Effects Of Encroachment Research Articles

Analysis on the influence of retailer's introduction of store brand under manufacturer's product line strategy

<p style='text-indent:20px;'>As the introduction of store brand (SB) by retailers becomes more common, national brand manufacturers (NBM) in the market often respond with a product line strategy. Then how should retailers decide their product lines under the situation that NBM adopt product line strategy? Under the manufacturer's product line strategy, this paper compares and analyzes three competitive strategies for retailers to introduce high-end SB, low-end SB and SB product line. The results show that: First, no matter what kind of competition strategy the retailer adopts, (1) the introduction of SB occupies the market share of NB; (2) the retailer gains the highest unit income from the high-end products of NB manufacturers. Second, the relationship between production cost and encroachment effects directly affects the retailer's choice of optimal competitive strategy and the manufacturer's preference for its competitive strategy choice. Finally, from the perspective of profit maximization, the optimal choice for retailers is the product line competition strategy, but this strategy is not obvious compared with the high-end competition strategy. Therefore, when retailers introduce product lines, if they are effectively threatened by national brand manufacturers (for example, NBM refuses to provide national brands to retailers), retailers may choose the suboptimal strategy, that is, to introduce store brand high-end products. When the high-end products of store brands are better than the low-end products of national brands and the production cost of products is relatively high, this strategy just meets the expectations of national brand manufacturers for retailers to introduce strategies.</p>

Response of bacterial communities to shrub encroachment and forage planting in alpine grassland of the Qinghai-Tibetan Plateau

Shrub encroachment and conversion of grazing land to forage cultivation are the main disturbance factors at alpine grasslands in the Qinghai-Tibetan plateau. Yet our understanding of soil bacterial communities impacts of these disturbances is limited. Using shrub (Potentilla fruticose) encroachment systems and forage lands (Medicago sativa lands, and Elymus sibiricus lands) as a model, we investigated the effects of shrub encroachment and land use on bacterial communities in alpine grass soil at the Eastern edge of the Qinghai-Tibetan plateau of China. Soil bacterial communities were examined using high-throughput sequencing of the 16S rRNA gene (V4-V5 region, Illumina MiSeq). Soil properties of TN and SOC were tested using an Elementar Variomax CNS Analyser (Elementar Corp., Germany). WEOC concentrations were determined following Ma's procedures, to answer the following hypotheses: i) shrub encroachment and forage cultivation would reduce soil organic carbon content, ii) the bacterial communities in shrub encroachment and forage lands are less diverse than those of alpine grassland, and iii) the occurrence of extensive mutualism or commensalism in alpine grassland, and competition or mutual exclusion in shrub encroachment and forage land. In this study, we found that SOC and TN decreased on shrub encroached and forage lands, supporting our first hypothesis. In total, 56 bacterial phyla were identified across the sampling sites. The dominant phyla at the four plots, Proteobacteria, Actinobacteria, Acidobacteria, Bacteroidetes and Chloroflexi, accounted for 27–28%, 13–30%, 13–26%, 4–8% and 4–9% of the total population, respectively. Contrary to our expectation, alpha-diversities (phylogenetic diversity, Operational Taxonomic Unit (OTU) richness, Shannon, and Chao1) were consistently higher in disturbed soils than in alpine grassland, and the highest appeared in Medicago sativa lands compared to other sites. Soil texture and soil organic carbon together explained 30% of the total variations of bacterial communities, indicating that bacterial habitat (e.g. soil texture) and substrate (soil organic carbon) were affected in shrub encroachment and forage lands. Copiotrophs (Actinobacteria and Proteobacteria) and Nitrospirae were enriched in alpine grassland, while oligotrophs (Acidobacteria) were concentrated in shrub encroached and forage lands, indicating that shrub encroachment and conversion of alpine grassland to forage land may alter bacterial life history strategies. Through the phylogenetic molecular ecological network approach, we found that the bacterial network of alpine grassland was more complex than that of shrub and forage lands. Furthermore, the bacterial network of alpine grassland was more modular, and the taxa tended to co-occur, with positive associations accounting for 95% of all potential interactions. By contrast, negative interactions appeared more in shrub encroached (34%) and forage land (33%) compared to alpine grassland. This indicated that bacterial species have greater niche-sharing and more collaboration in alpine grassland than in shrub and forage lands. In conclusion, our findings revealed that shrub encroachment and conversion of alpine grassland to forage increased competition of bacterial species for substrates, with potential for serious consequences such as elevating losses of soil carbon.

