Effects of fire on abundance of Eragrostis intermedia in a semi-arid grassland in southeastern Arizona

Abstract. Eragrostis intermedia (Plains lovegrass) is a midheight perennial bunchgrass native to semi-arid grasslands of the southwestern USA, that becomes an abundant and dominant component of these grasslands in areas long protected from livestock grazing. Substantial mortality of plains lovegrass occurred on a large livestock exclosure in southeastern Arizona, after a period of declining precipitation, but only in areas that had not burned in the previous three years. Lovegrass abundance subsequently increased on both undisturbed and burned sites, but remained substantially higher on the burned area. Long-term abundance of plains lovegrass may depend on episodic fire, particularly during periods of reduced precipitation.     

Tillering responses to red:far-red light ratio during different phenological stages in Eragrostis curvula

Tillering responses to light quality in different phenological stages of a perennial warm-season grass Eragrostis curvula were investigated in controlled environments. In vegetative plants, the tillering rate was greater (P<0.01) in the high (1.1–1.3) than in the low (0.59–0.70) red:far-red ratio (R/FR) light regime. Tillering rates were higher in the low R/FR treatment when the plants in the high R/FR regime reached the reproductive stage, while the plants in the low R/FR regime remained vegetative. After the reproductive tillers were removed by defoliation, more tillers were produced in the defoliated plants grown in the high R/FR regime. When the plants in both light treatments entered the reproductive stage, the tillering rate under the two light regimes became similar, suggesting a significant interaction between tillering and inflorescence development. The more advanced inflorescence development in the high R/FR regime may have reduced assimilate availability to tiller growth and overshadowed the effect of high R/FR on tillering. Both tillering and inflorescence development appeared to be controlled by R/FR ratio. The higher rate of aerial tiller production on the reproductive culms during the post-anthesis period in the high R/FR regime suggested that high R/FR ratio stimulated not only basal tillering, but also aerial tillering.     

Wildfire effects and post-fire responses of an invasive mesquite population: the interactive importance of grazing and non-native herbaceous species invasion

Aim To determine how responses of an established velvet mesquite (Prosopis velutina Woot.) population to a 2002 wildfire were shaped by grazing and non‐native herbaceous species invasions, both of which influenced fire behaviour. Location The study was conducted on contiguous ranches (one actively grazed by cattle, one that had not been grazed since 1968) in the Sonoita Valley of southern Arizona. Plant communities on both ranches were comprised of Chihuahuan semi‐desert grassland, savanna, and Madrean evergreen woodland ecosystems, but large areas were dominated by Lehmann and Boer lovegrass, African grass species that were introduced more than 50 years ago. Methods We selected 243 individuals that had been defoliated and bark scorched during the fire using a stratified random design based on pre‐fire grazing status and dominant grass cover. After the start of the 2003 growing season, we recorded individual tree characteristics, fire damage, and measures of post‐fire response, and tested for relationships among classes of: grazing status, bark damage, dominant grass cover type, abundance of live and dead aboveground branches, flowering status, and sprout number and size. Analyses of fire damage and post‐fire response were interpreted with respect to values of fireline intensity, scorch height and energy release that were projected by a fire behaviour model, nexus . Results Nearly all of the trees on grazed areas suffered low levels of fire damage, while a majority on ungrazed areas suffered moderate to severe damage. Trees on grazed areas consequently had significantly more leaf‐bearing twigs and branches in 2003 but a very low number of root sprouts, while individuals on ungrazed areas had a greater density of root sprouts but little post‐fire dead branching and almost no living branches. Among the ungrazed grassland types, more than 75% of the trees on Boer lovegrass plots suffered moderate to severe damage, while a similar percentage of trees in native grass areas suffered low damage. These differences were: (1) attributed to variations in fire characteristics that were caused by differences in litter production and removal, and (2) ecologically significant because trees in the severe damage class showed almost no aboveground post‐fire branching, either live or dead in 2003, while trees in the low damage class exhibited a greater amount of both. Main conclusions Our results affirm the notion that effective management of western grasslands where mesquite encroachment has or will become a problem requires a better understanding of how interactions among key ecosystem influences (e.g. fire, grazing, non‐native species) affect not only mesquite seedlings and saplings but also larger, established individuals and thereby the long‐term structure and functioning of semi‐desert grassland ecosystems. As managers shift their focus from eradication to management of mesquite in western grasslands and savannas, our results provide insights into how prescribed fires (and their effects on mesquite populations) differ from wildfires and how such effects may be mediated by the altered land uses and ecosystem characteristics that now exist in many western ecosystems.     

