Soil Seed Bank Composition Research Articles

Raised atmospheric CO2 levels affect soil seed bank composition of temperate grasslands

AbstractQuestionsSoil seed banks buffer plant populations against environmental variability. But environmental changes can have profound impact on them. Several studies addressed the effect of climate change on aboveground vegetation, but studies on changes in the seed bank are rare. Thus, we studied the seed bank of a temperate grassland at a long‐term FACE (Free‐Air Carbon dioxide Enrichment) site, with the following questions: (a) Are there general differences in the species composition between aboveground vegetation and seed bank; (b) what are the impacts of elevated CO2 (eCO2) on seed density and species composition of the seed bank; and (c) are there differences in the functional traits of the seed bank species under eCO2 versus ambient CO2 (aCO2)?LocationTemperate grassland, Gießen, Germany.MethodThirty soil cores were taken in six FACE rings. Emerging seedlings were identified to species level after germination and aboveground vegetation was sampled. From the seed bank data, we derived diversity measures and weighted means of species traits, e.g., seed longevity and regeneration type, and compared eCO2 (+20% CO2 above ambient conditions) with aCO2 treatment.ResultsNonmetric multidimensional scaling ordination revealed a clear separation between seed bank and aboveground vegetation but no clear CO2 effect. Analyses revealed higher seed densities under eCO2. Species diversity and Shannon diversity were not significantly affected. Evenness decreased significantly under eCO2. There are shifts in functional traits of seed bank species. Seed density of long‐term‐persistent species increased, while short‐term‐persistent species decreased. Seed densities of species with generative reproduction increased under eCO2, while numbers of species with vegetative reproduction decreased.ConclusionThe observed trait compositions of the seed bank under eCO2 indicate that species relying on generative reproduction and production of long‐term‐persistent seeds have a competitive advantage under eCO2. The changes in the plant communities described above may lead to profound changes in the supply of grassland ecosystem services.

Contrasting land use systems influence soil seed bank composition and density in a rural landscape mosaic in West Africa

Soil seed banks (SSBs) play a key role in the post-disturbance recruitment of many plant species. Seed bank diversity can be influenced by spatial and environmental variability and disturbance heterogeneity across the landscape. Understanding the recovery potential of native vegetation from SSBs is important for restoration and biodiversity conservation. Yet, in savanna-woodland, little is known about how SSBs vary in their germination, composition and density under different land uses, and how SSBs relate to aboveground vegetation (AGV). Using a sampling design based on the Land Degradation Surveillance Framework, we assessed the SSB and AGV in twelve 0.25 ha plots among sixteen in four contrasting land use systems of savanna-woodland in Burkina Faso: bushland, cultivated farmland, fallow and wetland. A total of 720 soil samples were taken from four stratified depths of 0–5 cm, >5–10 cm, >10–15 cm, and >15–20 cm. The SSB composition and richness was determined by the seedling emergence technique. Results showed that the SSB in all land uses was largely dominated by annual grasses with few perennial herbaceous and woody species. Seed density was highest in the fallow soil and highest in the upper soil layers for all land uses. A non-metric multidimensional scaling ordination of the SSB and AGV indicated that the SSBs were a poor reflection of the AGV. Based on these findings, spatial variations in landscape characteristics not only influence seed distribution and viability but also have the potential to influence population persistence. These results imply that successful restoration of fragmented ecosystems requires the addition of seeds and seedlings of target species.

