Recovery of Perennial Plant Communities in Disturbed Hyper-Arid Environments (Sharaan Nature Reserve, Saudi Arabia)

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.

Exclosures that exclude large herbivores are effective tools for the protection and restoration of grazed plant communities. However, previous studies have shown that the installation of an exclosure does not ensure plant community recovery. Our study aimed to determine the effects of the domination of unpalatable plants and the timing of exclosure installation on the plant community recovery process in montane grassland overgrazed by sika deer (Cervus nippon) in Japan. In this study we compared plant species composition and their cover with inside and outside exclosures installed at different times. Furthermore, we also compared them with those in 1981, when density of sika deer was very low. We used quadrats inside and outside fenced areas established in 2010 and 2011 to record both the cover and the height of species in each quadrat between 2011 and 2015. Plant cover, with the exception of graminoid species, increased in later years in all treatments. Non-metric multidimensional scaling (NMDS) plots showed significantly differentiated treatment trends. The species composition within the 2010 fenced area gradually shifted to greater similarity with the species composition reported in 1981. The plant community in the 2011 fenced area was slower to recover. Compositions of plant communities outside the fenced areas hardly changed from 2011 to 2015. Chao’s dissimilarity index decreased over time between the plant community surveyed between 2011 and 2015 and the past plant community in 1981 within the exclosures, and was higher in the 2011 fenced area than in the 2010 fenced area. In conclusion, we show that the reduction of graminoids and the time after exclosure installation were important for plant community recovery from deer grazing damage. A delay in exclosure installation of one year could result in a delay in plant community recovery of more than one year.

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.

Impacts of removing Chinese privet from riparian forests on plant communities and tree growth five years later

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.

Large, high‐severity wildfires are an important component of disturbance regimes around the world and can influence the structure and function of forest ecosystems. Climatic changes and anthropogenic disturbances have altered global disturbance patterns and increased the frequency of high‐severity wildfires worldwide. While the recovery of plant communities at different successional stages after fire is well known, the influence of prior disturbances and stand age is poorly understood. Despite this, high‐intensity wildfires can produce long‐lasting legacy effects, which can influence the resistance and resilience of ecosystems. Here, we quantified the influence of prior stand age and disturbance history on the recovery of plant communities in the Mountain Ash and Alpine Ash forests of south‐eastern Australia after high‐severity wildfire. Specifically, controlling for stand age, we compared the abundance (percent cover) of different plant life forms and reproductive strategies in forests that were, at the time of high‐severity wildfire in 2009, “young” (28–35 yr old and previously logged), “mixed” age (26, 70–83, >150 yr old), “mature” (70–83 yr old), and “old‐growth” (>150 yr old). We uncovered evidence that the legacy of prior disturbance and stand age at the time of high‐severity wildfire can influence the recovery of plant communities in early successional forests. Specifically, we found that “young” forests burnt in 2009 had a higher abundance of ruderal and graminoid species, but had a lower abundance of persistent, onsite seeders, includingAcaciaand eucalypt species, relative to “old‐growth” forests burnt in 2009. “Mature” aged forests burnt in 2009 also had a lower abundance ofAcacia, eucalypt, and shrub species, relative to “old‐growth forests” burnt in 2009. Our findings provide evidence of advanced recovery in forests that were older when burnt by high‐severity wildfire, relative to younger forests burnt by the same wildfire. Further, we also demonstrate the influence of different environmental conditions on plant communities. In a period of rapid, global, environmental change, our study provides insights into the recovery of plant communities post‐wildfire with implications for forest management. Further, our findings suggest that predicted increases in the frequency of high‐severity wildfires may have consequences for forest regeneration.

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.

