Species Composition Of Seed Bank Research Articles

Long‐term relationships between seed bank communities and wildfire across four North American desert sites

AbstractIt is well documented that the recovery of dryland plant communities following wildfire can be variable, and that legacies of fire can have long‐lasting effects on aboveground plant communities. However, our understanding of the degree to which dryland soil seed banks, or the viable seeds in situ, are impacted by fire and their subsequent postfire succession remains extremely poor. To address this important knowledge gap, we used a time‐since‐fire approach to investigate soil seed bank community changes approximately 15 and 30 years after wildfire and to determine the influence of microsites (e.g., shrub vs. interspace) on seed bank composition. We assessed soil seed bank metrics across four North American deserts, including two cold desert sites (Colorado Plateau and Great Basin) and two warm desert sites (Chihuahuan and Sonoran). In greenhouse emergence trials, we found that seed bank characteristics diverged between warm and cold desert sites, such that warm desert sites had seed banks dominated by annual plants while our cold desert sites had seed banks with greater proportions of perennial species, regardless of fire history. In cold desert sites, fire significantly altered seed bank species composition even 30 years after fire. Shrub versus interspace microsites had no observed influence on seed bank composition in any desert. However, seed bank species richness was greater under shrubs in both warm deserts. Non‐native species were present in the seed banks of all deserts and some were particularly abundant in the burned sites. Despite the presence of native species in both burned and unburned seed banks, the presence of non‐native species suggests some degree of vulnerability to future disturbances because fire can create amplifying feedback with many non‐native plants. Our results highlight strong differences in fires' relationship with seed banks for warm and cold desert sites and lend insight into how fire relates to the composition and diversity of the seeds that play a fundamental role in future plant communities.

Plant community dynamics following non‐native shrub removal depend on invasion intensity and forest site characteristics

AbstractGlobally, temperate deciduous forests are threatened by invasion of non‐native (exotic) plant species. In the eastern United States, Rosa multiflora is a dominant shrub invader in forests, which often forms dense thickets that reduce sunlight availability in the understory, where decreased native plant diversity and abundance are observed. Management and restoration are difficult but desirable, especially when invasion intensity is still low. Few studies have examined the relative success of different management strategies under varying invasion intensities. Our study objectives were to conduct a R. multiflora removal experiment in three forest sites experiencing different invasion intensities and to restore native plant biodiversity while preventing secondary invasion. We utilized three management strategies: invasive plant removal, removal followed by native seed addition, and removal plus native seed and mulched invasive stem addition. We investigated the similarity between seed bank species composition and existing vegetation before and after removal to assess the potential for passive restoration. Two seasons after removal, we found that simply removing roses increased native species richness, native floristic quality assessment (FQAIN), and native shrub abundance in our medium invasion site, and total species richness in our low and medium invasion sites. Compared to removal alone, native seed addition, with and without mulch addition, resulted in larger native and total species richness and FQAIN increases at all sites, larger increases in native shrub abundance and exotic species richness in our medium invasion site, and larger reductions in exotic and total shrub abundance in our low and medium invasion sites. Following removal, species similarity between the seed bank and vegetation improved for all three sites. Our results indicate that removal of R. multiflora alone increased native plant biodiversity in the medium invasion scenario, but the seed bank may not provide a large native species pool. Additional management strategies lead to improved outcomes, especially in our most invaded forest, demonstrating the need to conduct multiple plant removal treatments across forests with varying site conditions and plant invasion intensity to improve management recommendations.

