Eco-evolutionary context modifies a destructive plant invader's response to climate
No abstract available.
New Phytologist↗
Geology topics
Matthew Germino
Publications and source records attributed to Matthew Germino.
A matter of timing: Sagebrush steppe restoration seeding outcomes altered by species responses to warmer spring temperatures and interannual weather variation
Introduction Restoration outcomes in cold desert ecosystems like sagebrush steppe are affected by weather variability, particularly during the spring, a critical time period for seedling establishment. Seedling emergence phenology is also highly variable among species in these ecosystems. Seed-based restoration outcomes are likely affected by the emergence timing of species in seed mixes relative to periods of favorable soil microclimate in the spring. Objectives This study evaluated the effects of higher spring temperatures in different periods, and species differences in seedling emergence and survival, on restoration outcomes. We also tested the indirect effects of warming treatments on outcomes via abundance of cheatgrass, a competitive, widespread invasive annual sensitive to weather variability. Methods We used open-sided chambers to implement early- or late-spring warming on plots seeded with a diverse set of species that differed in timing of emergence, across multiple years and variable weather conditions in sagebrush steppe, Oregon, U.S.A. Results Spring warming treatment effects varied with yearly weather and species emergence timing relative to the rest of the seeded species. Later-emergence timing was associated with lower emergence rates, particularly with late spring warming, and lower survival with early spring warming, but higher survival without warming or with late spring warming. Seed mix scenarios tuned to warming treatment and yearly weather outperformed early- or late-emergence timing and even proportion mixes. Early spring warming increased invasive annual grass abundance, which was associated with lower survival of seeded species. Conclusions Species differences and yearly precipitation affected restoration outcomes under warmer spring temperatures.
Oregon↗
Loss of ecosystem resistance to invasion after wildfire facilitated by a pulse of soil nitrogen availability: Experimental evidence in the burned sagebrush steppe
The impacts of climate shifts on ecosystems dominated by long-lived perennials are likely most pronounced during community reassembly after disturbances such as fire and confounded by interactions between disturbances and plant community composition. A 30-year-experimental hydroclimate manipulation of multiple sagebrush steppe communities was completely consumed by a 2019 wildfire, providing an opportunity to evaluate effects of precipitation deficit on ecosystem recovery. Ambient precipitation was doubled for 23 years via irrigation in winter or summer in grassland or shrub–steppe communities until 2016. Plots that had received irrigation thus experienced drought for three years preceding and continuing after the fire. These landscapes are vulnerable to invasion by exotic annuals such as Bromus tectorum L. (cheatgrass) that promote wildfire occurrence, which favors even greater invasion levels. Thus, we asked whether patterns of invasion after the compound disturbance of drought and fire related to the long-term pre-fire climate and plant community structure. Established theory led to the prediction that plant communities developed under wetter climates would have greater resistance to invasion. The most resistant plots were the most arid (that is, never irrigated control plots with no drought) which had the least pre-fire canopy cover of shrubs and nitrogen-fixing forbs and greater proportional cover of perennial bunchgrasses. Plots that developed under winter irrigation had greater cover of shrubs and N-fixing forbs, corresponding to pulses of plant available soil nitrogen that were 8.2-fold greater than pre-fire levels, compared to a 0.20-fold post-fire reduction in soil nitrogen observed in the ambient plots. Nitrogen pulses and invasion were most evident in the inter-canopy bare-soil patches (‘interspaces’) and were least evident where perennial grasses were most abundant. Long-term hydroclimate altered pre-fire plant community composition in ways that affected post-fire resistance to invasion such that the combined effects of fire and water deficit led to greater than expected invasion in wetter regions that are conventionally considered resistant to invasion and resilient to wildfire.
