Revegetation Trials Research Articles

Are Ecological Risk Indices for Trace Metals Relevant for Characterizing Polluted Substrates in the Katangese Copperbelt (DR Congo) and for Assessment of the Performance of Remediation Trials?

This study aims to contribute to the characterization of Katangese Copperbelt’s (DR Congo) mining wastes and soils polluted with trace metals, using pollution indices and direct concentration measurements. This study also evaluated the use of these indices in assessing the success of remediation projects. Data from previous studies and samples collected from six types of discharge and one polluted soil were used to address the first objective. Soil and plant samples were collected at Kipushi and Penga Penga for the second objective. The results reveal very high concentrations of As, Cd, Co, Cu, Mn, Pb, and Zn in all mine tailings and polluted soils, compared with local references. The degree of contamination (DC) values (from 72 to 5440) and potential ecological risk (RI) values (from 549 to 162,091) indicate very high-risk situations associated with polluted discharges and soils. Regarding revegetation trials, the results show lower concentrations and RIs in tree rhizospheres compared with unamended areas at both sites. However, trace metal concentrations are higher in tree rhizospheres compared with local references, and RI values are in the considerable risk range for Penga Penga (RI = 533) and in the very high range (>1500) for Kipushi. Bioconcentration factor values are below 1, indicating low accumulation in roots, wood, and leaves, and low risk of contamination of the trophic chain. In this context, it seems that the pollution indices used are suitable for characterizing pollution and prioritization for remediation. However, their seems unsuitable for assessing the effectiveness of phytotechnology processes based on metal stabilization. Direct plant performance measurements combined with direct measurements of metals in substrates and plants to assess transfer and efficiency are more appropriate.

Establishing a climate‐ready revegetation trial in central Victoria – A case study

SummaryA promising approach in dealing with the detrimental effects of climate change on vegetation is to introduce pre‐adapted genotypes into restoration programmes. Bush Heritage’s Victorian reserves have experienced eucalypt dieback probably due to intense drought and heat shock linked to climate change. Planned revegetation on the Nardoo Hills reserve provided an opportunity to establish and test the potential for new climate‐matched genotypes to expand the adaptive capacity of the plantings. As NRM practitioners, here we document our experiences in implementing this approach. Using the Climate Analogues tool and the Australasian Virtual Herbarium, we selected provenances from four climate analogue regions where remnants of our focal species, Grey Box (Eucalyptus microcarpa) and Yellow Box (E. melliodora), were located. Replicated plots were established covering five provenances for Grey Box and 5 provenances for Yellow Box with up to 10 ‘families’ (mother trees) per provenance. Numerous challenges were encountered including locating suitable provenances, the design and scientific compromises associated with the experimental layout, sourcing of adequate seed from remote regions (especially drought affected) and high mortality during seedling establishment. Monitoring nine months after planting revealed not only high overall mortality (around 70%, probably due to drought conditions during establishment) but also significant differences in height between provenances and in mortality and height among families in both species. Despite the initial mortality, the nested design and level of replication applied in these plots appear adequate to test hypotheses about the value of climate matching and will continue to be monitored in the future.

Enhancing seedling survival on former floodplain grazing land in the Capertee Valley, Australia

SummaryActive revegetation is an essential component of biodiversity conservation for fragmented ecosystems and the species that depend on them. However, key knowledge gaps exist around the most cost‐effective revegetation strategies to employ in different contexts. This article reports on a revegetation trial undertaken in the Capertee Valley of New South Wales, Australia, to assist the conservation of the critically endangered bird, the Regent Honeyeater (Anthochaera phrygia). Seven treatments were compared to assess their cost‐effectiveness for enhancing plant survival at a floodplain site with a history of grazing on introduced pastures. While overall survival rates were low, treatments involving tree guards had higher survival rates and were more cost‐effective than treatments without guards. Weed growth, animal activity and water stress all appeared to play a role in the low survival rates at this site, with enhanced weed control emerging as a priority for future trials at similar sites.

From lithotroph- to organotroph-dominant: directional shift of microbial community in sulphidic tailings during phytostabilization.