Soil seed bank composition and aboveground vegetation in dry Afromontane forest patches of Northwestern Ethiopia

The species composition in the aboveground vegetation and soil seed bank (SSB) were described for the dry Afromontane forest patches of Northwestern Ethiopia. Plots (30 × 30 m) were established to collect the vegetation and environmental data. Soil samples were collected for the soil bank study from the small plots measuring 10 cm × 10 cm from four soil layers. Shannon Weiner index and evenness were used to assess the species diversity and richness of the forest. Density, DBH, basal area, frequency, and importance value indices (IVI) of woody species were computed to characterize the vegetation structure of the forest. Results indicate the presence of 176 plant species belonging to 80 families. The Shannon diversity index and evenness values of the study area were 2.79 and 0.95, respectively were medium, compared to other dry Afromontane forests of Ethiopia. The total basal area and density of woody species were 51.42 m2 ha−1 and 2679.33 individual ha−1, respectively. The most dominant species as and indicated by their important value index (lVI) was Prunus africana (17.97). A total of 2133 seedlings belonging to 44 species and 27 families were identified from the soil seed bank, with a viable seed density of 4636.95seeds/m2. The species composition of the seed bank was dominated by 29 herb species (65.9%) compared to 2 tree species, which accounted for only 4.54% of the total number of species. The highest number of species density was recorded in the litter and the upper 3 cm layer of the soil and gradually decreased with increasing depth. The Similarity between soil seed bank species composition and aboveground vegetation was low and conclude that the regeneration potential of the forest from seed bank is limited. Redundancy analysis (RDA) showed that emerged seedlings from the soil seed bank were significantly influenced by elevation and soil cation exchange capacity. The natural regeneration process of soil seed bank should be assisted through transplanting indigenous tree species in to the forests to accelerate the restoration of the vegetation and conservation and sustainable utilization of the reaming of forest patches is a necessity.

The Similarity between Species Composition of Vegetation and Soil Seed Bank of Grasslands in Inner Mongolia, China: Implications for the Asymmetric Response to Precipitation.

The asymmetric response of productivity to precipitation was recently proposed as an early warning signal for the shifts in temperate grassland function in China. It was hypothesized that the asymmetry was influenced by the increased growth of the newly emerged seedlings from the soil seed bank. Therefore, the seed density in the soil seed bank and the similarity between species composition of the vegetation and the soil seed bank should be maximized where asymmetry was maximized. However, this knowledge was still limited and unconfirmed. In this study, the desert steppe, typical steppe and the transition zone between them (with the highest asymmetry) were selected for studying the similarity index in both 2018 (dry year) and 2019 (wet year). Plant species composition was monitored in situ using an unmanned aerial vehicle. Soil seed bank samples were collected, and the seed bank density and species composition were then examined and identified in the laboratory. Results showed that: (1) The variation in vegetation species richness between the two years was the highest (41%) in the transition zone (p < 0.05), while it was only 7% and 13% for the desert steppe and typical steppe, respectively. The presence of herbaceous species mainly caused the differences in variation among three grassland types. (2) Seed density was the highest in the transition zone (114 seeds/m2 and 68 seeds/m2 in the transient and persistent soil seed bank, respectively) (p < 0.05). Additionally, herbaceous species were the main components of the soil seed bank. (3) The similarity index was the highest in the transition zone (p < 0.05), with 38%/44% and 33%/44% for the transient/persistent soil seed bank in 2018 and 2019, respectively. Our study demonstrated that variation in vegetation species composition was very similar to the composition of the seeds accumulated in the soil seed bank. These results warrant further investigation for the mechanism of asymmetric response of productivity to precipitation.

Extreme drought has limited effects on soil seed bank composition in desert grasslands

AbstractQuestionDoes climate change affect vegetation and seed bank composition in desert grasslands?LocationSevilleta National Wildlife Refuge, New Mexico, USA.MethodsVegetation and seed bank species composition were recorded in black grama (Bouteloua eriopoda) and blue grama (Bouteloua gracilis) grasslands. At each site, two rainfall manipulations and ambient controls were established in 2013 (n = 10). Treatments included extreme drought (−66% rainfall reduction during the growing season) and delayed monsoon (precipitation captured during July–August and reapplied in September–October). Above‐ground species composition was assessed, and composite soil samples were collected in 2017, five years after the experiment started. Seed bank was evaluated using the seedling emergence method.ResultsRainfall treatments increased the above‐ground vegetation and seed bank richness in the blue grama community, but not in the black grama community. Vegetation cover was reduced by both rainfall manipulations, but seed bank density increased or remained the same compared with controls. In above‐ground vegetation, cover of annual and perennial forbs increased, and dominant perennial grasses decreased under drought. In the soil seed bank, species composition was similar among all treatments and was dominated by annual and perennial forbs.ConclusionsThe seed bank was more resistant to drought than above‐ground vegetation. Because seed banks can enhance long‐term community stability, their drought resistance plays an important role in maintaining ecosystem processes during and following drought in these grassland communities.

