Mowing Reduces Exotic Annual Grasses but Increases Exotic Forbs in a Semiarid Grassland

Cheatgrass (Bromus tectorum) and other exotic winter‐active plants can be persistent invaders in native grasslands, growing earlier in the spring than native plants and pre‐empting soil resources. Effective management strategies are needed to reduce their abundance while encouraging the reestablishment of desirable native plants. In this 4‐year study, we investigated whether mowing and seeding with native perennial grasses could limit growth of exotic winter‐actives, and benefit growth of native plants in an invaded grassland in Colorado, United States. We established a split‐plot experiment in October 2008 with 3 mowing treatments: control, spring‐mowed, and spring/summer‐mowed (late spring, mid‐summer, and late summer), and 3 within‐plot seeding treatments: control, added B. tectorum seeds, and added native grass seeds. Cover of plant species and aboveground biomass were measured for 3 years. In March and June of 2010, 2011, and March of 2012, B. tectorum and other winter‐annual grasses were half as abundant in both mowing treatments as in control plots; however, cover of non‐native winter‐active forbs increased 2‐fold in spring‐mowed plots and almost 3‐fold in spring/summer‐mowed plots relative to controls. These patterns remained consistent 1 year after termination of treatments. Native cool‐season grasses were most abundant in spring‐mowed plots, and least abundant in control plots. There was higher cover of native warm‐season grasses in spring/summer‐mowed plots than in control plots in July 2011 and 2012. The timing of management can have strong effects on plant community dynamics in grasslands, and this experiment indicates that adaptive management can target the temporal niche of undesirable invasive species.     

Long‐term changes in semi‐arid vegetation: Invasion of an exotic perennial grass has larger effects than rainfall variability

Abstract. Questions: This paper examines the long‐term change in the herbaceous layer of semi‐arid vegetation since grazing ceased. We asked whether (1) there were differences in the temporal trends of abundance among growth forms of plants; (2) season of rainfall affected the growth form response; (3) the presence of an invasive species influenced the abundance and species richness of native plants relative to non‐invaded plots, and (4) abundance of native plants and/or species richness was related to the time it took for an invasive species to invade a plot. Location: Alice Springs, Central Australia. Methods: Long‐term changes in the semi‐arid vegetation of Central Australia were measured over 28 years (1976–2004) to partition the effects of rainfall and an invasive perennial grass. The relative abundance (biomass) of all species was assessed 25 times in each of 24 plots (8 m × 1 m) across two sites that traversed floodplains and adjacent foot slopes. Photo‐points, starting in 1972, were also used to provide a broader overview of a landscape that had been intensively grazed by cattle and rabbits prior to the 1970s. Species’abundance data were amalgamated into growth forms to examine their relationship with environmental variation in space and time. Environmental variables included season and amount of rainfall, fire history, soil variability and the colonization of the plots by the exotic perennial grass Cenchrus ciliaris (Buffel grass). Results: Constrained ordination showed that season of rainfall and landscape variables relating to soil depth strongly influenced vegetation composition when Cenchrus was used as a covariate. When Cenchrus was included in constrained ordination, it was strongly related to the decline of all native growth forms over time. Univariate comparisons of non‐invaded vs impacted plots over time revealed unequivocal evidence that Cenchrus had caused the decline of all native growth form groups and species richness. They also revealed a contrasting response of native plants to season of rainfall, with a strong response of native grasses to summer rainfall and forbs to winter rainfall. In the presence of Cenchrus these responses were strongly attenuated. Discussion: Pronounced changes in the composition of vegetation were interpreted as a response to removal of grazing pressure, fluctuations in rainfall and, most importantly, invasion of an exotic grass. Declines in herbaceous species abundance and richness in the presence of Cenchrus appear to be directly related to competition for resources. Indirect effects may also be causing the declines of some woody species from changed fire regimes as a result of increased fuel loads. We predict that Cenchrus will begin to alter landscape level processes as a result of the direct and indirect effects of Cenchrus on the demography of native plants when there is a switch from resource limited (rainfall) establishment of native plants to seed limited recruitment.     

