Vegetation and soil recovery following Eucalyptus grandis removal in Limpopo Province,South Africa

South African terrestrial ecosystems are invaded by hundreds of alien plant species, and large‐scale clearing based on the passive restoration assumption that cleared areas will recover unaided is underway. This study assessed the recovery of vegetation and soil properties, three years following Eucalyptus grandis clearing using fell‐and‐removal and fell‐and‐stackburn methods at Zvakanaka Farm in Limpopo Province, South Africa. The main aim was to ascertain the extent of vegetation and soil recovery, as well as determining which clearing methods facilitate passive vegetation and soil restoration. Results indicate significantly (p < 0.001) lower native species diversity, cover and composition in cleared than in uninvaded sites. However, the recorded low species diversity and composition in cleared sites were more pronounced in the fell‐and‐stackburn than in the fell‐and‐removal sites. Measured soil physical properties varied, with compaction being higher in fell‐and‐removal, whereas soils were more repellent in fell‐and‐stackburn sites. The study concludes that vegetation and soil recovery, following E. grandis clearing, is complex and involves several interacting factors, which are linked to invasion history and intensity. Therefore, for vegetation and soil properties to recover, following E. grandis removal, the clearing programme should consider active restoration techniques, for example soil manipulation and native plant seeding.     

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.     

Effect of woody vegetation clearing on nutrient and carbon relations of semi-arid dystrophic savanna

Throughout the savanna biome, woody vegetation is cleared to increase productivity of herbaceous pasture. While clearing can result in increased pasture production of semi-arid dystrophic savannas in the short term, it is uncertain whether production is sustained in the long term. There is insufficient knowledge of how clearing affects soil nutrient and organic carbon (SOC) stocks. Using cleared-uncleared site pairs, we evaluated techniques for time-integrated assessment of nutrient and carbon relations in Australian savanna. Short-term in situ resin incubation showed that soil at cleared sites had a higher time-integrated availability of ammonium and nitrate, indicating that nitrogen (N) may turn over faster and/or is taken up slower at cleared sites than uncleared savanna. Nitrate and ammonium availability was approximately 2-fold higher in spring than in summer, likely due to greater uptake and/or loss of nitrate during summer rains. Nitrate was a prominent N source for evergreen trees, especially before summer rain, pointing to a role of trees as permanent N sinks. Stable isotope signatures of soil and vegetation indicate that N input occurs via N₂ fixing microbiotic crusts and Acacia species. 30 years after clearing, SOC contained more C₄ grass-derived carbon than uncleared savanna, but this shift in C source was not associated with the net C gain often observed in grasslands. Interactions between altered nutrient and C relations and composition of the understorey should be assessed in context of introduced buffelgrass (Cenchrus ciliaris) which had higher macronutrient concentrations than native grasses. Heterogeneity of the studied soils highlights the need for replication at several spatial scales to infer long-term dynamics with space-for-time chronosequences. We conclude that the techniques presented here are useful for gaining knowledge of the biogeochemical processes governing savannas and the systems that result from clearing.     

Experimental evidence for a delayed response of the above-ground vegetation and the seed bank to the invasion of an annual exotic plant in deciduous forests

Invasions by alien plants significantly affect native biodiversity and ecosystem functioning. We conducted a 5-year field experiment to investigate potential effects of the annual invasive plant Impatiens glandulifera on both the native above-ground vegetation and the soil seed bank in a deciduous forest in Switzerland. Eight years after the establishment of I. glandulifera, we set up plots in patches invaded by the alien plant, in plots from which the invasive plant had been manually removed and in plots which were not yet colonized by the invasive plant. We examined plant species richness, diversity and plant species composition in the above-ground vegetation and soil seed bank in all plots one year and five years after the initiation of the experiment. The 36 plots (3 plot types × 6 replicates × 2 sites) were equally distributed over two forest sites. Neither the native above-ground vegetation nor the soil seed bank was influenced by the presence of I. glandulifera one year after the start of the field experiment. After five years, however, plant species richness of both the above-ground vegetation and the soil seed bank was reduced by 25% and 30%, respectively, in plots invaded by the alien plant compared to plots from which I. glandulifera had been removed or uninvaded plots. Furthermore, plots invaded by the alien plant had a lower total seedling density (reduction by 60%) and an altered plant species composition in the soil seed bank compared to control plots. Our field experiment indicates that negative effects of the annual invasive plant on the native above-ground vegetation and soil seed bank of deciduous forests become visible with a delay of several years.     

