Can soil seed banks contribute to the restoration of dune slacks under conservation management?

Questions: Does the soil seed bank resemble the former early successional stages of a dune slack system more than the established later successional vegetation? Does it have the potential to contribute to the conservation of a highly endangered habitat? Location: Dune slacks at Newborough Warren, UK. Methods: The composition of the soil seed bank in two depth layers was determined using the seedling emergence method between March 2004 and April 2005. Long-term monitoring data on the floristic composition of the established vegetation were obtained from the national conservation agency, and additional monitoring was undertaken in 2003. Floristic composition, seed weights, seed longevity of component species and Ellenberg indicator values were used to compare the seed bank and established vegetation. Results: The soil seed bank was diverse and contained typical dune slack species, species of early successional stages and species of conservation interest. A comparison between the composition of the seed bank and historical data on the composition of the established vegetation showed that the seed bank reflects earlier successional stages more closely than the current aboveground vegetation. This study increases the scarce information currently available on the seed bank ecology of several species, including two orchid species. Conclusions: The soil seed bank can be expected to contribute to vegetation change after disturbance. Stimulation of germination from the seed bank through management may contribute to the conservation of both characteristic and threatened species typical of dune slacks.     

Can we rely on forest reserves for primate conservation?

Tropical forests contain much of the world's biodiversity, yet their rate of decline is increasing. The strategy most frequently used to protect this biodiversity is to make parks and reserves. While there is a great deal of research on the effectiveness of parks for protecting biodiversity, there is little research on how well extractive reserves conserve biodiversity. Here, we evaluate the effectiveness of four forest reserves in western Uganda at maintaining populations of primates and compare census data from the reserves to data from the neighbouring well‐protected Kibale National Park. The relative abundance of the five most common primates in the park was approximately four times that of the forest reserves. In the forest reserves, evidence of new human encroachment was seen every 500 m, while in the park it was seen every 100,000 m. Two recommendations emerge from our research: (i) for forest reserves, such as those studied here, to have conservation value for primates, extraction must be reduced and (ii) until the long‐term viability of the populations in forest reserves can be ascertained, they should not be considered in estimates of the sizes of endangered species protected ranges.     

What we don’t seed: the role of long-lived seed banks as hidden legacies of invasive plants

Acacia dealbata is an invasive south-eastern Australian tree that produces a persistent soil seed bank. In order to characterize the seed bank in plots invaded by A. dealbata and to understand its implications for management and re-invasion risk, density, germinability, and viability of the seed bank were evaluated in five sites in central Portugal. Soil samples were collected in A. dealbata invaded plots and adjacent areas and screened for seeds, which were then quantified and germinated at 25 °C. A subset of seeds was first exposed to 60 °C to assess the effect of high soil temperature on dormancy breaking. Variables influencing differences between sites were explored with generalized linear mixed models with a Poisson distribution. Inside A. dealbata invaded plots the seed bank averaged 4608 seeds/m², reaching up to 62,747 seeds/m²; in adjacent areas, up to 14 m from the plots, only 9 seeds/m² were found. Seed bank densities were mostly influenced by stoniness, number of fires in the last 10 years, and density of trees and roots. Almost 90% of seeds were viable, but only 8.6% germinated without treatment. Nearly 70% of seeds exposed to 60 °C germinated without any physical stimulation, suggesting that high soil temperatures can effectively break seed dormancy. The high density and viability of A. dealbata’s seed bank and its ability to disperse seeds far from the parent plants contribute to the species’ invasive success. These features combined with heat events that can overcome seed dormancy need to be considered in the management of this species.     

Can the soil seed bank contribute to revegetation of the drawdown zone in the Three Gorges Reservoir Region?

