Early Successional Plant Research Articles

Leaf damage and functional traits along a successional gradient in Brazilian tropical dry forests

Herbivory has significant impacts on individual plants and plant communities, both at ecological and evolutionary time scales. In this context, this study aims to evaluate herbivore damage and its relationship with leaf chemical and structural traits, nutritional status, and forest structural complexity along a successional gradient. We predicted that trees in early successional stages support conservative traits related to drought tolerance (high specific leaf mass and phenolics), whereas trees in light-limited, late successional stages tend to enhance light acquisition strategies (high nitrogen content). We sampled 261 trees from 26 species in 15 plots (50 × 20 m; five per successional stage). From each tree, twenty leaves were collected for leaf trait measures. Phenolic content increased whereas specific leaf mass and nitrogen content decreased from early to late stages. However, leaf damage did not differ among successional stages. Our results partially corroborate the hypothesis that early successional plants in tropical dry forests exhibit leaf traits involved in the conservative use of water. The unexpected decrease in nitrogen content along the chronosequence is likely related to the fact that thinner leaves with low specific leaf mass could have less nitrogen-containing mesophyll per unit area. Mechanisms affecting herbivory intensity varied across scales: at the species level, leaf damage was negatively correlated with tannin concentration and specific leaf mass; at the plot level, leaf damage was positively affected by forest structural complexity. Herbivory patterns in tropical forests are difficult to detect because abiotic factors and multiple top-down and bottom-up forces directly and indirectly affect herbivores.

Earthworms increase plant biomass more in soil with no earthworm legacy than in earthworm‐mediated soil, and favour late successional species in competition

AbstractAs ecosystem engineers, earthworms greatly affect plant communities. They create persistent soil structures enriched by nutrients that improve the conditions for plant growth and modify competition between plant species. We therefore hypothesized that earthworm activity would be more important in early stages of the primary succession, when the soil is not modified by earthworms, than in the late stages of the succession, when the soil is already improved by earthworms. On the other hand, earthworms also affect plants via many other effects such as seed predation or excreting hormone‐like compounds, which could make earthworm presence important in late successional soil.To explore earthworm effects on plant community succession, we performed a laboratory microcosm experiment without and with earthworms (Lumbricus rubellusandAporrectodea caliginosa), with early successional plants (Poa compressa,Medicago lupulinaandDaucus carota) and late successional plants (Arrhenatherum elatius,Lotus corniculatusandPlantago lanceolata) and with soil previously unaffected by earthworms (young soil) and soil substantially affected by earthworms (developed soil). These soils were taken from the early and late successional post‐mining sites of the Sokolov coal mining district (northwest Czech Republic).When both early and late successional plants were grown separately, earthworms increased plant biomass proportionally more in the young soil than in the developed soil, indicating that earthworm activity is more important in undeveloped than in developed soil.When early and late successional plants were competing each other, the biomass of the early successional plants was reduced. In the young soil, the reduction was independent of earthworm presence. In the developed soil, the reduction was promoted by the earthworms. Late successional plants profited from the reduction of early successional plants and increased their biomass. This increase was promoted by the earthworm presence.Our results indicate that the direct effects of earthworm presence on plants decrease during succession because of the cumulative effects of earthworm activity on soil conditions. Such ecosystem engineering effects favour late successional competitors and therefore promote the replacement of species during succession.Aplain language summaryis available for this article.

Spatial distribution of functional traits indicates small scale habitat filtering during early plant succession

Two major theories on community assembly (habitat filtering and limiting similarity) predict contrasting patterns in the spatial distribution of plant species. The respective distribution of species functional traits has received much less attention but is essential to understand facilitative and competitive species interactions. Here we apply a recently developed technique for phylogenetic analysis to study the spatial distribution of major functional traits during seven years of primary plant succession at a re-established catchment in a German lignite mine. Habitat filtering induced a significant temporal trend towards underdispersed functional trait diversity leading to patches of functionally similar vegetation. This functional convergence was not mirrored by a respective trend towards species aggregation. Differences in soil pH and nitrogen content were positively correlated with respective differences in trait expression. Separate analyses of trait distribution for aggregated and segregated species revealed trait convergence in co-occurring and random patterns in spatially segregated species pairs except for leaf size showing a strong temporal tendency for trait convergence in spatially segregated species. Contrasting patterns of species co-occurrence did not translate into respective contrasts in trait distribution. We interpret the prevalence of random trait associations in spatially segregated species as an indication that species occurrence patterns alone are weak predictors of assembly mechanisms. Mechanistic inference of species co-occurrence needs to be accompanied by a detailed assessment of the patterns of functional trait assembly.

