Seasonal Inundation Research Articles

Evidence for local declines in Tanzania’s puku antelope (Kobus vardoni Livingstone, 1857) population between 1999 and 2003

Introduction The Kilombero Valley in Tanzania holds c. 75% of the world’s puku antelope (Kobus vardoni), which is an estimated 50,000–60,000 individuals (East, 1998; Jenkins, Maliti & Corti, 2003). Globally, survival of this species is closely related to this population (Rodgers, 1984; Tanzania Wildlife Conservation Monitoring, 1999), and therefore studies investigating changes in puku number in the valley are important for developing conservation management strategies for this species. Puku is a ‘Near Threatened’ species (IUCN SSC Antelope Specialist Group, 2008), which is habitat specific, occupying grasslands near permanent water within savannah floodplains (East, 1998). In the Kilombero Valley, following seasonal inundation of the floodplain during the long rainy season (March–May), puku move into habitat on the floodplain periphery, such as miombo woodland (Jenkins et al., 2002). A number of human activities, including livestock husbandry (Corti et al., 2002; Bonnington, Weaver & Fanning, 2007) and settlement (Haule, 1997), are encroaching on these favoured floodplain grasslands in the Kilombero Valley, and other activities such as poaching (Jenkins et al., 2002), negatively impact the puku population of the valley directly. Starkey et al. (2002) stated that there is an urgent need for surveys to be conducted in the Kilombero Valley in open areas of suitable foraging habitat and also in suitable peripheral habitat near human settlement to assess fluctuations in puku number in areas experiencing different levels of human impacts. In this paper, we describe the first ground-based study of puku in the Kilombero Valley assessing annual changes in the abundance of this species at two such localities. We report a significant decline in the relative abundance of puku at both locations over a 5-year period and discuss the possible implications for the conservation of this species in this stronghold.

Ectothermic vertebrates (Actinopterygii, Allocaudata, Urodela, Anura, Crocodylia, Squamata) from the Miocene of Sandelzhausen (Germany, Bavaria) and their implications for environment reconstruction and palaeoclimate

The Early to Middle Miocene fossil locality Sandelzhausen has yielded 48 species of ectothermic vertebrates and thus represents one of the most diverse ectotherm faunas of Miocene age. Thirty-five taxa of fishes, amphibians and reptiles, including three new species: Pelobates fahlbuschi nov. sp. (Pelobatidae, the most abundant vertebrate), Tropidophorus bavaricus nov. sp. (Lygosominae) and Bavaricordylus molassicus nov. sp. (Cordylidae), are described. Three additional species are new, but are not named yet: Ranidae indet. nov. gen. et sp., Anguidae gen. indet. sp. nov. and Palaeoblanus sp. nov. (Amphisbaenidae). In order to reconstruct the palaeoenvironment and past hydrologic conditions, a new methodology (the tooth replacement method, TRM) is introduced, which allows for the detection of autochthonous components within freshwater fish taphocoenose. TRM is tested on 45 localities from the Upper Freshwater Molasse and gives reasonable results in agreement with other analytical approaches. It is therefore viewed as a reliable method to distinguish perennial from seasonal water conditions at the Sandelzhausen locality. Using the TRM it was demonstrated that the palaeohydrology of Sandelzhausen is characterized by a change from temporary water to permanent water conditions. During the period of temporary water conditions (units B to D1, lower part) the ecosystem was driven by seasonal inundations, and the remaining riparian pools have yielded no autochthonous fish population, but acted as spawning places for amphibians (amphibian pool). A mostly open habitat in the close vicinity, with sandy and non-groundwater-affected soils during the dry season, is suggested based on the absolute dominance of the spadefoot Pelobates fahlbuschi nov. sp. This ecosystem changed up-section (late part of unit D1 and during D2 and E) due to the establishment of permanent water conditions of riparian pond type, preserving an autochthonous Palaeocarassius/Channa fish population (fish pond). The reconstructed precipitation values suggest that the observed change in hydrologic conditions was probably driven by climate. The lower part of the section gives semi-arid/sub-humid values, with 571 mm mean annual precipitation (MAP), whereas the upper part yields sub-humid/humid values of 847 mm MAP. The increase in precipitation by about 280 mm was perhaps caused by a less seasonal precipitation regime with concomitant higher regional groundwater tables during units D2 and E. Based on the occurrence of several thermophilous reptile species, and in agreement with palaeobotanical and oxygen isotope data, the climate of Sandelzhausen is interpreted as subtropical with mean annual temperatures from 18°C to 20.8°C, mean cold month temperatures from 12.6°C to 13.3°C and mean warm month temperatures from 25.1°C to 28.1°C.