Competition and herbivory can interact to influence the recovery of plant communities from disturbance. Previous attention has focused on the roles of dominant plant species in structuring plant communities, leaving the roles of subordinate species often overlooked. In this study, we examined how manipulating the density of a subordinate plant species, Solanum carolinense, and its insect herbivores influenced an old-field plant community in northern Florida following a disturbance. Five years following the disturbance, the initial densities of S. carolinense planted at the start of the experiment negatively influenced total plant cover and species diversity, and the cover of some grasses (e.g., Paspalum urvillei) and forbs (e.g., Rubus trivalis). Selectively removing herbivores from S. carolinense increased S. carolinense abundance (both stem densities and cover), increased the total cover of plants in the surrounding plant community, and affected plant community composition. Some plant species increased (e.g., Digitaria ciliaris, Solidago altissima) and others decreased (e.g., Paspalum notatum, Cynodon dactylon) in cover in response to herbivore removal. Herbivore effects on plant community metrics did not depend on S. carolinense density (no significant herbivory by density interaction), suggesting that even at low densities, a reduction of S. carolinense herbivores can influence the rest of the plant community. The recovery of the plant community was context dependent, depending on site- and plot-level differences in underlying environmental conditions and pre-disturbance plant community composition. We demonstrate that the density of and herbivory on a single subordinate plant species can affect the structure of an entire plant community.

<p>Plant and soil communities are intimately connected. Plants shape soil microbial community composition through their resource acquisition strategies and via root carbon (C) inputs, which has cascading effects on biogeochemical cycles. Drought has been shown to disrupt the connection between plants and soil microorganisms. However, the effects of drought intensity on soil microbial community functioning, including the uptake of recent plant-derived C, are largely unknown. Here, we determined how two plant communities with contrasting resource acquisition strategies (acquisitive versus conservative) responded to a gradient of drought (control, and eight drought intensities). Using a <sup>13</sup>C pulse labelling approach, we tracked C allocated from plants to soil and its uptake by the microbial community. We measured potential extracellular enzyme activity as a proxy of microbial community functioning. We hypothesized that (1) drought responses are non-linear, and (2) acquisitive plant communities have lower drought resistance but recover faster than conservative plant communities, which is reflected in lower <sup>13</sup>C transfer and reduced microbial functioning during drought and increases after drought. In general, we found that the responses we measured were non-linearly related to drought intensity. After three weeks of drought, drought intensity decreased aboveground net primary productivity (ANPP) of both plant communities. Soil extractable organic <sup>13</sup>C decreased with increasing drought intensity, indicating that less recently assimilated C was allocated to root exudation. Although microbial biomass remained stable over the drought intensity gradient, <sup>13</sup>C uptake into microbial biomass decreased at peak drought, and was lower in the conservative vs. acquisitive plant community at mild drought levels. Potential enzyme activity of β-1,4-glucosidase, involved in cellulose breakdown, and  β-N-acetyl-glucosaminidase, involved in chitin breakdown, decreased with increasing drought intensity. Urease activity was higher in conservative than acquisitive plant communities exposed to drought. Seven days after re-wetting, we found that microbial uptake of <sup>13</sup>C increased along the drought gradient and was higher than the control in communities previously subjected to high drought intensities. This fast microbial recovery could affect nutrient mobilisation, which could underlie longer-term plant community recovery. Two months after re-wetting, we indeed found that plant communities that had previously experienced high drought intensity (> 75% soil water deficit) had higher ANPP than the control. We conclude that drought intensity has significant non-linear effects on microbial uptake of recent plant C and on potential extracellular enzyme activities both during drought and recovery, with consequences for plant community recovery dynamics.  </p>

