Seed Bank Diversity Research Articles

Maintain Spatial Heterogeneity, Maintain Biodiversity—A Seed Bank Study in a Grazed Alpine Fen Meadow

AbstractWetland degradation is a source of anxiety and is more severe in cold regions than other areas. The soil seed bank acts as a propagule source for revegetation to affiliate the restoration of degraded wetlands. However, the effects of this approach are controversial and depend on the traits of the seed bank and its interactions with the environment. The seed bank in an alpine fen meadow was studied to determine its exact role in revegetation. The surveyed shore of a Tibetan lake, Gahai Lake, was divided into three sites under different levels of grazing pressure. Each site was separated into six transects along a water‐depth gradient to collect soil cores to determine the pattern of biodiversity through a germination experiment in a greenhouse. After an analysis of heterogeneity‐related diversity, partitioning of 58 discovered species indicated that 39.5 could be contributed to beta‐diversity, which was mainly contributed to water depth. Overgrazing (0.607 sheep unit/acre, November—March) decreased seed bank diversity in many respects, especially through decreasing spatial heterogeneity and homogenizing biota. A lightly grazed, well‐protected site had not only the highest beta‐diversity and species abundance but also the highest inter‐site species turnover rate compared with other sites under moderate grazing intensity. Despite the lack of target species, the seed bank serves as (i) a species‐rich pool; (ii) an extant legacy seed source for sustaining heterogeneity and floristic diversity; and (iii) an ecological indicator, and its effect can be reinforced by appropriate grazing practices (multiple intensity) and hydrological modifications. Copyright © 2016 John Wiley & Sons, Ltd.

Macroinvertebrate seedbank composition in relation to antecedent duration of drying and multiple wet‐dry cycles in a temporary stream

Summary The aquatic invertebrate ‘seedbank’ comprises life stages that remain viable in the bed sediments of temporary freshwaters during dry phases. This seedbank promotes persistence of temporary‐stream macroinvertebrates, but how its inhabitants respond to extended dry phases or repeated transitions between wet and dry phases remains unknown. We rehydrated samples collected from the dry bed of a temperate‐zone stream during a supra‐seasonal drought, to examine the seedbank assemblage. Samples were first collected in autumn, from 12 sites along the ephemeral (4 sites), intermittent (2) and near‐perennial (6) reaches, which had been dry for up to 8 months. Our first hypothesis was that assemblage composition would be related to the dry‐phase duration preceding sampling, with longer dry phases reducing abundance and richness. We revisited the same sites in three subsequent seasons, collecting and rehydrating sediments from all dry sites: five sites in early spring, three in late spring and four in late summer. Unpredictable flow resumption and redrying occurred between sampling dates. Our second hypothesis was that repeated wet‐dry cycles would not degrade the assemblage because temporary‐stream taxa would be adapted to fluctuating hydrological conditions. Multiple individuals of only Chironomidae, Oligochaeta and Pisidium were present at sites that experienced the longest dry phases, providing some support for our first hypothesis. An additional 21 taxa were recorded across the remaining (shorter dry phase) sites in autumn, indicating that such sites act as refuges and potential recolonist sources following flow resumptions. Although several insect orders first recorded in early spring were absent in later seasons, taxon‐specific life cycles indicated that these absences were probably seasonal and not due to repeated wet‐dry cycles. We recorded 38 taxa in total, highlighting the seedbank as a dry‐phase resistance mechanism for many temporary‐stream macroinvertebrates. Our results also suggest that seedbank diversity may be threatened by increases in drought extent and duration.

Analysis on Soil Seed Bank Diversity Characteristics and Its Relation with Soil Physical and Chemical Properties after Substrate Addition.

