Modeling cheatgrass distribution, abundance, and response to climate change as a function of soil microclimate.

Exotic annual grass invasions in water-limited systems cause degradation of native plant and animal communities and increased fire risk. The life history of invasive annual grasses allows for high sensitivity to interannual variability in weather. Current distribution and abundance models derived from remote sensing, however, provide only a coarse understanding of how species respond to weather, making it difficult to anticipate how climate change will affect vulnerability to invasion. Here, we derived germination covariates (rate sums) from mechanistic germination and soil microclimate models to quantify the favorability of soil microclimate for cheatgrass (Bromus tectorum L.) establishment and growth across 30 years at 2662 sites across the sagebrush steppe system in the western United States. Our approach, using four bioclimatic covariates alone, predicted cheatgrass distribution with accuracy comparable to previous models fit using many years of remotely-sensed imagery. Accuracy metrics from our out-of-sample testing dataset indicate that our model predicted distribution well (72% overall accuracy) but explained patterns of abundance poorly (R2 = 0.22). Climatic suitability for cheatgrass presence depended on both spatial (mean) and temporal (annual anomaly) variation of fall and spring rate sums. Sites that on average have warm and wet fall soils and warm and wet spring soils (high rate sums during these periods) were predicted to have a high abundance of cheatgrass. Interannual variation in fall soil conditions had a greater impact on cheatgrass presence and abundance than spring conditions. Our model predicts that climate change has already affected cheatgrass distribution with suitable microclimatic conditions expanding 10%-17% from 1989 to 2019 across all aspects at low- to mid-elevation sites, while high- elevation sites (>2100 m) remain unfavorable for cheatgrass due to cold spring and fall soils.

Interannual climate variability mediates changes in carbon and nitrogen pools caused by annual grass invasion in a semiarid shrubland.

Exotic plant invasions alter ecosystem properties and threaten ecosystem functions globally. Interannual climate variability (ICV) influences both plant community composition (PCC) and soil properties, and interactions between ICV and PCC may influence nitrogen (N) and carbon (C) pools. We asked how ICV and non-native annual grass invasion covary to influence soil and plant N and C in a semiarid shrubland undergoing widespread ecosystem transformation due to invasions and altered fire regimes. We sampled four progressive stages of annual grass invasion at 20 sites across a large (25,000 km2 ) landscape for plant community composition, plant tissue N and C, and soil total N and C in 2013 and 2016, which followed 2 years of dry and wet conditions, respectively. Multivariate analyses and ANOVAs showed that in invasion stages where native shrub and perennial grass and forb communities were replaced by annual grass-dominated communities, the ecosystem lost more soil N and C in wet years. Path analysis showed that high water availability led to higher herbaceous cover in all invasion stages. In stages with native shrubs and perennial grasses, higher perennial grass cover was associated with increased soil C and N, while in annual-dominated stages, higher annual grass cover was associated with losses of soil C and N. Also, soil total C and C:N ratios were more homogeneous in annual-dominated invasion stages as indicated by within-site standard deviations. Loss of native shrubs and perennial grasses and forbs coupled with annual grass invasion may lead to long-term declines in soil N and C and hamper restoration efforts. Restoration strategies that use innovative techniques and novel species to address increasing temperatures and ICV and emphasize maintaining plant community structure-shrubs, grasses, and forbs-will allow sagebrush ecosystems to maintain C sequestration, soil fertility, and soil heterogeneity.

Fire-driven vegetation type conversion in Southern California.

