Impact of three aquatic invasive species on native plants and macroinvertebrates in temperate ponds

Biological plant invasions pose a serious threat to native biodiversity and have received much attention, especially in terrestrial habitats. In freshwater ecosystems impacts of invasive plant species are less studied. We hypothesized an impact on organisms from the water column and from the sediment. We then assessed the impact of three aquatic invasive species on the plants and macroinvertebrates: Hydrocotyle ranunculoides, Ludwigia grandiflora and Myriophyllum aquaticum. Our research on 32 ponds in Belgium indicated that the reduction in the native plant species richness was a common pattern to invasion. However, the magnitude of impacts were species specific. A strong negative relationship to invasive species cover was found, with submerged vegetation the most vulnerable to the invasion. Invertebrate richness, diversity and abundance were measured in sediments of invaded and uninvaded ponds along a gradient of H. ranunculoides, L. grandiflora, and M. aquaticum species cover. We found a strong negative relationship between invasive species cover and invertebrate abundance, probably due to unsuitable conditions of the detritus for invertebrate colonization. Taxonomic compositions of aquatic invertebrate assemblages in invaded ponds differed from uninvaded ponds. Sensitive benthos, such as mayflies were completely absent in invaded ponds. The introduction of H. ranunculoides, L. grandiflora, and M. aquaticum in Belgian ponds has caused significant ecological alterations in the aquatic vegetation and the detritus community of ponds.     

Treatment by glyphosate-based herbicide allowed recovering native species after Oxalis pes-caprae L. invasion: indications from a Mediterranean island

Biological invasions represent a global threat to biodiversity. Particular attention should be devoted to the management of alien plants, focusing on the opportunity to obtain a rapid response to invasion and restoration of the invaded areas. In this study we aimed to evaluate five different methods for controlling Oxalis pes-caprae, a well-known invasive plant native to South Africa, also focusing on the restoration of the native flora. We set an experiment on the island of Montecristo (central Mediterranean). Treatment methods varied from chemical to low risk methods, including manual removal, covering with mulching sheets, and foliar spraying with acetic acid (30% solution) and two different concentrations of glyphosate (3 and 5% solutions, respectively). The total cover of O. pes-caprae and of other native plants was sampled before treatments, and then several times during the subsequent year; while the plant species composition was sampled in late winter (March 2015–2016) and late spring (May 2015–2016). The use of glyphosate was found to be the only efficient control method, leading to a significant decrease in O. pes-caprae cover as well as to a recovery in native species cover and richness. The effect of the other control methods was negligible.     

Does Eucalyptus grandis invasion and removal affect soils and vegetation in the Eastern Cape Province,South Africa?

Many invasive alien plants drive changes in native community composition, structure and diversity. They alter soil nutrient regimes of native communities and affect native plant recovery outcomes following their removal. We assessed whether Eucalyptus grandis invasion and removal alters the soil physico‐chemical properties and native vegetation recovery in the Eastern Cape Province, South Africa. We collected samples from topsoil in E. grandis invaded sites (canopy cover > 75%), cleared sites (eight years ago) and native sites (canopy cover > 80%) and quantified soil moisture, concentrations of soil macro elements (N, C and P), pH and exchangeable cations (K, Ca, Mg, Na) as well as measured soil water repellency using the Water Droplet Penetration Time and infiltration. We conducted vegetation surveys in plots measuring 10 × 10 m. Invasion by E. grandis had varying effects on soil physico‐chemical properties, causing increase in soil pH and P, while decreasing total N and C. The removal of E. grandis also showed varying effects on soil physico‐chemical properties, but seems to have further triggered the loss of some soil nutrients (especially soil P). Soil water repellency (a measure of soil compaction) has improved in cleared sites to non‐repellent soils compared to repellent soils in invaded site. Eucalyptus grandis reduced species richness of the invaded sites. The presence of native species on cleared sites indicates a positive trajectory towards vegetation recovery. We conclude that E. grandis invasion and removal trigger varying effects on soil properties (both increases and decreases). For soil and vegetation restoration of cleared sites to be effective, active restoration techniques such as soil transfer, nutrient manipulation and native plant seeding should be considered.     

