Vegetation Colonization Research Articles

Early Holocene climate variability and the timing and extent of the Holocene thermal maximum (HTM) in northern Iceland

The magnitude and timing of Holocene maximum warmth in the Arctic and sub-Arctic has been the subject of considerable recent interest, particularly in the context of future climate change. Although lying at a crucial location in the North Atlantic close to significant atmospheric and oceanic boundaries, terrestrial Holocene climatic data from Iceland are few and predominantly derive from glacial and palaeoecological evidence. Here we present new datasets from Tröllaskagi, based on chironomid-inferred temperatures (CI-T), using sub-fossil chironomids from the same lake sediments supplemented by pollen data. July air temperatures have been derived using an Icelandic training set, and the data suggest optimal temperatures at sea level up to 1.5 °C above current levels around 8 k cal. yr BP, a time when birch woodland was well developed in Tröllaskagi, but when woodland had still not fully developed in the more isolated NW peninsula. Our data thus suggest that optimal summer warmth did not occur in Iceland until 8 kcal. yr BP at the earliest, possibly lasting until 6.7 kcal. yr BP. The amount of warming for July was therefore at least 1.5 °C, but possibly up to 2–3 °C higher than the 1961–1990 average on the basis of the tree-line data. Comparison with data from elsewhere in adjacent Arctic regions, Greenland and Eastern Arctic Canada show peak warmth to be later in Iceland, and less pronounced. It also appears that there were enhanced temperature gradients during the first half of the Holocene between the two study areas Tröllaskagi and the NW Peninsula and that they influenced patterns of vegetation colonisation, with current spatial temperature patterns only developing as Holocene climate deteriorated after around 6 kcal. yr BP.

A conceptual model of depositional, rather than erosional, tidal channel development in the rapidly prograding Skagit River Delta (Washington, USA)

AbstractThe origin and growth of blind tidal channels is generally considered to be an erosional process. This paper describes a contrasting depositional model for blind tidal channel origin and development in the Skagit River delta, Washington, USA. Chronological sequences of historical maps and photos spanning the last century show that as sediments accumulated at the river mouth, vegetation colonization created marsh islands that splintered the river into distributaries. The marsh islands coalesced when intervening distributary channels gradually narrowed and finally closed at the upstream end to form a blind tidal channel, or at mid‐length to form two blind tidal channels. Channel closure was probably often mediated through gradient reduction associated with marsh progradation and channel lengthening, coupled with large woody debris blockages. Blind tidal channel evolution from distributaries was common in the Skagit marshes from 1889 to the present, and it can account for the origin of very small modern blind tidal channels. The smallest observed distributary‐derived modern blind tidal channels have mean widths of 0·3 m, at the resolution limit of the modern orthophotographs. While channel initiation and persistence are similar processes in erosional systems, they are different processes in this depositional model. Once a channel is obstructed and isolated from distributary flow, only tidal flow remains and channel persistence becomes a function of tidal prism and tidal or wind/wave erosion. In rapidly prograding systems like the Skagit, blind tidal channel networks are probably inherited from the antecedent distributary network. Examination of large‐scale channel network geometry of such systems should therefore consider distributaries and blind tidal channels part of a common channel network and not entirely distinct elements of the system. Finally, managers of tidal habitat restoration projects generally assume an erosional model of tidal channel development. However, under circumstances conducive to progradation, depositional channel development may prevail instead. Copyright © 2006 John Wiley & Sons, Ltd.

Spatial organization and ecohydrological interactions in oxygen‐limited vegetation ecosystems

Wetlands are characterized by extremely high biodiversity and primary productivity (comparable to tropical rain forests), provide critical habitats for rare and endangered vegetation and animal species, and mediate the effects of floods and the action of the sea on the coast. A deep understanding of wetland system functioning cannot be acquired by simply reducing its dynamics to a collection of parts but requires the explicit description of wetland physical and ecological processes as fully interacting components. In fact, the complex spatial ecohydrological patterns characterizing wetland areas arise as a result of the coupled evolution of their ecological, hydrological, and morphological features. Here we examine observations of prominent spatial patterns in wetland vegetation and link them to the relevant hydrological and ecological processes. We describe the limitations to vegetation development due to scarce soil oxygen availability and implement a mathematical model, based on Richards' equation, coupling subsurface water flow and plant water uptake in a tidal salt marsh. The soil aeration patterns arising from such interactions highlight the central role of vegetation in increasing soil aeration, possibly inducing the establishment of a permanently aerated soil layer (in spite of tidal flooding), and the influence of different soil characteristics on soil oxygen availability. Finally, we discuss how ecohydrological interactions can contribute to explain patterns of vegetation colonization and spatial heterogeneity.