Wireworms suppress spreading of the expansive weed Calamagrostis epigejos (L) Roth by feeding on its rhizomes

We tested whether wireworms (Elaterid beetle larvae) prefer the expansive grass Calamagrostis epigejos to other early-successional plant species from the spoil heaps in two microcosm experiments and in a field survey of wireworm abundance and C. epigejos coverage on the spoil heaps at different topographic positions at the spontaneously revegetated sites with an undulating surface. In the first experiment, wireworms reduced rhizome biomass of C. epigejos the most out of the belowground organs of the 5 plant species, but did not affect its root biomass. In the second greenhouse experiment, wireworms negatively affected the growth of rhizomes of a growing C. epigejos, whilst they did not affect the other plant species or the aboveground biomass. In the field survey, C. epigejos coverage was lowest at the bottoms of depressions, despite the higher moisture and nutrient levels at this position. Wireworm numbers were the highest in depressions. The results of this study support the hypothesis that wireworms can negatively impact the C. epigejos by feeding on its rhizomes and have the potential to slow down the expansion of this weed.

Effects of Northern Bobwhite Habitat Management Practices on Red Imported Fire Ants

Management practices that create early successional plant communities through disturbance (discing and prescribed fire) often are prescribed for restoration of declining northern bobwhite (Colinus virginianus) populations. Because disturbance may facilitate invasion of exotic flora and fauna such as red imported fire ants (RIFA, Solenopsis invicta), we hypothesized that habitat management practices commonly used to enhance bobwhite habitat might have the unintended consequence of increasing local abundance of RIFA. During 1999, we tested effects of 4 treatments (spring discing, spring prescribed burning, spring mowing, and no management), in a randomized complete block design (n = 10) on RIFA abundance in Conservation Reserve Program (CRP) fields in central Mississippi. We surveyed RIFA abundance using 3 measures: 1) mound density, 2) a population index based on worker ant and brood estimates, and 3) foraging activity as indexed by attraction to protein bait cups. During May 1999, mound density (P = 0.0136) and population index (P 0.0078) differed among treatments, with abundance values greatest in plots treated with fire, and lowest in disced plots. The index of foraging activity did not differ among treatments (P = 0.6637). During October 1999, mound density (P = 0.0334) and population index (P = 0.0451) differed among treatments with abundance values greatest in plots receiving fire and disc treatments, and lowest abundance in control plots. The index of foraging activity did not differ among treatments (P = 0.9079). Disturbance tools such as prescribed fire and discing are essential to maintain plant communities to which bobwhite are adapted; however, they may have the unintended consequence of facilitating invasion of RIFA and increasing local RIFA populations.

Fall Quail Densities on Public Lands in Missouri: A Decade of Monitoring

Northern bobwhite (Colinus virginianus) fall population density has been determined annually since 2005 on 19 public land areas managed by the Missouri Department of Conservation (MDC). These demonstration areas, known as Quail Emphasis Areas (QEAs), were created as part of the MDC Strategic Guidance for Northern Bobwhite Recovery: 2003-2013. Management of QEA bobwhite populations, habitat and hunting has been evaluated periodically at the area, regional and statewide scale, and the program has been perpetuated in an updated 2014-2024 Strategic Guidance. QEAs were selected to represent MDC administrative regions and are highly variable in many aspects, e.g., size range from 298 to 3,642 hectares. QEAs are managed adaptively, maximizing usable space and early-successional plant communities, with bobwhite population density and distribution, and hunting, as response variables. Fall bobwhite calling coveys are measured with point transect surveys, distributed to cover nearly 100% of each QE, coveys are flushed to estimate covey size, and density is calculated with the Distance program. Observers, mostly permanent staff, initially received rigorous training, and periodic updates. Across QEAs and years, there has been a high amount of variability in weather and habitat management, and subsequently, population responses have been equally variable, as revealed by preliminary analysis for 2005-2010: (1) Number of covey observations on a QEA in a single year ranged from 0 to 178; (2) Encounter rate (i.e., number of coveys/effort) ranged from 0- 5.95; (3) Density in areas where coveys were detected ranged from 0.003 coveys/ha to 0.103 coveys/ha (covey densities not adjusted for calling rate), and from 0.006 to 0.122 coveys/ha (covey densities adjusted for Missouri-specific calling rate); and (4) Some QEAs showed consistent declines in density from 2005-2010, whereas others increased. We discuss lessons learned from this long-term, statewide effort to demonstrate effective quail management based on quantification of population response to prescribed management.

