Herbivory affects salt marsh succession dynamics by suppressing the recovery of dominant species

Disturbance can generate heterogeneous environments and profoundly influence plant diversity by creating patches at different successional stages. Herbivores, in turn, can govern plant succession dynamics by determining the rate of species replacement, ultimately affecting plant community structure. In a south-western Atlantic salt marsh, we experimentally evaluated the role of herbivory in the recovery following disturbance of the plant community and assessed whether herbivory affects the relative importance of sexual and clonal reproduction on these dynamics. Our results show that herbivory strongly affects salt marsh secondary succession by suppressing seedlings and limiting clonal colonization of the dominant marsh grass, allowing subordinate species to dominate disturbed patches. These results demonstrate that herbivores can have an important role in salt marsh community structure and function, and can be a key force during succession dynamics.     

Spontaneous vegetation succession in human‐disturbed habitats: A pattern across seres

Abstract. Vegetation samples from 15 successional seres in various disturbed habitats in the western part of the Czech Republic were analysed to detect possible trends. For particular seres, data on species cover were available from the onset to 10–76 yr of succession. All seres started on bare ground. Species which attained at least 1% cover in any sere in any year were used as input data for Canonical Correspondence Analysis, assessing the effect of time as the environmental variable, for Detrended Correspondence Analysis and TWINSPAN classification. Two distinct groups ofseres were distinguished: ‘ruderal’, occurring in agricultural, industrial or urban landscapes altered by men, usually on fertile sites; and ‘non‐ruderul’, occurring in less altered, mostly forested landscapes, usually on acid, nutrient‐poor and wetter soils. The former type of succession starts with ruderal annuals, being followed by ruderal perennials. In the latter case non‐ruderal clonal perennials prevail from the onset of succession. The landscape frame is emphasized, beside site environmental conditions, as influencing the type of succession. The character of species attaining dominance in succession, participation of dominant woody plants and the character of late successional stages, i.e. features important from the point of view of potential restoration of human‐disturbed habitats, are discussed.     

典型草原退化群落不同恢复演替阶段羊草种群空间格局的比较

羊草(Leymus chinensis)为典型草原群落的主要建群种之一, 在群落中扮演着重要角色。应用摄影定位法测定处于不同恢复演替阶段的羊草种群空间格局, 通过点格局、种群空斑、种群领地及种群领地密度等方法分析发现, 羊草种群在恢复演替过程中经历了种群增长和种群衰退的过程。在此过程中, 羊草种群数量出现最高点, 此点之前, 种群拓殖大于自疏, 种群整体增长; 此点之后, 种间竞争及种内竞争致使种群衰退, 而种间竞争占主导地位, 种内竞争相对较弱。羊草种群的增衰导致种群空斑发生变化, 从而引起种群格局类型发生相应的变化, 表现为在恢复21 a的群落中, 羊草种群在10 m×10 m的取样范围内表现出两种格局分布类型: 在0~4.85 m之间呈现聚集分布, 当尺度大于4.85 m时, 则表现为随机分布; 在恢复8 a的群落中, 羊草种群在10 m×10 m的取样范围内出现3种格局分布类型: 在0~3.01 m之间呈聚集分布, 在3.01~3.37 m之间为随机分布, 当尺度大于3.37 m时则表现为均匀分布; 在严重退化群落中, 羊草种群在整个10 m×10 m测定尺度上呈现聚集分布。由此可见, 羊草种群格局在恢复演替过程中是变化的, 这种变化主要由群落剩余资源驱动下的种群拓殖及种内种间竞争所致。     

Condition-dependent dispersal of a patchily distributed riparian ground beetle in response to disturbance

