banks of ectomycorrhizal (EM) fungi in old-growth forests along an elevation gradient and compared the elevation pattern with the composition of EM fungi on existing roots in the field. In total, 150 soil cores were collected from three forests on Mt. Ishizuchi, western Japan, and subjected to bioassays using Pinus densiflora and Betula maximowicziana. Using molecular analyses, we recorded 23 EM fungal species in the assayed propagule banks. Eight species (34.8 %) were shared across the three sites, which ranged from a warm–temperate evergreen mixed forest to a subalpine conifer forest. The elevation pattern of the assayed propagule banks differed dramatically from that of EM fungi on existing roots along the same gradient, where only a small proportion of EM fungal species (3.5 %) were shared across sites. The EM fungal species found in the assayed propagule banks included many pioneer fungal species and composition differed significantly from that on existing roots. Furthermore, only 4 of 23 species were shared between the two host species, indicating a strong effect of bioassay host identity in determining the propagule banks of EM fungi. These results imply that the assayed propagule bank is less affected by climate compared to EM fungal communities on existing roots. The dominance of disturbance-dependent fungal species in the assayed propagule banks may result in higher ecosystem resilience to disturbance even in old-growth temperate forests.     

Changes along a disturbance gradient in the density and composition of propagule banks in floodplain aquatic habitats

This study used germination methods to examine the density, species composition and functional composition of propagule banks in a series of riverine wetland aquatic habitats subject to varying degrees of hydrological and management-related disturbance. Under permanent inundation (the conditions prevailing at most sites during the growing season) propagule germination and species richness was low, with floodplain perennials and helophytes particularly affected. Densities of floodplain annuals were largely maintained through continued germination of a few flooding tolerant species. On damp mud (conditions associated with hydrological instability) total seedling number and species richness increased significantly, but species richness of germinating hydrophytes declined. Mean seedling density at 0–0.1m depth was 15450 ± 4400 m–2, reaching a maximum (162 050 m–2) in temporary backwaters. Annual (e.g., Lindernia dubia, Cyperus fuscus) and facultative ruderal species (e.g., Lythrum salicaria and Alisma plantago-aquatica) predominated. Vertical zonation of the propagule bank was weakly developed. The numbers of individuals and species germinating varied significantly between sites. The seasonal, most intensely disturbed sites (temporary backwaters) supported a numerically large, species-rich propagule bank based on floodplain annuals, while the permanent, less disturbed sites (ditches and an oxbow pond) had a small, species-poor propagule bank composed of hydrophytes and helophytes supplemented by allochthonous seed inputs. Sites intermediate on the gradient had a propagule bank dominated by facultative amphibious, ruderal hydrophytes. The composition of the seed bank and the established vegetation was most similar at the heavily disturbed sites where the seed bank was maintained by vigorously fruiting annuals and supplemented by inputs from temporary habitats upstream. At permanent sites much of the propagule bank composition could be accounted for by inputs of floodborne seed from the immediately adjacent floodplain. The established vegetation at such sites appeared to be maintained mainly by vegetative propagation with recruitment from the propagule bank likely only after severe disturbance. The potential contribution of functionally diverse propagule banks to sucessional processes within fluvially dynamic floodplain aquatic habitats is emphasised.     

Restoration and creation of freshwater wetlands using seed banks

The minimum information about a seed bank needed for a wetland restoration or creation project is a species list. There are two basic techniques for determining the composition of seed banks: (1) mechanical separation of seeds from a volume of soil and (2) germination of seeds from a volume of soil under appropriate environmental conditions. The latter method always gives biased results. It is best to collect as many random samples as possible when sampling a wetland seed bank. These can be combined as needed for processing. Field studies in India have demonstrated that vestigial seed banks can be used to re-establish a former vegetation type in a monsoonal wet-land that had become overgrown by a species of grass. In less than a year, 9 of 1 I species in the vestigial seed bank were found growing in areas cleared of the grass. Vestigial seed banks of drained prairie wetlands in the northcentral United States contained a few wetland species after 70 years, although species diversity and seed density declined significantly after 20 to 30 years of drainage and cultivation. In Florida, U.S.A., wetlands have been established in strip-mined areas using donor soils from existing wetlands. Newly established wetlands quickly developed a dense cover of vegetation, although this vegetation often lacked many desirable wetland species. Experimental studies of soil moisture conditions using a seed bank from the Delta Marsh, Canada, demonstrated that soil moisture affected both the total number of seeds, and the relative proportion of seeds of each species that germinated from a seed bank. The density of seedlings of emergent wetland species in the treatments was directly proportional to soil moisture, while that of terrestrial annuals was inversely proportional. Emergent species made up nearly 90% of the seedlings in the wettest treatment and 0% in the driest.From a paper presented at the Third International Wetlands Conference, 19–23 September, 1988, University of Rennes, France.     