Manipulating disturbance regimes and seeding to restore mesic Mediterranean grasslands

Question: Can managing disturbance regimes alone or in combination with seeding native species serve to shift the balance from exotic towards native species? Location: Central coast of California, USA. Methods: We measured vegetation composition for 10 yr in a manipulative experiment replicated at three sites. Treatments included no disturbance, grazing and clipping at three frequencies with and without litter removal. We seeded eight native species into clipped plots and compared cover in comparable plots with no seeding. Results: Regardless of frequency, clipping generally shifted community dominance from exotic annual grasses to exotic annual forbs, rather than consistently favoring native species. At one site, perennial grass cover decreased in no‐disturbance plots, but only after 4 yr. Litter removal had minimal impact on litter depth and plant community composition. Grazing had a highly variable effect on the abundance of different plant guilds across sites and years. Seeding increased abundance of only two of eight native species. Conclusions: Managing disturbance regimes alone is insufficient to restore native species guilds in highly‐invaded grasslands and seeding native species has highly variable success.     

Soil Seed Bank as an Input of Seed Source in Revegetation of Lead / Zinc Mine Tailings

The goal of the present study was to assess a soil seed bank as an input seed source for revegetating lead/zinc (Pb/Zn) mine tailings. The seed bank source was abandoned farmland, whose top 10‐cm layer of topsoil contained 6,850 ± 377 seeds/m² from 41 species. The seeds in the soil were principally distributed in the upper 0–2 cm, which held 75.8% of total seeds and 92.7% of species composition. The top 2‐cm layer of topsoil may be sufficient to serve the purpose of providing a seed source for revegetation on derelict lands, including mined lands. Four different thicknesses of topsoil (1, 2, 4, and 8 cm, redistributed from the total 0–10‐cm layer from the farmland) were field‐tested on the Pb/Zn mine tailings. There was no significant difference in seedling density among the 4 thickness treatments. Many seeds in the treatments with more than 1‐cm of topsoil were unable to emerge from the deeper layer. Seedlings in plots with topsoil of 1‐, 2‐ and 4‐cm failed to establish within 1 year due to the extremely high acidity (pH 2.39 to 2.76). A shallow layer of topsoil cannot neutralize the sulfuric acid generated from oxidation of pyrites in the tailings. For establishment of seedlings on metalliferous lands, an insulating layer such as subsoil, building rubble, or domestic refuse is necessary before covering with valuable topsoil. The woody legume Leucaena leucocephala grown on the tailings with a topsoil cover of 8‐cm was the most dominant species. Lead was accumulated in root, branch, stem bark, and xylem, which accounted for more than 80% of the total metal concentration in the plant. This portion of Pb will reside in the plant for a long period, while the smaller portion of Pb in the leaf (about 15%) could be returned to the environment as litter during growth. Woody plants may have an advantage in metal‐phyto‐remediation over herbaceous plants.     

Do Native Parasitic Plants Cause More Damage to Exotic Invasive Hosts Than Native Non-Invasive Hosts? An Implication for Biocontrol

Field studies have shown that native, parasitic plants grow vigorously on invasive plants and can cause more damage to invasive plants than native plants. However, no empirical test has been conducted and the mechanism is still unknown. We conducted a completely randomized greenhouse experiment using 3 congeneric pairs of exotic, invasive and native, non-invasive herbaceous plant species to quantify the damage caused by parasitic plants to hosts and its correlation with the hosts' growth rate and resource use efficiency. The biomass of the parasitic plants on exotic, invasive hosts was significantly higher than on congeneric native, non-invasive hosts. Parasites caused more damage to exotic, invasive hosts than to congeneric, native, non-invasive hosts. The damage caused by parasites to hosts was significantly positively correlated with the biomass of parasitic plants. The damage of parasites to hosts was significantly positively correlated with the relative growth rate and the resource use efficiency of its host plants. It may be the mechanism by which parasitic plants grow more vigorously on invasive hosts and cause more damage to exotic, invasive hosts than to native, non-invasive hosts. These results suggest a potential biological control effect of native, parasitic plants on invasive species by reducing the dominance of invasive species in the invaded community.     