Influence of termites on the soil seed bank in an African savannah

AbstractIn savannah ecosystems, termites drive key ecosystem processes, such as primary production through creation of patchiness in soil nutrients availability around their nests. In this study, we evaluated the role of termites in altering the soil seed bank size, an important ecosystem component that has often been overlooked in previous work. Data on above ground vegetation and soil seed bank samples were collected from four microhabitats, that is, the wooded mound, unwooded mound, tree sub‐canopy and the open grassland matrix in a protected game reserve in south‐central Zimbabwe. The seedling emergence method was then used to identify species present in the soil samples. One‐way analysis of variance followed by Tukey's multiple comparison tests was executed to test for significant differences in plant species richness among the four microhabitats. The results indicate that plant species richness was high on wooded termite mound but did not differ between the unwooded and the sub‐canopy microhabitats. The open grassland microhabitat had the lowest plant species richness. The influence of termites on the soil seed bank composition was also life form specific. The herb and woody life forms had significantly (α = 0.05) higher species richness in the soil seed bank at wooded and unwooded termite mounds when compared to the other two microhabitats. Overall, these results imply that termites alter the soil seed bank and the findings enhance our understanding of the significant role termites play in regulating processes in savannah ecosystem.

Estimating the abundance and composition of soil seed bank at Bekol Savanna in Baluran National Park, West Java

The composition of soil-seed bank reflects the condition of vegetation in the past and could be used for predicting the composition of plants that will grow in the future. This study aims to determine the amount and composition of soil-seed bank in Bekol savanna, Baluran National Park. Soil samples were taken using a combination method of quadrat-transect on the invaded and not invaded areas by Acacia nilotica. Soil samples were extracted using wet-sieving method. After the extraction process, the seeds were identified and calculated using a stereo microscope. The result showed that soil-seed bank density was lower at the invaded location (7,566.88 seeds/m3) as compared to the uninvaded location (16,798.3 seeds/m3). The soil-seed bank was found in the invaded site comprising 12 species of broadleaved weeds and 5 species of grasses from 7 families, whereas those in the uninvaded area consisted of 10 species of broadleaved weeds and 7 species of grass from 8 families. This study showed that the invasion of A. nilotica significantly affected the amount and composition of soil-seed bank in various soil depths of Bekol savanna.

Sand dune stabilization changes the vegetation characteristics and soil seed bank and their correlations with environmental factors

Currently the amount of data available on the effect of sand dune stabilization on species conservation in inter-dune lowland is very limited, especially for the sand dune systems in semi-arid regions. In this study, we determined whether the characteristics of above-ground vegetation, soil seed bank and their relationships with environmental factors changed with sand dune stabilization in the inter-dune lowlands in Horqin Sandy Land, China. Species composition, abundance and coverage of aboveground vegetation as well as soil seed bank composition and density were surveyed and their correlations with environmental factors (pH, organic matter content, total nitrogen and total phosphorus) were determined. The results showed that changes in the relationship between aboveground vegetation, soil seed bank and soil quality followed the changes in aboveground vegetation and soil seed banks. Aboveground vegetation species richness increased with sand dune stabilization, but soil seed bank species richness declined. The inter-dune lowland of active sand dunes could provide specific habitats for some endemic species and pioneer psammophyte species as indicated by data on aboveground vegetation and soil seed bank. Our results suggested that both active and stabilized sand dunes should be maintained since active sand dunes are essential for the survival of endemic or pioneer species and stabilized sand dunes are important for sustaining species richness.

Comparison of aboveground vegetation and soil seed bank composition at sites of different grazing intensity around a savanna-woodland watering point in West Africa.

