The Initial Phase of a Longleaf Pine‐Wiregrass Savanna Restoration: Species Establishment and Community Responses

The significant loss of the longleaf pine‐wiregrass ecosystem in the southeastern United States has serious implications for biodiversity and ecosystem functioning. In response to this loss, we have initiated a long‐term and landscape‐scale restoration experiment at the 80,125 ha (310 mi²) Department of Energy Savannah River Site (SRS) located near Aiken, South Carolina. Aristida beyrichiana (wiregrass), an important and dominant grass (i.e., a “matrix” species) of the longleaf pine savanna understory, and 31 other herbaceous “non‐matrix” species were planted at six locations throughout SRS in 2002 and 2003. Of the 36,056 transplanted seedlings, 75% were still alive in June 2004, while mean 1–2 year survival across all planted species was 48%. Lespedeza hirta (hairy lespedeza) exhibited the greatest overall survival per 3 × 3 m cell at 95%, whereas Schizachyrium spp. (little bluestem) exhibited the greatest mean cover among individual species at 5.9%. Wiregrass survival and cover were significantly reduced when planted with non‐matrix species. Aggregate cover of all planted species in restored cells averaged 25.9% in 2006. High rates of survival and growth of the planted species resulted in greater species richness (SR), diversity, and vegetative cover in restored cells. Results suggest that the loss of the longleaf pine‐wiregrass ecosystem may be ameliorated through restoration efforts and illustrate the positive impact of restoration plantings on biodiversity and vegetative cover.     

Contingent Conclusions: Year of Initiation Influences Ecological Field Experiments,but Temporal Replication is Rare

Interannual variation in experimental field conditions produce variability in the results of experiments monitored over multiple years, termed here “year effects.” When experimental treatments are replicated in separate years, interannual variation may influence treatment effects and produce significant treatment by initiation‐year interactions. Understanding the frequency and strength of these effects requires initiating identical experiments across years. We conducted a review of literature covering more than 500 experimental articles published in 7 journals between 1966 and 2008. Only 5% of the 276 general ecological field studies initiated experiments in multiple years. This rarity was even more evident in the journal Restoration Ecology, in which none of the 173 surveyed experimental studies initiated experiments in multiple years. In contrast, 48% of the 58 field experiments published in an agronomy journal were replicated across years. We found only 17 studies that tested treatment by initiation‐year interactions. Despite their rarity, 76% of these studies found significant interactions between treatment and initiation year. We conclude that the results of many ecological field experiments are likely to be contingent on the year in which they are implemented. We discuss the importance of treatment by initiation‐year interactions in ecology and restoration, factors that have hindered the inclusion of temporal replication in the past, and some suggestions for the appropriate design and analysis of temporally replicated experiments. We argue for more deliberate investigation of temporal contingency in ecological experimentation, especially in the field of restoration ecology, which may be particularly sensitive to treatment by initiation‐year interactions.     

Experimental Studies on the Natural Restoration and the Artificial Culture of the Moss Crusts on Fixed Dunes in the Tengger Desert,China

Soil microbiotic crusts cover extensive portions of the arid and semiarid regions of the world and play an important ecological role.Moss is one of the major components in the crusts.The reproduction and establishment of the mosses are crucial to the formation of moss crusts.Bryum argenteum is the dominant species of moss crusts in the Shapotou region (104°57'E,37°27'N) of the Tengger Desert.In search for the characteristics of natural reproduction and establishment of the mosses,10 quadrates (10×10 cm for each) were obtained by removing the moss crusts in different positions of fixed dunes.These 10 quadrates were observed for 3 years depending on the species' components and coverage.Meanwhile,in the third year,two quadrates (1×1 m for each) were set up in a crustabsent area and two different experiments of the asexual reproduction (broadcast planting and offshoots) were conducted,respectively.The reproductive process was observed under the microscope,and the morphological indicators of the new individuals were measured.The results were compared with the ones from indoor experiments using the same methods.All the results showed the following:(1) 70% of the quadrates (i.e.,7 of the 10 quadrates) were recovered within 3-4 years;thus,the quick recovery might be due to the dispersal and reproduction of the fragments of stems and leaves of B.argenteum;(2) as for the two quadrates in the artificial reproduction test,the new plants occupied the uncovered space of the quadrates in 1 month,and there were two main reproduction approaches,one of which was that the stems continually branched and produced young plants,and the other was that the young plants and the fragments of the stems and leaves repeatedly and extensively reproduced protonema,which finally developed into a large number of new plants;(3) the reproductive characteristics were identical,though the protonema in the field was more robust and had more branches than the ones indoors.     