In common with many habitat elements of riverine landscapes, exposed riverine sediments (ERS) are highly disturbed, naturally patchy and regularly distributed, whose specialists are strongly adapted to flood disturbance and loss of habitat due to succession. Investigations of dispersal in ERS habitats therefore provide an important contrast to the unnaturally fragmented, stable systems usually studied. The present investigation analysed the three interdependent stages of dispersal: (1) emigration, (2) inter-patch movement and (3) immigration of a common ERS specialised beetle, Bembidion atrocaeruleum (Stephens 1828) (Coleoptera, Carabidae), in a relatively unmodified section of river, using mark–resight methods. Dispersal was correlated with estimates of local population size and density, water level and patch quality in order to test for condition-dependent dispersal cues. Flood inundation of habitat was found to increase strongly the overall rate of dispersal, and the rate of emigration was significantly higher from patches that were heavily trampled by cattle. Strongly declining numbers of dispersers with distance suggested low dispersal rates during periods of low water level. Dispersal in response to habitat degradation by cattle trampling would likely lead to a higher overall population fitness than a random dispersal strategy. Dispersal distances were probably adapted to the underlying habitat landscape distribution, high-flow dispersal cues and ready means of long-distance dispersal through hydrochory. Species whose dispersal is adapted to the natural habitat distribution of riverine landscapes are likely to be strongly negatively affected by reduced flood frequency and intensity and habitat fragmentation through flow regulation or channelisation.Electronic Supplementary Material Supplementary material is available to authorised users in the online version of this article at .     

高寒草甸不同扰动斑块植物功能群和根土复合体特征变化研究

高原鼠兔(Ochotonacurzoniae)活动在高寒草甸上会形成各种类型扰动斑块,扰动斑块类型的转变是导致草地退化的原因之一。目前,斑块类型发生转变的关键影响因子尚不清楚,因此,对高寒草甸活动斑块、非活动斑块和恢复斑块三个扰动斑块类型植物功能类群结构、根土复合体特征和斑块分布特征进行研究,旨在探讨斑块类型发生转变的主要因子,说明高寒草甸退化机理。研究结果表明,高寒草甸中活动斑块土壤表层由于放牧和高原鼠兔活动扰动强度大,无法形成稳定的植物群落,非活动斑块的植物群落处于次生演替早期阶段,但是恢复斑块已具备高寒草甸优势种莎草科植物生长的基本条件。退化高寒草甸中活动斑块与非活动斑块呈现镶嵌性分布,而恢复斑块相对独立没有镶嵌性分布现象。造成高寒草甸干扰斑块类型转变的主要原因是高原鼠兔活动强度由间歇性干扰转变为持续干扰的结果。     

Succession of Ephemeral Secondary Forests and Their Limited Role for the Conservation of Floristic Diversity in a Human-Modified Tropical Landscape

Both local- and landscape-scale processes drive succession of secondary forests in human-modified tropical landscapes. Nonetheless, until recently successional changes in composition and diversity have been predominantly studied at the patch level. Here, we used a unique dataset with 45 randomly selected sites across a mixed-use tropical landscape in central Panama to study forest succession simultaneously on local and landscape scales and across both life stages (seedling, sapling, juvenile and adult trees) and life forms (shrubs, trees, lianas, and palms). To understand the potential of these secondary forests to conserve tree species diversity, we also evaluated the diversity of species that can persist as viable metapopulations in a dynamic patchwork of short-lived successional forests, using different assumptions about the average relative size at reproductive maturity. We found a deterministic shift in the diversity and composition of the local plant communities as well as the metacommunity, driven by variation in the rate at which species recruited into and disappeared from the secondary forests across the landscape. Our results indicate that dispersal limitation and the successional niche operate simultaneously and shape successional dynamics of the metacommunity of these early secondary forests. A high diversity of plant species across the metacommunity of early secondary forests shows a potential for restoration of diverse forests through natural succession, when trees and fragments of older forests are maintained in the agricultural matrix and land is abandoned or set aside for a long period of time. On the other hand, during the first 32 years the number of species with mature-sized individuals was a relatively small and strongly biased sub-sample of the total species pool. This implies that ephemeral secondary forests have a limited role in the long-term conservation of tree species diversity in human-modified tropical landscapes.     