The drawdown zone of the Three Gorges Reservoir Region was assumed to be completely formed in 2009 and the water level would range from ~145 m in flood season (summer) to ~175 m during non-flood season (winter). The soil seed bank is an important propagule source for vegetation restoration. In order to evaluate the potential of the soil seed bank to revegetate the drawdown zone of this region, we examined the quantitative relationships between the germinable soil seed bank and the established vertical and horizontal vegetation patterns. A total of 45 soil samples at four sites was collected to examine seed bank density, species richness, and composition using the seedling-emergence method. Forty-five species (from 20 families) germinated from the soil seed bank, and the average seed density was 4578 m⁻². The seed bank was dominated by annual plants, suggesting reestablishment of some above-ground species was plausible. However, most established woody plants and perennials were absent from the seed bank indicating a low probability of reestablishment for non-annuals through the seed bank. Thus, due to low species compositional similarity to extant vegetation and the dominance of annual plants, the soil seed bank had a low potential to restore pre-dam vegetation in the drawdown zone of the Three Gorges Reservoir Region, but its potential as a propagule source should be considered regarding the management of the drawdown zone for vegetation cover.     

The effects of three years of fencing enclosure on soil seed banks and the relationship with above-ground vegetation of degraded alpine grasslands of the Tibetan plateau

Background and Aims

Fenced enclosures have become an important method for re-establishing degraded grassland on the Tibetan plateau, and examination of soil seed banks may provide useful insights to understanding the effects and mechanisms of fencing enclosure on the restoration.

Methods

An investigation was conducted into the effects of enclosure for 3 years on the soil seed banks of degraded natural and sown grasslands at eight study sites. Species composition, soil seed bank density and the relationships with above-ground vegetation were analysed based on 4800 soil core samples and counting of seeds extracted from soil samples.

Results

After 3 years of fencing enclosure, soil seed banks differed between the different communities across the study sites. Species numbers and seed density in soil seed banks decreased from natural grassland to sown grassland, with most seeds occurring in the upper 5 cm soil layer. In these alpine grasslands, relatively few species produced high numbers of seeds, although their occurrence across the eight study sites was variable. Total vegetation cover increased with enclosure due to the colonization capacity of the vegetation rather than soil seed banks.

Conclusions

This study provided evidence that soil seed banks do not play an important role in the restoration of degraded alpine grassland when using fencing enclosures. Further studies conducted over longer periods are needed to address this subject.     

The evolution of trade‐offs: where are we?

Trade-offs are a core component of many evolutionary models, particularly those dealing with the evolution of life histories. In the present paper, we identify four topics of key importance for studies of the evolutionary biology of trade-offs. First, we consider the underlying concept of 'constraint'. We conclude that this term is typically used too vaguely and suggest that 'constraint' in the sense of a bias should be clearly distinguished from 'constraint' in the sense of proscribed combinations of traits or evolutionary trajectories. Secondly, we address the utility of the acquisition-allocation model (the 'Y-model'). We find that, whereas this model and its derivatives have provided new insights, a misunderstanding of the pivotal equation has led to incorrect predictions and faulty tests. Thirdly, we ask how trade-offs are expected to evolve under directional selection. A quantitative genetic model predicts that, under weak or short-term selection, the intercept will change but the slope will remain constant. Two empirical tests support this prediction but these are based on comparisons of geographic populations: more direct tests will come from artificial selection experiments. Finally, we discuss what maintains variation in trade-offs noting that at present little attention has been given to this question. We distinguish between phenotypic and genetic variation and suggest that the latter is most in need of explanation. We suggest that four factors deserving investigation are mutation-selection balance, antagonistic pleiotropy, correlational selection and spatio-temporal variation, but as in the other areas of research on trade-offs, empirical generalizations are impeded by lack of data. Although this lack is discouraging, we suggest that it provides a rich ground for further study and the integration of many disciplines, including the emerging field of genomics.     

Are germination cues for soil‐stored seed banks different in structurally different fire‐prone communities?