Soil seed banks of two montane riparian areas: implications for restoration

Understanding the role of seed banks can be important for designing restoration projects. Using the seedling emergence method, we investigated the soil seed banks of two montane, deciduous riparian forest ecosystems of southeastern Arizona. We contrasted the seed banks and extant vegetation of Ramsey Canyon, which is the site of riparian restoration activities, with that of Garden Canyon, which has been less affected by human land uses. Fewer plant species were found at Ramsey Canyon than Garden Canyon, for both the seed bank and extant vegetation, and the vegetation at Ramsey Canyon (seed bank and extant) had consistently drier wetland indicator scores. As well, vegetation patterns within sampling zones (channel margins and adjacent riparian forests) differed between canyons. At Garden Canyon channel margins, the seed bank and extant vegetation had relatively high similarity, with herbaceous wetland perennial species dominating. Extant vegetation in the floodplain riparian forest zone at Garden Canyon had a drier wetland indicator score than the seed bank, suggesting that the floodplains are storing seeds dispersed from wetter fluvial surfaces. Vegetation patterns for Ramsey Canyon channel margins were similar to those for Garden Canyon floodplains. Vegetation patterns in the Ramsey Canyon riparian forest zone were indicative of non-flooded conditions with an abundance of upland species in the soil seed bank and extant vegetation. Channel geomorphology measurements indicated that much of the riparian forest zone at Ramsey Canyon is functionally a terrace, a condition that may be a legacy of channel erosion from historic land uses. Steep, erodible channel slopes may contribute to the low seed bank germinant density at Ramsey Canyon channel margins, and narrower flood-prone area may explain the greater terrestrialization of the vegetation in both sampling zones. We recommend testing the use of donor soils from more diverse stream reaches to restore biodiversity levels at Ramsey Canyon, following restoration activities such as channel-widening. Seed banks from Garden Canyon, for example, although predominantly consisting of herbaceous perennials, would supply species with a range of moisture tolerances, life spans, and growth forms. We also recommend that restorationists take care not to harm seed banks exposed during removal of introduced species; at Ramsey Canyon, soil seed banks were equally diverse in areas with high and low cover of the introduced Vinca major (a legacy of Ramsey Canyon land use).     

湿地土壤种子库与地上植被相似性关系研究评述

土壤种子库与地上植被的关系是土壤种子库研究的重要组成部分。当前,湿地生态系统面临严重威胁,研究湿地土壤种子库和地上植被关系既可以加强对土壤种子库和植物群落特征的认识,又可以为湿地保护与管理提供理论指导。检索了科学引文索引扩展版(SCIE)数据库中收录的1900—2012年间研究湿地土壤种子库与地上植被关系的文献,通过分析土壤种子库与地上植被的Srensen相似性系数,结果发现:不同湿地类型的土壤种子库和地上植被的相似性存在显著差异,河流湿地中两者的相似性最小;不同植被类型中土壤种子库与地上植被的相似性差异显著:草本群落的相似性大于乔木群落;不同气候带的湿地中两者的相似性也存在显著差异,其中亚热带地区相似性最小。总结了湿地种子库与地上植被相似性关系的时空变化特征。二者的相似性通常随着植物群落的演替而减小,在空间上也随着环境梯度而变化。分析了两者关系的影响因素,如种子传播、环境条件和繁殖策略等。对研究中存在的问题及发展方向提出建议。     

洞庭湖青山垸退耕地不同水位土壤种子库特征

研究退耕地土壤种子库的组成特点和分布规律是评价受损湿地生态恢复效应的重要组成部分.本文以洞庭湖典型退田还湖区——青山垸为对象,研究了不同水位及湿地土壤(0～2、2～5和5～10 cm)种子库的大小、物种组成多样性及其与地上植被的关系.结果表明: 青山垸土壤种子库密度、丰富度指数以及地上植被与土壤种子库的相似性系数沿低-中-高水位梯度呈“V”型变化.常淹区种子库密度最高,为(36943±5207)粒·m^-2,偶淹区最低,为(18618±6977)粒·m^-2,洪淹区居中,为(30572±5329)粒·m^-2;地上植被与土壤种子库的相似性系数(Sorensen系数)为常淹区(0.76)>洪淹区(0.53)>偶淹区(0.41).种子库密度、物种多样性指数和物种丰富度指数沿土壤剖面呈递减趋势,但不同水位的递减幅度存在差异.种子库密度、物种丰富度以及地上植被与湿地种子库的相似性系数沿水位梯度呈规律性变化,与其所处的地理位置水文波动和植被的物种生活型组成等密切相关.     