One consequence of global change causing widespread concern is the possibility of ecosystem conversions from one type to another. A classic example of this is vegetation type conversion (VTC) from native woody shrublands to invasive annual grasslands in the biodiversity hotspot of Southern California. Although the significance of this problem is well recognized, understanding where, how much, and why this change is occurring remains elusive owing to differences in results from studies conducted using different methods, spatial extents, and scales. Disagreement has arisen particularly over the relative importance of short-interval fires in driving these changes. Chronosequence approaches that use space for time to estimate changes have produced different results than studies of changes at a site over time. Here we calculated the percentage woody and herbaceous cover across Southern California using air photos from ~1950 to 2019. We assessed the extent of woody cover change and the relative importance of fire history, topography, soil moisture, and distance to human infrastructure in explaining change across a hierarchy of spatial extents and regions. We found substantial net decline in woody cover and expansion of herbaceous vegetation across all regions, but the most dramatic changes occurred in the northern interior and southern coastal areas. Variables related to frequent, short-interval fire were consistently top ranked as the explanation for shrub to grassland type conversion, but low soil moisture and topographic complexity were also strong correlates. Despite the consistent importance of fire, there was substantial geographical variation in the relative importance of drivers, and these differences resulted in different mapped predictions of VTC. This geographical variation is important to recognize for management decision-making and, in addition to differences in methodological design, may also partly explain differences in previous study results. The overwhelming importance of short-interval fire has management implications. It suggests that actions should be directed away from imposing fires to preventing fires. Prevention can be controlled through management actions that limit ignitions, fire spread, and the damage sustained in areas that do burn. This study also demonstrates significant potential for changing fire regimes to drive large-scale, abrupt ecological change.

Wildfire and the ecological niche: Diminishing habitat suitability for an indicator species within semi-arid ecosystems.

Globally accelerating frequency and extent of wildfire threatens the persistence of specialist wildlife species through direct loss of habitat and indirect facilitation of exotic invasive species. Habitat specialists may be especially prone to rapidly changing environmental conditions because their ability to adapt lags behind the rate of habitat alteration. As a result, these populations may become increasingly susceptible to ecological traps by returning to suboptimal breeding habitats that were dramatically altered by disturbance. We demonstrate a multistage modeling approach that integrates habitat selection and survival during the key nesting life-stage of a bird species of high conservation concern, the greater sage-grouse (Centrocercus urophasianus; hereafter, sage-grouse). We applied these spatially explicit models to a spatiotemporally robust dataset of sage-grouse nest locations and fates across wildfire-altered sagebrush ecosystems of the Great Basin ecoregion, western United States. Female sage-grouse exhibited intricate habitat selection patterns that varied across regional gradients of ecological productivity among sagebrush communities, but often selected nest sites that disproportionately resulted in nest failure. For example, 23% of nests occurred in wildfire-affected habitats characterized by reduced sagebrush cover and greater composition of invasive annual grasses. We found survival of nests was negatively associated with wildfire-affected areas, but positively associated with higher elevations with increased ruggedness and overall shrub cover. Strong site fidelity likely drove sage-grouse to continue nesting in habitats degraded by wildfire. Hence, increasing frequency and extent of wildfire may contribute disproportionately to reduced reproductive success by creating ecological traps that act as population sinks. Identifying such habitat mismatches between selection and survival facilitates deeper understanding of the mechanisms driving reduced geographic niche space and population decline at broad spatiotemporal scales, while guiding management actions to areas that would be most beneficial to the species.

Independent domestications of cultivated tree peonies from different wild peony species.

An understanding of plant domestication history provides insights into general mechanisms of plant adaptation and diversification and can guide breeding programmes that aim to improve cultivated species. Cultivated tree peonies (genus Paeonia L.) are among the most popular ornamental plants in the world; yet, the history of their domestication is still unresolved. Here, we explored whether the domestication in China of historically cultivated peonies, that is, the common and flare cultivated tree peonies, was a single event or whether independent domestications occurred. We used 14 nuclear microsatellite markers and a comprehensive set of 553 tree peonies collected across China, including common tree peonies, flare tree peonies and the wild species or subspecies that are potential contributors to the cultivated tree peonies, that is, Paeonia rockii ssp. rockii, P. rockii ssp. atava, P. jishanensis and P. decomposita. Assignment methods, a principal component analysis and approximate Bayesian computations provided clear evidence for independent domestications of these common tree and flare tree peonies from two distinct and allopatric wild species, P. jishanensis and P. rockii ssp. atava, respectively. This study provides the first example of independent domestications of cultivated trees from distinct species and locations. This work also yields crucial insight into the history of domestication of one of the most popular woody ornamental plants. The cultivated peonies represent an interesting case of parallel and convergent evolution. The information obtained in this study will be valuable both for improving current tree peony breeding strategies and for understanding the mechanisms of domestication, diversification and adaptation in plants.