Effect of alien riparian vegetation and its removal on a highly endemic river macroinvertebrate community

Invasive alien trees along river banks can reduce indigenous biodiversity, while their removal can restore it. We assessed here family- and species-level responses of river benthic macroinvertebrate assemblages to three riparian vegetation types (natural, alien trees, cleared of alien trees) in the Cape Floristic Region biodiversity hotspot. High species beta diversity of this highly endemic fauna meant that between-river, as well as seasonal effects, dominated assemblage patterns. SASS5, a qualitative, rapid bioassessment technique, based on the sensitivity of the families present, was used as a measure of river health and, indirectly, of water quality. SASS indicated a decline in water quality conditions after alien clearing, a likely response to the greater insolation and apparent erosion of cleared banks, resulting in elevated temperatures and suspended solids and lowered oxygen levels. Overall, cleared and natural sites were more similar to each other than to alien sites, suggesting some post-clearing recovery. However, many sensitive, endemic taxa survived in alien-invaded sites, and more than in the natural sites. These endemic species made use of shady, cool, high-oxygen levels under the alien tree canopy. However, endemics declined in overall abundance in sites cleared of aliens, being replaced by more tolerant, widespread taxa. Clearance of the alien trees opened up the rivers to sunny conditions, which had a major impact on community composition. Vegetation types, oxygen levels and river width were important environmental variables affecting these macroinvertebrate responses. Re-establishment of invertebrate biodiversity matched that of indigenous vegetation, with the most sensitive endemic taxa only recovering after establishment of bushy indigenous and shade-producing fynbos. Therefore, for biodiversity conservation objectives to be achieved, it is essential that indigenous plants are maintained and encouraged during and after clearing to ensure the recovery of endemic and sensitive taxa.     

Ants as indicators for vertebrate fauna at a local scale: an assessment of cross-taxa surrogacy in a disturbed matrix

We examined the spatial fidelity in the pattern in species richness, abundance and composition of ants, birds, mammals and reptiles in a Eucalyptus vegetation type in Australian tropical savanna woodland. We sampled 32 sites representing intact (uncleared) vegetation, and three treatments of different clearing age (2, 12 and 18 years). We investigated whether each fauna taxon could act a surrogate for pattern in the other, and whether they responded in parallel to time since clearing. Reptiles and mammals were combined into a single group. The correlation between taxa was low for abundance (the best being between rept/mamm and ant abundance R = 0.34) and moderate for species richness (varied from 0.36 to 0.44). Mantel tests identified a moderately strong relationship between bird and rept/mamm composition (R = 0.48). Recent clearing (2–12 years) depleted both abundance and species richness of the vertebrate fauna, whereas ant abundance spiked. Ant species richness was consistent over time since clearing. ANOSIM revealed that clearing age was a strong a priori predictor of birds and rept/mamm composition (Global R = 0.48, 0.65, respectively), whereas it was not for ants (Global R = 0.20). Pair-wise comparisons suggested that for birds, rept/mamm, there was consistent changes in composition from intact woodlands to different aged clearing. This was not the case for ants; most distinct variation in composition occurred between treatments of increasing in clearing age (2–18 years R = 0.69, 12–18 years R = 0.65). The results of this study do not support the use of ants as a surrogate of vertebrates at a local scale in a cleared and intact vegetation mosaic. We acknowledge that identification of universal surrogates and indicators are difficult to find, but funding and political expediency that demand rapid solutions to conservation planning necessitate continued investigation of the merits of using surrogate species.     