Bush Encroachment and Large Carnivore Predation Success in African Landscapes: A Review

Bush encroachment is a habitat change phenomenon that threatens savanna and grassland ecosystems worldwide. In Africa, large carnivores in bush encroached landscapes must adjust to increasing woody plant cover and biomass, which could affect predation success at multiple stages through complex and context-dependent pathways. We highlight, interpret, and compare studies that assessed how bush encroachment or related habitat parameters affect the predation stages of large African carnivores. Bush encroachment may directly or indirectly affect predation success in various ways, including by: (1) altering habitat structure, which may affect hunting efficiency and prey accessibility; (2) changing prey abundance/distribution, with smaller species and browsers being potentially favoured; (3) influencing interference competition within the carnivore guild. For habitat or dietary specialists, and subordinate predators that are vulnerable to both top-down and bottom-up ecosystem effects, these alterations may be detrimental and eventually incur population fitness costs. As the threat of bush encroachment continues, future studies are required to assess indirect effects on competitive interactions within the large African carnivore guild to ensure that conservation efforts are focused. Additionally, to better understand the effects of bush encroachment across Africa, further research is necessary in affected areas as overall little attention has been devoted to the topic.

Alder encroachment alters subsoil organic carbon pool and chemical structure in a boreal peatland of Northeast China

Boreal peatlands have been experiencing increased abundances of symbiotic dinitrogen-fixing woody plants (mainly alder species). However, how alder encroachment alters soil organic carbon (C) pool and stability is unclear. To examine the effects of alder encroachment on soil organic C, we measured soil organic C pool, phenol oxidase (POX) activity, organic C mineralization rate, and organic C chemical structure (alkyl C, O-alkyl C, aromatic C, and carbonyl C) using solid-state 13C nuclear magnetic resonance spectroscopy in the 0–10 cm, 10–20 cm, and 20–40 cm depths in the Alnus sibirica islands and adjacent open peatlands in the north of Da'xingan Mountain, Northeast China. A. sibirica islands had 28 %, 25 %, and 30 % greater POX activity and 36 %, 31 %, and 100 % higher organic C mineralization than open peatlands in the 0–10 cm, 10–20 cm, and 20–40 cm soil depths, respectively. Despite no significant changes in the 0–10 cm and 10–20 cm depths, alder encroachment reduced soil organic C pool in the 20–40 cm depth. Soil organic C pool in the 0–40 cm depth was lower in A. sibirica islands (298 Mg ha−1) than in the open peatlands (315 Mg ha−1). Moreover, alder encroachment increased alkyl (7 %) and carbonyl (57 %) C fractions but reduced O-alkyl C fraction (16 %) in the 20–40 cm depth, resulting in increased aliphaticity and recalcitrance indices. These findings suggest that alder encroachment will reduce soil organic C accumulation by accelerating microbial decomposition, and highlight that increased biochemical stabilization would attenuate soil organic C loss after alder expansion in boreal peatlands. Our results will help assess and project future C budgets in boreal peatlands.

Greater sage‐grouse habitat selection varies across the marginal habitat of its lagging range margin

