Annual Forbs Research Articles

Species differences in stoichiometric homeostasis affect grassland community stability under N and P addition

Unbalanced N and P input has substantially altered the relative importance of N and P limitation in grassland ecosystems, which resulted in profound impacts on species nutrient cycling, community structure, and ecosystem stability. However, the underlying species-specific nutrient use strategy and stoichiometric homeostasis in driving community structure and stability changes remain unclear. A split-plot N and P addition experiment (main-plot: 0, 25, 50, and 100 kgN hm-2 a-1; subplot: 0, 20, 40, and 80 kgP2O5 hm-2 a-1) was conducted during 2017-2019 in two typical grasslands (perennial grass and perennial forb) communities in the Loess Plateau. The stoichiometric homeostasis of 10 main component species, species dominance, stability changes, and their contribution to community stability were investigated. Perennial legume and perennial clonal species tend to perform higher stoichiometric homeostasis than non-clonal and annual forb. Large shifts in species with high homeostasis vs. low homeostasis caused by N and P addition showed consistently profound impacts on community homeostasis and stability in both communities. In both two communities, species dominance performed significantly positive relationships with homeostasis under no N and P addition. P alone or combined with 25 kgN hm-2 a-1 addition strengthened species dominance-homeostasis relationship and increased community homeostasis due to increased perennial legumes. Under 50 and 100 kgN hm-2 a-1 combined with P addition, species dominance-homeostasis relationships were weakened, and community homeostasis decreased significantly in both communities, which was due to that increased annual and non-clonal forb suppressed perennial legume and clonal species. Our results demonstrated that trait-based classifications of species-level homeostasis offer a reliable tool in predicting species performance and community stability under N and P addition, and conserving species with high homeostasis is important to enhance semiarid grassland ecosystem function stability on the Loess Plateau.

Plant and mule deer responses to pinyon‐juniper removal by three mechanical methods

AbstractLand managers in western North America often reverse succession by removing pinyon (Pinus spp.) and juniper (Juniperus spp.) trees to reduce fire risk and increase forage for wildlife and livestock. Because prescribed fire carries inherent risks, mechanical methods such as chaining, roller‐chopping, and mastication are often used. Mechanical methods differ in cost and the size of woody debris produced, and may differentially impact plant and animal responses. We implemented a randomized, complete‐block, split‐plot experiment in December 2011 in the Piceance Basin, northwestern Colorado, USA, to compare mechanical methods and to explore seeding (subplot) interactions. We assessed vegetation 1‐, 2‐, 5‐, and 6‐years post‐treatment, and mule deer (Odocoileus hemionus) response via GPS locations 3–8 years post‐treatment. By 2016, treated plots had 3–5 times higher perennial grass cover and ~10 times higher cheatgrass (Bromus tectorum) cover than untreated control plots. Roller‐chopped plots had both the highest non‐native annual forb cover, and when seeded, the highest density of bitterbrush (Purshia tridentata), a nutritious shrub used by mule deer. Masticated plots had higher bitterbrush use during summer and fall, leaving less forage available for winter. Days of winter mule deer use from GPS point locations in chained and roller‐chopped plots was ~70% higher than in control plots, while winter use in masticated plots was similar to control plots. Mule deer use appears related to a combination of hiding cover, resulting from residual woody debris, and winter forage availability. Roller‐chopped plots provide the best combination of hiding cover and winter forage, but mastication or chaining, applied leaving dispersed security cover, may be better options at large scales or when invasive species concerns exist.

Could biological soil crusts act as natural fire fuel breaks in the sagebrush steppe?

Could biological soil crusts act as natural fire fuel breaks in the sagebrush steppe?