Grazing removes a plant's aboveground vegetative and reproductive tissues and can modify the soil seed bank, potentially impacting the restoration of preferred species. Knowledge about aboveground vegetation and species composition of soil seed bank and the processes that contribute to vegetation recovery on and surrounding watering points subjected to grazing is lacking. Successful restoration strategies hinge on addressing these knowledge gaps. We assessed the effects of livestock grazing on aboveground vegetation and soil seed bank characteristics along a river bank and surrounding areas subject to different grazing intensities and draw implications for restoration. Plots (50 × 50m) were established along five transects representing differing levels of grazing intensity. Soil samples were taken from three layers within each plot to determine soil properties and species composition of soil seed bank using the seedling emergence method. Heavy grazing resulted in the disappearance of perennial grasses, a reduction in species diversity and a decrease in soil nutrients with increased soil depth. Overall, the similarity between the extant aboveground vegetation and flora within the soil seed bank was low. The soil seed bank was dominated by herbaceous species and two woody species, suggesting that many woody species are not accumulating in the soil. With increasing soil depth, the seed density and richness declined. Canonical correspondence analyses (CCAs) showed that emerged seedlings from the soil seed bank were significantly influenced by soil carbon, organic matter, total nitrogen, total potassium and soil cation exchange capacity. This finding suggests that current grazing practices have a negative impact on the vegetation surrounding watering points; hence there is a need for improved grazing management strategies and vegetation restoration in these areas. The soil seed bank alone cannot restore degraded river banks; active transfer of propagules from adjacent undisturbed forest areas is essential.

Regenerative Role of Soil Seed Banks of Different Successional Stages in A Saline-alkaline Grassland in Northeast China

Soil seed banks can act as a potential seed source for natural revegetation and restoration. However, in a saline-alkaline grassland, it remains unclear how the stages of vegetation succession affect the characteristics of soil seed banks and the potential of soil seed banks of different successional stages for vegetation restoration. In this study, seasonal changes of the soil seed bank, and seed production and dispersal dynamics along degradation successional gradients were investigated in a saline-alkaline grassland in Northeast China, where the dominant grass during the 1960s, Leymus chinensis was replaced with the secondary successional order of Puccinellia chinampoensis, Chloris virgata, and Suaeda salsa, together with bare patches. It was found that the soil seed bank composition varied according to the changing vegetation and had the highest species richness (7–16) in the climax successional stage, but had a low Sorensen similarity (0.22–0.37) with the aboveground vegetation. There was a high seed density of the soil seed bank (21 062–62 166/m2 in August and December) and also high Sorensen similarity index values (0.47–0.60) in the secondary successional stages of P. chinampoensis, C. virgata, and S. salsa. In bare patches, there were many seeds in the soil seed bank and some seedlings also appeared in the aboveground vegetation, indicating the existence of a persistent soil seed bank. Seed density and species richness differed substantially among the different successional stages, which was related to the reproductive characteristics of the standing plants in vegetation communities. Due to the lack of propagules of perennial species, especially the climax species of L. chinensis, in the soil, the successful restoration of the degraded saline-alkaline grassland was not possible. The study proved that in a degraded saline-alkaline grassland dominated by biennial or annual species, the soil seed bank was important for the revegetation of the current dominant plants, but not for the restoration of the original target species. Therefore, it is necessary to induce seeds or other propagules of the target perennial species.

Seed Bank—Vegetation Dynamics along a Restoration Management Gradient in Pine Flatwoods Ecosystems of the Florida Gulf Coast

Pine flatwoods ecosystems of the Gulf Coastal Plains of the southeastern United States are known for their species richness, mainly contributed by herbaceous groundcover. However, intensive silvicultural operations and exclusion of fire over a large extent of these ecosystems in the past century has led to a serious depletion of groundcover diversity. Consequently, restoration of these ecosystems has become a high priority for ecological management of forests in the area. The present study was carried out at mesic-hydric flatwoods sites in northwest Florida to examine the effects of restoration activities, including varying intensities of thinning and prescribed burning, on the dynamics of the vegetation and the soil seed bank composition and structure. Three site conditions—degraded, partially restored, and restored—representing a restoration management gradient were sampled for aboveground vegetation and soil seed bank. Vegetation and seed bank composition changed following restoration activities. However, there was little effect on the seed bank structure across the site conditions. A total of 24, 59, and 124 species in the aboveground vegetation, and 26, 39, and 64 species in the seed bank were observed in degraded, partially restored, and restored site conditions, respectively. Most of the species in the seed bank were ruderal, although native. The effect of site conditions on seed density and seed species richness and diversity was not statistically significant. However, these characteristics did vary significantly with the soil depth (main effect) where the soil sample was taken. Higher seed densities were observed in top 0–5 and 5–10 cm than 10–15 cm soil depths across all sites. Seed banks tended to resemble each other more than the vegetation and the vegetation and seed bank across all sites. The presence of mostly ruderal species in seed bank in degraded site indicates that seed bank is not a good source of regeneration of typical flatwoods communities.