Effects of introduced ungulates on forest understory communities in northern Patagonia are modified by timing and severity of stand mortality

Natural disturbances such as fires, windstorms, floods, and herbivory often act on plant communities, affecting their structure and the abundance and composition of their species. Most research has focused on the effects of single disturbances on plant communities whereas the synergistic effects of several disturbances have received less attention. In this study, we evaluated how timing and severity of tree mortality modified plant use by introduced deer and early post-mortality successional trajectories in northern Patagonian conifer forests. We sampled understory composition and deer use in Austrocedrus chilensis (ciprés de la cordillera) forest stands undergoing varying timing and severity of forest mortality as reconstructed using dendroecological techniques. In addition, we evaluated the effect of fallen logs on plant composition and deer use of plants by monitoring areas of massive dieback where fallen logs had been removed for fire hazard reduction, and nearby control areas not subjected to such removal. Stepwise regression analyses showed that history and severity of tree mortality strongly influence plant composition and deer use of plants. For deer use (with pellet counts and browsing index as response variables), results showed a positive relationship with degree of stand mortality and a negative relationship with cover of fallen logs. Similarly, cover of unpalatable shrub species was explained by canopy mortality history, whereas cover of palatable shrub species was positively associated with severity of canopy mortality. In areas where fallen logs had been removed, pellet counts were six times higher than those in control areas. Though total shrub species cover was similar between log removal and control areas, proportion of unpalatable shrubs increased in areas where fallen logs had been removed. In conclusion, deer use of plants was strongly limited by tall fallen logs, allowing palatable species to establish and grow. Fallen log removal accelerated deer entrance and changed understory composition toward more browse-resistant and unpalatable species. These results underscore the importance of considering the dynamics (timing, severity, and extent) of fallen woody debris influencing understory herbivory and post-disturbance succession. In addition, experimental results underpin the importance of maintaining snags and large woody debris in disturbed landscapes where salvage logging is a routine procedure.     

Structural analysis of woody species in Mediterranean old fields

Abstract

The study analyses the changes in vegetation structure and composition within a sere of secondary succession at Pantelleria Island (Sicilian Channel, Italy). It aims to show that not only phytosociological data but also structural parameters, like woody species’ height and spatial distribution indices are useful to describe and interpret renaturation processes. Woody species structure was recorded on abandoned terraces, both on north-facing and on south-facing slopes. Relevés were made in fallows representing five different stages of succession. The pace of succession, measured through the analysis of woody species cover, basal area, height distribution and spatial indices, resulted quite rapid: already after 50 years of abandonment terraces are covered by dense maquis communities. Our study also revealed that different plant species or groups prevail during colonisation dynamics, mostly depending on exposition, a factor which strongly influences also the speed of colonisation by woody species. In this case study, human activity seems to be unnecessary to accelerate the process of renaturation, except in some unfavourable contexts. Species turnover rate, biodiversity value, and structural evolution along progressive succession must be taken into account in nature management and conservation policies of terraced landscapes, which are nowadays one of the most endangered landscape types throughout the Mediterranean area.     

Dispersal traits as indicators of vegetation dynamics in long-term old-field succession

Succession is a key ecological process that supports our understanding of community assembly and biotic interactions. Dispersal potential and dispersal strategies, such as wind- or animal-dispersal, have been assumed to be highly relevant for the success of plant species during succession. However, research yielded varying results on changes in dispersal modes between successional stages. Here, we test the hypotheses that (a) vascular plant species that use a number of dispersal modes dominate in early stages of succession while species specialized on one/few dispersal modes increase in abundance towards later stages of succession; (b) species well adapted to wind-dispersal (anemochory) will peak in abundance in early successional stages and (c) species well adapted to adhesive dispersal (epizoochory) will increase with proceeding succession. We test these hypotheses in four sites within agriculturally dominated landscapes in Germany. Agricultural use in these sites was abandoned 20–28 years ago, leaving them to secondary succession. Sites have been monitored for plant biodiversity ever since. We analyze changes in plant species richness and abundance, number of dispersal modes and two ranking indices for wind- and adhesive dispersal by applying generalized linear mixed-effect models. We used both abundance-weighted and unweighted dispersal traits in order to gain a comprehensive picture of successional developments. Hypothesis (a) was supported by unweighted but not abundance-weighted data. Anemochory showed no consistent changes across sites. In contrast, epizoochory (especially when not weighted by abundance) turned out to be an indicator of the transition from early to mid-successional stages. It increased for the first 9–16 years of succession but declined afterwards. Species richness showed an opposing pattern, while species abundance increased asymptotically. We suggest that plant-animal interactions play a key role in mediating these processes: By importing seeds of highly competitive plant species, animals are likely to promote the increasing abundance of a few dominant, highly epizoochorous species. These species outcompete weak competitors and species richness decreases. However, animals should as well promote the subsequent increase of species richness by disturbing the sites and creating small open patches. These patches are colonized by weaker competitors that are not necessarily dispersed by animals. The changes in the presence of epizoochorous species indicate the importance of plant traits and related plant–animal interactions in the succession of plant communities.     