Effects of exotic guava (Psidium guajava L.) invasion on soil properties in Limpopo,South Africa

Many studies in South Africa have examined the impacts of alien plants on ecosystems, but none have assessed the impact of guava (Psidium guajava L.) invasion on soil properties. In this study, soils underneath guava-invaded sites were assessed to determine if they had different soil physico-chemical properties (pH, P, C, N, Na, K, Ca, Mg, moisture, penetration resistance, infiltration and water repellency) as compared to soils underneath uninvaded sites. Comparisons were made from three different sites over three autumn months. Results show that soil pH was significantly (p < 0.005) higher underneath uninvaded than guava-invaded sites. Soil P was three times higher underneath guava-invaded as compared to invaded sites. The soils collected underneath guava-invaded sites had a significantly (p < 0.001) higher moisture content and were less compact but more repellent than soils from the uninvaded sites. Infiltration rate was significantly (p < 0.001) higher in the uninvaded than the guava-invaded sites. The study concludes that guava invasion alters some soil properties, thus creating favourable conditions for its growth and making it potentially more invasive. From a management standpoint, guava removal is encouraged; however, given guava's socio-economic importance more research on cost and benefits is required.     

Agricultural acceleration of soil carbonate weathering

Soil carbonates (i.e., soil inorganic carbon or SIC) represent more than a quarter of the terrestrial carbon pool and are often considered to be relatively stable, with fluxes significant only on geologic timescales. However, given the importance of climatic water balance on SIC accumulation, we tested the hypothesis that increased soil water storage and transport resulting from cultivation may enhance dissolution of SIC, altering their local stock at decadal timescales. We compared SIC storage to 7.3 m depth in eight sites, each having paired plots of native vegetation and rain‐fed croplands, and half the sites having additional irrigated cropland plots. Rain‐fed and irrigated croplands had 328 and 730 Mg C/ha less SIC storage, respectively, compared to their native vegetation (grassland or woodland) pairs, and irrigated croplands had 402 Mg C/ha less than their rain‐fed pairs (p < .0001). SIC contents were negatively correlated with estimated groundwater recharge, suggesting that dissolution and leaching may be responsible for SIC losses observed. Under croplands, the remaining SIC had more modern radiocarbon and a δ¹³C composition that was closer to crop inputs than under native vegetation, suggesting that cultivation has led to faster turnover and incorporation of recent crop carbon into the SIC pool (p < .0001). The losses occurred just 30–100 years after land‐use changes, indicating SIC stocks that were stable for millennia can rapidly adjust to increased soil water flows. Large SIC losses (194–242 Mg C/ha) also occurred below 4.9 m deep under irrigated croplands, with SIC losses lagging behind the downward‐advancing wetting front by ~30 years, suggesting that even deep SIC were affected. These observations suggest that the vertical distribution of SIC in dry ecosystems is dynamic on decadal timescales, highlighting its potential role as a carbon sink or source to be examined in the context of land use and climate change.     

The invasive alien plant species Solidago gigantea alters ecosystem properties across habitats with differing fertility

Question: Invasive alien plants can affect biomass production and rates of biogeochemical cycling. Do the direction and intensity of such effects depend upon the functional traits of native and alien species and upon the properties of the invaded habitat, with the same alien species having differing impacts in different habitats? Location: Lowlands of Switzerland. Methods: Fourteen grassland and wetland sites invaded by Solidago gigantea and widely differing in biomass production and soil P availability were surveyed. To determine whether the impact of the species was related to site fertility, we compared the invaded and native vegetation in terms of biomass, species composition, plant traits and soil properties. Results: S. gigantea generally increased the above‐ground biomass production of the vegetation and soil C content, while reducing nutrient concentrations in biomass and N availability in the soil. However, it had no significant effect on plant species richness, soil respiration, soil pH and P availability. Leaves of S. gigantea had a greater C content than those of native species; other leaf traits and root phosphatase activity did not differ significantly. Conclusions: Our results suggest that a conservative nutrient‐use strategy allows S. gigantea to invade a broad range of habitats. The observed effects of invasion did not vary according to biomass production of the invaded sites, but some effects did depend on soil P availability, being more pronounced at more P‐rich sites. Thus, the full range of invaded habitats should be considered in studying the potential impact of plant invasions on ecosystem processes.     