Ecosystems↗
Local adaptation to climate has facilitated the global invasion of cheatgrass
Local adaptation may facilitate range expansion during invasions, but the mechanisms promoting destructive invasions remain unclear. Cheatgrass ( Bromus tectorum ), native to Eurasia and Africa, has invaded globally, with particularly severe impacts in western North America. We aimed to identify mechanisms and consequences of local adaptation in the North American cheatgrass invasion. We sequenced 307 range-wide genotypes and conducted controlled experiments. We found that diverse lineages invaded North America, where long-distance gene flow is common. Nearly half of North American cheatgrass is comprised of a mosaic of ~19 locally adapted near clonal genotypes, each seemingly very successful in a different part of its range. Additionally, ancestry- and phenotype- environment clines in the native range predicted those in the invaded range, indicating pre-adapted genotypes colonized different regions. Common gardens showed directional selection on flowering time that reversed between warm and cold sites, potentially maintaining clines. In the Great Basin, genomic predictions of strong local adaptation identified sites where cheatgrass is most dominant. Our results indicate that multiple introductions and ongoing migration within the invaded range likely fueled pre-adaptation and subsequent dominance of cheatgrass in western North America. Understanding how environment and gene flow shape invasive adaptation is critical for managing ongoing invasions.
Nature Communications↗
A systematic review and meta-analysis of post-fire seeding and herbicide treatment effectiveness for controlling exotic annual grasses in the sagebrush biome
Introduction Outcomes of ecological restoration treatments can be highly variable and challenging to generalize, even for the same treatment type applied in similar ecological communities at different times and places. Notable examples are the herbicide and seeding treatments that have been extensively applied across the perennial sagebrush steppe of the United States to reduce impacts of fire-promoting exotic annual grasses (EAGs) such as Cheatgrass ( Bromus tectorum ). Objectives We asked if statistically based generalizations about the effects of pre-emergent herbicide and drill seeding of perennials, implemented following wildfires when threats of annual-grass invasion are greatest, could be made from the available literature. Methods We conducted a meta-analysis of these treatment effects for 1228 treatment-control comparisons from 35 studies published from 1990 to 2023 that met basic criteria for topical relevance and repeatability. Results EAGs and forbs were each reduced by herbicides and by seeding perennial grasses. The combination of herbicide and seeding reduced annuals and led to the largest increases in perennials. Although these outcomes support the intended effects of the treatments, there was high variability in outcomes among studies. Conclusions Combined use of pre-emergent herbicides and seeding can increase the success of restoration interventions that are aimed at reducing the invasion of exotic annual grasses and increasing perennials after fire in sagebrush steppe. Our analysis revealed, however, that the available literature was not suited to answering more specific questions, in spite of the massive amount of post-fire herbicide and seedings that have been applied in burned sagebrush steppe. Specifically, there were too few topically relevant studies with adequate scientific reporting to properly evaluate differences among specific treatment methodologies, including specific herbicides, that affect restoration success.
Restoration Ecology↗
Soil-microbial communities respond less than plant communities to synthetic- or bio-herbicides applied to address the exotic grass-fire cycle in rangelands
The exotic grass-fire cycle is degrading semiarid rangelands, such as the vast areas of shrub-steppe in North America now invaded by fire-promoting cheatgrass. Chemical- or bio-herbicides are sprayed onto soils to inhibit the invaders, but information on chemical- or bio-herbicide impacts to soil microbial communities is limited. We asked how the soil-microbiome responded to the bioherbicide Pseudomonas fluorescens strain ACK55 in comparison to the separate and combined effects of a conventional pre-emergent chemical herbicide, imazapic, in two cheatgrass-invaded sagebrush-steppe sites. First-year microbial responses were evaluated using targeted sequencing of the 16S and LSU rRNA genes for bacteria+archaea and fungi, respectively, and were related to plant-community responses. A strong cheatgrass reduction with imazapic at one site was accompanied by a small shift in bacteria+archaea (16S) community composition with no effect on microbial alpha diversity, and this shift was small in comparison to natural microbiome variation between sites. ACK55 was not detected in soil a year after application, and it caused only transient and marginally significant reductions in annual grass cover accompanied by small reductions in soil fungi species richness. Full-length sequencing of the ACK55 16S rRNA gene and phylogenetic analyses revealed that ACK55 is more likely P. salmonii than P. fluorescens . Knowledge gaps remain on the duration and consequences of microbial-community shifts with imazapic and why molecular analyses showed ACK55 did not persist in soils. Confusion regarding microbial biopesticides can result where isolation, effectiveness testing, commercial release, and regulation are not guided by molecular taxonomic analyses.