Community assembly during vegetation succession after metal mining is driven by multiple processes with temporal variation

The mechanisms governing community assembly is fundamental to ecological restoration and clarification of the assembly processes associated with severe disturbances (characterized by no biological legacy and serious environmental problems) is essential. However, a systematic understanding of community assembly in the context of severe anthropogenic disturbance remains lacking. Here, we explored community assembly processes after metal mining, which is considered to be a highly destructive activity to provide insight into the assembly rules associated with severe anthropogenic disturbance. Using a chronosequence approach, we selected vegetation patches representing different successional stages and collected data on eight plant functional traits from each stage. The traits were classified as establishment and regenerative traits. Based on these traits, null models were constructed to identify the processes driving assembly at various successional stages. Comparison of our observations with the null models indicated that establishment and regenerative traits converged in the primary stage of succession. As succession progressed, establishment traits shifted to neutral assembly, whereas regeneration traits alternately converged and diverged. The observed establishment traits were equal to expected values, whereas regenerative traits diverged significantly after more than 20 years of succession. Furthermore, the available Cr content was linked strongly to species'' ecological strategies. In the initial stages of vegetation succession in an abandoned metal mine, the plant community was mainly affected by the available metal content and dispersal limitation. It was probably further affected by strong interspecific interaction after the environmental conditions had improved, and stochastic processes became dominant during the stage with a successional age of more than 20 years.     

Convergence of community composition during secondary succession on Zokor rodent mounds on the Tibetan Plateau

Aims The community succession theory is much debated in ecology. We studied succession on Zokor rodent mounds on the Tibetan Plateau to address several fundamental questions, among them: (i) During secondary succession, does the community composition converge towards one community state or multiple states depending on the initial colonization? (ii) Do mound communities located in different background communities exhibit different assembly trajectories?Methods In a sub-alpine meadow, we investigated a total of 80 mound communities at several successional stages in three different background communities resulting from different management histories and compared their changes in species composition. The distribution of plant communities over time was analyzed with quantitative classification and ordination methods. The co-occurrence patterns of species were evaluated at each successional stage, and the degree of convergence/divergence among communities was obtained by calculating two beta-diversity indices.Important findings During secondary succession, species richness of mound communities changed over time, and this change was dependent on the background community. Five life-form groups exhibited different dynamic patterns in species richness and plant cover. Community composition and the degree of species co-occurrence between communities increased over time since disturbance. There was much variation in species composition at earlier stages of succession, but communities on older mounds became more similar to each other and to their surrounding vegetation over the course of secondary succession. Post-disturbance succession of Zokor mound communities transitioned from 'multiple alternative states' to 'background-based deterministic community assembly' over time. Tradeoffs between competition and colonization, as well as the characteristics of different life-forms and mass effects within a limited species pool are the mechanisms responsible for convergence of mound communities.     