AimsConsidered as an essential measure in the application of soil seed bank (SSB) projects, the mixing of substrate and surface soil can effectively improve soil condition. This research is aimed at exploring the diversity characteristics of SSBs and the relationships between SSBs and soil properties.MethodsCanonical correspondence analysis (CCA) was adopted to describe the ordination of SSBs on soil properties’ gradients; multiple linear regressions were adopted to analyze the relationship between average growth height and soil properties, density and soil properties.ResultsExperimental groups of mixed substrate (the mixture of organic and inorganic substrates) had high diversity indexes, especially the Shannon-Wiener Index compared with those of single substrate. Meanwhile, a higher number of species and increased density were also noted in those of mixed substrate. The best test group, No.16, had the highest diversity indexes with a Shannon-Wiener of 1.898, Simpson of 0.633 and Pielou of 0.717, and also showed the highest density of 14000 germinants /m2 and 21 species. In addition, an improvement of the soil’s chemical and physical properties was noted when the substrates were mixed. The mixed substrate of turfy soil and perlite could effectively enhance the soil moisture content, whilst a mixed substrate of rice husk carbon and vermiculite could improve the content of available potassium (AK) and phosphorus (AP) and strengthen soil fertility. The germinated plants also reflected obvious regularities of ordination on soil factor gradients. Three distinct cluster groups were presented, of which the first cluster was distributed in an area with a relatively higher content of AK and AP; the second cluster was distributed at places with relatively higher soil moisture content; and the third cluster of plants didn’t show any obvious relationship with soil physical and chemical properties. Through CCA analysis, AK and AP were considered the most important soil factors to influence the SSB, which was illustrated in regression analysis with a high correlation coefficient when dependent values were growth height and density respectively. The linear regression equations with: growth height = 142.728 − 1.514TC + 30.218AP − 5.083TN + 10.839AK + 1.234mc; density = −68.216 − 4.609TC + 9.566AP − 35.492TN + 19.779AK − 1.591mc.were established by multiple linear regression.Conclusions(1) The mixed substrates showed a greater advantage for SSBs than single substrates, both in improving the number of species, density and diversity indexes. (2) The germinated plants reflected an obvious preference to different soil conditions, which different mixed substrates could improve accordingly. (3) AK, AP were important soil factors to influence SSBs, especially in the growth of plants and density.

Características Ecosistémicas asociadas a la actividad ganadera en Arauca (Colombia): Desafíos frente al cambio climático

En la llanura inundable de la Orinoquía colombiana (departamento de Arauca) se realizó la caracterización de cuatro tipos ecosistémicos con diferentes grados de intervención por ganadería, durante la intensa temporada seca de enero a marzo 2010: sabana de pastizal, sabana arbolada, bosque de galería y bosque conservado del piedemonte. En cada uno de ellos se evaluaron las condiciones microclimáticas (humedad y temperatura del aire), las características físico químicos del suelo (capacidad de retención de agua, capacidad de intercambio catiónico, pH, contenido de fósforo y de micronutrientes), la diversidad vegetal (riqueza y abundancia) y el potencial regenerativo (diversidad y porcentaje de germinación del banco de semillas del suelo), con el fin de establecer cuáles parámetros ecosistémicos son los más afectados por la ganadería durante la sequía, y evaluar la capacidad de regulación ambiental y el potencial de recuperación natural. Los resultados demostraron que en casi todos los aspectos el tipo ecosistémico de pastizal es ampliamente contrastante con relación a los bosques conservados del piedemonte, siendo estos últimos los lugares con mayor biodiversidad, menor variabilidad en temperatura y humedad relativa, mayor capacidad de retención de agua, mayor variabilidad topográfica que brinda sitios específicos de regeneración y contenidos más balanceados de micronutrientes en el suelo. Los bancos de semillas, que albergan propágulos que soportan la temporada seca para germinar en condiciones más favorables, fueron más diversos y abundantes en la sabana arbolada, mostrando que este ecosistema tiene mayores opciones de recuperación ecológica que la sabana de pastizal. El estudio demuestra la importancia de la cobertura arbórea en la llanura inundable, especialmente en la autorregulación ecosistémica durante temporadas climáticas desfavorables. Se recomienda la implementación de sistemas de producción ganadera que involucren el componente forestal, y la conservación de los remanentes de bosque.Palabras clave: Bosque de galería; bosque del piedemonte Orinoquía; pastizal; regulación climática; sabana arbolada; suelo; Gallery forest; piedmont forest; Orinoquía; pastureland; climate regulation; wooded savannah; soil.