Patterns of Plant Invasions: A Case Example in Native Species Hotspots and Rare Habitats

Land managers require landscape-scale information on where exotic plant species have successfully established, to better guide research, control, and restoration efforts. We evaluated the vulnerability of various habitats to invasion by exotic plant species in a 100,000 ha area in the southeast corner of Grand Staircase-Escalante National Monument, Utah. For the 97 0.1-ha plots in 11 vegetation types, exotic species richness (log₁₀) was strongly negatively correlated to the cover of cryptobiotic soil crusts (r = −0.47, P < 0.001), and positively correlated to native species richness (r = 0.22, P < 0.03), native species cover (r = 0.23, P < 0.05), and total nitrogen in the soil (r = 0.40, P < 0.001). Exotic species cover was strongly positively correlated to exotic species richness (r = 0.68, P < 0.001). Only 6 of 97 plots did not contain at least one exotic species. Exotic species richness was particularly high in locally rare, mesic vegetation types and nitrogen rich soils. Dry, upland plots (n = 51) had less than half of the exotic species richness and cover compared to plots (n = 45) in washes and lowland depressions that collect water intermittently. Plots dominated by trees had significantly greater native and exotic species richness compared to plots dominated by shrubs. For the 97 plots combined, 33% of the variance in exotic species richness could be explained by a positive relationship with total plant cover, and negative relationships with the cover of cryptobiotic crusts and bare ground. There are several reasons for concern: (1) Exotic plant species are invading hot spots of native plant diversity and rare/unique habitats. (2) The foliar cover of exotic species was greatest in habitats that had been invaded by several exotic species.(3) Continued disturbance of fragile cryptobiotic crusts by livestock, people, and vehicles may facilitate the further invasion of exotic plant species. This revised version was published online in July 2006 with corrections to the Cover Date.     

Restoration potential of invaded abandoned agricultural fields: what does the seed bank tell us?

Soil seed banks can play an important role in the restoration of degraded ecosystems, especially where indigenous species are well represented in, and invasive species are largely absent from, the seed bank. Here, we studied the potential contribution of the soil seed bank to the restoration of invaded, abandoned agricultural fields in the Eastern Cape, South Africa. We recorded the aboveground cover and belowground abundance of all vascular plant species from 120 quadrats that differ in cover of the extralimital woody invader, Pteronia incana. Our results show that higher cover of P. incana is associated with lower species richness, aboveground cover, and belowground seed abundance. Furthermore, community similarity between the above‐ and belowground component was low, with the seed bank and standing vegetation having only 15 species in common and 49 species being recorded only from the seed bank. We suggest that this large number of seed bank‐only species is a relic of previous vegetation, prior to large‐scale invasion by P. incana. The most important finding from our study is the absence of P. incana from the soil seed bank. This finding, combined with the large number of mostly native species from the seed bank, holds promise from a restoration perspective. However, given the susceptibility of the invaded systems to erosion, coupled with the low grazing value of the seed bank species, we suggest that P. incana removal should be accompanied by both erosion control measures and reseeding with palatable grass species, to secure the livelihoods of local communities.     

Invasion,alien control and restoration: Legacy effects linked to folivorous insects and phylopathogenic fungi

Invasive alien trees increase native tree stress and may increase attack by herbivores and pathogenic fungi. Alien tree removal should ameliorate such impacts. Here we compared the levels of damage by phylopathogenic fungi and folivorous insects on Brabejum stellatifolium and Metrosideros angustifolia (native trees) and Acacia mearnsii (invasive tree species) among near‐pristine, invaded and restored sites. Generally, foliar damage levels were higher at invaded than at near‐pristine sites. Damage levels at restored sites were similar, or even higher than those at invaded sites. Decreased native tree species richness did not explain these patterns, as restored sites had native tree species richness levels similar to those of near‐pristine sites. Increased host abundance and leaf nitrogen content did not significantly correlate with increased damage in most cases. Therefore, plant species richness recovers following restoration, but native trees still experience increased pressure from folivores and phylopathogenic fungi, which may even exceed levels experienced at invaded sites, thus impacting recovery trajectories.     