Effects of rotation grazing time on the characteristics of soil seed bank in desert steppe.

Exploring the characteristics of soil seed bank under seasonal grazing plays an important role in the reasonable use of desert steppe. We examined seed bank species composition, density, vertical distribution, diversity in the soil of 0-5, 5-10, 10-15 cm soil layers and the relationship with vegetation and soil environmental factors in Ningxia desert steppe. The treatments included enclosure (FY), traditional time rotation grazing (FG), delayed to start rotation grazing (YG), early to end rotation grazing (TG), delayed to start and early to end rotation grazing (YT) and free grazing (ZY). The results showed that there were nine families and 21 species in the soil seed bank in the study area. The species composition of soil seed bank in TG seed bank with 13 species was the largest, while FY and ZY soil seed banks had the least, with 8 species, respectively. The den-sity of ZY soil seed bank was significantly higher than that of FY, YG, TG and YT. The number of perennial species seeds in the soil seed bank of FY was the largest, reaching 32.0%, while that in the ZY was the least, only 12.4%, mainly with sexually reproduced annual weeds. Soil seed bank was mainly concentrated in the 0-5 cm surface layer. With increasing soil depth, the size of soil seed bank decreased. The dominance and diversity of soil seed bank were the highest in FY, while the dominance, diversity and uniformity were the lowest in ZY. The similarity between soil seed bank and aboveground vegetation was generally low. In contrast, the FG and ZY seed banks had higher similarity with vegetation, and the FY was the lowest. Soil moisture, organic matter, total nitrogen concentration, total phosphorus concentration, and soil bulk density were the main soil factors affecting soil seed bank. Compared with traditional whole year free grazing, seasonal four-zone rotation grazing could increase species richness and abundance of perennial plants in soil seed bank of desert steppe, as well as the total species richness, diversity and uniformity of the seed bank. Although the effect sof seasonal four-zone rotation grazing on seed bank was not as good as the long-term enclosure grassland, it was of great significance to the utilization and protection of desert steppe.

Effects of exotic plantation expansion and management intervention on woody plant species diversity, regeneration and soil seed bank in Tarmaber district, Ethiopia

This study was carried out to determine the effect of plantation forest with management intervention on woody plant species diversity in Tarmaber district north shewa zone Ethiopia, regeneration and soil seed bank species composition in five different forest types. A total of 75 circular sample plots of 314 m2 were established along a transect lines. Soil seed bank analysis was done from soil samples collected in each of the plots (225 samples). Different diversity index and ANOVA was used in SPSS software for analysis. The result showed that a total of 51 woody plant species was recorded in adjacent natural forest (41), managed C. lusitanica (27), not managed C. lusitanica (9), managed E. globules (22) and not managed E. globules (13) species. Regeneration of seedlings were 3538, 5567, 707, 1462 and 2524 mean stems ha-1 for natural forest, managed C. lusitanica, not managed C. lusitanica, managed E. globules and not managed E. globules respectively. Unmanaged C. lusitanica plantations had significantly lower densities of mature tree stems ha-1 as compared to managed C. lusitanica, managed E. globules and adjacent natural forest (F=14.03, p&lt;0.05). Similarly in terms of sapling density ha-1 unmanaged C. lusitanica was significantly lower from other forest types (F=7.37, p &lt;0.05). However managed C. lusitanica had significantly higher seedling regeneration (stem density ha-1) than other plantation and adjacent natural forests (F = 16.11, p &lt; 0.05). Generally mean stem densities including tree, sapling and seedling of woody species among different forest types managed C. lusitanica was significantly higher among different forest types (F= 13.01, p&lt;0.05). From the soil seed bank a total of 22 plant species (20 native and 2 exotic) species were recovered. In different forest types the number of species recorded was in adjacent natural forest (19), managed C. lusitanica (11), unmanaged C. lusitanica (4), managed E. globules (7) and unmanaged E. globules (5). Generally, with appropriate management intervention, undergrowth vegetation and soil seed bank status in plantation forest had good species composition and diversity.