Biogeochemical Contributions of Tree Islands to Everglades Wetland Landscape Nitrogen Cycling During Seasonal Inundation

In the Florida Everglades, tree islands are conspicuous heterogeneous elements in the herbaceous wetland landscape. We characterized the biogeochemical role of a seasonally flooded tree island during wet season inundation, specifically examining hydrologically mediated flows of nitrogen (N) and N retention by the tree island. We estimated ecosystem N standing stocks and fluxes, soil and litter N transformation rates, and hydrologic fluxes of N to quantify the net ecosystem N mass flux. Results showed that hydrologic sources of N were dominated by surface water loads of nitrate (NO3) and ammonium (NH4). Nitrate immobilization by soils and surficial leaf litter was an important sink for surface water dissolved inorganic N (DIN). We estimated that the net annual DIN retention by a seasonally flooded tree island was 20.5 ± 5.0 g m−2 during wet season inundation. Based on the estimated tree island surface water DIN loading rate, a seasonally flooded tree island retained 76% of imported DIN. As such, seasonally flooded tree islands have the potential to retain 55% of DIN entering the marsh landscape via upstream canal overland flow in the wet season. By increasing reactive surface area and DOC availability, we suggest that tree islands promote convergence of elements that enhance DIN retention. Tree islands of this region are thus important components of landscape-scale restoration efforts that seek to reduce sources of anthropogenic DIN to downstream estuaries.

Reconstructing middle to late Holocene palaeogeographies of the lower Messenian plain (southwestern Peloponnese, Greece): Coastline migration, vegetation history and sea level change

The glacio-eustatic sea level rise after the Last Glacial Maximum (LGM) led to a worldwide flooding of shelf areas and the evolution of marine embayments and indentations. Its significant deceleration in mid-Holocene times resulted in the overcompensation by sediment yields and shoreline progradation in many areas. At the southeastern part of the lower Messenian plain (southwestern Peloponnese, Greece) detailed investigations of the Holocene stratigraphy revealed a maximum landward shoreline displacement around 3000 BC. Subsequently, aggradational processes started to form a prominent beach ridge in the late 3rd millennium BC. This is the substratum on which the early Iron Age Poseidon Sanctuary of Akovitika was founded approx. 900–850 BC. Palaeogeographic reconstructions based on 18 corings in the sanctuary and its surroundings revealed the later extension of adjacent marshland and gradual surface levelling due to seasonal inundations. These findings represent probable reasons for the abandonment of the ceremonial site around 380–350 BC. Palynological studies of the vegetational changes provide evidence for early land use and reflect regional settlement activities. Initial degradation and burning of woodland during late Neolithic times (c. 3500–3100 BC) as well as significantly reduced human impact during the Protogeometric Dark Ages (c. 1060–900 BC) are proven. Additionally, local relative mean sea level (RSL) change since 5000 BC was reconstructed based on 14C dated paralic peats.

