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

Chinese privet (Ligustrum sinense Loureiro) (Oleaceae) is a shade-tolerant invasive shrub first introduced from China into the US in the mid-19th Century as an ornamental (Wyman 1973, Shrubs and Vines for American Gardens, Macmillan, NY). Chinese privet is an aggressive invader across the southeastern United States and is now found in 27 U.S. states, including Hawaii (EDDMapS, http://www.eddmaps.org/; 20 May 2021), resulting in loss of native species richness across much of its invaded range (Hanula et al. 2009, Invas. Plant Sci. Manag. 2: 292–300; Hudson et al. 2014, Forest Ecol. Manag. 324: 101–108; Merriam and Feil 2003, Biol. Invasions 4: 369–373; Wilcox and Beck 2007, Southeast. Nat. 6: 535–550). Ward (2002, Southeast Geogr. 1: 29–48) documented an 8% increase in Chinese privet cover in the Upper Oconee River floodplain in northern Georgia between 1951 and 1999.Where Chinese privet establishes, it can dominate as an understory monoculture (e.g., Wilcox and Beck 2007), reducing flowering plant richness needed to support pollinators and, over the long term, likely reducing woody debris diversity necessary as harborage and food for a number of arthropods. Several studies have investigated these impacts of Chinese privet infestation on various taxa, including arthropod communities, with most reporting similarly negative results. A more abundant and diverse bee fauna was found on Chinese privet removal plots compared to control (infested) plots 1 and 2 yr after treatment, and again 5 yr after treatment (Hanula and Horn 2011a, Insect. Conserv. Divers. 4: 275–283; Hudson et al. 2013, Biol. Conserv. 167: 355–362). In a later study on bees at the same study site, Ulyshen et al. (2020, Forest Sci. 66: 416–423) placed traps at 0.5, 5, and 15 m above the forest floor. Bee abundance and diversity were higher near the forest floor in plots where Chinese privet was removed, but similar among plots in the elevated traps. Likewise, beetle richness was increased near ground level after Chinese privet removal in the same experimental plots (Ulyshen et al. 2010, Biol. Invasions 12:1573–1579). In another study, butterfly abundance increased after Chinese privet removal, although richness and evenness did not differ between treatments (Hanula and Horn 2011b, For. Ecol. Manage. 262: 674–680).Ants (Hymenoptera: Formicidae) are abundant and ecologically important arthropods—turning and aerating soil, dispersing seeds, playing a major role in food webs, and serving as environmental indicators and ecosystem engineers (Jones et al. 1994, Oikos 69: 373–386; Folgarait 1998, Biodivers. Conserv. 7: 1221–1244). As such, understanding the effects of Chinese privet and other invasive plants on ant communities is an imperative area of invasion biology research. Many ants are highly successful invasive species, transported around the globe via commerce and other human activity (McGlynn 2002, J. Biogeo. 26: 535–548). Both native and nonnative ants inhabit Georgia forests where Chinese privet occurs. In this paper, we present data on ant diversity and seasonal occurrence in experimental plots with and without Chinese privet, as well as in areas with no history of extensive Chinese privet infestation, reporting on native and nonnative ants in our study sites in northern Georgia.Experimental Chinese privet removal plots were established in four locations in northern Georgia within the Oconee River watershed in October–November 2005 as detailed in Hanula et al. (2009). Sites included Sandy Creek Nature Center north of Athens, GA (Sandy Creek); the Georgia State Botanical Gardens south of Athens (Botanical Garden); the Scull Shoals Experimental Forest in the Oconee National Forest (Scull Shoals); and the University of Georgia Warnell School of Forest Resources Watson Springs Forest (Watson Springs). Briefly, treatments consisted of hand-felling, mechanical removal (mulching with a Gyrotrac® mulching machine) (Klepac et al. 2007, USDA. For. Serv. Southern Res. Sta. Res. Paper SRS43), and no treatment (control). Hand-felling and mechanical removal treatments were followed by herbicide application to stumps and, in 2006, to sprouts, seedlings, and saplings. By 2007, virtually all privet had been removed from the hand-felling and mechanical removal plots, and in 2012 reinfestation of treated plots was minimal (3% and 7% in hand-felling and mechanical removal plots, respectively) (Hudson 2013, Effects of removing Chinese privet (Ligustrum sinense) on plant communities, pollinator communities, and tree growth in riparian forests five years after removal with mechanisms of reinvasion. MS Thesis, Univ. Georgia, Athens). Three additional “desired future condition” plots (riparian hardwood forest with little or no Chinese privet) were established in the Oconee National Forest: one near the Apalachee River (Apalachee) (Greene Co., GA); one near Harris Creek (Harris) (Greene Co., GA), and one near Falling Creek (Falling) (Oglethorpe Co., GA).Ground-dwelling arthropods were sampled using pitfall traps operated for 7-d periods seven times (March, April, May, June, July, August, and October) during 2006, 2007, and 2011. The pitfall traps consisted of a 480-ml plastic cup buried to ground level. A small funnel (8.4-cm diameter) was inserted into the cup and directed crawling insects into a 120-ml specimen cup below. The cup was placed at the intersection of two, 1-m long