Spatial and temporal variability in early successional patterns of an invertebrate assemblage at an offshore oil platform

The effects of selected physical and biological factors on the early development of a subtidal invertebrate assemblage were examined at an offshore oil platform in the Santa Barbara Channel (California, USA). The effects of date, year, length, and depth of submersion were investigated by replacing sets of ceramic tiles with new tiles at frequencies of 2, 4, 6, 12, and 24 months at three depths (6, 12, and 18 m) over a period of 24 months. The effects of existing colonists and depth were explored in a second experiment by removing selected early colonists from ceramic tiles deployed at the same three depths over a period of 12 months. More than 40 invertebrate taxa from seven phyla colonized the tiles. Colonial tunicates and encrusting bryozoans appeared early in the successional sequence (∼2 months), in cover ranging from <5% to 80% and from <5% to 55%, respectively. Tubiculous amphipods, barnacles, and sponges could also appear early, but in low cover (<20%). Composition of the assemblage changed over time with barnacles, sponges, and mussels becoming the principal space holders on tiles submerged for 24 months. When potential competitors were removed monthly, variation in the cover of dominant taxa (i.e., bryozoans, amphipods, barnacles) was maintained to 12 months, suggesting that other factors, such as larval availability or post-settlement mortality, were responsible for these patterns. Development of this assemblage appeared to fit a pattern of early succession that was largely predictable in terms of the composition and sequence of occurrence of dominant taxa, but variable in rate of development, depending on date of submersion, year, and depth.     

Population patterns through twenty years of oldfield succession

Using 48 permanent, 0.5×2.0 m quadrats, changes in species composition and cover were followed in an oldfield abandoned after plowing in the spring of 1960. Twenty years of data collected since then show the succession to be individualistic, that is, composed of broadly overlapping population curves through time. In general, the population curves exhibit long, persistent tails, indicating that, through this time span, succession is a process in which species that are present for much of the time become dominant at different times. Invasion and extinction are not the major mechanisms of community change. Bi- or multi-modal peaks were discovered in some species, but there is no clear explanation of such patterns yet. Many species which are important later in the sequence invade early. Information on the biologies of representative species from early, middle, and late portions of the sequence are correlated with the population patterns. In particular, the mode of dispersal, life cycle, germination behavior, and assimilation requirements are related to species positions. However, there is need for coordinated, comparative study of species strategies as well as experimental study of species interactions in order to more fully understand the mechanisms of this succession. The patterns discovered in this oldfield are compatible with contemporary concepts of succession as an organism-based phenomenon, in which probabilistic gap creation and filling are critical.Nomenclature follows Fernald (1958).The late Dr. Murray F. Buell, Dr. Helen F. Buell, and the late Dr. John A. Small deserve special mention because, in 1958, they began the long-term, permanent quadrat study partly reported here. Such unselfish, prospective behavior merits notice and I am happy to acknowledge my debt to them. I thank Helen Buell for her patient teaching and helpful discussion and criticism. Dr. Thomas G. Siccama encoded the pre-1971 data. I thank Ms. Angela Salvemini for patient and trustworthy entry of the more recent data. The Research Council of Rutgers University partially defrayed the cost of a computer terminal, and Dr. R. T. T. Forman, Director of HMF, provided computing funds. I have benefitted from discussions with Dr. R. J. Frye, and from criticism by Dr. F. A. Bazzaz and Dr. T. D. Lee. The figures were prepared by Lisa Bandazian.     

Vegetation recovery patterns in early volcanic succession

Permanently plots were monitored from 1983 to the present on Mount Usu after the eruptions of 1977–78 which destroyed the pre-eruption vegetation by 1–3 m thick accumulations of ash and pumice in order to clarify the processes and mechanisms of succession. Until now, 163 species were recorded in the summit area. Most of these species were derived from vegetative reproduction throughout the volcanic deposits. Vegetative reproduction plays a major role on increases in cover. Although long-distance seed-dispersal species could immigrate to the crater basin, their cover increase was slow. Seedbank species only established in gullies where the original topsoil was exposed by erosion. Most annuais were supplied by the seedbank in the original topsoil and woody species originated via immigration, suggesting that the source greatly determines the species composition of establishing vegetation. Annual seedlings showed low survival, while overwintering perennial seedlings steadily established. Ground surface movements strongly restricted increases in plant cover and the distance from source vegetation was the principal determinant of plant density. Due to differences in disturbance intensity, successional rates were higher in the stable substrates outside gullies and lower on the exposed original topsoil in some gullies. Recipient of the Botanical Society Award of Young Scientists, 1994     