Feeding Ecology of the Cuvier’s Gazelle (Gazella cuvieri, Ogilby, 1841) in the Sahara Desert

Knowledge of the feeding ecology of ungulates in arid biomes offers an interesting model for understanding the drought resistance of large desert-adapted herbivores, a crucial issue in the face of increasing desertification due to climate change. To assess the feeding ecology of the endangered Cuvier's gazelle (Gazella cuvieri) in the Sahara desert, we used a multi-method approach combining faecal samples, direct observations, and the recording of indirect signs of feeding. We hypothesised that browser behaviour is the best foraging strategy for species living in hyper-arid environments, mainly due to long periods without grazing opportunities. Complementarily, we explored the effects of the main environmental descriptors (rainfalls and NDVI) on feeding patterns and diet quality. We found that Cuvier's diets are based mainly on acacias (Vachellia tortilis, V. flava) and occasionally on the annual forb Anastatica hierochuntica. In total, eighteen species (five trees, nine shrubs, three herbs, and one grass) belonging to fifteen families were recorded. Our result confirmed the browsers' characteristic of this species, reaffirming its ability to settle in a hostile environment. Acacias stand out as key species consumed at the southernmost limit of their range; hence, future conservation plans and strategies should take this into account for the survival of Cuvier's gazelle in desert environments.

Early ecosystem establishment using forest floor and peat cover soils in oil sands reclamation

ABSTRACT Early trends of plant community development provide the basis of ecosystem function and reclamation success of oil sand extraction sites. However, few studies have explicitly investigated species-level interactions with different cover soil types, placement depths, and time since reclamation during early plant community development in boreal forests. We investigated effectiveness of forest floor mineral mix (FMM) and peat mineral mix (PMM) cover soils and placement depths (10 and 20 cm) at four research sites 4 to 13 years after reclamation. Outcomes of this study indicate FMM had a more positive influence on woody plant densities, vegetation cover, and species richness than PMM. Species assemblage, composition, dominance, and types (successional stages, habitat types, competitive-stress tolerant-ruderal strategies) also showed FMM cover soil performed better than PMM. Greater vegetation cover and richness on deeper (20 cm) cover soil placements were evident. However, this effect of cover soil depth would likely decrease with time. Dominant and subdominant species on FMM were native and early to late successional, thus trajectory community development on FMM followed typical early succession of boreal forests (from ruderal and annual to perennial communities), while PMM was dominated by non-native and annual forbs which could slow succession and ecosystem recovery.

Promoting vegetation coverage using fertilization treatments in abandoned farmland in Mongolia

AbstractWe investigated the changes in vegetation responses following fertilization in abandoned farmland in Mongolia. Nitrogen (N), phosphorus (P) and potassium were sprayed alone or in combination on abandoned farmland on a typical steppe in Mongolia, and changes in soil nutrients, species composition and vegetation cover were investigated. Abandoned farmland had lower vegetation cover and soil N and P levels than natural grassland. Phosphorus fertilization significantly affected soil phosphate levels. Nitrogen fertilization in abandoned farmland effectively increased vegetation cover. Moreover, combined N and P fertilization increased plant cover over either element alone, possibly via improved uptake of nitrate ions and the promotion of growth. The effect of increasing cover following fertilization was primarily observed in the genus Artemisia. These results suggest that fertilization of abandoned farmland might not contribute to a return to natural steppe vegetation but rather increase the vegetation cover of annual forbs such as field weeds. Species composition did not appear to be affected by fertilization. This speaks to the difficulty of promoting species regeneration in abandoned farmland using fertilization alone. However, combining fertilization with the introduction of native plant material, e.g., seed sowing, may be beneficial in early restoration treatments, given the promotion of plant growth via fertilization and the importance of reducing wind erosion via the establishment of ground cover.

Native annual forbs decline in California coastal prairies over 15 years despite grazing.

Livestock grazing is often used as a land management tool to maximize vegetation diversity in grassland ecosystems worldwide. Prior research has shown that cattle grazing benefits native annual forb species in California's coastal prairies, but drought and increasing aridity may alter this relationship. In 2016 and 2017, we resurveyed the vegetation structure, native annual forb cover, and native annual forb richness in ten grazed and ungrazed prairies that were originally measured in 2000 and 2001 along a 200-km gradient from Monterey to Sonoma counties in California. We found that grazed prairies continued to have significantly lower vegetation height and thatch depth than ungrazed prairies, and that shrub encroachment over the 15-year period was significantly greater in ungrazed prairies. Furthermore, grazed prairies continued to have greater native annual forb richness (4.9 species per site) than ungrazed sites (3.0 species per site), but native annual forb richness declined by 2.8 species per site in grazed prairies and 0.1 species per site in ungrazed prairies between survey periods. We suggest that severe drought and increasing aridity may be driving declines in native annual forb richness in grazed prairies. The species we recorded only in earlier surveys were disproportionately wetland-associated and had higher average specific leaf area than species that remained through the second survey period. Finally, the cover of native annual species increased regardless of whether prairies were grazed, suggesting that the high precipitation in 2017 may have benefitted the native annual forb species that persisted at sites between surveys. Our study shows that weather conditions affect the outcomes of land management strategies.