Engineering microbial diversity to enhance soil functions may improve the success of direct revegetation in sulphidic mine tailings. Therefore, it is essential to explore how remediation and initial plant establishment can alter microbial communities, and, which edaphic factors control these changes under field conditions. A long-term revegetation trial was established at a Pb-Zn-Cu tailings impoundment in northwest Queensland. The control and amended and/or revegetated treatments were sampled from the 3-year-old trial. In total, 24 samples were examined using pyrosequencing of 16S rRNA genes and various chemical properties. The results showed that the microbial diversity was positively controlled by soil soluble Si and negatively controlled by soluble S, total Fe and total As, implying that pyrite weathering posed a substantial stress on microbial development in the tailings. All treatments were dominated by typical extremophiles and lithotrophs, typically Truepera, Thiobacillus, Rubrobacter; significant increases in microbial diversity, biomass and frequency of organotrophic genera (typically Nocardioides and Altererythrobacter) were detected in the revegetated and amended treatment. We concluded that appropriate phytostabilization options have the potential to drive the microbial diversity and community structure in the tailings toward those of natural soils, however, inherent environmental stressors may limit such changes.

Do young trees contribute to soil labile carbon and nitrogen recovery?

Purpose This study aimed to evaluate the effects of tree cover (tree plots (Acacia disparrima and Eucalyptus crebra) vs. non-tree plots) on soil labile carbon (C) and nitrogen (N) recovery in revegetation trials, without and with topsoil removal, 3 years following tree planting.

Physiological traits of Acacia concurrens and Eucalyptus crebra with respect to radical site preparation practices in a revegetation trial, south east Queensland, Australia

Purpose To successfully establish revegetation, there is a need for weed control. Herbicide application and top soil removal (scalping) may be used to suppress weeds. However, scalping alters soil water and nitrogen availability which in turn may affect plant physiology and performance during the early phase of establishment.

Soil carbon and nitrogen dynamics in the first year following herbicide and scalping in a revegetation trial in south-east Queensland, Australia

During revegetation, the maintenance of soil carbon (C) pools and nitrogen (N) availability is considered essential for soil fertility and this study aimed to evaluate contrasting methods of site preparation (herbicide and scalping) with respect to the effects on soil organic matter (SOM) during the critical early establishment phase. Soil total C (TC), total N (TN), hot-water extractable organic C (HWEOC), hot-water extractable total N (HWETN), microbial biomass C and N (MBC and MBN), total inorganic N (TIN) and potentially mineralizable N (PMN) were measured over 53 weeks. MBC and MBN were the only variables affected by herbicide application. Scalping caused an immediate reduction in all variables, and the values remained low without any sign of recovery for the period of the study. The impact of scalping on HWETN and TIN lasted 22 weeks and stabilised afterwards. MBC and MBN were affected by both herbicide and scalping after initial treatment application and remained lower than control during the period of the study but did not decrease over time. While scalping had an inevitable impact on all soil properties that were measured, that impact did not worsen over time, and actually improved plant growth (unpublished data) while reducing site establishment costs. Therefore, it provides a useful alternative for weed control in revegetation projects where it is applied only once at site establishment and where SOM would be expected to recover as canopy closure is obtained and nutrient cycling through litterfall commences.

Study on Lowcost Revegetation Technical Measures on Ferrum Tailings Bank in Huludao, Northeast China

This study focused on the technical measures of revegetation on ferrum tailings bank in Huludao, China. Adopting field test method, a revegetation trial was conducted on the Yangjiazhangzi waste ferrum tailings bank. By composting the urban sludge + river mud + straw inside planting pit to ameliorate tailings matrix, planting perennial herb to establish closed type sand barrier to shelter bush-herbage growth, transplanting nutrition cup bush seedlings and sowing herbage seed on the composting pit to establish bush-herbage clump, these technical measures can solve the major constraints to plant growth and establish survival bush-herbage vegetation at lowcost. The results show that Pit layered composting is the cost-effective measure to improve ferrum tailings planting matrix; Planting perennial herb sand barrier t is a good measure to improve microhabitat; Planting bush-herbage clump is a good pattern to resist the extreme ferrum tailing environment; Hippophae rhamnoides Linn., Caragana Korshinskii Kom., Medicago sativa Linn.and Astragalus adsurgens Pall are good pioneer species for revegetation on the ferrum tailings bank. Experiment proved that the combination of these technical measures can reconstruct vegetation, this revegetation pattern is worthy of reference for similar mine ecological restoration.