Spatio‐temporal scales of dispersal limitation in the recolonization of a semi‐arid mediterranean old‐field

Dispersal and establishment limitations have been proposed as important mechanisms that control vegetation colonization processes. While many studies have emphasized the role of dispersal limitation in the dynamics of plant communities, little is known about the spatial and temporal scales at which dispersal limitation affects plant population dynamics. In this study we investigate spatial and temporal scales of dispersal limitation in a system of semi‐arid Mediterranean old‐fields recolonized by the dominating dwarf shrub Sarcopoterium spinosum (Rosaceae). Our analysis was based on a combination of two complementary approaches: 1) age analysis of S. spinosum shrubs growing at different distances from source populations, and 2) a corresponding analysis of changes in vegetation cover since recolonization onset (ca 55 yr ago), based on information obtained from historical aerial‐photographs. Shrubs sampled in plots near the source populations were similar in their age distribution to the source populations, but significantly different from shrubs sampled far from the source populations. Increasing distance from source populations was associated with a decrease in median age of the shrubs, and in the density and relative frequency of adult shrubs (>15 yr). These patterns of changes in age structure occurred over distances of several tenths of meters. Young age groups (<5 yr) were scarcely represented in all plots, suggesting that establishment limitation was also important in determining recolonization rates. Analysis of the aerial photographs supported the results of the age analysis, showing evidence for both distance effect and establishment limitation. We conclude that dispersal limitation may have a long‐term impact on vegetation patterns, even at small spatial scales, and that dispersal limitation interacts with establishment limitation in determining recolonization processes.

Short-term Periglacial Processes, Vegetation Succession, and Soil Development within Sorted Patterned Ground: Jotunheimen, Norway

Small (1 ≤ m diameter) sorted patterned ground features were studied on the Little Ice Age forelands of three Jotunheimen glaciers. Patterned ground appears to be most active near the ice margins, declining in intensity of activity with distance from the glaciers. Vegetation and soil development are negligible within patterned ground that is “Recent” (decadal time frame). Significant (P < 0.05) fine scale differences in vegetation and soil development occur within patterned ground on terrain ∼70 yr in age, with patterned ground borders having higher values of vegetation cover and thicker soils than that in patterned ground centers. With increasing age of terrain and patterned ground, soil development and vegetation encroach inward toward patterned ground centers, implying that a short-term, active periglacial zone exists near the ice margin, decaying with time and glacier retreat. Specifically, terrain that has been deglaciated for ∼70 years and is approximately ∼350–500 m from the ice margin shows a significant decline in frost activity, allowing for the initiation of pedogenesis and vegetation colonization.

Ice-wedge casts in Late Wisconsinan glaciofluvial deposits, southern Ontario, Canada

Ice-wedge casts in Late Wisconsinan glaciofluvial sand and gravel deposits in southern Ontario taper downwards to form a V- or funnel-shaped morphology, ranging from 1 to over 3 m deep and from 1.0 to 2.5 m wide at the top. Pressure-derived primary structures, caused by repeated thermal contraction and expansion, include upturned strata, realigned stones, and small folds in the enclosing sediments. Although paleotemperature is difficult to estimate, the presence of ice-wedge casts testifies to the former presence of permafrost under prevailing periglacial conditions over this area. The regional till stratigraphy constrains the timing of ice-wedge growth to ca. 15 000 to ca. 13 000 BP. At this time, newly exposed terrains would have occurred in an interlobate area where severe climate created favourable conditions for permafrost to develop due to the close proximity to the receding ice. Inactive areas in braided rivers such as raised topographic surfaces and sand-filled channels with limited vegetation cover and minimal capability to trap drifting snow would have greatly enhanced ice-wedge growth. Rapid climatic amelioration and vegetation colonization across this area beginning ca. 13 000 BP probably slowed or stopped the growth of ice wedges. This limited window of opportunity, both geographically and in time, probably accounts for the limited occurrence of ice-wedge casts in southern Ontario.