Effects of Wild Pig Disturbance on Forest Vegetation and Soils

In North America, wild pigs (Sus scrofa; feral pigs, feral swine, wild boars) are a widespread exotic species capable of creating large-scale biotic and abiotic landscape perturbations. Quantification of wild pig environmental effects has been particularly problematic in northern climates, where they occur only recently as localized populations at low densities. Between 2016 and 2017, we assessed short-term (within ~2 yrs of disturbance) effects of a low-density wild pig population on forest features in the central Lower Peninsula of Michigan, USA. We identified 16 8-ha sites using global positioning system locations from 7 radio-collared wild pigs for sampling. Within each site, we conducted fine-scale assessments at 81 plots and quantified potential disturbance by wild pigs. We defined disturbance as exposure of overturned soil, often resulting from rooting behavior by wild pigs. We quantified ground cover of plants within paired 1-m² frames at each plot, determined effects to tree regeneration using point-centered quarter sampling, and collected soil cores from each plot. We observed less percent ground cover of native herbaceous plants and lower species diversity, particularly for plants with a coefficient of conservatism ≥5, in plots disturbed by wild pigs. We did not observe an increase in colonization of exotic plants following disturbance, though the observed prevalence of exotic plants was low. Wild pigs did not select for tree species when rooting, and we did not detect any differences in regeneration of light- and heavy-seeded tree species between disturbed or undisturbed plots. Magnesium and ammonium content in soils were lower in disturbed plots, suggesting soil disturbance accelerated leaching of macronutrients, potentially altering nitrogen transformation. Our study suggested that disturbances by wild pigs, even at low densities, alters short-term native herbaceous plant diversity and soil chemistry. Thus, small-scale exclusion of wild pigs from vulnerable and rare plant communities may be warranted. © 2020 The Wildlife Society.     

Does Seeding a Locally Adapted Native Mixture Inhibit Ingress by Exotic Plants?

Non‐native plant species often colonize retired agricultural lands, creating monocultures with low species diversity that provide poor wildlife habitat. We assessed whether sowing a mix of 29 locally adapted native species reduced invasion of non‐native plant species compared to allowing vegetation to colonize naturally following tillage. There was a sampling date × treatment interaction for canopy cover of perennial exotic plant species. Plots that were not sown to natives had two to six times greater canopy cover of exotic species than did plots with both preparation (woody vegetation removed, plowed, and disked) and control (no preparation or sowing) plots. Canopy cover of exotic plants was similar in prepared‐only and control treatments from October 2008 to June 2010, ranging from 8 to 40%. Percent absolute canopy cover of native vegetation was 10–20 times greater on prepared and planted plots than on prepared‐only plots during March 2009 to June 2010. Sowing a mix of locally adapted native species may inhibit encroachment by non‐native species for up to two years after sowing on retired agricultural land in the Lower Rio Grande Valley of Texas.     

Seasonal Effects of Four Control Methods on the Invasive Morrow's Honeysuckle (Lonicera morrowii) and Initial Responses of Understory Plants in a Southwestern Pennsylvania Old Field

The first step in restoration often involves the removal of invasive plants, but few studies have determined if the response of plant communities matches management goals. The shrub Morrow's honeysuckle ( Lonicera morrowii Gray) is one of a suite of exotic bush honeysuckle species that have become pervasive woody invaders in eastern North America. In 2004, we tested four control methods (cut, mechanical removal, stump application of glyphosate, and foliar application of glyphosate) during late spring and early autumn within a degraded meadow at Fort Necessity National Battlefield, Pennsylvania, U.S.A. Our restoration goals are to control Morrow's honeysuckle, restore native vegetation, and mimic the conditions present in the mid-1700s. We established forty-five 5 × 5–m plots to measure woody species; five plots of each treatment method were treated in spring, whereas the remaining five were treated in autumn. We maintained five control plots. Before control, mean density of Morrow's honeysuckle was 67,920 ± 4,480 shrubs/ha. Foliar application of herbicide and mechanical removal were most effective at reducing the number of shrubs (≥62%). Overall, our treatments were less successful (26–68% reduction) than reported control efforts of other bush honeysuckle species; the sheer number of shrubs coupled with their open habitat made control efforts difficult. Spring treatments, particularly cut and mechanical treatments, had higher metrics of herbaceous community quality. However, continued restoration efforts, including follow-up treatments, White-tailed deer ( Odocoileus virginianus ) control, and the planting of native seeds and saplings, should be employed to favor the establishment of native seedlings and herbs.     