The missing link in grassland restoration: arbuscular mycorrhizal fungi inoculation increases plant diversity and accelerates succession

Summary Because soil microbial communities are often altered by anthropogenic disturbance, successful plant community restoration may require the restoration of beneficial soil microbes, such as arbuscular mycorrhizal (AM) fungi. Recent evidence suggests that later successional grassland species are more strongly affected by AM fungi relative to early successional plants and that late successional plants consistently benefit from some AM fungi but not other AM fungal species. Many of these late successional species are also often missing in restorations despite being heavily seeded. To assess the effects of AM fungal composition within grassland restorations, we inoculated plots with six different AM fungal community treatments including one of four different AM fungal species isolated from a prairie, a mixture of all four fungal species, and a non‐inoculated control. AM fungi were introduced by planting 16 different inoculated nurse plants into replicated plots. We also seeded the restoration with a diverse, 54 species prairie seed mixture. We found that AM fungal inoculation drove plant community composition; plots inoculated with certain AM fungal treatments were dominated by desirable prairie plants, whereas plots inoculated with other AM fungal species and the non‐inoculated control were dominated by non‐desirable plants including weeds and exotic species. Specifically, we found that many early successional species established well regardless of AM fungal inoculation, whereas the establishment and growth of many late successional species was strongly dependent on the presence of specific AM fungal species. Many conservative late successional species did not occur without inoculation. Overall, total plant community richness, diversity, and Floristic Quality Index were all significantly improved with AM fungal inoculation, whereas we observed that non‐desirable plant abundance was significantly greater in the non‐inoculated plots. Synthesis and applications. Our results suggest that the lack of late successional establishment reported in many previous restorations may be due to ineffective arbuscular mycorrhizal fungal communities at these sites. We conclude that the reintroduction of arbuscular mycorrhizal fungi from reference prairie environments could improve restoration outcomes by promoting plant diversity and richness, especially for desirable later successional plant species, while simultaneously inhibiting less desirable weedy plants.

Interspecific variation in persistence of buried weed seeds follows trade‐offs among physiological, chemical, and physical seed defenses

Soil seedbanks drive infestations of annual weeds, yet weed management focuses largely on seedling mortality. As weed seedbanks increasingly become reservoirs of herbicide resistance, species‐specific seedbank management approaches will be essential to weed control. However, the development of seedbank management strategies can only develop from an understanding of how seed traits affect persistence.We quantified interspecific trade‐offs among physiological, chemical, and physical traits of weed seeds and their persistence in the soil seedbank in a common garden study. Seeds of 11 annual weed species were buried in Savoy, IL, from 2007 through 2012. Seedling recruitment was measured weekly and seed viability measured annually. Seed physiological (dormancy), chemical (phenolic compound diversity and concentration; invertebrate toxicity), and physical traits (seed coat mass, thickness, and rupture resistance) were measured.Seed half‐life in the soil (t 0.5) showed strong interspecific variation (F 10,30 = 15, p < .0001), ranging from 0.25 years (Bassia scoparia) to 2.22 years (Abutilon theophrasti). Modeling covariances among seed traits and seedbank persistence quantified support for two putative defense syndromes (physiological–chemical and physical–chemical) and highlighted the central role of seed dormancy in controlling seed persistence.A quantitative comparison between our results and other published work indicated that weed seed dormancy and seedbank persistence are linked across diverse environments and agroecosystems. Moreover, among seedbank‐forming early successional plant species, relative investment in chemical and physical seed defense varies with seedbank persistence. Synthesis and applications. Strong covariance among weed seed traits and persistence in the soil seedbank indicates potential for seedbank management practices tailored to specific weed species. In particular, species with high t 0.5 values tend to invest less in chemical defenses. This makes them highly vulnerable to physical harvest weed seed control strategies, with small amounts of damage resulting in their full decay.

Urban parks: refuges for tropical butterflies in Southeast Asia?