Many plant species are dependent on soil‐stored seeds for their persistence in fire‐prone systems. Seed germination is often stimulated by fire‐related cues including heat and smoke, but the way these cues promote germination may differ between structurally distinct plant communities with historically different fire regimes. In this study, we examined the effects of heat, smoke and their interactions on the germination of soil‐stored seeds from shrubby woodlands and herbaceous forests in south‐east Australia. The effect of these treatments on species richness, diversity and composition, and species richness and density of germinants within life‐forms (grass, forb and shrub) were assessed. Soils from each community were subjected to low heat (40°C), low heat with smoke, smoke, high heat (80°C), high heat with smoke and untreated (control) before being placed in a glasshouse, where the germinants were identified and counted. Greater species richness was stimulated by high heat treatments and smoke in both communities, a trend driven by shrubs and forbs, rather than grasses. Greater species diversity was stimulated by high heat with smoke in both communities. Greater densities of grass germinants were stimulated by all treatments, except low heat, in both communities. For forbs and shrubs, the effect of treatment depended on community. Compared to the control, low heat with smoke (forbs) and both low heat and low heat with smoke (shrubs) increased densities in the woodland but not in the forest. There were unique species compositions, different from the control, in all treatments in the forest but not in the woodland, where composition in low heat was not different from the control. These results indicate the importance of high soil temperatures and smoke in both communities. In the absence of wildfires, recurring prescribed burns that heat the soil to low temperatures are likely to reduce plant richness, diversity, and density resulting in a change in understorey species composition and structure.     

Life in earth: the impact of GM plants on soil ecology?

The impact of changes incurred by agricultural biotechnology has led to concern regarding soil ecosystems and, rightly or wrongly, this has focused on the introduction of genetically modified (GM) crops. Soils are key resources, with essential roles in supporting ecosystems and maintaining environmental quality and productivity. The complexity of soils presents difficulties to their inclusion in the risk assessment process conducted for all GM plants. However, a combined approach, informed by both soil ecology and soil quality perspectives, that considers the impacts of GM crops in the context of conventional agricultural practices can provide a regulatory framework to ensure the protection of soils without being overly restrictive.     

The size and diversity of the soil seed banks and the light requirements of the species in sunny and shady natural communities of the Białowieża Primeval Forest

The research was conducted in two natural forest communities: Potentillo albae-Quercetum (oak forest) which allows much light to reach the forest floor and Tilio-Carpinetum typicum (hornbeam forest) which shades the herb layer heavily. The seed banks were estimated from numbers of seedlings emerging from soil samples over one growing season.(1) Our results confirm the hypothesis that persistent seed banks are mainly formed by species with high light requirements. Of the species found predominantly in the seed bank and absent from the herb layer or occurring there very rarely in both communities 83% of species and 70% of seedlings were strongly light-demanding (Ellenberg's light index 6–9). However, the results do not support the hypothesis that seed banks in natural deciduous forest communities are small, poor in species and do not reflect the species composition of herb layer.(2) The seed banks of both communities were rich in species and relatively large. Species richness in the oak forest turned out to be higher than in the hornbeam forest (51 vs 45 species/2.4 m₂), but size was smaller (2659 vs 5789 seedlings/2.4 m₂). In the oak forest the most abundant species in the seed bank was Galium boreale, but it constituted only 19% of the total number of seedlings, whereas in the hornbearn forest the dominant species, Urtica dioica, constituted 57% of the total.(3) In each community the species composition of the seed bank and the herb layer was very similar (>70%).(4) The seed bank was more diverse in the oak forest than in the hornbeam forest (H 2.34 vs 1.68).(5) The seed banks of both communities differed in the contribution of species with varied light requirements; in the sunny oak forest species with high light requirements dominated, whereas in the shady hornbeam forest both strongly and moderately light-demanding species had similar contributions.Nomenclature: Follows Ehrendorfer (1973) and Matuszkiewicz (1981).     

Can spatial variation and inter-annual variation in precipitation explain the seed density and species richness of the germinable soil seed bank in a tropical dry forest in north-eastern Brazil?