A New Species of Spinetail (Furnariidae:Synallaxis) from the Río Orinoco of Venezuela

ABSTRACT. We describe a new species of spinetail, Synallaxis beverlyae (Rio Orinoco Spinetail), from river island scrub in the lower and middle sections of the main river channel of the Rio Orinoco in Venezuela and adjacent Colombia. This taxon has been overlooked previously because river islands were not examined by earlier collecting expeditions. In plumage the species is closest to the widespread Pale-breasted Spinetail (S. albescens), but in vocalizations it is most similar to Dark-breasted Spinetail (S. albigularis), Cinereous-breasted Spinetail (S. hypospodia), and Spix's Spinetail (S. spixi). The new species is, as far as we know, restricted to scrubby river island vegetation and adjacent river edges that are subject to seasonal inundation. It is presently known only from two well-separated areas but is likely to occur on appropriate intervening islands. The restricted range and narrow ecological requirements of S. beverlyae are a conservation concern.

Applications and Analyses of Satellite‐borne L‐band Synthetic Aperture Radar Data in Coastal Environments

AbstractThere is rapid population growth in coastal environments. Development and competing demands for resources and natural hazards offer an additional threat to coastal communities. Remote sensing provides a means of monitoring the intra‐ and inter‐annual variability both natural and human impacts cause. In this article, we review the application of satellite‐borne Synthetic Aperture Radar (SAR) to the coastal zone and provide two examples, seasonal inundation mapping on coastal floodplains at the regional scale in eastern North Carolina, USA, and shoreline delineation and change in estuary of Pamlico Peninsula, Dare County, North Carolina. The results SAR data provide are reliable and repeatable, and can potentially be used to identify critical areas in coastal environments where there is a need to respond to the pressures caused by population growth, land use and land cover change, natural hazards and sea level rise that may be brought about by global climate change.

Seasonal variation in the composition of fish assemblages in small Amazonian forest streams: evidence for predictable changes

Summary1. The effects of seasonal inundation on the biology of fishes on floodplains of large Amazonian rivers are well studied. However, the small seasonal changes in headwater streams are generally considered to have little effect on fish assemblages.2. In this study, we analysed seasonal changes in the species composition and abundance of fish in small Amazonian forest streams. We sampled fish with hand and seine nets in headwater streams in a 10 000 ha terra‐firme forest reserve near Manaus, Brazil. Each stream was surveyed at the end of the 2005 dry season, at the beginning of the 2006 rainy season and at the beginning of the 2006 dry season, by means of a standardized sampling effort.3. The numbers of individuals and species caught were higher in the dry season, but rarefaction analyses indicated that greater species numbers could have been due simply to the larger number of individuals caught.4. Between the dry and rainy season, the direction of changes in species composition in multivariate space varied among sites, especially for quantitative (abundance) data. However, the observed variation among sites was the less than expected if the directions of change were random.5. Fish assemblages in the second dry season were more similar to those in the previous dry season than expected if changes in species composition among seasons were random. This indicates that a general seasonal pattern in fish assemblages can be detected, despite the existence of some erratic site‐specific changes.6. Most of the species that showed large seasonal variations in density occupy temporary ponds during the rainy season, when much of the valley is inundated and pond networks form adjacent to streams. Short‐duration lateral migrations to these ponds may play an important role in the seasonal fish‐assemblage dynamics in Amazonian headwater streams.7. Our results contrast with previous studies on small Amazonian streams, which have found little seasonal change in fish assemblages, and highlight the importance of the abundance of common species as an indicator of general fish assemblage structure in biological monitoring programmes.

Coleanthus subtilis (Poaceae), New to Northwest Territories, and Its Status in North America