Environmental heterogeneity and spatiotemporal variability in plant defense traits

At the scale of the local plant community, we know very little about how spatial and temporal environmental heterogeneity affects the diversity in types and levels of plant defenses. If environmental heterogeneity is an important mechanism influencing plant defense traits, then defense expression should co‐vary spatially with environmental conditions and change as succession progresses. In this study, we examined how spatial heterogeneity and succession influence putative resistance and tolerance trait levels in late goldenrod Solidago altissima. We quantified the spatial distributions of herbivore damage and traits associated with resistance (leaf toughness, phenolics), tolerance (specific leaf area, relative growth rate, leaf addition rate and leaf senescence rate), and fitness (height, diameter, inflorescence biomass) of goldenrods within replicate early‐ and late‐successional fields. Also, we characterized the local neighborhood (stem density, canopy cover, ground vegetative cover) and edaphic conditions (soil moisture, pH, N) surrounding each target ramet, and determined relationships between these environmental variables and goldenrod trait levels. The distribution of traits within fields was strongly non‐random, and defense‐trait levels were more strongly spatially structured (i.e. autocorrelated) in late‐ than in early‐successional fields. Also, defense traits were most strongly correlated with aspects of the local plant neighborhood, and these relationships differed in important ways between successional stages. In late‐successional fields, tolerance trait specific leaf area was positively correlated with canopy cover and negatively correlated with stem density. In early‐successional fields, the relationship between ground vegetative cover and resistance (i.e. 1 – damage) was significantly stronger than in late‐successional fields. A novel insight from this study is the possibility that changes in the biotic environment during succession may shift the expression of defense from a resistance to a tolerance strategy in our system. This study highlights the context dependence of plant defense trait levels, which may promote their spatial and temporal variability in heterogeneous landscapes.     

Nutrient limitation drives response of <Emphasis Type="Italic">Calamagrostis epigejos</Emphasis> to arbuscular mycorrhiza in primary succession

Little is known about the functioning of arbuscular mycorrhizal (AM) symbiosis over the course of primary succession, where soil, host plants, and AM fungal communities all undergo significant changes. Over the course of succession at the studied post-mining site, plant cover changes from an herbaceous community to the closed canopy of a deciduous forest. Calamagrostis epigejos (Poaceae) is a common denominator at all stages, and it dominates among AM host species. Its growth response to AM fungi was studied at four distinctive stages of natural succession: 12, 20, 30, and 50 years of age, each represented by three spatially separated sites. Soils obtained from all 12 studied sites were γ-sterilized and used in a greenhouse experiment in which C. epigejos plants were (1) inoculated with a respective community of native AM fungi, (2) inoculated with reference AM fungal isolates from laboratory collection, or (3) cultivated without AM fungi. AM fungi strongly boosted plant growth during the first two stages but not during the latter two, where the effect was neutral or even negative. While plant phosphorus (P) uptake was generally increased by AM fungi, no contribution of mycorrhizae to nitrogen (N) uptake was recorded. Based on N:P in plant biomass, we related the turn from a positive to a neutral/negative effect of AM fungi on plant growth, observed along the chronosequence, to a shift in relative P and N availability. No functional differences were found between native and reference inocula, yet root colonization by the native AM fungi decreased relative to the reference inoculum in the later succession stages, thereby indicating shifts in the composition of AM fungal communities reflected in different functional characteristics of their members.     

Soil respiration associated with plant succession at the meadow steppes in Songnen Plain,Northeast China

Aims Soil CO₂ emission from steppes is affected by soil properties and vegetation in different successional stages. Primary and secondary succession of plants frequently occurred at the meadow steppe in Songnen Plain, Northeast China, which indicates the large uncertainty associated with CO₂ emission in this environment. This study aims to investigate the temporal variations of soil respiration (Rs) and the effect of plant succession on cumulative soil CO₂ emission during the growing season.Methods Using a LI-6400 soil CO₂ flux system, Rs of five vegetation types which represented different stages of plant succession in meadow steppes of Songnen Plain, China, was investigated during the growing seasons of 2011 and 2012.Important findings Soil temperature (Ts) was the dominant controlling factor of Rs, which could explain ~64% of the change in CO₂ fluxes. The Q 10 values of Rs were ranged from 2.0 to 6.7, showing a decreasing trend with the plant successional stages. The cumulative CO₂ emission increased with the degree of vegetation succession and it averaged to 316±6g C m ?2 (ranges: 74.8±6.7 to 516.5±11.4g C m ?2) during the growing season. The magnitude of soil CO₂ emission during the growing season was positively correlated with aboveground plant biomass, soil organic carbon content and mean soil water content, while negatively linked to mean Ts, pH, electrical conductivity and exchangeable sodium percentages. The results implied that soil CO₂ emission increased with the development of plant communities toward more advanced stages. Our findings provided valuable information for understanding the variations of CO₂ emission in the process of vegetation succession.     