Sediment microbial activities and physic-chemistry as progress indicators of salt marsh restoration processes

Physicochemical (organic matter content, relative humidity, humic acid content, carbon, nitrogen and phosphorous content) and microbiological activities (extracellular enzymatic activities, basal and substrate induced respiration and bioenergetical parameters) were evaluated in salt marsh degraded sediments, during a 1 year revegetation trial starting at the end of the growing season. For this revegetated with Halimione portulacoides and also in nearby sediments with savage H. portulacoides plants and bare sediments were monitored for comparison proposes. Sediments colonized by savage plants showed higher water content, organic matter, carbon, nitrogen and phosphorous contents, in contrast with the low values observed in bare and colonized by transplants sediments. Overlooking the microbial metabolic and respiratory parameters it was observed that the more efficient microbial communities were present in the sediments colonized by the savage plants. Also the extracellular enzymes showed differences. In the transplant colonized sediments and also in the bare ones, peroxidase showed high and similar activities. By the contrary urease showed lower in these last sediments. Only acid phosphatase showed a different trend being higher in the bare sediments and in the sediments colonized by savage plants. Applying a rhizosphere sediment microbial index (RSMI) it was assessed that the more important factors for these sediments evaluation were the Basal respiration, urease activity, metabolic coefficient, total phosphorous content and total carbon content. Using this index for evaluation it showed not only that the sediments colonized by savage plants presented microbial quality, but also it was shown that the bare sediments and the sediments colonized by the transplants after a 1 year period still have the same microbial characteristics and thereby similar microbial qualities. This allowed to conclude that over the duration of this experiment, the revegetated sediments were still far from reaching the quality levels of the sediments naturally colonized, indicating that the 1 year period of revegetation was not enough to a successful restoration of a degraded salt marsh. Although the restoration process was not successful, the elaboration of the RSMI proved to be useful with applications in future monitorization programs.

Controlling Kalmia and reestablishing conifer dominance enhances soil fertility indicators in central Newfoundland, Canada

Growth rates of young conifers can be poor on disturbed sites dominated by Kalmia angustifolia L. Hence, a conifer revegetation trial was established on a Kalmia -dominated site to evaluate the effects of various silvicultural options and planted species on selected soil organic layer characteristics. Larix laricina (Du Roi) K. Koch, Pinus banksiana Lamb., and Picea mariana (Mill.) BSP seedlings were planted in plots with or without Kalmia control with herbicides. The effect of fertilizer amendment was also assessed. Seventeen years postplanting, organic layer fertility indicators suggest that soil fertility improved after Kalmia control and conifer reestablishment, especially if nitrogen (N) – phosphorus – potassium fertilizer was also applied. When Kalmia was controlled, aerobically mineralizable N and exchangeable sodium concentrations were increased; fertilizer addition to herbicided plots also increased exchangeable potassium and calcium concentrations, and cation exchange capacity compared with untreated control plots. Conifer height, diameter, and canopy closure were Larix > Pinus > Picea. Kalmia cover in control plots was 87%; Kalmia reinvasion in herbicided plots achieved 40%–43% cover but did not differ among the conifer species. Principal component analysis indicated that aerobically mineralizable N and total N were positively correlated with canopy closure. Our results suggest that increases in organic-layer fertility were related to increased conifer size resulting from Kalmia control.

Distribution and Nodulation of Spontaneous Legume Species in Grasslands and Shrublands in Mediterranean Lebanon

