Soil Seed Bank Composition Research Articles

Soil Seed Bank Dynamics of a Riparian Forest and its Adjacent Upland Vegetation

The present study was conducted to determine the densities and soil seed bank composition of a riparian forest and its adjacent upland vegetation for a better understanding the potentials of the soil seed banks in facilitating succession towards a more natural forest of native tree species. Three contiguous 20 m x 20 m plots were systematically established on both riparian forest and upland vegetation. Species enumeration, identification and distribution into families of the standing vegetation were carried out. Furthermore, five replicates soil samples were collected at two different depths (0-15 cm, 15-30 .The seedling emergence test was carried out for six months in the greenhouse to determine the species composition and the density of the seed in both vegetation types. The results of the seedling emergence revealed that more seeds were deposited at the upper depth (0-15 cm) than the lower depth 15-30 cm in the two vegetation types in both dry and rainy season. There was low similarity in species composition between the standing vegetation and soil seed bank in each of the two vegetation types. Herbaceous species recorded the highest number of seedlings as compared to the other habit. The low similarity between seed bank and standing vegetation of the riparian forest and the adjacent upland vegetation suggested that soil seed bank was insignificant in their restoration.

Soil Seed Bank Dynamics of a Riparian Forest and its Adjacent Upland Vegetation

The present study was conducted to determine the densities and soil seed bank composition of a riparian forest and its adjacent upland vegetation for a better understanding the potentials of the soil seed banks in facilitating succession towards a more natural forest of native tree species. Three contiguous 20 m x 20 m plots were systematically established on both riparian forest and upland vegetation. Species enumeration, identification and distribution into families of the standing vegetation were carried out. Furthermore, five replicates soil samples were collected at two different depths (0-15 cm, 15-30 .The seedling emergence test was carried out for six months in the greenhouse to determine the species composition and the density of the seed in both vegetation types. The results of the seedling emergence revealed that more seeds were deposited at the upper depth (0-15 cm) than the lower depth 15-30 cm in the two vegetation types in both dry and rainy season. There was low similarity in species composition between the standing vegetation and soil seed bank in each of the two vegetation types. Herbaceous species recorded the highest number of seedlings as compared to the other habit. The low similarity between seed bank and standing vegetation of the riparian forest and the adjacent upland vegetation suggested that soil seed bank was insignificant in their restoration. &nbsp

Species shifts in above-ground vegetation and the soil seed bank in the inter-dune lowlands of an active dune field in Inner Mongolia, China

Degradation of semi-arid ecosystems leading to desertification presents a global environmental challenge. However, few studies have investigated seed bank and above-ground species composition in degraded semi-arid dune systems, particularly in relation to their potential to contribute to stabilisation and revegetation. We determined whether soil seed bank and above-ground species composition differed along a chronosequence in the inter-dune lowlands of an active dune field in Inner Mongolia, China. Soil cores were collected in early April 2011 and soil seed bank composition determined using a combination of the seedling emergence and seed extraction methods. Established vegetation, including species composition and abundance, was also surveyed. Relative importance values for all above-ground species and similarities in species composition of vegetation and soil seed bank along the chronosequence were analysed. A clear successional trend was shown for established vegetation along the first three stages identified, followed by a final stage reverting to more mobile substrate due to disturbance by dune movement. This trend was not reflected in the seed bank. Plant and seed bank density increased over time, however, species composition of the seed bank reflected earlier stages rather than the corresponding established vegetation. There was a relationship between established vegetation and the soil seed bank at the earliest stage, driven mainly by the persistence of seeds of the pioneer species Agriophyllum squarrosum and Corispermum candelabrum. A relatively close relationship was also found at the final stage, where frequent disturbance occurred as a result of increasing sand burial, caused by constant directional sand dune movement. While a clear relationship between the seed bank and associated vegetation was not found along the whole chronosequence, the seed bank displayed potential for restoration of pioneer psammophytes and annual herb species, suggesting that it would contribute to regeneration, as well as support latter-stage annuals and several rare and endemic species.