Seed position in spikelet as a contributing factor to the success of the winter annual invasive grass Aegilops tauschii.

Seed position - dependent effects on seed dormancy/germination are well documented at the inflorescence/infructescence level, but less is known about seeds at different positions within a dispersal unit. For the invasive winter annual grass Aegilops tauschii, we quantified morphology, mass and dormancy/germination of seeds from basal (1), middle (2), and distal (3) positions in two spikelet types (Left and Right). We also investigated seedling emergence, survival, plant size and seed production of plants from seeds in different spikelet positions of two spikelet types under different soil nutrient and water conditions. We found that these seed, seedling and plant traits performed as mirror images between the Left and Right spikelet types. The middle seed was significantly the longest and had the maximum mass, while the basal seed was the shortest and had medium mass. Middle seeds had the highest increase in mass during imbibition and the highest germination percentages and rates, while basal seeds had the lowest. Seedling emergence and survival, plant size and seed production for each position of seeds were highest in the added fertilizer combined with regular watering treatment and lowest in the no fertilizer combined with natural moisture, while height of plants derived from the middle and the distal seeds was significantly higher than that of plants derived from the basal seeds under all soil nutrient and water conditions. Seedling survival, number of tillers per plant and seed production per plant from the middle and distal seeds were significantly lower than those from basal seeds under all soil nutrient and water treatments. The considerable variation in seedling emergence and survival, plant size and seed production between seeds in different positions in the spikelet results in much flexibility in all stages of the life cycle, thereby likely contributing to the invasiveness of A. tauschii.

Community invasion resistance is influenced by interactions between plant traits and site productivity.

Plant communities are predicted to be more resistant to invasion if they are highly productive, harbor species with similar functional traits to invaders, or support species with high competitive potential. However, the strength of competition may decrease with increasing abiotic stress if species more heavily invest in traits that confer stress tolerance over competitive ability, potentially influencing community trait-resistance relationships. Recent research examining how community traits influence invasion resistance has been predominantly focused on single vegetation types, and results between studies are often conflicting. Few studies have evaluated the extent to which abiotic factors and community traits interact to influence invasion along vegetation gradients. Here, we use an in situ seed addition experiment to examine how above- and below-ground plant traits and vegetation type interact to influence community resistance to invasion by a recently introduced annual grass, Ventenata dubia, along a productivity gradient in eastern Oregon, USA. To measure invasion resistance, we evaluated V. dubia biomass in seeded subplots with varying trait compositions across three vegetation types situated along a productivity gradient: scab-flats (sparsely vegetated dwarf-shrublands), low sage-steppe, and ephemeral wet meadows. Trait-resistance relationships were highly context dependent. In wet meadows (the most productive sites), resistance to invasion increased with increasing resident biomass and as community weighted mean trait values for specific leaf area, fine-to-total root volume, and height become more similar to V. dubia's trait values, although these relationships were relatively weak. We did not find evidence that neighboring species influenced invasion resistance in less productive vegetation types, in contrast to our expectations that facilitative interactions may increase with decreasing productivity as posited by the stress-gradient hypothesis. Unlike V. dubia, which heavily invaded all three vegetation types, introduced species with similar trait values, including Bromus tectorum, were not abundant throughout the study area demonstrating V. dubia's unique ability to take advantage of available resources. Our results illustrate how community traits and site productivity interact to influence community resistance to invasion and highlight that communities with lower overall biomass and few functionally similar species to V. dubia may be at the greatest risk for invasion.

Taxonomic Description of Stenodiplosis tectori n. sp. (Diptera: Cecidomyiidae), a Seed Parasite of Cheatgrass, Anisantha tectorum, Based on Morphological and Mitochondrial DNA Data.