Effects of Exotic Plantation and Management Intervention on Woody Plant Species Diversity, Regeneration and Soil Seed Bank in Tarmaber District, Ethiopia

Plantations have many economic and environmental benefits, but exotic plantations are widely viewed negatively mainly in relation to biological diversity conservation, and regenerations to prove this dilemma this study is necessary. This study was carried out in Tarmaber district north shewa zone Ethiopia to determine the effect of plantation forest with management intervention on woody plant species diversity, regeneration and soil seed bank species composition in five different forest types. A total of 75 circular sample plots of 314 m² were established along a transect lines. Soil seed bank analysis was done from soil samples collected in each of the plots (225 samples) to examine the similarity between the soil seed bank and aboveground flora. Different diversity index and ANOVA was used in SPSS software for analysis. The result showed that a total of 51 woody plant species was recorded in adjacent natural forest (41), managed <i>C. lusitanica</i> (27), not managed <i>C. lusitanica</i> (9), managed <i>E. globules</i> (22) and not managed <i>E. globules</i> (13) species. Regeneration of seedlings were 3538, 5567, 707, 1462 and 2524 mean stems ha^-1 for natural forest, managed <i>C. lusitanica</i>, not managed <i>C. lusitanica</i>, managed <i>E. globules</i>and not managed <i>E. globules</i>respectively. Unmanaged <i>C. lusitanica</i>plantations had significantly lower densities of mature tree stems ha^-1 as compared to managed <i>C. lusitanica</i>, managed <i>E. globules</i>and adjacent natural forest (F=14.03, p<0.05). Similarly in terms of sapling density ha^-1 unmanaged <i>C. lusitanica</i> was significantly lower from other forest types (F=7.37, p <0.05). However managed <i>C. lusitanica</i>had significantly higher seedling regeneration (stem density ha^-1) than other plantation and adjacent natural forests (F = 16.11, p < 0.05). Generally meanstem densities including tree, sapling and seedling of woody species among different forest types managed <i>C. lusitanica</i> was significantly higher among different forest types (F= 13.01, p<0.05). From the soil seed bank a total of 22 plant species (20 native and 2 exotic) species were recovered. In different forest types the number of species recorded was in adjacent natural forest (19), managed <i>C. lusitanica</i> (11), unmanaged <i>C. lusitanica</i> (4), managed E. globules (7) and unmanaged <i>E. globules</i> (5). The similarity of the soil seed bank was more or less similar to the above ground flora with maximum Sorenson’s similarity values of 0.633. Generally with appropriate management intervention undergrowth vegetation and soil seed bank status in plantation forest had good species composition and diversity.

Strategies to persist in the community: Soil seed bank and above‐ground vegetation in Patagonian pine plantations

AbstractQuestionsIn terms of biodiversity conservation, forest plantations are often considered problematic because they usually have negative effects on natural ecosystems. Soil seed banks could play an important role in restoring vegetation that was originally present, by recruiting species that have disappeared above‐ground. We addressed this topic in plantations located in the Patagonian steppe by asking the following questions: Are richness, abundance and composition of steppe above‐ground vegetation and soil seed bank affected by plantations? Is species composition of the above‐ground vegetation and soil seed bank similar in plantations and in the steppe?LocationNW of Chubut Province, Patagonia, Argentina.MethodsWe selected three plantations located in the steppe, and delimited three sectors: steppe, plantation edge and plantation interior. We compared richness and abundance by species origin and growth form among sectors for the above‐ground vegetation and soil seed bank compartments, using generalized linear mixed models. We compared species composition for each compartment and between them using permutational multivariate analysis of variance and non‐metric multidimensional scaling.ResultsIn above‐ground vegetation, we found a decrease in richness and abundance, and changes in composition from the steppe to the plantation interior. Richness and abundance of the soil seed bank did not show differences among steppe and the plantation sectors, although composition was different among them. Above‐ground vegetation and soil seed bank species composition were always different; native perennial herbs and shrubs were predominant in the above‐ground vegetation while exotic annual herbs dominated the soil seed bank.ConclusionsOur findings suggest that plant recruitment from the soil seed bank would not be sufficient for restoring depleted species pools in the above‐ground vegetation of plantations. Therefore, actions promoting native species reestablishment and control of exotics should be considered to reach the aim of restoring biodiversity in former plantations.

