Nutrient Addition Dramatically Accelerates Microbial Community Succession

The ecological mechanisms driving community succession are widely debated, particularly for microorganisms. While successional soil microbial communities are known to undergo predictable changes in structure concomitant with shifts in a variety of edaphic properties, the causal mechanisms underlying these patterns are poorly understood. Thus, to specifically isolate how nutrients – important drivers of plant succession – affect soil microbial succession, we established a full factorial nitrogen (N) and phosphorus (P) fertilization plot experiment in recently deglaciated (∼3 years since exposure), unvegetated soils of the Puca Glacier forefield in Southeastern Peru. We evaluated soil properties and examined bacterial community composition in plots before and one year after fertilization. Fertilized soils were then compared to samples from three reference successional transects representing advancing stages of soil development ranging from 5 years to 85 years since exposure. We found that a single application of +NP fertilizer caused the soil bacterial community structure of the three-year old soils to most resemble the 85-year old soils after one year. Despite differences in a variety of soil edaphic properties between fertilizer plots and late successional soils, bacterial community composition of +NP plots converged with late successional communities. Thus, our work suggests a mechanism for microbial succession whereby changes in resource availability drive shifts in community composition, supporting a role for nutrient colimitation in primary succession. These results suggest that nutrients alone, independent of other edaphic factors that change with succession, act as an important control over soil microbial community development, greatly accelerating the rate of succession.     

Pathways, mechanisms and predictability of vegetation change during tropical dry forest succession

The development of forest succession theory has been based on studies in temperate and tropical wet forests. As rates and pathways of succession vary with the environment, advances in successional theory and study approaches are challenged by controversies derived from such variation and by the scarcity of studies in other ecosystems. During five years, we studied development pathways and dynamics in a chronosequence spanning from very early to late successional stages (ca. 1–60 years) in a tropical dry forest of Mexico. We (1) contrasted dynamic pathways of change in structure, diversity, and species composition with static, chronosequence-based trends, (2) examined how structure and successional dynamics of guilds of trees shape community change, and (3) assessed the predictability of succession in this system. Forest diversity and structure increased with time but tree density stabilized early in succession. Dynamic pathways matched chronosequence trends. Succession consisted of two tree-dominated phases characterized by the development and dynamics of a pioneer and a mature forest species guild, respectively. Pioneer species dominated early recruitment (until ca. 10 years after abandonment), and declined before slower growing mature-forest species became dominant or reached maximum development rates (after 40–45 years). Pioneers promoted their replacement early in succession, while mature-forest species recruited and grew constantly throughout the process, with their lowest mortality coinciding with the peak of pioneer abundance. In contrast to prevailing stochastic views, we observed an orderly, community driven series of changes in this dry forest secondary succession. Chronosequences thus represent a valuable approach for revealing system-specific successional pathways, formulating hypotheses on causes and mechanisms and, in combination with repeated sampling, evaluating the effects of vegetation dynamics in pathway variation.     

Vegetation convergence during early succession on coal wastes: a 6‐year permanent plot study

Question: Does the course of succession on a coal mine restored by hydroseeding converge with a reference community in terms of species composition and vegetation structure? What is the rate of succession on restored areas? How does the balance between local colonization and extinction rates change during succession? Which species group (native or hydroseeded) determines the successional process? Location: Large reclaimed coal mine in the north of Palencia province, northern Spain (42°50′N, 4°38′W). Methods: Between 2004 and 2009 we monitored annually vascular plant species cover in nine permanent plots (20 m² each) at a restored mine; these plots were structured to account for site aspect (north, south and flat). Three identical permanent plots were established in the surrounding reference community and monitored in 2004 and 2009. We used detrended correspondence analysis to assess successional trends and rates of succession, generalized linear mixed models to derive patterns of vegetation structural changes and turnover through time, and Huisman–Olff–Fresco modelling to illustrate response of individual species through time. Results: The three restored mine areas exhibited a successional trend towards the reference community through time, although speed of convergence differed. However, after 6 years the restored sites had diverged considerably and this was greater than the dissimilarity reduction with respect to the reference community. Richness, diversity and native species cover increased linearly through time, whereas hydroseeded species cover decreased. Success of hydroseeded species initially differed in the three areas, and this was negatively related with native species colonization rates. Response patterns through time of ten hydroseeded and 20 most common native species are described. Conclusions: Vegetation structural parameters rapidly converged with the reference community, whereas compositional convergence needed much longer. At the same time, successional composition trajectories and rates were related to site properties (here aspect).     