Removal experiments to test mechanisms of plant succession in oldfields

We investigated the effects of total (TR) or partial (PR) removal of the above-ground biomass of the dominant species on early successional trends in two oldfields in central New Jersey, USA. Our objective was to assess the occurrence of facilitation, tolerance, or inhibition as mechanisms of species replacement in the fields studied. In a 2nd-yr oldfield dominated by Ambrosia artemisiifolia, floristic composition and distribution of species cover changed markedly between the 2nd and the 3rd yr, regardless of the removal treatment. In both TR and PR plots and in control plots dominance shifted from an annual (A. artemisiifolia) to a biennial (Erigeron annuus). This indicates that the presence of the annual dominant is not necessary to promote this successional replacement, and therefore facilitation can be ruled out. Most species present in the 3rd-yr community were late summer and fall invaders which were not initially present. In a 7-yr oldfield dominated by Solidago canadensis, a clonal perennial, very little change in the distribution of species cover could be detected between years. Overall physiognomy remained the same, but there was a gradual change in floristic composition. In this field, TR and PR treatments enhanced vegetational change by allowing the increase in cover of suppressed understory species. Both inhibition and tolerance mechanisms may be involved in the pattern of vegetational change in this field. Finally, we stress that the mechanisms of species replacement operating in early secondary succession are dependent on structural and life history characteristics of the species assemblage on a particular site.     

Do pioneers have r-selected traits? Life history patterns among colonizing terrestrial gastropods

We examine whether pioneer species of terrestrial gastropods (snails and slugs) possess particular life history traits commonly associated with r-selection, using data on gastropod colonization in four areas in north-west Europe (the Kvarken and Tvärminne archipelagos in the Baltic, polder woods in IJsselmeer, and a rehabilitated quarry near Maastricht). Data on age at first reproduction, longevity, clutch size, egg size and lifetime fecundity were gathered from the literature. In order to control for potentially confounding effects of body size on life history traits, we compared the residuals from the allometric relations between life history traits and body size for pioneers and non-pioneers. In snails, all life history traits examined were related to body size. In slugs, all traits except age at first reproduction scaled with body size. Body sizes did not differ between pioneers and non-pioneers in any area. In all four areas, there were no significant differences between pioneers and non-pioneers in any of the life history traits examined, after body size had been taken into account. This indicates that pioneer terrestrial gastropods generally cannot be regarded as r-selected. Pioneer species may possess any of several life history strategies, and the combinations of traits shown by them may have little in common with the r-K selection concept.     

Vegetation dynamics in Brittany heathlands after fire

The vegetation dynamics of heathlands in Brittany have been followed for three years in areas subject to fire in August 1976. The pre-fire vegetation had been analysed and mapped before its destruction. The structure of the community and the processes taking place in it (in terms of biomass, primary productivity, phenology, mineral nutrition and food value) had been examined. The redevelopment of the canopy was studied by the point-contact method along permanent line transects. This semi-quantitative study permits calculation of the relative frequency of each species and, from this, its cover. The growth form of each species and the stratification of the community are also indicated by this method. Permanent plots were also used to record changes in the vegetation, by means of a census of individuals and records of the development and growth strategy of each species. The plots were located in homogeneous areas, or on bare soil around seed parents in order to examine seed dispersal and seedling establishment. These two methods yielded detailed information on the nature of the secondary successions following fire in the heathlands of Brittany.

