Removing the sands (sins?) of our past: dredge spoil removal and saltmarsh restoration along the Indian River Lagoon, Florida (USA)

Estuarine saltmarshes are widely recognized as highly productive and biologically diverse systems. The Indian River Lagoon (IRL) is a 250?km long ??Estuary of National Significance?? along Florida??s east coast and is known as one of North America??s most diverse estuaries. Like most North American estuaries, the IRL is facing a number of problems, among them loss of emergent wetlands. Between 75 and 90% of the original mangrove and saltmarsh acreage historically bordering the IRL has been lost or impacted, either through direct filling for development or impoundment for mosquito control. This loss has affected IRL water quality and fisheries, since these habitats are now removed from the estuarine system. Active programs are now underway to restore mosquito impoundments by reconnection with culverts or removal of dikes, but restoration of dredge spoil is more problematic, as many of these sites have been developed. However, where undeveloped spoil is found on public lands, restoration is a possibility. One such site, Pine Island Conservation Area (PICA), jointly owned by the Brevard County Environmentally Endangered Lands Program and the St. Johns River Water Management District, contained 25.4?ha of dredge spoil, originating from 1969, when the property was owned by a development company. Following public acquisition in 1996, plans were developed to remove the spoil and restore the site to historic saltmarsh elevation. Between 2003 and 2006 all of the material was removed and the restoration of normal hydrology has resulted in ??volunteer?? recruitment by appropriate marsh vegetation, without a need for any plantings.     

Application of palynology to describe vegetation succession in estuarine wetlands on Great Barrier Island,northern New Zealand

Question: This paper compares published palynological studies from coastal swamps containing the same suite of species. We ask the following questions: (1) does succession follow the same pathways in different swamp systems, or (2) at different times? If not, (3) how variable are the patterns and (4) what are the likely driving factors? Location: Great Barrier Island, Northern New Zealand. Methods: Eighteen pollen profile diagrams were studied from four estuarine wetlands, ranging from mangroves to swamp forest. Recognition of a transition between vegetation stages was by subjective consideration of the relative abundances of pollen of key indicator species at different depths in the sedimentary sequence. Results: A linear sequence of vegetation communities beginning with mangroves and followed by estuarine marsh communities composed of Juncus kraussii, Leptocarpus similis and Baumea juncea was recognised in almost all pollen diagrams. Further transitions, from Baumea to a terrestrial system of Leptospermum shrubland or Cordyline/Dacry‐carpus swamp forest, followed two main pathways associated with autogenic accumulation of peat and terrigenous sediment input respectively. At Kaitoke and Awana the marine/freshwater transition occurred before the arrival of humans on Great Barrier Island. At Whangapoua, increased sedimentation followed anthropogenic burning of adjacent forest, and this transition was faster and is still in progress. Conclusion: Palynology and current vegetation zonation patterns concur to demonstrate that the marine sedimentation phase of estuarine succession is predictable and linear. Baumea marks the transition to the freshwater phase, in which varied successional patterns are determined by interactions between hydrology, sediment input, and peat accumulation. Natural and human disturbances drive sedimentation rates, and interact with autogenic factors, to dictate vegetation transitions in these later stages. The intensive impact (mainly burning) during Polynesian times had a much greater effect on estuaries and swamps than the pre‐Polynesian natural processes, greatly accelerating plant succession.     

Changing the fire management regime in the renosterveld and lowland fynbos of the Bontebok National Park

This paper evaluates the history of fire management in the Bontebok National Park (3435 ha) over a period of almost four decades. A GIS database was compiled of all fires between 1972 and 2009 and the fire regime was analysed in terms of the frequency, season, size and cause of fires. Since the early 1970s, short interval burning was implemented to promote grazing for bontebok, but from 2004 the fire interval was lengthened to favour plant species diversity, an increasingly urgent conservation priority for the park. In total, 43 fires were recorded, ranging in size from 9 to 1007 ha, collectively spanning 14 013 ha. The majority of fires were large (100–500 ha), with fires of >100 ha accounting for 96% of the area burnt. The overall mean fire return period (FRP) for the park was 7.2 years, which is short judged by fynbos standards. FRPs under the old and new management regimes were 6.7 and 10.9 years respectively. Under the old regime, FRPs in renosterveld and fynbos were 5.8 and 8.0 years respectively. Large parts of the park repeatedly experienced fires at immature vegetation ages resulting in the elimination of slow-maturing seed-regenerating plant species such as Protea repens. Post-fire age distribution was highly skewed towards young vegetation, with 75% of fire-prone vegetation burning at post-fire ages of ≤7 years, and <10% of fire-prone vegetation surviving beyond 10 years of age. Prescribed and accidental fires respectively accounted for 70% and 30% of the total area burnt. Prescribed burning was mostly done in March–April, and only 8% of the total area burnt, burnt outside of the ecologically acceptable fire season. This study identified areas which have been subject to ecologically appropriate and inappropriate fire return intervals, providing a basis for informed future management and research.     