Epicuticular wax of Eragrostis curvula

Epicuticular wax of Eragrostis curvula contains hydrocarbons (6%), esters (13%), acids (3%), alkanols (4%), tritriacontane-12,14-dione (47%), 5(S)-5-hydroxytritriacontane-12,14-dione (14%) as major components. The esters consist of triterpenol esters (42%) as well as alkanol esters. The free alkanols consist principally Of C₁₆C₃₂ components, resembling those of waxes from panicoid, and some other eragrostoid, grasses. Minor components are triterpenols (0.7%), triterpenones (0.5%), triacylglycerols (0.3%), secondary alkanols (0.1%) and 5-oxotritriacontane-12,14-dione (0.1%).     

Competitive effects and responses of the invasive grass Eragrostis plana in Río de la Plata grasslands

The ability of an invasive species to establish is mostly determined by its biotic interactions with native species from the recipient community. Here, we evaluate the competitive effects and responses of the invasive Eragrostis plana when interacting with native species, in order to identify possible mechanisms driving invasion in Río de la Plata grasslands. A pairwise competition experiment was performed consisting of treatments that varied in the identity of neighbour plant species: (i) control (no interaction); (ii) intraspecific interaction; (iii) interspecific interaction between native and invasive species; and (iv) interspecific interaction between two co‐occurring native species. Data analysis was separated into the effect of E. plana on the performance of three native perennial grasses (target species: Aristida laevis, Eragrostis neesii and Paspalum notatum) and the response of E. plana to natives (target species: E. plana). Separately for each target species, components of plant performance were compared between neighbouring species treatments. We found that the strength of competitive interactions depended on both target and neighbour species identity. Regarding natives, interspecific competition was stronger than intraspecific. Native species showed distinctive responses to whether the neighbour was the invasive or a co‐occurring native (Eragrostis lugens). Competition between E. plana and native species was stronger than between co‐occurring natives. We demonstrated E. plana had a greater negative effect on native's species performance than the native congener E. lugens. Regarding E. plana, intraspecific competition was stronger than interspecific, and its response was positive or neutral when interacting with natives, suggesting its high tolerance to grow in competition with neighbours. We conclude E. plana's negative effects on native species performance, and its positive or neutral responses to neighbouring native plants demonstrate its strong competitive ability in the recipient community. This may explain its invasion success in southern Brazil and in the encompassing Río de la Plata grasslands. Abstract in Spanish is available with online material.     

不同光照质量和刈割强度对小糠草无性繁殖特性的影响

本实验于1996年在美国德克萨斯理工大学草原,野生动物和渔类系的温室和实验室中进行,实验材料均为盆栽糠草,实验设计为在自然光照下（R／FR＝1．1）,以不同留茬高度（10,15,20cm和不刈割）作为不同刈割强度,用不同红光／远红光比例（R／FR＝1．3和0．7）处理不同刈割强度的小糠草,观测不同处理对小糠草无性繁殖特性的影响,结果表明,小糠草净增蘖数随刈割强度增加而减少,除不刈割处理外,光照质量变化（R／FR的比例）对分蘖性能影响不大,所有刈割强度下都不存在分蘖的补偿性生长效应,但幼叶伸长速度随刈割强度的增大而加快,可以认为小糠草应适度利用,强度利用或不利均不利于该草生长发育。     

Impacts of introduced grasses on breeding season habitat use by northern bobwhite in the South Texas plains

Introduced grasses may affect diversity of native fauna and flora adversely, and disrupt ecosystem processes. Many rangelands in South Texas have been seeded to or have been colonized by buffelgrass (Pennisetum ciliare) and Lehmann lovegrass (Eragrostis lehmanniana), perennial bunchgrasses native to Africa. The objective of this research was to quantify impacts that these 2 species of introduced grasses may have on northern bobwhite (Colinus virginianus) habitat use on South Texas rangelands during the breeding period (Apr–Aug). We evaluated the effects of buffelgrass and Lehmann lovegrass on northern bobwhite nest habitat (n = 35 nests) and general habitat use sites (n = 86 radiomarked quail) with logistic regression and habitat selection functions based on simple saddlepoint approximations. Buffelgrass was used as a nesting substrate at 11% of nests; however, vegetation height and visual obstruction between 1 cm and 30 cm were the best predictors of nest site use. Areas of introduced grass coverage ≥15–20% were avoided by northern bobwhites at general habitat use organism-centered points, but not at nest site use points. Introduced grass coverage and forb coverage were the best predictors of general habitat use, and bobwhites avoided areas with ≥18% introduced grass cover. These results suggest that avoidance of areas with extensive introduced grass cover may indicate a reduction in usable habitat space for northern bobwhite in the western South Texas plains. Maintaining native grass stands while implementing localized control of introduced grasses could be used as a strategy to promote habitat for northern bobwhites. © 2011 The Wildlife Society.