Idaho↗
Low genetic differentiation across restored and natural populations shortly after a large-scale, post-fire seeding in the Great Basin
Genetic diversity is essential for species to adapt to environmental changes. In restoration efforts, such as those after large wildfires in the sagebrush steppe of the Great Basin, commercially produced native seeds are used to revegetate the burned areas. While native seed certification and procurement protocols assure that genetically appropriate seeds are used for restoration, how post-fire seeding affects the genetic integrity of wildland populations at the landscape scale is unknown. To assess the effects of seeding on the genetic diversity of wildland populations, we conducted a genetic survey of Bluebunch wheatgrass ( Pseudoroegneria spicata [Pursh] Á.Löve ssp. Spicata ) populations within the perimeter of a recent megafire in southeastern Oregon and southwestern Idaho, United States. We genotyped 760 samples with 10 polymorphic loci. We found similar genetic diversity in populations four to 5 years after seeding compared to unseeded populations that were either burned or unburned. Furthermore, genetic diversity neither increased nor decreased with distance from the fire's edge, suggesting that wind dispersal from neighboring remnant populations plays a minor role in immediate post-fire recovery compared to resprouting and germination from the seed bank. Though no change was detected in the short term, this survey of genetic variation after a post-fire seeding provides an empirical baseline that can be used to track changes in genetic diversity of these wildland populations over time.
Idaho↗
Risks and rewards of pre-emergent herbicide (indaziflam) to defend core sagebrush-steppe ecosystems under suboptimal precipitation
Protection of intact habitat from the spread of invasive plants is a global priority, especially where invaders alter wildfire occurrence. Invasion of perennial sagebrush-steppe ecosystems by cheatgrass and other fire-promoting exotic annual grasses (EAGs) is one of the most notorious examples of this problem. Protection and expansion of the remaining intact “core” sagebrush areas are key management goals, and whether this can be accomplished by temporarily inhibiting annual plant populations with pre-emergent herbicides is a key question. We applied indaziflam in fall 2019 to replicate plots within two sagebrush-steppe sites in the Northern Great Basin, USA: 1) a relatively intact, uninvaded, unburned “core” site and 2) a partially invaded site that burned in the 2015 Soda Wildfire. Vegetation cover, density, and growth responses of native perennials were measured annually to 2024. We asked whether our treatments “defended” and “grew” core sagebrush areas. EAG cover remained <15% in indaziflam-treated plots while increasing to >30% in control plots by the fifth year after treatment at the unburned site but did not differ with treatment at the burned site. Native perennial grasses, forbs, and big sagebrush cover and growth did not differ with indaziflam treatment at either site. Moss cover was temporarily lower in indaziflam-treated plots at the unburned site, and cover of a native annual forb was significantly lower in indaziflam-treated plots throughout the study across both sites. Despite posttreatment drought and apparent patchiness in treatment implementation, our treatments “defended the core” by preventing crossing of the 20% EAG invasion threshold in the unburned site but not did not “grow the core.” Our results provide an example of a case in which proactive protection may be easier to accomplish than reactive restoration. Herbicide treatment effects may be sensitive to weather and application details. Implementation monitoring could help explain variability and improve success.
Idaho↗
Post-fire abundances of soil cyanobacteria relate more to variations in sparse tree cover and soil properties than to fire history, in semiarid shrub steppe
The frequency and extent of wildfire are increasing globally, and understanding the ecosystem impacts of fire can help guide management of burned areas. Cyanobacteria are widespread in surface soils of semi-arid and arid rangelands and confer soil stabilization and resistance to exotic-plant invasions. We examined the probability of encountering cyanobacteria of the order Oscillatoriales in 2022, via microscopic counts of rewetted soils in the lab, following nine recent wildfires that burned as recently as 2012–2017 and up to four times repeatedly until then, in the northern Great Basin of the western U.S. Much of the variability in Oscillatoriales was attributed to the identity of the wildfire, i.e. unexplained variation. Tree cover estimated from gridded satellite-based models was scarce before and especially after fire yet was the second-most predictive covariate. Estimated cover of Oscillatoriales (lab derived) was 0.48 where trees were absent compared to 0.42 where tree cover was detected in the 30-m pixel surrounding soil samples. Presence of sand conferred nearly the opposite effect, which was counter to expectations but could be related to reduced vegetative cover on coarser soils. Other site factors including climatic precipitation and soil fertility were also predictive of Oscillatoriales. Cyanobacteria are considered to be cosmopolitan, i.e. ubiquitous in soils, but these spatial patterns of Oscillatoriales indicate relationships to landscape factors that have not been considered before. Understanding these relationships could aid land managers in identifying post-fire conditions most favorable to soil stabilizing cyanobacteria, which, in turn, could help achieve management goals of moderating soil erosion and additional invasion of fire-promoting exotic plants.