Patterns of seed bank and vegetation diversity along a tidal freshwater river

Species richness and diversity may increase with spatial scale related to increased area and heterogeneity of habitat. Yet, in bidirectional hydrologically connected tidal ecosystems, secondary dispersal via hydrochory has the potential to homogenize seed banks, and both life history characteristics and tolerances to environmental conditions influence the composition of plant communities. How species richness, diversity, and composition of seed banks and vegetation change along environmental gradients and at different spatial scales is not well understood. We explored the relationships of seed bank and vegetation diversity across 135 plots along a tidal freshwater river in the Delaware Estuary, USA. Species richness and diversity were partitioned across three hierarchical spatial scales: individual plots, transects perpendicular to the tidal channel, and river kilometers. Community structure was also examined as it related to distance from the tidal channel and location along the tidal river. Species richness was 89 in the seed bank and 54 in the vegetation. Species-area relationships revealed that species richness reached a near maximum asymptote inland (20 m from channel) for the seed bank and at the edge (0 m) for the vegetation. Rare occurrences of species in the seed bank and vegetation were greatest 5 m from the channel edge. As spatial scale increased, seed bank richness increased, associated with the progressive accumulation of species. Seed bank diversity, however, was maximized within small plot areas and along the river. Diversity of the vegetation was maximized locally due to the abundance of a few common species. These findings suggest that suites of common species contributed to high localized vegetation diversity, yet large spatial scales maximized the number and diversity of species in the seed bank and vegetation through rare encounters, as well as the complexity of the landscape.

Weed seed bank diversity and community shift in a four-decade-old fertilization experiment in rice–rice system

The development of management practices that allow the prediction of timing and extent of weed emergence is essential for planning more effective weed control strategies as well as maintenance of biodiversity in agricultural systems. A better understanding of the seed bank could provide useful insights into the long-term effects of organic and chemical fertilization for maintaining diversity. The effects of organic and inorganic fertilization on weed seed bank composition, density and diversity were studied in the soil of a long-term fertilizer experiment established four decades ago in CRRI, Cuttack, India. Weed seed density was lowest for Paspalidium flavidum (22 individuals per m2) and highest for Ammania baccifera (11,616 individuals per m2) irrespective of the treatments. Highest weed seed density was observed in farm yard manure (FYM) treatment whereas, lowest was in NK treatment, which was 232% higher in FYM over NK treatment. Weed seedling emergence was higher in kharif flushes and lowest in rabi. Principal component analysis ordination indicated little similarity in the weed community composition particularly among NP, NPK and NPK+FYM, while application of N alone was quite distant. Weed species diversity was reduced significantly with application of inorganic N either applied with K or alone; therefore, lowest diversity and species richness was observed in NK treatment followed by N alone. The results of the study may contribute to the development of effective weed management strategies as well as maintenance of weed diversity which leads to transition from an herbicide-dependent cropping system to a more environmentally friendly cropping system.

Lack of soil seedbank change with time since fire: relevance to seed supply after prescribed burns

Soil seedbanks play a key role in the post-fire recruitment of many plant species. Seedbank diversity can be influenced by spatial variability (e.g. geographic location), environmental variability (e.g. soils) and temporal disturbance heterogeneity (e.g. time since fire, TSF) across the landscape. Unlike for aboveground vegetation, relationships between these factors and soil seedbank diversity remain largely unknown. Partitioning the influence of spatial and environmental variability from that of TSF, and explaining how these factors interact with seedbank diversity, will assist conservation managers in their application of prescribed burning. We germinated soil seedbank samples from sites ranging from 1 to 75 years since fire in a heathy-woodland ecosystem across the Otway Ranges in Victoria, Australia. We also measured spatial and environmental variability across sites to partition the influence of these variables and TSF on propagules available for recruitment. We found weak positive relationships between seedbank richness and TSF; however, these relationships varied across the landscape. We found composition did not change considerably over time, suggesting, in this ecosystem, pre-fire age is not strongly influencing propagules available for recruitment post-fire. Our results suggest that spatial and environmental variability influence seedbank composition more than TSF.