Rapid economic development has accelerated urbanisation and biodiversity loss in Southeast Asia. Studies of urban ecology have suggested urban parks can be effective refuges for wildlife in temperate regions, but their effectiveness as refuges in rapidly urbanising tropical regions is understudied. We examined the species diversity of butterflies in urban parks in the Federal Territory of Kuala Lumpur and investigated the relationships between butterfly species richness and three park variables: i) park size, ii) distance from the central business district and iii) park age. Standardised butterfly sampling was conducted across different microhabitat types at each park: i) groves, ii) hedges, iii) flowerbeds and iv) unmanaged areas. We recorded 572 butterflies belonging to 60 species (97 % considered common) from five families. Although species richness was positively correlated with park size and age and negatively correlated with distance from the central business district; the correlations were weak and not statistically significant. However, species richness of host-specialist species was significantly positively correlated with park size and age. The highest species richness (65 % of observed species) was recorded in the unmanaged microhabitat. It is likely that both park planting scheme and the presence of early successional plants in unmanaged microhabitat led to highest butterfly species richness in parks that contained all four microhabitat types. Whether a diverse planting scheme and increased size and number of unmanaged areas in urban parks can improve the ability of parks to sustain populations of rare butterflies in the face of future urbanisation remains to be seen.

Protist diversity on a nature reserve in NW England—With particular reference to their role in soil biogenic silicon pools

Soil protists play fundamental roles in many earth system processes, yet we are only beginning to understand the true diversity of the organisms involved. In this study we used conventional (microscopy-based) methods to characterise the diversity and estimate protist population sizes in soils from a variety of distinct habitats within Mere Sands Wood nature reserve in NW England. We produced population size data for over ninety soil protists belonging to two major eukaryotic functional groups: testate amoebae (TA) and diatoms, adding substantial ‘cryptic diversity’ to the nature reserves recorded biota. From these population size data we estimated relative contributions of TA and diatoms to soil biogenic silicon (BSi) pools and found significant correlations between taxon richness and the TA and diatom Si pool. This could indicate that protist functional diversity can influence terrestrial BSi pools, especially in early successional plant communities where TA and diatoms can potentially increase Si mineralisation and/or create Si ‘hot spots’ and hence, the biological availability of this element for subsequent plant uptake. TA were particularly abundant in mor humus type soils further supporting the idea that they could be important players in nutrient cycling in such soils. Overall, we demonstrate this is a useful approach in order to start to attempt to estimate the role of protists in the Si cycle and other ecological processes.

Diversity of Riparian Plants among and within Species Shapes River Communities.

Organismal diversity among and within species may affect ecosystem function with effects transmitting across ecosystem boundaries. Whether recipient communities adjust their composition, in turn, to maximize their function in response to changes in donor composition at these two scales of diversity is unknown. We use small stream communities that rely on riparian subsidies as a model system. We used leaf pack experiments to ask how variation in plants growing beside streams in the Olympic Peninsula of Washington State, USA affects stream communities via leaf subsidies. Leaves from red alder (Alnus rubra), vine maple (Acer cinereus), bigleaf maple (Acer macrophyllum) and western hemlock (Tsuga heterophylla) were assembled in leaf packs to contrast low versus high diversity, and deployed in streams to compare local versus non-local leaf sources at the among and within species scales. Leaves from individuals within species decomposed at varying rates; most notably thin leaves decomposed rapidly. Among deciduous species, vine maple decomposed most rapidly, harbored the least algal abundance, and supported the greatest diversity of aquatic invertebrates, while bigleaf maple was at the opposite extreme for these three metrics. Recipient communities decomposed leaves from local species rapidly: leaves from early successional plants decomposed rapidly in stream reaches surrounded by early successional forest and leaves from later successional plants decomposed rapidly adjacent to later successional forest. The species diversity of leaves inconsistently affected decomposition, algal abundance and invertebrate metrics. Intraspecific diversity of leaf packs also did not affect decomposition or invertebrate diversity. However, locally sourced alder leaves decomposed more rapidly and harbored greater levels of algae than leaves sourced from conspecifics growing in other areas on the Olympic Peninsula, but did not harbor greater aquatic invertebrate diversity. In contrast to alder, local intraspecific differences via decomposition, algal or invertebrate metrics were not observed consistently among maples. These results emphasize that biodiversity of riparian subsidies at the within and across species scale have the potential to affect aquatic ecosystems, although there are complex species-specific effects.