Florística da vegetação arbustivo - arbórea colonizadora de uma área degradada por mineração de caulim, em Brás Pires, MG

Este estudo teve como objetivos analisar a composição florística da vegetação arbustivo-arbórea colonizadora de uma área degradada por mineração de caulim, em Brás Pires, MG, compará-la com outros fragmentos florestais e caracterizar aspectos de auto-ecologia das espécies e o solo da área. O levantamento florístico abrangeu uma área de 0,5 ha, subdividida em 50 parcelas contíguas de 10 m x 10 m. Foram incluídos todos os indivíduos com CAP igual ou superior a 10 cm. A composição florística é o resultado desse levantamento acrescida de coletas fora da área de amostragem, totalizando 64 espécies, distribuídas em 50 gêneros e 30 famílias. As famílias com maior número de espécies foram Leguminosae (11), Annonaceae (5), Lauraceae e Melastomataceae (4), enquanto o gênero mais rico foi Machaerium (3). A análise do substrato, nas condições em que se encontrava, revelou que este não impedia o estabelecimento da vegetação. A síndrome de dispersão preponderante era a zoocórica, destacando-se a importância de indivíduos remanescentes, fragmentos próximos e sua fauna associada. A maior similaridade florística ocorreu com o fragmento em Cruzeiro, SP, estando ambas as áreas em início de sucessão.

Changes in land cover and shallow landslide activity: A case study in the Spanish Pyrenees

The Pyrenees, like many other mountain areas in Europe, have experienced depopulation and land abandonment during the 20th century. This has encouraged vegetation recovery in formerly occupied areas, including reforestation to promote woodland. The objective of this study is to analyse the effects of these changes on shallow landsliding, a process responsible for erosion and land degradation in many mountain areas. A sequence of aerial images reveals a slight decrease in the landslide occurrence rate in the last half of the 20th century and a parallel increase in the landslide extinction rate, i.e. the rate at which evidence of landslide activity is removed by vegetation colonisation. A logistic regression routine was used to assess the influence of land use and vegetation recovery in the occurrence of shallow landslides. The result shows that the former arable fields on the valley slopes still facilitate landsliding, even after land abandonment and revegetation by shrubs or trees. A shift in the topographic location of landslides was also detected, pointing to an increased importance of water redistribution in the slopes after prolonged rainfall periods.

Environmental impacts of surface mining on mined lands, affected streams and agricultural lands in the Dabaoshan Mine region, southern China

AbstractImpacts of surface mining on ecosystems were investigated in the Guangdong Dabaoshan Mine region, southern China. Significant soil acidification has been induced by mining activities which cause oxidation of metal sulfides contained in the mine spoils. Natural colonization of vegetation in the mine site has been impeded and this has resulted in severe soil erosion. Acid mine drainage from this mine site has caused the degradation of the downstream aquatic ecosystems. Mine water with pH&lt; 3·5 has been continuously flowing into a first‐order tributary of the Beijiang River and has destroyed all the aquatic life to a distance of at least 25 km downstream of the discharge point, even when the pH rose to above 6 in the Hengshishui River (a third‐order tributary of the Beijiang River). Further downstream, macroinvertebrates first occurred at about 30 km from the discharge point, and only one species was found. This is in contrast to a reference site that was not affected by acid mine drainage, where 36 macroinvertebrate taxa were found. Acidic mine water also had marked impacts on the agricultural lands irrigated with it. Severe contamination of the soils by mine drainage is responsible for the extremely high concentrations of some heavy metals in the edible portions of a variety of food crops grown on the agricultural lands. Copyright © 2005 John Wiley &amp; Sons, Ltd.