Burning reveals cryptic plant diversity and promotes coexistence in a California prairie restoration experiment

Grassland and prairie restoration projects in California often result in long‐term establishment of only a few native plant species, even when they begin with a diverse seed palette. One explanation for the disappearance of certain native species over time is that they are excluded through competition. If so, management that reduces interspecific competition may favor “subordinate” natives and promote greater native species diversity in restored communities. Potential management approaches to accomplish this goal include intraspecific spatial aggregation during seeding and prescribed fire. However, no studies have experimentally evaluated the effects of fire on a controlled (restoration) species pool or the interaction between fire and spatial aggregation. In a previous California prairie restoration experiment, we demonstrated that aggregated plantings protected competitively subordinate species from exclusion and increased community diversity for three years. However, native species richness declined throughout the study, and the benefits of aggregated seeding had begun to disappear by the third year. For the present study, we resurveyed the experimental plots five years after seeding and in the following year carried out controlled burns on half of the plots. The four subordinate species and one of the previously dominant species continued to decline and essentially disappeared aboveground during years four and five. However, burning in year five decreased the cover of dominant natives, triggered the reappearance of the three subordinate species that had disappeared or nearly disappeared in previous years, and increased diversity of the restored community. Seeding treatments (aggregated or interspersed) did not significantly affect community‐level responses to the burning treatment. These results confirm that although initial intraspecific aggregation may promote species coexistence in the short term, re‐establishing disturbance regimes can allow coexistence over a longer time scale by revealing and potentially renewing seed bank diversity.

Seed bank composition varies along invasion and inundation gradients in vernal pool wetlands

Environmental filters are well-known influences on aboveground vegetation community structure; however, less is known about their role on belowground seed banks. Understanding the influence of environmental filters on the composition of seed banks can reveal community dynamics across known environmental gradients and facilitate restoration efforts. We examined the influence of environmental filters on seed banks of vernal pools by characterizing seed density and diversity along seasonal inundation gradients. We also sampled seed banks from both naturally occurring and restored vernal pools that differed in their aboveground communities (invasive or native species dominated) in a long-term field study in Solano Co., California, USA. We found that the highest seed densities were associated with the longest inundation period and in the naturally occurring pools. Inundation gradients within a pool had little influence on seed bank diversity, yet among the pool types diversity and community metrics varied. The naturally occurring pools, regardless of invasion status, displayed a greater species richness and diversity than constructed pools. Our greenhouse germination trials did not show a strong relationship of inundation depths influencing species and total germination. Overall, we found that local position in the field along inundation gradients within a pool strongly affected soil seed bank density, while seed bank diversity varied more across pool types. Environmental filters may be limiting germination with the pool bottoms having the highest inundation and maintain the densest seed bank, but our lack of difference in the germination trials suggests alternative mechanisms other than inundation may be hindering germination.

The Peninsula Shale Renosterveld of Devil's Peak, Western Cape: A study into the vegetation and seedbank with a view toward potential restoration

Peninsula Shale Renosterveld is a poorly understood and critically threatened vegetation type. Less than 13% of its original extent remains and the surviving fragments are restricted to the area surrounding the Cape Town city bowl. A substantial portion of Peninsula Shale Renosterveld is situated in the Groote Schuur Estate, currently conserved within the Table Mountain National Park. Due to a history of diverse land-use impacts what remains today is a complex mosaic of alien invasive species and indigenous vegetation in various states of degradation and to improve the conservation value restoration is required. However, it is imperative that prior to restoration initiation data is collected from the site. To enhance the understanding of the ecosystem drivers of Peninsula Shale Renosterveld with a view to evaluate restoration potential and inform future restoration initiatives a detailed analysis of four typical vegetation states found within the study area was undertaken. This was accomplished through a vegetation survey investigating different ‘states’ of the contemporary condition of the study area and an examination of the health of the seedbank through a burning and greenhouse experiment to ascertain whether it could prove a useful asset in future restoration initiatives. The results show how historical drivers have created a novel ecosystem with vegetation states ranging from relatively healthy Renosterveld vegetation, indigenous vegetation requiring intervention to maintain its integrity, and regions of the study area which are dominated by alien grasses and Pinus plantations. The seedbank diversity was found to be poor, dominated by alien ephemeral species and unlikely to assist in restoration efforts. Although certain areas may retain their ecological integrity through passive restoration, large swathes of the study area require active restoration to return the degraded vegetation to functional Peninsula Shale Renosterveld.