AbstractStudying wildlife–habitat relationships at the edges of their range can provide valuable insights into the environmental factors limiting wildlife distributions and most likely to drive extirpations and range shifts in response to landscape change. Yet the relative impact of those factors is likely different along the range margin, so it is important to identify the limitations to suitable habitat at both regional and local scales. Some of the most drastic impacts of large‐scale landscape changes in North America have occurred and are forecasted in the sagebrush steppe ecosystems, where species unable to seek new habitat in the fragmented landscape will be vulnerable to climatic extremes, vegetation community shifts, and anthropogenic land use change. One of the species likely under major threat from landscape changes is the greater sage‐grouse (Centrocercus urophasianus), a sagebrush obligate with habitat constraints that make it susceptible to habitat loss impacts as sagebrush systems contract and fragment at their southern range margin, already naturally fragmented. In this study, we evaluated factors of topography and land cover directly impacting habitat selection by sage‐grouse in four study areas along their lagging range edge. We used >116,000 GPS locations from >90 grouse across four study areas in southern Utah and Nevada from 2014 to 2020 in habitat selection analyses using random forest models. Our results showed that sage‐grouse exploit topography and sagebrush cover, possibly to break predator sight lines and moderate the risk posed by avian predators using tree perches, complicating the effects of tree cover and conifer encroachment into sagebrush habitat. We found similar trends across all four study areas, suggesting sage‐grouse along the southern range margin face similar limitations. However, the effects were nonlinear and varied—models trained in one study area were only moderately successful at predicting selection in others. The local idiosyncrasies along this southern range margin indicate a need for place‐based conservation for sage‐grouse and other potentially imperiled species. Incorporating new understandings of local impacts will refine regional and range‐wide models and support efforts to effectively create habitat and plan for range shifts by vulnerable species in response to environmental change.

Decrease in species richness and diversity, and shrub encroachment in Cerrado grasslands: A 20 years study

AbstractQuestionThe Cerrado is a global biodiversity hotspot, highly threatened by changes in land use. Alterations in species composition and the colonization of Cerrado grasslands by woody species can lead to long‐term changes in these communities. In this study, we investigated changes over 20 years in three grassland areas, in terms of species richness and diversity and growth‐form cover, as well as the effects of shrub and grass encroachment on species richness.LocationCerrado Brazilian savanna, moist grassland and dry shrub grassland. Areas under low and high anthropogenic pressure.MethodsPlant species composition and cover were sampled on seven occasions between the years 2000 and 2020, in permanent line‐transects. We compared plant cover, richness, diversity and growth‐form cover between the periods for each area. Next, we developed mixed‐effect linear models to test whether species richness in grasslands at the latest sampling event was altered by species representing 70% of the species cover at this time.ResultsGrasslands located in areas under higher anthropogenic pressure presented reduced richness and diversity, and cover concentrated on a few species of shrubs and large tussock grasses. Moist grassland undergoing encroachment by the native shrub Trembleya parviflora had lost over 50% of its diversity since encroachment. In the same area, a shrub grassland undergoing encroachment by native shrub Raulinoreitzia tremula, three native grass species and one exotic grass presented significantly reduced species richness. The moist grassland in an area under low anthropogenic pressure showed a reordering of the species cover over time, but a decrease in species richness.ConclusionWe observed changes in plant richness, diversity, cover, composition and growth‐form cover over a period of 20 years in grassland communities. We found, however, different trajectories in the three grassland areas sampled, mainly due to the encroachment of a few species, leading to floristic homogenization in grasslands located in areas under high anthropogenic pressure.

Shrub encroachment impaired the structure and functioning of alpine meadow communities on the Qinghai–Tibetan Plateau

AbstractShrub encroachment has been rapidly occurring due to climate change, with profound ecological consequences for the alpine meadows of the Qinghai–Tibetan Plateau. Here, we conducted field surveys along a shrub coverage gradient to examine the effects of shrub encroachment on the structure and functioning of alpine meadows' plant communities. Our results showed that the overall coverage, density, aboveground biomass, species richness, and diversity of meadow community gradually declined with increasing levels of shrub encroachment, especially when shrub coverage exceeded 60%. Aboveground ecosystem multifunctionality also decreased along the shrub coverage gradient. With 90% shrub coverage, the relative importance value of the forbs functional group significantly increased while the Cyperaceae functional group showed the opposite trend: the originally dominant sedges Carex moorcroftii and Kobresia myosuroides were replaced by the forbs Androsace umbellate and Polygonum sparsipilosum. Additionally, shrub encroachment had a strong effect on nonrandom herb species extinction and colonization. At shrub coverages higher than 60%, there were 9 herb species absent and 18 new species colonizing—7 of which were only observed in meadows with 90% shrub coverage. Rare species and those with lower stature were more likely to go extinct, while taller and shade‐tolerant species tended to colonize areas with increasing shrub coverage. Overall, our results indicate that shrub encroachment negatively affects herbaceous community structure and functioning, which has important implications for the management of alpine meadows of the Qinghai–Tibetan Plateau under ongoing climate change.