The composition of the soil seedbank and its role in ecosystem dynamics and rehabilitation potential in the arid Tankwa Karoo Region, South Africa

Very few soil seedbank studies have been conducted in South Africa, especially in arid rangelands. Insight into the soil seedbank could therefore improve assessment of rangeland dynamics and enhance rehabilitation efforts. This study aimed to characterise the soil seedbanks in various vegetation types of the Tankwa Karoo National Park, an arid environment in South Africa. At 43 sites soil was sampled twice at the end of spring and the end of autumn, and the composition and structure of aboveground vegetation were described at the peak growth period in spring. Seeds were isolated from the soil samples by means of flotation in a salt solution, seedbank species composition was obtained by seedling germination, and the vegetation was investigated using a line-point survey method. Overall seed density was 8 034 seeds m−2 of which 55% was viable, and the common life-forms were therophytes and chamaephytes. Species richness and diversity were lower in the seedbank compared with those of the vegetation, and the two vegetation spheres were 25% similar. While seedbank composition suggested poor veld condition, there was enough seed density and viability for future regeneration and rehabilitation initiatives. However, this may be impeded by the absence of many perennial species in the soil seedbank.

Effect of heat on soil seedbank of three contrasting physiognomies in Shasha forest reserve, Southwestern Nigeria

The effects of soil heating which usually occur during forest fires on the floristic composition and seed density of the soil seed bank of Shasha forest reserve in Southwestern Nigeria was investigated and the potential of the soil seedbank in forest restoration process (especially after a fire) was examined. Three distinct sites (Regrowth forest, Gmelina and Pinus plantations) were selected in the forest reserve. Species enumeration, identification and distribution into families of the standing vegetation were carried out. Soil samples were collected at 0–15 cm depth from each plot in March 2012. One set of replicate samples was heated in an oven until the soil reached 80 °C (to simulate typical temperature at soil surface during forest fires) while the other serves as a control. They were subjected to seedling emergence for six months to determine the density and species composition of the seed banks of the study sites. Seedling emergence result for heated and unheated soil samples showed that the seedbank density was higher in control than heated samples in the three sites. Few woody species emerged from the soil seedbank of three study sites and in both control and heated samples. There was a significant difference in total seed density when treatments were compared (P < 0.05) and no significant difference (P > 0.05) when sites were compared. Diversity and evenness indices follow the order Regrowth forest > Pinus plantation > Gmelina plantation. NMDS (non-metric multi-dimensional scaling) ordination revealed low similarity in the species composition of extant vegetation and seedbank. The potential of vegetation restoration of the disturbed forest reserve from seed bank is limited, and heat from fire had negative effects on the seed bank characteristics of the forest but selectively enhanced the emergence of species like Pinus carribaea.

Divergence between riparian seed banks and standing vegetation increases along successional trajectories