Arbuscular mycorrhiza can be disadvantageous for weedy annuals in competition with paired perennial plants

Arbuscular mycorrhizal (AM) fungi can support the establishment of mycotrophic plants in new environments. However, the role of mycorrhizal symbiosis in interactions between perennial and weedy annual plants is not well understood. In our current study, we examine how widespread generalist AM fungi and soil disturbance, including disturbance of AM fungal networks (CMNs), affect the performance of two late-successional perennial plants of Central Europe, Senecio jacobaea and Crepis biennis, co-occurring with weedy annual forbs, Conyza canadensis and Erigeron annuus. Although presence of weedy annual E. annuus or C. canadensis did not affect the performance of the paired perennials, AM fungi supported perennial C. biennis in competition with weedy annual E. annuus. However, this AM-aided underpinning was independent of disturbance of CMNs. Conversely, although AM fungi benefited perennial S. jacobaea, this did not affect its competitive abilities when grown with weedy annual C. canadensis. Similarly, soil disturbance, independent of AM fungal presence, improved plant tissue P and biomass production of S. jacobaea, but not its competitive abilities. Our results show AM fungi may be advantageous for perennial plants growing in competition with weedy annual plants. Therefore, maintaining healthy soils containing an abundance of AM fungi, may encourage late successional perennial plants, potentially limiting establishment of weedy annual plant species.

Efficacy of strip seeding to restore grassland plant communities

Strip seeding is a novel restoration practice of strategically planting in strips, resulting in alternating seeded and unseeded areas to target efforts and reduce costs while achieving ecological outcomes similar to conventional methods of seeding entire sites. However, there has been limited work testing the efficacy of this method, including how strip width and percent seeded area affect restoration outcomes. We evaluated four native grass strip seed treatments (33%, 50% narrow, 50% wide, and 66% of area seeded), an unseeded control, and a conventional 100% seeded control to investigate: (1) how plant communities in seeded and unseeded strips change over time; (2) how initial strip width affect native species biomass, invasive species biomass, and plant species diversity; and (3) cost‐effectiveness of strip seeding in terms of management costs and benefits accrued. Four years post‐seeding, seeded and unseeded strips exhibited unique plant communities; seeded strips were characterized by native perennial grasses while unseeded strips had a higher abundance of annual forbs (majority non‐native) and non‐native annual grasses. Plant communities were similar within strips across strip seeding treatments. Invasion resistance and productivity scaled with percent area initially seeded, but by year four all strip seed treatments (33–66%) provided similar benefits to conventional seeding (100%). Overall, this suggests strip seeding is a promising, cost‐effective method to restore targeted species and maintain native grassland communities. Further research is needed on long‐term effects, ecological and economic barriers and opportunities, and provisioning of a broad suite of ecosystem services across different environmental contexts and management practices.

Comparing socioeconomic vulnerability index and land cover indices: Application of fuzzy TOPSIS model and geographic information system