Effects of desiccation on the toxicant sensitivity of rotifers

Non-native aquatic macrophytes have invaded different types of ecosystems all over the world. The exotic submersed macrophyte Hydrilla verticillata recently invaded the Paraná basin, Brazil, being recorded by the first time in the natural habitats of this river in 2005. We investigated the effects of this species on ostracod assemblages and compared the abundance, richness, and Shannon–Wiener diversity of ostracod assemblages that colonize the invading species with those that colonize Egeria najas, a native submersed species with similar architecture and physical complexity. Fragments of these two species were left for 28 days in tanks to root and grow and then they were transferred to a floodplain lake where they remained in pairs (one plant of each species; N = 7) during 30 days for colonization by ostracods. A detrented correspondence analysis was used to summarize ostracod assemblage composition. Although there were no significant differences in ostracod abundance, richness and Shannon diversity when analyzed separately, cumulative curves, which permit to eliminate effects of abundance on richness, indicated a significantly higher number of ostracod species on H. verticillata. Assemblage composition was significantly different between both plant species, as shown by the first DCA axis. Our results show that H. verticillata might provide favorable habitats for native ostracod assemblages.     

Restoring native understory to a woodland invaded by Euonymus fortunei: multiple factors affect success

Invasive species are capable of causing change in native plant communities, but invasion is often associated with other anthropogenic impacts on natural areas, such as habitat fragmentation and associated dispersal limitation for native species. Consequently, invasive species removal alone may not always be sufficient to meet restoration objectives. We tested if invasion and dispersal limitation interact to limit plant community restoration within a forest fragment invaded by Euonymus fortunei. Removal of Euonymus alone did not lead to the recolonization of native plant species. However, planting seedlings increased total native cover in invaded, Euonymus removal, and uninvaded control treatments. The consistent establishment of native plant seedlings across all treatments indicates that Euonymus invasion may have limited ability to displace established plants. In contrast, plant species that we added as seed were unable to establish in invaded plots, indicating that Euonymus invasion limits recruitment of native plant species from seed. Over the course of our experiment, a number of setbacks and surprises occurred, including high levels of herbivory, a windstorm, and extreme drought, all of which likely limited restoration success. Overall, our results indicate that Euonymus may contribute to native species declines, but other factors are important. Thus, invasive species removal alone may not be sufficient to reestablish a diverse native plant community. Instead, impacts on natural areas may need to be mitigated along with invasive species removal for restoration to be successful.     

Giant invasive Heracleum persicum: Friend or foe of plant diversity?

The impact of invasion on diversity varies widely and remains elusive. Despite the considerable attempts to understand mechanisms of biological invasion, it is largely unknown whether some communities’ characteristics promote biological invasion, or whether some inherent characteristics of invaders enable them to invade other communities. Our aims were to assess the impact of one of the massive plant invaders of Scandinavia on vascular plant species diversity, disentangle attributes of invasible and noninvasible communities, and evaluate the relationship between invasibility and genetic diversity of a dominant invader. We studied 56 pairs of Heracleum persicum Desf. ex Fisch.‐invaded and noninvaded plots from 12 locations in northern Norway. There was lower native cover, evenness, taxonomic diversity, native biomass, and species richness in the invaded plots than in the noninvaded plots. The invaded plots had nearly two native species fewer than the noninvaded plots on average. Within the invaded plots, cover of H. persicum had a strong negative effect on the native cover, evenness, and native biomass, and a positive association with the height of the native plants. Plant communities containing only native species appeared more invasible than those that included exotic species, particularly H. persicum. Genetic diversity of H. persicum was positively correlated with invasibility but not with community diversity. The invasion of a plant community by H. persicum exerts consistent negative pressure on vascular plant diversity. The lack of positive correlation between impacts and genetic diversity of H. persicum indicates that even a small founder population may cause high impact. We highlight community stability or saturation as an important determinant of invasibility. While the invasion by H. persicum may decrease susceptibility of a plant community to further invasion, it severely reduces the abundance of native species and makes them more vulnerable to competitive exclusion.     