Nurse plant effects of a dominant shrub (Duma florulenta) on understorey vegetation in a large, semi‐arid wetland in relation to flood frequency and drying

AbstractQuestionsDo nurse plant interactions significantly influence understorey vegetation diversity in a large, semi‐arid, shrub‐dominated wetland? How do the modes and net effects of nurse plant interactions vary spatially along a flood frequency gradient, and temporally in response to drying?LocationNarran Lakes Ramsar site, New South Wales, Australia.MethodsMicrohabitat characteristics, understorey vegetation and germinable soil seed banks were investigated in shrub and open habitats across a flood frequency gradient in a large, semi‐arid wetland dominated by open shrubland under productive conditions following floodwater recession and again following 6 mo of drought. Split‐plot ANOVA and multivariate analyses were used to determine the effects of shrubs on microhabitat character, understorey vegetation cover, species diversity, richness and composition and germinable soil seed banks.ResultsMicrohabitat characteristics, including canopy cover, litter cover and soil character, all differed between shrub and open habitats, especially in the most frequently flooded sites. Under productive conditions following flooding, lignum shrubs suppressed understorey vegetation cover but increased species richness at the site scale across the flood frequency gradient and, in the most frequently flooded sites, supported higher species density at a microhabitat scale. Under dry conditions, lignum shrubs had a positive effect on understorey vegetation cover, species richness and species density across the flood frequency gradient, but particularly in frequently flooded sites. A significant difference in soil seed bank composition between shrub and open habitats was only observed in frequently flooded sites.ConclusionsNurse plant interactions appear to play an important role in determining understorey vegetation diversity in the lignum shrubland of the Narran Lakes wetland system. The modes and net effects of these nurse plant interactions vary in space and time in relation to flood history and drying. Positive interactions, probably involving microhabitat amelioration, appear to be particularly important to plant diversity and abundance under dry conditions. Under more favourable wetter conditions, lignum shrubs also contribute to understorey vegetation diversity by facilitating the establishment of different species than those dominating open habitats. Our findings have implications for the management of perennial shrubs and hydrological regimes in such wetlands.

Effects of 10-year management regimes on the soil seed bank in saline-alkaline grassland.

BackgroundManagement regimes for vegetation restoration of degraded grasslands can significantly affect the process of ecological succession. However, few studies have focused on variation in the soil seed bank during vegetation restoration under different management regimes, especially in saline-alkaline grassland habitats. Our aim was to provide insights into the ecological effects of grassland management regimes on soil seed bank composition and vegetation establishment in mown, fenced, transplanted and natural grassland sites, all dominated by the perennial rhizomatous grass Leymus chinensis.MethodologyWe studied species composition and diversity in both the soil seed bank and aboveground vegetation in differently managed grasslands in Northeast China. An NMDS (nonmetric multidimensional scaling) was used to evaluate the relationship between species composition, soil seed banks, aboveground vegetation and soil properties.Principal FindingsFenced and mown grassland sites had high density and species richness in both the soil seed bank and aboveground vegetation. The Transplanted treatment exhibited the highest vegetation growth and seed production of the target species L. chinensis. Seeds of L. chinensis in the soil occurred only in transplanted and natural grassland. Based on the NMDS analysis, the number of species in both the soil seed bank and aboveground vegetation were significantly related to soil Na+, Cl-, RSC (residual sodium carbonate), alkalinity, ESP (exchangeable sodium percentage) and AP (available phosphorus).ConclusionsSoil seed bank composition and diversity in the saline-alkaline grassland were significantly affected by the management regimes implemented, and were also significantly related to the aboveground vegetation and several soil properties. Based on vegetative growth, reproductive output and maintenance of soil seed bank, the transplanting was identified as the most effective method for relatively rapid restoration of the target species L. chinensis. This approach could be beneficial for the restoration of dominant species in a wide range of degraded grassland ecosystems.

Invasive earthworms shape forest seed bank composition

AbstractAimTo assess how non‐native earthworm and non‐native plant invasions shape soil seed bank composition in deciduous temperate forests.LocationNew York State, USA.MethodsWe recorded earthworm density, earthworm biomass and vegetation composition in 12 deciduous forests and subsequently collected soil cores and recorded emergence of plant species from the seed bank. We used path analysis to assess direct and indirect contributions of earthworms and vegetation composition (species richness and cover of native and non‐native plants) to the species richness and abundance of emergent seedlings.ResultsHigh earthworm populations were positively associated with increased species richness and seedling density of both native and non‐native plant species emerging from the seed bank. This relationship held for all life‐form groups, although the earthworm effect was indirect for non‐native graminoid abundance. Non‐native plants were positively correlated with earthworms and while they influenced both aboveground vegetation cover and species richness, they had no direct influence on emergent abundance or species richness.Main conclusionsOur results suggest that forest seed bank composition is strongly influenced by the presence and abundance of non‐native earthworms, and only weakly influenced by non‐native plants. Forest understorey recovery from seed banks is possible following earthworm invasion, but resulting communities bear little similarity to standing vegetation. Recovery of the full desirable and typical complement of aboveground vegetation will require input to seed banks by (1) fostering seed production of existing vegetation and/or (2) planting seed of desired species. We suggest managing understorey vegetation to allow herbaceous species to set seed.