Long‐term effects of prairie restoration on plant community structure and native population dynamics

The key to restoring degraded grassland habitats is identifying feasible and effective techniques to reduce the negative impacts of exotic species and promote self‐sustaining native populations. It is often difficult to extend monitoring of restoration efforts to evaluate long‐term success, but doing so is essential to understanding how initial outcomes change over time. To assess how initial treatment effects persist, we revisited degraded patches of Pacific Northwest prairie habitat 6 years after experimental restoration efforts ceased. We evaluated plant community composition to determine the lasting effects of supplemental native seeding and disturbance treatments (burning, mowing, and herbicide to reduce exotic species). We tracked the persistence of seeded species and measured spread of their populations to evaluate suitability of species for restoration and the ability of the habitat to support native plant populations. We found that plots that received supplemental seeding continued to exhibit higher richness of native species than those left unseeded, and that both seeding and disturbance treatments could positively influence native species abundance over the long term. The initially observed effects of disturbance treatments on reducing exotic grass abundance had diminished, highlighting the importance of long‐term monitoring and ongoing control of exotic species. Nevertheless, these treatments significantly influenced the population trajectories of 4 out of 8 seeded native species. There was evidence of spatial advance of most seeded species. Results from extended monitoring confirm that dispersal limitation of native species and difficulties maintaining the reduction of exotic grasses continue to be major barriers to success in restoration of invaded grasslands.     

Biological soil crusts determine the germination and growth of two exotic plants

In arid and semiarid ecosystems, the potential threats of exotic invasive species are enhanced due to increasing human activities. Biological soil crusts (BSCs), acting as arid ecosystem engineers, may play an important role in preventing the establishment of exotic invasive plants. Our goal was to examine whether BSCs could inhibit the establishment of probable exotic plant species originating from adjacent grasslands located along the southeast edge of the Tengger Desert. In our study, we investigated the effects of three BSC types (cyanobacteria, lichen, and moss crusts) under two disturbance conditions (intact and disturbed) on the establishment of two exotic plant species (Ceratoides latens and Setaria viridis) using indoor experiments. We found both negative and positive effects of BSCs on the establishment of the two exotic plant species. Compared with the disturbed BSCs, the germination percentages of C. latens and S. viridis were reduced by 54% to 87% and 89% to 93%, respectively, in intact BSCs. In contrast, BSCs significantly promoted the height growth and aboveground biomass of the two exotic plant species (p < .05) by enhancing the soil water and nutrient availability for the exotic plants. Our results confirm that BSCs strongly suppress the rapid expansion of exotic plant populations by inhibiting germination of seed with big size or appendages and have a weak inhibitory effect on exotic plant with small and smooth seeds. This may decrease the threat of propagation of exotic species. In the meantime, BSCs promote the growth of a few successful engraftment seedlings, which increased the beta diversity. Our work suggests that better understanding the two opposing effects of BSCs on the establishment of exotic plant species in different growth stages (germination and growth) is important for maintaining the health and stability of revegetated regions.     

Autumn olive (<Emphasis Type="Italic">Elaeagnus umbellata</Emphasis>) presence and proliferation on former surface coal mines in Eastern USA

Invasive plants threaten native plant communities. Surface coal mines in the Appalachian Mountains are among the most disturbed landscapes in North America, but information about land cover characteristics of Appalachian mined lands is lacking. The invasive shrub autumn olive (Elaeagnus umbellata) occurs on these sites and interferes with ecosystem recovery by outcompeting native trees, thus inhibiting re-establishment of the native woody-plant community. We analyzed Landsat 8 satellite imagery to describe autumn olive’s distribution on post-mined lands in southwestern Virginia within the Appalachian coalfield. Eight images from April 2013 through January 2015 served as input data. Calibration and validation data obtained from high-resolution aerial imagery were used to develop a land cover classification model that identified areas where autumn olive was a primary component of land cover. Results indicate that autumn olive cover was sufficiently dense to enable detection on approximately 12.6 % of post-mined lands within the study area. The classified map had user’s and producer’s accuracies of 85.3 and 78.6 %, respectively, for the autumn olive coverage class. Overall accuracy was assessed in reference to an independent validation dataset at 96.8 %. Autumn olive was detected more frequently on mines disturbed prior to 2003, the last year of known plantings, than on lands disturbed by more recent mining. These results indicate that autumn olive growing on reclaimed coal mines in Virginia and elsewhere in eastern USA can be mapped using Landsat 8 Operational Land Imager imagery; and that autumn olive occurrence is a significant landscape vegetation feature on former surface coal mines in the southwestern Virginia segment of the Appalachian coalfield.     