Diet switching of seed-eating birds wintering in grazed habitats of the central Monte Desert, Argentina

ABSTRACT Although bird population declines associated with land degradation are common, the initial response of organisms to rapid human-induced environmental change is usually behavioral. Reductions in seed availability due to cattle grazing may trigger diet switching in seed-eating birds, but empirical examples of such behavior are lacking. We asked whether cattle grazing changed the composition and reduced the size of seed reserves, and whether seed shortage caused diet shifts in 4 species of seed-eating birds wintering in the central Monte Desert, Argentina. We assessed the soil seed bank composition and the granivorous fraction of each species' diet. Digestive tract or crop contents were obtained by using the flushing method on individuals captured with mist nets, and seeds were sorted and assigned to 1 of 3 functional groups (small grass seeds, large and medium-sized grass seeds, or forb seeds). Cattle grazing reduced the abundance of the preferred large and medium-sized grass seeds by 60–90%. The g...

Spatial Variation of Soil Seed Bank under Cushion Plants in a Subalpine Degraded Grassland

AbstractCushion plants can affect wind speed and sediment movement patterns that probably modify the water and sediment redistribution along slopes and increase the accumulation of seeds under and around their canopies. This study was carried out to assess the spatial variability of soil seed bank (SSB) and seed bank composition around cushion plants to estimate the SSB potential for restoration of degraded area. Twenty cushions of Onobrychis cornuta were selected in a mountainous rangelands in northern Alborz in Iran, measuring density, richness and composition of SSB at four locations of each cushion (upslope edge, downslope edge, centre and outside). SSB composition and density were determined by seedling emergence method. The results showed that the locations of cushions had significant effect on density and richness of the SSBs. The highest SSB density and richness were observed in the centre and upslope edge of the cushions, while there was no significant differences of density and richness between downslope edge and outside (bare grassland soil) of the cushions. In addition, the results showed that seed bank composition was highly correlated between the four locations in the same cushion. We concluded that cushion plants can act as seed traps specially trapping seeds dispersed by barochory and hydrochory and therefore play an important role in conservation and recovery of degraded areas. Copyright © 2017 John Wiley & Sons, Ltd.

Weed Dynamics in No-Till Rainfed Crops in Chaouia, Semi-Arid Morocco

Three on-farm research-managed trials were conducted in Settat province, Chaouia, semi-arid Morocco, from 2012-13 to 2014-15, to investigate the dynamics of germinable soil seedbank, weed density, and community composition of weeds in 3 crop rotations: continuous durum wheat, barley + pea/durum wheat/durum wheat, and canola/durum wheat/durum wheat. Initial germinable weed seedbank density estimated in September 2012, before no-till planting in November 2012 was 1890 seeds m-2. After two growing seasons, seedbank reductions were 23% in continuous durum wheat, 68% in canola/durum wheat/durum wheat, and 72% in barley + pea/durum wheat/durum wheat. In continuous durum wheat, weed densities before no-till planting were 273, 46, and 59 plants m-2 in November 2012, December 2013, and November 2014, respectively. In herbicide-free barley + pea/durum wheat/durum wheat, weed densities before no-till planting durum wheat were 128 and 42 plants m-2 in December 2013 and November 2014, respectively. In canola/durum wheat/durum wheat, weed densities before no-till planting wheat were only 20 and 25 plants m-2 in December 2013 and November 2014, respectively. This study demonstrated the combined merits of pre-plant glyphosate, herbicide use in wheat, herbicide-free barley + pea haying, and durum wheat rotation with either canola or barley + pea to manage weeds in no-till systems in semi-arid Morocco.