Soil Seed Bank of An Exotic Acacia sp. Plantation and An Adjacent Tropical Heath Forest in Brunei Darussalam

We compared seedling emergence and soil seed bank composition under an Acacia mangium plantation and an adjacent tropical heath forest in the Andulau Forest Reserve, Brunei Darussalam. Soil samples were collected from ten 20 x 20 m plots set up in three contrasting habitats: the Acacia plantation, the adjacent heath forest, and the transition zone in-between. Soil samples were subjected to smoke and heat treatments, following which seedling emergence was observed daily over a 12-week period. In a parallel investigation, variations in species richness, seed density and seed viability of the soil seed banks of the ten plots were investigated. Seedling emergence was significantly highest in the plantation and lowest in the heath forest plots respectively. However, no significant differences among treatments, and no significant treatment-habitat interactions were detected. Species richness, seed density and seed viability in the plantation plots were significantly lower than the transition zone and intact heath forest plots. A. mangium seeds were not recorded in the heath forest soil seed banks but were detected in the plantation and transition zone plots. Lower native plant species richness, seed density and viability in the A. mangium plantation could imply higher regeneration potential for the heath forest habitat if severe habitat destruction was to occur in this forest reserve. We suggest that proper plantation management practices and close monitoring of soil seed banks are the best mechanisms that could be adopted to minimize the gradual spread of invasive Acacias into natural tropical heath forests of Borneo.

Soil seed banks of fringing salt lake vegetation in arid Western Australia – density, composition and implications for postmine restoration using topsoil

SummaryAlthough studies of seed banks in arid ecosystems are commonplace, they are lacking for the large arid zone of Western Australia. Across the six major plant communities fringing a large salt lake within this zone, topsoil (0–5 cm depth) was collected from 12 to 36 sites per community. Samples were dried, spread out on a bed of vermiculite in seedling trays and placed in a well‐watered glasshouse to determine the readily germinable component of the soil seed bank. Subsamples of topsoil were treated with smoke water, hot water or flooding to help determine seed bank of species with dormancy mechanisms. As with other studies of arid seed banks, large numbers of grasses and forbs emerged from the topsoil, with relatively small numbers of woody perennial species and hummock grasses (Triodia spp.) present, even in communities where such species were dominant. There were, however, a few exceptions where a reasonable density of dominant trees/shrub seed was present in topsoil. Soil treatment generally had limited effect on composition and density of emergent seedlings. Although floristic similarity between soil seed banks and corresponding above‐ground vegetation was modest, there were clear differences in soil seed bank composition between communities. The implications of the results for using topsoils to restore landforms of the study area after mining or other disturbance are discussed.

Soil seed-bank composition reveals the land-use history of calcareous grasslands

We compared soil seed banks and vegetation of recent (established on abandoned arable fields) and ancient (continuously managed as pastures at least since 1830) calcareous grasslands if there is any impact of former arable field use. The study was carried out in two regions of Southern Germany with well-preserved dry grassland vegetation: the western Jurassic mountains (Kaltes Feld) and the climatically drier eastern part of Southern Germany (Kallmünz).Total number of species in the seed bank was similar in both regions, but species composition partly differed, reflecting phytogeographical differences between the regions. The total number of emerged seedlings showed a large disparity (5457 compared to 2523 seedlings/m2 in Kaltes Feld and Kallmünz, respectively).Though there were differences in seed bank composition and size, we found a uniform pattern of plant traits (affiliation to phytosociological groups, Raunkiaer plant life-forms and seed longevity), which depended on the age of the grassland.The main conclusion is that seed banks in contemporary calcareous grasslands still reflect the history of former land use – in this case arable cultivation, even though it occurred a long time ago (up to 150 years). Indicators of former arable fields are germinable seeds of weeds which have persisted in the soil to the present. By contrast, weedy species are completely absent from the seed banks of ancient grasslands. Soil seed banks of recent grasslands may be of substantial conservation importance because they may store seeds of rare and endangered weed species such as Kickxia spuria, Silene noctiflora and Stachys annua, the majority of which have already gone extinct from the current vegetation of the study sites.