Ecology, disturbance and restoration of coastal saltmarsh in Australia: a review

It is clear that saltmarshes are a unique and important component of the coastal biosphere of Australia. Their contribution ranges from stabilisation of fine sediments and providing an excellent protective buffer between land and sea, to their diverse blend of terrestrial and marine fauna. Further, saltmarsh plants are highly specialised and adapted to fill a harsh niche allowing them to act in roles that other vegetation types cannot. Saltmarsh habitats are recognised for their importance to migratory waders under the Ramsar convention, but it is becoming increasingly evident that they are also important to a variety of commercially valuable fish and native mammal species. Activities that are detrimental to saltmarshes continue and need to be addressed in order to conserve remaining saltmarsh areas. In general, urbanisation of the catchment has lead to filling of saltmarshes, tidal restriction, use by recreational vehicles, grazing, trampling and increased sedimentation and nutrient runnoff allowing colonisation and invasion of mangroves. These disturbances have a number of ecological consequences ranging from weed infestation to complete changes in the species composition and ecology. Reversing the disturbance is not always simple and can require extensive groundwork to be successful. Rehabilitation of existing saltmarsh areas has been a successful means to enhance this habitat. In general, it requires relatively little effort to remove weeds and fence off areas to regenerate naturally. Saltmarsh areas have been shown to respond well to this type of manipulation. Restoration and creation require substantial effort and planning to ensure a successful outcome. However, given the right environmental combinations of elevation, tide and salinity, saltmarsh will establish and grow. To speed the process transplantation of saltmarsh plants can be considered either from donor sites or plants propagated in green houses.     

The impact of grazing by Eastern Grey Kangaroos (Macropus giganteus) on vegetation recovery after fire at Reef Hills Regional Park,Victoria

Summary In southeastern Australia ecological burning is frequently used to maintain a number of plant and animal populations. However, many of these prescribed fires are small, and may focus intense grazing activity on new regrowth. At Reef Hills Regional Park, Victoria shrub species have senesced, presumably due to the absence of fire. Ecological burning may be necessary to promote regeneration, however, the population density of the Eastern Grey Kangaroo (Macropus giganteus) is high (approx 38 per km2), and grazing pressure presents a significant risk to postfire vegetation recovery. An assessment of grazing patterns and their effects on postfire recovery was carried out at Reef Hills Regional Park through grazing exclusion plots. Preferential grazing by Eastern Grey Kangaroos occurred on small burnt plots compared to adjacent unburnt areas as determined by faecal pellet counts. On burnt areas, there was a significant reduction in shrub diversity on grazed plots compared to ungrazed plots. Most observations of kangaroos were of animals grazing on farmland surrounding the Park, and it is likely that any burning might shift grazing from farmland to burnt areas when new growth occurs. This needs to be considered before any ecological burn plan is applied to manage vegetation communities, particularly if the plan requires small areas to be burnt. We recommended that a large area up to 200 ha area be burnt and monitored to determine whether burning larger areas disperses grazing pressure from macropods to a level where impacts on vegetation are reduced and localized plant extinctions do not occur.     