AbstractQuestionsPlant community resilience largely depends on the secondary succession induced by species re‐colonization from seed banks. Soil seed bank resilience is, however, poorly understood, especially in regularly disturbed habitats like riparian zones. Two questions were asked: (1) what are the changes in species diversity experienced by riparian soil seed banks along successional trajectories, and (2) to what extent do riparian soil seed banks promote vegetation resilience during secondary succession?LocationSoutheast Quebec, Canada.MethodsSoils were collected along five rivers in field edges and riverbanks of post‐agricultural riparian zones with three contrasting successional stages (unplanted, planted with trees 15–17 yr prior to sampling, natural riparian forests), and their seed bank composition determined with the seedling emergence method. Species richness in seed banks was assessed along successional trajectories for distinct ecological groups, using LMM. The compositions of soil seed banks and standing vegetation (from botanical surveys) were compared based on NMDS and indicator species analysis.ResultsSeed bank species richness decreased along successional trajectories. Tree‐planted riparian zones were generally closer to unplanted riparian zones than to natural riparian forests, the latter being more species‐rich for natives, trees, shrubs and zoochores, and species‐poor for exotics, forbs and stress‐tolerators. Likewise, seed bank species composition of unplanted and tree‐planted riparian zones was similar but differed from that of natural riparian forests. Conversely, standing vegetation of tree‐planted riparian zones was intermediate between early and late successional stages, at least at field edges. For the three successional stages, seed bank composition clearly differed from standing vegetation.ConclusionsThe high resilience of riparian plant communities appeared poorly related to the dynamics of their soil seed banks. This species shift between seed banks and standing vegetation during secondary succession is likely due to periodic flooding, leading to the regular turnover of seeds. The resilience of riparian communities might thus be more influenced by spatial dispersal along rivers and across landscapes than by in situ temporal dispersal in soils.

Relationship between the standing vegetation, soil properties and soil seed bank of an industrially degraded vegetation of Iron Smelting Factory

This study assessed the floristic composition, soil properties and the soil seedbank of the vegetation around the Iron smelting factory. This was with a view to determining the functional role played by soil chemical composition and the seed bank in the modifications of vegetation patterns. Five 100 m × 5 m plots were selected from the study site; vegetation, soil seed bank and some soil chemical parameters were assessed. One-way Analysis of Variance and Duncan multiple range tests were employed for data analysis. The results showed that the soil samples collected were slightly basic (or neutral) with the total Nitrogen in all the five plots ranged from 0.22 to 0.33%. There was a little contribution by woody species to the floristic composition of both the standing vegetation and soil seed bank. There was very low similarity (10.6% - 28.57%) between the standing vegetation and the soil seed bank species composition in the study site. The results of seedling emergence showed that herbaceous species dominated the soil seed bank compared to other life forms. Our result revealed a shift between seed-bank and vegetation composition which could be a consequence of the soil chemical properties and also as a result of different level of disturbance occurring due to the citing of industry in the area. Keywords : Emergence, nutrient cycling, regeneration, soil properties, soil seed bank, standing vegetation.

Vertebrate seed dispersers maintain the composition of tropical forest seedbanks.

The accumulation of seeds in the soil (the seedbank) can set the template for the early regeneration of habitats following disturbance. Seed dispersal is an important factor determining the pattern of seed rain, which affects the interactions those seeds experience. For this reason, seed dispersal should play an important role in structuring forest seedbanks, yet we know little about how that happens. Using the functional extirpation of frugivorous vertebrates from the island of Guam, together with two nearby islands (Saipan and Rota) that each support relatively intact disperser assemblages, we aimed to identify the role of vertebrate dispersers in structuring forest seedbanks. We sampled the seedbank on Guam where dispersers are absent, and compared this with the seedbank on Saipan and Rota where they are present. Almost twice as many species found in the seedbank on Guam, when compared with Saipan and Rota, had a conspecific adult within 2 m. This indicates a strong role of vertebrate dispersal in determining the identity of seeds in the seedbank. In addition, on Guam, a greater proportion of samples contained no seeds and overall species richness was lower than on Saipan. Differences in seed abundance and richness between Guam and Rota were less clear, as seedbanks on Rota also contained fewer species than Saipan, possibly due to increased post-dispersal seed predation. Our findings suggest that vertebrate seed dispersers can have a strong influence on the species composition of seedbanks. Regardless of post-dispersal processes, without dispersal, seedbanks no longer serve to increase the species pool of recruits during regeneration.