The impact of pine plantations on fynbos above-ground vegetation and soil seed bank composition

Pine plantations and pine invasions have numerous impacts on native ecosystems in the Fynbos biome of South Africa. The severity of these impacts greatly determines the extent of potential ecosystem recovery after the pines are felled. The recovery potential of fynbos after felling of pine plantations of varying longevity and the subsequent application of ecological burns was investigated in the Helderberg Nature Reserve, Western Cape Province, South Africa. Above-ground vegetation, soil seed bank and abiotic variables were sampled across three treatments (reference fynbos and sites that had been under pines for 30 and 50years respectively) using 1m2 quadrats placed along 50m line transects. The soil seed bank samples were smoke treated and then monitored in a greenhouse to determine the soil seed bank species and growth form composition. Areas previously under 30year old pine plantations had high native species and growth form density (number of species/growth forms per unit area) and similar plant density (number of individuals per unit area) to the reference fynbos areas. Conversely, areas previously under 50year old pine plantations had significantly lower native species and growth form density and plant density than the reference fynbos and were dominated by alien species. In addition, areas previously under 50year old pine plantations had lower species diversity than the reference fynbos areas and areas previously under 30year old pine plantations which were found to be similar to one another. Felled pine plantations were shown to minimally impact on soil abiotic variables, with only soil temperature and pH showing significant differences. Therefore, areas previously under 30year old pine plantations have higher recovery potential following pine removal than 50year old plantations, owing to the depleted native soil seed bank in the latter. Consequently, active restoration may be needed to re-introduce the missing long-lived growth forms and to prevent soil erosion. Pine plantation and invasion management in the Fynbos biome should aim to fell pines before the native seed bank is depleted to maintain the recovery potential of fynbos and prevent the need for active restoration.

Leafy spurge (Euphorbia esula) Control and Soil Seedbank Composition Fifteen Years after Release of Aphthona Biological Control Agents

Aphthona spp. flea beetles were released in two ecological sites of the Little Missouri National Grasslands in southwestern North Dakota in 1999 to control leafy spurge. The change in leafy spurge density and soil seedbank composition was monitored to evaluate the effectiveness of the biological weed control agent and the associated change in plant communities 5, 10, and 15 yr after release in loamy overflow (valleys) and loamy sites (ridges). In 2014, 15 yr after release, leafy spurge stem density had decreased 94% from 110 to 7 stems m−2 in the loamy overflow sites and 88% from 78 to 9 stems m−2 in the loamy sites. Leafy spurge represented only 2% and 6% of the loamy overflow and loamy seedbanks in 2004, respectively, compared with nearly 67% and 70%, respectively, in 1999. There was a slow shift to reintroduction of native species into the seedbank over the last 15 yr. The number of desirable species increased to 21 by 2014 (more than three times the number of species in 1999) in the loamy overflow sites, and doubled to 14 species in the loamy sites, while less desirable forb species doubled in both sites. Desirable grass species doubled in the loamy overflow sites by 2014 but remained unchanged in loamy sites. Aphthona spp. successfully controlled leafy spurge for more than 15 yr without any additional control methods or costs to land managers and resulted in the slow return of a subset of native species.