The effectiveness of active and passive restoration on recovery of indigenous vegetation in riparian zones in the Western Cape,South Africa: A preliminary assessment

Riparian ecosystems in South Africa's fynbos biome are heavily invaded by alien woody plants. Although large-scale clearing of these species is underway, the assumption that native vegetation will self-repair after clearing has not been thoroughly tested. Understanding the processes that mediate the recruitment of native species following clearing of invasive species is crucial for optimising restoration techniques.This study aimed to determine native species recovery patterns following implementation of different management interventions. We tested the influence of two clearing treatments (“fell & remove” and “fell & stack burn”) on the outcomes of passive restoration (natural recovery of native riparian species) and active restoration (seed sowing and planting of cuttings) along the Berg River in the Western Cape. Under greenhouse conditions we investigated seed viability and germination pre-treatments of selected native species.There was no recruitment of native species in sites that were not seeded (passive restoration sites), possibly because of the dominance of alien herbaceous species and graminoids or the lack of native species in the soil-stored seed bank. Germination of our targeted native species in the field was low in both “fell & remove” and “fell & stack burn” treatments. However, “fell & stack burn” gave better germination for the species Searsia angustifolia, Leonotis leonurus and Melianthus major. Seedling survival in the field was significantly reduced in summer, with drought stress being the main cause for seedling mortality. Germination rates in the greenhouse were high, an indication that harvested seeds were viable. Most seeds germinated without germination pre-treatments.We conclude that failure of native seeds to germinate under field conditions, secondary invasion of alien herbs and graminoids, the lack of native species in the soil-stored seed bank, and dry summer conditions hamper seedling establishment and recovery on sites cleared of dense stands of alien trees. For active restoration to achieve its goals, effective recruitment and propagation strategies need to be established.     

Environmental Controls on Fungal Community Composition and Abundance Over 3 Years in Native and Degraded Shrublands

Soil fungal communities have high local diversity and turnover, but the relative contribution of environmental and regional drivers to those patterns remains poorly understood. Local factors that contribute to fungal diversity include soil properties and the plant community, but there is also evidence for regional dispersal limitation in some fungal communities. We used different plant communities with different soil conditions and experimental manipulations of both vegetation and dispersal to distinguish among these factors. Specifically, we compared native shrublands with former native shrublands that had been disturbed or converted to pasture, resulting in soils progressively more enriched in carbon and nutrients. We tested the role of vegetation via active removal, and we manipulated dispersal by adding living soil inoculum from undisturbed native sites. Soil fungi were tracked for 3 years, with samples taken at ten time points from June 2006 to June 2009. We found that soil fungal abundance, richness, and community composition responded primarily to soil properties, which in this case were a legacy of plant community degradation. In contrast, dispersal had no effect on soil fungi. Temporal variation in soil fungi was partly related to drought status, yet it was much broader in native sites compared to pastures, suggesting some buffering due to the increased soil resources in the pasture sites. The persistence of soil fungal communities over 3 years in this study suggests that soil properties can act as a strong local environmental filter. Largely persistent soil fungal communities also indicate the potential for strong biotic resistance and soil legacies, which presents a challenge for both the prediction of how fungi respond to environmental change and our ability to manipulate fungi in efforts such as ecosystem restoration.     