Idaho, Nevada, Oregon, Utah↗
Local adaptation to climate facilitates a global invasion
Local adaptation may facilitate range expansion during invasions, but the mechanisms underlying successful invasions remain unclear. Cheatgrass ( Bromus tectorum ), native to Eurasia and Africa, has invaded globally, with severe impacts in western North America. We aimed to identify mechanisms and consequences of local adaptation in the North American cheatgrass invasion. We sequenced 307 range-wide genotypes and conducted controlled experiments. We found that diverse lineages invaded North America, where long-distance gene flow is common. Nearly half of North American cheatgrass comprises a mosaic of ∼19 locally adapted, near-clonal genotypes, each seemingly very successful in a different part of North America. Additionally, ancestry, phenotype, and allele frequency-environment clines in the native range predicted those in the invaded range, indicating pre-adapted genotypes colonized different regions. Common gardens showed directional selection on flowering time that reversed between warm and cold sites, potentially maintaining clines. In the USA Great Basin, genomic predictions of strong local adaptation identified sites where cheatgrass is most dominant. Our results indicate that multiple introductions and migration within the invaded range fueled local adaptation and success of cheatgrass in western North America. Understanding how environment and gene flow shape adaptation and invasion is critical for managing ongoing invasions.
BioRxiv↗
Interannual variation in climate contributes to contingency in post-fire restoration outcomes in seeded sagebrush steppe
Interannual variation, especially weather, is an often-cited reason for restoration “failures”; yet its importance is difficult to experimentally isolate across broad spatiotemporal extents, due to correlations between weather and site characteristics. We examined post-fire treatments within sagebrush-steppe ecosystems to ask: (1) Is weather following seeding efforts a primary reason why restoration outcomes depart from predictions? and (2) Does the management-relevance of weather differ across space and with time since treatment? Our analysis quantified range-wide patterns of sagebrush ( Artemisia spp.) recovery, by integrating long-term records of restoration and annual vegetation cover estimates from satellite imagery following thousands of post-fire seeding treatments from 1984 to 2005. Across the Great Basin, sagebrush growth increased in wetter, cooler springs; however, the importance of spring weather varied with sites' long-term climates, suggesting differing ecophysiological limitations across sagebrush's range. Incorporation of spring weather, including from the “planting year,” improved predictions of sagebrush recovery, but these advances were small compared to contributions of time-invariant site characteristics. Given extreme weather conditions threatening this ecosystem, explicit consideration of weather could improve the allocation of management resources, such as by identifying areas requiring repeated treatments; but improved forecasts of shifting mean conditions with climate change may more significantly aid the prediction of sagebrush recovery.
California, Colorado, Idaho, Nevada, Oregon, Utah,↗
Predictive models of selective cattle use of large, burned landscapes in semiarid sagebrush-steppe
The fire-exotic annual grass cycle is a severe threat to shrub-steppe rangelands, and a greater understanding of how livestock grazing relates to the problem is needed to guide effective management interventions. Grazing effects vary throughout shrub-steppe rangelands because livestock are selective in their use within pastures. Thus, knowing where cattle are located and concentrate their use in a postfire landscape is important for enhancing plant community resiliency to disturbance and resistance to exotic annual grass invasion. We asked how the distribution and intensity of cattle use varied across 113 000 ha of recently burned, environmentally varied shrub-steppe. Generalized linear mixed effects models were used to determine the relationship of cattle dung (presence/absence and counts), which was recorded during the third to fifth postfire year (after grazing deferment) on 1166 (531-m 2 ) plots, to water sources, burn severity, grass cover, and topographic predictors. Our distribution and intensity of use models revealed similar relationships between cattle use and landscape predictors. Cattle use was greater in areas that were flatter and closer to water and that had moderate burn severity and less heat load and ruggedness. Slope had the strongest effect on cattle use of the predictors. The probability of cattle being present decreased by 10% for every 5° increase in slope until slope exceeded 15°, and then the effect of slope weakened. Despite moderate slopes χ ¯ "> χ¯ = 14°), cattle use was greater in areas of moderate burn severity, presumably because these areas provided greater perennial grass production. While there was much unexplained variation, these models suggest that cooler climate, water access, topographic factors, and burn severity affect maneuverability to create greater livestock use of certain areas within grazing pastures. Restoration investment planning or assessments and expectations of restoration success could be improved by considering that these livestock hotspots may recover differently from the surrounding landscape.