The interaction between microhabitat and inter-annual variation in precipitation has an important role on the dynamics of the seed bank and can play a crucial role in survival and maintenance of plant populations in semi-arid environments. We hypothesized that the type of microhabitat and the inter-annual variability in precipitation can explain the richness and density of the seed bank in a semi-arid region in Brazil. The study was conducted in an area of tropical dry forest with shrub-tree physiognomy, locally called caatinga. We collected 35 soil samples in three distinct microhabitats, at the end of rainy and dry seasons, respectively, over three years, totalling 630 samples. The seed bank (richness and seed density) were determined by seedling emergence method. Over the three years, 79 species emerged from the seed bank, 64, 45 and 42 in riparian, non-riparian and rocky microhabitats, respectively. We recorded differences in species richness and average density between microhabitats and between years, with significant statistical interaction between them. Inter-annual precipitation explained 48% and 5% of the variation in richness and seed density, respectively. Spatial variation explained 7% of the species richness and 31% of the density. Our results show that the interaction between spatial variation and precipitation has an important role on the spatial and temporal heterogeneity of the richness and density of seed banks in dry environments.     

How much seed remains in the soil after a fire?

Soil seed banks that persist after a fire are important in fire-prone habitats as they minimise the risk of decline or local extinction in plants, should the fire-free interval be less than the primary juvenile periods of the species. In two common woody plant genera (Acacia and Grevillea) in southeastern Australia, we examined the size and location of the residual seed bank after fire across areas of varying seedling densities at three locations in comparison to the distribution of seeds in the soil at an unburnt site. We found viable dormant seeds remaining in the soil after fire (evidence of residual soil seed bank). A significantly lower proportion of seeds remained in the top 5 cm of soil than at 5–10 cm or 10–15 cm soil depths, independent of seedling density or plant genus. This was due to greater germination, and possibly some seed mortality, near the soil surface. Reduced germination below 5 cm was probably due to the reduced efficacy of the fire cues that break seed dormancy, a declining ability of seeds to emerge successfully from such depths, and the lower abundance of seeds in the soil at such depths. The magnitude of the residual seed bank was similar across 0–5, 5–10 and 10–15 cm soil depths in Acacia suaveolens. For two Grevillea species, most residual seeds were at 0–5 and 5–10 cm. The residual soil seed bank in the top 10 cm of soil after fire varied across sites with estimates of 0, 19 and 27% in G. speciosa and 23, 35, and 55% in A. suaveolens. At two sites, both species had similar residual seed bank sizes, while at a third, there were large differences between the species (0–55%). The observed patterns imply that the fire-related cues that break seed dormancy generally declined with soil depth. For Acacia, seed dormancy is broken by heat shock, a fire-cue that declines with soil depth. Some 250 species (approx 15% of the fire-prone flora) in the region are thought to have dormancy broken by heat shock. For Grevillea, where seed dormancy is broken by the interaction of smoke and heat shock, at two sites, we suggest three possibilities: (i) the smoke cue declined with soil depth; (ii) both heat and smoke are obligatory for breaking seed dormancy; or (iii) the cues may be independent and additive and below the zone of soil heating, only a proportion of available seeds had dormancy broken by smoke alone. At a third site (no residual seed bank detected) the smoke cue was predicted not to have declined with soil depth. Up to 900 species (just under half the fire-prone flora) in the study region are thought to have seed dormancy broken by the interaction of heat and smoke during the passage of a fire.     

The consequences of a drastic fish stock reduction in the large and shallow Lake Wolderwijd,The Netherlands. Can we understand what happened?

In 1990 an experiment started in the large and shallow lake Wolderwijd (2700 ha, mean depth 1.5 m) to improve the water quality. About 75% of the fish stock was removed (425 000 kg fish). The fish was mainly composed of bream and roach. In May 600000 young pikes (3–4 cm) were introduced.In May 1991 the water became very clear (Secchi depth 1.8 m) during a spring bloom of large Daphnia. Then the grazing by zooplankton was eight times higher than the primary production of algae and the total suspended matter concentration became very low. Compared to the situation before the fish reduction, the grazing had increased only slightly, while the primary production had decreased significantly in early spring. The fish stock reduction might have contributed to the reduction in primary production by a reduced internal nutrient load. The clear water period lasted six weeks. Daphnia disappeared in July due to food limitation, the algal biomass increased and the Secchi depth became 50 cm. Daphnia did not recover during summer, due to predation that was not caused by 0 + fish but by the mysid shrimp Neomysis integer. Neomysis could develop abundantly, because of the reduced biomass of the predator perch. The production of young fish had been low because of the cold spring weather. The cold weather was probably also responsible for the slow increase in density of macrophytes. After 1991, perch probably can control Neomysis. Due to lack of spawning places and shelter for 0 + pike, pike was probably not able to control the production of 0 + fish. In a lake of this scale, it will not be easy to get more than 50% coverage of macrophytes, which seems necessary to keep the algal biomass low by nutrient competition. Therefore, we expect also in the future a decrease in transparency in the summer. Locally, especially near Characeae, the water might stay clear.     