Effect of shrub encroachment on land surface temperature in semi-arid areas of temperate regions of the Northern Hemisphere

Under the influences of climate change and human activities, grassland ecosystems are being invaded by shrubs around the world, especially in temperate semi-arid regions of the Northern Hemisphere. Shrub encroachment can not only affect the properties of grassland ecosystem, but also have an important impact on regional or global climate by affecting biogeochemical and biophysical processes. Although shrub encroachment has become a serious ecological problem in the northern temperate region during the past decades, the possible effects of shrub encroachment on regional climate in northern temperate grasslands remain unclear due to a lack of in situ and long-term environmental records. Based on the satellite-derived land use data, land surface temperature (LST), evapotranspiration, leaf area index, and albedo data, this study quantified, for the first time, the biophysical effects of shrub encroachment on regional climate in semi-arid areas of temperate regions of the Northern Hemisphere. The results indicate that shrub encroachment tends to increase the average annual daytime and mean LST in most of the northern temperate semi-arid region due to increased bare soil fraction. In contrast, shrub encroachment could decrease the daytime LST in relatively humid region of southwest of North America by increasing evapotranspiration (vegetation coverage) and decreasing bare soil fraction. In the arid center region of Central Asia, grassland conversion to shrubland slightly decreases the surface temperature during both daytime and nighttime due to increased albedo caused by decreasing soil water content. Our findings imply that the biophysical effects of shrub encroachment on regional climate should be considered in climate models if they are to accurately simulate climate change in temperate regions of the Northern Hemisphere. More attention should be paid to the climate feedbacks of shrub encroachment, especially considering the distinct effects in different regions and how these climate feedbacks are likely to further impact ecosystem properties.

Shrub encroachment enhances the infiltration capacity of alpine meadows by changing the community composition and soil conditions

Due to global changes and anthropogenic disturbances shrubs are widely encroaching into alpine meadows, which may have profound impacts on the ecohydrological functioning of these key ecosystems. This phenomenon is particularly alarming in the alpine meadows of the Qinghai-Tibetan Plateau, the headwaters for many of Asia’s largest rivers. However, little is known about the extant in which shrub encroachment alters the infiltration capacity of those soils. Here we examined the effects of shrub encroachment on the plant community and soil infiltration processes by contrasting vegetation and infiltration variables between three areas: a reference alpine meadow, an alpine meadow lightly encroached by smaller shrubs, and an alpine meadow heavily encroached by larger shrubs. We found that shrub encroachment reduced herbaceous plants aboveground biomass by 10–24 g m−2 and root biomass by 1346–2239 g m−2. The sedge functional group was gradually replaced by forbs. Initial infiltration rates gradually increased with shrub encroachment, and were approximately doubled and tripled at the earlier and later stages of encroachment, respectively. Overall, shrub encroachment improved the soil infiltrability by changing soil conditions and inhibiting herbaceous species due to the reduction of surface mattic epipedon and the formation of dead root channels. These findings suggest that the rapid transformation of alpine meadows into shrublands could have drastic effects on the surface runoff and streamflow dynamics of the Qinghai-Tibetan Plateau.

Thinning the thickets: Foraging of hardy cattle, sheep and goats in green alder shrubs

