Successional Changes In Vegetation Research Articles

Pocket gopher disturbance slows soil carbon accumulation in abandoned agricultural lands.

Soil carbon (C) sequestration rates vary widely in abandoned agricultural lands, and factors determining this variation, beyond climate, soil type, and productivity, are poorly understood. One such factor is soil disturbance by burrowing mammals. Despite being ubiquitous in all grasslands, the impact of burrowing mammals on soil C dynamics is not well understood. We quantified the major ecosystem processes that are influenced by one such burrowing mammal, plains pocket gophers (Geomys bursarius), in old field ecosystems located in east-central Minnesota, USA. We found that pocket gopher abundance varied among old fields and that newly formed gopher mounds covered up to 6% of the soil surface annually. We first measured short-term C pool and flux changes induced by gopher activities. Soil N mineralization did not differ between the soil in gopher mounds and undisturbed soil. However, for the soil under gopher mounds, N mineralization was 30% lower compared with the undisturbed soil. We developed a process model to simulate the long-term gopher disturbance impact on old field soil C accumulation. This simulation showed that pocket gophers reduced both the rate of soil C accumulation and the total C pool. This reduction is primarily driven by reduced plant C input due to the time it requires for the vegetation to recolonize gopher mounds. Soil organic matter (SOM) decomposition changes had only a minor impact. The process model showed that the depth from which burrowing mammals redistribute soil to the surface is a key factor in determining the overall impact on SOM. In total, our study indicated that soil disturbance by burrowing animals could significantly reduce C storage in old field ecosystems when the mammals are mostly active at the surface soil and can be a significant factor in decreasing overall C sequestration after land abandonment. However, at our study site, gopher abundance decreased with abandonment age, which was likely to have been cause by successional vegetation changes, therefore the gopher disturbance-induced reduction in soil C is transient and decreases with abandonment age.

Successional changes in vegetation and litter structure in traditional Lacandon Maya agroforests

ABSTRACTThe Lacandon Maya is an indigenous group who live in Chiapas, Mexico. Their traditional lifeways involve swidden, sequential agroforestry management that mimics ecological disturbance and modifies succession. Lacandon farmers use fire to clear small plots for polyculture milpa agroforests, which they subsequently fallow. They actively manage all stages of their agroforests to provide ecosystem services and facilitate site recovery. However, it is unclear whether or how quickly the ecosystem structure of Lacandon agroforests matches that of a mature forest. Therefore, this study quantified canopy cover, basal area, ground cover, and litter layers and depth to empirically evaluate successional trends in vegetation and litter structure. Our results show that the Lacandon agroforest structure typically recovers to mature forest levels, but the speed and nature of this recovery vary by metric. They also indicate Lacandon traditional agroforestry is predicated on nuanced understanding of tropical forest successional dynamics, as illustrated by Lacandon farmers’ recognition of successional stages that correspond to patterns in vegetation and leaf litter structure. As such, Lacandon ecological knowledge has the potential to facilitate the restoration of degraded tropical forests in Chiapas, Mexico. However, our findings also demonstrate that shortening fallow periods will undermine the ecological integrity of this traditional agricultural system.

Effect of spring grass fires on vegetation patterns and soil quality in abandoned agricultural lands at local and landscape scales in Central European Russia

IntroductionAbandonment of agricultural land is often happening all over the world and widespread in Russia. Such lands are subject to successional changes in vegetation and it seems necessary to provide effective methods for a sustainable ecosystem management of those lands. However, factors which determine successional processes, especially fires, have not been studied in detail. The aim of this article is to reveal how spring grass fires affect the abandoned arable lands in the study area at the landscape and local scales.MethodsA region of 265.5 km2 located in the south of Moscow was studied. At the landscape scale, we analyzed the spatial characteristics of the area in relation with a 30-year history of spring fire events extracted from the Landsat archive, and climatic data. Logistic regression was used. At the local scale, we sampled soil and vegetation at two sites and in three biotopes at each site: mature forest and two neighboring biotopes affected and unaffected by fire. Plant species diversity, soil quality, and relationship between soil and vegetation were assessed by ANOVA, v test, NMDS, and dbRDA.ResultsAbandoned lands covered 39% of the study area and not less than 72% of these were affected by grass fires, happening mainly between 1998 and 2014. Man causes the ignition of the field layer accidentally, but the area over which the fire spreads is determined by climatic factors and the presence of flammable material (dry grass and litter) for burning. High March temperatures and low precipitation values in April increase the inflammability of dry grasses which are abundant on the former fields. As a result, burnt areas are steadily expanding in abandoned lands where trees are scarce. On abandoned lands that were either affected or unaffected by fires, two different plant communities developed, respectively: grassy vegetation mainly dominated by Calamagrostis epigeios and young forest of pioneer trees with high crown coverage. Practically all soil variables were statistically different in three biotopes at the research sites. Plant species composition was best explained by six soil variables: P2O5, C/N, pH, K, SOC, and N values.ConclusionsWe showed the key role of grass fires in the formation of differences in soil and vegetation during the successional recovery of abandoned lands at the local and landscape scales.