Management strategies for plant invasions: manipulating productivity, disturbance, and competition

The traditional approach to understanding invasions has focused on properties of the invasive species and of the communities that are invaded. A well‐established concept is that communities with higher species diversity should be more resistant to invaders. However, most recently published field data contradict this theory, finding instead that areas with high native plant diversity also have high exotic plant diversity. An alternative environment‐based approach to understanding patterns of invasions assumes that native and exotic species respond similarly to environmental conditions, and thus predicts that they should have similar patterns of abundance and diversity. Establishment and growth of native and exotic species are predicted to vary in response to the interaction of plant growth rates with the frequency and intensity of mortality‐causing disturbances. This theory distinguishes between the probability of establishment and the probability of dominance, predicting that establishment should be highest under unproductive and undisturbed conditions and also disturbed productive conditions. However, the probability of dominance by exotic species, and thus of potential negative impacts on diversity, is highest under productive conditions. The theory predicts that a change in disturbance regime can have opposite effects in environments with contrasting levels of productivity. Manipulation of productivity and disturbance provides opportunities for resource managers to influence the interactions among species, offering the potential to reduce or eliminate some types of invasive species.     

Does Invasion of Exotic Plants Promote Invasion of Exotic Flower Visitors? A Case Study from the Temperate Forests of the Southern Andes

Habitat disturbance, particularly of human origin, promotes the invasion of exotic plants, which in turn might foster the invasion of alien-interacting animals. Here we assess whether the invasion of exotic plants – mostly mediated by habitat disturbance – facilitates the invasion of exotic flower visitors in temperate forests of the southern Andes, Argentina. We recorded visit frequencies and the identity of visitors to the flowers of 15 native and 15 exotic plant species occurring in different highly disturbed and less disturbed habitats. We identified three alien flower visitors, the hymenopterans Apis mellifera, Bombus ruderatus, and Vespula germanica. We found significantly more visitation by exotic insects in disturbed habitats. This pattern was explained, at least in part, by the association between alien flower visitors and flowers of exotic plants, which occurred more frequently in disturbed habitats. However, this general pattern masked different responses between the two main alien flower visitors. Apis mellifera exploited almost exclusively the flowers of a subset of herbaceous exotic plants that thrive under disturbance, whereas B. ruderatus visited equally flowers of both exotic and native plants in both disturbed and undisturbed habitats. We did not find any strong evidence that flowers of exotic plants were more generalist than those of native plants, or that exotic flower visitors were more generalist than their native counterparts. Our results suggest that alien plant species could facilitate the invasion of at least some exotic flower visitors to disturbed habitats. Because flowering plants as well as flower visitors benefit from this mutualism, this association may enhance, through a positive feedback, successful establishment of both exotic partners.     

Do arbuscular mycorrhizal fungi recolonize revegetated grasslands?

Fifteen native and common exotic herbaceous species from four functional groups (C4 grass, C3 grass, chamaephyte and hemicryptophyte) occurring within remnant and revegetated grassland and grassy woodlands were sampled for evidence of structures associated with functioning arbuscular mycorrhizal fungi (AMF) from across a broad geographical range of central and south‐western Victoria, Australia. Revegetated communities had been established on ex‐agricultural land by direct seeding. They included sites that had been kept fallow with herbicide for up to 3 years prior to seeding and those from which topsoil had been removed (scalped) to a depth of 100 mm prior to seeding. Structures associated with AMF (external and internal aseptate hyphae, arbuscules and vesicles) were observed in root samples from all native and exotic species, regardless of site history (remnant or revegetated; fallowed or scalped). These findings indicate that AMF are ubiquitous in the herbaceous flora of this region (native and exotic), even in situations where sites had been intensively disturbed prior to revegetation treatment. However, while there was evidence of AMF in all revegetated communities, only sites which had been scalped prior to direct seeding supported species‐rich native herbaceous communities.     