Soil seed bank community structure of pastures and hayfields on an organic farm

Sanderson, M. A., Stout, R., Goslee, S., Gonet, J. and Smith, R. G. 2014. Soil seed bank community structure of pastures and hayfields on an organic farm. Can. J. Plant Sci. 94: 621–631. Understanding the composition of seed banks in pasture soils would help farmers anticipate and manage for weed problems. We characterized the soil seed bank in eight pastures and hayfields [two alfalfa (Medicago sativa L.) and two predominantly grass hayfields; two recently established and two permanent pastures] within an organic dairy farm in southeastern New Hampshire. Seed banks were sampled in the upper 5 cm of soil in each field at a point scale in 2007 and 2010. In 2010, the seed bank was characterized at the field scale by taking soil samples on six 52-m transects in each field. Seed banks sampled at the field scale in 2010 contained 66 plant species. The total number of seeds in the seed bank ranged from 1560 m−2 in grass hayfields in autumn to more than 20 000 m−2 in alfalfa hayfields in summer. Annual forbs dominated the seed bank of alfalfa fields and recently established pastures, whereas perennial graminoids dominated in one grass hayfield and the permanent pastures. These results suggest that management history affects soil seed bank composition and abundance, and these effects should be considered before implementing management practices that could stimulate recruitment from the seed bank.

Assessment of Soil Seedbank Composition of Woody Species in Hgumbirda National Forest Priority Area, Northeastern Ethiopia

Detail study on soil seedbank composition and regeneration potential is needed for Ethiopian forests. In present work, soil seedbank assessment of woody plant species was made in Hgumbirda national forest priority area so as to evaluate composition and estimate their regeneration status. A total of 36 quadrates were established in selected four sites of the forest. The quadrates (20 m x 20 m) were laid along line transects. Soil samples were collected from sub-quadrates measuring 10 cm x 10 cm. Composition and status were determined by direct count and seedling emergence technique. Results showed the presence of seeds of 19 plant species in the soil. Juniperus procera had the highest viable seed density. Only Afrocarpus falcatus seeds were non-viable although very abundant (266.7seeds/m2). Except Cupressus lusitanica, no exotic woody species were found. The Shannon diversity index demonstrated low value for soil seedbank in Hgumbirda NFPA (H’=1.763). There was also significant variation of seed distribution between soil layers of the four selected forest sites (p<0.05). Jaccard’s coefficient of similarity between the standing vegetation and soil seedbank showed low value (JCS = 0.21 - 0.43). From the results, appropriate management strategies including preparation of nursery sites for selected indigenous plant species is suggested. Keywords : Soil, Seedbank, Woody species, Viable seeds, Afromontane, Hgumbirda forest, Regeneration, Ethiopia.

Effects of fire regime shift in Mediterranean Basin ecosystems: changes in soil seed bank composition among functional types

We studied the soil seed bank in a possible scenario of fire regime shift and asked: (1) Does high fire frequency impact the density of seeds stored, species richness and evenness? (2) Overall, does high fire frequency produce changes in the presence–absence and abundance of species? The study was implemented in a Mediterranean Basin ecosystem in plots with increasing fire frequency (unburned, burned once and burned twice in the last 66 years). The number of seeds increased with fire frequency for all life forms (shrub, scrub, perennial forb, annual forb and perennial graminoid). Species richness of annual forbs also increased. Evenness of shrubs diminished because the number of seeds in all the species decreased, except C. albidus, which increased. Overall, differences in the abundance of species were found, mainly by depleting shrubs and increasing forbs. There were no differences in the presence–absence data. In conclusion, high fire frequencies act as a filtering factor for species of a larger size and advanced maturity age. In contrast, life forms of small size and rapid onset of reproductive maturity can be enhanced. This community conversion from woody to herbaceous soil seed banks is fundamental to identify vegetation changes in future regimes of high fire frequency.