Effects of disturbance intensity and frequency on early old‐field succession

Abstract. Early old‐field succession provides a model system for examining vegetation response to disturbance frequency and intensity within a manageable time scale. Disturbance frequency and intensity can interact with colonization and competition to influence relative abundance of earlier and later successional species and determine, respectively, how often and how far succession can be reset. We tested the joint effects of disturbance frequency and intensity on vegetation response (species richness, abundance, canopy structure) during the first six years of succession by clipping the dominant species (D) or all species (T) in spring and fall of each year (S), once per year in summer (Y1), each two years in summer (Y2), or each four years in summer (Y4). Vegetation response reflected disturbance effects on expansion of a later monospecific dominant perennial herb, Solidago altissima, and persistence of the early, richer flora of annuals. A more abundant and taller top Solidago canopy developed on plots clipped each 2 yr or less frequently. Plots clipped yearly or seasonally were richer, but had less abundant, shorter, and differently stratified canopy. Disturbance mediated the relative abundance of early and later successional species; however, frequency and intensity effects were not completely congruent. Persistence of a richer early successional flora increased through the most frequent disturbance (S), and was magnified by disturbance intensity. Disturbance as extreme as clipping all vegetation twice yearly did not cause a drop in species richness, but maintained the early successional community over the first six years of succession. We conclude that clipping disturbance influenced the rate of succession, but the early community could rebound through the range of disturbance frequency and intensity tested.     

Testing successional hypotheses of stability, heterogeneity, and diversity in pitcher-plant inquiline communities

Succession is a foundation concept in ecology that describes changes in species composition through time, yet many successional patterns have not been thoroughly investigated. We highlight three hypotheses about succession that are often not clearly stated or tested: (1) individual communities become more stable over time, (2) replicate communities become more similar over time, and (3) diversity peaks at mid-succession. Testing general patterns of succession requires estimates of variation in trajectories within and among replicate communities. We followed replicate aquatic communities found within leaves of purple pitcher plants (Sarracenia purpurea) to test these three hypotheses. We found that stability of individual communities initially decreased, but then increased in older communities. Predation was highest in younger leaves but then declined, while competition was likely strongest in older leaves, as resources declined through time. Higher levels of predation and competition corresponded with periods of higher stability. As predicted, heterogeneity among communities decreased with age, suggesting that communities became more similar over time. Changes in diversity depended on trophic level. The diversity of bacteria slightly declined over time, but the diversity of consumers of bacteria increased linearly and strongly throughout succession. We suggest that studies need to focus on the variety of environmental drivers of succession, which are likely to vary through time and across habitats.     

Rate of succession in restored wetlands and the role of site context

Question: Are changes in plant species composition, functional group composition and rates of species turnover consistent among early successional wetlands, and what is the role of landscape context in determining the rate of succession? Location: Twenty‐four restored wetlands in Illinois, USA. Methods: We use 4 years of vegetation sampling data from each site to describe successional trends and rates of species turnover in wetlands. We quantify: (1) the rate at which composition changes from early‐successional to late‐successional species and functional groups, as indicated by site movement in ordination space over time, and (2) the rate of change in the colonization and local extinction of individual species. We correlate the pace of succession to site area, isolation and surrounding land cover. Results: Some commonalities in successional trends were evident among sites. Annual species were replaced by clonal perennials, and colonization rates declined over time. However, differences among sites outweighed site age in determining species composition, and the pace of succession was influenced by a site's landscape setting. Rates of species turnover were higher in smaller wetlands. In addition, wetlands in agricultural landscapes underwent succession more rapidly, as indicated by a rapid increase in dominance by late‐successional plants. Conclusions: Although the outcome of plant community succession in restored wetlands was somewhat predictable, species composition and the pace of succession varied among sites. The ability of restoration practitioners to accelerate succession through active manipulation may be contingent upon landscape context.     