Disentangling Effects of Time Since Fire, Overstory Composition and Organic Layer Thickness on Nutrient Availability in Canadian Boreal Forest

Wildfire is the primary abiotic disturbance in the boreal forest, and its long-term absence can lead to large changes in ecosystem properties, including the availability and cycling of nutrients. These effects are, however, often confounded with the effects of successional changes in vegetation toward nutrient-conservative species. We studied a system of boreal forested lake islands in eastern Canada, where time since last fire ranged from 50 to 1500 years, and where the relative abundance of the most nutrient-conservative tree species, black spruce, was largely independent of time since last fire. This allowed us to disentangle the effects of time since fire and the dominant vegetation on ecosystem properties, including nutrient stocks and concentrations. Effects of time since fire independent of vegetation composition mostly involved an increase in the thickness of the organic layer and in nitrogen concentration in both soil and leaves. Domination by black spruce had strong negative effects on nutrient concentrations and was associated with a shift toward more fungi and Gram-positive bacteria in the soil microbial community. Path modeling showed that phosphorus concentration was inversely related to organic layer thickness, which was in turn related to both time since fire and black spruce abundance, while nitrogen was more directly related to time since fire and the composition of the overstory. We conclude that discriminating between the effects of vegetation and time since fire is necessary for better understanding and predicting the long-term changes that occur in forest nutrient availability and ecosystem properties.

Distribution of waterfowl of the Malozemelskaya tundra (Nenets autonomous district, Russia) among different wetland types

Investigations were conducted between 1993 and 2005 in the Malozemelskaya tundra of Nenets autonomous district of the Arkhangelskaya region in Russia. The study site spanned the area along the Barents Sea from the saltwater Indigskaya Bay, across the saltwater Kolokolkova Bay, to the freshwater Korovinskaya Bay, and along the region’s major rivers of the Malozemelskaya tundra. We divided the region into 6 different subregions and compared physical, biological, and chemical features of the lakes and ponds among the subregions, including number of waterfowl species and individuals by life stage (e.g., breeding and post-breeding), water surface area, spatial configuration of adjacent wetlands, water depth, pH, shoreline vegetation, and ratio of open water to vegetation. We used the information to categorize wetlands into 5 types and evaluated waterfowl use among the wetland types. The study area was strongly influenced by cryogenic processes with thermokarst formations with associated lakes and ponds of various ages, assessed by successional changes in vegetation. The hilly and hilly-ridge landscape of the area between the Urdjuzskoe lake subregion is dominanted by lakes of glacial and glacial cumulative origin. We also investigated waterfowl use within the saltwater-dominated Kolokolkova Bay, the freshwater Korovinskaya Bay, and within the Indiga, Neruta, and Velt river basins that bisect the region, and lastly wetlands of the Russkij Zavorot peninsula. We observed 42 species from 25 genera using about 72% of the wetland of the region. Thermokarst lakes had the greatest species diversity with 23 species observed. Glacial lakes and cumulative wetlands hosted the fewest species with 17 and 14 species, respectively. Oxbow lakes and lagoon lakes hosted 20 and 16 waterfowl species, respectively. We counted 20 species on saltwater Kolokolkova Bay and 19 on freshwater Korovinskaya Bay. The average number of species using any one of the 5 wetland types was 23. The greatest diversity of waterfowl species was observed on Rivers Neruta (22 species) and Velt (21 species) and in Pechora River Delta (17 species). During summer, species composition in river habitats was richer than in lakes.

Changes over 26 Years in the Avifauna of the Bogotá Region, Colombia: Has Climate Change Become Important?