Early successional plant community dynamics on a reclaimed oil sands mine in comparison with natural boreal forest communities

ABSTRACTForming the majority of plant diversity in boreal forests, understory communities are important drivers of nutrient cycling and overstory succession. In western Canadian boreal forests, fire is the primary mechanism of natural disturbance, with oil sands mining a substantial anthropogenic disturbance in north-eastern Alberta. An operational reclamation trial, at an oil sands mine, was established the same year as a nearby forest fire, allowing for direct comparison of plant community development between reclaimed and naturally regenerated fire-origin and mature stands. This work reflects a case study with large, but unreplicated, areas of both fertilized and unfertilized reclamation treatments on forest floor-mineral mix (FFMM) and peat-mineral mix (PMM) capping materials. After three years, reclamation sites are compositionally distinct from post-fire and mature natural stands, with more non-native species in reclamation treatments than in natural stands. Communities developing on FFMM are more similar to post-fire successional communities than those on PMM, with high species richness and diversity on FFMM comparable with post-fire stands. Cover soil had a stronger impact on plant community development than fertilization, with fertilization effects dependent on cover soil. A standard dose of fertilizer lowered richness and diversity on FFMM and is not recommended for use with that soil.

Species interactions and random dispersal rather than habitat filtering drive community assembly during early plant succession

Theory on plant succession predicts a temporal increase in the complexity of spatial community structure and of competitive interactions: initially random occurrences of early colonising species shift towards spatially and competitively structured plant associations in later successional stages. Here we use long‐term data on early plant succession in a German post mining area to disentangle the importance of random colonisation, habitat filtering, and competition on the temporal and spatial development of plant community structure. We used species co‐occurrence analysis and a recently developed method for assessing competitive strength and hierarchies (transitive versus intransitive competitive orders) in multispecies communities. We found that species turnover decreased through time within interaction neighbourhoods, but increased through time outside interaction neighbourhoods. Successional change did not lead to modular community structure. After accounting for species richness effects, the strength of competitive interactions and the proportion of transitive competitive hierarchies increased through time. Although effects of habitat filtering were weak, random colonization and subsequent competitive interactions had strong effects on community structure. Because competitive strength and transitivity were poorly correlated with soil characteristics, there was little evidence for context dependent competitive strength associated with intransitive competitive hierarchies.

Diazotrophic Endophytes of Poplar and Willow for Growth Promotion of Rice Plants in Nitrogen‐Limited Conditions

ABSTRACTRice (Oryza sativa L.) is one of the most important staple food crops. Its cultivation requires a relatively high input of N fertilizers; however, rice plants do not absorb a significant proportion of added fertilizers, resulting in soil and water pollution. The use of diazotrophic (N‐fixing) endophytes can provide benefits for rice cultivation by reducing the demand of N fertilizers. Diazotrophic endophytes from the early successional plant species poplar (Populus trichocarpa Torr. &amp; A. Gray) and willow (Salix sitchensis C. A. Sanson ex Bong.) were added to rice seedlings. Inoculated rice plants were grown in N‐limited conditions in the greenhouse, and plant physical characteristics were assessed. Endophyte‐inoculated rice plants had greater biomass, higher tiller numbers, and taller plant stature than mock‐inoculated controls. Endophyte populations were quantified and visualized in planta within rice plants using fluorescent microscopy. The endophytes colonized rice plants effectively in both roots and foliage. These results demonstrated that diazotrophic endophytes of the eudicots poplar and willow can colonize rice plants and enhance plant growth in N‐limited conditions.

Mycorrhizal response trades off with plant growth rate and increases with plant successional status.

Early-successional plant species invest in rapid growth and reproduction in contrast to slow growing late-successional species. We test the consistency of "trade-offs between plant life history and responsiveness on arbuscular mycorrhizal fungi. We selected four very early-, seven early-, 11 middle-, and eight late-successional plant species from six different families and functional groups and grew them with and without a mixed fungal inoculum and compared root architecture, mycorrhizal responsiveness, and plant growth rate. Our results indicate mycorrhizal responsiveness increases with plant successional stage and that this effect explains more variation in mycorrhizal response than is explained by phylogenetic relatedness. The mycorrhizal responsiveness of individual plant species was positively correlated with mycorrhizal root infection and negatively correlated with average plant mass and the number of root tips per unit mass, indicating that both plant growth rate and root architecture trade off with investment in mycorrhizal mutualisms. Because late-successional plants are very responsive to mycorrhizal fungi, our results suggest that fungal community dynamics may be an important driver of plant succession.

