Prior disturbance legacy effects on plant recovery post‐high‐severity wildfire

Climate change predictions indicate that summer droughts will become more severe and frequent. Yet, the impact of soil communities on the response of plant communities to drought remains unclear. Here, we report the results of a novel field experiment, in which we manipulated soil communities by adding soil inocula originating from different successional stages of coastal dune ecosystems to a plant community established from seeds on bare dune sand. We tested if and how the added soil biota from later-successional ecosystems influenced the sensitivity (resistance and recovery) of plant communities to drought. In contrast to our expectations, soil biota from later-successional soil inocula did not improve the resistance and recovery of plant communities subjected to drought. Instead, inoculation with soil biota from later successional stages reduced the post-drought recovery of plant communities, suggesting that competition for limited nutrients between plant community and soil biota may exacerbate the post-drought recovery of plant communities. Moreover, soil pathogens present in later-successional soil inocula may have impeded plant growth after drought. Soil inocula had differential impacts on the drought sensitivity of specific plant functional groups and individual species. However, the sensitivity of individual species and functional groups to drought was idiosyncratic and did not explain the overall composition of the plant community. Based on the field experimental evidence, our results highlight the adverse role soil biota can play on plant community responses to environmental stresses. These outcomes indicate that impacts of soil biota on the stability of plant communities subjected to drought are highly context-dependent and suggest that in some cases the soil biota activity can even destabilize plant community biomass responses to drought.

Background and aims: Pioneer plants may improve the ecological restoration of degraded ultramafic areas by plant-soil interaction processes. In this study, we assess the effect of the pioneer actinorhizal tree C. terminale (Casuarinaceae) on the recovery of plant communities and soil functions on degraded tropical ultramafic sites. Methods: Soil and plant samples were collected along a tree-age gradient in two degraded ultramafic sites in Sabah (Northern Borneo, Malaysia): a Technosol and a Leptosol. Chemical composition of plants and soils, and biological activity of soils were assessed at both sites. Plant colonisation was assessed by plot vegetation surveys. Results: An improvement in soil fertility parameters (pH reduction from 8.5 to 6.8, an increase in the concentrations of several nutrients and enhanced soil enzyme activities) was observed along the C. terminale age gradient. However, plant cover and diversity was only improved around mature trees at the site that was not impacted by mining. Conclusion: C. terminale promotes the recovery of several soil functions, mainly related to the storage and recycling of N, P, K, S. Besides plant-soil feedback, other environmental factors (i.e. exposition to sunlight, drought) may play an important role on revegetation of ultramafic soils.

Ecological restoration is expected to reverse the loss of biodiversity and ecosystem services. Due to the low number of well‐replicated field studies, the extent to which restoration recovers plant communities, and the factors underlying possible shortcomings, are not well understood even in medium term. We compared the plant community composition of 38 sites comprising pristine, forestry‐drained, and 5 or 10 years ago restored peatlands in southern Finland, with special interest in understanding spatial variation within studied sites, as well as the development of the numbers and the abundances of target species. Our results indicated a recovery of community composition 5–10 years after restoration, but there was significant heterogeneity in recovery. Plant communities farthest away from ditches were very similar to their pristine reference already 10 years after restoration. In contrast, communities in the ditches were as far from the target as the drained communities. The recovery appears to be characterized by a decline in the number and abundance of species typical to degraded conditions, and increase in the abundance of characteristic peatland species. However, we found no increase above the drained state in the number of characteristic peatland species. Our results suggest that there is a risk of drawing premature conclusions on the efficiency of ecological restoration with the current practice of short‐term monitoring. Our results also illustrate fine‐scale within‐site spatial variability in the degradation and recovery of the plant communities that should be considered when evaluating the success of restoration. Overall, we find the heterogeneous outcome of restoration observed here promising. However, low recovery in the number of characteristic species demonstrates the importance of prioritizing restoration sites, and addressing the uncertainty of recovery when setting restoration targets. It appears that it is easier to eradicate unwanted species than regain characteristic species by restoration.