Influence of spoil type on afforestation success and natural vegetative recolonization on a surface coal mine in Appalachia,United States

Surface mining has altered a vast land area in the Appalachian Region, threatening highly biodiverse native forest, contributing to habitat fragmentation, and generating severely disturbed sites that are unsuitable for succession to native ecosystems. Although there are many factors that influence species colonization and establishment on these sites, selection of topsoil substitutes suitable for native species is of particular concern. A series of experimental plots was installed in 2005 on a reclaimed mine site in eastern Kentucky, United States, to examine the suitability of three spoil types (unweathered GRAY sandstone, weathered BROWN sandstone, and MIXED sandstone/shale) as topsoil substitutes. Bareroot 1:0 seedlings of four native hardwood species (Fraxinus pennsylvanica, Quercus rubra, Q. alba, and Liriodendron tulipifera) were planted in the spoil. Seed required for ground cover was not applied so that natural colonization could be evaluated. Two years after installation, researchers concluded that tree growth was highest on BROWN; in addition, species richness and ground cover of volunteer vegetation were higher on BROWN. In 2013, tree volume was over 50 times higher in BROWN than GRAY. In addition to planted hardwoods, naturally colonizing vegetation provided nearly 100% cover on BROWN compared to 20% on MIXED and less than 10% on GRAY plots. Species richness of volunteer vegetation continued to be higher on BROWN (41) than GRAY (30) or MIXED (30), with native species comprising 65–70% of total species richness on all plots. Findings suggest that when topsoil substitutes are used, weathered spoils are more favorable to reforestation than unweathered spoil.     

Secondary succession is influenced by belowground insect herbivory on a productive site

We investigated the effects of insect herbivory on a plant community of a productive old-field community by applying foliar and soil insecticides in a full factorial design. During the first 3 years of succession, insecticide treatments had only minor effects on total cover abundance and species richness. However, species ranking within the plant community was strongly affected by soil insecticide but not by foliar insecticide. Creeping thistle, Cirsium arvense , dominated the experimental plots with reduced root herbivory, while square-stemmed willow-herb, Epilobium adnatum , dominated the control and the plots with foliar insecticide. When soil insecticide was applied, cover abundance of monocarpic forbs increased and cover abundance of polycarpic herbs decreased compared to the control. However, this effect was due to a few abundant plant species and is not based on a consistent difference between life history groups. Instead, application of soil insecticide promoted persistence of species that established at the start of succession, and suppressed species that established in the following years. We conclude that below-ground herbivory reduces competitive ability of resident species and, thus, facilitates colonization by late-successional species. Hence, soil insects can exert strong top-down effects on the vegetation of productive sites by affecting dominant plant species and altering competitive balances.     

Native and invasive plant interactions in wetlands and the minimal role of invasiveness

The effects of invasive plants on plants native to areas that are being invaded can be quite variable, depending on the species of the invasive plant involved as well as the physical characteristics of the location being invaded. My study focuses on the effects of Phragmites australis Linnaeus (common reed) and Lythrum salicaria L. (purple loosestrife) on the same native plant community. Uninvaded plots dominated by native plants Typha angustifolia L. (narrowleaf cattail) and Typha latifolia L. (broadleaf cattail) served as the control. I surveyed percent cover of species during early summer and midsummer for 3 years in six Hudson River freshwater tidal wetlands (sites). Differences in species richness, composition and abundance were small, but significant among invaded and uninvaded plots and among sites. However, these differences remained significant when data for dominant species (invasive and native) were removed. Differences in native plant species abundance were attributed to invasive plant species-specific characteristics and differences in species richness and composition were attributed to physical location (zonation) in these freshwater tidal marshes. “Invasive” status of a dominant plant species was less important in invasive plant–native plant interactions than species-specific characteristics and zonation. Further research into the effects of site and land-use on invasive plant impacts is recommended.     