The role of breeding system in community dynamics: Growth and mortality in forests of different successional stages

Plant sexual systems appear to play an important role in community assembly: Dioecious species are found to tend to have a higher propensity to colonize communities in early successional stages. Here, we test two demographic hypotheses to explain this pattern in temperate forests. First, we test demographic differences between hermaphrodite and dioecious species in stressful younger successional stages: Previous theory predicts that hermaphrodite seed production is more harmed in stressful environments than that of dioecious populations leading to an advantage for females of dioecious species. Second, in primary forest, we hypothesized that dioecious species would show demographic advantage over monomorphic ones. We used data from two temperate forest plots in Northeast China surveyed over 10 years to compare the rates of growth and mortality of tree species with contrasting breeding systems in both secondary and primary forests. We assessed the effect of breeding system on the growth‐mortality trade‐off, while controlling for other traits usually considered as correlates of growth and mortality rates. We show that in the secondary forest, dioecious species showed weak advantage in demographic rates compared with monomorphic species; dioecious species showed considerably both lower relative growth and mortality rates compared to the hermaphrodites in the primary forest over 10 years, consistent with a priori predictions. Hermaphrodites showed strong growth‐mortality trade‐offs across forest stages, even when possibly confounding factors had been accounted for. These results suggest that sexual system influences community succession and assembly by acting on the rates of growth and mortality, and the trade‐off between them. As vegetation develops, the demographic differences between breeding systems are much larger. Our results demonstrate the association between breeding system, succession, and community assembly and that this relationship is succession‐stage dependent. Our findings support the suggestion that the demographic advantage of dioecious species facilitates the coexistence of sexual systems in primary forest.     

Convergence and divergence in a long‐term old‐field succession: the importance of spatial scale and species abundance

Whether plant communities in a given region converge towards a particular stable state during succession has long been debated, but rarely tested at a sufficiently long time scale. By analysing a 50‐year continuous study of post‐agricultural secondary succession in New Jersey, USA, we show that the extent of community convergence varies with the spatial scale and species abundance classes. At the larger field scale, abundance‐based dissimilarities among communities decreased over time, indicating convergence of dominant species, whereas incidence‐based dissimilarities showed little temporal tend, indicating no sign of convergence. In contrast, plots within each field diverged in both species composition and abundance. Abundance‐based successional rates decreased over time, whereas rare species and herbaceous plants showed little change in temporal turnover rates. Initial abandonment conditions only influenced community structure early in succession. Overall, our findings provide strong evidence for scale and abundance dependence of stochastic and deterministic processes over old‐field succession.     

Temporal patterns in rates of community change during succession

While ecological dogma holds that rates of community change decrease over the course of succession, this idea has yet to be tested systematically across a wide variety of successional sequences. Here, I review and define several measures of community change rates for species presence-absence data and test for temporal patterns therein using data acquired from 16 studies comprising 62 successional sequences. Community types include plant secondary and primary succession as well as succession of arthropods on defaunated mangrove islands and carcasses. Rates of species gain generally decline through time, whereas rates of species loss display no systematic temporal trends. As a result, percent community turnover generally declines while species richness increases--both in a decelerating manner. Although communities with relatively minor abiotic and dispersal limitations (e.g., plant secondary successional communities) exhibit rapidly declining rates of change, limitations arising from harsh abiotic conditions or spatial isolation of the community appear to substantially alter temporal patterns in rates of successional change.     

Diversity and community biomass depend on dispersal and disturbance in microalgal communities

The evidence for species diversity effects on ecosystem functions is mainly based on studies not explicitly addressing local or regional processes regulating coexistence or the importance of community structure in terms of species evenness. In experimental communities of marine benthic microalgae, we altered the successional stages and thus the strength of local species interactions by manipulating rates of dispersal and disturbance. The treatments altered realized species richness, evenness and community biomass. For species richness, dispersal mattered only at high disturbance rates; when opening new space, dispersal led to maximized richness at intermediate dispersal rates. Evenness, in contrast, decreased with dispersal at low or no disturbance, i.e. at late successional stages. Community biomass showed a non-linear hump-shaped response to increasing dispersal at all disturbance levels. We found a positive correlation between richness and biomass at early succession, and a strong negative correlation between evenness and biomass at late succession. In early succession both community biomass and richness depend directly on dispersal from the regional pool, whereas the late successional pattern shows that if interactions allow the most productive species to become dominant, diverting resources from this species (i.e. higher evenness) reduces production. Our study emphasizes the difference in biodiversity–function relationships over time, as different mechanisms contribute to the regulation of richness and evenness in early and late successional stages.     