     

Spatial patterns of mycorrhizal infectiveness of soils long a successional chronosequence

 This study quantified intersite variation and spatial pattern in arbuscular mycorrhizal (AM) and ectomycorrhizal (ECM) infectivity of soils among six sites constituting a successional chronosequence in southwestern Ohio, USA. The study sites included an active agricultural field (chronic disturbance), a site which had been stripped of its surface soil (pseudo-stripmine, acute disturbance), 5- and 10-year-old fields, a 25- to 30-year-old prairie restoration, and an undisturbed, mature forest. AM infectivity was lower in the agricultural field, successional fields, and prairie than in the mature forest, but there was no clear correlation between time since disturbance and the overall level of AM infectivity. Spatial structure in AM infectivity decreased with time since disturbance. In the pseudo-stripmine site and active soybean field, semivariance analysis attributed 44–50% of the total variance in AM infectivity among samples to spatial structure, whereas spatial dependancy accounted for only 18% of total variance in the mature forest. Kriging of AM infectiveness demonstrated small, isolated areas in the disturbed plots that were devoid of AM infectiveness, whereas the kriged AM maps of the other four sites showed AM infectiveness to become progressively more homogeneous. ECM infectiveness was lacking from 35–50% of the samples from the disturbed sites, and both overall ECM infectiveness and ECM diversity increased with time since disturbance. Approximately 44% of the variance in ECM infectiveness was related to spatial structure in the two disturbed sites, and large areas entirely devoid of ECM infectivity were present on the kriged ECM maps for these sites. There was less spatial structure in ECM in the old fields and prairie and very little in the mature forest. The results of this study emphasize the need to explicitly evaluate spatial heterogeneity in mycorrhizal infectivity in studies of the role of mycorrhizae in succession. Accepted: 4 August 1995     

Interactions between mycorrhizal colonization and plant life forms along the successional gradient of coastal sand dunes in the eastern Mediterranean, Turkey

The mycorrhizal status of dune plant species in relation to their plant life forms was surveyed along a successional gradient of sand dune on the southern Mediterranean coast of Turkey. Roots of 64 dune plant species belonging to 30 families were collected from sand dune communities at four different successional stages: embryonic dunes (ED), mobile dunes (MD), fixed dunes (FD), and remnant dunes (RD). Of the plant species surveyed in all successional stages, 54 (84%) had formed mycorrhizal associations. Nonmycorrhizal plants with cryptophyte life forms predominated in the earlier successional stages (ED and MD), whereas the number and percent coverage of mycorrhizal plant species belonging to hemicryptophytes, phanerophytes, and chamaephytes generally increased with the stabilization of sand dunes. Arbuscular mycorrhizal (AM) colonization was found to be the dominant mycorrhizal type in ED, MD, and RD. But phanerophytes with dual colonization, AM and ectomycorrhizal, became the dominant life form with high plant coverage in the FD stage. Total percentage of mycorrhizal root length colonization showed significant positive correlations relating to soil parameters such as organic matter and nitrogen content, while negatively correlating to high soil reaction (pH).     

Fine‐scale persistence of boreal bog plants

Abstract. Persistence, or the tendency of a species to remain in its original position without colonizing new sites, is studied for 24 species on the ombrotrophic Northern Kisselbergmossen in SE Norway. Data sets comprise presence/absence in 436 sample plots (16 cm x 16 cm) and 6976 subplots (4 cm x 4 cm) analysed with a 5‐yr interval. Persistence was calculated for both spatial scales, and the observed values were compared with null models of completely random presence/absence of species. Species characteristics (plot occurrences and persistence) were related to depth to the water table and species optima along ecologically interpreted DCA ordination axes. The observed persistence was significantly higher than predicted from the random model for all vascular plants and cryptogams at both spatial scales. All taxonomic groups showed higher persistence at the sample plot scale than at the subplot scale. No general relationship between persistence and depth to the water table was found, but for the cryptogams there was somewhat higher persistence for the less peat‐producing species. The persistence of the vascular plants depended on ramet longevity, growth form and vegetative mobility. In general, the observed persistence of most cryptogams was high, probably because of their perenniality, low growth rates and high reproductive output. Differences in growth‐form and life history, as well as the higher number of occurrences, are the most likely reasons for somewhat higher mean persistence of hepatics and Sphagna than of vascular plants at the subplot scale.     