In Lebanon, a country known for its biodiversity and plant richness, many threats including quarries endanger its natural habitats and ecosystems. With the objective of finding the most suitable legume-rhizobia associations for revegetation trials, we surveyed grasslands and shrublands in an altitudinal transect up to 1302 m in Mediterranean subhumid and humid regions. For comparison, two abandoned quarries on hard limestone were studied as well. Based on a number of criteria, the level of degradation of each site was estimated as: high, medium, or low. Sites submitted to a high degradation pressure presented a smaller number of species and lower ground coverage. The emphasis was put on the legume species encountered on these sites: 52 species were identified and separated according to their frequency. Of these, 18 target species were studied in the second season in terms of their habitat, frequency, and ground coverage. Ten common legume species were found regardless of the level of degradation. As the level of degradation increased, the number of annual legume species significantly decreased as well as their coverage coefficient, to the contrary of perennials. Spontaneous nodulation was encountered in individuals belonging to the genera Alhagi, Astragalus, Bituminaria, Calicotome, Cicer, Hippocrepis, Hymenocarpos, Lathyrus, Lotus, Lupinus, Medicago, Melilotus, Onobrychis, Ononis, Physanthyllis, Scorpiurus, Securigera, Spartium, Trifolium, and Vicia. The nodulation of Medicago coronata was reported for the first time. Individuals were better nodulated in medium-degraded sites as compared to high-degraded. Inoculated perennial (Calicotome, Spartium, Bituminaria) and annual legumes (Hymenocarpos, Onobrychis, Trifolium purpureum, T. campestre, T. tomentosum, Securigera, Physanthyllis, and Medicago polymorpha, M. minima) could be recommended as part of plant associations in revegetation projects.

Bacterial Community Changes during Plant Establishment at the San Pedro River Mine Tailings Site

Mine tailings are moderately to severely impacted sites that lack normal plant cover, soil structure and development, and the associated microbial community. In arid and semiarid environments, tailings and their associated contaminants are prone to eolian dispersion and water erosion, thus becoming sources of metal contamination. One approach to minimize or eliminate these processes is to establish a permanent vegetation cover on tailings piles. Here we report a revegetation trial conducted at a moderately impacted mine tailings site in southern Arizona. A salt and drought-tolerant plant, four-wing saltbush [Atriplex canescens (Pursh) Nutt.], was chosen for the trial. A series of 3 by 3 m plots were established in quadruplicate on the test site to evaluate growth of four-wing saltbush transplants alone or with compost addition. Results show that >80% of the transplanted saltbush survived after 1.5 yr in both treatments. Enumeration of heterotrophs and community structure analysis were conducted to monitor bacterial community changes during plant establishment as an indicator of plant and soil health. The bacterial community was evaluated using denaturing gradient gel electrophoresis (DGGE) analysis of 16S rDNA PCR gene products from tailings samples taken beneath transplant canopies. Significant differences in heterotrophic counts and community composition were observed between the two treatments and unplanted controls throughout the trial, but treatment effects were not observed. The results suggest that compost is not necessary for plant establishment at this site and that plants, rather than added compost, is the primary factor enhancing bacterial heterotrophic counts and affecting community composition.

Rehabilitation of Swamp Paperbark (Melaleuca ericifolia) wetlands in south-eastern Australia: effects of hydrology, microtopography, plant age and planting technique on the success of community-based revegetation trials

Wetlands dominated by Swamp Paperbarks (Melaleuca spp., Myrtaceae) are common in coastal regions across Australia. Many of these wetlands have been filled in for coastal development or otherwise degraded as a consequence of altered water regimes and increased salinity. Substantial resources, often involving community groups, are now being allocated to revegetating the remaining wetland sites, yet only rarely is the effectiveness of the rehabilitation strategies or on-ground procedures robustly assessed. As part of a larger project investigating the condition and rehabilitation of brackish-water wetlands of the Gippsland Lakes, we overlaid a scientifically informed experimental design on a set of community-based planting trials to test the effects of water depth, microtopography, plant age and planting method on the survival and growth of seedlings of Melaleuca ericifolia Sm. in Dowd Morass, a degraded, Ramsar-listed wetland in south-eastern Australia. Although previous laboratory and greenhouse studies have shown M. ericifolia seedlings to be salt tolerant, the strongly interactive effects of waterlogging and salinity resulted in high seedling mortality (>90%) in the field-based revegetation trials. Seedlings survived best if planted on naturally raised hummocks vegetated with Paspalum distichum L. (Gramineae), but their height was reduced compared with seedlings planted in shallowly flooded environments. Age of plants and depth of water were important factors in the survival and growth of M. ericifolia seedlings, whereas planting method seemed to have little effect on survival. Improved testing of revegetation methods and reporting of success or otherwise of revegetation trials will improve the effectiveness and accountability of projects aiming to rehabilitate degraded coastal wetlands.