Influence of stand age and physical environment on the herb composition of second-growth forest, Strouds Run, Ohio, USA

Aim Historical land use in eastern North America and much of Europe has created a mosaic of successional forest stands of widely varying age. An estimate of the rate of successional community development would allow the conservation value of individual stands to be assessed. We estimate the rate of herb community development in secondary forests in our region, and the extent to which physical gradients determine herb distributions. Location Second‐growth forest in the Appalachian Oak section of the Central Hardwoods Region, southeastern Ohio, USA. Methods Thirty‐five plots were surveyed in old (82–193 years) and young (35–40 years since pasture) deciduous forest stands and pine plantations. In each plot, herb species cover and environmental factors were measured. Results Herb community composition was clearly distinguishable between oak‐dominated upland sites and mixed mesophytic stands in moist ravines. In both community types, young stands were compositionally distinct from old stands. Species lacking obvious seed dispersal mechanisms were disproportionately uncommon in young stands, implying dispersal limitation in the process of recolonization. Among old stands, distributions of many species showed significant regressions on the environmental variables, whereas few showed significance in young stands. Species with weak dispersal tended to be more frequently linked to environmental gradients in old stands than in young stands. Main conclusions Early arriving forest species appear to assort rapidly along physical gradients, defining communities early in the successional trajectory. The re‐assembly of the full forest community continues over a longer period as individual species assort on environmental gradients at rates determined by their dispersal abilities. Thus, long‐established stands show more spatial variation than successional stands, and offer greater opportunities for conservation of the forest community.     

Environmental Heterogeneity Influences Successional Trajectories in Colombian Seasonally Dry Tropical Forests

Environmental characteristics have a major effect on the species composition of seasonally dry tropical forest. However, this effect has been little considered when describing secondary succession of this ecosystem. We tested the hypothesis that local environmental heterogeneity influences successional trajectories when high species richness is available. Changes in species composition and structure were described in 126 vegetation plots differing in successional stage and located along a topographical and soil nutrient gradient. Variation in community composition was partitioned between successional stage, environmental characteristics, and spatial structure using redundancy analyses. In addition, relationships between plot distance matrices for these factors were analysed by means of Mantel tests. High species turnover was observed during succession and species composition similarity was higher among late successional forest than among early and intermediate forests. A higher portion of variation in species composition was explained by environmental characteristics compared to successional stage, whereas the spatial structure of the data was weak. Our results suggest that in the region of study, variation in the successional trajectories is occurring owing to environmental heterogeneity, as well as to human disturbance and other unmeasured processes.     

Dynamic and static views of succession: Testing the descriptive power of the chronosequence approach

Chronosequence and permanent plot studies are the two most common methods for evaluating successional dynamics in plant communities. We combined these two approaches by re-sampling an old-field chronosequence at Cedar Creek Natural History Area (Minnesota, USA) to: (1) measure rates of secondary succession; and (2) to test the ability of the chronosequence approach to predict actual successional dynamics over a 14-year survey interval. For each of 19 chronosequence fields we calculated four complimentary indices of succession rate for community changes that actually occurred within each of these fields between 1983 and 1997. We found that measures of compositional dissimilarity, species turnover, and the change rates of perennial and native species cover over this 14-year period were all negatively correlated with field age, indicating that the rate of successional change in these old-fields generally declines over time. We also found that data collected from the initial static chronosequence survey (1983) accurately predicted many of the observed changes in species abundance that occurred between 1983 and 1997, but was a poor predictor of changes in species richness. In general, chronosequence re-sampling confirmed the validity of using the chronosequence approach to infer basic patterns of successional change.     

Using functional trait diversity to evaluate the contribution of multiple ecological processes to community assembly during succession

Successional chronosequences provide a unique opportunity to study the effects of multiple ecological processes on plant community assembly. Using a series of 0.5 × 0.5 m² plots (n = 30) from five successional sub‐alpine meadow plant communities (ages 3, 5, 9, 12, and undisturbed) in the Qinghai‐Tibetan Plateau, we investigated whether community assembly is stochastic or deterministic for species and functional traits. We tested directional change in species composition, functional trait composition, and then functional trait diversity measured by Rao's quadratic entropy for four traits – plant height, leaf dry matter content, specific leaf area, and seed mass – along two comparable successional chronosequences. We then evaluated the importance of species interactions, habitat filtering and stochasticity by comparing with random communities and partitioning the environmental and spatial components of Rao's quadratic entropy. We found no directional change in species composition, but clear directionality in functional trait composition. None of the abiotic environmental variables (except P) showed linear change with successional age, but soil moisture and nitrogen were positively related to functional diversity within meadows. Functional trait diversity increased significantly with the increase in successional age. Comparison with random communities showed a significant shift from trait divergence in early stages of succession (3‐ and 5‐yr) to convergence in the later stages of succession 9‐, 12‐yr and undisturbed). The relative importance of abiotic variables and spatial structure for functional trait diversity changed in a predictable manner with successional age. Stochasticity at the species level may indicate dispersal limitation, but deterministic effects on functional trait distributions show the role of both habitat effects and biotic interactions.     