Fire severity influences the post-fire habitat structure and abundance of a cool climate lizard

In the spring and summer of 2019–2020, the ‘Black Summer’ bushfires burned more than 97 000 km² of predominantly Eucalyptus dominated forest habitat in eastern Australia. The Black Summer bushfires prompted great concern that many species had been imperilled by the fires. Here, we investigate the effects that fire severity had on the habitat and abundance of a cool climate lizard Eulamprus tympanum that was identified as a species of concern because 37% of its habitat was burnt in the Black Summer bushfires. We quantified habitat structure and the abundance of E. tympanum at sites which were unburnt, burnt at low severity and at high severity 10, 15 and 23 months after the fires. Our classification of fire severity based on scorch height and canopy status corresponded well with the Australian Government Google Earth Engine Burnt Area Map (AUS GEEBAM) fire severity layer. Ten months after the fires, sites burnt at high severity had less canopy cover, more bare ground and less fine fuel than sites burnt at low severity or unburnt sites. The abundance of E. tympanum varied with survey occasion and was greatest during the warmest sampling period and lowest during the coolest sampling period. The abundance of E. tympanum was consistently lower on sites burnt at high severity than sites burnt at low severity or unburnt sites. Our findings show that higher severity fires had a greater effect on E. tympanum than low severity fires. Our results suggest that E. tympanum were likely to have persisted in burnt sites, with populations in low severity and unburnt sites facilitating population recovery in areas burnt at high severity. Our results also suggest that wildfire impacts on E. tympanum populations will increase because the frequency and extent of severe fires are expected to increase due to climate change.     

Use of seagrass wrack in restoring disturbed Australian saltmarshes

Summary Saltmarshes are threatened in many parts of the world, considered wastelands rather than valued as wetlands. This is particularly true in urbanized parts of Australia. Approximately 85% of saltmarsh has been lost or severely damaged in the Tuggerah Lakes of the Central Coast of New South Wales, Australia. Wrack (rotting vegetation) can promote diversity of saltmarshes, by shading soil and reducing physical stress and/or by providing nutrients to nutrient‐poor soil. In many parts of the world, wrack derives from the saltmarsh plants. On the shores of the Tuggerah Lakes, large amounts of seagrass wrack (with varying amounts of macro‐algae), are stranded along the shoreline and in the remaining saltmarshes. This is perceived to reduce public amenity and have no ecological value. Thus, the local council is under pressure to remove wrack. This experimental study examined the influence of wrack on cover and diversity of saltmarsh and provided preliminary data on changes to organic matter and benthos in the sediment. On average, there was a rapid increase in biomass of the dominant plant, Sarcocornia quinqueflora, in experimental areas where wrack was added, although the response was patchy, but there was no change in diversity over 22 months. There were limited changes to benthos, but no changes to nutrients in the sediment in wracked compared to unwracked treatments. Nevertheless, increased biomass in dominant species may reduce physical stress for other smaller saltmarsh plants. This study is part of a programme examining the interaction between the persistence and growth of saltmarshes and recycling of wrack in the lakes. The ultimate aim is to develop ecologically and economically sound plans of management for an increasingly urbanized area of the NSW coast.     

Fine-scale movement and assimilation of carbon in saltmarsh and mangrove habitat by resident animals

Despite theories of large-scale movement and assimilation of carbon in estuaries, recent evidence suggests that in some estuaries much more limited exchange occurs. We measured the fine-scale movement and assimilation of carbon by resident macroinvertebrates between adjacent saltmarsh and mangrove habitats in an Australian estuary using δ¹³C analysis of animals at different distances into adjacent patches of habitat. δ¹³C values of crabs (Parasesarma erythrodactyla –15.7 ± 0.1‰, Australoplax tridentata –14.7 ± 0.1‰) and slugs (Onchidina australis –16.2 ± 0.3‰) in saltmarsh closely matched that of the salt couch grass Sporobolus virginicus (–15.5 ± 0.1‰). In mangroves, δ¹³C values of crabs (P. erythrodactyla –22.0 ± 0.2‰, A. tridentata –19.2 ± 0.3‰) and slugs (–19.7 ± 0.3‰) were enriched relative to those of mangroves (–27.9 ± 0.2‰) but were more similar to those of microphytobenthos (–23.7 ± 0.3‰). The δ¹³C values of animals across the saltmarsh-mangrove interface fitted a sigmoidal curve, with a transition zone of rapidly changing values at the saltmarsh-mangrove boundary. The width of this transition indicated that the movement and assimilation of carbon is limited to between 5 and 7 m. The δ¹³C values of crabs and slugs, especially those in saltmarsh habitat, clearly indicate that the movement and assimilation of carbon between adjacent saltmarsh and mangrove habitat is restricted to just a few metres, although some contribution from unmeasured sources elsewhere in the estuary is possible. Such evidence demonstrating the extent of carbon movement and assimilation by animals in estuarine habitats is useful in determining the spatial arrangement of habitats needed in marine protected areas to capture food web processes.     