High Neotropical mountains are among the most threatened ecosystems by climate change and this problem could be accentuated in cities where temperatures are higher. However, there are few data of long-term avifaunal changes in Neotropical cities, and the potential impact of climate change has yet to be addressed. Using data from 26 years of Christmas Bird Counts (CBCs) in the Bogota area (ca. 2600-3100m in Colombia’s eastern Andes), we analyze long-term changes of the avifauna using linear regressions corrected for species’ habitat preferences and compared urban and rural sites. For the CBC we followed the Audubon Society’s methodology in which birds are counted over a 24-hour period within a fixed circle 24km in diameter. We recorded 235 species in the Bogota circle with an average of 122spp/year, including 46 boreal migrants, three endemic species and four endemic subspecies, two globally and four locally threatened species. Species richness was higher in rural than in urban areas and most species were associated with native forest and scrub and wetlands. Among the species that were analyzed for changes in time 31% increased, 20% decreased and 49% did not change. Strong fluctuations or changes in abundance were more frequent in urban than rural environments. Many of the species that increased or became established during the CBC interval came from lower elevations or the warmer, drier parts of the region beyond the count circle. By contrast, the lower elevational limits moved to higher elevations in several species that decreased. Climate change with its related effects represented the factor associated with the most changes in abundance. Other potential causes were direct human actions, mostly associated with urbanization, and “natural” successional changes in vegetation; predation by feral dogs and cowbird parasitism also affected several species negatively. Observations indicate that these factors will continue into the future, and the effects of climate change and urbanization in particular will probably intensify. The Bogota CBC has provided much valuable information for Neotropical urban ornithology and its practice should be encouraged in other Latin American cities and should definitely continue in Bogota for many years to come.

Spatial distribution of insect indicator taxa as a basis for peat bog conservation planning

Peat bogs are highly endangered ecosystems worldwide. In the Western Balkans, they represent fragmented habitat patches, where insect diversity and implications for the habitat loss are poorly known. Carabid beetles and ants, widely used environmental indicators, were sampled by pitfall trapping in the largest and oldest Croatian peat bog and at its edges. We found that tyrphobiontic—bog specialist—species were absent in both taxonomic groups, which is likely due to biogeographical limitation for dispersal of these species into this region. With this study, tyrphophilous—typical of bogs—species have been recognised as environmental indicators in the Western Balkans peat bogs. Assemblages of both taxa were strongly affected by specific conditions in the peat bog – high soil moisture and Sphagnum moss dominance, showing that edges are more favourable habitats for both taxa. Overall, carabid beetle activity density was significantly higher at the edge than at the peat bog, while species richness increased for both taxa at the edge, but not significantly. Spatial distribution of tyrphophilous species differed between studied taxa, with ants being more abundant in the peat bog, and carabid beetles at the edge. Additionally, some stenotopic and globally endangered species preferred edges. Occurrence of tyrphophilous and globally endangered species highlights the great conservation value of peat bog habitats in the Western Balkans. However, successional changes in vegetation are changing hydrological conditions of the peat bog. Here we suggest active conservation measures to preserve these unique soil invertebrate zoocoenoses.

Choice of biodiversity index drives optimal fire management decisions.

Preservation of biodiversity is a central goal of conservation management, yet the conditions that promote persistence may differ for the species in the community. For systems subject to stochastic disturbances such as fire, understanding which management practices promote persistence for all species in a community is complex. Before deciding on the best course of action, an objective must be specified. Yet an overarching goal of species persistence can be specified into a measureable objective many different ways. We investigated four alternative management objectives for maximizing species persistence that use common biodiversity indices: (1) attaining the minimally acceptable mix of successional vegetation states to support species' relative abundances, (2) maximizing the arithmetic mean abundance of species, (3) maximizing the geometric mean abundance of species, and (4) minimizing the average extinction risk of species. We used stochastic dynamic programming to model successional changes in vegetation in the presence of both planned and unplanned fires, and utilize an extensive data set on the occurrence of birds, reptiles, and small mammals in different successional states in semiarid Australia. We investigated the influence the choice of objective function and taxonomic focus has on the optimal fire management recommendations. We also evaluated a recent hazard reduction policy to annually burn a fixed amount of the landscape and compare results to the optimal solution. The optimal management strategy to maximize species persistence over a 100-year period is predominantly to minimize wildfires. This is because the majority of species are more likely to occur in intermediate, and late successional vegetation. However the optimal solution showed sensitivity to the objective and the species included in the analysis. These results highlight the need for careful consideration when specifying an objective to represent overarching conservation goals. Using the extinction risk objective, we show that a policy to annually burn 5% of the landscape could increase the average probability of extinction for the modelled species by 7% over the next 100 years compared to the optimal management scenario.