Factors affecting soil seed banks of riparian communities in an agricultural ecosystem: potential for conservation of native plant diversity

AbstractQuestionsDo agricultural land use and nitrogen (N) enrichment have negative effects on riparian soil seed banks? What is the potential of the soil seed bank for the conservation and restoration of native riparian plant diversity? Are non‐native dominant grass species affected by agriculture and do they affect species richness?LocationSouth Nation River watershed (an agricultural watershed), Ontario, Canada.MethodsWe examined the riparian above‐ground vegetation at 24 sites located across a large (~4000 km2) North American watershed and identified the corresponding soil seed bank composition from soil cores using the seedling emergence method. The above‐ground vegetation and soil seed bank species compositions were compared in terms of species richness, percentage of non‐native species and a floristic quality index. Factors affecting these descriptors of plants communities (concentration of in‐stream nitrate and percentages of surrounding natural habitat and annual crop land) were assessed. The effects of agriculture on two dominant non‐native grasses species and their effects on species richness were also assessed.ResultsIn total, 274 plant taxa were identified, including 181 taxa in the soil seed bank and 231 taxa in the vegetation. Overall species richness was high in both the soil seed bank and above‐ground vegetation and was unaffected by measures of agricultural intensity (surrounding annual crop land and N enrichment). Above‐ground vegetation species richness was strongly negatively affected by the widespread and dominant non‐native grasses, Phalaris arundinacea and Bromus inermis, whereas soil seed bank species richness was unaffected. The community compositions of both the soil seed bank and vegetation were negatively affected by the loss of natural habitat and by N enrichment. In fact, an increase in the percentage of non‐native species and a decrease in floristic quality were observed along a gradient of agricultural intensity.ConclusionsSpecies richness of the soil seed bank demonstrated resilience to invasions by P. arundinacea and B. inermis, and the soil seed bank showed good potential for conservation of taxonomic diversity. However, the loss of natural habitat and N enrichment had negative effects on the soil seed bank community composition that may lead to an eventual decline in above‐ground species richness.

Characteristics of the soil seed bank of planted and natural restored draw-down zones in the Three Gorges Reservoir Region

The large-scale reverse seasonal water-level fluctuation caused by the Three Gorges Reservoir Project has dramatically changed the ecology of draw-down zones leading to degradation of local riparian vegetation. We studied the Wanzhou draw-down zones in the Three Gorges Reservoir Region via field investigations and soil seed bank (SSB) germination experiments. The composition and spatial distribution of the SSB in the planted and natural restored sites revealed the effects of restoration modes on seed bank development and demonstrated responses of SSB composition and structure to water fluctuation. The SSB of planted sites contained 43 species of plants, with a mean seed bank density of 9418.79 seeds/m2, where annual herb species accounted for 57.34%. The SSB at natural restored sites had 38 species of plants, with a mean seed bank density of 6090.09 seeds/m2, where annual herb species accounted for 52.57% of the species. Species diversity was low and annual plants dominated the two restoration sites. SSB species diversity was the highest in mid to upper levels of the draw-down zones. Plantation has increased co-occurrence species of SSB and standing vegetation, and increased their similarity. The number of co-occurrence dominant species of SSB and standing vegetation in planted areas was greater than in natural restored areas. However, the stability of plant communities naturally restored was greater than artificial plant communities as there was a higher proportion of perennials in the SSB with more dominant species similar to standing plant communities. In conclusion, the reverse water-level fluctuation simplified the species composition and shaped the spatial distribution of the SSB at the two restoration sites, and plantation promotes the development both of SSB and vegetation. However, plant communities of the two restoration areas, influenced by water-level fluctuations, will be mainly grasslands dominated by annual plants.

Tree species determine soil seed bank composition and its similarity with understory vegetation in a semi-arid African savanna