Although consumers can strongly influence community recovery from disturbance, few studies have explored the effects of consumer identity and density and how they may vary across abiotic gradients. On rocky shores in Maine, recent experiments suggest that recovery of plant- or animal- dominated community states is governed by rates of water movement and consumer pressure. To further elucidate the mechanisms of consumer control, we examined the species-specific and density-dependent effects of rocky shore consumers (crabs and snails) on community recovery under both high (mussel dominated) and low flow (plant dominated) conditions. By partitioning the direct impacts of predators (crabs) and grazers (snails) on community recovery across a flow gradient, we found that grazers, but not predators, are likely the primary agent of consumer control and that their impact is highly non-linear. Manipulating snail densities revealed that herbivorous and bull-dozing snails (Littorina littorea) alone can control recovery of high and low flow communities. After ∼1.5 years of recovery, snail density explained a significant amount of the variation in macroalgal coverage at low flow sites and also mussel recovery at high flow sites. These density-dependent grazer effects were were both non-linear and flow-dependent, with low abundance thresholds needed to suppress plant community recovery, and much higher levels needed to control mussel bed development. Our study suggests that consumer density and identity are key in regulating both plant and animal community recovery and that physical conditions can determine the functional forms of these consumer effects.

Drivers of ecosystem stability have been a major topic in ecology for decades. Most studies have focused on the influence of species richness on ecosystem stability and found positive diversity‐stability relationships. However, land use and abiotic factors shape species richness and functional composition of plant communities and may override species richness‐stability relations in managed grasslands. We analysed the relative importance of land‐use intensity (LUI), resident plant species richness and functional composition for recovery of plant communities (plant species richness, plant cover, above‐ and below‐ground biomass) and release of soil nutrients after a severe mechanical disturbance. Experimental sward disturbance was applied to 73 grassland sites along a LUI gradient in three German regions. We considered relative (ln(disturbance/control)) and absolute (disturbance − control) treatment effects. Using structural equation modelling, we disentangled direct effects of LUI and resident species richness on recovery and indirect effects via changes in functional richness. Community‐weighted‐mean traits rarely mattered for recovery or nutrient release, while functional richness especially increased relative recovery of plant communities but also relative release of NO3‐N and NH4‐N. These effects were enhanced by increasing resident plant species richness and decreasing LUI. Next to these indirect influences of LUI and resident plant species richness via functional community composition, grasslands of high compared with grasslands of low resident plant species richness generally showed decreased recovery of plant communities. In grasslands of high LUI, absolute recovery of some aspects of plant communities was decreased. We did not find consistent differences between the relative importance of the different drivers of recovery after the first and the second season. Overall, resident species richness seemed most important for relative recovery and less important for absolute recovery, where direct effects of LUI were more common. Synthesis. The stability of ecosystems in managed grasslands depends on more than species richness. Thus, drivers that directly affect species richness and functional community composition have to be considered when studying the stability of real‐world ecosystems. More specifically, in managed grasslands high resident species richness but also high land‐use intensity (LUI) decreased the stability of ecosystem functions, which was partially buffered by increases in functional richness.