Plant distribution patterns during early succession on an artificial protosoil

Abstract. Plant succession has been studied since 1977 in permanent plots on a calcareous protosoil in the northern outskirts of Göttingen (Central Germany). At the beginning the substrate was extremely poor in organic carbon and nitrogen. On 128 plots of 100 m², the temporal and spatial distribution of the most conspicuous plant species showed remarkable changes and correlations to soil site factors. While presenting data on Melilotus alba, Medicago lupulina, Agropyron repens, Arrhenatherum elatius, Dactylis glomerata, and Picris hieracioides the mechanisms of successional changes on nutrient-poor soils are discussed. It is demonstrated that a high cover of legumes favours the accumulation of soil nitrogen. Grassland species were more abundant in areas with low humus content whereas ruderal plant species preferred those parts of the area which contained more humus in the substrate. Life-form, colonization and population strategies play an important role in the described successional processes, in addition to resource competition. Finally, some methodological conclusions for permanent plot studies are presented.     

Optimal age and size at maturity in annuals and perennials with determinate growth

Summary A model predicting optimal age and size at maturity is presented, exploring the conflict between growth and energy allocation to reproduction. According to the model, the factors promoting delayed maturity and large adult body size are as follows: (1) high rate of somatic growth, (2) high percentage increase in reproductive rate with body size increase, (3) long life expectancy at maturity for annuals or large number of expected productive days (when either growth or reproduction is possible) for perennials with growth ceasing at maturity, (4) life expectancy increasing with body size. All these factors are combined in the mathematical formula predicting optimal age and size at maturity, which allows for quantitative predictions. The optimal schedule of growth and reproduction may be achieved by natural selection, developmental plasticity, or when one species replaces another. Sexual size dimorphism is also discussed, resulting from different optimal age at maturity for either sex.     

Small-scale variability as a mechanism for large-scale stability in mountain grasslands

Abstract. Data from a 7-yr permanent plot study of grassland dynamics were used to address the relationship between processes at two levels of resolution (3.3 cm x 3.3 cm, 50 cm x 50 cm). Grasslands mown and manured in the traditional way in the Krkonose Mts. (Riesengebirge) were used as a model system. Spatial dynamics at the finest scale were very high, as demonstrated by turnover of individual species in 3.3 cm x 3.3 cm subplots and year-to-year transition matrices of the same subplots. The direction of these dynamics was not correlated with grassland treatment, although there was some correlation within years. An extrapolation of such year-to-year dynamics to larger time scales would result in big large-scale changes on the community level, and large shifts in species composition of the whole sward. However, dynamics at larger spatial or temporal scales were generally small. Some directional change occurred in manured plots, whereas little change occurred in unmanured plots. Large-scale dynamics were not correlated with small-scale dynamics in plots without manuring, but some correlation was detectable in manured plots. There are probably several processes that drive small-scale dynamics, such as non-linear interactions and environmental fluctuations. We argue that within certain limits these forces act on species composition so as to make small-scale dynamics non-directional. This results in both large-scale species diversity and apparent large-scale stability of these grasslands. However, if these forces are beyond these limits, the small-scale dynamics may become directional, resulting in rapid changes at larger spatial scales.     

Old-field successional dynamics on the Inland Pampa,Argentina

Abstract. The first 10 yr of old-field successional dynamics on the Argentine Inland Pampa were studied on a series of adjacent plots established consecutively between 1978 and 1989. We examined differences in species abundance patterns among plots in order to detect the spatial and temporal variability of succession. Perennial grasses steadily increased in cover and replaced the dominant annual species after 5 yr. Pioneer dicots persisted in older seral stages with 20 — 23 species/plot. Overall, exotic species (mostly the grasses Lolium multiflorum and Cynodon dactylon) contributed much to the plant cover in these communities. Native grasses comprised 45 % of total cover at years 7 — 10 of succession, but occurred with less than 7 species/plot. Substantial variation was found in the successional pathway, which reflected the particular sequence from annual forbs to short-lived and perennial grasses in the various plots. The course of succession was apparently influenced by a 2-yr period of unusually high rainfall. Deyeuxia viridiflavescens, a native perennial grass virtually absent before the wet period, spread over the study area and dominated seral communities for 3 yr, irrespective of plot age. Climatic conditions thus affected the successional turnover of life forms by increasing the rate of colonization by perennial grasses. We further point out the constraints imposed on secondary succession by the life histories of ‘available’ species.     