Change in weed seed bank diversity over 13 consecutive years of rice-duck and straw returning farming system in the rice-wheat rotated wheat fields

Change in weed seed bank diversity over 13 consecutive years of rice-duck and straw returning farming system in the rice-wheat rotated wheat fields

Diversity in weed seed production and the soil seed bank: Contrasting responses between two agroecosystems

This study was carried out to compare the diversity in seed production and the soil seed bank in a dryland and an irrigated agroecosystem in the dry tropics. Both agroecosystems showed a comparable number of species, but only 25% and 38% similarity during the winter and rainy cropping seasons, respectively. In the irrigated agroecosystem, the amount of seed production diversity was almost double in the winter season, compared to the rainy season. The weed seedbank diversity was low but was sensitive to cropping practices and seasons in both agroecosystems. A considerably smaller soil seedbank size in the irrigated agroecosystem (cf. dryland) was related to lowered weed seed production. The dryland agroecosystem showed a greater accumulation of the seeds of broad‐leaved weeds, whereas the irrigated agroecosystem accumulated more seeds of the grasses or sedges. About three‐fourths of the seeds during the winter season were accounted for by Anagallis arvensis and Chenopodium album in the dryland agroecosystem and by C. album and Melilotus indica in the irrigated agroecosystem. However, during the rainy season, Ammannia baccifera, Echinochloa colona and Cyperus rotundus dominated in both agroecosystems. The changes in the weed seed bank and its diversity are mainly attributed to differences in water management, which tends to reduce species diversity, especially at a lower depth, but leads to the dominance of some potentially noxious weeds (e.g. Phalaris minor and M. indica). Approximately double the soil seedbank size and a greater diversity at a lower depth might indicate an adaptive mechanism in the storage of weed seeds in the dryland agroecosystem.

Plant and soil seed bank diversity across a range of ages of Eucalyptus grandis plantations afforested on arable lands

Aims Plantation forests are often assumed to have reduced biodiversity relative to unmanaged forests. However, existing knowledge is based on studies of rotation-aged tree crops. We investigated how Eucalyptus afforestation of agricultural land affected plant species composition and biodiversity across a range of plantation ages (1–10 years). We also studied whether the soil seed bank could contribute to regeneration of existing vegetation in such plantations.

Environmental factors driving seed bank diversity in alkali grasslands

For an effective conservation and management in grasslands it is essential to understand mechanisms sustaining biodiversity. To gain knowledge is especially crucial in stressed grasslands harbouring a unique flora and fauna, like alkali grasslands. Aboveground vegetation, seed bank and environmental factors were studied in three stands of the following alkali grassland types: (i) Artemisia dry alkali grasslands at highest elevations; (ii) Puccinellia high and (iii) Puccinellia low grasslands at medium to low elevations, and (iv) Juncus wet alkali grasslands at the lowest elevations. We tested the following hypotheses: (i) Seed bank species diversity and density are the highest in the most stressed grassland types, where regeneration by seeds could have a major importance in sustaining vegetation diversity. (ii) Seed bank density of hygrophytes increases with decreasing elevation, because the cover of hygrophytes in the vegetation increases with decreasing elevation. The mean seed bank density ranged from 30,104 up to 51,410seeds/m2, which is higher than in most dry grasslands. Both the lowest seed bank density and diversity were detected in the most stressed Puccinellia high grasslands; Spergularia salina was the only abundant seed bank species (possessing at least 1000seeds/m2). These results not supported our first hypothesis. We detected the highest seed densities of almost all hygrophyte species in the lowest-elevated Juncus grasslands. But, we did not find a significant monotonous correlation between elevation and the overall hygrophyte seed bank density; because most of the hygrophyte species were missing from the seed bank at the medium-elevated, but most saline Puccinellia grasslands. Thus, our results only partly supported the second hypothesis. In total we detected more species in the seed bank than in the aboveground vegetation which emphasises that seed bank plays an important role in sustaining the diversity of alkali grasslands. However, characteristic graminoids possessed no considerable seed bank, except for Juncus compressus (up to 38,619seeds/m2). We can conclude that persistence and establishment of most alkali grassland species are not supported by the local persistent seed bank.