Environmental factors drive changes in plant functional traits, which in turn promote community recovery. The environmental conditions of the community are different at different recovery stages. Changing environmental factors may drive the changes in plant functional traits at the community level and affect species adaptation. We studied plant communities in five different recovery stages (herb, grass and shrub, shrub, tree and shrub, and tree) in the karst plateau of Zhenning, Guizhou (The vegetation in the study area has undergone a gradual natural recovery process after the forests were deforested in 1958–1960). We studied functional traits and their links to environmental factors. The main results include the following. (1) Over time, plant height, leaf dry matter content, leaf nitrogen content and leaf phosphorus content increased significantly in the tree stage, while leaf thickness and specific leaf area decreased significantly in the tree stage. (2) Soil organic carbon, soil N content, soil P content, soil C:P and soil C:K showed an increasing trend, and were significantly higher in tree stage than in other stages. Soil potassium content fluctuated and soil bulk density decreased gradually, reaching the lowest value in the tree stage, but the difference was not significant. (3) During the restoration process, the functional characteristics changed from a combination of plant communities with high specific leaf area and low dry matter content with a short plant height to plant communities with low specific leaf area and high dry matter content with a tall plant height. (4) As recovery proceeded, the study area gradually changed from a soil nutrient‐poor environment to a nutrient‐rich environment. Overall, the environmental factors vary greatly during the recovery of plant communities in karst areas. The plant community shifts from an aggressive (resource acquisition) to a conservative (environmental barrenness resistance) ecological strategy. The soil phosphorus content and soil C:K are the main environmental factors affecting the changes in functional traits during the restoration of karst plant communities in Zhenning.

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

This paper reports on the recovery of desert plant communities after 20 years of oil‐derived hydrocarbon contamination in desert habitats of Kuwait, caused by the First Gulf War (1990–1991). The hypothesis that certain native desert plant species can tolerate weathered oil‐polluted soils and can potentially function as bioindicators and phytoremediator species for oil‐polluted soil was tested. A field survey of 200 quadrat sampling plots at seven hydrocarbon‐contaminated and unpolluted desert areas in Kuwait was performed and recorded 42 plant species, with Haloxylon salicornicum (Moq.) Bunge ex Boiss., Cyperus conglomeratus Rottb., and Rhanterium epapposum Oliv. as the dominant species. Analysis of plant tissues indicated plant uptake and accumulation of some polycyclic aromatic hydrocarbons (PAHs), depending on plant species and specific PAH compounds. Total PAHs in plant tissues in the most contaminated sites were over 200 μg kg−1. H. salicornicum could develop in both oil‐contaminated soil and uncontaminated soil although their biomass was about 16.7% smaller than usual. However, the plants appeared green and healthy in both sites, and showed no overt stress. The results suggest that some desert plant communities can recover after severe oil pollution and that H. salicornicum may serve as a phytoremediator of oil‐contaminated desert soils. Our results also demonstrated that some desert plant communities could be cultivated in oil fields to reduce hydrocarbon contamination and provide support to other ecosystem services through improving soil quality and biodiversity.

Summary 1 Past land use can have long‐term effects on plant species’ distributional patterns if alterations in resources and environmental conditions have persistent effects on population demography (environmental change) and/or if plants are intrinsically limited in their colonization ability (historical factors). 2 We evaluated the role of environmental alteration vs. historical factors in controlling distributional patterns of Gaultheria procumbens, a woody, clonal understorey species with a pronounced restriction to areas that have never been ploughed, and near absence from adjoining areas that were ploughed in the 19th century. The demographic study was conducted in scrub oak and hardwood plant communities on an extensive sand plain, where it was possible to control for the effect of variation in environment prior to land use. 3 The observed demographic effects were contrary to the hypothesis that persistent environmental alteration depressed demographic performance and limited the distribution of G. procumbens. We observed no overall effect of land‐use history on stem density, stem recruitment or flower production. In fact, some aspects of performance were enhanced in previously ploughed areas. Populations in previously ploughed areas exhibited less stem mortality in scrub oak transitions, an increase in germination, seedling longevity and proportion of potentially reproductive stems in both plant communities, a trend for slower observed rates of population decline in both plant communities, and a higher projected rate of population growth in the scrub oak transitions. Thus, particularly in scrub oak communities, the lower abundance of G. procumbens in formerly ploughed than in unploughed areas contrasted with its performance. 4 The limited occurrence of G. procumbens in formerly farmed areas was explained instead by its slow intrinsic growth rate, coupled with limited seedling establishment. Lateral population extension occurred exclusively through vegetative growth, allowing a maximum expansion of 43 cm year−1. 5 We conclude that inherent limitations in the colonizing ability of some plant species may present a major obstacle in the restoration or recovery of plant communities on intensively disturbed sites, even in the absence of persistent environmental effects that depress population growth.