A floristic survey of a polje lakebed, which is full in the spring but drains completely as the season progresses, revealed a community of small mud-bottom plants including the globally rare Coleanthus subtilis, not previously recorded from Northwest Territories, Canada. The newly discovered site is 1077 miles NNW of its nearest North American location in southern British Columbia, which is the northern edge of a region of occurrence including southern British Columbia and the Columbia River in Washington and Oregon. The lakebed flora included four zones of vascular plants. Coleanthus subtilis was confined to the lowest level mud-bottom community, which had been exposed for the shortest period and included a rich assemblage of annuals including Juncus bufonius, Limosella aquatica, and Ranunculus hyperboreus. The lakebed flora included mostly widespread boreal species, and C. subtilis may be included in this category. It appears restricted to specific montane and boreal areas by its requirement of pronounced seasonal inundation in a cool climate. Coleanthus subtilis may have persisted at the Washington and British Columbia locations, near the limit of the continuous montane glaciation, since early postglacial times. The occurrence in Northwest Territories may be either a result of dispersal from unglaciated areas of Beringia nearby to the west or from the south. Although it has sometimes been considered introduced in the United States parts of its North American range, it is here considered native at all of its North American sites on the basis of: (1) its restricted and unusual habitat; (2) global rarity; (3) suffusive rarity, which is known to lead to mistaken assumptions of introduction; (4) occurrence in botanically rich regions and close association with rare native species; (5) relatively early year of collection; (6) distribution corresponding to a well recognized native pattern; (7) lack of evidence of spread to anthropogenic habitats; and (8) the fact that it is easily overlooked by early collectors as a result of only appearing at intervals of several years when water levels have dropped sufficiently.

Tree Species Composition, Structure, and Aboveground Wood Biomass of a Riparian Forest of the Lower Miranda River, Southern Pantanal, Brazil

The aboveground wood biomass (AWB) of tropical forests plays an important role in the global carbon cycle, and local AWB estimates provide essential data that enable the extrapolation of biomass stocks to ecosystem or biome-wide carbon cycle modelling. Few AWB estimates exist in Neotropical freshwater floodplains, where tree species distribution and forest structure depend on the height and duration of periodic inundations. We investigated tree species composition, forest structure, wood specific gravity, and AWB of trees ≥10 cm dbh in 16 plots totalling an area of 1 ha in a seasonally inundated riparian forest of the lower Miranda River, southern Pantanal, Brazil. The 443 tree individuals belonged to 46 species. Four species (Inga vera, Ocotea suaveolens, Tabebuia heptaphylla and Cecropia pachystachya) comprised more than 50% of the Total Importance Values (TIV), and floristic similarities between the plots averaged 38%. Although we detected an overall increase in species diversity correlated with decreasing flood levels, the most important tree species had almost identical distribution patterns along the flooding gradient. The stand basal area per plot (± s.d.) amounted to 3.0 ± 1.1 m2 (47.8 ± 18.1 m2/ha), and the tree heights averaged 10.9 ± 1.4 m. Multiplying the individual basal areas by individual tree heights and a form factor of 0.6, we estimated the aboveground wood volume (AWV) for each individual, and for each plot (24.4 ± 11.7 m3, 391.1 ± 188 m3/ha). Wood specific gravity (SG) varied between 0.39 g/cm3 (Cecropia pachystachya) and 0.87 g/cm3 (Tabebuia heptaphylla), with a stand level average of 0.63 ± 0.12 g/cm3. Multiplying the individual AWV with species SG, we estimated the plot AWB to be 16.2 ± 6.4 Mg (259.4 ± 102 Mg/ha). This value is comparable to that reported for late-successional forest stands of Amazonian floodplain forests, and it is close to the worldwide tropical average AWB. Because tree heights in the present forest were comparatively low when compared to other Neotropical forests, we found that resprouting of stems accounted for comparatively high basal areas. We argue that stem resprouting is an adaptation of tree species originating in non-flooded Cerrado to the seasonal inundations of riparian forests.