Cheatgrass is an annual grass species from Eurasia that has become invasive in much of western North America. It has been implicated in recent increases in the frequency, size, and intensity of wildfires, contributing to severe economic, environmental, and social destruction. In order to reduce this damage, the USDA-ARS established a classical biological control program against cheatgrass. In 2018 and 2019, adult gall midges were collected emerging from cheatgrass seed heads collected at several sites in Bulgaria and Greece; this is the first gall midge ever recorded from cheatgrass. Morphological comparisons with related midge species recorded from other plant hosts revealed that this midge from cheatgrass is a new species, described here as Stenodiplosis tectori n. sp. This status was supported by sequence comparisons of a barcode region of the gene encoding the mitochondrial cytochrome c subunit I (CO1) protein in Stenodiplosis tectori n. sp. and three congeners. The present study is the first to report MT-CO1 data in the genus Stenodiplosis. The ingroup Stenodiplosis tectori n. sp. collected in the Balkans grouped in one phylogenetic supported clade, with an average K2P-distance from its closest related congener, S. sorghicola, of 7.73% (SD = 1.10). The findings indicated relatively high year-to-year within-population diversity. Implications for this gall midge's utility as a biological control agent of cheatgrass are discussed.

Dataset of plant composition change over seven years at the Zumwalt Prairie Preserve, Oregon, USA.

The data and analyses presented here were collected at the Zumwalt Prairie Preserve (ZPP), northeastern Oregon. Vegetation composition was measured within 124 (1-ha) plots using the line point intercept method [1,2]. These data include vascular plant species abundance matrices at two different time periods, seven years apart (2008/2009 & 2015/2016); boxplots of species abundance (cover and frequency) change over time; Non-parametric Multiplicative Regression (NPMR) estimated abundance of Ventenata dubia, an invading non-native annual grass, in geographic and ordination (Non-metric Multidimensional Scaling ordination; NMS) space over time.

To burn or not to burn: Comparing reintroducing fire with cutting an encroaching conifer for conservation of an imperiled shrub-steppe.

Woody vegetation has increased on rangelands worldwide for the past 100-200 years, often because of reduced fire frequency. However, there is a general aversion to reintroducing fire, and therefore, fire surrogates are often used in its place to reverse woody plant encroachment. Determining the conservation effectiveness of reintroducing fire compared with fire surrogates over different time scales is needed to improve conservation efforts. We evaluated the conservation effectiveness of reintroducing fire with a fire surrogate (cutting) applied over the last ~30 years to control juniper (Juniperus occidentalis Hook.) encroachment on 77 sagebrush-steppe sites. Critical to conservation of this imperiled ecosystem is to limit juniper, not encourage exotic annual grasses, and promote sagebrush dominance of the overstory. Reintroducing fire was more effective than cutting at reducing juniper abundance and extending the period of time that juniper was not dominating the plant community. Sagebrush was reduced more with burning than cutting. Sagebrush, however, was predicted to be a substantial component of the overstory longer in burned than cut areas because of more effective juniper control. Variation in exotic annual grass cover was explained by environmental variables and perennial grass abundance, but not treatment, with annual grasses being problematic on hotter and drier sites with less perennial grass. This suggests that ecological memory varies along an environmental gradient. Reintroducing fire was more effective than cutting at conserving sagebrush-steppe encroached by juniper over extended time frames; however, cutting was more effective for short-term conservation. This suggests fire and fire surrogates both have critical roles in conservation of imperiled ecosystems.

Prefire grazing by cattle increases postfire resistance to exotic annual grass (Bromus tectorum) invasion and dominance for decades.

UNLABELLED: Fire, herbivory and their interaction influence plant community dynamics. However, little is known about the influence of prefire herbivory on postfire plant community response, particularly long-term resistance to postfire exotic plant invasion in areas that historically experienced limited large herbivore pressure and infrequent, periodic fires.We investigated the long-term postfire effects of prefire herbivory by cattle, an exotic herbivore, in Artemisia (sagebrush) plant communities in the northern Great Basin, USA. Study areas were moderately grazed or not grazed by cattle since 1936 and then were burned in 1993. Plant community response was measured the 19th through the 22nd year postfire. Prior to burning exotic annual grass presence was minimal (<0.5% foliar cover) and plant community characteristics were similar between grazed and ungrazed treatments, with the exception of litter biomass being two times greater in the ungrazed treatment.Two decades postfire, Bromus tectorum L., an exotic annual grass, dominated the ungrazed treatment. Native bunchgrasses, species richness, and soil biological crusts were greater in prefire grazed areas compared to ungrazed areas.These results suggest that moderate prefire herbivory by cattle increased the resistance of the plant community to postfire invasion and dominance by B. tectorum. We presume that herbivory reduced mortality of large perennial bunchgrasses during the fire by reducing fine fuel (litter) and subsequently burn temperatures. SYNTHESIS: This research demonstrates that a moderate disturbance (herbivory) may mediate the effects of a subsequent disturbance (fire). The effects of disturbances are not independent; therefore quantifying these interactions is critical to preventing oversimplification of complex plant community dynamics and guiding the conservation of endangered ecosystems.