IntroductionThe presence of larger trees in semi-arid African savannas creates sub-habitats, which influences on herbaceous plant communities grown under their canopies differently from opened areas. Knowledge of seed banks accumulated in the soils over time beneath larger trees could facilitate the recovery of plant communities that might disappear due to sustained heavy grazing, prolonged fire, or other anthropogenic factors in semi-arid African savannas. However, the impact of larger trees on soil seed bank composition and its similarity with plant communities grown under their canopies are less understood in semi-arid African savannas. Therefore, we studied the effect of leguminous and non-leguminous tree species and their canopies on soil seed bank (SSB) composition and its similarity with understory vegetation (USV) in a semi-arid savanna of Ethiopia.MethodsWe selected 20 matured trees from 3 dominant tree species, representing one leguminous (Acacia robusta Burch) and 2 non-leguminous tree species (Ziziphus spina-Christi and Balanites aegyptiaca (L.) Del), found in isolation, a total of 60 trees for this study. Under each selected individual tree, the species composition of USV were recorded using 1-m2 quadrat in four directions (north, south, east, and west) under the inside and outside tree canopies during the flowering stage. Similarly, soil samples in a 1-m2 quadrat were also collected under the inside tree canopies and their corresponding outside canopies, in each individual tree, for the determination of SSB composition, using a seed emergence method. Then, the soil was thoroughly mixed after removal of all roots and plant fragments, and spread over sand in plastic pots to a depth of 20 mm. The pots were placed at random in a glasshouse, examined every 3 days, for the first 2 months, and thereafter weekly for 6 months. A total of 960 soil samples were used for the determination of SSB composition during this study.ResultsA total of 64 species were emerged from the SSB samples, of which 27 were grasses (19 annual and 8 perennial grasses), 35 annual forbs and 2 woody species. Acacia robusta had a higher seedling density in the SSB compared to other tree species, whereas Z. spina-Christi had higher species diversity in the SSB than other tree species. Moreover, seedling density and species diversity were higher under the inside canopies than outside tree canopies. The mean similarity in species composition between the SSB and USV was low. However, it was higher under the leguminous trees than non-leguminous trees, and under the inside tree canopies than outside canopies.ConclusionsWe found that mature tree species maintained a higher SSB species diversity and abundance under their canopies than the surrounding opened areas. Therefore, conservation of mature dominant tree species is of paramount importance for ecological stability and possible restoration of degraded semi-arid savannas under the changing climate and global warming.

Impact of Cardamom Cultivation on the Composition and Dynamics of Soil Seed Banks in a Conservation Forest in Sri Lanka: Implications for Conservation

Cultivation of cash crops, such as cardamom (Elettaria cardamomum) in the forest understorey is a common practice in many tropical forests. Over time, cultivation may change forest structure and species composition, leading to gradual degradation of biodiversity and ecosystem services. Effective conservation of these forests requires an enhanced understanding of the demographic processes such as soil seed bank that may greatly influence future forest composition. We examined how the soil seed bank structure and composition responds to cardamom cultivation in a high conservation value Sri Lankan montane rain forest. Soil samples from natural forest with abandoned cardamom plantations (CP) and adjacent natural forest (NF) patches without cardamom were collected in dry and wet seasons. Soil samples were spread out in trays in a shade house and germination was recorded weekly for 19 weeks. The density of seeds in the soil seed bank was much higher in CP than NF. While grasses and forbs contributed the highest number and percentage of seeds in soils of both forest types, their densities in the soil seed bank were 9 and 2 times greater in the CP than the NF, respectively. Seeds of the non-native herbs Ageratina riparia and E. cardamomum were 4 and 20 times greater in the soil of CP, respectively. Seeds of light demanding tree species such as Macaranga indica were restricted to soils of CPs. Overstorey tree community of each forest type was poorly represented in their respective soil seed banks. The high density of seeds of pioneer trees and non-native herbs in the soil of CPs, combined with higher light transmission to the ground floor may exacerbate competition for resources with the seedlings of late successional trees of high conservation value. To overcome this barrier and enhance conservation value of the forest, restoration strategies may need to focus on transplanting seedlings of these species into forest with abandoned cardamom plantations.