Evaluating Hydroperiod Response in Restored Carolina Bay Wetlands Using Soil Physicochemical Properties

Carolina bays are shallow depression wetlands found in the southeastern United States that have been severely altered by human activity. The need to restore these complex and diverse systems is well established, but our limited understanding of wetland hydrologic processes in these systems hinders our ability to assess the effectiveness of bay restoration efforts. Carolina bays exhibit a wide range of moisture regimes from seasonally saturated to semipermanently inundated. Differing physicochemical properties of soils within bay interiors may control bay hydrology. However, previous efforts to establish relationships between soil characteristics and bay hydrology have been inconclusive. An assessment of soil and hydroperiod was initiated in 16 bays designated to be restored and 6 bays that were not restored (reference). Soil morphology was described, and permanent monitoring wells were installed at each site. Multiple regression analysis was used to determine relationships between the soil physicochemical characteristics and the bay hydroperiod for restored and reference bays in both pre‐ and postrestoration periods. A significant relationship (r²= 0.75, p= 0.02) between prerestoration hydroperiod and clay content in the argillic horizon (Bt) of the reference bays was observed. This relationship was then used to evaluate hydroperiod change in the restored bays from the postrestoration period. The relationship accurately identified sites that exhibited high prerestoration hydroperiods and did not need hydrologic restoration (n= 4) and effectively showed sites that exhibited substantial increases in hydroperiod due to the restoration activities (n= 7).     

Effects of ungulates and prairie dogs on seed banks and vegetation in a North American mixed-grass prairie

The relationship between vegetation cover and soil seed banks was studied in five different ungulate herbivore-prairie dog treatment combinations at three northern mixed-grass prairie sites in Badlands National Park, South Dakota. There were distinct differences in both the seed bank composition and the aboveground vegetation between the off-prairie dog colony treatments and the on-colony treatments. The three on-colony treatments were similar to each other at all three sites with vegetation dominated by the forbs Dyssodia papposa, Hedeoma spp., Sphaeralcea coccinea, Conyza canadensis, and Plantago patagonica and seed banks dominated by the forbs Verbena bracteata and Dyssodia papposa. The two off-colony treatments were also similar to each other at all three sites. Vegetation at these sites was dominated by the grasses Pascopyrum smithii, Bromus tectorum and Bouteloua gracilis and the seed banks were dominated by several grasses including Bromus tectorum, Monroa squarrosa, Panicum capillare, Sporobolus cryptandra and Stipa viridula. A total of 146 seedlings representing 21 species germinated and emerged from off-colony treatments while 3069 seedlings comprising 33 species germinated from on-colony treatments. Fifteen of the forty species found in soil seed banks were not present in the vegetation, and 57 of the 82 species represented in the vegetation were not found in the seed banks. Few dominant species typical of mixed-grass prairie vegetation germinated and emerged from seed banks collected from prairie dog colony treatments suggesting that removal of prairie dogs will not result in the rapid reestablishment of representative mixed-grass prairie unless steps are taken to restore the soil seed bank.     

Fifteen Years of Vegetation and Soil Development after Brackish-Water Marsh Creation

