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1. Germination and early establishment of dryland grasses and shrubs on intact and wind-eroded soils under greenhouse conditions

   https://doi.org/10.1007/s11104-021-05005-9  

   Niu, Furong ; Pierce, Nathan A. ; Archer, Steven R. ; Okin, Gregory S. ( May 2021 , Plant and Soil)

   Grassland-to-shrubland transition is a common form of land degradation in drylands worldwide. It is often attributed to changes in disturbance regimes, particularly overgrazing. A myriad of direct and indirect effects (e.g., accelerated soil erosion) of grazing may favor shrubs over grasses, but their relative importance is unclear. We tested the hypothesis that topsoil “winnowing” by wind erosion would differentially affect grass and shrub seedling establishment to promote shrub recruitment over that of grass.

   We monitored germination and seedling growth of contrasting perennial grass (Bouteloua eriopoda,Sporobolus airoides, andAristida purpurea) and shrub (Prosopis glandulosa,Atriplex canescens, andLarrea tridentata) functional groups on field-collected non-winnowed and winnowed soils under well-watered greenhouse conditions.

   Non-winnowed soils were finer-textured and had higher nutrient contents than winnowed soils, but based on desorption curves, winnowed soils had more plant-available moisture. Contrary to expectations, seed germination and seedling growth on winnowed and non-winnowed soils were comparable within a given species. The N₂-fixing deciduous shrubP. glandulosawas first to emerge and complete germination, and had the greatest biomass accumulation of all species.

   Germination and early seedling growth of grasses and shrubs on winnowed soils were not adversely nor differentially affected comparing with that observed on non-winnowed soils under well-watered greenhouse conditions. Early germination and rapid growth may giveP. glandulosaa competitive advantage over grasses and other shrub species at the establishment stage in grazed grasslands. Field establishment experiments are needed to confirm our findings in these controlled environment trials.

    

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2. The role of arbuscular mycorrhizal fungi in nonnative plant invasion along mountain roads

   https://doi.org/10.1111/nph.16954  

   Clavel, Jan ; Lembrechts, Jonas ; Alexander, Jake ; Haider, Sylvia ; Lenoir, Jonathan ; Milbau, Ann ; Nuñez, Martin A. ; Pauchard, Anibal ; Nijs, Ivan ; Verbruggen, Erik ( October 2020 , New Phytologist)

   Plant associated mutualists can mediate invasion success by affecting the ecological niche of nonnative plant species. Anthropogenic disturbance is also key in facilitating invasion success through changes in biotic and abiotic conditions, but the combined effect of these two factors in natural environments is understudied.

   To better understand this interaction, we investigated how disturbance and its interaction with mycorrhizas could impact range dynamics of nonnative plant species in the mountains of Norway. Therefore, we studied the root colonisation and community composition of arbuscular mycorrhizal (AM) fungi in disturbed vs undisturbed plots along mountain roads.

   We found that roadside disturbance strongly increases fungal diversity and richness while also promoting AM fungal root colonisation in an otherwise ecto‐mycorrhiza and ericoid‐mycorrhiza dominated environment. Surprisingly, AM fungi associating with nonnative plant species were present across the whole elevation gradient, even above the highest elevational limit of nonnative plants, indicating that mycorrhizal fungi are not currently limiting the upward movement of nonnative plants.

   We conclude that roadside disturbance has a positive effect on AM fungal colonisation and richness, possibly supporting the spread of nonnative plants, but that there is no absolute limitation of belowground mutualists, even at high elevation.

    

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3. Biomass removal at the initiation of a biodiversity experiment at the Jornada Basin LTER site in 1995

   https://doi.org/10.6073/pasta/d2fb9649ee33bb24c9442b1b6757cea7  

   Huenneke, Laura F ( January 2023 , Environmental Data Initiative)

   This dataset contains data on vegetation biomass removed from treatment plots during the establishment of a biodiversity experiment at the Jornada Basin LTER site in southern New Mexico, USA. In fall of 1995, various combinations of plant functional groups or species were experimentally removed from 25 x 25 meter plots with the objective to distinguish the differential effects of plant community biomass, functional groups, and biodiversity within functional groups on ecosystem and plant community function. Eight different treatments were established with selective removal of species or functional groups: control (C, no removals); four functional group removal treatments (PG, perennial grass removed; S, shrubs removed; SSh, subshrubs removed; Succ, succulents removed), and three species richness manipulation treatments. Richness manipulations included a simplified treatment (Simp), where only the single most abundant species of each growth form is preserved and all other species in the growth form are removed, a reduced‐Larrea treatment (rL), where the Larrea is assumed to be the dominant and is removed while minority components remain, and a reduced-Prosopsis treatment (rP), where Prosopis rather than Larrea is removed as the shrub dominant. The amount of plant material removed during the establishment of these treatments was recorded for later use as covariate or measure of disturbance. Removed fresh material was weighed in the field by species, then converted to dry mass using a subset of removed plot vegetation that was oven-dried and weighed in the lab. Variables in this file summarize the dry mass of plants removed by growth form (functional group, i.e. shrub, subshrub, perennial grass, succulent), and by total live dry mass, for each plot in the biodiversity experiment. Also provided are masses of dead material collected from plots (same groups as live material removed for each treatment) and total dry mass, live plus dead. Species-level data are available upon request. This study is complete. 