Diurnal Habitat Use by Lower Keys Marsh Rabbits

Abstract: We used radiotelemetry to locate daytime forms of endangered Lower Keys marsh rabbits (LKMRs; Sylvilagus palustris hefneri) throughout their range so we could determine habitat characteristics of diurnal cover. We typically found forms (n = 1,298) of 36 rabbits in brackish wetlands in patches of saltmarsh or buttonwoods. In freshwater wetlands, forms (n = 54) were located most often in patches of freshwater hardwoods embedded in or adjacent to freshwater marshes. Forms (n = 942) in brackish wetlands were characterized by thick groundcover (>75%), whereas those (n = 42) in freshwater wetlands had both thick groundcover and canopy vegetation. The mean minimum convex polygon around forms of 15 rabbits was 1.4 ha (SD = 1.7), with smaller ranges characterized by thick bunchgrasses or clump-forming sedges. To increase the amount of annual space usable by LKMRs, managers should provide more saltmarsh habitat interspersed with buttonwoods and enhance ground cover in existing habitat.     

Patterns of Fish Use and Piscivore Abundance within a Reconnected Saltmarsh Impoundment in the Northern Indian River Lagoon, Florida

Nearly all saltmarshes in east-central, Florida were impounded for mosquito control during the 1960s. The majority of these marshes have since been reconnected to the estuary by culverts, providing an opportunity to effectively measure exchange of aquatic organisms. A multi-gear approach was used monthly to simultaneously estimate fish standing stock (cast net), fish exchange with the estuary (culvert traps), and piscivore abundance (gill nets and bird counts) to document patterns of fish use in a reconnected saltmarsh impoundment. Changes in saltmarsh fish abundance, and exchange of fish with the estuary reflected the seasonal pattern of marsh flooding in the northern Indian River Lagoon system. During a 6-month period of marsh flooding, resident fish had continuous access to the marsh surface. Large piscivorous fish regularly entered the impoundment via creeks and ditches to prey upon small resident fish, and piscivorous birds aggregated following major fish movements to the marsh surface or to deep habitats. As water levels receded in winter, saltmarsh fish concentrated into deep habitats and emigration to the estuary ensued (200% greater biomass left the impoundment than entered). Fish abundance and community structure along the estuary shoreline (although fringed with marsh vegetation) were not analogous to marsh creeks and ditches. Perimeter ditches provided deep-water habitat for large estuarine predators, and shallow creeks served as an alternative habitat for resident fish when the marsh surface was dry. Use of the impoundment as nursery by transients was limited to Mugil cephalus Linnaeus, but large juvenile and adult piscivorous fish used the impoundment for feeding. In conclusion, the saltmarsh impoundment was a feeding site for piscivorous fish and birds, and functioned as a net exporter of forage fish to adjacent estuarine waters.     

Habitat linkages: the effect of intertidal saltmarshes and adjacent subtidal habitats on abundance, movement, and growth of an estuarine fish

In this study we used pinfish (Lagodon rhomboides) in field experiments to examine linkages between intertidal saltmarsh and adjacent subtidal habitats. Pinfish are more than twice as abundant in intertidal marshes adjacent to seagrass beds than in those adjacent to the unvegetated subtidal bottom. Movement of pinfish between the marsh edge and the adjacent subtidal habitat was greater for fish captured in areas with both intertidal and subtidal vegetation than in those with intertidal vegetation and adjacent unvegetated mudflats. This movement provides an important link between habitats, allowing transfer of marsh-derived secondary production to subtidal seagrass beds and vice versa. Pinfish held in enclosures with both intertidal and subtidal vegetation were, on average, approximately 90% heavier than fish held in enclosures with intertidal vegetation and unvegetated subtidal bottom. Because saltmarshes and seagrass beds contribute to the production of living marine resources, active measures are being taken to preserve and restore these habitats. The results from this study have direct application to decisions concerning site selection and optimal spatial proximity of saltmarsh and seagrass habitats in the planning of restoration and mitigation projects. To maximize secondary production and utilization of intertidal marshes, managers may opt to restore and/or preserve marshes adjacent to subtidal seagrass beds. Received: 31 May 1996 / Accepted: 23 October 1996     