Radar Architecture and Evolution of Channel Bars in Wandering Gravel-Bed Rivers: Fraser and Squamish Rivers, British Columbia, Canada

Abstract The alluvial architecture and evolution of two kilometer-scale compound bars in the wandering gravel-bed Fraser and Squamish rivers, British Columbia, Canada, are described. Integrating ground-penetrating radar, bathymetry, and aerial photographs enables the internal architecture to be linked to the evolution of the gravelly barforms over the previous 50 years. These linkages reveal the sedimentary mechanisms that formed the various architectural packages within compound bars and unit bars. Growth of compound bars is controlled by the accretion of unit bars onto discrete segments along their gravelly edges. The attachment of unit bars deflects the thalweg to impinge on and erode specific portions of bars and channel banks. Bar growth leads to the stabilization of bars, vegetation colonization of bar interiors, and island formation. It is the formation of islands, along with channel avulsions, that maintains channel division in wandering rivers. Seven styles of gravelly deposition are imaged in the alluvial architecture. Vertical-accretion deposits formed from the deposition of gravelly bedload sheets are the most common strata. A moderate abundance of slipface deposits preserves high-relief bar margins. Lateral accretion dominates point-bar deposits. Downstream-accretion deposits govern some phases of down-bar growth. Partial and complete channel-fill and chute-fill deposits are eroded into underlying sediments, as are scour-and-fill deposits. Upstream-accretion deposits are uncommon. A depositional model of gravelly channel bars in the two rivers is presented and reveals that the architecture is made up of depositional styles similar to those observed in braiding-river successions, although the sedimentary packages are preserved in different proportions. Differences in braiding-river and wandering-river sedimentology largely reflect the relatively frequent migration of channels and bars in braiding rivers, which preserve high proportions of channel fill and chute fill, and confluence scour-and-fill deposits. Conversely, the moderately stable island and channel network in wandering rivers limits channel shifting and consequently preserves a low number of channel fills. Moderate proportions of slipface strata and coherent patterns of sand deposition along bar tops provide evidence of comparatively uniform flow patterns in independent channel segments divided by islands. These patterns of bar sedimentation and channel shifting preserved in the alluvial architecture appear to be signature characteristics of wandering rivers. The occurrence of similar architecture in both the Fraser and Squamish rivers suggests that the model likely applies to most wandering gravel-bed rivers.

Soil seed bank of the waste landfills in South Korea

The restoration of urban landfill is a topic of growing interest in reclamation ecology as the acreage of abandoned sites near cities increases. The goals of this study were to assess the ecological status of waste landfills and to elucidate the role of seed banks in the establishment of vegetation at these sites. The study sites were located at five landfills around Seoul and Kyongki Province. On average, soils were sampled on 20 plots per landfill in 2001 to record species composition and to estimate the number of seeds in the soil. Soil seed bank vegetation and the individual number of seedlings that germinated were recorded using the seedling emergence method. Relative density per species was calculated from the number of individual seedlings. We conducted canonical correspondence analysis (CCA) using the program CANOCO to survey the relationships between 23 environmental variables and plant importance values. Environmental variables included categorical and numerical variables (landfill age, landfill size, distance from landfill edge, human disturbance level, slope, periodic management level) and soil physico-chemical variables (bulk density, soil moisture content, organic matter content, total N, available P, K, Na, Ca, Mg, Cd, Cr, Cu, Fe, Mn, Ni, Pb, and Zn). The mean seedling density per m 2 differed significantly among sites (P < 0.05). As landfill age increased, the mean seedling density per m 2 decreased. The mean seedling density of the Sangpaedong landfill, which was less than 1 year old, was higher than that found in 6- and 7-year-old landfills. The Sangpaedong landfill mainly contained seeds of Chenopodium albumL. and Digitaria ciliaris(L.) SCOP. With regard to early vegetative colonization in landfills, our results highlighted the importance of seed banks occurring in cover soils. Cover soils, derived from various sources, will determine landfill landscapes because of different seed banks present in them. The first axis of the CCA was correlated with landfill age, Na, and human disturbance level, while the second axis was correlated with landfill size, slope, periodic management level, Zn, total N, and organic matter content. Understanding seed banks in landfill cover soils is important, therefore, for proper landfill management and restoration.