drift fences and the specimen cup filled with a soap and NaCl-formaldehyde solution (New and Hanula 1998, South. J. Appl. For. 22: 175–183) as a preservative. We used five pitfall traps per plot, each being placed within a subplot. Subplots were located at the plot center and half the distance from the center to each plot corner. Trap samples for each plot were combined into one collective sample per plot and stored in 70% alcohol until they were sorted and identified. Ants were identified using published keys. For the 2006 and 2007 samples, ants were sorted and identified to genus only. Those samples subsequently degraded and were eventually lost. Ants from the 2011 samples were identified to species, and vouchers deposited at the Mississippi Entomological Museum, Mississippi State, MS.We tested for possible treatment effects on ant richness (for ant genera in 2006 and 2007 samples and for species in 2011 samples) using rarefaction and extrapolation with Hill numbers (Chao et al. 2014, Ecol. Monogr. 84: 45–67) using iNEXT Online (Chao et al. 2016, iNEXT (iNterpolation and EXTrapolation, http://chao.stat.nthu.edu.tw/wordpress/software_download/, 1 June 2021]). Because ants are colonial organisms and pitfall catch can be heavily influenced by proximity to nests, we used sampling-unit-based incidence data rather than abundance data (Gotelli et al. 2011, Myrmecol. News 15: 13–19). We set q = 0 to yield species richness, specified an endpoint of 206, and accepted default values for number of knots (40), bootstraps (50), and confidence interval (95%). For species-level 2011 data, we also set q = 1 to yield Shannon diversity using the same parameters.To compare ant communities among the three treatments and the desired condition plots, using species-level data from 2011 we performed nonmetric multidimensional scaling (NMS) using PC-ORD (McCune and Mefford 2010, PC-ORD v. 6.0. MjM Software, Gleneden Beach, OR). We used the Jaccard distance measure on presence–absence data for this analysis. We used the same presence–absence matrix and distance measure to perform a multiresponse permutation procedure (MRPP) to test for differences between treatments. Finally, to test for associations between ant taxa and one or more treatments, we performed indicator species analysis in R using the package “indicspecies” (De Cáceres et al. 2010, Oikos 119: 1674–1684). We used the function multipatt (multilevel pattern analysis) to conduct this analysis, using 9,999 permutations to calculate P-values for each combination. The resulting indicator values range from 0 to 1 (no association to complete association).Lastly, we subjected the four most abundant species to analysis of variance using log-transformed data (logX + 1) to test for treatment effects on those species. Site was used as a blocking factor, and we tested for effects of treatment and date using the F-statistic.We collected and identified 50 species of ants from the pitfalls (Table 1), including the invasive Asian needle ant, Brachyponera chinensis (Emery). While only present at five of the seven sites, Asian needle ant was greater than 4× more abundant than the next-most commonly collected species, Lasius americanus Emery. Asian needle ant was most abundant in the Botanical Gardens control plot, where it was captured in increasing numbers throughout the season (2, 15, 12, 125, 511, 1,000+, and 1,000+ for March, April, May, June, July, August, and October, respectively). When Asian needle ant numbers exceeded 1,000 in a sample, counting of individual ants was stopped. Zungoli and Benson (2008, Pp. 51–57, In Robinson and Bajomi [eds.], Proc. 6th Intern. Conf. Urban Pests, Budapest, Hungary) observed peak worker activity in August, followed by a decline in September and inconsistent activity in October. We do not have exact numbers for August and October, but clearly foraging activity and/or the number of available foragers in colonies increases in this species later in the season.For ant genera identified in 2006 and 2007 (1 and 2 yr after treatment, respectively) there were no significant differences in ant diversity among the treatments. The 95% confidence intervals for extrapolated species richness data (q = 0) from 2011 overlapped among treatments, but 95% confidence intervals for desired future condition plots diverged from control and mulched plots using extrapolated Shannon diversity (q = 1) (Fig. 1). There was an overall trend toward increased ant diversity in desired condition plots in 2007 and 2011. Mean species richness for all years and treatments is presented in Table 2.Our NMS analysis yielded a three-dimensional solution with a final stress of 8.29. The desired plots form a distinct cluster within the ordination space, suggesting a relatively distinct ant community, while there is considerable overlap among the three other treatments (Fig. 2). Based on MRPP, there was a marginally significant difference in community composition among treatments (T = –1.38, P = 0.09). Pairwise comparisons reveal that the ant communities in the desired plots differed significantly from those in the control (T = –2.26, P = 0.03) and chainsaw (T = –1.57, P = 0.05) plots. No other pairwise comparison was significant. Indicator species analysis found four ant species to be significantly associated with the desired plots, with one of them also associated with the control plots (Table 3). The first species, Nylanderia vividula Nylander (“Nylander's