How the litter‐feeding bioturbator Orchestia gammarellus promotes late‐successional saltmarsh vegetation

Summary Traditionally, studies on vegetation succession have focused either on plant–plant interactions or on interactions between plants and their physical environment, for example through organic matter build‐up and increased nutrient cycling. These interactions can change conditions for macrodetritivores that feed on plant litter, but their role in vegetation succession is rarely studied. In this paper, we explore whether the bioturbating crustacean macrodetritivore Orchestia gammarellus alters soil conditions in a saltmarsh ecosystem in such a way that it promotes late‐successional, less stress‐tolerant plant species at the expense of early successional species. To answer this, we performed a field and a laboratory experiment in which we manipulated abundances of O. gammarellus, and studied the consequences for soil physical and chemical parameters and for vegetation community composition. Our field experiment showed that O. gammarellus stimulated nitrogen mineralization, likely resulting from the positive effect of this macrodetritivore on soil aeration and litter decomposition. Moreover, results from the laboratory experiment showed that O. gammarellus negatively affected dicot seedling survival of mainly early successional plant species, likely through grazing, thus affecting plant community composition. The experiments together provided evidence that O. gammarellus promotes late‐successional plant species in multiple ways: by alleviation of anoxic conditions, by promoting nutrient cycling and by selective herbivory on early successional species. Synthesis. By demonstrating that a species traditionally considered as part of the detrital (‘brown’) food web is thus an important accelerator of vegetation succession, this study documents an important but often overlooked link in food web and ecosystem ecology.

Complementarity and selection effects in early and mid‐successional plant communities are differentially affected by plant–soil feedback

Summary Many studies that provided evidence for a positive relationship between plant diversity and productivity have proposed that this effect may be explained by complementarity among species in resources utilization, or selection of particularly productive species in high‐diversity plant communities. Recent studies have related the higher productivity in diverse plant communities to suppression of pathogenic soil biota. If soil biota plays a role in diversity–productivity relationships, the question remains about how they may influence complementarity and selection effects. Here we examine how complementarity and selection effects may depend on soil biota using a plant–soil feedback approach. We used monocultures and mixtures of early successional plant species, which are known to have mostly negative plant–soil feedback effects, and mid‐successional plant species, which generally have neutral plant–soil feedback. We found that plant–soil feedback effects differed between monocultures and mixed plant communities, as well as between early and mid‐successional plants. This resulted in a significant interaction effect between diversity and successional stage. In monocultures, plant–soil feedback tended to be negative for early and positive for mid‐successional plant species. Interestingly, the community feedback responses of the mixed communities were opposite, being positive for early and negative for mid‐successional community. Plant–soil feedback differentially affected complementarity and selection effects of early and mid‐successional plant communities: it enhanced complementarity effects of early and decreased selection effects of mid‐successional species. Synthesis. Soil biota that drive plant–soil feedback effects can influence the diversity–productivity relationship not only through decreased biomass production in monocultures compared to mixtures, but also through influencing complementarity and selection effects among species in mixed plant communities. Our results reveal that biodiversity–productivity relationships depend on plant–soil feedback interactions, which depend on the successional position of the plant. We propose that including successional position and trait‐based analyses of plant–soil feedback in diversity‐functioning studies will enhance understanding consequences of biodiversity loss for productivity and other ecosystem processes.

Interspecific competition of early successional plant species in ex-arable fields as influenced by plant–soil feedback

Plant–soil feedback can affect plants that belong to the same (intraspecific feedback) or different species (interspecific feedback). However, little is known about how intra- and interspecific plant–soil feedbacks influence interspecific plant competition. Here, we used plants and soil from early-stage ex-arable fields to examine how intra- and interspecific plant–soil feedbacks affect the performance of 10 conditioning species and the focal species, Jacobaea vulgaris. Plants were grown alone and in competition in both conditioned and control soils. Overall, plant–soil feedback of the 10 plant species influenced the competitiveness of J. vulgaris more strongly than their own competitiveness. However, effects depended on species combination: competitiveness of J. vulgaris was significantly enhanced by interspecific plant–soil feedback from Anthoxanthum odoratum, Agrostis capillaris, and Trifolium dubium, and significantly decreased by interspecific feedback from Achillea millefolium. Intraspecific feedback from Taraxacum officinale and A. odoratum decreased their competitiveness with J. vulgaris. There was a positive relationship between the strength of interspecific feedback and competitiveness of J. vulgaris in conditioned soil. Multiple linear regression showed that the competitiveness of J. vulgaris in conditioned soil was determined by interspecific feedback and competitiveness of neighbour plants. The positive relationship between interspecific feedback and competitiveness in control soil suggests that the soil feedback effect of the competing species on J. vulgaris can build up quickly during competition. We conclude that the effect of plant–soil feedback on interspecific competition may be due to either legacy effects of plant species previously colonizing the soil, or immediate interspecific feedback of the competing plant species via the soil. Therefore, our results suggest that plant–soil feedback can influence interspecific plant competition through a multitude of intra- and interspecific plant–soil interactions both from predecessors, and from the currently competing plant species.