Natural recovery from accelerated forest ditch and stream bank erosion five years after harvesting of plantation forest on Plynlimon, mid‐Wales

AbstractErosion rates surveyed using 230 erosion pins on 24 occasions over eight years (1994–2001) on forested stream banks, tributaries and forest ditches in the 0·89 km2 Nant Tanllwyth catchment, part of the Hafren Forest on Plynlimon, mid‐Wales, showed statistically significant increases of up to 40 mm a−1 in mean erosion rates during the two‐year period in which environmentally sensitive plot‐scale timber harvesting operations took place (1996–97). In the four years following timber harvesting mean erosion rates at all sites recovered to levels that were lower than before the harvesting operations began. This is attributed to increased light levels, following canopy removal, allowing vegetation to colonize exposed banks. There was a statistically significant relationship (p &lt; 0·05) between mean erosion rate in 2000–01 (four years after harvesting) and percentage vegetation cover at erosion monitoring sites in the clearfelled (south tributaries) area though the same relationship did not hold for sites on the mainstream banks or for sites on the north (mature forest) ditch sites. The implications of natural vegetation colonization for management of such streams are discussed. Copyright © 2005 John Wiley &amp; Sons, Ltd.

Recent stabilization of active sand dunes on the Canadian prairies and relation to recent climate variations

The historical activity of sand dunes on the southern Canadian prairies was investigated in order to determine the relation with recent climate variations. Changes in dune activity were determined from historical aerial photographs at seven sites with active parabolic dunes in Saskatchewan and Manitoba. The methodology developed combines digital image processing and geographical information system (GIS) analysis to measure changes in dune activity from the aerial photographs, as well as correlation analysis to determine the relation between dune activity and climate variations. Overall, dune activity has been decreasing since the early to mid 1900s as evidenced by greater vegetation colonization than sand dune migration or reactivation. The decrease in dune activity is significantly correlated with decadal-scale variations in aridity and is coincident with a decrease in annual wind speed. Evidence suggests that this response is superimposed on a longer trend towards stabilization, possibly in place since the late 1700s. Taken together, the effect of this complex response is that dune recovery on the southern Canadian prairies is prolonged well after an initial disturbance and therefore gives the impression of anomalous levels of activity for extended periods thereafter. For this reason, dune mobility indices predicated on short-term climate variations (years to decades) do not fully describe the present level of dune activity on the southern Canadian prairies.

Vegetation establishment, succession and microsite frost disturbance on glacier forelands within patterned ground chronosequences

AbstractAim The impact of microscale frost disturbance on vegetation colonization and successionary trends was examined within patterned ground features of Little Ice Age chronosequences. The goal was to investigate and compare vegetation response to micro‐site frost disturbance with that of previous studies done at a coarser landscape scale.Location The study sites occur on Little Ice Age glacier forelands within Jotunheimen, Norway (61°–62° N). The forelands of the glaciers Slettmarkbreen, Styggedalsbreen and Vestre Memurubreen have been well studied providing chronological controls for landscape studies. Sorted patterned ground features are found within the chronosequences, typically declining with frost intensity and disturbance with increasing terrain age.Methods Micro‐plots (8.3 × 8.3 cm) were placed at the inner borders and centres of patterned ground features. Species were identified and per cent species cover and per cent cover of life‐form category were noted. Nonparametric Kruskal–Wallis and Mann–Whitney U‐tests were used to test for differences between percent cover of life‐form categories within patterned ground features as well as to identify thresholds of successional change across the chronosequences.Results Significant relationships between life‐from groups and patterned ground positions of varying ages were deduced using nonparametric statistics. Findings were then used to discuss trends of succession within patterned ground features and across the chronosequences. Vegetation establishment occurs at the border positions of young (&lt; 30 years) patterned ground features. With time and distance from the ice margin, vegetation encroaches inwards toward the disturbed centres. Succession within patterned ground exhibits several stages: (1) bryophytes/crusts and lichens, (2) grasses/sedges and (3) woody shrubs. The occurrence of forbs was sporadic and generally non‐significant.Main conclusions Frost disturbance in patterned ground appears to delay successional trends of vegetation communities when compared with previous studies on ‘stable’ terrain, producing micro‐site lag effects. These small patches of disturbed ground are therefore important regarding vegetation assemblages across the landscape and are unlikely to be detected at the landscape scale.