Abstract Green alder shrubs Alnus viridis increasingly overgrow European mountain pastures but hinder natural forest succession. This nitrogen‐fixing, autochthonous invasive species has numerous negative effects including the loss of biodiversity and landscape aesthetic, eutrophication of soils and downstream waters, and greenhouse gas emission. Over centuries, A. viridis encroachment was impeded by grazing livestock, particularly goats. However, in modern agriculture, livestock numbers decreased on remote mountain pastures and goat farming became unprofitable. A grazing experiment tested if hardy breeds of the more economically attractive livestock species, cattle and sheep can replace goats as A. viridis antagonists. On a subalpine pasture heavily encroached by A. viridis, space use and debarking (bark foraging) by Dexter cattle, Engadine sheep and Pfauen goats were analysed using GPS tracking and vegetation mapping. Dexter cattle used space least evenly (Camargo evenness: cattle = 0.39; sheep = 0.52; and goats = 0.47) and preferred flat slopes and open pastures. They spent least time foraging in A. viridis stands (relative presence while foraging: cattle = 0.55; sheep = 0.76; and goats = 0.80). Dexter cattle did not debark any A. viridis, but damaged shrubs by trampling. Engadine sheep visited A. viridis stands nearly as often as goats, but preferred flat slopes, short vegetation and shrub edges more clearly than goats. This sheep breed debarked significantly more A. viridis branches (average 244 branches per paddock; 7.4% of all A. viridis branches) than goats (45; 0.8%). Goats preferred mountain‐ash shrubs Sorbus aucuparia covering only 2% of the shrub layer. Synthesis and applications. Green alder shrubs, controlled by goats traditionally, overgrow valuable mountain pasture ecosystems today. Cattle, kept instead of goats, may slow down but not hinder shrub encroachment, because they avoid shrub stands and do not debark green alder. However, this study is the first to show that Engadine sheep are even better suited for green alder clearance than goats. Moreover, if management goals include forest re‐establishment, Engadine sheep outperform goats, because they debark green alder (which hinders forest regeneration), but do not destroy elderberry—a valuable forest pioneer. Hardy breeds are an important tool to maintain biodiverse, open pastures, restore natural mountain forests and mitigate the negative environmental effects of shrub encroachment.

Spatial distribution of natural hazards and their proximity to heritage sites: Case of the United Arab Emirates

The United Nations Educational Scientific and Cultural Organization (UNESCO) investigated World Heritage sites and listed some in the United Arab Emirates (UAE). Heritage sites in any country have important cultural and economic value. However, many of the sites are subjected to potential impact by natural hazards, considering their age and the effects of climate. In the interest of reducing these impacts, the Sendai Framework for Disaster Risk Reduction (2015–2030) and the World Heritage Committee called for a detailed hazard assessment. This research falls within this assessment scope by applying remote sensing and Geographic Information System (GIS) methods to assess the spatial distribution of natural hazards and their proximity to heritage sites in the UAE. Results show that heritage sites in the northeastern UAE are more vulnerable to earthquakes, floods, and sea-level rise. Still, risk varies depending on elevation and the proximity to fault lines and the coastline. In the western UAE, the majority of heritage sites are prone to the effects of desertification and sand encroachment. This study is large-scale in nature, and specific vulnerability assessments for each heritage site are beyond the scope of this paper. The database, methodology, and output from this research could be useful for many organizations, such as those working in the fields of culture and heritage, tourism, disaster management, and urban planning. Compilation of a GIS database centering upon the heritage sites in the UAE is considered a major step forward for future studies related to the sites. The GIS database is available for interested users upon request.

Effects of channel encroachment on the software and service decisions in it supply chains

<p style='text-indent:20px;'>Currently, many upstream software developers not only sell software through downstream service providers, but also directly sell it to clients. However, in the field of IT service supply chain management, there is a lack of research on the channel encroachment of software developers. In this study, we consider an IT service supply chain with a software developer, a service provider and client enterprises. Clients can either purchase the software (developed by the software developer) from the provider with a high price and additional pre-sale services, or directly purchase it from the developer with a low price but without pre-sale service. After purchasing the software, the clients can also purchase the extended warranty service from the developer. The study shows that the market size occupied by the developer and the intensity of competition between the two parties will neither affect the developer's product and service pricing decisions, nor influence the total demand for software products and extended warranty services, and thus will not impact his own profit. However, these factors will impact the provider's decisions for pre-sale service quality and software sales price, thereby affecting the provider's software demand and profit, and thus impact the performance of the supply chain. In addition, as the intensity of competition between both parties increases, the provider will simultaneously choose to reduce the pre-sales service quality and the software sales price to compete with the developer. Different from conclusions of the existing research on competition, we surprisingly observe that as the sensitivity of client enterprises to the extended warranty services price increases, both parties will increase the software price to compete. The encroachment of the developer will reduce the provider's software demand and profit, and thus lead to a decline in the performance of the supply chain. Therefore, the encroachment of the developer is an act of squeezing out partners by decreasing the profit of the provider, but without affecting his own profit.</p>