Contrasting patterns of tree mortality in late‐successional Picea abies stands in two areas in northern Fennoscandia

Question: What are tree mortality rates and how and why do they vary in late‐successional Picea abies‐dominated forests? Do observed tree mortality patterns allow comparative assessment of models of long‐term stand development? Location: Northern boreal Fennoscandia. Methods: We measured stand structure in 10 stands in two different areas. We determined age distributions and constructed a chronology of tree deaths by cross‐dating the years of death of randomly sampled dead trees. Results: The stands in the two areas had contrasting tree age distributions, despite similar live tree structure. In one area, stands were relatively even‐aged and originated following a stand‐replacing fire 317 years earlier. The stands in the second area had an uneven age structure and virtually no signs of past fires, suggesting a very long period since the last major disturbance. The younger stands were characterized by a high mortality rate and inter‐annual variation, which we attributed to senescence of the relatively even‐aged stands approaching the maximum age of P. abies. In contrast, the tree mortality rates in the older stands were low and relatively stable. Conclusions: Patterns of tree mortality were, to a large extent, dependent on the time since the last stand‐replacing disturbance, suggesting that northern boreal P. abies stands eventually reach a shifting mosaic state maintained through small‐scale dynamics, but the time needed to reach this state appears to be lengthy; even 300 years after a forest fire stands showed changes in patterns of tree mortality that were related to the developmental stage of the stands.     

Fine‐scale five‐year vegetation change in boreal bog vegetation

Abstract. Within an ombrogenous part of N. Kisselbergmosen, Rødenes, SE Norway, fine‐scale changes in species abundance, successional trends relative to the main gradients (as represented by DCA axes), and co‐ordinated change within pairs of the bottom layer species are studied. Data sets were sampled twice with a five‐year interval, and included species abundance and cover of mud bottom, naked peat and litter in 436 sample plots (16 cm× 16 cm), and species abundance in 6976 subplots (4 cm× 4 cm). Depth from the surface of subplots to the water table was estimated in 1991. Most summers and growing seasons were somewhat drier than normal in the 5‐yr period. The area covered by mud‐bottom, naked peat and litter increased significantly, as did the frequencies of the dwarf shrubs Calluna vulgaris and Andromeda polifolia in hummocks and upper lawn. Sample plots were significantly displaced downward the peat productivity gradient (DCA 2), reflecting the reduced cover of many bottom layer species, including all Sphagnum spp. Significant coordinated changes in cover of bottom layer species are described. The changes observed in hummocks support the existence of a local regeneration cycle, as suggested by other researchers. Some of the vegetation changes seem parallel to those reported from areas with a higher nitrogen deposition, but it is not likely that nitrogen deposition alone is the major cause of the observed changes. Between‐year variation in population size and climatic fluctuations may as well explain the observed changes.     

Changes in tree and liana communities along a successional gradient in a tropical dry forest in south-eastern Brazil

We investigated changes in species composition and structure of tree and liana communities along a successional gradient in a seasonally dry tropical forest. There was a progressive increase in tree richness and all tree structural traits from early to late stages, as well as marked changes in tree species composition and dominance. This pattern is probably related to pasture management practices such as ploughing, which remove tree roots and preclude regeneration by resprouting. On the other hand, liana density decreased from intermediate to late stages, showing a negative correlation with tree density. The higher liana abundance in intermediate stage is probably due to a balanced availability of support and light availability, since these variables may show opposite trends during forest growth. Predicted succession models may represent extremes in a continuum of possible successional pathways strongly influenced by land use history, climate, soil type, and by the outcomes of tree–liana interactions.     