Recolonization dynamics in a mixed seagrass meadow: The role of clonal versus sexual processes

Recolonization dynamics from disturbance on a Philippine mixed seagrass meadow, containing species spanning more than 10-fold in rhizome elongation rates and reproductive effort, was examined by following the recovery of a 1,200 m2 gap over 2.5 yr. The objective was to assess the contribution of contrasting species to the recovery process and to evaluate the importance of sexual versus vegetative colonization. Large, slow-growing species,Thalassia hemprichii andEnhalus acoroides, that produce large, broadly-dispersed seeds dominated sexual colonization with a total of 2,643 and 210 seedlings, respectively, recruiting to the area. Despite very rapid turnover of sexual recruits, the high frequency of seedling establishment ensured successful development of new patches in areas devoid of vegetation, leading to a scattered and evenly distributed presence of vegetation inside the gap. The small seagrass speciesCymodocea rotundata andHalodule uninervis, characterized by fast rhizome elongation rates but low reproductive output and limited seed dispersal, were the major contributors to the overall 450 m2 increase in vegetation cover through fast lateral extension (144±6 cm yr−1) from meadow edge and surviving patches, forming a compact vegetation cover in one edge of the denuded area. We conclude that contrasting recruitment strategies in the mixed-species seagrass community examined have implications for colonization potential at different spatial scales. Fast clonal growth is only an efficient mechanism for colonization of disturbances within established meadows (small gaps), whereas the large species, which combined high reproductive output with high seed dispersal capacity, may act to accelerate the colonization process in large gaps or distant from established meadows.

Patterns of channel adjustment to impoundment of the upper River Spey, Scotland (1942–2000)

AbstractOver the last 30 years, understanding of how river channel morphology adjusts to upstream impoundment has been improved considerably with clearwater erosion close to the dam and aggradation downstream of unregulated tributary confluences being identified. In a UK context our understanding of channel response to impoundment has been based principally on analysis of a number of regulated rivers using a time–space substitution approach but the temporal pattern of channel change was not fully observed. This paper details channel change over almost six decades following impoundment of the River Spey, Scotland, primarily via the use of cartographic and aerial photographic evidence. Channel change initially involved the formation of tributary confluence bars followed by bench development and vegetation colonization and development on the benches and gravel bars. Sixty years after impoundment, the channel is still adjusting its form at distance from the dam to be in quasi‐ equilibrium with its regulated flow regime; indeed adjustment was most rapid between 1989 to 1995. This accelerated adjustment is due to the occurrence of a greater number of large and geomorphologically significant flood events in this period. Sediment supply limitation from unregulated tributaries will have stemmed the rate of narrowing and bench development prior to 1989. This spatial and temporal pattern of adjustment supports, for the most part, the model advocated by Petts (Progress in Physical Geography, 1979, Vol. 3, pp. 329–362). The wider implications of the channel change for river conservation and management are addressed. Copyright © 2003 John Wiley &amp; Sons, Ltd.

Rapid vegetation change during the early Holocene in the Faroe Islands detected in terrestrial and aquatic ecosystems

AbstractHigh‐resolution pollen, plant macrofossil and sedimentary analyses from early Holocene lacustrine sediments on the Faroe Islands have detected a significant vegetation perturbation suggesting a rapid change in climate between ca. 10 380 cal. yr BP and the Saksunarvatn ash (10 240±60 cal. yr BP). This episode may be synchronous with the decline in δ18O values in the Greenland ice‐cores. It also correlates with a short, cold event detected in marine cores from the North Atlantic that has been ascribed to a weakening of thermohaline circulation associated with the sudden drainage of Lake Agassiz into the northwest Atlantic, or, alternatively, a period with distinctly decreased solar forcing.The vegetation sequence begins at ca. 10 500 cal. yr BP with a succession from tundra to shrub‐tundra and increasing lake productivity. Rapid population increases of aquatic plants suggest high summer temperatures between 10 450 and 10 380 cal. yr BP. High pollen percentages, concentrations and influx of Betula, Juniperus and Salix together with macrofossil leaves indicate shrub growth around the site during the initial phases of vegetation colonisation. Unstable conditions followed ca. 10 380 cal. yr BP that changed both the upland vegetation and the aquatic plant communities. A decrease in percentage values of shrub pollen is recorded, with replacement of both aquatics and herbaceous plants by pioneer plant communities. An increase in total pollen accumulation rates not seen in the concentration data suggests increased sediment delivery. The catchment changes are consistent with less seasonal, moister conditions. Subsequent climatic amelioration reinitiated a warmth‐driven succession and catchment stabilisation, but retained high precipitation levels influencing the composition of the post‐event communities. Copyright © 2003 John Wiley &amp; Sons, Ltd.