Vegetation restoration patterns and their relationships with disturbance on the Giant Panda Corridor of Tudiling, Southwest China

Human activities such as deforestation, cultivation, and overgrazing have contributed to the destruction of forest ecosystems in the upper Minjiang River basin for a long time, which has led to the reduction in forest coverage and biodiversity. On the Giant Panda Corridor of Tudiling in this basin, the effects of the existing disturbance regimes on plant communities after the vegetation restoration in the 1980s were assessed, and the community composition, the species diversity and their relationships with environmental factors significantly associated with the disturbance were analyzed using the transect sampling method, the two-way indicator species analysis (TWINSPAN) and the detrended canonical correspondence analysis (DCCA). The results were as follows: communities could be classified into six types, and species were clustered into four functional groups (responsive to disturbance, retarded disturbance, resistant to intermediate disturbance, and resistant to heavy disturbance) based on both TWINSPAN and DCCA. DCCA with species composition of plots is similar to that with species diversity of plots. The communities were separated into distinct groups along the DCCA axis, and this pattern was significantly correlated with environmental factors. Elevation differences, shape, slope, distance to roads, and the number of paths in the plots had an evident influence on the distribution of the species and communities. Environmental factors including slope, distance to roads, and the number of paths revealed the gradient of disturbance among the communities along the DCCA axis. High disturbance intensity caused significantly lower species diversity and inhibited the regeneration of vegetation compared with the more diverse undisturbed communities. Artificial restoration was more effective than natural restoration in maintaining high species diversity. The process of succession was inhibited in natural restoration because of the failure of tree establishment, growth, and survival during regeneration.     

Molecular provenance analysis for shy and white-capped albatrosses killed by fisheries interactions in Australia, New Zealand, and South Africa

Shy and white-capped albatrosses, Thalassarche cauta and T. steadi, respectively, are phenotypically similar and are known to suffer fisheries-related bycatch mortality across their foraging range. Assessments of the extent or scale of impact of bycatch mortality on these species have previously been precluded by difficulties identifying bycatch carcasses to species level. In this study, a fast and simple molecular test based on a single nucleotide polymorphism in mtDNA of shy and white-capped albatrosses was used to determine the species composition of fisheries bycatch carcasses recovered from Australian, New Zealand, and South African waters. The only area where bycatch mortality of both species co-occurred was in Tasmanian waters; in all other zones the bycatch was exclusively comprised of white-capped albatrosses. Genotypic provenance assignment tests of shy albatrosses, a species with significant genetic structure between island colonies, correctly assigned 72% to their island of origin. These data are the first to provide insight into the relative vulnerability of shy and white-capped albatrosses to bycatch mortality across their foraging range, and to establish the vast differences in the at-sea distributions of these two species.     

A genetic test for recruitment enhancement in Chesapeake Bay oysters, Crassostrea virginica, after population supplementation with a disease tolerant strain

Many of the methods currently employed to restore Chesapeake Bay populations of the eastern oyster, Crassostrea virginica, assume closed recruitment in certain sub-estuaries despite planktonic larval durations of 2–3 weeks. In addition, to combat parasitic disease, artificially selected disease tolerant oyster strains are being used for population supplementation. It has been impossible to fully evaluate these unconventional tactics because offspring from wild and selected broodstock are phenotypically indistinguishable. This study provides the first direct measurement of oyster recruitment enhancement by using genetic assignment tests to discriminate locally produced progeny of a selected oyster strain from progeny of wild parents. Artificially selected oysters (DEBY strain) were planted on a single reef in each of two Chesapeake Bay tributaries in 2002, but only in the Great Wicomico River (GWR) were they large enough to potentially reproduce the same year. Assignment tests based on eight microsatellite loci and mitochondrial DNA markers were applied to 1579 juvenile oysters collected throughout the GWR during the summer of 2002. Only one juvenile oyster was positively identified as an offspring of the 0.75 million DEBY oysters that were planted in the GWR, but 153 individuals (9.7%) had DEBY ×wild F1 multilocus genotypes. Because oyster recruitment was high across the region in 2002, the proportionately low enhancement measured in the GWR would not otherwise have been recognized. Possible causes for low enhancement success are discussed, each bearing on untested assumptions underlying the restoration methods, and all arguing for more intensive evaluation of each component of the restoration strategy.     