Vulnerability Assessment (VA) has numerous management implications, particularly for locating the most vulnerable areas affected by land cover degradation. This study aims to assess and compare the relationship between socioeconomic vulnerability (SEV) and land cover indices (LCIs) in summer rangelands (Natanz county) and winter rangelands (Aran-V-Bidgol county) in Isfahan Province, Iran. To assess the socioeconomic vulnerability index (SEVI), a survey was conducted. Based on the SEVI, summer and winter rangelands were classified and mapped using a combination of fuzzy TOPSIS model and geographic information system (GIS) techniques. Field research was conducted to estimate LCIs, including plant cover, plant yield, litter (dead biomass), sand and gravel, bare soil, and forage production. Finally, the correlations between SEVI and LCIs were verified, and the SEV of winter rangelands and summer rangelands was examined. Results showed the rangelands of Chah Robat, Bidhend, and Tar were the most vulnerable summer rangelands, while the rangelands of Chah Zard, Cheshmeh Sefid, and Kandeh Matin were the most vulnerable winter rangelands. Findings further revealed more LCIs, including total ground cover, the yield of shrubs, and total yield had a significant relationship with SEVI in summer rangelands compared to winter rangelands (yield of annual forbs and total yield). Moreover, there was a significant difference between SEVI, determined by the fuzzy TOPSIS model, in summer and winter rangelands. It can be concluded that while the fuzzy TOPSIS model and GIS can be used to gain a better understanding of VA, the type of rangeland has an impact on how well these techniques can assess the SEV of rangelands.

Efficacy of labile carbon addition to reduce fast‐growing, invasive non‐native plants: A review and meta‐analysis

Abstract Elevated soil nitrogen (N) resulting from pollution, fertilizer and woody encroachment in grasslands enhances invasion pressures from weedy plant species. Sawdust, sucrose and other labile carbon (C) sources can be used as a soil amendment to combat the growth of fast‐growing, invasive non‐native plants by immobilizing soil N. Here, we present a systematic review of 83 publications, and a meta‐analysis from 48 publications. Using hierarchical mixed‐effects meta‐analytic models, we synthesized 655 responses from native plants and 486 responses from non‐native weeds to quantify the overall effect of C addition. We explored the possible explanations for variation in effect, such as differences in study conditions and how C was applied. Carbon addition studies were almost exclusively reported from the United States, Australia and Canada (93%). The majority of papers (63%) did not include any cost information. Overall, C addition significantly decreased non‐native weed abundance, but did not significantly affect native plant abundance. A C application rate of at least 210 g C m−2 year−1 (5 Mg sucrose ha−1 year−1 or 4.6 Mg sawdust ha−1 year−1) decreased non‐native weed abundance, but a rate of 2110–3000 g C m−2 year−1 (50–71 Mg sucrose ha−1 year−1 or 46–65 Mg sawdust ha−1 year−1) was required to significantly increase native plant abundance. Carbon addition was most effective in the western USA and southeastern Australia, and when used to suppress non‐native grasses (annual or perennial) and annual forbs. Simultaneous seeding of native species prevented an overall decrease in native plant abundance. Synthesis and application. When there is a nearby and inexpensive source of C available, we recommend C addition with simultaneous seeding of native species to control invasive non‐native grasses and annual forbs in semi‐arid and arid regions of the western USA and southeast Australia. In contrast to other weed control measures, especially herbicide, C addition does not significantly harm native perennial plants. Future studies should implement longer‐term monitoring, establish larger plots and include cost analysis to improve guidance for land managers.

Competition induces negative conspecific allelopathic effects on seedling recruitment.

Some plant species suppress competitors through release of chemical compounds into the environment. As the production of allelochemicals may be costly, it would be beneficial if their production would only be induced when plants experience competition. We tested whether two plant species that frequently co-occur show evidence for induced allelopathy in response to intra- and interspecific competition. We used the annual forb Crepidiastrum sonchifolium and the perennial forb Achyranthes bidentata, which are native to China and predominantly occur in ruderal communities, as focal species. We first grew the species without competition, with intraspecific competition and in competition with each other. We chemically analysed aqueous extracts made from these plants to test for evidence that the competition treatments affected the metabolomic profiles of the species. We then tested the effects of the aqueous extracts on seed germination and seedling growth of both plant species. Metabolomic analysis revealed that competition treatments modified the chemical profiles of the two study species. The root lengths of A. bidentata and C. sonchifolium seedlings were reduced by the aqueous plant extracts. For seedling root length of A. bidentata, heterospecific allelopathy was more negative than conspecific allelopathy, but for germination of C. sonchifolium seeds, the reverse was true. Moreover, conspecific allelopathic effects on germination of A. bidentata seeds and on seedling root length of both species were most negative when the aqueous extracts were made from plants that had experienced competition. In the case of seedling root length of A. bidentata, this effect was most negative when the plants had experienced interspecific instead of intraspecific competition. We showed that plants change their metabolomic profiles in response to competition, and that this correlated with allelopathic inhibition of conspecific seed germination and seedling growth. We suggest that autoallelopathy for seed germination could function as a mechanism to avoid strong competition by keeping the seeds in a dormant state.