Bryophyte colonization history of the virgin volcanic island Surtsey, Iceland

Abstract. The island Surtsey was formed in a volcanic eruption south of Iceland in 1963–1967 and has since then been protected and monitored by scientists. The first two moss species were found on Surtsey as early as 1967 and several new bryophyte species were discovered every year until 1973 when regular sampling ended. Systematic bryophyte inventories in a grid of 100 m × 100 m quadrats were made in 1971 and 1972: the number of observed species doubled, with 36 species found in 1971 and 72 species in 1972. Here we report results from an inventory in 2008, when every other of the grid's quadrats were searched for bryophytes. Despite lower sampling intensity than in 1972, distributional expansion and contraction of earlier colonists was revealed as well as the presence of new colonists. A total of 38 species were discovered, 15 of those were not encountered in 1972 and eight had never been reported from Surtsey before (Bryum elegans, Ceratodon heterophyllus, Didymodon rigidulus, Eurhynchium praelongum, Schistidium confertum, S. papillosum, Tortula hoppeana and T. muralis). Habitat loss due to erosion and reduced thermal activity in combination with successional vegetation changes are likely to have played a significant role in the decline of some bryophyte species which were abundant in 1972 (Leptobryum pyriforme, Schistidium apocarpum coll., Funaria hygrometrica, Philonotis spp., Pohlia spp, Schistidium strictum, Sanionia uncinata) while others have continued to thrive and expand (e.g. Schistidium maritimum, Racomitrium lanuginosum, R. ericoides, R. fasciculare and Bryum argenteum). Some species (especially Bryum spp.) benefit from the formation of new habitats, such as grassland within a gull colony, which was established in 1984. Several newcomers are rarely producing sporophytes on Iceland and are unlikely to have been dispersed by airborne spores. They are more likely to have been introduced to Surtsey by seagulls in the form of vegetative fragments or dispersal agents (Bryum elegans, Didymodon rigidulus, Eurhynchium praelongum, Ceratodon heterophyllus and Ulota phyllantha). The establishment of the gull colony also means that leakage of nutrients from the nesting area is, at least locally, downplaying the relative importance of nitrogen fixation by cyanobacteria growing in bryophyte shoots.

Monitoring and conservation of Saga pedo (Orthoptera: Tettigoniidae) in an isolated nothwestern population

The bush cricket Saga pedo is a critically endangered species in the EU and is included in Annex IV of Council Directive 92/43/EEC. This species is therefore subject to mandatory regular monitoring within all member countries where it occurs. Because its abundance is low and little information is available concerning its ecology, however, an effective monitoring method that would yield standardized results has yet to be devised. We found S. pedo passing through 6 instars during its development in Central European conditions. Our findings indicate that, after hatching, S. pedo moves constantly through terrain with optimal vegetation and thereby reduces its population density. Based on recaptures of marked individuals, adults moved usually between 0.5 and 2 m in 24 h, the largest distance moved during a day was recorded as 37.5 m. Combined with a high mortality rate, this continual movement leads to very low density late in the season. Based on extensive surveys conducted during 2006–2011 at 10 sites in the Palava Protected Landscape Area (Czech Republic), we show that the optimal time for monitoring in order to achieve comparable results from different investigators in different locations is the period just after nymphs hatch (1–10 May in Central Europe). Because S. pedo populations in Europe are threatened by habitat destruction resulting from successional overgrowth of habitat by vegetation and afforestation, ensuring the survival of this species will require that successional changes in vegetation and afforestation be stopped by mowing and removal of woody plants and seedlings or by farming (extensive grazing). Management need not be performed every year but should occur when the S. pedo population is already adult and dispersed. The most suitable period for partial machine mowing (1/3–1/2 of a specific area) is September. Mowing with scythes and extensive rotational grazing are the best methods for managing sites where S. pedo is found.