崇明东滩盐沼植被扩散格局及其形成机制

长江河口盐沼植被的形成和演化是生物与其生长环境相互作用的结果。以崇明东滩盐沼植被典型扩散前沿为研究对象,2011至2012年期间调查了盐沼植被扩散前沿实生苗扩散、定居以及形成的扩散格局,同时测定了盐沼植被扩散前沿的潮滩冲淤动态和水文动力条件。研究结果表明,崇明东滩盐沼植被在扩散前沿形成了互花米草-光滩(Spartina alterniflora-Mudflat,SM)和互花米草-海三棱藨草-光滩(Spartina alterniflora-Scirpus mariqueter-Mudflat,SSM)两种典型的扩散格局。冲淤动态和水文动力条件是影响盐沼植被扩散格局的重要因子,尤其是在4—6月盐沼植物实生苗传播和定居的关键阶段。在此基础上,分析了东滩盐沼植被扩散前沿的生物-物理相互作用以及盐沼植被扩散格局的形成机制。研究结果不仅有助于理解长江河口地区盐沼植被扩散的生物物理过程,并对全球气候变化和海平面上升条件下滨海生态系统动态预测与湿地保护与管理具有重要的意义。     

Spatial, geomorphological, and seasonal variability of CDOM in estuaries of the Florida Coastal Everglades

This paper demonstrates the usefulness of fluorescence techniques for long-term monitoring and assessment of the dynamics (sources, transport and fate) of chromophoric dissolved organic matter (CDOM) in highly compartmentalized estuarine regions with non-point water sources. Water samples were collected monthly from a total of 73 sampling stations in the Florida Coastal Everglades (FCE) estuaries during 2001 and 2002. Spatial and seasonal variability of CDOM characteristics were investigated for geomorphologically distinct sub-regions within Florida Bay (FB), the Ten Thousand Islands (TTI), and Whitewater Bay (WWB). These variations were observed in both quantity and quality of CDOM. TOC concentrations in the FCE estuaries were generally higher during the wet season (June–October), reflecting high freshwater loadings from the Everglades in TTI, and a high primary productivity of marine biomass in FB. Fluorescence parameters suggested that the CDOM in FB is mainly of marine/microbial origin, while for TTI and WWB a terrestrial origin from Everglades marsh plants and mangroves was evident. Variations in CDOM quality seemed mainly controlled by tidal exchange/mixing of Everglades freshwater with Florida Shelf waters, tidally controlled releases of CDOM from fringe mangroves, primary productivity of marine vegetation in FB and diagenetic processes such as photodegradation (particularly for WWB). The source and dynamics of CDOM in these subtropical estuaries is complex and found to be influenced by many factors including hydrology, geomorphology, vegetation cover, landuse and biogeochemical processes. Simple, easy to measure, high sample throughput fluorescence parameters for surface waters can add valuable information on CDOM dynamics to long-term water quality studies which can not be obtained from quantitative determinations alone.     

The impact of encroachment of mangroves into saltmarshes on saltwater mosquito habitats

Will mangrove encroachment into saltmarshes affect saltwater mosquito habitats? To address this, we synthesized information from two perspectives: 1) at a detailed level, the immature mosquito habitat within mangroves; 2) at a more general or regional level, changes due to mangrove expansion into saltmarshes. This is a synthesis of two research projects. One showed that mosquito larval habitats in mangroves are complex, related to the detailed interactions between topography and tidal patterns and that not all parts of a mangrove forest are suitable habitat. The other, based on remote sensing and analysis of rainfall data, showed that mangrove encroachment in eastern Australia is related to both climate and human land use over several decades (1972–2004). An important question emerged: when mangroves encroach into saltmarshes will they displace saltmarsh immature mosquito habitats or will they replace them with mangrove ones? There is no simple answer: it will vary with climate change and sea level scenario and how these affect the system. We conclude that mosquito management, which is locally implemented, needs to be integrated with land use planning systems, which often operate at a more general level.     