Using MODIS data to characterize seasonal inundation patterns in the Florida Everglades

Information regarding the spatial extent and timing of flooding in the world's major wetlands is important to a wide range of research questions including global methane models, water management, and biodiversity assessments. The Florida Everglades is one of the largest wetlands in the US, and is subject to substantial development and pressures that require intensive hydrological modeling and monitoring. The Moderate Resolution Imaging Spectrometer (MODIS) is a global sensor with high frequency repeat coverage and significant potential for mapping wetland extent and dynamics at moderate spatial resolutions. In this study, empirical models to predict surface inundation in the Everglades were estimated using MODIS data calibrated to water stage data from the South Florida Water Management District for the calendar year 2004. The results show that hydropatterns in the Florida Everglades are strongly correlated to a Tasseled Cap wetness index derived from MODIS Nadir Bidirectional Reflectance Function Adjusted Reflectance data. Several indices were tested, including the Normalized Difference Wetness Index and the diurnal land surface temperature difference, but the Tasseled Cap wetness index showed the strongest correlation to water stage data across a range of surface vegetation types. Other variables included in the analysis were elevation and percent tree cover present within a pixel. Using logistic regression and ensemble regression trees, maps of water depth and flooding likelihood were produced for each 16-day MODIS data period in 2004. The results suggest that MODIS is useful for dynamic monitoring of flooding, particularly in wetlands with sparse tree cover.

The Use By Red Imported Fire Ants, Solenopsis Invicta (Hymenopgefa: Formicidae), Of Potamogeton Nodosus (Potamogetonaceae) Leaves As Platforms Into The Littoral Zone In Texas, U.S.A

It has become increasingly clear that waterways facilitate the invasion process for many species, including terrestrial species, such as ants (Walker 2006). The underlying reason may be directly related to transportation, as in the case of the red imported fire ant, Solenopsis invicta Buren whose colonies can spread by rafting on moving water (Banks et al., 1981). In other instances, periodic flooding along riparian courses often creates disturbance regimes, which promote invasions (Ellis et al., 2001). Additional habitat considerations include elevated soil moisture (Holway et al., 2002) and high productivity associated with riparian ecosystems (Kennedy 1998, Paetzold et al., 2006). These conditions are likely to promote high colony growth rates and an associated higher propagule pressure, furthering the invasion process. Ants that are predisposed to be around water are more likely to be able to take opportunistic advantage of waterways for their dispersal (Suarez et al., 2005). Many Solenopsis species, especially the most widely distributed species, commonly forage around water (Wilson 1986). The black imported fire ant, for instance, has been found preying on tubeworms exposed during low tides (Palomo et al., 2003), while S. invicta is considered a threat to wildlife in wetland habitats (Freed and Neitman 1988). The latter study noted that the fire ants were able to extend their reach into the pond by utilizing unspecified vegetation as a walkway but gave no additional details. This note offers further information as to the use by fire ants of floating vegetation as natural roads. In June of 2002, I first observed S. invicta workers crossing long leaf pondweed, Potamotegon nodusus leaves lying on the water surface of a manmade lake in Lee County, TX (N30.14, W96.88). Potamotegon nodosus is a fast-growing aquatic plant that forms extensive platforms of networked leaves on the water surface of the littoral zone. In the situation observed, these platforms were growing in an emergent area of the lake with seasonal inundation. I was able to observe the ants closely out over the water because of the presence of a 15m long raised pier that paralleled the pondweed. Many of my observations were made using a Sony PCV DCR-TRV9. Volume 118, Number 5, November and December 2007 527

Distribution, structure and simulation modelling of the Wattled Crane population in the Marromeu Complex of the Zambezi Delta, Mozambique

The status of the Vulnerable Wattled Crane (Grus carunculatus) in Mozambique is poorly known, but historical accounts indicate that the species was previously more abundant and widespread than today. Annual surveys during 1995–2002 suggest a core population of about 120 breeding pairs remains in the Zambezi Delta region. Wattled Cranes in the delta are exclusively associated with sedges of the genus Eleocharis, the tubers of which provide the adult cranes' main food supply. The main Eleocharis areas in the delta, and those supporting the highest density of Wattled Cranes, occur below the adjacent Cheringoma escarpment, where unregulated streams flow onto the floodplain. These wetlands experience some seasonal inundation in all years — conditions essential for the production of underground tubers — and high soil penetrability to enable the cranes to extract tubers. Eleocharis tuber production and soil penetrability is extremely low in the remaining vast areas of the delta that no longer receive regular annual flooding due to regulation of the Zambezi River. Significant differences in crane density between the Eleocharis beds of the Cheringoma and Zambezi floodplains suggest that the carrying capacity of the delta for cranes has been reduced. Simulation modelling suggests that the present population of Wattled Cranes in the Zambezi Delta is viable, despite the long-term, severe hydrological degradation of large parts of the floodplain. Restoration of the hydrological conditions in the delta may have global implications for the species, however. In 1990, an estimated 2 570 Wattled Cranes (more than 30% of the global population) were observed in the delta. This was likely an occasional flock from elsewhere in southern Africa, as prolonged regional drought resulted in failed floods, low tuber productivity and relatively impermeable soils in the region.