Seedling Establishment and Survival on Restored Campsites in Subalpine Forest

This study experimented with common restoration techniques (scarification, soil amendments, mulch, and seeding) on six closed wilderness campsites in subalpine forests in Oregon. Effectiveness in encouraging seedling establishment, growth, and survival was assessed every year for the first 7 years following treatment. Closure and restoration of the campsites increased the density of plants established from seed. Despite an original density of virtually zero, mean density of perennial plants was 55 plants/m² 7 years after closure. All the treatments, with the exception of the biodegradable mulch mat, increased plant density. Seven years after treatment, seeding had increased plant density 5‐fold, whereas scarification and soil amendments (organic matter, compost, and soil inoculum) had each increased density 3‐fold. The organic and compost amendments also had the positive benefit of increasing growth rates and shortening the time‐to‐reproductive maturity. Results suggest that restoration of the herbaceous cover on these campsites can occur rapidly using the techniques employed. All but one of the species we seeded established in substantial quantities and survived at densities exceeding their density in the naturally sparse herbaceous cover on these sites. Thirty‐six perennial species volunteered on these sites. The remaining challenge is reestablishment of the shrub species that comprise much of the ground cover in these forests. These species seldom establish from seed.     

Plant Recruitment and Soil Microbial Characteristics of Rehabilitation Seedings Following Wildfire in Northern Utah

One goal of post‐fire native species seeding is to increase plant community resistance to exotic weed invasions, yet few studies address the impacts of seeding on exotic annual establishment and persistence. In 2010 and 2011, we investigated the influence of seedings on exotic annuals and the underlying microbial communities. The wildfire site in northern Utah was formerly dominated by Artemisia tridentata ssp. wyomingensis, but burned in September 2008. Experimental seeding treatments were installed in November 2008 to examine strategies for establishing native species using two drills, hand broadcasts and different timing of seed applications (resulting in 13 seeding treatments). We collected aboveground biomass of invasive annuals (Halogeton glomeratus, Salsola kali, and Bromus tectorum), other volunteer plants from the extant seed bank, and seeded species from all treatments in the second and third years after fire. We sampled soils within microsites beneath native perennial bunchgrass and exotic annuals to characterize underlying soil microbial communities. High precipitation following seeding led to strong seedling establishment and we found few differences between seeding treatments established with either drill. All seeded treatments reduced exotic biomass by at least 90% relative to unseeded controls. Soil microbial communities (phospholipid fatty acid analysis), beneath B. tectorum, Poa secunda, and Pseudoroegneria spicata microsites differed little 3 years after fire. However, microbial abundance beneath P. spicata increased from June to July, suggesting that microbial communities beneath successful seedings can vary greatly within a single growing season.     

Establishment of Fabaceae Tree Species in a Tropical Pasture: Influence of Seed Size and Weeding Methods

The successful establishment of trees in pastures may be related to species, seed size, and weed control treatments. This study experimentally evaluated the emergence, establishment after 2 years, and growth of individuals of 7 tree species with different seed sizes sowed under three weeding methods (no weeding, grasses clipped, and grasses removed). The experiment was carried out in a tropical abandoned pasture in Midwestern Brazil, dominated by the exotic invasive grass Urochloa brizantha. The effect of seed size on seedling emergence was significant and was more intense in the no weeding and weeding treatment plots than in grasses clipped. Furthermore, an increase in seed size resulted in an increase in the probability of establishment of tree species, although this pattern also differed among weeding treatments. The increase in seed size reflected negatively on tree growth in the absence of grasses, whereas in the presence of grasses there was an inverse relationship. The experimental results suggested that the use of seeds of different sizes for direct seeding in pastures is a possible strategy of Fabaceae tree species reintroduction in pastures within the Cerrado. Fabaceae species with seeds larger than 100 mg can establish in areas with no weeding, whereas species with seeds smaller than 50 mg can establish preferentially in areas with weeding, growing faster than larger ones. Thus, weeding strategies can determine the success of direct seeding of different species in restoration projects of tropical pastures.     