Changing assembly rules during secondary succession: evidence for non-random patterns

Describing the rules of community assembly is a central topic of ecology. Studying successional processes through a trait-based null model approach can help to better understand the rules of community assembly.According to theoretical considerations, at the beginning of succession - after getting over the dispersal limitation stage - community composition is primarily shaped by environmental filters (generating functional convergence), while in later stages limiting similarity (generating functional divergence) will be dominant. However, empirical evidence does not clearly support theoretical expectations.Our aim was to detect the presence and changes of trait-based assembly processes during old-field succession based on twelve traits. Changes in vegetation composition were evaluated by a combination of time series and space-for-time substitution: conducting three resurveys of permanent plots on four old-field age-groups. The individual dispersion of traits was transformed into effect size (i.e. departure from null model expectation). The impact of time since abandonment on effect sizes was tested by generalized additive mixed effect models.We detected a non-random pattern for each trait in at least some part of the succession. Departure from randomness did not change significantly over time for six traits: seed mass, lateral spread and pollination type were divergent, while leaf size, generative height and length of flowering were convergent. Six traits had changing patterns along the succession. Four of them showed increasing divergence (e.g. dispersal type, LDMC), which supports our hypothesis. While two (SLA, life form) displayed increasing convergence, contrary to expectations.We confirmed the general hypothesis that convergence is predominant initially and that divergence can be detected later in succession for four traits. However, the large variation found in trait dispersion indicates that complex processes operate during succession.     

陕西子午岭生态因素对植物群落的影响

为探讨生境对植被格局分布的影响,对黄土高原马栏林区60块样地进行植被学调查的基础上,采用17个环境指标刻画植物群落的空间位置、地形和土壤特征;利用双向指示种分析(TWINSPAN)划分了该区不同演替阶段的植物群落类型;利用前向选择法(forward selection)及Monte Carlo检验对不同演替阶段植物群落物种组成影响显著(p＜0.05)的环境因子进行筛选;利用去势典范对应分析(DCCA)排序方法分析不同演替阶段植物群落分布格局与环境的关系;利用偏典范对应分析(partial CCA)定量分离环境、空间及其交互作用对植被格局总体变异的影响.结果表明:(1)马栏林区的植物群落可划分为13个类型,分别属于4个不同的演替阶段;(2)对演替初期阶段群落影响显著的环境因子是土壤含盐量和碱解氮,对演替过渡阶段群落影响显著的环境因子是海拔和腐殖质厚度,对演替亚顶级阶段群落影响显著的因子是海拔、坡向、枯落物厚度、腐殖质厚度和pH值,而对演替顶级阶段群落分异影响显著的因子是海拔、坡向、pH值和速效磷;(3)不同演替阶段群落的生态学特性和分布规律与环境空间的生态梯度格局吻合较好;(4)随着演替的进行,环境因子单独对植物群落的影响越来越大,而样地位置单独作用和样地位置与环境因子的交互作用之和越来越小.     

Vegetation succession among and within structural layers following wildfire in managed forests

Question: How does vegetation develop during the initial period following severe wildfire in managed forests? Location: Southwestern Oregon, USA. Methods: In severely burned plantations, dynamics of (1) shrub, herbaceous, and cryptogam richness; (2) cover; (3) topographic, overstory, and site influences were characterized on two contrasting aspects 2 to 4 years following fire. Analysis of variance was used to examine change in structural layer richness and cover over time. Non‐metric multidimensional scaling, multi‐response permutation procedure, and indicator species analysis were used to evaluate changes in community composition over time. Results: Vegetation established rapidly following wildfire in burned plantations, following an initial floristics model of succession among structural layers. Succession within structural layers followed a combination of initial and relay floristic models. Succession occurred simultaneously within and among structural layers following wildfire, but at different rates and with different drivers. Stochastic (fire severity and site history) and deterministic (species life history traits, topography, and pre‐disturbance plant community) factors determined starting points of succession. Multiple successional trajectories were evident in early succession. Conclusions: Mixed conifer forests are resilient to interacting effects of natural and human‐caused disturbances. Predicting the development of vegetation communities following disturbances requires an understanding of the various successional components, such as succession among and within structural layers, and the fire regime. Succession among and within structural layers can follow different successional models and trajectories, occurs at different rates, and is affected by multiple interacting factors.     