Influence of aboveground vegetation on seed bank composition and distribution in a Great Basin Desert sagebrush community

The quantity, composition, and spatial dispersion of seed banks can greatly affect community dynamics. While seed banks of hot deserts have been studied extensively, little is known about seed banks in cold deserts, in particular the relationship between the seed bank and the aboveground vegetation. We investigated the relationship between the seed bank and aboveground vegetation and the effect of microhabitat (shrub interspace or beneath shrub) and aboveground community phase (high or low perennial bunchgrass cover) on the seed bank of a Great Basin Desert sagebrush community. The seed bank and aboveground vegetation differed in their most dominant species, resulting in moderately dissimilar species compositions as determined by Sørensen's similarity index and Bray–Curtis distance. In contrast, comparing the seed bank species composition to the aboveground vegetation structure (functional groups) using non-metric multidimensional scaling (NMDS) revealed a correspondence between the two communities. Shrub seed densities were higher beneath shrubs. Neither microhabitat nor community phase explained variation in total seed density or species richness. Therefore, our measures of the aboveground vegetation did not influence seed density across functional groups or species richness, and the similarity between the seed bank and aboveground vegetation varied depending on the aboveground organizational level used in comparisons.

The influence of Pechuel-Loeschea leubnitziae (wild sage) on grass sward and soil seed bank composition

Soil seed banks provide not only a historical record of vegetation composition but also the potential for post-disturbance revegetation. Pechuel-Loeschea leubnitziae (wild sage) is a multistemmed, aromatic shrub, occurring in Namibia, Botswana, Swaziland, Zimbabwe and the northern regions of South Africa, that colonises disturbed regions on sandy, alkaline soils. The influence of differing levels of P. leubnitziae cover on soil seed-bank characteristics and aboveground herbaceous species composition was determined by examining aboveground species composition, recorded in the field, and soil seed-bank species composition, determined by recording germinations from topsoil samples collected at each of 104 sites in the southern Okavango Delta. No correlation was observed between aboveground and soil seed-bank composition (p = 0.209). Cover of P. leubnitziae did not affect soil seed-bank species composition (p = 0.31) or the grass:non-grass ratio within the seed bank (p = 0.308). It did, however, affect aboveground grass composition (p = 0.018), with increasing P. leubnitziae cover associated with increasing abundance of poor-quality, shade-tolerant grass species. This confirms the observations that encroachment of P. leubnitziae may be associated with a decrease in veld quality and carrying capacity, and highlights the necessity for further study to facilitate a better understanding of the species for management purposes.

Does aboveground vegetation composition resemble soil seed bank during succession in specialized vegetation on gypsum soil?

AbstractThis paper evaluates the aboveground vegetation in relation to the soil seed bank throughout a 60‐year succession process following agricultural abandonment in a semi‐arid Mediterranean gypsum habitat. There is little information regarding the relationship between these two community components in the context of succession on semi‐arid gypsum soils. Aboveground vegetation and the corresponding seed bank of gypsum plant communities were sampled through a chronosequence of 24 abandoned fields. Generalized linear models were used to model seed species richness and density, redundancy analyses to model the effect of time since abandonment and the effect of soil physicochemical parameters on seed bank species composition, and Mantel tests to analyze resemblance between above‐ and belowground species composition. In this last case, the effect of time since abandonment was controlled using a partial Mantel test. Mantel correlograms using time intervals instead of distances were used to describe the resemblance of above‐ to belowground species occurrence in different aged fields. No significant variability in seed species richness, seed density, or species composition due to time since abandonment was found. Differences in seed species composition were mainly due to small spatial scale predictors such as slope and soil calcium content. High correlations between species composition in the soil seed bank and the aboveground vegetation were detected during succession. The lack of a significant trend in aboveground species replacement over time was also reflected in seed bank composition. We concluded that the rapid establishment of strict gypsophyte species relied mainly on the long‐term persistence of these species in the seed bank.