Deer Browsing Delays Succession by Altering Aboveground Vegetation and Belowground Seed Banks

Soil seed bank composition is important to the recovery of natural and semi-natural areas from disturbance and serves as a safeguard against environmental catastrophe. White-tailed deer (Odocoileus virginianus) populations have increased dramatically in eastern North America over the past century and can have strong impacts on aboveground vegetation, but their impacts on seed bank dynamics are less known. To document the long-term effects of deer browsing on plant successional dynamics, we studied the impacts of deer on both aboveground vegetation and seed bank composition in plant communities following agricultural abandonment. In 2005, we established six 15×15 m fenced enclosures and paired open plots in recently fallowed agricultural fields near Ithaca, NY, USA. In late October of each of six years (2005–2010), we collected soil from each plot and conducted seed germination cycles in a greenhouse to document seed bank composition. These data were compared to measurements of aboveground plant cover (2005–2008) and tree density (2005–2012). The impacts of deer browsing on aboveground vegetation were severe and immediate, resulting in significantly more bare soil, reduced plant biomass, reduced recruitment of woody species, and relatively fewer native species. These impacts persisted throughout the experiment. The impacts of browsing were even stronger on seed bank dynamics. Browsing resulted in significantly decreased overall species richness (but higher diversity), reduced seed bank abundance, relatively more short-lived species (annuals and biennials), and fewer native species. Both seed bank richness and the relative abundance of annuals/biennials were mirrored in the aboveground vegetation. Thus, deer browsing has long-term and potentially reinforcing impacts on secondary succession, slowing succession by selectively consuming native perennials and woody species and favoring the persistence of short-lived, introduced species that continually recruit from an altered seed bank.

Effects of disturbance and altitude on soil seed banks of tropical montane forests

Abstract:Vast areas of tropical forests have been deforested by human activities, resulting in landscapes comprising forest fragments in matrices of deforested habitats. Soil seed banks (SSB) are essential sources for the regeneration of tropical forests after disturbance. In a fragmented montane landscape in the Bolivian Andes, we investigated SSB in three different habitat types that were associated with different degrees of disturbance, i.e. in forest interior, at forest edges and in deforested habitats. Sampling of habitats was replicated at six sites ranging in altitude from 1950 to 2450 m asl. We extracted seeds from dried soil samples by sieving, classified seeds into morphospecies and size classes, and characterized SSB in terms of density, species richness and composition. We tested effects of disturbance (i.e. habitat type) and altitude on SSB characteristics. Overall, small seeds (&lt;1 mm) dominated SSB (81% of sampled seeds). Seed density and species richness were lowest in deforested habitats, especially in large seeds and distant from adjacent forests (≥20 m), while small-seeded species were most numerous near forest margins. Species turnover between habitats was high. Altitude altered the composition of SSB, but had no effects on seed density and species richness. We conclude that the potential of SSB for natural regeneration of deforested habitats is low and decreases with increasing distance from forest remnants and that forest edges may be eventually invaded by small-seeded species from deforested habitats.

Soil seed bank in selected patches of vegetation in the beech forest of Beskid Śląski (Southern Poland)

The aim of this study was to examine the size and composition of soil seed bank in the beech forest of Beskid Śląski (southern Poland). The study was conducted in autumn 2009 on two patches of vegetation. The applied method of research was seedling germination from the soil samples. The soil was sampled to the depth of 10 cm using a 5 cm diameter cylinder. The observation of the seedling's growth was conducted in laboratory conditions for 5 months. The size of the soil seed bank was estimated at 592 seeds/m (16 species) for Dentario glandulosae-Fagetum community and 2030 seeds/m (9 species) for Luzulo nemorosae-Fagetum comunnity. Dominant species in the seed bank was Juncus sp. and Luzula luzuloides. In addition, the composition of the seed bank and the above-ground vegetation did not show any significant similarities and a greater number of seeds were located in the upper 5cm layer of soil.

Long‐term monitoring of mammals in the face of biotic and abiotic influences at a semiarid site in north‐central Chile

AbstractThe data set covers a 16‐year period (1989–2005) of monthly small‐mammal surveys and associated habitat and environmental data. Small mammals are trapped every month on all experimental plots, and both ephemeral and perennial plant cover and soil seed bank composition are measured at regular intervals. Rainfall is recorded and compiled annually (through 1998) or monthly; information on captured small mammals and on all vegetative and rainfall data is contained in associated files. These data have been applied to diverse population‐ and community‐level analyses and remain useful for investigations of population dynamics, species interactions, and the relative influence of biotic and abiotic factors. Sampling is ongoing, and data will be added over time.