Increase in nonnative understorey vegetation cover after nonnative conifer removal and passive restoration

Nonnative conifers are widespread in the southern hemisphere, where their use as plantation species has led to adverse ecosystem impacts sometimes intensified by invasion. Mechanical removal is a common strategy used to reduce or eliminate the negative impacts of nonnative conifers, and encourage native regeneration. However, a variety of factors may preclude active ecological restoration following removal. As a result, passive restoration – unassisted natural vegetation regeneration – is common following conifer removal. We asked, ‘what is the response of understorey cover to removal of nonnative conifer stands followed by passive restoration?' We sampled understorey cover in three site types: two‐ to ten‐year‐old clearcuts, native forest and current plantations. We then grouped understorey species by origin (native/nonnative) and growth form, and compared proportion and per cent cover of these groups as well as of bare ground and litter between the three site types. For clearcuts, we also analysed the effect of time since clearcut on the studied variables. We found that clearcuts had a significantly higher average proportion of nonnative understorey vegetation cover than native forest sites, where nonnative vegetation was nearly absent. The understorey of clearcut sites also averaged more overall vegetation cover and more nonnative vegetation cover (in particular nonnative shrubs and herbaceous species) than either plantation or native forest sites. Notably, 99% of nonnative shrub cover in clearcuts was the invasive nonnative species Scotch broom (Cytisus scoparius). After ten years of passive recovery since clearcutting, the proportion of understorey vegetation cover that is native has not increased and remains far below the proportion observed in native forest sites. Reduced natural regeneration capacity of the native ecosystem, presence of invasive species in the surrounding landscape and land‐use legacies from plantation forestry may inhibit native vegetation recovery and benefit opportunistic invasives, limiting the effectiveness of passive restoration in this context. Abstract in Spanish is available with online material.     

Alien molluscs affect the composition and diversity of native macroinvertebrates in a sandy flat of Lake Neuchâtel,Switzerland

The spread of alien molluscs is a serious threat to native biodiversity in fresh waters. Alien freshwater molluscs may deplete the resources of native species and alter the physical structure of the habitat through their shell mass. These changes might have both positive and negative effects on native community members. We investigated the native macroinvertebrate community in relation to the densities of four alien mollusc species (Corbicula fluminea, Dreissena polymorpha, Potamopyrgus antipodarum and Lithoglyphus naticoides) in a sandy flat of Lake Neuchatel, Switzerland. The habitat examined was dominated by these alien mollusc species. The abundance of the alien molluscs did not directly impact the native community assembly. However, C. fluminea and D. polymorpha influenced the composition and diversity of native macroinvertebrates by transforming the sandy substratum into a partly hard substratum habitat. Substantial differences in community composition between shallow (<3.5 m) and (≥5 m) deep sites were recorded. At shallow sites, the abundance of D. polymorpha was significantly reduced as a result of depth-selective feeding of ducks. A controlled shell decay study revealed that shells of alien molluscs (C. fluminea, D. polymorpha) persist for a longer period in the sediment than those of native molluscs. Consequently, shells of alien molluscs have a long-lasting impact by modifying the sandy habitat. This form of ecosystem engineering favours the occurrence of several native taxa, but is disadvantageous for other taxa with specific habitat requirements, and thus can be regarded as an indirect impact of competition.     

Comparative footprint of alien, agricultural and restored vegetation on surface-active arthropods