Successional Changes and Habitat Selection in Hayfield Bird Communities

I examined the effects of successional changes in vegetation on the breeding dispersion of grassland birds in hayfields in New York. I sampled vegetation and counted birds in 90 hayfields of various ages (i.e. number of years since planting) and sizes that were originally planted to a legume-dominated seed mixture. I also resampled a subset of these fields two years later. Over time, these hayfields changed from tall, dense, homogeneous stands of legume-dominated vegetation to short, sparse, patchy stands of grass-dominated vegetation. Fields of all ages were dominated by introduced plant species. Red-winged Black- birds (Agelaius phoeniceus), the most common bird species breeding in these fields, were most common in fields of intermediate ages, whereas numbers of Bobolinks (Dolichonyx oryzivorus), the second most abundant species, increased logarithmically with field age. Upland Sand- pipers (Bartramia longicauda), Eastern Meadowlarks (Sturnella magna), Grasshopper Sparrows (Ammodramus savannarum), and Henslow's Sparrows (A. henslowii) were most abundant in the oldest hayfields, whereas abundances of Savannah Sparrows (Passerculus sandwichensis, the third most common species) did not differ in fields of different ages. Bird-species richness and diversity increased linearly with hayfield age. Three species (Red-winged Blackbird, Bobolink, Savannah Sparrow) accounted for more than 90% of the breeding individuals. Vegetation structure, composition, and patch size were the most important proximate cor- relates of habitat selection for these species. Hayfield size was positively correlated with abundance for five of the seven most common species. Furthermore, those species that nested late in the season (Bobolinks, Grasshopper Sparrows, and Henslow's Sparrows) had low

Responses of two species of heathland rodents to habitat manipulation: Vegetation density thresholds and the habitat accommodation model

AbstractThe abundance of two native rodent species, Rattus lutreolus and Pseudomys gracilicaudatus, has been shown to correlate with vegetation density in coastal wet heath. Fox's habitat accommodation model relates relative abundances of such small mammal species to heathland vegetation regeneration following disturbance. Implicit in the model is recognition that it is successional changes in vegetation, not time per se, that drives the responses of small mammal species along a regeneration axis. Using a brush‐cutter we deliberately removed approximately 85% of vegetation around trapping stations and recorded significant reductions in the abundance of both P. gracilicaudatus (an earlier‐stage colonizing species) and R. lutreolus (a late seral‐stage species). A significant decrease in the abundance of only the latter had been demonstrated previously when 60–70% of the vegetation had been removed. Following the brush‐cutting both species re‐entered the mammalian secondary succession at different times, first P. gracilicaudatus followed by R. lutreolus after the vegetation cover thresholds of each species had been reached. The impact of this habitat manipulation experiment was to produce a retrogression of the small mammal succession, experimentally demonstrating causality between changes in vegetation density and subsequent small mammal habitat use.

Grassland compositional change in relation to the identity of the dominant matrix-forming species

Background: Grasslands have only a few dominants and most of the diversity consists of subdominants. Because dominants differ widely in phenology and resource use, dominants may control the recruitment and establishment of other species. Aims: To explore the relationship between the identity of the dominant species and successional vegetation changes in grassland communities. Methods: The compositional change over 23 years in 1900 permanent plots dominated by four grasses (Andropogon gerardii, Elymus repens, Poa pratensis and Schizachyrium scoparium) was examined within 19 old fields in Minnesota. Fields were abandoned 1–56 years before sampling. Rate of directional change and degree of compositional dissimilarity were determined. Results: Non-natives, P. pratensis and E. repens, were associated with either no or a slow directional change. Elymus repens was associated with high dissimilarity and P. pratensis with intermediate dissimilarity. Natives, A. gerardii and S. scoparium, were associated with compositional change that followed expectations based on field age. The rate of directional change and degree of dissimilarity between sampling intervals was lower for A. gerardii relative to S. scoparium, the only species to be associated with strong directional change. Conclusions: Dominance by non-native grass species may impede traditional successional processes and result in a community composition quite dissimilar from native prairies.