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4. Nitrogen alters effects of disturbance on annual grassland community diversity: Implications for restoration

   https://doi.org/10.1111/1365-2745.13245  

   Brandt, Angela J. ; Seabloom, Eric W. ; Cadotte, Marc W. ; Barber, ed., Nicholas ( August 2019 , Journal of Ecology)

   In an era of anthropogenically altered disturbance regimes and increased nutrient loads, understanding how communities respond to these perturbations is essential for successful habitat restoration. Disturbance and resource supply can affect community diversity by altering community assembly processes, such as recruitment, mortality or competitive inequalities. The mechanisms behind community responses to these drivers will differentially affect multiple facets of diversity.

   Here we examine how factorial manipulations of disturbance (raking to remove above‐ground vegetation) and nitrogen supply affect taxonomic and phylogenetic diversity of predominantly annual California grassland communities spanning a 500‐km latitudinal and twofold rainfall gradient. The disturbance caused density‐independent biomass removal and increased access to resources such as space and light, thus mimicking demographic effects of disturbance as considered in ecological models and broadly applicable to empirical systems. We used paired metrics of richness, evenness and community composition to compare evidence from taxonomy and phylogeny.

   Disturbance increased species and phylogenetic diversity (richness and evenness metrics). However, nitrogen addition interacted with disturbance to reduce species richness and phylogenetic diversity. Undisturbed communities were more strongly clustered phylogenetically, but disturbance eroded this clustering such that communities became more random (i.e. indistinguishable from a null model of assembly). Species composition differed between disturbed and undisturbed communities, and many species were observed in only one community type. Disturbance interacted with nitrogen supply to alter phylogenetic composition of communities, and recently disturbed communities were more spatially variable in phylogenetic composition than undisturbed communities. Phylogenetic composition of communities also differed among nitrogen treatments.

   Synthesis.Our results suggest that disturbing these grassland communities by removing above‐ground vegetation increased community diversity by increasing recruitment. Seed addition following this type of disturbance is thus likely to be an effective restoration technique. However, we have shown that disturbance combined with nitrogen enrichment reduces community diversity. The mechanism for this enrichment effect does not appear to be linked to increased productivity leading to light limitation. This work suggests restoration efforts employing biomass removal must take nutrient availability into account to maximize local community diversity.

    

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5. Minimal mortality and rapid recovery of the dominant shrub Larrea tridentata following an extreme cold event in the northern Chihuahuan Desert

   https://doi.org/10.1111/jvs.12777  

   Ladwig, Laura M. ; Collins, Scott L. ; Krofcheck, Dan J. ; Pockman, William T. ; Paruelo, ed., José ( July 2019 , Journal of Vegetation Science)

   Woody encroachment into grasslands is a worldwide phenomenon partially influenced by climate change, including extreme weather events.Larrea tridentatais a common shrub throughout the warm deserts of North America that has encroached into grasslands over the past 150 years. Physiological measurements suggest that the northern distribution ofL. tridentatais limited by cold temperatures; thus extreme winter events may slow or reverse shrub expansion. We tested this limitation by measuring the response of individualL. tridentatashrubs to an extreme winter cold (−31°C) event to assess shrub mortality and rate of recovery of surviving shrubs.

   Sevilleta National Wildlife Refuge, Socorro County, New Mexico, USA.

   Canopy dieback and recovery following an extreme cold event were measured for 869 permanently marked individualL. tridentatashrubs in grass–shrub ecotone and shrubland sites. Individual shrubs were monitored for amount of canopy dieback, rate of recovery, and seed set for three growing seasons after the freeze event.

   Shrubs rapidly suffered a nearly complete loss of canopy leaf area across all sites. Although canopy loss was high, mortality was low and 99% of shrubs resprouted during the first growing season after the freeze event. Regrowth rates were similar within ecotone and shrubland sites, even when damage by frost was larger in the latter. After three years of recovery,L. tridentatacanopies had regrown on average 23–83% of the original pre‐freeze canopy sizes across the sites.

   We conclude that isolated extreme cold events may temporarily decrease shrubland biomass but they do not slow or reverse shrub expansion. These events are less likely to occur in the future as regional temperatures increase under climate change.

    

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