Plant invasion alters nitrogen cycling by modifying the soil nitrifying community.

Plant invasions have dramatic aboveground effects on plant community composition, but their belowground effects remain largely uncharacterized. Soil microorganisms directly interact with plants and mediate many nutrient transformations in soil. We hypothesized that belowground changes to the soil microbial community provide a mechanistic link between exotic plant invasion and changes to ecosystem nutrient cycling. To examine this possible link, monocultures and mixtures of exotic and native species were maintained for 4 years in a California grassland. Gross rates of nitrogen (N) mineralization and nitrification were quantified with 15 N pool dilution and soil microbial communities were characterized with DNA-based methods. Exotic grasses doubled gross nitrification rates, in part by increasing the abundance and changing the composition of ammonia-oxidizing bacteria in soil. These changes may translate into altered ecosystem N budgets after invasion. Altered soil microbial communities and their resulting effects on ecosystem processes may be an invisible legacy of exotic plant invasions.

Abiotic stress, competition, and the distribution of the native annual grass Vulpia microstachys in a mosaic environment.

We analyzed how abiotic stress and competition interact to control the abundance and performance of the native annual grass Vulpia microstachys (Lonard and Gould; Poaceae) in a heterogeneous environment. At our study site, V. microstachys grows in nonserpentine grasslands dominated by tall invasive grasses, serpentine meadows dominated by short native forbs, and rocky serpentine slopes with a sparse native herb cover. We hypothesized that these three intermixed habitats acted as a gradient of increasing abiotic stress and decreasing aboveground competition, respectively. We further expected that the abundance and performance of V. microstachys would be highest in serpentine meadows, where neither aboveground competition nor abiotic stress were maximal. Soil and biotic variables showed roughly the expected patterns, but V. microstachys did not show the predicted peak in the middle of the gradient. Emergence, seedling survival, and abundance of V. microstachys were highest, and growth and seed production of survivors were lowest, on rocky serpentine slopes. Field experiments revealed that removal of competitors enhanced all demographic parameters, but only in the more productive habitats. An interaction between seed source and habitat, affecting emergence and survival, indicated ecotypic adaptation to the rocky serpentine slope habitat. We conclude that individual variation caused by local adaptation and phenotypic plasticity allows V. microstachys to survive in widely different habitats, none of which are optimal, resulting in considerable variation in demography.

Respostas do híbrido de sorgo-sudão às adubações nitrogenada e potássica: características estruturais e produtivas / Nitrogen and potassium fertilization effects on a sorghum hybrid: forage production, structural traits

A pesquisa foi instalada no Setor de Forragicultura da FCAV/UNESP-Jaboticabal, para avaliar o híbrido de sorgo-sudão AG 2501C no outono e inverno. O manejo da pastagem foi conduzido, simulando o sistema de lotação intermitente. O experimento foi desenvolvido de março a setembro de 2002. A forrageira foi submetida a nove tratamentos: três doses de N (100, 200 e 300 kg/ha) e três doses de K (0, 80 e 160 kg/ha de K2O), em delineamento experimental de blocos casualizados com três repetições em esquema de parcelas subdivididas. As características estudadas foram massas, secas, inicial de planta inteira, folha e colmo e massa seca residual; relação lâmina/colmo; índice de área foliar (IAF); interceptação da radiação fotossinteticamente ativa (RFA) e coeficiente de extinção luminosa. Os tratamentos não influenciaram a massa seca inicial (MSI) e residual (MSR) da planta inteira, folha e colmo e massa seca residual. Os resultados médios para MSI, MSR, folha e colmo foram 2801,2; 964,7; 1462,8 e 1085,2 kg/ha de MS, por ciclo de pastejo, respectivamente. Houve redução da relação lâmina/colmo e da porcentagem de folhas, enquanto a porcentagem de colmos aumentou. Houve interação entre N e K para IAF, interceptação de luz e coeficiente de extinção.