Leaf trait-environment relationships in a subtropical broadleaved forest in South-East China

Although trait analyses have become more important in community ecology, trait-environment correlations have rarely been studied along successional gradients. We asked which environmental variables had the strongest impact on intraspecific and interspecific trait variation in the community and which traits were most responsive to the environment. We established a series of plots in a secondary forest in the Chinese subtropics, stratified by successional stages that were defined by the time elapsed since the last logging activities. On a total of 27 plots all woody plants were recorded and a set of individuals of every species was analysed for leaf traits, resulting in a trait matrix of 26 leaf traits for 122 species. A Fourth Corner Analysis revealed that the mean values of many leaf traits were tightly related to the successional gradient. Most shifts in traits followed the leaf economics spectrum with decreasing specific leaf area and leaf nutrient contents with successional time. Beside succession, few additional environmental variables resulted in significant trait relationships, such as soil moisture and soil C and N content as well as topographical variables. Not all traits were related to the leaf economics spectrum, and thus, to the successional gradient, such as stomata size and density. By comparing different permutation models in the Fourth Corner Analysis, we found that the trait-environment link was based more on the association of species with the environment than of the communities with species traits. The strong species-environment association was brought about by a clear gradient in species composition along the succession series, while communities were not well differentiated in mean trait composition. In contrast, intraspecific trait variation did not show close environmental relationships. The study confirmed the role of environmental trait filtering in subtropical forests, with traits associated with the leaf economics spectrum being the most responsive ones.     

Mycorrhizal fungal growth responds to soil characteristics,but not host plant identity,during a primary lacustrine dune succession

Soil factors and host plant identity can both affect the growth and functioning of mycorrhizal fungi. Both components change during primary succession, but it is unknown if their relative importance to mycorrhizas also changes. This research tested how soil type and host plant differences among primary successional stages determine the growth and plant effects of arbuscular mycorrhizal (AM) fungal communities. Mycorrhizal fungal community, plant identity, and soil conditions were manipulated among three stages of a lacustrine sand dune successional series in a fully factorial greenhouse experiment. Late succession AM fungi produced more arbuscules and soil hyphae when grown in late succession soils, although the community was from the same narrow phylogenetic group as those in intermediate succession. AM fungal growth did not differ between host species, and plant growth was similarly unaffected by different AM fungal communities. These results indicate that though ecological filtering and/or adaptation of AM fungi occurs during this primary dune succession, it more strongly reflects matching between fungi and soils, rather than interactions between fungi and host plants. Thus, AM fungal performance during this succession may not depend directly on the sequence of plant community succession.     

Mechanisms of succession along the emersion gradient in intertidal rocky shore assemblages

Theoretical models predict that the relative importance of competition and facilitation vary inversely along gradients of abiotic stress, with facilitation dominating under harsh conditions (the so called "stress-gradient hypothesis"). To date, very few studies have tested this hypothesis in the framework of succession. Moreover, the generality of the hypothesis is currently under debate and the necessity to examine responses at the community level and using different stress levels has been emphasized. We evaluate the mechanisms of succession across the emersion gradient in a rocky shore system. After complete clearing of experimental plots at four shore heights, we removed two separate components of the assemblage: ephemeral green algae, early colonists and canopy-forming species, main space holders in undisturbed assemblages. We aimed to test two hypotheses: (a) the net effect of ephemeral algae on canopy-forming species shift along the emersion gradient according to the predictions of the stress-gradient hypothesis and (b) the net effect of the canopy-forming group on associate species change, from neutral/negative to positive, as succession progresses and plants grow, especially at the highest shore heights. Our results did not support the predictions of the stress gradient hypothesis in the framework of succession. We did detect changes through time in the effect of canopy-forming species, from negative to positive, but this was not dependent on the shore height. The outcome of interactions depended on the identity and life-stage of the species. Moreover, indirect interactions among species could also create a less predictable relationship between successional mechanisms and the environmental gradient.