Assessing various rehabilitation strategies for coarse coal washery reject dumps in the Hunter Valley, Australia. I. Chemical characteristics

At several coal mines in the Hunter Valley (New South Wales, Australia), the use of coarse coal washery reject (chitter) as a top-dressing material has resulted in successful establishment rates of tree and shrub species by direct seeding. However, concerns have arisen about the potential to downgrade the rural capability of the land for grazing, poor understanding of the material's long-term benefits, and spontaneous combustion issues. To ascertain the suitability of chitter as a final landform surface, a revegetation research trial was initiated at United Collieries coal mine in the Hunter Valley of New South Wales. Experimental plots were established in autumn (May 1998) and spring (November 1998) on a freshly shaped stockpile of chitter. The revegetation trials incorporated four substrate treatments, namely a 1 m and 20 cm capping of overburden, a 20 cm topsoil dressing and a treatment of only chitter. Each of the four substrate treatments incorporated five revegetation treatments, namely pasture species and mulch (straw), pasture species and no mulch, native seed (shrub and tree) and mulch, native seed and no mulch, and planted tubestock trees. Chemical characteristics (pH, EC, total N, nitrate-N, available-P, total P, total S, Ca, Na, Mg, K, organic C and soil moisture) across the substrate and vegetation treatments were assessed at 0, 3, 6 and 12 months after establishment. Laboratory analyses of soil samples from the autumn and spring substrate sowings concluded that the chitter treatment contained a significantly higher concentration of organic carbon (23 – 41%), Na (2.8 – 13 me/100g), total N (2600 – 5300 mg/kg) and S (900 – 4000 mg/kg), and pH was elevated (7.5 – 9.8), relative to the other substrates. The topsoil substrate had significantly greater moisture content and more nitrate-N in comparison to the overburden and chitter materials, and exhibited a significantly lower pH over time. The two overburden treatments showed similar chemical properties and contained significantly higher levels of available P relative to topsoil and chitter. In comparison to recommended levels, all substrates recorded adequate levels of Ca, Mg and K across the autumn and spring assessments and were generally deficient in nitrate-N. In the overburden materials, levels of organic carbon, electrical conductivity, exchangeable bases, total P and available P were generally adequate. However, the pH (8.1 – 8.9) and S (200 – 700 mg/kg) content of overburden was consistently high, and deficiencies in total and available nitrogen were commonly detected. Assessment of substrate samples across vegetation treatments showed few differences with only K, available P and nitrate-N varying significantly between treatments. In both the autumn and spring trials, the concentration of available P in pasture plots was significantly higher in comparison to the other vegetation treatments, while K levels were significantly higher in the pasture and mulch treatment relative to tubestock plots. This probably resulted from greater uptake of these nutrients by trees and shrubs compared to pasture species. In the autumn trials, seeded native tree plots contained significantly more nitrate-N than the other treatments, probably due to N-fixation by Acacia spp. Across both establishment seasons, topsoil provided the best chemical substrate for the establishment of vegetation and chitter was deemed the least hospitable substrate, while the different vegetation treatments appeared to have little effect on the chemical characteristics of the substrates. Vegetation characteristics across the treatments are presented in an accompanying paper (Charnock and Grant, Assessing various rehabilitation strategies for coarse coal washery reject dumps in the Hunter Valley, Australia. II. Vegetation characteristics. International Journal of Surface Mining, Reclamation and Environment, 2005 (in review)).

The potential of Lolium perenne for revegetation of contaminated soil from a metallurgical site