Rangeland Ecology and Management↗
The role of genome duplication in big sagebrush growth and fecundity
Premise Adaptive traits can be dramatically altered by genome duplication. The study of interactions among traits, ploidy, and the environment are necessary to develop an understanding of how polyploidy affects niche differentiation and to develop restoration strategies for resilient native ecosystems. Methods Growth and fecundity were measured in common gardens for 39 populations of big sagebrush ( Artemisia tridentata ) containing two subspecies and two ploidy levels. General linear mixed-effect models assessed how much of the trait variation could be attributed to genetics (i.e., ploidy and climatic adaptation), environment, and gene–environment interactions. Results Growth and fecundity variation were explained well by the mixed models (80% and 91%, respectively). Much of the trait variation was attributed to environment, and 15% of variation in growth and 34% of variation in seed yield were attributed to genetics. Genetic trait variation was mostly attributable to ploidy, with much higher growth and seed production in diploids, even in a warm-dry environment typically dominated by tetraploids. Population-level genetic variation was also evident and was related to the climate of each population's origin. Conclusions Ploidy is a strong predictor growth and seed yield, regardless of common-garden environment. The superior growth and fecundity of diploids across environments raises the question as to how tetraploids can be more prevalent than diploids, especially in warm-dry environments. Two hypotheses that may explain the abundance of tetraploids on the landscape include selection for drought resistance at the seedling stage, and greater competitive ability in water uptake in the upper soil horizon.
American Journal of Botany↗
Weed-suppressive bacteria effects differ in culture compared to in soils and with or without microbial competition and separation of active ingredient
Weed-suppressive bacteria (WSB), specifically the D7 and ACK55 strains of Pseudomonas fluorescens , were previously reported to selectively inhibit growth of invasive annual grasses (IAGs) that have caused severe ecosystem degradation across much of the western US. However, recent studies show highly mixed evidence for WSB effectiveness in field settings. We evaluated how the effectiveness of WSB, specifically selective inhibition of exotic annual but not native perennial grasses, was altered by (1) growth media (soil vs. agar culture), (2) pre-sterilization to remove competing microbes, and (3) WSB concentration, reduced by centrifuging with and without filtration. WSB had no effects in soil microcosms with or without pre-sterilization, but WSB did have effects in agar cultures. On agar, WSB effects were amplified by pre-sterilizing seeds prior to treatment with WSB inoculum – but effects were non-selective (i.e., native and exotic plants were equally inhibited) with or without pre-sterilization at high WSB concentration. The only selective effects of WSB were observed on agar at low WSB concentrations, made possible by centrifuging WSB cells out of the inoculum prior to treatment application (from ~10 7 to ~10 5 live cells/ml). Completely removing WSB cells from inoculum by filtration led to no WSB effects. While these results suggest the desired effects of WSB can be reproduced on agar with a supernatant containing the putative active agent and a low density of WSB cells, the effect is still not reproducible for plants in soil, even when competing microbes are removed. Thus, additional research is needed to determine if, when, where, and how WSB could be effective in field settings.