天童常绿阔叶林五个演替阶段凋落物中的土壤动物群落

为探讨森林凋落物中土壤动物群落的结构特征以及土壤动物群落随植被演替而发生的变化 ,于 2 0 0 3年冬季 ,对浙江天童常绿阔叶林 5个演替阶段凋落物中的土壤动物群落 ,按代表不同分解阶段的新鲜凋落物层、腐叶层和腐殖土层进行了调查研究。共获得土壤动物 13381只 ,分别隶属于 2门 8纲 2 0目。优势类群为蜱螨目 (Arcarina)和弹尾目 (Collem bola) ,二者共占总数的 94 .2 4 % ,A/ C为 7.6 6 ;常见类群为双翅目 (Diptera)。研究结果表明 :(1)凋落物中的土壤动物群落存在明显的有别于真土层的垂直分布 ,类群数和个体数总体表现为向下递增的趋势。共有 19类、5 9.0 3%的土壤动物分布在底部腐殖土层 ,仅 8类、5 .35 %的土壤动物分布在新鲜凋落物层 ,其余共 8类分布在中间腐叶层。而且 ,不同类群在各演替阶段的分布表现出一定的差异 ;(2 )凋落物中土壤动物群落随植物群落的演替而发生明显的变化 :个体总数和类群总数在演替顶极阶段最高 ,其次为中期阶段 ,演替初期最低。但是 ,在目这一分类等级上 ,各演替阶段凋落物中土壤动物群落的主要类群基本一致 ,均为蜱螨目、弹尾目、双翅目和鳞翅目 (L epidoptera) ;(3)相似性分析表明 ,演替中期凋落物中土壤动物群落与顶极阶段最为相似 ;但它们的Shannon- Wiener多样性     

Successional dynamics of the bee community in a tropical dry forest: Insights from taxonomy and functional ecology

Despite the recent rapid growth of tropical dry forest succession ecology, most studies on this topic have focused on plant community attribute recovery, whereas animal community successional dynamics has been largely overlooked, and the few existing studies have used taxonomic approaches. Here, we analyze the successional changes in the bee community in a Mexican tropical dry forest, by integrating taxonomic (species, genus, and family diversity) and functional (sociability, nesting strategy, and body size) information for bees. Over one year, in a successional chronosequence (2–67 years after abandonment) we collected 469 individual bees, representing five families, 36 genera, and 69 species. Linear modeling showed decreases in taxonomic diversity with succession, more strongly so for species. Bee species turnover along succession ranged from moderate to high, decreasing slightly at intermediate stages. An RLQ analysis (ordination method that allows relating environmental variables with functional attributes) revealed clear relations between bee functional traits and the plant community. RLQ axis 1 was positively related to vegetation structural and diversity variables, and to eusociality, while solitary, parasociality, and ground nesting was negatively associated with it. Early successional fallows attract mostly solitary and parasocial bees; older fallows tend to attract eusocial bees with aerial nesting. The continuous taxonomic turnover observed by us and the functional analysis suggest that the disappearance of old fallows from agricultural landscapes would likely result in significant reductions and even local extinctions of particular bee guilds. Considering the low viability of preserving large mature tropical dry forest tracts, the conservation of older successional stands emerges as a crucial component of landscape management.Abstract in Spanish is available with online material.     