High precision U–Pb zircon geochronology for Cenomanian Dakota Formation floras in Utah

The Cretaceous Dakota Formation on and near the Colorado Plateau represents the time-transgressive shoreline deposits of the Western Interior Seaway and is a rich repository of fossil plants and animals. However, given the basin architecture and depositional setting, correlations between localities are difficult without geochronology. Here we present new high precision ID-TIMS U–Pb zircon dates from five air-fall ash deposits from Westwater (n = 3) and Henrieville (n = 2) that obey stratigraphic superposition and precisely constrain the ages of these two floras. Three air-fall ashes from the Westwater locality record weighted mean Th-corrected 206Pb/238U dates of 97.949 ± 0.037/0.12 Ma, 97.943 ± 0.023/0.12 Ma, and 97.601 ± 0.049/0.13 Ma, providing the first U–Pb dates from this locality. Two ash beds from the Henrieville locality record weighted mean Th-corrected 206Pb/238U dates of 95.070 ± 0.036/0.12 Ma and 94.879 ± 0.032/0.11 Ma. The new dates indicate that the two floras are separated by ca 2.5 Ma and are both within the Cenomanian. The assemblage of fossil plants collected from the mudstone and ash-bed localities at Westwater show no compositional overlap, despite the presence of 28 distinct morphotypes. This lack of compositional overlap is repeated between the mudstone facies from the Westwater and Henrieville localities, where two different morphotypes of “Liriodendron” are the taxa in common. The species incongruence at Westwater is likely due to rapid colonization of early successional plants post deposition of the volcanic ash. For the mudstone floras at Westwater and Henrieville, the different floral composition may be due to rapid species evolution during the rise of angiosperms, the influence of climate in the mid-Cretaceous, the expression of high regional diversity of localities separated by 300 km, or a highly partitioned floodplain vegetation. Estimated sediment accumulation rates from the new radioisotopic dates, combined with existing proxy records for pCO2, suggest that the rise in pCO2 preceding Ocean Anoxic Event 2 (OAE2) began 513 ka (range from 384 to 641 ka) prior to the positive δ13C excursion that defines the event. This estimate from terrestrial rocks is within error of estimates for the timing of changes in δ34Ssulfate (570 ka; range from 420 to 814 ka) in marine sections at the GSSP for the Cenomanian–Turonian boundary. The overlap indicates synchronous perturbation of marine and terrestrial environments related to an increase in pCO2 prior to the onset of OAE2, providing further support for the volcanic initiation hypothesis.

Changes in spatial point patterns of pioneer woody plants across a large tropical landslide

We assessed whether the relative importance of positive and negative interactions in early successional communities varied across a large landslide on Casita Volcano (Nicaragua). We tested several hypotheses concerning the signatures of these processes in the spatial patterns of woody pioneer plants, as well as those of mortality and recruitment events, in several zones of the landslide differing in substrate stability and fertility, over a period of two years (2001 and 2002). We identified all woody individuals with a diameter >1 cm and mapped them in 28 plots measuring 10 × 10-m. On these maps, we performed a spatial point pattern analysis using univariate and bivariate pair-correlation functions; g (r) and g12 (r), and pairwise differences of univariate and bivariate functions. Spatial signatures of positive and negative interactions among woody plants were more prevalent in the most and least stressful zones of the landslide, respectively. Natural and human-induced disturbances such as the occurrence of fire, removal of newly colonizing plants through erosion and clearcutting of pioneer trees were also identified as potentially important pattern-creating processes. These results are in agreement with the stress-gradient hypothesis, which states that the relative importance of facilitation and competition varies inversely across gradients of abiotic stress. Our findings also indicate that the assembly of early successional plant communities in large heterogeneous landslides might be driven by a much larger array of processes than previously thought.