Satellite radar imagery for monitoring inland wetlands in boreal and sub‐arctic environments

1. Knowledge about the distribution and types of wetlands is in high demand by ecosystem modellers for full greenhouse gas accounting. The scope of this paper is to demonstrate the suitability of satellite radar data for the delineation of wetlands in the tundra and boreal forest biomes of central Siberia. 2. An area of more than 3 million km2 in central Siberia was investigated using satellite data. It covers freshwater ecosystems of the tundra and non-forested peatlands in tundra and boreal forest biomes. The satellite data represent the growing seasons of 2003/2004. 3. Microwave data were acquired by the Advanced Synthetic Aperture Radar (ASAR) instrument onboard ENVISAT. The multi-temporal capabilities and resolution (150 m × 150 m in WS mode) of the ASAR wide swath mode enabled the detection of dynamic features >2 ha over this vast area. Scatterometer (QuikScat) data could be employed to distinguish hydro-periods. 4. Wetland types have been identified on the basis of seasonal changes in backscatter. In a first step scatterometer data were used to identify the transition period from frozen to unfrozen conditions over a range of 15° latitude. Inundation patterns and soil moisture changes could be identified for the different hydro-periods and used to classify wetlands. Results for peatlands have been compared with Russian forest inventory data which contain information on wetland distribution. 5. The database of permanently inundated areas is an intermediate product which enables the mapping of wetlands in two ways: (1) identification of seasonal inundation in relation to snowmelt and high permafrost tables and (2) input for density analysis of permanent small and shallow lakes in tundra areas which are important freshwater ecosystems as well as a methane source. Differences in intensity and duration of soil moisture conditions allow the identification of peatlands. Copyright © 2007 John Wiley & Sons, Ltd.

Influences of environmental conditions on macrophyte communities in drought‐affected headwater streams

AbstractA 10‐year study of groundwater‐dominated headwater streams in the chalklands of southern England has highlighted the major influence that stream flow has on the composition of in‐channel macrophyte communities. Macrophytes supply much of the physical structure within these headwater channels, as well as providing habitats for a rich assemblage of higher life forms, some of them specialized and rare. The overall influence of stream flow however, is modulated by many environmental factors operating at diverse spatial scales. Data describing the relevant environmental variables were accumulated for six chalk streams in the Thames basin and related directly to the vegetation record by means of Canonical Correspondence Analysis, correlation tests and other analyses, to reveal the circumstances in which communities would be likely to thrive and those in which they would be negatively impacted by variations in stream flow. It was found that local topography and channel dimensions had a direct influence on the composition of communities at local level and that land use and rates of water abstraction had an underlying, but no less important, influence at catchment level. The species most associated with positive species diversity were those of sluggish flow and damp margins indicating the importance of velocity and moisture gradients across the channel in producing a full manifestation of the flora. Strong negative correlations were produced by non‐aquatic grasses and herbs, which represent prolonged periods of channel desiccation. The environmental parameters most associated with positive diversity were high local water stages, wide channels and a high degree of semi‐natural land use within the catchment. Steep channel gradients were strongly associated with negative diversity. The results have confirmed that optimal channel conditions, as exemplified by the classic ‘winterbourne’ with its low‐flow channel, extensive margins, gently sloping banks and high seasonal inundation, will produce good conditions for species diversity and make communities more resistant to the effects of drought. These conditions can be enhanced through sensitive catchment management that encourages rainfall percolation, limits abstractions and seeks to maintain a low intensity of landcover management. Copyright © 2006 John Wiley & Sons, Ltd.

