Effects of Revegetation on Soil Microbial Biomass,Enzyme Activities,and Nutrient Cycling on the Loess Plateau in China

Revegetation is a traditional practice widely used for soil and water conservation on the Loess Plateau in China. However, there has been a lack of reports on soil microbial–biochemical indices required for a comprehensive evaluation of the success of revegetation systems. In this study, we examined the effects of revegetation on major soil nutrients and microbial–biochemical properties in an artificial alfalfa grassland, an enclosed natural grassland, and an artificial shrubland (Caragana korshinskii), with an abandoned cropland as control. Results showed that at 0–5, 5–20, and 20–40 cm depths, soil organic carbon, alkaline extractable nitrogen and available potassium were higher in natural grassland and artificial shrubland compared with artificial grassland and abandoned cropland. Soil microbial biomass C (Cmic) and phosphorous (Pmic) substantially decreased with depth at all sites, and in abandoned cropland was significantly lower than those of natural grassland, artificial grassland, and artificial shrubland at the depth of 0–5 cm. Soil microbial biomass N (Nmic) was higher in artificial shrubland and abandoned cropland compared with that in natural and artificial grasslands. Both Cmic and Pmic were significantly different between the 23‐year‐old and the 13‐year‐old artificial shrublands at the 0–5 cm depth. The activities of soil invertase, urease, and alkaline phosphatase in natural grassland and artificial shrubland were higher than those in artificial grassland and abandoned cropland. This study demonstrated that the regeneration of both natural grassland and artificial shrubland effectively preserved and enhanced soil microbial biomass and major nutrient cycling, thus is an ecologically beneficial practice for recovery of degraded soils on the Loess Plateau.     

Growth Response of Coyote Willow (Salix exigua) Cuttings in Relation to Alluvial Soil Texture and Water Availability

A common approach to re‐establishing cottonwood–willow habitat along regulated rivers is through installing dormant, rootless cuttings, yet there is little published information exploring floodplain characteristics that optimize growth of southwestern riparian willows planted in this manner. The goal of this project was to evaluate relationships between growth attributes of Salix exigua and soil texture and soil water availability. Monitoring plots were established in five willow swales planted with dormant S. exigua cuttings along the banks of the Middle Rio Grande in central New Mexico. Data analysis revealed significantly higher aerial cover, height, and stem density for S. exigua plants installed in plots with intermediate levels (15–25%) of fine textured soils distributed through the soil profile. Similar relationships were found in relation to soil water availability. Regression analysis of percent fines and available water at different depth increments provided limited explanation of variability in willow growth attributes at different plots. Findings indicate that S. exigua plants established from cuttings can achieve heights and aerial cover values similar to naturally established willow bars if the floodplain soil profile contains intermediate levels of fine textured soils and the maximum depth to groundwater is within 1.5 m of the ground surface. Where sites are dominated by coarse sand, S. exigua growth may be improved if maximum depth to groundwater is within 1 m of the ground surface.     

Effects of water additions,chemical amendments,and plants on in situ measures of nutrient bioavailability in calcareous soils of southeastern Utah,USA

Barren, subgrade serpentine substrates are difficult to revegetate due to N, P, and K deficiencies, low Ca:Mg molar ratios, potentially high levels of heavy metals including Ni, Cr, and Co, low organic matter, low CEC, and poor water holding capacity. Several large, bare roadcuts exist in the North Coast Ranges along the west coast of California, USA. Substrate was collected from a large roadcut that has remained barren for more than a decade despite conventional surface amendment with NPK fertilizer and seeding with a mix including nonserpentine grasses and herbs. Although serpentine plant communities have been studied globally in great detail, very little information exists on how to effectively restore these communities after drastic disturbance (removal of topsoil and loss of biological activity). This rhizotron study examined how surface layering and mixing yard waste compost into serpentine substrate affected biomass production, rooting distribution, and tolerance of native, as well as invasive grass species that grow on serpentine. Roots of less serpentine-tolerant species became necrotic upon contact with the serpentine substrate in the layered compost application treatment. The roots of highly serpentine-tolerant species, however, displayed a superior tolerance to the serpentine substrate and were able to grow through its entire depth. Mixing the compost into the serpentine substrate significantly improved the Ca content of the growing medium, allowing the less serpentine-tolerant species to root through the entire depth. Although the compost surface layer treatment promoted growth of the highly serpentine-tolerant species in the serpentine substrate, mixing the compost amendment into the substrate would also permit additional desirable revegetation species to become established.     