Bacterial Communities Associated with Chenopodium album and Stellaria media Seeds from Arable Soils

The bacterial community compositions in Chenopodium album and Stellaria media seeds recovered from soil (soil weed seedbank), from bulk soil, and from seeds harvested from plants grown in the same soils were compared. It was hypothesized that bacterial communities in soil weed seedbanks are distinct from the ones present in bulk soils. For that purpose, bacterial polymerase chain reaction denaturing gradient gel electrophoresis (PCR-DGGE) fingerprints, made from DNA extracts of different soils and seed fractions, were analyzed by principal component analysis. Bacterial fingerprints from C. album and S. media seeds differed from each other and from soil. Further, it revealed that bacterial fingerprints from soil-recovered and plant-harvested seeds from the same species clustered together. Hence, it was concluded that microbial communities associated with seeds in soil mostly originated from the mother plant and not from soil. In addition, the results indicated that the presence of a weed seedbank in arable soils can increase soil microbial diversity. Thus, a change in species composition or size of the soil weed seedbank, for instance, as a result of a change in crop management, could affect soil microbial diversity. The consequence of increased diversity is yet unknown, but by virtue of identification of dominant bands in PCR-DGGE fingerprints as Lysobacter oryzae (among four other species), it became clear that bacteria potentially antagonizing phytopathogens dominate in C. album seeds in soil. The role of these potential antagonists on weed and crop plant growth was discussed.

Seasonal variation in seed bank composition and its interaction with nutrient enrichment in the Everglades wetlands

In the Florida Everglades, nutrient enrichment from agricultural outflow and the change in hydrology have collectively contributed to the expansion of cattails ( Typha spp.). To assess the effectiveness of prescribed fire in controlling cattails and to predict vegetation dynamics after the fire, it is important to understand the seasonal variation of the soil seed bank and how the seed bank is affected by nutrient enrichment and fire. This paper investigates the effects of season, nutrient enrichment, and fire on soil seed bank species composition, richness, and density along a nutrient gradient in Water Conservation Area 2A (WCA 2A) of the Florida Everglades. Species richness was significantly affected by nutrient enrichment and season but not their interaction. Total seed density, however, was significantly affected by the interaction between nutrient enrichment and season. Yet, at species level, the relationship between seed density, nutrient enrichment and season varied. The highest seed density of cattail occurred in summer at highly enriched sites, but that of sawgrass occurred in fall regardless of enrichment; the seed density of water lily was very low regardless of season and nutrient enrichment, and the highest Amarathus seed density occurred at highly enriched sites year round. Moreover, germination timing differed greatly among species. While cattail seeds had a short incubation period and started to germinate 2–3 days after initiation of the germination assay, sawgrass seeds generally started to germinate 4 weeks later. Further, both the prescribed summer fire at the highly enriched site and the natural winter fire at the moderately enriched site reduced the seed density of cattail but not of sawgrass. Our results suggest that fire application for vegetation recovery in WCA 2A would benefit from explicitly considering seasonal dynamics of the seed bank.

Seasonal and spatial variance of seed bank species composition in an oligotrophic wet meadow

Seasonal and small-scale spatial variation of the seed bank in an oligotrophic wet meadow ( Molinion) was assessed by two methods: (1) direct determination of seeds extracted from soil samples (6 cm in diameter, 10 cm depth) and (2) germination of seeds according to Ter Heerdt et al. [1996. An improved method for seed bank analysis: seedling emergence after removing the soil by sieving. Funct. Ecol. 10, 144–151]. Samples were taken three times during the year (July and November 2001, March 2002) from three distinct microhabitats (moss layer, gaps, Molinia caerulea tussocks). Using the extraction method, more seeds were found in the upper 0–3 cm soil layer than in the deeper 3–7 cm layer, significant differences in the number of seeds were found among microhabitats (with the lowest seed bank densities in Molinia tussocks). The highest number of seeds was found in the spring census, but the test was not significant ( P<0.10). However, seasonal variation was found when damaged seeds were included in the analysis. Changes in damaged/undamaged and light/heavy seed ratios, and in numbers of grass/herbs/sedges seeds are also discussed. The spatial distribution of seeds is probably influenced to a great degree by abiotic factors, such as microtopography (round and heavy seeds of sedges prevail in gaps and in deeper soil layers). The species composition of the seed bank varied among microhabitats, depth, and throughout the year. No differences were found by the seed germination method.