Assessing the response of area burned to changing climate in western boreal North America using a Multivariate Adaptive Regression Splines (MARS) approach

AbstractFire is a common disturbance in the North American boreal forest that influences ecosystem structure and function. The temporal and spatial dynamics of fire are likely to be altered as climate continues to change. In this study, we ask the question: how will area burned in boreal North America by wildfire respond to future changes in climate? To evaluate this question, we developed temporally and spatially explicit relationships between air temperature and fuel moisture codes derived from the Canadian Fire Weather Index System to estimate annual area burned at 2.5° (latitude × longitude) resolution using a Multivariate Adaptive Regression Spline (MARS) approach across Alaska and Canada. Burned area was substantially more predictable in the western portion of boreal North America than in eastern Canada. Burned area was also not very predictable in areas of substantial topographic relief and in areas along the transition between boreal forest and tundra. At the scale of Alaska and western Canada, the empirical fire models explain on the order of 82% of the variation in annual area burned for the period 1960–2002. July temperature was the most frequently occurring predictor across all models, but the fuel moisture codes for the months June through August (as a group) entered the models as the most important predictors of annual area burned. To predict changes in the temporal and spatial dynamics of fire under future climate, the empirical fire models used output from the Canadian Climate Center CGCM2 global climate model to predict annual area burned through the year 2100 across Alaska and western Canada. Relative to 1991–2000, the results suggest that average area burned per decade will double by 2041–2050 and will increase on the order of 3.5–5.5 times by the last decade of the 21st century. To improve the ability to better predict wildfire across Alaska and Canada, future research should focus on incorporating additional effects of long‐term and successional vegetation changes on area burned to account more fully for interactions among fire, climate, and vegetation dynamics.

Changes in structure of macrophyte communities in the chosen lakes of Łęczna-Włodawa Lake District

Changes in the aquatic vegetation structure were analyzed in 4 lakes of Łęczyńsko-Włodawskie Lake District. The macrophytes’ structure has changed quite essentially in lakes in the last 10 years. A tendency of reduction the number of plant associations was observed in meso- and slightly eutrophic lakes, while an increase was observed in eutrophic ones. The range of macrophytes occurrence decreased in all investigated lakes.At first, phytocenoses of submerged macrophytes retreated from the lakes, especially charophyte communities. However, the number of phytocenoses of the rush vegetation grew up. The increase in Phragmitetum australis occurrence, was observed in each investigated lake. It is the typical phenomenon connected with successional changes in vegetation from mesotrophic to eutrophic lakes.

Plant growth simulation for landscape-scale hydrological modelling

Landscape-scale hydrological models can be improved by incorporating realistic, process-oriented plant models for simulating crops, perennial grasses and woody species. The objective of this project was to present some approaches for plant modelling applicable to daily time step hydrological transport models, such as SWAT. Accurate simulation of plant growth can improve the accuracy of simulations of hydrological and biogeochemical cycles. First, we describe some unique aspects of the general plant model ALMANAC. Next, we describe a modification of the original ALMANAC model used to simulate complex successional vegetation changes in the years following disturbance of a variety of different forest ecosystems, such as forest fires, clear cuts and insect infestations. Finally, we discuss alternative physiological and physical process simulation techniques of plant growth that could increase simulation accuracy in landscape-scale hydrological and transport models such as SWAT.

Management of three endangered plant species in dynamic Baltic seashore meadows

AbstractQuestion: Arctophila fulva var. pendulina, Primula nutans var. jokelae and Puccinellia phryganodes are threatened early successional species growing in the seashore meadows of the northern Baltic Sea. Patches formed by these species are destined to be replaced by other species during primary succession and in order to persist in the area they have to continuously colonize new areas. We studied whether the displacement of the species could be slowed down and their sexual and/or vegetative reproduction enhanced by management targeted to surrounding vegetation.Location: Bothnian Bay, Baltic Sea, W Finland.Methods: Vegetation surrounding patches of all study species was mown in four successional growing seasons. Moreover, the impact of additional soil turning on creating new favourable growing sites was tested for A. fulva.Results: Deterioration of suitable habitats of A. fulva and P. nutans was markedly slowed down by management and the vegetative and/or sexual reproduction of these species was enhanced. In the case of P. phryganodes, however, no positive response to management was obtained.Conclusions: In order to improve the long‐term persistence of these three species successional vegetation changes should be slowed down and their dispersal and colonization success improved by continuous management of the populations. We further suggest that the colonization of new areas should be aided by transplantations to the non‐vegetated islets, which have recently risen from the sea and cannot be reached by means of dispersal.