Understory vegetation response to thinning disturbance of varying complexity in coniferous stands

Question: Can augmented forest stand complexity increase understory vegetation richness and cover and accelerate the development of late‐successional features? Does within‐stand understory vegetation variability increase after imposing treatments that increase stand structural complexity of the overstory? What is the relative contribution of individual stand structural components (i.e. forest matrix, gaps, and leave island reserves) to changes in understory vegetation richness? Location: Seven study sites in the Coastal Range and Cascades regions of Oregon, USA. Methods: We examined the effects of thinning six years after harvest on understory plant vascular richness and cover in 40‐ to 60‐year‐old forest stands dominated by Douglas‐fir (Pseudotsuga menziesii). At each site, one unthinned control was preserved and three thinning treatments were implemented: low complexity (LC, 300 trees ha^?1), moderate complexity (MC, 200 trees ha^?1), and high complexity (HC, variable densities from 100 to 300 trees ha^?1). Gaps openings and leave island reserves were established in MC and HC. Results: Richness of all herbs, forest herbs, early seral herbs and shrubs, and introduced species increased in all thinning treatments, although early seral herbs and introduced species remained a small component. Only cover of early seral herbs and shrubs increased in all thinning treatments whereas forest shrub cover increased in MC and HC. In the understory, we found 284 vascular plant species. After accounting for site‐level differences, the richness of understory communities in thinned stands differed from those in control stands. Within‐treatment variability of herb and shrub richness was reduced by thinning. Matrix areas and gap openings in thinned treatments appeared to contribute to the recruitment of early seral herbs and shrubs. Conclusions: Understory vegetation richness increased 6 years after imposing treatments, with increasing stand complexity mainly because of the recruitment of early seral and forest herbs, and both low and tall shrubs. Changes in stand density did not likely lead to competitive species exclusion. The abundance of potentially invasive introduced species was much lower compared to other plant groups. Post‐thinning reductions in within‐treatment variability was caused by greater abundance of early seral herbs and shrubs in thinned stands compared with the control. Gaps and low‐density forest matrix areas created as part of spatially variably thinning had greater overall species richness. Increased overstory variability encouraged development of multiple layers of understory vegetation.     

An exotic woody weed in a pastoral landscape provides habitat for many native species,but has no apparent threatened species conservation significance

Exotic woody plants are often used by native organisms, but may also be targets of expensive control justified by nature conservation. We determine the use of a weed of national significance, Gorse (Ulex europaeus L.), by native mammals, birds, reptiles and vascular plants in pastoral areas in an Australian biodiversity hotspot. Large numbers of fauna species were observed using Gorse within our 43 × 1 ha sample sites in riparian, woodland and pasture vegetation. Gorse cover and/or height positively influenced: the detection of mammals as a whole in an interaction with visibility at 50–75 cm above ground, but not their species richness or individual species abundances; bird abundance, but not richness; and, reptile richness but not abundance. In terms of flora, Gorse cover and/or height positively affected: non‐native plant species richness and the height and fecundity, but not the richness, of native grasses and forbs—but Gorse cover negatively influenced the height of native herbs. The only species of conservation significance using Gorse were three mammals, only one of which, the Tasmanian Pademelon (Thylogale billardieri), was sufficiently common to analyse. Its abundance had no relationship with Gorse cover or height. Even in the wider context of complementary work, there is no strong threatened species conservation justification for retaining Gorse thickets in the Northern Midlands pastoral landscape. Equally, expending scarce conservation resources to remove Gorse, as is taking place, is unlikely to achieve any threatened species conservation outcome but may help reduce long‐term loss of native animal and plant species.     

Toxicity of rhizomes of the invasive Hedychium coronarium (Zingiberaceae) on aquatic species

The production and release of chemical compounds by invasive plants can affect competitors and native species overall, destabilizing ecological interactions and harming ecosystem functioning. Hedychium coronarium is an invasive macrophyte common on Brazilian riparian areas that produces a wide variety of allelochemicals, but little is known about their effect on aquatic species. Here, we identified the major chemical compounds of the aqueous extract of H. coronarium rhizomes and assessed its toxicity, evaluating the growth inhibition of one alga (Raphidocelis subcapitata) and one macrophyte (Lemna minor), and the lethality of cladoceran (Ceriodaphnia silvestrii and Daphnia similis) and Chironomidae larvae (Chironomus sancticaroli). The majoritarian compounds of H. coronarium rhizomes were Coronarin D and Coronarin D Ethyl Ether. The aqueous extract was toxic for all tested species. We observed growth inhibition in R. subcapitata, as well as reduction in biomass in L. minor. Chironomus sancticaroli and cladoceran were the most sensible species. The aqueous extract of H. coronarium rhizomes was toxic on tested conditions, suggesting that the rhizome compounds may interfere on aquatic organisms and in the dynamic of trophic webs of aquatic ecosystems on invaded areas.