Aerial and aquatic feeding in the silver arawana, Osteoglossum bicirrhosum

The silver arawana, Osteoglossum bicirrhosum, hunts along shorelines and within flooded forests in the Amazon River basin and supplements its limited consumption of aquatic vertebrates by leaping from the water to obtain terrestrial and arboreal prey. We offered O. bicirrhosum prey both suspended above and submerged below the surface of the water. From high-speed digital recordings, we measured kinematic variables associated with the jaws, cranium, pectoral fins, and body during orientation and prey capture. Aquatic and aerial feeding events were kinematically distinct, with aerial events generally involving faster, larger movements and a distinct delay in the onset of lower jaw depression until the head had left the water. The comparatively large gape during leaping may facilitate prey capture by overcoming variability in the apparent position of the prey due to refraction, while the delayed onset of mouth opening may serve to reduce the effects of drag. This distinctive leaping behaviour allows exploitation of the terrestrial prey base, especially during seasonal inundation of the Amazon River basin when the aquatic food base is widely dispersed.

Adaptive Management of Flows in the Lower Roanoke River, North Carolina, USA

The lower Roanoke River in North Carolina, USA, has been regulated by a series of dams since the 1950s. This river and its floodplain have been identified by The Nature Conservancy, the US Fish and Wildlife Service, and the State of North Carolina as critical resources for the conservation of bottomland hardwoods and other riparian and in-stream biota and communities. Upstream dams are causing extended floods in the growing season for bottomland hardwood forests, threatening their survival. A coalition of stakeholders including public agencies and private organizations is cooperating with the dam managers to establish an active adaptive management program to reduce the negative impacts of flow regulation, especially extended growing season inundation, on these conservation targets. We introduce the lower Roanoke River, describe the regulatory context for negotiating towards an active adaptive management program, present our conservation objective for bottomland hardwoods, and describe investigations in which we successfully employed a series of models to develop testable management hypotheses. We propose adaptive management strategies that we believe will enable the bottomland hardwoods to regenerate and support their associated biota and that are reasonable, flexible, and economically sustainable.

Seasonal inundation patterns in two large savanna floodplains of South America: the Llanos de Moxos (Bolivia) and the Llanos del Orinoco (Venezuela and Colombia)

AbstractInundation patterns in two of the largest savanna floodplains of South America were studied by analysis of the 37‐GHz polarization difference observed by the Scanning Multichannel Microwave Radiometer (Nimbus‐7 satellite). Flooded area was estimated at monthly intervals for January 1979 through to August 1987 using mixing models that account for the major landscape units with distinctive microwave emission characteristics. Results are presented separately for five subregions in each of the two floodplain regions to show the spatial as well as temporal variability in inundation patterns. The total area inundated during the 9 years varied between 2069 and 78 460 km2 in the Llanos de Moxos (also spelled as Mojos; median area, 23 383 km2) and 1278 and 105 454 km2 in the Llanos del Orinoco (median, 25 374 km2), not including the open‐water area of permanent lakes and river channels. The correlation between flooded area and river stage was used to extend the inundation records over a 30‐year period in the Moxos (1967–97) and a 58‐year period (1927–85) in the Orinoco. Interannual variability in inundation is greater in the Moxos than the Orinoco. Comparison of these data, however, with a previously published analysis of the Pantanal wetland shows that inundation patterns in these two floodplain regions are not as variable across years as they are in the Pantanal. Copyright © 2004 John Wiley & Sons, Ltd.