Grassland is one of the most important terrestrial ecosystems,however,in recent years,degradation and desertification of grassland ecosystem becomes more and more serious due to intensive human activities,such as overgrazing,mowing,and conversion of grassland to cropland.Effective countermeasures,such as pasture enclosure,are suggested to maintain the grassland productivity and sustainability.Most studies on ecological restoration of degraded grassland focused on recovery of plant communities,while little information is available as for the parallel succession of belowground microbial communities,especially for symbiotic microbes associated with plants. Abuscular mycorrhizal(AM) fungi are ubiquitous symbionts for higher plants in most natural and agricultural ecosystems.It has been widely accepted that these symbiotic fungi play important roles in stimulating biodiversity and productivity of plant communities.To reveal the impacts of grassland enclosure on recovery of the degraded grassland ecosystem,especially for the recovery of AMF communities,we conducted an investigation based on a long-term field experiment where experimental plots under different grazing intensities(heavily,moderately,slightly grazed and the ungrazed control) have been enclosed for 14 years.Plant coverage,height and species richness were recorded in situ,while soil samples were collected for analysis of soil chemo-physical properties and AM fungal parameters.As a newly developed molecular tool,the second-generation sequencing technology,454 pyrosequencing,was applied for predicting AMF community composition and biodiversity. The experimental results indicated that,after enclosure for 14 years,the coverage,diversity and evenness index of plant communities on different experimental plots did not show significant difference;The soil organic matter,available N,total N and total C contents tended to be higher in lightly and moderately grazed plots compared with heavily grazed plots,but statistically there were no significant differences among different plots.Available soil P was lowest in the heavily grazed plots(1.00 mg/kg),which was significantly lower than that in the lightly grazed plots(2.25 mg/kg).The 454 pyrosequencing of AM fungi from all soil samples yielded a total of 59,382 Glomeromycota sequences,assigned to 87 virtual taxa(VT) in the MaarjAM database,belonging to 7 genera,namely Diversispora,Otospora,Scutellospora,Glomeraceae Glomus,Rhizophagus,Paraglomus and Archaeospora.Similar to previous reports,Glomus was the dominant genera on the grassland,as 83.9% of the 87 VTs belonged to Glomeraceae Glomus;while only 13 sequences(1 VT) were identified as Archaeospora,which was undoubtedly the rarest genus in the research area.In contrast with plant communities,the AM fungal communities had not equally recovered in different experimental plots.Although there were common VTs for all plots,but each plot clearly exhibited some specific VTs,and most specific VTs were recorded in CK plot.Furthermore,the diversity index and evenness index were lowest in CK plot,lower than any other plots,and significantly lower than that in the moderately grazed plot. This investigation suggested that grassland enclosure after overgrazing is essentially important for the recovery of plant communities,soil chemo-physical properties and also soil microbial communities.However,recovery of AM fungal communities was out of synch with plant communities.Further research is still necessary to reveal the interactions between plant and functional soil microbial communities during the ecological restoration of degraded grassland.

Key perspectives on early successional forests subject to stand-replacing disturbances

Background: Human activities such as agriculture are known to markedly affect natural ecosystems, including plant communities and soil properties. Biological activities are reduced in hot, hyper-arid ecosystems compared to temperate and tropical climatic conditions. Anthropogenic disturbances therefore have greater impacts on the ecosystem’s recovery potential. This study aimed to assess the diversity and recovery of post-agriculture plant communities in the Sharaan Nature Reserve (SNR), located in northern Saudi Arabia. Methods: Three types of habitats representative of different disturbance situations were identified in the reserve and sampled through 103 floristic and pedological surveys. The floristic composition was recognized and relative quantification of soil atomic elements was performed. The obtained data were processed using different statistical treatments such as the Shannon index and Bray–Curtis dissimilarities, non-metric multidimensional scaling (NMDS), Kruskal–Wallis tests and Redundant analysis (RDA). Results: Investigations led to the identification of 48 plant species belonging to 24 genera and 22 botanical families. Specific plant community structures were correlated with each habitat, and bioindicator plant species were identified. Polycarpaea repens and Stipagrostis plumosa were linked with natural habitats, while Atriplex leucoclada was specific to disturbed habitats. In contrast, Asteriscus graveolens and Haloxylon salicornicum were found to be ubiquitous species. Conclusions: The presence of bioindicator species was closely associated with the different soil properties measured in each habitat. Restoration strategies related to the overall dynamic plant community succession pattern observed in the Sharaan Nature Reserve are discussed. Active ecological restoration strategies based on targeted active ecological restoration interventions should facilitate the recovery and restoration of disturbed plant communities in hyper-arid areas.