crazy ant”) is an indoor pest in many situations, widely distributed throughout the U.S. Gulf Coast states. Pseudomyrmex ejectus (Smith) nests in dead twigs and stalks of herbaceous plants. Solenopsis carolinensis Forel is a common thief ant in forests in the southeastern United States and is known to nest in the bark of pine trees (J.A.M., pers. obs.). Strumigenys louisianae Roger is widespread and is a specialized predator on collembola (Wilson 1953, Ann. Entomol. Soc. Am. 46: 479–495). It is thought to be the only native species in the genus. It cannot be determined from our data if these species-level patterns were driven by differences in privet invasion history or by other factors affecting ant distribution across our sampling area.Analysis of variance results for the four most abundant species varied. Brachyponera chinensis catches were related to site, and site × date × treatment (F = 4.75; df = 4, 79; P = 0.002; and F = 7.52, df = 2, 70, P = 0.001, respectively), with more being captured late in the season and a single control plot at the Botanical Gardens yielding thousands of individuals compared to 0–13 in all other plots. For Crematogaster ashmeadi, site, site × date, and site × date × treatment were all significant (F= 3.12, df = 4, 79, P= 0.021; F= 2.56, df = 7, 72, P= 0.021; F = 18.8, df = 2, 70, and P < 0.001, respectively). Fewer C. ashmeadi were collected at the Botanical Gardens site than the other sites, and seasonal activity was highest June–August, although they were collected on all sampling dates. More C. ashmeadi were collected in mulched (7.4 ±1.9) (x̄ ± SE) and chainsaw (2.29 ± 0.65) plots than in controls (1.25 ± 0.36). There were no significant treatment effects noted for L. americanus or Aphaenogaster carolinensis Wheeler.Although a few species with specialized nesting habits were collected in this study (e.g., arboreal species, twig and cavity nesting species), the majority of ant species collected are known to nest in soil, under debris, and/or in decaying wood. Plots where Chinese privet was hand-felled may have offered more nesting sites for some ant species for a limited time after treatment. Differences in pitfall catches for individual species suggest that dense populations of Chinese privet may favor (B. chinensis) or suppress (C. ashmeadi) some ants; however, these results should be interpreted cautiously given the potential local variation in pitfall traps with respect to nest proximity. Regardless, presence of Chinese privet did not appear to impact our measures of ant diversity relative to the removal treatments. Species contributing to increased diversity in desired condition plots included myrmicine species in the specialized predator genus Strumigenys and the uncommonly collected myrmicine Aphaenogaster mariae Forel, an arboreal species that has usually been collected from the trunks of live trees using bait (DeMarco 2015, Phylogeny of North American Aphaenogaster species [Hymenoptera: Formicidae] reconstructed with morphological and DNA data. PhD Dissertation. Michigan State Univ., East Lansing).Ant sampling is biased by sampling method, with pitfall traps generally collecting fewer species than more-targeted methods such as hand-collecting in quadrats (Gotelli et al. 2011, Myrmecol. News 15: 13–19; Salata et al. 2020, Biodiv. Conserv. 29: 3031–3050 and references therein). Collections at the Sandy Creek site in 2011–2012 using a modified Winkler litter extraction method captured >47 ant species (D. Booher, pers. comm.), whereas we collected and identified 31 species at Sandy Creek in this study; our results are somewhat limited in contrast to more-exhaustive collecting methods. Long-term studies with multiple collection methods would be informative in terms of ant communities in restored areas where Chinese privet has been removed versus similar, undisturbed areas with no or little history of Chinese privet infestation, and in Chinese privet-infested controls. Understory plant cover in both privet removal treatments and desired condition plots was similar (∼40–60%) 2 yr after treatment, but the plant communities in desired condition plots were highly dissimilar to both controls and privet removal treatments (Hanula et al. 2009) with early successional species abundant in the treated plots. Plants may provide ants with vegetative matter for foraging, food bodies, nesting sites, nectar, and eliasomes (Beattie and Hughes 2002, Pp. 211–235. In Herrera and Pellmyr [eds.], Plant-Animal Interactions: An Evolutionary Approach, Blackwell Science, Oxford, U.K.), and higher diversity of plants in desired condition plots may support a more diverse ant population. As pointed out by Hanula et al. (2009), it is likely that Chinese privet suppression may be required for long periods of time, or that active understory restoration may be necessary, to realize understory and forest conditions similar to areas with no history of Chinese privet. The same is likely true for arthropod groups such as ants that interact with shrubs and forbs in the understory.We thank Doug Booher, Timothy Menzel, and two anonymous reviewers for many helpful comments on the manuscript and Frank Roesch for statistical expertise. This work was funded by USDA Forest Service Research and Development. The findings and conclusions in this publication are those of the authors and should not be construed to represent any official USDA or U.S. Government determination or policy.