草灌植被转变对草地生态系统及其水碳过程的影响研究进展

PDF HTML阅读 XML下载 导出引用 引用提醒 草灌植被转变对草地生态系统及其水碳过程的影响研究进展 DOI: 10.5846/stxb202106011441 作者: 作者单位: 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金项目（42007057）；第二次青藏高原综合科学考察研究资助（2019QZKK0307）；国家科技基础资源调查专项项目（2021FY100704）；西南民族大学中央高校基本科研业务费国家民委若尔盖高寒草甸生态站专项资助（2021PTJS27） Research progress on the effect of the transition between shrub and grass vegetation on grassland ecosystem and its water-carbon processes Author: Affiliation: Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:气候变暖和过度放牧的共同作用使全球草地出现明显的灌丛化现象，灌木去除是草地灌丛化控制的重要方式，识别这些草灌植被转变对生态系统、生态水文、土壤侵蚀和侵蚀碳流失的影响对草地可持续管理具有重要意义。综述了草地灌木入侵及其控制对植物群落和土壤功能（如土壤有机碳）的影响，以及这些草灌植被变化对生态水文、土壤侵蚀和土壤侵蚀碳流失等水碳耦合过程的影响机制。针对目前草地灌木入侵和去除对植物群落、植被格局、水土过程和功能影响研究的薄弱环节，对未来相关研究提出以下建议：（1）需深化草灌植被转变对碳、氮等生物地球化学循环的影响机制研究，（2）需重视核磁共振光谱、生物标志物、同位素等新技术和植被格局的指数与连通性等新方法在草灌植被转变的水、碳等生态效应研究中的应用，（3）需加强草灌植被格局和生态水文、土壤侵蚀与土壤侵蚀碳等水碳过程的多要素、多过程和多尺度的综合研究。本文旨在为灌丛化草地科学有效的生态恢复与多目标的土地利用管理提供理论支撑。 Abstract:The combined effects of overgrazing and climate warming drive shrubs to encroach into grassland ecosystems worldwide, while removal of the shrub is an important controlling measure for shrub encroachment. It is meaningful for sustainable grassland management to identify the impacts of transitions between grass and shrub vegetation on the ecosystem, eco-hydrology, soil erosion, and soil erosional carbon loss. In this paper, we reviewed the effects of shrub encroachment and its removal on the plant community and soil function (e.g., soil organic carbon), and the impact mechanism of these transitions between grass and shrub vegetation on the water-carbon coupling processes such as the ecohydrological, soil erosional, and erosional carbon loss processes. According to the weakness of previous research on the impacts of shrub encroachment and its removal control on plant community, vegetation pattern, and soil-water processes and functions, we provided several suggestions for future research directions:further studying the influence mechanism of transitions between grass and shrub vegetation on biogeochemical cycles such as carbon and nitrogen cycle, paying more attention to applying new techniques such as nuclear magnetic resonance (NMR) spectroscopy, biomarker, isotopes, and methods (e.g., indicators and connectivity of vegetation pattern) to determine the ecological effects of water and carbon for transitions between grass and shrub vegetation, and strengthening the multi-factor, multi-process and multi-scale comprehensive study among grass-shrub vegetation pattern and water-carbon processes such as eco-hydrology, soil erosion and soil erosional carbon loss. These can provide theoretical support for scientific and practical ecological restoration and multi-objective land-use management of shrub-encroached grassland. 参考文献 相似文献 引证文献

Deyeuxia angustifolia Kom. encroachment changes soil physicochemical properties and microbial community in the alpine tundra under climate change

Plant encroachment in alpine regions, caused by global changes and human activities, has been well documented. However, our knowledge of the effects of plant encroachment on belowground microbial communities is limited. Here, we investigated soil physicochemical properties and microbial community structures under the impact of plant encroachment along an elevation gradient in the alpine tundra of the Changbai Mountain, China. We found that plant encroachment had insignificant (P > 0.05) and inconsistent effects on the α-diversity (number of observed OTUs, Shannon, Chao1, Faith's PD) of soil microbial communities. Plant encroachment indirectly influenced soil microbial community structures by altering soil physicochemical properties, which differed between elevations and plant types (P < 0.05). In all, 40 bacterial indicator taxa and 57 fungal indicator taxa significantly shifted in response to plant encroachment, some of which were involved in soil biogeochemical cycle. Overall, our results documented the impacts of plant encroachment on soil microbial diversity and community composition, and provided a scientific basis for predicting future changes in alpine ecosystem structure and function and its subsequent feedbacks to global change.