Assessing the significance of soil erosion for arable weed seedbank diversity in agro-ecosystems

Accelerated soil erosion threatens sustainable food production by degrading the physical and biogeochemical functioning of arable field soils and lowering crop yields. Much less recognized is the potential for soil erosion to impinge on wider ecosystem services including the weed seedbank that underpins much of the biodiversity in temperate agro-ecosystems of northern Europe. This paper assesses the likely impact of soil erosion on the composition and abundance of the arable weed seedbank, and presents an overview of erosion mechanisms affecting arable land coupled with an outline of the main factors influencing arable weed seedbank abundance and composition. The information presented on both these sets of processes enables assessment of the likely impact of soil erosion on arable seedbank biodiversity at the field and landscape scales. Combining mean annual net erosion rates of c. 7 t ha−1 yr−1 and seedbank densities c. 2000 seeds m−2, both figures broadly representative of UK conditions, produces an average annual loss of the field seed inventory of c. 0.5% yr−1. Where seedbank abundance is otherwise relatively stable (i.e. losses through death, germination and weed control are largely balanced by gain through seed rain), average soil loss rates could export c. 10% of the arable weed seedbank in 20 years. Net erosion data conceal within-field sediment deposition within swales, foot slopes, buffer strips and hedgerows which provides a further dimension of spatial restructuring of weed assemblages. Seed size and shape also influence hydrodynamic behaviour through selective entrainment and preferential deposition. It is concluded that earth surface processes play an under-recognized role in structuring field-scale weed-based biodiversity in agro-ecosystems over decadal timescales.

Winter cover crops and fertiliser effects on the weed seed bank in a low-input maize-based conservation agriculture system

This study investigated the effects of grazing vetch (Vicia dasycarpa L.) and oat (Avena sativa L.) cover crops and fertiliser on the seed bank of some problematic weeds in a maize-based conservation agriculture system. Soil sampling for seed bank analysis was carried out at the 0–5 and 5–20 cm depths after four years of rotations. The winter cover crops reduced the seed-bank density of Digitaria sanguinalis (L.) Scop., Eleusine indica (L.) Gaertn., Amaranthus retroflexus L. and Datura stramonium L. in the 0–5 cm depth by 30–70%. Vetch was more effective on depleting the D. sanguinalis seed bank than oat. Fertiliser application reduced the A. retroflexus seed bank by 41.6% in the weedy fallow, but had no significant effect in plots grown to the cover crops. The winter cover crops did not significantly affect seed-bank weed species diversity.

Does soil seed bank diversity limit post-fire regeneration in small, fragmented, long-unburnt remnants of fire adapted vegetation?

Soil collected from 38 sites on Kangaroo Island in South Australia, containing small remnants of senescent Eucalyptus cneorifolia-dominated mallee, was subject ex situ to both smoke aerosol and heat treatment to simulate burning. Further soil from a subset of 29 of the sites was left untreated as a control. A total of 113 native plant species and 50 introduced species germinated across all sites. Fifty-three of the native plant species that germinated were absent in the above-ground vegetation, including twelve rare or threatened species, and three species previously unrecorded from Kangaroo Island. Fourteen native species and six introduced species germinated in heat plus smoke treated soil but not in untreated soil from the same sites. Non-metric multidimensional scaling ordination indicated differences in native species composition between sites with a long history of sustained livestock grazing (“grazed” sites) and largely ungrazed sites (“ungrazed” sites). On average, significantly more native species germinated from treated soil sampled from “ungrazed” sites than were found in the standing vegetation, while for “grazed” sites this difference was not significant. This indicates the greater potential for post-fire regeneration of native vegetation from the soil seed bank of ungrazed sites than from that of long grazed sites. Both “ungrazed” and “grazed” sites contained weeds in their soil seed banks, including some species which were stimulated by heat plus smoke. This indicated that competition from weeds is potentially a problem when fire is used as a management tool to regenerate senescent understoreys.