Aboveground biomass, macro‐organic matter (MOM), and wetland soil characteristics were measured periodically between 1983 and 1998 in a created brackish‐water marsh and a nearby natural marsh along the Pamlico River estuary, North Carolina to evaluate the development of wetland vegetation and soil dependent functions after marsh creation. Development of aboveground biomass and MOM was dependent on elevation and frequency of tidal inundation. Aboveground biomass of Spartina alterniflora, which occupied low elevations along tidal creeks and was inundated frequently, developed to levels similar to the natural marsh (750 to 1,300 g/m²) within three years after creation. Spartina cynosuroides, which dominated interior areas of the marsh and was flooded less frequently, required 9 years to consistently achieve aboveground biomass equivalent to the natural marsh (600 to 1,560 g/m²). Aboveground biomass of Spartina patens, which was planted at the highest elevations along the terrestrial margin and seldom flooded, never consistently developed aboveground biomass comparable with the natural marsh during the 15 years after marsh creation. MOM (0 to 10 cm) generally developed at the same rate as aboveground biomass. Between 1988 and 1998, soil bulk density decreased and porosity and organic C and N pools increased in the created marsh. Like vegetation, wetland soil development proceeded faster in response to increased inundation, especially in the streamside zone dominated by S. alterniflora. We estimated that in the streamside and interior zones, an additional 30 years (nitrogen) to 90 years (organic C, porosity) are needed for the upper 30 cm of created marsh soil to become equivalent to the natural marsh. Wetland soil characteristics of the S. patens community along upland fringe will take longer to develop, more than 200 years. Development of the benthic invertebrate‐based food web, which depends on organic matter enrichment of the upper 5 to 10 cm of soil, is expected to take less time. Wetland soil characteristics and functions of created irregularly flooded brackish marshes require longer to develop compared with regularly flooded salt marshes because reduced tidal inundation slows wetland vegetation and soil development. The hydrologic regime (regularly vs. irregularly flooded) of the “target” wetland should be considered when setting realistic expectations for success criteria of created and restored wetlands.     

Revegetation following experimental disturbance in a boreal old-growth Picea abies forest

Abstract. We studied revegetation patterns after experimental fine-scale disturbance (e.g. uprooting) in an old-growth Picea abies forest in southeastern Norway. An experimental severity gradient was established by manipulation of the depth of soil disturbance; two types of disturbed areas were used. Species recovery was recorded in the disturbed patches in three successive years after disturbance. The cover of vascular plants and, even more so the cover of bryophytes and lichens, recovered slowly after disturbance. The least severe treatments (removal of vegetation and removal of vegetation and the litter layer) was followed by the fastest recovery. The mean number of vascular plant species was usually higher three years after disturbance than before disturbance, while the opposite was true for bryophytes. Several vascular plant species that were abundant in intact forest floor vegetation (Vaccinium myrtillus, V. vitis-idaea and Deschampsia flexuosa) recovered during a three-year period primarily by resprouting from intact rhizomes and clonal in-growth. Other important recovery mechanisms included germination from a soil-buried propagule bank (e.g. Luzula pilosa, Plagiothecium laetum agg., Pohlia nutans and Polytrichum spp.) and dispersal of propagules into the disturbed patches (e.g. Betula pubescens and Picea abies). Microsite limitation seemed to occur in several species that were abundant in the soil propagule bank (e.g. the ferns Athyrium filix-femina, Gymnocarpium dryopteris and Phegopteris connectilis) but which did not appear in disturbed patches. Disturbance severity influenced revegetation patterns, recorded both as trajectories of vegetation composition in a DCA ordination space and as change in floristic dissimilarity. The length of the successional path (compositional change measured in β-diversity units) increased with increasing disturbance severity, and was also influenced by the area of the disturbed patch and the distance to intact vegetation. The rate of succession depended on the method by which it was measured; decreasing year by year in floristic space, while first decreasing and then increasing in ordination space. The reason for this difference is explained.     

Resilience of soil seed banks to site degradation in intermittently flooded riverine woodlands

Questions: (1) What is the recovery potential of soil seed banks of intact, average and degraded floodplain woodlands? (2) Will soil seed banks of different functional groups (native and exotic, dryland and wetland) display contrasting responses to site degradation? Location: Semi‐arid, seasonally flooded woodland of eastern Australia. Methods: Diversity, abundance and composition of soil seed banks were assessed using a glasshouse study. Surface soil samples were taken from a total of nine sites with three levels of degradation (intact, average, degraded) from three microsites (sub‐canopy, canopy edge, open). Results: A total of 26 662 individuals of 82 species germinated. Seed abundance increased tenfold from intact to degraded sites, but there was no effect on richness. Species composition of all functional groups varied significantly among degradation states. Seeds of native wetland and exotic dryland species were more abundant in degraded than in intact sites. However, the abundance of native dryland germinants did not differ among degradation classes and no seeds of exotic wetland species were observed. Richness of exotic dryland species was significantly higher in degraded sites. Conclusions: Increasing disturbance promoted seed banks of exotic but not native dryland species and native but not exotic wetland species. Unexpectedly, disturbance promoted the abundance of native seeds more than exotics, although this was driven by a single species. Our results suggest that the dryland phase of the floodplain community is more resilient to degradation than predicted.