Influence of inbreeding depression on a lake population of Nymphoides peltata after restoration from the soil seed bank

The negative effects of inbreeding depression on fragmented small populations are likely to be expressed more strongly after restoration efforts if regeneration processes have been highly restricted in degraded habitats. We examined the potential influences of inbreeding depression on a population of Nymphoides peltata (Menyanthaceae) restored from the remnant soil seed bank. A hand-pollination experiment demonstrated self-compatibility of a single remaining homostyle genet and significant inbreeding depression in selfed progeny, especially in parameters related to seedling growth (–0.6 for biomass, and –0.4 for relative growth rate). Our genetic analysis indicated that the presumed number of parents contributing to the current soil seed bank was only 2–8 genets and that a single sib-family dominated at each of three sampling sites. The results also showed that the selfed progeny of the homostyle genet were overwhelmingly dominant at two sites (86.8 and 94.7%). As a result, the growth performance of the seed bank seedlings was significantly reduced, to a level as low as that of the selfed progeny. Active restoration efforts to minimize the negative effects of the genetic bottleneck and continuous monitoring based on genetic and demographic study are recommended.     

Reporting vegetation condition using the Vegetation Assets, States and Transitions (VAST) framework

Summary   The Vegetation Assets, States and Transitions (VAST) framework classifies vegetation by degree of human modification as a series of states, from intact native vegetation through to total removal. VAST is a simple communication and reporting tool designed to assist in describing and accounting for human-induced modification of vegetation. A benchmark is identified for each vegetation association based on structure, composition and current regenerative capacity. Benchmarks are based on the best understanding of pre-European conditions (sometimes called 'fully natural'). Relative change in condition from this benchmark is assessed for each site or patch. Three case studies demonstrate use of the diagnostic criteria that underpin VAST. We argue that VAST has potential to provide a consistent framework for monitoring and reporting vegetation modification at a range of scales. Uses of VAST datasets for natural resource planning and management are discussed including a reporting and communication framework for describing the response of vegetation to changes in land use and land management practices, measuring progress toward vegetation targets and describing and mapping vegetation changes and trends.     

Community maturity, species saturation and the variant diversity-productivity relationships in grasslands

Detailed knowledge of the relationship between plant diversity and productivity is critical for advancing our understanding of ecosystem functioning and for achieving success in habitat restoration efforts. However, effects and interactions of diversity, succession and biotic invasions on productivity remain elusive. We studied newly established communities in relation to preexisting homogeneous vegetation invaded by exotic plants in the northern Great Plains, USA, at four study sites for 3 years. We observed variant diversity–productivity relationships for the seeded communities (generally positive monotonic at three sites and non-monotonic at the other site) but no relationships for the resident community or the seeded and resident communities combined at all sites and all years. Community richness was enhanced by seeding additional species but productivity was not. The optimal diversity (as indicated by maximum productivity) changed among sites and as the community developed. The findings shed new light on ecosystem functioning of biodiversity under different conditions and have important implications for restoration.     

Vegetation Response Following Invasive Tamarisk (Tamarix spp.) Removal and Implications for Riparian Restoration

Using a retrospective study of tamarisk removal sites across five states in the southwestern United States, we investigated (1) decreases in tamarisk cover; (2) the effects of tamarisk removal on vegetation; and (3) whether cutting or burning tamarisk has differing effects on plant communities. Our study provides an important first step in recognizing the effects of removing a dominant invasive species on meeting long-term goals of riparian restoration. We found that (1) both cutting and burning reduced mean tamarisk foliar cover by 82–95%, and this reduction was sustained over time. (2) Native foliar cover was 2- to 3-fold higher on tamarisk removal sites, but total foliar cover remained 60–75% lower than on control transects. No trend toward increases in native cover was noted over time. When tamarisk was included in the analyses, diversity in tamarisk removal sites was 2- to 3-fold higher than in the control sites and vegetation communities differed between treated and untreated sites. When tamarisk was excluded from the analyses, diversity was not greater at tamarisk removal sites, and there were no community differences between the treated and untreated transects. Differences in diversity were found to be driven by differences in evenness; overall species richness did not change following tamarisk removal. Sites in the Mojave showed the strongest increase in native foliar cover and diversity, Chihuahuan-transition sites showed a slight increase, and sites on the Colorado Plateau showed no overall increase. (3) There were no differences between plant communities at burned and cut sites. Our research indicates that vegetation response to tamarisk removal is often negligible. Land managers should be prepared for persistent depauperate plant communities following tamarisk removal if additional restoration measures are not instigated.