Control of Exotic Annual Grasses to Restore Native Forbs in Abandoned Agricultural Land

Exotic annual grasses are a major challenge to successful restoration in temperate and Mediterranean climates. Experiments to restore abandoned agricultural fields from exotic grassland to coastal sage scrub habitat were conducted over two years in southern California, U.S.A. Grass control methods were tested in 5 m² plots using soil and vegetation treatments seeded with a mix of natives. The treatments compared grass‐specific herbicide, mowing, and black plastic winter solarization with disking and a control. In year two, herbicide and mowing treatments were repeated on the first‐year plots, plus new control and solarization plots were added. Treatments were evaluated using percent cover, richness and biomass of native and exotic plants. Disking alone reduced exotic grasses, but solarization was the most effective control in both years even without soil sterilization, and produced the highest cover of natives. Native richness was greatest in solarization and herbicide plots. Herbicide application reduced exotics and increased natives more than disking or mowing, but produced higher exotic forb biomass than solarization in the second year. Mowing reduced grass biomass and cover in both years, but did not improve native establishment more than disking. Solarization was the most effective restoration method, but grass‐specific herbicide may be a valuable addition or alternative. Solarization using black plastic could improve restoration in regions with cool, wet summers or winter growing seasons by managing exotic seedbanks prior to seeding. While solarization may be impractical at very large scales, it will be useful for rapid establishment of annual assemblages on small scales.     

Plant traits and regeneration of urban plant communities after disturbance: Does the bud bank play any role?

Questions: What is the relative role of the bud bank, seed and various species traits in the regeneration of urban plant communities after severe disturbances? Do invasive and exotic species, highly abundant in disturbed communities, regenerate better than native species after disturbance? Methods: Hand tilling was applied to three urban plant communities with and without additional herbicide treatment to exclude regeneration from the bud bank. Plant traits were determined from the literature and databases. Species responses to the treatments were evaluated with RDA analyses in CANOCO. Linear models were applied to identify traits that could predict the responses of species to disturbance. Results: The bud bank played a key role in regeneration in the plots without herbicide. In the plots with herbicide treatment, the seed bank was important in re‐establishing vegetation after disturbance. Exclusion of the bud bank by using herbicide allowed the establishment of small annuals, whereas biennials and perennials were successful in plots where the bud bank was not inhibited by herbicide. Exotic species with a long residence time in the local flora were successful in plots where regeneration from the bud bank was excluded, whereas species with short residence times or that were invasive were suppressed by both types of disturbance. Conclusion: In response to various types of disturbance, species with different regeneration strategies (either seeds or bud bank) were promoted. Exotic species were suppressed primarily by disturbance, which suggests that factors other than just regenerative capability contributed to the high abundance of exotics in urban communities.     

Flood‐deposited wood creates regeneration niches for riparian vegetation on a semi‐arid South African river

Question : The formation of large woody debris (LWD) piles during floods has significant impacts on riparian succession through pioneering plants often establishing in association with wood. We assess the importance of LWD for seed regeneration of riparian plants after a century‐scale flood disturbance in a semi‐arid environment. Location : The Sabie River within Kruger National Park in the semi‐arid northeast of South Africa. Methods : Our approach was to quantify the riparian soil seed bank, to record the frequency of establishment of riparian plants in woody debris piles, and to conduct experimental out‐plantings of common riparian trees in plots with and without LWD. Results : We found the abundance and diversity of seedlings were higher in soils taken from wood piles than from open reference areas, and most seedlings were herbaceous species. Surveys indicated that numbers of seedlings recorded within woody debris were significantly greater than in open reference areas or within established vegetation. Seedling establishment in various cover‐types also varied for different riparian tree species. Experimental out‐planting of seedlings of two riparian tree species (Philenoptera violacea and Combretum erythrophyllum) revealed that, after 433 days, planted seedlings survived only in woody debris piles. Conclusion : LWD formed after a large flood creates heterogeneous patches that may influence post‐disturbance regeneration of riparian vegetation by providing a variety of environmental niches for seedlings establishment. We suspect that higher seedling survival in LWD is due to increased moisture (particularly in the dry season) and nutrients, and protection from seasonal flooding and herbivory.