A greenhouse study was carried out to determine the possibility of using Lolium perenne for revegetation of soil from a former ferrous metallurgical plant (Naples, South Italy) contaminated by Cu, Pb and Zn at levels above current Italian regulatory limits. Surface soil samples (0–40 cm) from the facility area where raw minerals were disposed (RM1 and RM2), from a nearby unpolluted cultivated soil (C) as control and a 1:3 mixture of the control with the polluted ones (RM1+C and RM2+C) were utilized for the experiment. Revegetation trials were conducted in the greenhouse. At 90 days from seeding, shoot length, chlorophyll content, biomass yield, plant metal uptake and changes of organic carbon content and metal distribution among soil extractable phases defined by sequential extraction were determined. In the mixed substrates (RM1+C and RM2+C) concentrations of Cu, Pb and Zn were still two to three times higher than the Italian regulatory limits. Plants were healthy with 100% survival in all substrates, with no macroscopic symptoms of metal toxicity. The high pH of the soil could be one of the most important parameters responsible for the limited plant availability of the metals. On RM1, RM2 and mixed media, plants experienced retarded growth, reduced shoot length and biomass yield and higher total chlorophyll content compared to those cropped on the control soil, without any evident phytotoxic symptoms. In RM1 and RM2, the plant contents of Cu (19.3 and 12.6 mg kg −1), Pb (0.98 and 0.67 mg kg −1) and Zn (99 and 88 mg kg −1) were higher than that of plants grown on non-contaminated soil (Cu 10.1, Pb<0.2, Zn 79 mg kg −1), but still in the range of physiologically acceptable levels. The distribution of metals in soil was slightly affected by Lolium growth with changes only regarding the organic-bound Cu and Zn pool, with reduction up to 24%. Results indicated that an acceptable healthy vegetative cover can be achieved on the contaminated soil by the proposed revegetation approach and that metals will remain stable over the study period with slight variation of the more available metal forms.

Revegetating fly ash landfills with Prosopis juliflora L.: impact of different amendments and Rhizobium inoculation

A revegetation trial was conducted to evaluate the feasibility of growing a legume species, Prosopis juliflora L., on fly ash ameliorated with combination of various organic amendments, blue-green algal biofertilizer and Rhizobium inoculation. Significant enhancements in plant biomass, photosynthetic pigments, protein content and in vivo nitrate reductase activity were found in the plants grown on ameliorated fly ash in comparison to the plants growing in unamended fly ash or garden soil. Higher growth was obtained in fly ash amended with blue-green algae (BGA) than farmyard manure or press mud (PM), a waste from sugar-processing industry, due to the greater contribution of plant nutrients, supply of fixed nitrogen and increased availability of phosphorus. Nodulation was suppressed in different amendments of fly ash with soil in a concentration–duration-dependent manner, but not with other amendments. Plants accumulated higher amounts of Fe, Mn, Cu, Zn and Cr in various fly ash amendments than in garden soil. Further, inoculation of the plant with a fly ash tolerant Rhizobium strain conferred tolerance for the plant to grow under fly ash stress conditions with more translocation of metals to the above ground parts. The results showed the potential of P. juliflora to grow in plantations on fly ash landfills and to reduce the metal contents of fly ash by bioaccumulation in its tissues.

Assisted revegetation trials in degraded salt‐marshes

Summary1. At coastal sites adjacent to the Hudson Bay lowlands, intensive foraging by increasing numbers of lesser snow geeseAnser caerulescens caerulescenshas converted salt‐marsh swards to hypersaline mudflats largely devoid of vegetation. Assisted revegetation trials were undertaken in order to determine the ability of plants to establish in degraded salt‐marsh sediments.2. Soil plugs of the former dominant graminoids,Puccinellia phryganodesandCarex subspathacea, were transplanted into plots of hypersaline bare soil. Some plots were treated with fertilizer and peat mulch to determine if ameliorations enhance plant growth.3. Transplants ofP. phryganodesestablished in degraded sediments, but those treated with fertilizer and peat showed significantly higher growth than those in bare soil after two growing seasons. The ratio of the mean basal area of plants in treated plots compared with bare plots was between 1·7 and 4·0 : 1 at different sites. Transplants ofC. subspathaceadid not establish readily in degraded sediments and no growth enhancement was observed with soil amendments.4. Growth rate and mortality of plants both varied between sites and years, reflecting variation in the frequency of hot, dry weather from late June to early August of each year, and the salinity and water content of soils during that period. The potential for revegetation of mudflats is discussed in the context of the soil degradation processes. Fine‐grain variation in soil conditions presents a major challenge for the restoration of plant assemblages in these coastal marshes.5. The extent of soil degradation and of vegetation loss makes it unlikely that unassisted revegetation will occur at some sites, even in the absence of goose foraging, without erosion of consolidated sediments and the establishment of plant assemblages in fresh unconsolidated sediments.