Removing Chinese privet from riparian forests still benefits pollinators five years later

Abstract. 1. Chinese privet ( Ligustrum sinense Lour.) was removed from riparian forests in the Piedmont of Georgia in November 2005 by mulching with a track‐mounted mulching machine or by chainsaw felling. The remaining privet in the herbaceous layer was killed with herbicide in December 2006. 2. Bee (Hymentoptera: Apoidea) abundance, diversity and community similarity in the forests were measured for 2 years after shrub removal and compared with heavily invaded controls and with non‐invaded forests (desired future condition) using pan traps. 3. In 2006, control plots averaged 8.8 species and 34.8 bees per plot. Privet mulching resulted in 32.5 bee species and 418.3 bees per plot, and privet felling plots had 29 species and 259 bees per plot. In 2007, control plots averaged only10 species per plot and 32.8 bees per plot, while mulched and felled plots had 48 and 38 species per plot and 658.2 and 382.5 bees per plot, respectively. 4. The bee community on untreated control plots was dissimilar from the communities on privet felling, mulched and desired future condition plots during both years; however, by 2007, desired future condition, felling and mulched plots had similar bee communities. 5. Removal of an invasive shrub provided immediate benefits for native pollinators and resulted in bee communities similar to non‐invaded forests even without further restoration of native plant communities.