Physical and Functional Responses to Experimental Marsh Surface Elevation Manipulation in Coos Bay's South Slough

AbstractDike material was used as fill to construct high, mid, and low intertidal elevations in a subsided marsh located in the South Slough National Estuarine Research Reserve, Oregon. Marsh surface elevation change (including fill consolidation and compression of the original marsh soils), vertical accretion, tidal channel development, emergent vegetation colonization, and fish use were monitored over 3 years. Significant marsh surface elevation loss was detected at all elevations, with fill consolidation accounting for 70% of the loss at the highest elevation. Vertical accretion averaged 0.19 cm/yr in the sparsely vegetated Kunz Marsh compared with 0.70 cm/yr at the densely vegetated reference sites. Tidal channel development was influenced as much by marsh surface gradient as by marsh surface elevation. Vegetation colonization was directly correlated with elevation, whereas density and species richness of fish was inversely correlated with elevation. Manipulating the marsh surface to mid‐marsh elevations favors rapid vegetation colonization and facilitates vertical accretion‐dominated tidal channel development. Low marsh elevations result in initially slower developing vegetation colonization and channel development but are more beneficial to fish during the early stages of marsh recovery. High marsh elevations appear to sacrifice tidal channel development and associated fish access for rapid vegetation colonization.

Drainage and Elevation as Factors in the Restoration of Salt Marsh in Britain

AbstractIntertidal restoration through realignment of flood defenses has become an important component of the U.K. coastal and estuarine management strategy. Although experimentation with recent deliberate breaches is in progress, the long‐term prognosis for salt marsh restoration can be investigated at a number of sites around Essex, southeast England where salt marshes have been reactivated (unmanaged restoration) by storm events over past centuries. These historically reactivated marshes possess higher creek densities than their natural marsh counterparts. Both geomorphology and sedimentology determine the hydrology of natural and restored salt marshes. Elevation relative to the tidal frame is known to be the primary determinant of vegetation colonization and succession. Yet vegetation surveys and geotechnical analysis at a natural marsh, where areas with good drainage exist in close proximity to areas of locally hindered drainage at the same elevation, revealed a significant inverse relationship between water saturation in the root zone and the abundance of Atriplex portulacoides, normally the physiognomic dominant on upper salt marsh in the region. Elsewhere in Essex natural and restored marshes are typified by very high sediment water contents, and this is reflected in low abundance of A. portulacoides. After a century of reestablishment no significant difference could be discerned between the vegetation composition of the storm‐reactivated marshes and their natural marsh counterparts. We conclude that vegetation composition may be restored within a century of dike breaching, but this vegetation does not provide a reliable indicator of ecological functions related to creek structure.

Physical Evolution of Restored Breached Levee Salt Marshes in the San Francisco Bay Estuary

AbstractSince 1972 over 940 ha (2,300 ac) of leveed former salt marsh sites around San Francisco Bay have been restored to tidal action, purposely or through natural processes. The evolution of these sites can inform predictions of rates of marshplain evolution and establishment of tidal channel systems. A review of the history of 15 re‐flooded sites ranging in size from 18 to 220 ha (45 to 550 ac) and in age from 2 to 29 years indicates that marshplain vegetation with more than 50% cover was established at nine of the sites within 4 to 20 years. The remaining six sites aged 2 to approximately 20 years continue to be less than 50% vegetated. The evolution of these sites is consistent with the following simple conceptual model of the physical evolution of restored tidal marshes in subsided breached sites. Initially, deposition of estuarine sediment builds up mudflats that allow vegetation establishment once elevations are high enough for vegetation to survive. Sites that are initially lower in the tidal frame take longer to vegetate than those that are initially higher. Three factors appear to retard the time frame for vegetation establishment: limited estuarine suspended sediment supply, erosion of deposited estuarine muds by internally generated wind waves, and restricted tidal exchange. These factors affect evolution more significantly in larger sites. The comparatively short time frame for vegetation colonization and marshplain evolution experienced in earlier, smaller, and/or less subsided breached levee restorations may not necessarily be replicable by simple levee breaching on larger subsided restoration sites now being planned. Our review of the 15 sites also indicates that the formation of tidal channels within the marshes is greatly dependent on whether and how high the site was filled before breaching. Filled sites at high intertidal elevations (above approximately 0.3 m below mean higher high water) can vegetate quickly but after several decades may show little development of tidal channels.