Phylogenetic and functional structures of succession in plant communities on mounds of Marmota himalayana in alpine regions on the northeast edge of the Qinghai–Tibet Plateau

Few studies have examined the succession of plant communities in the alpine zone. Studying the succession of plant communities is helpful to understand how species diversity is formed and maintained. In this study, we used species inventories, a molecular phylogeny, and trait data to detect patterns of phylogenetic and functional community structure in successional plant communities growing on the mounds of Himalayan marmots (Marmota himalayana) on the southeast edge of the Qinghai-Tibet Plateau. We found that phylogenetic and functional diversities of plant communities on marmot mounds tended to cluster during the early to medium stages of succession, then trended toward overdispersion from medium to late stages. Alpine species in early and late stages of succession were phylogenetically and functionally overdispersed, suggesting that such communities were assembled mainly through species interactions, especially competition. At the medium and late stages of succession, alpine communities growing on marmot mounds were phylogenetically and functionally clustered, implying that the communities were primarily structured by environmental filtering. During the medium and late stages of succession the phylogenetic and functional structures of plant communities on marmot mounds differed significantly from those on neighboring sites. Our results indicate that environmental filtering and species interactions can change plant community composition at different successional stages. Assembly of plant communities on marmot mounds was promoted by a combination of traits that may provide advantages for survival and adaptation during periods of environmental change.     

High specialization and limited structural change in plant‐herbivore networks along a successional chronosequence in tropical montane forest

Secondary succession is well‐understood, to the point of being predictable for plant communities, but the successional changes in plant‐herbivore interactions remains poorly explored. This is particularly true for tropical forests despite the increasing importance of early successional stages in tropical landscapes. Deriving expectations from successional theory, we examine properties of plant‐herbivore interaction networks while accounting for host phylogenetic structure along a succession chronosequence in montane rainforest in Papua New Guinea. We present one of the most comprehensive successional investigations of interaction networks, equating to > 40 person years of field sampling, and one of the few focused on montane tropical forests. We use a series of nine 0.2 ha forest plots across young secondary, mature secondary and primary montane forest, sampled almost completely for woody plants and larval leaf chewers (Lepidoptera) using forest felling. These networks comprised of 12 357 plant‐herbivore interactions and were analysed using quantitative network metrics, a phylogenetically controlled host‐use index and a qualitative network beta diversity measure. Network structural changes were low and specialisation metrics surprisingly similar throughout succession, despite high network beta diversity. Herbivore abundance was greatest in the earliest stages, and hosts here had more species‐rich herbivore assemblages, presumably reflecting higher palatability due to lower defensive investment. All herbivore communities were highly specialised, using a phylogenetically narrow set of hosts, while host phylogenetic diversity itself decreased throughout the chronosequence. Relatively high phylogenetic diversity, and thus high diversity of plant defenses, in early succession forest may result in herbivores feeding on fewer hosts than expected. Successional theory, derived primarily from temperate systems, is limited in predicting tropical host‐herbivore interactions. All succession stages harbour diverse and unique interaction networks, which together with largely similar network structures and consistent host use patterns, suggests general rules of assembly may apply to these systems.     

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.     

Crab herbivory regulates re‐colonization of disturbed patches in a southwestern Atlantic salt marsh

Recent work exploring the effects of physical stress and herbivory on secondary succession in estuarine plant communities agrees with basic stress models and reveal that herbivory is an important force in brackish and oligohaline marshes but negligible in physically stressful salt marshes. In these systems, herbivores are terrestrial, and thus negatively affected by the same stressful factors that affect marsh plants (i.e. frequent flooding or high salinities). We evaluated the effects of a marine herbivore (i.e. the crab Neohelice granulata) on plant secondary succession in a southwestern Atlantic salt marsh. Field surveys revealed that disturbance‐generated bare patches have harsh physical conditions and that their edges suffer higher herbivore pressure compared to the marsh matrix. A factorial experiment demonstrated that asexual expansion of the surrounding plants is the only possible mechanism to re‐colonize disturbed patches and that crab exclusion can increase this colonization rate by more than 30 times. Our results show that even in highly stressful environments, herbivores strongly impact marsh structure by regulating patch recovery. The synergism of physical stress and herbivory may make plant succession an extremely slow process and lead to the prevalence of bare areas.