Watershed and fire severity are stronger determinants of soil chemistry and microbiomes than within-watershed woody encroachment in a tallgrass prairie system.

Fire can impact terrestrial ecosystems by changing abiotic and biotic conditions. Short fire intervals maintain grasslands and communities adapted to frequent, low-severity fires. Shrub encroachment that follows longer fire intervals accumulates fuel and can increase fire severity. This patchily distributed biomass creates mosaics of burn severities in the landscape-pyrodiversity. Afforded by a scheduled burn of a watershed protected from fires for 27 years, we investigated effects of woody encroachment and burn severity on soil chemistry and soil-inhabiting bacteria and fungi. We compared soils before and after fire within the fire-protected, shrub-encroached watershed and soils in an adjacent, annually burned and non-encroached watershed. Organic matter and nutrients accumulated in the fire-protected watershed but responded less to woody encroachment within the encroached watershed. Bioavailable nitrogen and phosphorus and fungal and bacterial communities responded to high-severity burn regardless of encroachment. Low-severity fire effects on soil nutrients differed, increased bacterial but decreased fungal diversity and effects of woody encroachment within the encroached watershed were minimal. High-severity burns in the fire-protected watershed led to a novel soil system state distinct from non-encroached and encroached soil systems. We conclude that severe fires may open grassland restoration opportunities to manipulate soil chemistry and microbial communities in shrub-encroached habitats.

Divergent Patterns and Spatial Heterogeneity of Soil Nutrients in a Complex and Dynamic Savanna Landscape

AbstractMany grassy ecosystems around the world are experiencing woody encroachment. These woody encroachers often cause nutrient enrichment in the plant‐soil environment, potentially facilitating their growth and reproduction. However, studies of encroachment effects on nutrient distributions have been confined to a few major elements (e.g.,N, and P) and limited in spatial extent. We analyzed 19 elements in dominant plants and in georeferenced soils across a subtropical savanna landscape experiencing woody encroachment to quantify their spatial patterns and elucidate drivers responsible for these patterns. We found divergent patterns of spatial heterogeneity of these elements in surface soils across this complex landscape. Nutrient accumulation and redistribution underneath woody canopies occurred in a subset of elements (i.e., N, P, S, Ca, Cu, and Sr). Though some of these elements are not necessarily growth‐limiting, they do occur in higher concentrations in woody compared to herbaceous plants. Distributions of the other elements were closely related to spatial variation in soil pH, clay content, and slope rather than to woody encroachment. Our nuanced spatial sampling approach and analysis reveal significant variation in nutrient distributions in response to woody encroachment, and illustrate the role of landscape patterns in mediating ecosystem processes. These changes in the concentrations and distributions of key essential nutrients broaden our understanding of the biogeochemical consequences of woody encroachment, and provide new insights regarding the significance of long‐term vegetation dynamics in dryland ecosystems.

Agricultural land use affects the heterogeneity of Odonata communities in the Brazilian Pampa

Farming expansion has negative impacts on freshwater biodiversity. However, the effects of agricultural land use are not similar across taxa and depend on local context. For instance, the impacts of agricultural expansion are understudied in the Neotropics (one of the leading regions in cropland expansion). Knowledge of the effects of agricultural land use on aquatic insects from South American subtropical grasslands (Pampa) is even more incipient. We tested whether landscape modification related to increased agricultural land use was associated with taxonomic homogenization in odonate communities in waterbodies in the Brazilian Pampa. Odonates were collected in waterbodies differing in the main land-use class in their surroundings (cropland or grassland). Cropland and grassland sites differed with respect to their abiotic conditions (water chemistry) and species composition of Odonata. Additionally, we found higher variation in the composition of Odonata (and suborders Anisoptera and Zygoptera separately) in grassland than cropland sites. We found an interplay between agricultural and grassland land uses and the variation in the composition of odonate communities in the Brazilian Pampa. Specifically, landscape modification by agriculture modified the abiotic conditions in the waterbodies, which may have favored species able to establish as larvae under harsher environmental conditions. We suggest that the maintenance of mixed-grassland and cropland land uses in the fields adjacent to waterbodies can limit the negative effects of agricultural encroachment on Odonata communities with respect to biotic homogenization in the Brazilian Pampa.