Recovery of native plant communities after eradication of rabbits from the subantarctic Kerguelen Islands, and influence of climate change

Temporal patterns of vegetation recovery after wildfire in two obligate seeder ash forests

Removal experiments are useful tools for assessing two important aspects of plant community invasion: (1) resistance to invasion and (2) recovery after invasive species removal. We discuss the potential of such experiments based on a brief systematic review of the literature on community resistance, as measured by invasibility after removal of resident species (reduction of taxonomic/functional richness), and on community recovery, as measured by resident community response after invasive species removal. We found 62 research articles, most of them related to invasive species removal. Few studies used removals to test biotic resistance, despite the importance of resident removals for identifying community components that play key roles in the often‐controversial invasion resistance hypotheses. Furthermore, appropriate experimental controls were rarely used, which would allow separation of the effect of local species extinction from that of disturbance. We hope this review stimulates plant ecologists to adopt removal experiments for studying invasion processes.

Ecosystem resilience is a fertile topic for research, but there are two senses in which the concept is being examined. When restoration ecologists refer to ‘resilience’, they are usually referring to capacities of species to recover from natural disturbances (developed through adaptation to perturbation regimes over evolutionary timescales; Westman 1978; Dell et al. 1986). This ‘biological’ resilience is conferred to higher levels (communities and ecosystems) by dint of the fact that assemblages of species are often subject to similar landscape-scale disturbances. Restorationists can trigger residual resilience on damaged sites by measured manipulations – skills referred to in Robin Buchanan's guest editorial on vocational training for restorationists in this issue. Such skills are essential to successful restoration at site level, as illustrated in the feature article of Anderson et al. (this issue) on the Puckapunyal Restoration Programme – a program that has achieved extensive recovery of indigenous plant and animal communities after control of pest species, fencing and supplementary revegetation. When researchers working in the transdisciplinary field of ecology and society refer to resilience theory, however, they are often referring to the field of research that focuses on recovery and degradation processes at much larger ‘systems’ scales, particularly where ecosystems and society are linked (Holling 1973; Walker et al. 2006– and see book reviews in this issue). As problems at these scales are harder to detect, researchers need to anticipate trajectories of degradation that can be turned around (or responded to by social transformation) before it is too late (see topics of all three comment pieces in this issue and the research report by Baldwin et al. and Mendham et al. also in this issue). Both ecological and transdisciplinary approaches are equally important, and are cross-fertilizing each other. Restoration ecologists are familiar with state and transition models and acknowledge thresholds of reversibility, points beyond which autogenic recovery will not occur and where a system can precipitously change to something quite different (Holling 1973). But combining these concepts with bigger-picture social–ecological analysis is novel and potentially powerful for the restoration and management of ecosystems. As pointed out by Sam Lake (see interview in this issue) and demonstrated by Anderson et al., big-picture effects cannot be achieved without multiple-site-level projects, but site-level projects need strategic coordination to be effective due to their dependence on and exposure to larger-scale processes in social–ecological systems. It is important that these ideas of thresholds of ‘irreversibility’ are used more and more by researchers and managers in all disciplines, but it is particularly important that these empowering ways of seeing ecosystem change are taken on board by planners and decision-makers. Many planners and policy-makers are working very hard to reduce future damage, but it will not be possible to maintain the health of our systems by simply reducing tomorrow's ‘rights’ to pollute or harvest. Such actions are an indispensable and worthy start, but if a dangerous trajectory is already in train (such as with salinization and greenhouse pollution), alleviation of the problems will not occur after the reduction of future causal factors alone. Interventions to compensate for existing damage – restorative industries – are also needed. In this context, it might be useful to point out that the restoration associated with ‘no net loss’ policies in land clearing (referred to in Gibbons & Lindenmeyer's thought-provoking comment piece, this issue) should not be confused with restoration for compensating existing problems at big-picture level. ‘No net loss’, by definition, is about maintaining a current or future status quo, not addressing past losses. It is very important therefore that ‘bigger-picture restoration’ arguments are not invoked to support the adoption of land-clearing trade-offs referred to as ‘offsets’. Indeed, big-picture arguments could be more logically invoked to define clearing of any bushland technically capable of restoration as a ‘loss’ (and restoration of any other bushland as simply ‘compensation for past losses’) rather than as a ‘gain’. Pragmatism can be useful in times of sudden change and when there is really no other alternative. But as pragmatism is fundamentally about avoiding conflict by slicing the cake ever smaller, its application as a general rule is simply ‘more of the same’. ‘More of the same’ will perpetuate rather than solve our environmental problems (Walker et al. 2006). A more thoughtful and radical shift of mindsets and mechanisms of business is needed, empowered by collective recognition of the large scale of our problems and their potential for sudden collapses. This needs to be a shift not only to ‘resilience thinking’ but also to ‘restoration thinking’ at a very large scale; value adding with creative endeavour – or we may be running the risk of ecological sustainability becoming a mere fantasy.