Chinese privet is a major invasive shrub within riparian zones throughout the southeastern United States. We removed privet shrubs from four riparian forests in October 2005 with a Gyrotrac® mulching machine or by hand-felling with chainsaws and machetes to determine how well these treatments controlled privet and how they affected plant community recovery. One year after shrub removal a foliar application of 2% glyphosate was applied to privet remaining in the herbaceous layer. Three “desired-future-condition” plots were also measured to assess how well treatments shifted plant communities toward a desirable outcome. Both methods completely removed privet from the shrub layer without reducing nonprivet shrub cover and diversity below levels on the untreated control plots. Nonprivet plant cover on the mulched plots was > 60% by 2007, similar to the desired-future-condition plots and higher than the hand-felling plots. Both treatments resulted in higher nonprivet plant cover than the untreated controls. Ordination showed that after 2 yr privet removal plots were tightly grouped, suggesting that the two removal techniques resulted in the same plant communities, which were distinctly different from both the untreated controls and the desired-future-condition. Both treatments created open streamside forests usable for recreation and other human activities. However, much longer periods of time or active management of the understory plant communities, or both, will be required to change the forests to typical mature forest plant communities.

Human influence on the environment is so extensive that virtually all ecosystems on the planet are now affected by biological invasions. And, often, ecosystems are invaded by multiple co‐occurring non‐native species. Hence, it is important to understand the impacts these invasions are producing on biodiversity and ecosystem processes.Here, we present results of a 2‐year long field experiment where we tested the effects of co‐occurring invasive C4African grasses in a Cerrado area in central Brazil. We compared plant and arthropod communities, plant biomass, and soil nitrogen dynamics and soil chemical characteristics across five experimental treatments:Urochloa decumbensremoval;Melinis minutifloraremoval; bothU.decumbensandM.minutifloraremoval;U.decumbensandM.minutiflorainvaded plots; and uninvaded Cerrado. We hypothesized that selective removal of invasive grasses would have distinct effects on the native ecosystem structure and functioning. We expected that each invasive grass would produce a different type of impact on the native ecosystem and that their impacts would be synergistic when co‐occurring.Removal ofM.minutifloradoubled native plant diversity and biomass when compared to invaded plots, whereas removal ofU.decumbensdid not alter these parameters. Cerrado plots had four times more plant species than plots cleared of invasives. Removal of invasive grasses did not affect the species richness or community composition of soil epigeal fauna. Cerrado soils had lower fertility, organic matter content and pH than invaded soils. The effects were generally higher when both invasive grasses were removed, suggesting impacts were synergistic, butM.minutiflorahad greater effects on plants and soils thanU.decumbens. Both invasive species produced negative impacts, but a single species was the main driver. We also detected persistent effects of the invasive grass species on the ecosystem after 2 years of removal.We conclude that invasive species of the same functional group have similar types of effects in native ecosystems, but the magnitude of impact was largely dependent on invasive species biomass and cover. Where multiple invasive species are present, research and management of invaded ecosystems should tackle the interacting effects of co‐occurring invaders.