     

Native–Exotic Species Richness Relationships Across Spatial Scales in a Prairie Restoration Matrix

In highly invaded ecosystems, restoration of native plant communities is dependent upon reducing exotic species relative to native species. Even so, in monitoring, the native–exotic species richness ratio has been shown to be scale‐dependent. Measurement at small spatial scales (<1 m²) can reveal a negative native–exotic richness relationship, where niche occupation may prevent invasion. Conversely, at larger scales, a positive correlation may exist, where environmental heterogeneity and equally favorable conditions may drive native–exotic relationships. Here, we compare slopes of native–exotic relationships across spatial scales in a prairie undergoing active restoration. The observed native–exotic richness ratios varied considerably over scales ranging from 1 to 1,000 m², emphasizing the importance of choosing a measurement scale that is most pertinent to the treatment and ecological mechanism used to evaluate restoration success. Our native–exotic richness slopes were positive over all scales, but lower than would be expected in a random community assembly, suggesting the influence of niche‐based competition. Correspondingly, our native–exotic cover slope was more negative than a null model; however, areas of frequent fire treatments showed a significant deviation from null only for richness, indicating that burning may enhance native–exotic competitive dynamics for number of species but not cover. The negative native–exotic cover relationships appear to be driven in this system mainly by exotic graminoids, across burn treatments and native functional groups, supporting the concept that frequent burning can alter the dominant competitive mechanism from coverage of these exotic grasses to an improved environment for germination and dispersal of more native species.     

Shrubland Restoration Following Woody Alien Invasion and Mining: Effects of Topsoil Depth, Seed Source, and Fertilizer Addition

Invasion by woody alien plants, construction, and mining operations are among the major disturbances degrading vegetation in the Cape Floristic Kingdom, South Africa. The aim of this study was to assess whether native fynbos shrubland vegetation could be restored following dense alien invasion and disturbance by mining. An area supporting dense alien trees was cleared and topsoil was stripped and stockpiled to simulate mining disturbance. A field trial investigated the effects of topsoil depth, seed mix application, and fertilizer on native species recruitment and vegetation development over a three‐year period. Soil‐stored seed banks contributed 60% of the species recruited, indicating that areas invaded for three decades have good restoration potential. The addition of a fynbos seed mix, which included serotinous overstory species, improved both the richness and structural composition of the vegetation. Most species sown in untopsoiled plots established, but survival and growth was low compared to topsoil plots. Poor growth in combination with a lack of soil seed bank species, indicate that restoring a diverse and functional cover of indigenous vegetation on subsoil is not possible in the short‐term. Soil amelioration is required to improve rooting conditions and initiate ecosystem processes. Shallow and deep topsoil treatments yielded high plant density, richness, and projected canopy cover, but canopy cover was higher in deep topsoil plots throughout the trial. Fertilizer addition increased canopy cover in untopsoiled and shallow topsoil plots via an increase in alien annual species. Fertilizer addition ultimately may lead to increased native vegetation cover in untopsoiled areas, but as it increased proteoid mortality on deep topsoil plots, it is not recommended for sites where topsoil is available. A species‐rich and structurally representative fynbos community may be restored on topsoiled areas provided that the native disturbance regime is simulated and seeds of major structural guilds not present in the soil seed bank are included in the seed mix.     

Efficacy and non-target effects of herbicides in foothills grassland restoration are short-lived

Questions

Selective herbicides are frequently used in ecological restoration to control invasive non-native forbs and recover plant communities. However, the long-term efficacy of this practice, its non-target effects on native plants, and its role in facilitating secondary invasions are not well understood. Similarly, little is known about the extent to which herbicide drift may affect native plant communities.