Both invasive alien trees and agricultural conversion have major impacts on biodiversity. We studied here the comparative impact of these two types of land transformation on a wide range of surface-active arthropod species using pitfall traps, with evergreen sclerophyllous natural vegetation (fynbos) as the control. The study was in the Cape Floristic Region, a global biodiversity hotspot, where alien trees are of major concern and where vineyards replace natural fynbos vegetation. Surface-active arthropods were selected as they are species rich, relatively immobile, and occur in high abundance. We hypothesized that the impact of the two types of land cover transformation would produce similar qualitative and quantitative effects on the arthropods. We also compared the results in the transformed and natural areas with those in areas cleared of alien trees. Arthropod species richness in cleared areas was higher than in vineyards and more similar to that in natural fynbos, while alien trees had the lowest. Overall abundance scores were highest in cleared areas, closely followed by fynbos, then vineyards and lowest in alien trees. Several species were restricted to each vegetation type, including alien trees. In terms of assemblage composition, all vegetation types were significantly different, although fynbos and vineyards grouped, suggesting that vineyards have less impact on the arthropod community than do alien trees. When rare species were excluded, vineyards and cleared sites grouped, indicating some recovery but only involving those species that were common and habitat tolerant. Our results suggest that vineyards retain a greater complement of indigenous species than alien trees, but that clearing of these aliens soon encourages establishment of indigenous species. Although there were significant differences in soil moisture and litter depth within and between vegetation types, we did not record them as significantly affecting species richness or abundance, even in alien vegetation, an encouraging sign for restoration.     

Soil physiochemical changes following 12 years of annual burning in a humid–subtropical tallgrass prairie: a hypothesis

Burning is known to stimulate growth of grassland vegetation, promote species diversity, and inhibit natural invasion by woody plants. However, the frequency at which grasslands are burned as part of their management can affect soil nutrient content and, ultimately, productivity. The objective of this study was to characterize changes in soil physical and chemical properties in a native tallgrass prairie after 12 years of annual burning. In 1989, five soil samples from the 0 to 10 cm depth were collected along a transect through a 3 ha parcel of native tallgrass prairie in central Arkansas. Soil sampling was repeated in 2001 to assess changes over time. Results showed that soil bulk density, electrical conductivity, extractable P, Na, Fe, and Mn decreased significantly (P < 0.05), while soil organic matter, total N and C, and the C/N ratio increased significantly (P < 0.05) within the 12-year period during which annual burning was the only imposed management practice. Mean extractable K, Ca, Mg, S, and Zn levels were all lower in 2001 than in 1989, but differences were not significant, while soil pH did not change. The results of this study indicate that annual export of several essential plant nutrients during prescribed burning of relatively small, remnant prairie fragments exceeds annual imports from atmospheric deposition and/or organic matter mineralization. Annual prescribed burning may be too frequent to maintain optimal ecosystem functioning and productivity. Decreasing the frequency of prescribed burning for native grassland management may help to retain more soil nutrients to sustain a higher level of productivity.     

Carbon sequestration and soil restoration potential of grazing lands under exclosure management in a semi‐arid environment of northern Ethiopia

Exclosures are used to regenerate native vegetation as a way to reduce soil erosion, increase rain water infiltration and provide fodder and woody biomass in degraded grazing lands. Therefore, this study assessed the impact of grazing exclosure on carbon sequestration and soil nutrients under 5 and 10 years of grazing exclosures and freely grazed areas in Tigray, northern Ethiopia. Carbon stocks and soil nutrients increased with increasing grazing exclusion. However, open grazing lands and 5 years of grazing exclosure did not differ in above‐ and belowground carbon stocks. Moreover, 10 years of grazing exclosure had a higher (p < 0.01) grass, herb and litter carbon stocks compared to 5 years exclosure and open grazing lands. The total carbon stock was higher for 10 years exclosure (75.65 t C ha^‐1) than the 5 years exclosure (55.06 t C ha^‐1) and in open grazing areas (51.98 t C ha^‐1). Grazing lands closed for 10 years had a higher SOC, organic matter, total N, available P, and exchangeable K + and Na + compared to 5 year's exclosure and open grazing lands. Therefore, establishment of grazing exclosures had a positive effect in restoring degraded grazing lands, thus improving carbon sequestration potentials and soil nutrients.     