This research was carried out in the Forage Section of FCAV/UNESP-Jaboticabal, to evaluate hybrid sorghum AG 2501C (Sorghum bicolor x Sorghum sudanense) during autumn/winter. Pasture management was accomplished by a simulation of intermittent stocking. The experiment was developed from March to September of 2002. The forage was submitted to nine treatments: three doses of N (100, 200, and 300 kg/ha) and three doses of K (0, 80, and 160 kg/ha of K2O) in a randomized block design with three replications in a split plot scheme. Characteristics including forage mass before grazing (FMBG), after grazing (residual), leaf and stem, leaf/stem ratio, leaf area index (LAI), interception of light, and light extinction coefficient (LEC) were evaluated. No differences for FMBG, residual, leaf, and stem were found. The averages were 2801.2, 964.7, 1462.8, and 1085.2 kg/ha of DM, per grazing cycle for FMBG, residual, leaf, and stem. There was significant interaction (p<0,01) between N and K for LAI, interception of light, and LEC.

Resposta do híbrido de sorgo-sudão à adubação nitrogenada e potássica: composição química e digestibilidade in vitro da matéria orgânica / Nitrogen and potassium fertilization effects on a sorghum hybrid: chemical composition and in vitro digestibility of organic matter

A pesquisa foi instalada no Setor de Forragicultura da FCAV/UNESP-Jaboticabal, objetivando avaliar a composição química e a digestibilidade in vitro da matéria orgânica (DIVMO) do híbrido de Sorgo-sudão cv. AG 2501C, no outono e inverno. O manejo da pastagem foi conduzido simulando o sistema de lotação intermitente. O experimento foi desenvolvido de março a setembro de 2002. A forrageira foi submetida a nove tratamentos: três níveis de nitrogênio (100, 200 e 300 kg de N/ha) e três níveis de potássio (0, 80 e 160 kg de K2O/ha), em delineamento experimental em blocos casualizados e parcelas subdivididas. A adubação nitrogenada e potássica não foram significativas para a DIVMO. O nitrogênio influenciou a proteína bruta (PB) com valores de 15,1; 16,4 e 15,7 por cento, a fibra em detergente neutro (FDN) com valores de 65,3; 65,8 e 64,5 por cento e fibra em detergente ácido (FDA) com 35,5; 37,8 e 39,6 por cento para 100; 200 e 300 kg N/ha. O potássio aumentou significativamente a lignina das plantas. O melhor nível obtido foi 100 kg/ha de nitrogênio, sem potássio.

The research was carried out in the Forage Section of FCAV/UNESP-Jaboticabal, to evaluate the chemical composition and the in vitro digestibility of organic matter (IVDOM) of the hybrid sorghum cv. AG 2501C (Sorghum bicolor x Sorghum sudanense) during autumn/winter. The management of pasture was conducted by a simulation of a rotational stocking. The experiment was developed from March to September 2002. The forage was submitted to nine treatments: three nitrogen levels (100, 220 and 300 kg/ha) and three potassium levels (0, 80 and 160 kg/ha) in a randomized blocks design and split plot. No effect of nitrogen and potassium fertilization on IVDOM was found. Nitrogen had influence on crude protein with values of 15.1, 16.4 and 15.7 percent of CP and 65.3, 65.8 and 64.5 percent of neutral detergent fiber (NDF) and 35.5, 37.8, 39.6 percent of acid detergent fiber (ADF), for 100, 200 and 300 kg N/ha. The potassium fertilization increased the lignin of plant. We concluded that, the best level was 100 kg/ha of nitrogen fertilization, without potassium.