Location

Foothills grasslands of Montana, USA.

Methods

We conducted a 6-year experiment to investigate changes in the abundance of a target invasive plant, knapweed (Centaurea stoebe subsp. micranthos) and plant community structure in response to the herbicides Tordon® (picloram) and Milestone® (aminopyralid), applied at a recommended rate and a diluted rate that simulated drift.

Results

Knapweed cover and the richness of native and non-native forb species declined in the first 3 years in response to treatment at recommended rates, but not drift rates. Secondary invasion by non-native monocots was significant but weak. The cover of native forbs and the cover and richness of native monocots did not differ among treatments but changed significantly with the year. Surprisingly, 6 years after treatments, there were no differences among treatments in the cover of the target invasive plant or community structure.

Conclusions

Our results demonstrate that the efficacy and non-target effects of herbicides in grassland restoration can be short-lived and idiosyncratic because of year effects. Restoration of knapweed invasions might require other active interventions, such as seeding or repeated spraying. Our study supports previous calls for long-term monitoring of herbicides application in ecological restoration.     

Ecological succession in areas degraded by bauxite mining indicates successful use of topsoil

Brazilian ironstone outcrops (cangas) are nutrient‐poor stressful habitat dominated by slow‐growing woody species with high biodiversity and unique evolutionary history. Mining has produced great impacts on this ecosystem. Spontaneous regeneration of abandoned canga mined areas has not been observed. One of the active methods most widely used for ecological restoration in environments where soil has been lost or severely degraded is topsoil transposition due to the physical, chemical, and microbiological improvement of the substrate, in addition to the seed bank. Thus, plant succession was monitored for 40 months after topsoil transposition in a canga area degraded by aluminum mining, without any other type of management. A completely randomized design with 70 permanent plots (1 × 1 m) was used. Annual phytosociological surveys were carried out and floristic and vegetational spectra were constructed with the life‐forms proposed by Raunkiaer. Floristic composition was compared with a reference site. Overall, 105 species were identified. Both flora and vegetation changed over time, increasing resemblance to the reference areas. The floristic and vegetational spectra after 4 years of topsoil deposition are similar to pristine ones. The vegetation spectrum showed an increase in the dominance of phanerophytes and hemicryptophytes, while therophytes reduced their proportion. The early successional stage is dominated by weeds, like in other canga restoration studies, but did not impede the native species regeneration. Cangas's species recruited well from transposed topsoil. Unlike other studies with fertilized topsoil, our findings show the efficiency of topsoil transposition to provide initial conditions for the ecological restoration of this ecosystem.     

Inferring relationships between native plant diversity and Lonicera japonica in upland forests in north Mississippi,USA

Question: Do anthropogenic disturbances interact with local environmental factors to increase the abundance and frequency of invasive species, which in turn exerts a negative effect on native biodiversity? Location: Mature Quercus‐Carya and Quercus‐Carya‐Pinus (oak‐hickory‐pine) forests in north Mississippi, USA. Methods: We used partial correlation and factor analysis to investigate relationships between native ground cover plant species richness and composition, percent cover of Lonicera japonica, and local and landscape‐level environmental variables and disturbance patterns in mature upland forests. We directly measured vegetation and environmental variables within 34 sampling subplots and quantified the amount of tree cover surrounding our plots using digital color aerial photography. Results: Simple bivariate correlations revealed that high species richness and a high proportion of herbs were associated with low Lonicera japonica cover, moist and sandy uncompacted soils, low disturbance in the surrounding landscape, and periodic prescribed burning. Partial correlations and factor analysis showed that once we accounted for the environmental factors, L japonica cover was the least important predictor of composition and among the least important predictors of species richness. Hence, much of the negative correlation between native species diversity and this invasive species was explained by soil texture and local and landscape‐level land‐use practices. Conclusions: We conclude that negative correlations between the abundance of invasive species and native plant diversity can occur in landscapes with a gradient of human disturbance, regardless of whether there is any negative effect of invasive species on native species.