Ecological Assessment of Dune Restorations in the Great Lakes Region

Because of the economic and environmental importance of stabilizing fragile sand dune habitats, restoration of dunes has become a common practice. Restoration efforts in the Great Lakes and East Coast regions of North America often consist of planting monocultures of the dominant native grass species, Ammophila breviligulata. We evaluated 18 dune restoration projects in the Great Lakes region conducted over the past 25 years. We characterized attributes of diversity (plants and insects), vegetation structure (plant biomass and cover), and ecological processes (soil nutrients and mycorrhizal fungi abundance) in each restoration, and we compared these measures to geographically paired natural dune communities. Restoration sites were similar to reference sites in most measured variables. Differences between restorations and reference sites were mostly explained by differences in ages, with the younger sites supporting slightly lower plant diversity and mycorrhizal spore abundance than older sites. Plant community composition varied little between restored and reference sites, with only one native forb species, Artemisia campestris, occurring significantly more often in reference sites than restored sites. Although it remains unclear whether more diverse restoration plantings could accelerate convergence on the ecological conditions of reference dunes, in general, traditional restoration efforts involving monoculture plantings of A. breviligulata in Great Lakes sand dunes appear to achieve ecological conditions found in reference dunes.     

Influence of nests of leaf‐cutting ants on plant species diversity in road verges of northern Patagonia

Abstract. It has been suggested that ant nests are the most frequent small‐scale disturbance that affect vegetation patterns. However, their effects on plant diversity are little studied. We document effects of nests of the leaf‐cutting ant Acromyrmex lobicornis on physical‐chemical soil properties and their influence on plant diversity near road verges in a desert steppe in NW Patagonia, Argentina. We analysed nest soils and controls for nitrogen, phosphorus, organic matter, moisture retention capacity and texture. We also analysed the vegetation on 42 nests (30 active and 12 abandoned or without life) and 42 areas without nests. Soil around nests had a greater nutrient content and capacity to retain moisture than control soils, which is mainly due to the presence of organic waste that the ants deposit on the soil surface. We found no association between the occurrence of nests and specific groups of plants, but plant diversity was higher at nest‐sites than at nearby non‐nest sites. This increased diversity – which is also found on abandoned nests – is mainly due to the occurrence of a larger number of native and exotic plant species on nest‐sites that are uncommon elsewhere in the study area. The most abundant plant species showed similar cover values at nest and non‐nest sites. This suggests that changes in diversity are associated to edaphic changes caused by nests rather than by changes in competitive balance caused by dominant species exclusion. We propose that the nests of Acromyrmex lobicornis, through increasing the availability of resources, generate favourable microsites that can function both as ‘refuges’ for less frequent native species, and as‘stepping stones’ for less frequent exotic plant species.     

Relationships between anthropogenic disturbance,soil properties and plant invasion in endangered Cumberland Plain Woodland,Australia

Abstract Invasive exotic plants are a significant threat to areas of conservation value, with endangered ecological communities being especially vulnerable. We assessed the role of different anthropogenic disturbances in determining the success of exotic plants in the endangered Cumberland Plain Woodland community of western Sydney and examined the impact of these disturbances on soil characteristics that are likely to impact on vegetation, including total P, pH, water retention capacity, organic matter content and electrical conductivity. The disturbance types were: (i) land use incorporating clearing, agriculture and grazing by stock; (ii) creeks draining a developed catchment; and (iii) roads. Remnants that had been cleared and grazed had higher exotic and lower native species richness and cover than all other disturbance types. Areas that had been grazed but not cleared did not have more exotic species richness or cover than uncleared/ungrazed areas, thus retaining high conservation value. Areas within 2 m of a creek edge had higher exotic species richness and cover than areas further from the creek edge. Areas downslope of sealed roads had significantly higher exotic species richness and cover than areas below unsealed roads. No single soil attribute or combination of soil attributes was consistently able to account for variation in exotic species cover under the different disturbance types. Thus it appears that other factors such as site history and propagule pressure may be more important in determining exotic species success than soil characteristics alone, in this vegetation community.