Nest trampling and ground nesting birds: Quantifying temporal and spatial overlap between cattle activity and breeding redshank

Conservation grazing for breeding birds needs to balance the positive effects on vegetation structure and negative effects of nest trampling. In the UK, populations of Common redshank Tringa totanus breeding on saltmarshes declined by >50% between 1985 and 2011. These declines have been linked to changes in grazing management. The highest breeding densities of redshank on saltmarshes are found in lightly grazed areas. Conservation initiatives have encouraged low‐intensity grazing at <1 cattle/ha, but even these levels of grazing can result in high levels of nest trampling. If livestock distribution is not spatially or temporally homogenous but concentrated where and when redshank breed, rates of nest trampling may be much higher than expected based on livestock density alone. By GPS tracking cattle on saltmarshes and monitoring trampling of dummy nests, this study quantified (i) the spatial and temporal distribution of cattle in relation to the distribution of redshank nesting habitats and (ii) trampling rates of dummy nests. The distribution of livestock was highly variable depending on both time in the season and the saltmarsh under study, with cattle using between 3% and 42% of the saltmarsh extent and spending most their time on higher elevation habitat within 500 m of the sea wall, but moving further onto the saltmarsh as the season progressed. Breeding redshank also nest on these higher elevation zones, and this breeding coincides with the early period of grazing. Probability of nest trampling was correlated to livestock density and was up to six times higher in the areas where redshank breed. This overlap in both space and time of the habitat use of cattle and redshank means that the trampling probability of a nest can be much higher than would be expected based on standard measures of cattle density. Synthesis and applications: Because saltmarsh grazing is required to maintain a favorable vegetation structure for redshank breeding, grazing management should aim to keep livestock away from redshank nesting habitat between mid‐April and mid‐July when nests are active, through delaying the onset of grazing or introducing a rotational grazing system.     

Frequent burning promotes invasions of alien plants into a mesic African savanna

Fire is both inevitable and necessary for maintaining the structure and functioning of mesic savannas. Without disturbances such as fire and herbivory, tree cover can increase at the expense of grass cover and over time dominate mesic savannas. Consequently, repeated burning is widely used to suppress tree recruitment and control bush encroachment. However, the effect of regular burning on invasion by alien plant species is little understood. Here, vegetation data from a long-term fire experiment, which began in 1953 in a mesic Zimbabwean savanna, were used to test whether the frequency of burning promoted alien plant invasion. The fire treatments consisted of late season fires, lit at 1-, 2-, 3-, and 4-year intervals, and these regularly burnt plots were compared with unburnt plots. Results show that over half a century of frequent burning promoted the invasion by alien plants relative to areas where fire was excluded. More alien plant species became established in plots that had a higher frequency of burning. The proportion of alien species in the species assemblage was highest in the annually burnt plots followed by plots burnt biennially. Alien plant invasion was lowest in plots protected from fire but did not differ significantly between plots burnt triennially and quadrennially. Further, the abundance of five alien forbs increased significantly as the interval (in years) between fires became shorter. On average, the density of these alien forbs in annually burnt plots was at least ten times as high as the density of unburnt plots. Plant diversity was also altered by long-term burning. Total plant species richness was significantly lower in the unburnt plots compared to regularly burnt plots. These findings suggest that frequent burning of mesic savannas enhances invasion by alien plants, with short intervals between fires favouring alien forbs. Therefore, reducing the frequency of burning may be a key to minimising the risk of alien plant spread into mesic savannas, which is important because invasive plants pose a threat to native biodiversity and may alter savanna functioning.     

寒温带湿地火后植被恢复的影响因子

寒温带湿地在维护区域生态平衡方面发挥着重要作用.火是湿地的重要干扰因子.重度火烧会导致湿地生态功能明显退化.火后植被恢复,特别是火后早期植被的恢复是生态系统功能恢复的前提和基础.本文对火后湿地植被恢复影响因子的国内外研究进展进行了综述.寒温带湿地火后植被恢复受到火强度、火面积、火前植被类型、物种更新特性、立地条件等多因子的制约.寒温带湿地火后恢复的长期监测、植被恢复的关键影响因子、冻土层在植被恢复过程中的作用、植被恢复的理论与技术将是今后研究的重要方向.     