Changes in soil seed bank composition during early succession of rehabilitated quarries

To evaluate the contribution of seed bank to natural revegetation, a soil seed bank study was carried out at different phases on three quarries in Hong Kong. A total of 2188 seedlings from 57 species were found, among which 36 species were herbaceous and graminoid plants while 21 were woody species. The soil seed banks were dominated by a few annual species, i.e. Ageratum conyzoides, A. houstonianum, Cynodon dactylon, Digitaria longiflora and Kyllinga brevifolia, which accounted for more than 35% of the total abundance. With ecological development, greater species number as well as seed density and diversity were recorded at older rehabilitated sites, which indicated that the process favors the increase in species richness. However, non-woody species predominated in all phases including those that were even more than 10 years after rehabilitation. The result of DCA showed that only 21 woody species which included 15 native species were better represented on the older quarry sites, which may still be insufficient to initiate natural succession at the later successional stage. As most native species in the soil seed banks were dispersed by birds, management strategies should take into account the possibility of enrichment planting with native species in the early stage and sowing some late successional species in the later stage for quarry rehabilitation.

Change in Leafy Spurge (Euphorbia esula) Density and Soil Seedbank Composition 10 Years following Release of Aphthona spp. Biological Control Agents

AbstractFlea beetles (Aphthona spp.) were released in the Little Missouri National Grasslands (LMNG) in western North Dakota in 1999 to control leafy spurge. The changes in leafy spurge density and soil seedbank composition were evaluated on two ecological sites 10 yr (2009) after Aphthona spp. release to monitor the effectiveness of the insects on weed control and the associated changes in plant communities. In 2009, leafy spurge stem density averaged 2 and 9 stems m−2 (0.19 to 0.84 ft−2) in the loamy overflow and loamy sites, respectively, compared with 110 and 78 stems m−2, respectively, in 1999. Leafy spurge constituted nearly 67% of the loamy overflow seedbank in 1999, compared with 2% in 2009. In the loamy seedbank, the weed represented nearly 70% in 1999, compared with approximately 15% in 2009. As leafy spurge abundance was reduced, native species richness and seed count increased 10 yr after Aphthona spp. release. Late seral species represented 17% of the loamy overflow seedbank in 2009, an increase from 5% in 1999. However, Kentucky bluegrass, a nontarget weedy species, increased more than 250% in the loamy overflow seedbank. Late seral species were 38% of the loamy seedbank in 2009, compared with 13% in 1999. The number of native species increased from 31 in 1999 to 39 in 2009 in the loamy overflow seedbank, but only changed from 32 to 34 species in the loamy site during the same period. The reestablishment of native species has been slow, but seedbank analysis indicates the number and type of species found before the leafy spurge infestation have increased. Planting native species in selected areas may have reduced the lag time in these species return to the seedbank and reduced invasion from other nondesirable species, such as Kentucky bluegrass.

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.

Effects of elevated nitrogen and exotic plant invasion on soil seed bank composition in Joshua Tree National Park

We investigated the effects of exotic species invasion and 3 years of nitrogen (N) fertilization on the soil seed bank in Joshua Tree National Park, California, USA at four sites along an N deposition gradient. We compared seed bank composition and density in control (no N added) and fertilized (30 kg N ha−1 year−1) plots to determine if the seed bank would reflect aboveground changes due to N fertilization. Soil samples were collected and germinated in a greenhouse over 2 years. In the field, invasive species cover responded positively to N fertilization. However, we did not observe increased seed density of exotic invasive species in fertilized plots. While no significant differences were detected between treatments within sites, exotic invasive grass seeds overwhelmed the seed bank at all sites. Significant differences between sites were found, which may be due to differences in level of invasion, historic N deposition, and soil surface roughness. Sites experiencing low N deposition had the highest seed bank species richness for both control and fertilized treatments. Aboveground plant density did not correlate well with seed bank density, possibly due to the inherent patchiness of soil seed banks and differential ability of species to form seed banks. This seed bank study provided insight into site-specific impacts on native versus invasive species composition of soil seed banks, as well as magnitude of invasion and restoration potential at invaded sites.