The role of aeolian dust in ecosystems

The recent upsurge in research attention to aeolian dust has shown that dust transport systems operate on very large spatial and temporal scales, and involve much larger quantities of sediment than was previously realized. An inevitable consequence of this is that researchers from a range of neighbouring disciplines, including ecology, are beginning to realize that this new knowledge has important implications for their study areas. In the present paper, we examine the ecological implications (real and potential) of this expanding knowledge of dust transport systems, with a particular emphasis upon the Australian dust transport system. We track these ecological effects from source to sink. At source, wind erosion–soil–vegetation relationships are often dominated by temporal changes in rainfall. Nine years of measurements in the Channel Country of the Lake Eyre Basin, Australia show that vegetation and soils in dune fields can recover from drought, whereas on inter-fluve grasslands uni-directional and negative successional vegetation changes can result from wind erosion during drought. On floodplains, both wind erosion and vegetation responses are complicated by flood frequency. Up to 1999 flooding of saline claypans did not increase vegetation but did increase wind erosion through the supply of alluvial fines. However, after three floods within as many months vegetation became established and wind erosion rates were dramatically reduced. Wind erosion research attention is now gradually turning from the physical to the organic content of eroded dusts. In Australia organic matter content can reach 65% by mass, but this cannot be explained by removal of soil organic matter alone. Biological soil crusts not only stabilize soils against wind erosion but contribute to some of the organic dusts. The role of dust as a vector for pathogens is an area which deserves greater research attention in the future. Downwind from source, we show that dust contributions to soils are more widespread and more variable (in time and space) than earlier work on dust-derived loess soils has suggested. Recent studies also show positive dust impacts upon nutrient budgets within distant forest ecosystems, and significant contributions to river nutrient loads, especially in the arid sectors of internally draining river basins. The number of studies of dust impacts upon marine ecosystems is increasing dramatically. Studies of dust within Antarctic ice cores combined with dust modelling provide compelling evidence that increased soluble iron-rich dust inputs to the Southern Ocean have stimulated phytoplankton populations. Modern process studies are, however, yet to clearly demonstrate these relationships. Finally we examine the potential for major dust impacts upon global climates, using its positive and negative effects upon solar radiation and precipitation as examples of the complexity and importance of this new research area.

Seedling recruitment of Succisella inflexa in fen meadows: Importance of seed and microsite availability

Abstract. The effects of different forms of land use on germination and establishment of the rare fen species Succisella inflexa were investigated in seed introduction experiments in a mown and an abandoned fen meadow in SE Germany. Treatments included abandonment, mowing in fall and mowing with creation of gaps in the moss and litter layer. Floating capacity of seeds was tested in order to estimate potential dispersal by water.On the mown meadow, gaps had a slightly positive effect on germination rates, while greatly increasing seedling survival until the next spring. At the abandoned site, litter inhibited germination, whereas mosses had a negative effect on germination and a positive effect on survival rates during the first year after germination. Both germination and seedling establishment were negatively affected by the presence of slug herbivores. On the abandoned site, no seedlings at all survived until the next spring. Even though seeds of Succisella inflexa were capable to float for several weeks and to germinate thereafter, the situation at the field sites indicates that longdistance dispersal is highly unlikely. Our results showed that not only direct effects of abandonment, such as accumulation of litter, may have led to poor germination and poor seedling establishment of the species. Additionally, indirect consequences of changes in land use, such as higher seedling herbivory by slugs and successional vegetation changes due to abandonment, were important in determining habitat quality and availability of microsites for seedling recruitment. Furthermore, early mowing imposed seed limitation on plant populations.

High‐resolution pollen analysis of tundra polygons from the North Slope of Alaska

Modern and fossil pollen analyses have established the local vegetation succession and landscape evolution along the Meade River near Atqasuk, Alaska. Three data sets were analyzed: (1) a 142‐cm‐long peat deposit on the exposed river bluff face, (2) a short, 13‐cm peat monolith from the near‐surface sediment, and (3) a modern data set of surface samples collected along a transect representative of a geomorphic gradient of low‐center, transitional, and high‐center polygons. Pollen‐microfossil assemblages changed significantly along this gradient. Detailed analysis of the short pollen profile shows successional vegetation changes over the last 250 years. The long profile, a 9400‐year record of past vegetation, indicates that initially, the site was covered by shallow lakes. Eolian activity had a substantial effect on sediment deposition, but a period of rapid peat growth from 8500 to 5000 14C year B.P. is coincident with increased vegetation cover of mixed grass‐shrub tundra. Following this period, peat growth slowed, and shrub vegetation was replaced by tussock‐forming sedge vegetation.