Fire shapes ecosystems globally, including semi-arid ecosystems. In Australia, semi-arid ‘mallee’ ecosystems occur primarily across the southern part of the continent, forming an interface between the arid interior and temperate south. Mallee vegetation is characterized by short, multi-stemmed eucalypts that grow from a basal lignotuber. Fire shapes the structure and functioning of mallee ecosystems. Using the Murray Mallee region in south-eastern Australia as a case study, we examine the characteristics and role of fire, the consequences for biota, and the interaction of fire with other drivers. Wildfires in mallee ecosystems typically are large (1000s ha), burn with high severity, commonly cause top-kill of eucalypts, and create coarse-grained mosaics at a regional scale. Wildfires can occur in late spring and summer in both dry and wet years. Recovery of plant and animal communities is predictable and slow, with regeneration of eucalypts and many habitat components extending over decades. Time since the last fire strongly influences the distribution and abundance of many species and the structure of plant and animal communities. Animal species display a discrete set of generalized responses to time since fire. Systematic field studies and modeling are beginning to reveal how spatial variation in fire regimes (‘pyrodiversity’) at different scales shapes biodiversity. Pyrodiversity includes variation in the extent of post-fire habitats, the diversity of post-fire age-classes and their configuration. At regional scales, a desirable mix of fire histories for biodiversity conservation includes a combination of early, mid and late post-fire age-classes, weighted toward later seral stages that provide critical habitat for threatened species. Biodiversity is also influenced by interactions between fire and other drivers, including land clearing, rainfall, herbivory and predation. Extensive clearing for agriculture has altered the nature and impact of fire, and facilitated invasion by pest species that modify fuels, fire regimes and post-fire recovery. Given the natural and anthropogenic drivers of fire and the consequences of their interactions, we highlight opportunities for conserving mallee ecosystems. These include learning from and fostering Indigenous knowledge of fire, implementing actions that consider synergies between fire and other processes, and strategic monitoring of fire, biodiversity and other drivers to guide place-based, adaptive management under climate change.

ABSTRACTLarge ungulate populations can threaten forest regeneration and many rare or declining understory plants, birds, and small mammals. Reintroduction of large predators is often proposed as a remedy to reduce negative ecosystem effects associated with high ungulate populations, but we know little about the effectiveness of this approach. We assessed whether wolves (Canis lupus) can protect forest understory plants from excessive white‐tailed deer (Odocoileus virginianus) browse. We planted white oak (Quercus alba), red oak (Quercus rubra), and zigzag goldenrod (Solidago flexicaulis) seedlings across a gradient of wolf density and residence time in northern Wisconsin and recorded deer browse and frequency of 11 common understory plants at each site. We found that wolf density and residence time had negative effects on deer browse intensity, but these effects were generally weak except when understory vegetation was abundant. Additionally, the presence of common understory plants decreased as a function of wolf density, opposite to what we would expect for a wolf‐driven trophic cascade. The weak reduction in browse probability that is associated with wolves, particularly when vegetation is scarce, is unlikely to improve forest regeneration and recovery of understory plant communities currently threatened by high deer populations.

Recovery of native plant communities after the control of a dominant invasive plant species, Foeniculum vulgare: Implications for management