The distribution and state of mangroves along the coast of Transkei,Eastern Cape Province,South Africa

The mangrove communities along the coastline of the former Transkei, now part of the Eastern Cape Province, have not been looked at in detail since Ward and Steinkes survey in 1982. Mangroves previously occurred in 17 estuaries but were now found in only 14 of the 76 estuaries visited, with a complete loss of mangroves evident in the Mnyameni, Mzimvubu and Bulungula estuaries amounting to 7.5 ha. Total mangrove loss amounted to 17.6 ha which represents a 6.5% loss over 17 years or 1.04 ha per annum. Tree cover had increased by 16.15 ha in eight other estuaries. This increase could be attributed to the inaccessibility of mangrove stands or to protection afforded by provincial nature reserves and hotel resorts. No new mangrove stands were recorded, although Steinke (pers. comm.) has recently recorded mangroves along the north bank of the Kei River. There has been little change in mangrove species composition in the different estuaries over the past 17 years. Total mangrove loss amounted to 17.6 ha which represents a 6.5% loss over 17 years or 1.04 ha per annum and the species recorded included Avicennia marina, Bruguiera gymnorhiza and Rhizophora mucronata. The mangrove fern Acrostichum aureum L. was recorded for the first time in the Mkozi estuary. Tree density for all estuaries was between 10 and 2594 trees ha^–1. The Mngazana and Mntafufu estuaries had the highest tree densities of 2594 and 1402 trees ha^–1 respectively, typical of riverine mangrove forests. Fringe mangroves were evident in most other systems. Removal of trees for wood has the greatest impact on mangrove cover. Fringe mangrove stands are particularly accessible to harvesters. Only 6% of the current area of trees is afforded some protection in conservation areas. The Mdumbi, Mzamba and Kobonqaba estuaries receive no conservation protection and harvesting has resulted in more than 50% of the trees being removed. The density of dead tree stumps was greater than the number of living trees and no seedlings or juvenile trees were found. Further removal of mangroves within the estuaries south of the Mzimvubu River is expected in the fringe mangroves, as most are unprotected and easily accessible.     

Modelling the recovery of an annual savanna grass following a fire-induced crash

Abstract The native annual Sorghum populations of the Australian wet-dry tropics are highly resilient to dry season fires. During the early wet season, however, fires that occur after the new grass population has emerged can cause catastrophic population crashes. We examined savanna plots that had been burnt in this way, and compared them with adjacent unburnt plots. We found that Sorghum densities in the burnt plots were lower on average by a factor of 10, but that some fires had reduced the density only to one-third of the unburnt plots. It is not clear whether these differences relate directly to site or seasonal factors, or to differences in the way the burning was carried out. Other vegetation components responded to the fires differently: forbs (dicotyledonous herbs) increased in cover, while perennial grasses, woody plants, and overall species richness, were not significantly affected. The amount of leaf litter declined. A population model for Sorghum based on the demography of unburnt populations predicted that they should recover from a wet season burn, taking 7–16 years to return to normal densities. However, the actual field populations did not seem to be recovering, suggesting that wet season fires not only lower densities, but may also fundamentally change population processes in these annual grasses.     

Established and potential impacts of eukaryotic mycelial decomposers in marine/terrestrial ecotones

Marine mycelial decomposers (eumycotes, members of Kingdom Fungi, and oomycotes, zoosporic members of the Kingdom Protoctista) are highly adapted for capture of solid substrate by pervasion and digestion from within. Thus they exert their influence in areas of large input of litter of vascular plants, especially at some types of terrestrial/marine ecosystemic interfaces (ecotones). Unavailability of methods easily used by general microbial ecologists has hampered progress in the study of marine mycelial decomposers, and there are still pockets of difficulty in this regard (especially for oomycotes). Recently published or refined methods for measuring fungal mass and productivity have begun to allow us to realize the impacts of fungi in marine ecotones. For example, it is now clear that the older paradigm reflecting negligible contribution of microbial mass to litter nitrogen content is false for the standing-decay system of saltmarsh grasses — in these decay systems, fungal mass can account for virtually all of the nitrogen present at some point(s) in the standing-decay period. Another generally held belief about marine fungi has also been reversed — ascomycetes (Fungi) of a saltmarsh grass (smooth cordgrass) clearly do digest lignocellulose under natural-decay circumstances. Much more work is needed to clarify the situation, but at present it appears that major types of marine ecotones (e.g., saltmarshes and mangroves) differ sharply in the balance among major groups of decomposers (eumycotes, oomycotes, and bacteria) with regard to their utilization of vascular-plant litter. In saltmarshes, microbial production in standing grass litter is strongly dominated by fungi, and oomycotes do not show evidence of a substantial role in decomposition. In mangroves, submerged fallen leaves appear to support minor fungal occupancy, but ubiquitous and rapid occupancy by oomycotes (especially Halophytophthora vesicula). Many exciting areas of research are now more open than ever before to marine microbial ecologists interested in working with mycelial decomposers.