Long-Term Management Affects the Community Composition of Arable Soil Seedbanks

The intensification of farming practices has reduced weed infestations, but it has also led to a reduction in weed diversity and changes in species composition. These effects are well described for aboveground flora; however, it is less clear how these effects might be expressed in the soil weed seedbank. We evaluated the effects of different long-term farm management strategies on the weed seedbank abundance, diversity, and community composition in the DOK (bioDynamic, bioOrganic, and Konventionell) field trial established in 1978 at Therwil, Switzerland. The trial compares biodynamic, organic, and conventional farming systems, which mainly differ in fertilization, weed control strategies, and pest control. The species richness and seed abundance of the weed seedbank were higher in the organic and biodynamic systems compared with the conventional ones. The different farming systems favored shifts in species assemblages, because specific management practices, such as herbicide application and type of fertilization, acted as filters that selected against certain species but promoted others that were more adapted.

Effect of grazing removal on aboveground vegetation and soil seed bank composition in sub-alpine grasslands of northern Iran

Background: Knowledge about vegetation and soil seed bank composition and the processes that contribute to vegetation recovery after the removal of heavy grazing is lacking in sub-alpine ecosystems.Aims: In order to assess the effects of large herbivores on above-ground vegetation (AGV) and soil seed bank (SSB) characteristics, intensively sheep-grazed areas were compared to adjacent areas where grazing had been removed 10 years previously in a sub-alpine grassland of northern Iran.Methods: A total of 40 4-m2 (2 m × 2 m) plots were established in each treatment, and soil samples were collected from each plot within a depth of 10 cm. Plant species composition was determined for each plot during the flowering stage of herbaceous species in June 2011. The seedling emergence method was used to estimate SSB composition.Results: A total of 45 species (23 annuals and 22 perennials) emerged from the soil samples of the grazed area, while the number of species emerged from the soil samples of the previously grazing area was 76 (37 annuals and 39 perennials). The removal of grazing led to a significant increase in species richness and seed density in the SSB. Species turnover of AGV was higher, and that of the SSB was similar for grazed areas compared with areas that were formerly grazed. Detrended correspondence analysis ordination of AGV composition showed a clearly separate structure between grazed plots and plots where grazing has been removed, while the segregation was less clear for SSB composition.Conclusions: We concluded that restoration of locally degraded sites cannot rely on the SSB when grazing is stopped simultaneously and unvegetated gaps are colonised by vegetative growth rather than by seed.

Factors driving species assemblage in Mediterranean soil seed banks: from the large to the fine scale.

Many studies have analysed the mechanisms that determine plant coexistence in standing vegetation, but the determinants of soil seed bank species assemblies have rarely been studied. In gypsum soil communities, aerial vegetation and seed banks are tightly connected in space and time, but the mechanisms involved in their organization may differ. The aim of this study is to understand the relative importance of biotic and abiotic factors controlling soil seed bank composition and structure. Persistent and complete (i.e. persistent plus transient) soil seed banks were investigated at two spatial scales in a very species-rich semi-arid community dominated by annuals. A water addition treatment equivalent to 50 % annual increase in average precipitation (abiotic factor) was applied for two consecutive years, and the relationships of the soil seed bank to the biological soil crust (BSC), above-ground vegetation and the presence of Stipa tenacissima tussocks (biotic factors) were simultaneously evaluated. As expected, the standing vegetation was tightly related to seed abundance, species richness and composition in both seed banks. Remarkably, BSC cover was linked to a decrease in seed abundance and species richness in the persistent seed bank, and it even determined complete seed bank composition at the fine spatial scale. However, this effect disappeared at coarser scales, probably because of the high spatial heterogeneity induced by BSCs. In contrast to findings on standing vegetation, Stipa and the irrigation treatment for two consecutive years had no effect on soil seed banks. Soil seed bank assemblies in our semi-arid plant community were the result of above-ground vegetation dynamics and of the direct filtering processes on seed fate operated by the spatially heterogeneous BSCs. Cover of BSCs was negatively correlated with seed abundance and species richness, and affected seed species composition in the soil. Changes in species composition and enrichment when the BSC cover is low suggest that BSCs promote a fine scale niche differentiation in the soil seed bank and thereby potentially enhance species coexistence and high species diversity in these communities.