Stochastic and deterministic processes regulate spatio‐temporal variation in seed bank diversity

AbstractQuestionSeed banks often serve as reservoirs of taxonomic and genetic diversity that buffer plant populations and influence post‐disturbance vegetation trajectories; yet evaluating their importance requires understanding how their composition varies within and across spatial and temporal scales (α‐ and β‐diversity). Shifts in seed bank diversity are strongly governed by the deterministic role of differential seed longevities. Nevertheless, spatio‐temporal variability in propagule depletion from and recruitment into seed banks may alter both α‐ and β‐diversity. Here, we ask to what degree deterministic seed exhaustion, stochasticity in recruitment and mortality, or both, shape α‐ and β‐diversity?LocationTemperate hardwood forest stands of varying ages in northernPennsylvania,USA.MethodsWe surveyed the seed bank and herbaceous vegetation communities at 39 sites and examined whether the species richness, abundance and composition of either community differs among and within sites of increasing age ranging from 43 to 106 yr old. We explored how α‐diversity (species richness) and abundance (percentage cover, seed density) varied across the chronosequence age using regression analyses. We analysed differences in β‐diversity (community composition) using permutational multivariate analyses (i.e.PERMANOVA,PERMDISP). Finally, we tested whether community composition of the herbaceous layer and seed bank communities exhibited nestedness, where nestedness refers to the degree to which less species‐rich sites are a non‐random subset of more species‐rich sites.ResultsWe found seed bank α‐diversity and abundance consistently declined across a gradient of increasingly older sites. Moreover, nestedness analyses indicated species composition at older sites represented a subset of the species found at younger sites characterized by species with persistent seeds. Nevertheless, seed bank communities demonstrated divergent compositional trajectories, whereby older sites were increasingly dissimilar, not only from younger sites, but also from each other.ConclusionsOur results suggest that even in assemblages strongly structured by deterministic forces, such as seed banks, minor stochastic differences in colonization and extinction events may increase β‐diversity over time. Therefore, we argue deterministic and stochastic processes are complementary factors governing post‐disturbance turnover in species assemblages, and suggest that seed banks contribute to species‘ persistence and overall forest community diversity across space and time.

Aboveground plant community and seed bank composition along an invasion gradient

Invasive plants can reduce plant diversity and abundance in native grassland communities; however, the effect on the native seed bank is less clear. The objective of this study was to assess the effects of invasion by the exotic grass old world bluestem (OWB; Bothriochloa spp.) on native aboveground plant species composition and seed bank diversity and abundance (i.e., cover, density). In this central Great Plains grassland, OWB invasion had differential effects on native diversity and abundance of both aboveground and seed bank plant communities. Native plant species diversity and cover showed a steep decline as OWB cover increased. No change in native seed density or richness was observed in response to OWB invasion, however, OWB seed density increased with increasing invasion, thus increasing total seed density. Our results indicate that as OWB invasion increases, the native plant community decreases in diversity and abundance. Although, no effect on native seed bank diversity and density was observed in this study, as native seeds are lost through a loss of native species in the plant communities, native seed bank diversity and density is expected to decline.

Viable seed banks under grazing and exclosure conditions in montane mesic grasslands of Argentina

Grazing by large herbivores affects the composition of established vegetation and seed banks. Montane Pampas grasslands are highly productive and have evolved with the influence of grazing by native herbivores. Thus we proposed, firstly that grazing by feral horses would increase seed bank diversity, without changing seed density in grazed areas and secondly that there is a greater similarity between the seed bank and aboveground vegetation in exclosure areas. The study area is located in sub-humid montane grassland in mid-eastern Argentina. Sampling took place at the beginning and end of summer in 2008 and 2009, in three one-year-old exclosures and grazed areas. Soil and litter samples were collected and established vegetation cover was visually recorded in every area. Each sample was elutriated and sieved. Seed composition was recorded using a dissecting microscope. Seed density and species richness of the samples was analyzed using ANOVA and species composition was analyzed by multivariate analysis. Grazing reduces the seed density and richness of grasses, but forb species are not affected. The seed density of grasses increases in soil samples at the end of summer, while the density of forb species does not change. Similarity between the established vegetation and the seed bank was low. Grazing affects seed bank composition which could limit restoration time after the removal of herbivores. However, grass seed availability increases considerably during a short period after exclosure establishment, showing high potential for recovery in sub-humid grasslands.