Summary Though co‐occurrence of invasive plant species is common, few studies have compared the community and ecosystem impacts of invaders when they occur alone and when they co‐occur. Prioritization of invasive species management efforts requires sufficient knowledge of impacts – both among individual invasive species and among different sets of co‐occurring invaders – to target resources towards management of sites expected to undergo the largest change. Here, we observed differences in above‐ and below‐ground impacts of two invasive woody shrubs, Lonicera maackii and Ligustrum sinense, among plots containing both shrubs (mixed), each species singly or lacking both species (control). We found additive and non‐additive effects of these co‐occurring invasives on plant communities and soil processes. Mixed plots contained two times more subdominant invasive plant species than L. maackii or L. sinense plots. Compared to control plots, mixed plots had three times the potential activity of β‐glucosidase, a carbon‐degrading extracellular soil enzyme. L. maackii plots and mixed plots had less acidic soils, while L. sinense plots had higher soil moisture than control plot soils. Differences in soil properties among plots explained plant‐ and ground‐dwelling arthropod community composition as well as the potential microbial function in soils. Synthesis and applications. Our study highlights the importance of explicitly studying the impacts of co‐occurring invasive plant species singly and together. Though Lonicera maackii and Ligustrum sinense have similar effects on ecosystem structure and function when growing alone, our data show that two functionally similar invaders can have non‐additive impacts on ecosystems. These results suggest that sites with both species should be prioritized for invasive plant management over sites containing only one of these species. Furthermore, this study provides a valuable template for future studies exploring how and when invasion by co‐occurring species alters above‐ and below‐ground function in ecosystems with different traits.

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.

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.

Invasive non-native woody shrubs pose a major threat to forested ecosystems in many parts of the world and there is an urgent need for research on the restoration and recovery of these areas. We studied patterns of tree growth and regeneration 13 years after the experimental eradication (by chainsaw or mulching machine followed by herbicide treatments) ofLigustrum sinenseLour. (Chinese privet) from riparian forests in Georgia, United States. We also followed the recovery of bee and butterfly populations using sites with no history of privet invasion as a reference. By the end of the study, the basal area of restored plots was 24% greater, on average, than still-invaded control plots. Because tree growth rates did not differ among treatments, this increase is attributable to the 60% increase in the number of regenerating native stems (dominated byAcer negundoL.) following privet removal. The benefits of privet removal on pollinators were immediate and long-lasting with the richness and abundance of bees and butterflies being consistently higher in restored plots than in control plots. The diversity, abundance, and composition of bees in restored and reference (i.e., never invaded) plots were comparable by the end of the study. This was less true for butterflies, however, possibly due to the legacy effects of privet invasion on plant communities. Our results demonstrate the long-term benefits of removing privet on forest regeneration and pollinator communities. Indeed, without such efforts, it is probable that forest cover will gradually thin and ultimately disappear from privet-invaded areas as overstory trees die without replacement.

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.

Urban forests represent patches of biodiversity within otherwise degraded landscapes, yet these forests are threatened by invasion by exotic plant species. We investigated the response of a forest understory to removal of four common exotic species: Elaeagnus umbellata Thunb., Lonicera japonica Thunb., Ligustrum sinense, Laur., and Microstegium vimineum (Trin.) A. Camus in a forest within the city of Raleigh, NC, USA. In the summer of 2001, we initiated a removal experiment with three treatments. In the “repeated removal” treatment, all understory vegetation was initially removed by clipping and new exotic seedlings were repeatedly removed every 2 weeks throughout the study period. The “initial removal” treatment involved a one-time understory vegetation removal with no further weeding. Control plots had no intervention throughout the study period. We conducted vegetation surveys of the plots prior to treatment initiation and in April and August of 2002 and 2003. With a non-metric multidimensional scaling (NMS) ordination, we were able to discern differences in species composition between the repeated removal treatment and the other two treatments. However, using repeated measures ANOVA, we found no significant differences in native species richness, cover, and abundance among treatments during most sampling periods. We also used a seedbank study to determine that while some early successional species were present, no native shrubs and few native trees emerged from the seedbank. These results suggest that (1) repeated removal is required to decrease the importance of exotic species, especially if the site is in close proximity to a source of exotic propagules; and (2) subsequent to exotic removal, native species may not recover sufficiently without supplemental plantings. Therefore, restoration plans for urban forests should incorporate both long-term monitoring and native plant re-introduction to achieve a diverse native community.