Forcing uncertainty and salinity response to dredging in a tidal freshwater river

ABSTRACT This study evaluates the salinity response to dredging under different forcing regimes for a 75-kilometer segment of the flood-prone Vermilion River located in coastal Louisiana, USA. The Vermilion is a tidal freshwater river affected by baseflow regulation, rapid urbanization, and hydromodification. This river also serves as major freshwater resource for the region. An efficient one-dimensional model calibrated previously for stage and water temperature is used to analyse the salinity impacts due to a large-scale flood control dredging. The analysis is based on 200 alternative scenarios based on combinations of uncertain key forcing variables for a critical 13-day intrusion period. The analysis reveals a nonlinear effect on mean salinities and position of the brackish water limit as a function of uncertain forcing variables. Dredging also increases the variability of salinity encroachment effects due to uncertainty in future forcing conditions (e.g. relative sea level rise, baseflow diversion volumes, and salinities at the river mouth). The robust analysis presented here provides a foundation for future model-based assessments of under-studied tidal freshwater rivers and provides key insights for coastal management and sustainability efforts in general.

The role of brush encroachment in Mediterranean ecosystems: a review

Abstract Encroachment of woody plants into grasslands and subsequent brush management are among the most prominent changes occurring in arid and semiarid ecosystems over the past century. The reduced number of farms, the abandonment of marginal land and the decline of traditional farming practices have led to encroachment of the woody and shrubby components into grasslands. This phenomenon, specifically in the Mediterranean region, which is followed by a reduction in herbage production, biodiversity and increased fire risk, is generally considered an undesirable process. Sarcopoterium spinosum has had great success in the eastern Mediterranean as a colonizer and dominant bush species on a wide variety of sites and climatic conditions. In the Mediterranean dehesa, the high magnitude and intensity of shrub encroachment effects on pastures and on tree production were shown to be dependent on temporal variation. Accordingly, there are attempts to transform shrublands into grassland-woodland matrices by using different techniques. The main management interventions that are commonly used include grazing, woodcutting, shrub control with herbicides or by mechanical means, amelioration of plant mineral deficits in the soil, and fire. However, the effects of these various treatments on the shrubs under diverse environmental conditions were found to be largely context-specific. As such, the most efficient option for suppressing encroachment of shrubs is combining different interventions. Appropriate management of grazing, periodic control of the shrub component, and occasional soil nutrient amelioration can lead to the development of attractive open woodland with a productive herbaceous understory that provides a wider range of ecological services.

Changes in soil water retention and content during shrub encroachment process in Inner Mongolia, northern China

Soil water retention is the link between hydrologic processes and ecological patterns, and is one of the vital hydrological properties of soils. However, the influence of shrub encroachment on soil water retention and content remains unclear, and the factors influencing soil water retention and content are also not well understood. Therefore, this study aims to investigate the changes in soil water retention and content during the shrub encroachment process and to reveal their influencing factors. In this study, three states of shrub encroachment were identified according to the percentage of shrub cover. Soil samples of the shrub patches and adjacent interspace grass patches were collected in each state of shrub encroachment. The soil water retention curves of the samples were generated, and the soil water contents of the samples were measured. The results showed that the field capacity (FC) and plant-available water capacity (PAWC) of both shrub patches and interspace grass patches increased during shrub encroachment, which suggests that shrub encroachment has positive effects on soil water retention. The FC and PAWC of the shrub patches were 14.7% and 14.5% higher than those of the interspace grass patches, respectively. The shrub patches were also characterized by higher soil water content and storage than the interspace grass patches. Shrub roots, soil organic matter, and clay content were the three most crucial factors positively affecting soil water retention and content during shrub encroachment process. This study can further our understanding of the ecohydrological effects of shrub encroachment in arid and semiarid grasslands and facilitate related modeling studies.