River Restoration in Victoria, Australia: Change is in the Wind, and None too Soon

Stream restoration has become a multibillion dollar industry worldwide, yet there are few clear success stories and the scientific basis for effective stream restoration remains uncertain. We compiled data on completed river restoration projects from four management authorities in Victoria, Australia, to examine how the available data could inform the science of restoration ecology in rivers, and thus improve future restoration efforts. We found that existing data sources are limited and much historical information has been lost through industry restructuring and poor data archiving. Examining records for 2,247 restoration projects, we found that riparian management projects were the most common, followed by bank stabilization and in‐stream habitat improvement. Only 14% of the project records indicated that some form of monitoring was carried out. It is evident that overall there is little scientific guidance and little or no monitoring and evaluation of the projects for which we had information. However, recent advances with mandatory, statewide reporting and an increased emphasis on project design and monitoring strongly suggest that the design, implementation, monitoring, and reporting of stream restoration projects have improved in recent years and will continue to do so.     

Edge effects across boundaries between natural and restored jarrah (Eucalyptus marginata) forests in south‐western Australia

Edge effects are a widespread and ubiquitous ecological phenomenon, yet they remain poorly studied across edges between restored and natural forests. To address this lack of knowledge, we studied vertebrate communities across edges between 3‐year old restored mine‐pits and adjacent unmined forest in the jarrah (Eucalyptus marginata) forest of south‐western Australia. We found that mammal communities showed no edge response but reptile communities did. Overall reptile abundance and Morethia obscura abundance were higher in unmined forest along edges, Egernia napoleonis abundance was lower in unmined forest along edges, while Pogona minor abundance was lower in restored mine‐pits along edges. Predictive models were unable to predict species edge responses, due to the lack of knowledge of the ecology of jarrah forest reptiles, but proved useful in identifying potential ecological mechanisms behind observed edge responses and suggested that potential mechanisms were likely different for each species. Our study is the first to show edge responses in both habitats forming the edge between restored and natural forests, emphasizing the importance of studying both habitats forming the edge. Our results also suggest that, despite being poorly studied, edge responses are common across edges between restored and natural forest and result from a variety of ecological mechanisms. An increased understanding of the ecological mechanisms driving edge responses across edges between restored and natural forests will improve our ability to integrate restored areas into cross‐landscape management and, ultimately, improve our ability to manage landscapes for biodiversity conservation.     

Restoring habitat connectivity over the road: vegetation on a fauna land‐bridge in south‐east Queensland

The Compton Road overpass in southern Brisbane is known to be allowing passage by numerous birds, reptiles and amphibians; but what type of vegetation is providing habitat suitable for these movements? An evaluation of the reconstructed vegetation on the overpass shows that 45 species of plants were present after 4 years of growth. Most of these were in the original planting list but over 40% have almost certainly come from salvaged native topsoil used in the bypass construction. The resulting habitat, 4 years later, now appears similar to a typical coastal eucalypt forest secondary succession, although not yet identical to nearby forest. The current presence of a dense mid‐layer of small trees and shrubs may be an important factor in allowing even the edge‐avoiding species to cross the road. On‐going investigation of successional changes and the changing responses of the birds and other taxa will contribute to understanding the functionality of such crossing structures.     