Leaf Traits Predict Water‐Use Efficiency in U.S. Pacific Northwest Grasslands Under Rain Exclusion Treatment

AbstractDoes drought stress in temperate grasslands alter the relationship between plant structure and function? Here we report data from an experiment focusing on growth form and species traits that affect the critical functions of water‐ and nutrient‐use efficiency in prairie and pasture plant communities. A total of 139 individuals of 12 species (11 genera and four families) were sampled in replicated plots maintained for three years across a 520 km latitudinal gradient in the Pacific Northwest, USA. Rain exclusion did not alter the interspecific relationship between foliar traits and stoichiometry or intrinsic water‐use efficiency (iWUE). Rain exclusion reduced iWUE in grasses, an effect was primarily species‐specific, although leaf morphology, life history strategy, and phylogenetic distance predicted iWUE for all 12 species when analyzed together. Variation in specific leaf area explained most of the variation in iWUE between different functional groups, with annual forbs and annual grasses at opposite ends of the resource‐use spectrum. Our findings are consistent with expected trait‐driven tradeoffs between productivity and resource‐use efficiency, and provide insight into strategies for the sustainable use and conservation of temperate grasslands.

Prefire Vegetation Structure of High Severity Wildfires in Nonherbaceous‐Dominated Rangelands in the Western United States

AbstractHigh severity rangeland wildfires have enormous negative impacts on human safety and infrastructure and may have long‐term consequences on ecosystem structure, function, and services, across the vast rangelands in the western United States. We explored prefire vegetation structure of all high severity wildfires, as well as associated areas with low and moderate burn severity, in nonherbaceous‐dominated rangelands in western United States from 1985 to 2018, based on fractional cover of annual forbs and grasses, perennial forbs and grasses, shrubs and trees from the Rangeland Analysis Platform. These wildfires were grouped into nine clusters using Expectation Maximization algorithms and patterns of prefire vegetation structure and the major vegetation types were assessed. High woody cover is a common characteristic of the prefire vegetation structure. Four of the clusters, which accounted for more than 70% of the areas of high severity wildfires, were characterized by high (∼50%) woody cover in prefire vegetation structure. The areas with high severity burns also had significantly higher woody cover than the areas with low or moderate severity burns in eight of the nine clusters. Some of these ecosystems can have abundant fine fuel, structural connectivity such as fuel laddering, and/or highly flammable materials, which can facilitate the ignition of the woody crowns, leading to high severity wildfires. Management strategies (such as prescribed burning) that can decrease woody cover and reduce standing dead vegetation and fuel laddering could be effective in reducing the risk and extent of high severity wildfires on rangelands in the western United States.

Evaluating the restoration potential of soil seed banks in degraded semi-arid oak forests: Influence of canopy cover types and fire-related cues on seed germination

Soil seed bank is an important driver of vegetation dynamics, particularly in fire-prone Mediterranean ecosystems. In this study, we disentangle the effects of fire-related cues on the dynamics of the soil seed bank in semiarid oak forests of western Iran. Soil samples were collected in two types of forests: below closed canopy or below the open canopy of more intensively used forests. In a greenhouse experiment, the effects of five treatments were tested application of: ash (Ash), smoke (Smoke), 50 °C temperature (Heat50), 100 °C temperature (Heat100) and control. Soil samples were regularly monitored and the number of germinated seeds (seedlings) by species were recorded in each treatment. Diversity indices were also computed. Knowing the effects of fire and its cues on fied 18 species from 16 genera and 9 families. 56 % of the seedlings emerged from the closed canopy forest soils and 44 % from the open canopy forests. Seedling density and diversity values were the lowest in the Heat100 treatment. No annual grasses and tree species were recorded in this treatment. In contrast, the influence of the other fire-related cues was mediated by the forest type cover: the number of emerged seedlings was the highest in Smoke and Heat50 in the open canopy and closed canopy, respectively. This mediation effect was also reflected in the composition of the control as tree species were only present in the closed canopy and annual forbs were less abundant there compared to the open canopy type. Considering all fire treatments together, the seedling density was significantly higher in the closed canopy type than in the open canopy (309.6 ± 28.03 vs 240.8 ± 20.78 seeds/m2). Our results showed that intense fires leading to high soil temperatures are largely detrimental to soil seed bank germination and species diversity, whereas less intense fires can be favourable depending on species life form and the type of forest. Our findings highlight that post-fire regeneration from the soil seed bank is more promising in closed forests than in forests with an open canopy in the studied ecosystem.