Forecasting the spatial extent of the annual flood in the Okavango delta, Botswana

The pristine Okavango Delta wetland of northern Botswana is potentially under threat due to water abstraction from its tributaries. We have developed a statistical model which makes it possible to predict the extent of wetland loss which will arise from water abstraction. The model also permits prediction of the maximum area of flooding, and its spatial distribution, three months in advance of the flood maximum. The model was calibrated using maximum areas of seasonal inundation extracted from satellite imagery covering the period 1985–2000, which were correlated with rainfall and total flood discharge. A technique was developed to translate the modelled flood area into a flood map. The methodology can predict maximum area of flooding and its distribution with better than 90% accuracy. An important, although relatively minor, source of error in the spatial distribution of the flood arises from a secular change in flood distribution in the distal Delta which has taken place over the last 15 years. Reconstruction of flooding history back to 1934 suggests that the Delta may be subject to a quasi 80 year climatic oscillation. If this oscillation continues, the extent of flooding will increase in the coming decades.

Exotic plant invasions of vernal pools in the Central Valley of California, USA

AbstractAim To better understand patterns of community invasibility, we examined exotic plant invasions along an environmental gradient found in vernal pools in the Central Valley of California. Specifically, we analysed the distribution and abundance of exotic plants in relation to pool size, seasonal inundation, soil and nutrient properties, the native plant community, and disturbance history.Location We studied patterns of exotic plant invasions in a complex of natural and restored vernal pools at Travis Air Force Base near Fairfield, California.Methods In thirty natural and thirty restored pools, we conducted field surveys to measure the distribution and abundance of exotic and native plants and several descriptors of the abiotic environment. We used multiple linear regressions to analyse exotic species richness and cover and the abundances of individual exotic species in relation to pool type, fire history, pool size, water depth, native plant cover, and six soil and nutrient properties.Results Exotic species richness was greater in burned than unburned pools, and exotic plant cover was greater in natural than restored pools. Both exotic species richness and cover decreased with increasing water depth. Exotic species richness was not related to native plant cover, but exotic plant cover decreased with increasing native plant cover. Eighteen of the nineteen most common exotic species showed significant relationships with pool type (twelve species), water depth (eleven species), fire history (nine species), native plant cover (six species), and pool size (five species). Most species increased in abundance with decreasing water depth (nine species) or were more abundant in natural (eight species) or burned pools (six species).Main conclusions These results suggest that both abiotic factors, especially those associated with seasonal inundation, and interactions with the native plant community play important roles in determining the invasibility of vernal pool plant communities. In particular, abiotic constraints may limit exotic plant invasions in more stressful environments, and interactions with the native plant community may limit invasions in more benign environments.

Soil, hydroperiod and bedding effects on restoring bottomland hardwoods on flood-prone agricultural lands in North Louisiana, USA

Summary Many of the bottomland hardwood forests of the Lower Mississippi Alluvial Valley, USA have been converted to agriculture, thus constituting a sizable loss in ecological and socio-economic functions. Bottomland hardwood forest afforestation on marginal agricultural lands has grown considerably since 1990. However, many failures in bottomland hardwood afforestation have occurred for various reasons, including misunderstandings or ignoring the relationships between species, soil and hydrology. In October 1996, a 32-ha tract on an abandoned agricultural field in Catahoula Parish, Louisiana, USA was site prepared for afforestation by bedding (moulding soil in parallel ridges). The following January it was planted with seedlings of Nuttall oak (Quercus nuttallii Palmer) and green ash (Fraxinus pennsylvanica Marsh.), and direct seeded with Nuttall oak. The objective of this study was to evaluate the effects of bedding (within three soil types) on species survival and growth. Soil redox potential measurements indicated that the soils were intensely anaerobic during frequent prolonged seasonal inundation and saturation events. Bedding clayey soils significantly increased mean height of planted and direct-seeded Nuttall oak, but not that for green ash. Bedding appears to be somewhat effective in restoring site microtopography, reducing soil hydroperiod and enhancing planted Nuttall oak height growth on poorly drained, clayey soils.