Biological Control↗
Warming of alpine tundra enhances belowground production and shifts community towards resource acquisition traits
Climate warming is expected to stimulate plant growth in high‐elevation and high‐latitude ecosystems, significantly increasing aboveground net primary production (ANPP). However, the effects of simultaneous changes in temperature, snowmelt timing, and summer water availability on total net primary production (NPP)—and elucidation of both above‐ and belowground responses—remain an important area in need of further study. In particular, measures of belowground net primary productivity (BNPP) are required to understand whether ANPP changes reflect changes in allocation or are indicative of a whole plant NPP response. Further, plant functional traits provide a key way to scale from the individual plant to the community level and provide insight into drivers of NPP responses to environmental change. We used infrared heaters to warm an alpine plant community at Niwot Ridge, Colorado, and applied supplemental water to compensate for soil water loss induced by warming. We measured ANPP, BNPP, and leaf and root functional traits across treatments after 5 yr of continuous warming. Community‐level ANPP and total NPP (ANPP + BNPP) did not respond to heating or watering, but BNPP increased in response to heating. Heating decreased community‐level leaf dry matter content and increased total root length, indicating a shift in strategy from resource conservation to acquisition in response to warming. Water use efficiency (WUE) decreased with heating, suggesting alleviation of moisture constraints that may have enabled the plant community to increase productivity. Heating may have decreased WUE by melting snow earlier and creating more days early in the growing season with adequate soil moisture, but stimulated dry mass investment in roots as soils dried down later in the growing season. Overall, this study highlights how ANPP and BNPP responses to climate change can diverge, and encourages a closer examination of belowground processes, especially in alpine systems, where the majority of NPP occurs belowground.
Colorado↗
Postfire growth of seeded and planted big sagebrush - Strategic designs for restoring Greater Sage-grouse nesting habitat
Wildfires change plant community structure and impact wildlife habitat and population dynamics. Recent wildfire‐induced losses of big sagebrush ( Artemisia tridentata ) in North American shrublands are outpacing natural recovery and leading to substantial losses in habitat for sagebrush‐obligate species such as Greater Sage‐grouse. Managers are considering restoration strategies that include planting container‐grown sagebrush to improve establishment within areas using more conventional seeding methods. Although it is thought that planting sagebrush provides initial structural advantages over seeding, empirical comparisons of sagebrush growth are lacking between individuals established post‐fire using both methods. Using a Bayesian hierarchical approach, we evaluated sagebrush height and canopy area growth rates for plants established in 26 seeded and 20 planted locations within the Great Basin. We then related recovery rates to previously published nesting habitat requirements for sage‐grouse. Under average weather conditions, planted or seeded sagebrush will require 3 or 4 years, respectively, and a relatively high density (≥ 2 plants/m 2 ) to achieve the minimum recommended canopy cover for sage‐grouse (15 %). Sagebrush grown in warmer and drier conditions met this cover goal months earlier. Although planted sagebrush reached heights to meet sage‐grouse nesting requirements (30 cm) one year earlier than seeded plants, seeded individuals were ~19 cm taller with 410 cm 2 more canopy area than planted sagebrush after 8 years. However, big sagebrush establishment from seed is unreliable. Strategically planting small, high density patches of container‐grown sagebrush in historic sage‐grouse nesting habitat combined with lower density seedings in larger surrounding areas may accelerate sage‐grouse habitat restoration.
California, Idaho, Nevada, Oregon, Utah↗
Colonisation of the alpine tundra by trees: Alpine neighbours assist late-seral but not early-seral conifer seedlings
Background Climate change is projected to alter the elevation and latitude of treeline globally. Seed germination and seedling survival are critical controls on treeline expansion. Neighbouring alpine plants, either through competition for resources or through altered microclimate, also affect seedlings emerging in the alpine zone. With warming, alpine plant species may interact with each other more or less strongly. Aims To determine whether establishing tree seedlings and an alpine herb are similarly sensitive to alpine plant neighbours under ambient and altered climate. Methods We imposed active heating, watering, and removed all plants adjacent to emerging conifer seedlings and an alpine herb. Results Picea engelmannii seedlings showed lower survival compared with Pinus flexilis 3 weeks following neighbour removal, and after 1 year only survived in watered plots. Pinus seedlings responded to neighbour removal by lowering the quantum yield of photosynthesis (ϕ PSII ). Contrary to expectations from the stress gradient hypothesis, survival was reduced without neighbours near the low-elevation range limit of Chionophila jamesii . Conclusions Pinus flexilis has higher expansion potential into the alpine, while Picea engelmannii requires moist conditions that could be facilitated by neighbours to expand its range. This implies likely range expansion by P. flexilis with consequences for alpine plant diversity and ecosystem function.
Colorado↗