Grazing alters seedling emergence number, dynamics, and diversity of herbaceous plants in a semiarid sandy grassland

AbstractOvergrazing in semiarid grassland is a major cause of vegetation degradation. Understanding the changes in seedling patterns driven by grazing is crucial to unveiling mechanisms of plant community regeneration and succession in grazed grassland. However, the dynamics of seedling emergence and species diversity under grazing are rarely studied. This study used periodical field investigation to examine the variation in seedling emergence, plant diversity, species composition, and seedling survival of herbaceous plants under four grazing intensities, including light (LG), moderate (MG), heavy (HG), and non‐grazed (NG), in a semiarid sandy grassland. The results showed that seedling number and density were significantly higher in HG plots, while the seedling survival rate was significantly lower in HG, and that seedling emergence dynamics varied with grazing. Seventy‐five percent of the seedlings in HG emerged during early spring in April, while approximately 50% of the seedlings in LG, MG, and NG emerged in May. Differences in species richness and diversity varied with growth stages and the diversity was always higher in LG than in other grazing habitats during the main growing season. Annual forb seedlings increased while annual grass seedlings decreased after grazing with no perennial grass seedlings in HG. Our study suggests that high seedling emergence but low seedling survival rate, and simple species composition especially the disappearance of perennial plants caused by HG may be an important factor leading to vegetation degradation in the semiarid grazed grassland.

Aphids and Mycorrhizal Fungi Shape Maternal Effects in Senecio vulgaris.

Plant performance in any one generation is affected not only by the prevailing environmental conditions, but also by the conditions experienced by the parental generation of those plants. These maternal effects have been recorded in a many plant species, but the influence of external biotic (as opposed to abiotic) factors on shaping maternal effects have been rarely examined. Furthermore, almost all previous studies have taken place over one plant generation, rather than across multiple generations. Here, we studied the influence of insect herbivory and arbuscular mycorrhizal (AM) fungal colonisation on the shaping of maternal effects in the annual forb Senecio vulgaris. We grew plants with and without aphids (Myzus persicae) and AM fungi (hereafter termed ‘induction events’) over four successive generations, wherein seeds from plants in any one treatment were used to grow plants of the same treatment in the next generation, all in identical environmental conditions. We found strong evidence of maternal effects in the second plant generation, i.e., after one induction event. These plants took longer to germinate, flowered in a shorter time, produced lighter seeds and were shorter and of lower biomass than their parents. Aphid attack tended to enhance these effects, whereas AM fungi had little influence. However, thereafter there was a gradual recovery in these parameters, so that plants experiencing three inductions showed similar life history parameters to those in the original generation. We conclude that experiments investigating maternal effects need to be performed over multiple plant generations and that biotic factors such as insects and mycorrhizas must also be taken into account, along with abiotic factors, such as nutrient and water availability.

Small effects of livestock grazing intensification on diversity, abundance, and composition in a dryland plant community.