Two Decades of River Restoration in California: What Can We Learn?

As part of the National River Restoration Science Synthesis (NRRSS), we developed a summary database of 4,023 stream restoration projects built in California since 1980, from which we randomly selected 44 records for in‐depth interviews with project managers. Despite substantial difficulties in gathering the data, we were able to draw conclusions about current design, implementation, monitoring, and evaluation practices used in California projects and compare them with national trends. Although more than half of the projects for which we conducted interviews were located in watersheds for which a management or assessment plan had been prepared, these plans had a limited impact on site selection. We also found that the state lacks a consistent framework for design, monitoring, and reporting restoration projects, and that although monitoring is far more widespread than the information in the NRRSS summary database would suggest, there are still problems with the type, duration, and reporting of monitoring. The general lack of systematic, objective assessment of completed projects hinders the advance of restoration science.     

Restoration on abandoned tropical pasturelands—do we know enough?

Tropical rainforests have been disappearing at an alarming rate. In addition to preserving remaining tropical rainforests, we need to convert degraded and abandoned pasturelands into secondary forests. To accelerate this, human intervention in the recovery process is essential. In this review paper we (i) encapsulate some of the problems, which might surface when converting abandoned land to secondary forest. (ii) Look at some of the restoration techniques used in restoration programs and propose additional techniques for consideration. Major barriers to natural regeneration on abandoned and degraded pasturelands are: weed infestation, lack of indigenous soil seed bank, lack of seed supply/movement, soil compaction, depletion of soil nutrients and unsuitable microclimate and microhabitat. Although several restoration techniques have been recommended, most restoration programs have been carried out using native seedling transplants to accelerate natural recruitment. Most restoration groups in the tropics are still in the initial stages of determining which species or species combination to chose to gain maximum benefit. On the other hand restoration ecologists are struggling to detect which techniques are most appropriate to restore degraded and abandoned pasturelands. Our review shows that there is immediate need for further research and development on restoration techniques by examining the ecological and economic effectiveness of: direct seeding, stem cuttings using native pioneer or climax species and simple manipulation such as displacing branches of pioneer species with mature seeds on abandoned and degraded pasturelands and artificial perching to accelerate natural regeneration. These techniques are essential to successfully heal the wound humans have inflicted on the most spectacular and species-rich ecosystems on earth.     

Restoration of Seminatural Grasslands: What is the Impact on Ants?

The number of species‐rich seminatural grasslands in Northern Europe has decreased significantly due to the abandonment of traditional land use practices. To preserve these habitats, an increasing number of abandoned and overgrown grasslands have been restored by cutting down trees and shrubs and reintroducing grazing. These practices are considered a useful tool to recover the species richness of vascular plants, but their impact on other taxa is hardly known. Here we studied ants as one important group of grassland insects. We investigated (1) the effects of restoration of nongrazed and afforested seminatural grasslands, compared to continuously managed reference sites; and (2) the modulating impacts of habitat characteristics and time elapsed since restoration. We found a total of 27 ant species, 11 of these were characteristic of open habitats and seven characteristic of forests. Neither species richness per site nor the number of open‐habitat species, nor the number of forest species differed between restored and reference sites. Yet, within the restored sites, the total species richness and the number of open‐habitat species was positively related to the time since restoration and the percentage of bare rock. High frequencies of most open‐habitat species were associated with low vegetation, older restored sites, and reference sites. Most forest species showed their highest frequencies in tree‐ and shrub‐dominated habitat. We conclude that restoration efforts have been successful in terms of retrieving species richness. A regular and moderate grazing regime subsequent to the restoration is suggested in order to support a high abundance of open‐habitat species.