Understanding ecological community succession: Causal models and theories,a review

Critical review of explanations for patterns of natural succession suggests a strong, common basis for theoretical understanding, but also suggests that several well known models are incomplete as explanations of succession. A universal, general cause for succession is unlikely, since numerous aspects of historical and environmental circumstances will impinge on the process in a unique manner. However, after disturbance, occupation of a site by any species causes changes in the conditions at the site. Sorting of species may result, since different species are adapted to different regions of environmental gradients. Such sorting can generate several patterns of species abundance in time, but commonly results in sequential replacements of species adapted to the varying conditions. This may be due to constraints on species' strategies, or life history traits, placed by the limited resources available to the organism. These constraints often result in inverse correlation between traits which confer success during early and late stages of succession. Facilitatory or inhibitory effects of species on each other are best understood in terms of these life history interactions, perhaps as restrictions on, or as moderation of, these processes.Strong support for the importance of correlations in life history traits stems from comparisons of simulated succession with and without these correlations. These simulations are reviewed in some detail, and followed by brief reviews of other prominent models for succession. Several aspects of the confusion and controversies in the successional literature are then discussed, with a view to a more optimistic synthesis and direction for successional ecology.     

Small-scale plant dynamics in temperate Themeda triandra grasslands of southeastern Australia

Abstract. Vegetation subjected to two long-term burning regimes (annual or biennial burning) was studied in permanent plots, at two spatial scales: 0.01 m² and 1 m², to determine the small-scale dynamics of plants in temperate Themeda triandra grasslands of southeastern Australia. Species turnover rates were estimated by presence/absence data while species mobility was assessed using cumulative frequency data. While mean species richness did not fluctuate greatly between years, the vegetation was internally dynamic rather than static. Cumulative species richness increased by 50% at both spatial scales and sites over the 4-yr study period. However, few species became cumulatively frequent (i.e. occurred in 80% of plots in the first and/or subsequent years), suggesting that cumulative species richness increases were due to small- or local-scale movements of plants, rather than ‘shifting clouds’ of species moving across the entire site. The vegetation's dynamics did not differ greatly at sites subject to different (frequent) fire intervals. Species turnover and mobility were individualistic, but the dynamics of many species was greater at the smaller spatial scale: 31–48% of the species present at both spatial scales at the two sites had higher turnover rates at the 0.01 m² scale. Similarly, some ‘non-mobile’ species at the 1-m² scale (i.e. ‘constant’ or ‘local’ mobility types), were more mobile at the smaller-scale. Turnover rate and mobility type were strongly associated with life form in some cases, particularly at the annually-burnt site. In general, therophytes (and to a lesser degree, geophytes) were positively associated with high turnover and mobility in most years, while hemicryptophytes were negatively associated with high turnover in many instances. Hemicryptophytes included many species with a range of mobility types and hence, few significant associations between mobility and this life form were found. The previously unrecognized internal dynamics of this community under ‘stable’ management regimes contributes to species coexistence by allowing plants with different dynamics properties to persist in a spatially and temporally unpredictable manner. Frequent burning is presumably the important component driving much of the non-directional, small-scale dynamics because it regularly destroys individual plants and aerial plant parts and creates opportunities for seedling regeneration, whilst permitting the vegetative persistence and spread of established plants in non-light-limited microsites.     

Factors affecting migration patterns of juvenile river herring in a coastal Massachusetts stream

Juvenile anadromous river herring (alewives, Alosa pseudoharengus, and blueback herring, Alosa aestivalis) spend 3–7 months in freshwater before migrating to the ocean, often exhibiting waves of early and late migrations. Migratory patterns and associated abiotic and biotic factors were examined for both species migrating in 2003 from Herring River in Bourne Massachusetts. Migrating herring were grouped into two temporal periods and separated by species. Relationships between abiotic (water temperature, lunar phase, and precipitation) and biotic (size, age, growth rate, and hatch date) factors and the timing of out-migration (transition to seawater) were examined. Blueback herring migration coincided with a sharp decrease in temperature consistent with the time of year. Peaks in alewive migration may reflect adaptive traits maximizing likelihood of survival through seasonal marginal stream habitats and also avoiding lethal water temperatures in winter. Migrating bluebacks exhibited a single migratory period (late September–October) which occurred between the early and late migratory pulses of the alewives. These patterns may also represent distinct migration strategies between early and late migrating alewives and between the two species of river herring. Early migration may be a mechanism by which factors such as competition and low food availability are mitigated. In contrast, environmental conditions during the post hatching time of late migrators may allow for a size maximizing strategy that promotes migration from the nursery area as late as possible.