Livestock grazing is a globally important land use and has the potential to significantly influence plant community structure and ecosystem function, yet several critical knowledge gaps remain on the direction and magnitude of grazing impacts. Furthermore, much of our understanding of the long-term effects on plant community composition and structure are based on grazer exclusion experiments, which explicitly avoid characterizing effects along grazing intensity gradients. We sampled big sagebrush plant communities using 68 plots located along grazing intensity gradients to determine how grazing intensity influences multiple aspects of plant community structure over time. This was accomplished by sampling plant communities at different distances from 17 artificial watering sources, using distance from water and cow dung density as proxies for grazing intensity at individual plots. Total vegetation cover and total grass cover were negatively related to grazing intensity, and cover of annual forbs, exotic cover, and exotic richness were positively related to grazing intensity. In contrast, species richness and composition, bunchgrass biomass, shrub density and size, percentage cover of bare ground, litter, and biological soil crusts did not vary along our grazing intensity gradients, in spite of our expectations to the contrary. Our results suggest that the effects of livestock grazing over multiple decades (mean=46 years) in our sites are relatively small, especially for native perennial species, and that the big sagebrush plant communities we sampled are somewhat resistant to livestock grazing. Collectively, our findings are consistent with existing evidence that indicates the stability of the big sagebrush plant functional type composition under current grazing management regimes.

The impacts of wildfires of different burn severities on vegetation structure across the western United States rangelands

Large wildfires have increased in western US rangelands over the last three decades. There is limited information on the impacts of wildfires with different severities on the vegetation in these rangelands. This study assessed the impacts of large wildfires on rangeland fractional cover including annual forbs and grasses (AFG), perennial forbs and grasses (PFG), shrubs (SHR) and trees (TREE) across the western US, and explored relationships between changes in fractional cover and prefire soil moisture conditions. The Expectation Maximization (EM) algorithm was used to group wildfires into nine clusters based on the prefire rangeland fractional cover extracted from the Rangeland Analysis Platform. The Standardized Precipitation Evapotranspiration Index (SPEI) with various lag scales from the Gridded Surface Meteorological (GRIDMET) dataset was used to represent antecedent soil moisture conditions. The results showed generally that fractional cover decreased most for AFG and PFG during the fire year, one year postfire for SHR, and two years postfire for TREE. High severity wildfires led to the greatest decrease in cover for all plant functional types, while low severity wildfires caused the least decrease in the functional type cover in most cases, though some variations existed. Furthermore, the impacts of wildfires on vegetation cover were greater in woody (SHR and TREE) types than in herbaceous (AFG and PFG) types. Significant negative correlation existed between percent changes in AFG and PFG cover and SPEI indicating higher prefire soil moisture conditions likely increased fine fuel loads and led to a larger decrease in AFG and PFG cover following wildfires. Significant positive correlation existed between percent changes in SHR and TREE cover and SPEI indicating drier prefire conditions resulted in larger decreases in SHR and TREE cover following wildfires. These findings help better understand the impacts of wildfires on rangelands and provide insights for rangeland management.

Short-Term Vegetation Response to Bulldozed Fire Lines in Northern Great Plains Grasslands

A bulldozed fire line is a fire-suppression technique that limits fire movement by altering fuel continuity through vegetation removal and mineral soil exposure. The ecological impacts of a bulldozed fire line may exceed the effects of the fire itself through lasting changes in the soil and vegetation properties; however, little research has been performed to quantify these impacts in grassland systems. In this study, we compared vegetation properties among burned, unburned, and bulldozed fire line conditions on two August 2012 grassland wildfires in Montana. Standing biomass, by growth form, was quantified in 2013 and 2014, and compared using a generalized linear model. Perennial grass production was significantly reduced, while annual grass and annual forb biomass increased in response to the fire line treatment. Shrub and total vegetation standing crop were reduced in response to the fire line in 2013; however, the treatment effects were diminished by 2014. The burned and unburned treatments were generally similar within two years post-fire. The loss of perennial grasses and invasion of competitive annual grasses such as cheatgrass (Bromus tectorum L.) may limit the vegetation recovery of the fire line and promote further invasion of annual grasses into these systems. The marginal impact of the fires on these plant communities suggests the need to limit the use of ad hoc bulldozed fire lines as a suppression activity. If a bulldozed fire line is constructed, we suggest limiting soil disturbance by restricting blade depth to remove only surface vegetation and restricting bulldozer use to flat slopes, even if working with the contour, and incorporating re-seeding as part of or immediately after fire line construction.