Macroalgal canopies provide corals limited protection from bleaching and impede post-bleaching recovery

Overabundant deer populations pose significant challenges to the conservation of native plant communities. We examined the effects of a protected white-tailed deer (Odocoileus virginianus Zimm.) population on forest plant communities in Cades Cove, Great Smoky Mountains National Park. The Cove deer herd reached 43 deer km−2 at its peak in the late 1970s. While current densities are somewhat lower, the diversity and coverage of many understory species remains greatly reduced. To elucidate the influence of contemporary deer browsing, an exclosure study was established in 1997. Ten 10-m × 10- m sample plots were randomly located at three sites, half of which per site were exclosed. Understory vegetation on all 30 plots was intensively sampled in August 2004. While the diversity and richness of herbaceous species was similar in exclosures and controls following eight years of deer exclusion, exclosures contained significantly more diverse sapling layers (tree species ≤2 m in height). Correspondingly, exclosures contained significantly greater sapling densities than control plots (P < 0.001). Herbaceous and sapling layer composition varied between exclosures and controls. Forbs, vines, and low woody shrubs were consistently more abundant within exclosures than control plots. Graminoids (both native and exotic) dominated both exclosures and controls, but typically had greater relative abundance on control plots. Given the modest recovery of the herbaceous layer and the persistence of non-preferred browse species following eight years of deer exclusion, plant community recovery would be slow and uncertain even if the density of deer within the Cove was reduced.

Grassland degradation has become a worldwide ecological problem. Although soil microorganisms, as the main participants in the process of grassland degradation, play a key role in maintaining ecosystem function and improving soil productivity, little is known about the changes in microbial communities caused by grassland degradation and their relationship with soil properties and plant communities. In this study, we used Illumina MiSeq sequencing to analyze the soil fungal communities of subalpine meadow soil at four different degradation stages[i.e., non-degraded (ND), lightly degraded (LD), moderately degraded (MD), and heavily degraded (HD)] on Mount Wutai. The results showed that Ascomycota, Basidiomycota, and Zygomycota were the dominant phyla of soil fungi in the subalpine meadow, regardless of degradation stage. LEfSe showed that the subalpine meadows with different degradation degrees were enriched with different biomarkers. Compared with ND, MD and HD were enriched with more pathogenic fungi. Moreover, HD apparently decreased the richness and Shannon indexes of soil fungal communities compared with those of ND. Non-metric multidimensional scaling (NMDS) and similarity analysis (ANOSIM) indicated that the compositions and structures of fungal communities were significantly different among meadows with different degradation degrees (P<0.05). Redundancy analysis (RDA) showed that soil water content, total nitrogen, plant richness, and ammonium nitrogen were significantly correlated with the compositions and structures of fungal communities (P<0.05). There were significant correlations between α diversity and β diversity between plant and fungal communities (P<0.05), indicating strong coupling. The results of our study provide a theoretical basis for further research on the changes in soil fungal communities and their driving mechanism in different degradation stages of subalpine meadows.

Chinese privet (Ligustrum sinense Lour.), an invasive shrub from Asia, is well established in the southeastern United States where it dominates many floodplain forests. We used flight intercept traps to sample beetles at three heights (0.5, 5 and 15 m) in ~2 ha plots in which L. sinense had (by chainsaws or mulching machine) or had not been removed from forests in northeastern Georgia. Removing L. sinense, particularly by machine, increased the richness and diversity of beetles and affected composition near the ground (0.5 m) but not in the forest canopy (15 m). There were no differences among treatments above the L. sinense canopy (5 m) aside from Xylosandrus crassiusculus, an exotic ambrosia beetle from Asia, dominating the beetle community at that height in control plots. Removing the L. sinense layer greatly increased beetle richness near the ground, resulting in vertical distribution patterns more similar to those observed in areas of forest devoid of L. sinense. We suspect that even organisms in the canopy will benefit from privet removal in the long term given that tree regeneration is nearly impossible in forests in which L. sinense has become well established.