Assessment of Riparian Revegetation Trials on In‐Channel Benches in the Hunter Valley of Southeast Australia

Large‐scale river training works have been carried out in the Hunter valley since 1955 in response to flood‐driven channel changes. Vegetation was planted on in‐channel benches induced by river training works to consolidate the deposits and to increase channel boundary roughness. Exotic species of vegetation such as willows and poplars were previously used. In 1983, ten trial sites were planted with various species of native vegetation. Survival rates were evaluated in 1987 and 1997. The most successful species planted was Eucalyptus camaldulensis with an overall survival rate of 77 per cent in 1997. The Acacia species were found to be short‐lived, exhibiting a significant decline in survival rates between 1987 and 1997. Survival rates for most species were higher on sand‐bed than on gravel‐bed sites. This difference may be attributed to better drainage on benches at the sand‐bed sites. Investigations of flood disturbance showed that between 1983 and 1997 the sites were flooded between four and 13 times. The survival rates of Grevillea robusta and Eucalyptus melliodora trees were negatively correlated with the total number of recorded floods at each site. Poor natural regeneration of planted species is attributed to a combination of periodic flooding, intensive weed growth, low light intensities at ground level and grazing disturbance. These trials were not well designed for statistical analysis but provide valuable long‐term information on the suitability of various species for planting in riparian rehabilitation programs. Such information is of relevance not only to river and catchment management authorities, but also to community groups.

Myrmecochory in Australia's seasonal tropics: Effects of disturbance on distance dispersal

Abstract Successful ecosystem restoration requires the re‐establishment of fundamental ecological processes, many of which involve plant‐animal interactions. Myrmecochory (seed dispersal by ants) is a particularly important plant‐animal mutualism in Australia, but little is known about its response to either disturbance or restoration following disturbance. Here we investigate the effects of disturbance on seed dispersal by ants, and the extent to which the ant‐seed relationship has re‐established at sites undergoing rehabilitation, at Ranger uranium mine in the seasonal tropics of Australia's Northern Territory. We focused on the composition of seed‐dispersing ant assemblages, rates of seed removal by ants, and the dispersal curves generated by ants, as determined by observations of removal from seed depots. Ten sites were studied, comprising four ‘natural’ (undisturbed) sites representing a range of savanna habitats occurring in the region, four disturbed sites representing a range of habitat disturbance but with intact soil, and two waste rock sites subject to preliminary revegetation trials. A total of 22 ant species from 10 genera were observed during 154 observations of seed removal, most commonly Rhytidoponera aurata (53 records), Monomorium (rothsteini gp) sp. 1 (14), Iridomyrmex sanguineus (13), Iridomyrmex pallidus (12) and Pleidole sp. 3 (10). Removal rates (over 3 h) averaged 29% across all sites and time periods, varying markedly both between and within sites. However, mean rates of removal were similar between natural, disturbed and waste rock sites (29%, 28% and 31%, respectively). A high incidence (62% of all depots) of'aril robbing’ by ants (primarily Monomorium spp.) eating arils in situ, without removal, was observed. Dispersal distances varied markedly between ant species, with Iridomyrmex sanguineus having both the highest mean (7.25m) and maximum (13.08 m) dispersal distances. Species of Pheidole typically dispersed seeds less than 0.5 m, and Meranoplus, Monomorium and Tetramorium spp. only ever moved seeds a few centimetres, usually dropping and abandoning them before reaching the nests. The dispersal curves characteristic of each site varied markedly due to the different composition of seed‐dispersing ants. The mean dispersal distance at disturbed sites (3.91 m) was significantly higher than at natural sites (2.19 m), and the curves were strongly skewed in the former, but relatively uniform in the latter. The implications of these differences for recovery following disturbance are unclear. At rehabilitated waste rock sites, all observed removals involved distances less than 0.5 m, with a mean of 17 cm. This lack of effective ant‐seed relationships might represent a barrier to further vegetation development at rehabilitated sites.

Reverdissement des terrains miniers en Nouvelle-Calédonie

Open-cut mines have produced nickel ore in New-Caledonia for over a century. The exploited areas remain bare and subject to erosion, the soils involved being poor and of an unusual type deficient in N. P. K. and with high levels of Ni, Co, Mg. Mechanical means to rehabilitate the environment have been followed by a biological approach. Revegetation trials started between 1793 and 1981, tested 8 herbaceous and 72 woody species which were evaluated over 15 years. The 16 continuing trials cover a wide range of sites and techniques (density, fertilization, preparation of the soil, mulching...)