Mating system and early viability resistance to habitat fragmentation in a bird-pollinated eucalypt

Habitat fragmentation has been shown to disrupt ecosystem processes such as plant-pollinator mutualisms. Consequently, mating patterns in remnant tree populations are expected to shift towards increased inbreeding and reduced pollen diversity, with fitness consequences for future generations. However, mating patterns and phenotypic assessments of open-pollinated progeny have rarely been combined in a single study. Here, we collected seeds from 37 Eucalyptus incrassata trees from contrasting stand densities following recent clearance in a single South Australian population (intact woodland=12.6 trees ha⁻¹; isolated pasture=1.7 trees ha⁻¹; population area=10 km²). 649 progeny from these trees were genotyped at eight microsatellite loci. We estimated genetic diversity, spatial genetic structure, indirect contemporary pollen flow and mating patterns for adults older than the clearance events and open-pollinated progeny sired post-clearance. A proxy of early stage progeny viability was assessed in a common garden experiment. Density had no impact on mating patterns, adult and progeny genetic diversity or progeny growth, but was associated with increased mean pollen dispersal. Weak spatial genetic structure among adults suggests high historical gene flow. We observed preliminary evidence for inbreeding depression related to stress caused by fungal infection, but which was not associated with density. Higher observed heterozygosities in adults compared with progeny may relate to weak selection on progeny and lifetime-accumulated mortality of inbred adults. E. incrassata appears to be resistant to the negative mating pattern and fitness changes expected within fragmented landscapes. This pattern is likely explained by strong outcrossing and regular long-distance pollen flow.     

The Role of the Forest Soil Propagule Bank in Assisted Natural Recovery after Oil Sands Mining

This study was undertaken to determine if use of stratified organic layers of intact litter, fragmented litter, and humus on the forest floor (LFH) improves establishment of upland native boreal plant species during oil sands reclamation in Alberta, Canada. The abundance and composition of vascular plant species in the soil propagule bank were determined for LFH and peat materials before salvage from donor sites and 18 months after application on the receiver site. Applications of 10 and 20 cm were evaluated. Various soil properties were assessed to determine impacts of donor materials. In the growth chamber, LFH donor material had significantly more plant species emerge (37) from the propagule bank than did peat donor material (19). In the field, LFH treatments had significantly higher species richness (49, 47, 24, and 25 species for LFH 10 cm, LFH 20 cm, peat 10 cm, and peat 20 cm treatments, respectively), plant abundance, and soil nutrients than peat treatments. Application thickness of peat had little effect, but 20 cm of LFH was more beneficial for plant community establishment than 10 cm. LFH treatments had narrower C:N ratios and higher soluble potassium and available phosphorus than peat. Applying 10 versus 20 cm of donor material increased admixing of fine‐textured subsoil, reducing organic carbon, nitrogen, and potassium; these effects were greater for LFH than peat treatments. Thus, addition of LFH aids in creating diverse ecosystems on reclaimed upland landscapes by providing a source of propagules for revegetating upland boreal forest communities and improving nutrient availability for plants.     

Polyploidy: a missing link in the conversation about seed transfer of a commonly seeded native grass in western North America

The use of local, native plant materials is now common in restoration but testing for polyploidy in seed sources is not. Diversity in cytotypes across a landscape can pose special seed transfer challenges, because the methods used to determine genetically appropriate materials for seed transfer do not account for cytotypic variation. This lack of consideration may result in mixing cytotypes through revegetation, which could reduce long‐term population viability. We surveyed nine populations of a native bunchgrass, Pseudoroegneria spicata, in three EPA Level III Ecoregions in the western United States to determine the frequency of polyploidy, whether there are differences in traits (phenotype, fecundity, and mortality) among plants of different cytotypes, and whether cytotype frequency varies among ecoregions. We assessed trait variation over 2 years in a common garden and determined ploidy using flow cytometry. Polyploidy and mixed cytotype populations were common, and polyploids occurred in all ecoregions. Four of the nine populations were diploid. The other five had tetraploids present: three had only tetraploid individuals whereas two had mixed diploid/tetraploid cytotypes. There was significant variation in traits among cytotypes: plants from tetraploid populations were larger than diploid or mixed populations. The frequency and distribution of cytotypes make it likely that seed transfer in the study area will inadvertently mix diploid and polyploid cytotypes in this species. The increasing availability of flow cytometry may allow ploidy to be incorporated into native plant materials sourcing and seed transfer.