Marginal croplands, such as those in the Conservation Reserve Program (CRP), have been suggested as a source of biomass for biofuel production. However, little is known about the composition of plant ...species on these conservation grasslands or their potential for ethanol production. Our objective was to assess the potential of CRP and other conservation grasslands for biofuel production, describing the relationships of plant species richness and tall native C4 prairie grass abundance with plant chemical composition and the resulting potential ethanol yield. We determined plant species composition and diversity at multiple scales with the modified Whittaker plot technique, aboveground biomass, plant chemical composition, and potential ethanol yield at 34 sites across the major ecological regions of the northeastern USA. Conservation grasslands with higher numbers of plant species had lower biomass yields and a lower ethanol yield per unit biomass compared with sites with fewer species. Thus, biofuel yield per unit land area decreased by 77% as plant species richness increased from 3 to 12.8 species per m2. We found that, as tall native C4 prairie grass abundance increased from 1.7% to 81.6%, the number of plant species decreased and aboveground biomass per unit land area and ethanol yield per unit biomass increased resulting in a 500% increased biofuel yield per unit land area. Plant species richness and composition are key determinants of biomass and ethanol yields from conservation grasslands and have implications for low-input high-diversity systems. Designing systems to include a large proportion of species with undesirable fermentation characteristics could reduce ethanol yields.
1. Seeding is an important management tool in aridland restoration, but seeded species often fail to establish. Previous research has largely focused on the technical aspects of seeding with little ...effort directed at identifying demographic processes driving recruitment failures. 2. In tilled plots, in each of 3 years, we estimated life stage transition probabilities for three species commonly used in sage steppe restoration. We also took similar measurements on seed sown by managers following four major fires. 3. Point estimates and associated Bayesian confidence intervals demonstrated germination probabilities that were consistently high, averaging 0·72. However, estimates suggest only 17 and 7% of the germinated seeds emerged in the tilled plots and fire sites, respectively. Following emergence, survival across the seedling, juvenile and adult transitions averaged 0·72. This suggests the transition from a germinated seed to an emerged seedling was the major bottleneck in recruitment. Although most individuals died during emergence, this was not always the principal source of variation in recruitment across sites. 4. Synthesis and applications. Processes occurring after emergence, such as mortality during spring and summer drought, may contribute to site-to-site variation in recruitment but are unlikely to be the main causes of restoration failures. Instead, recruitment may largely be determined by processes occurring during emergence, such as freezing and thawing of the seedbed, development of physical soil crusts and pathogen attack on germinated seeds. Using tools such as seed coatings and soil amendments to manage processes inhibiting emergence and developing seed mixes with higher emergence probabilities are likely to greatly improve restoration outcomes in the sage steppe and similar aridland systems.
Woody‐plant encroachment is a global phenomenon that has been affecting the southwestern United States since the late 1800s. Drought, overgrazing, herbivory, and competition between grasses and shrub ...seedlings have been hypothesized as the main drivers of shrub establishment. However, there is limited knowledge about the interactions among these drivers. Using a rainfall manipulation system and various herbivore exclosures, we tested hypotheses about how precipitation (PPT), competition between grasses and shrub seedlings, and predation affect the germination and first‐year survival of mesquite (Prosopis glandulosa), a shrub that has encroached in Southern Great Plains and Chihuahuan Desert grasslands. We found that mesquite germination and survival (1) increased with increasing PPT, then saturated at about the mean growing season PPT level, (2) that competition between grasses and shrub seedlings had no effect on either germination or survival, and (3) that herbivory by small mammals decreased seedling establishment and survival, while ant granivory showed no effect. In addition to its direct positive effect on survival, PPT had an indirect negative effect via increasing small mammal activity. Current models predict a decrease in PPT in the southwestern United States with increased frequency of extreme events. The non‐linear nature of PPT effects on Mesquite recruitment suggests asymmetric responses, wherein drought has a relatively greater negative effect than the positive effect of wet years. Indirect effects of PPT, through its effects on small mammal abundance, highlight the importance of accounting for interactions between biotic and abiotic drivers of shrub encroachment. This study provides quantitative basis for developing tools that can inform effective shrub management strategies in grasslands and savannas.
During the revision of the Stipeae (Poaceae) for the Argentinean flora and in accordance to the latest phylogenetic studies in the tribe, it became necessary to transfer some recently described taxa ...from the genus Stipa to Nassella, Jarava or Pappostipa. As a result, 12 new combinations are here proposed: Jarava ichu var. pungens, Nassella brachyglumis, N. macrotricha, Pappostipa arenicola, P. choconensis, P. colloncurensis, P. frigida var. longifolia, P. jucunda, P. kieslingii, P. mapuche, P. marqueziana and P. zulmae. A key to identify the genera of Stipeae in Argentina is also included.
1. The stress-gradient hypothesis (SGH) predicts an increasing importance of facilitative mechanisms relative to competition along gradients of increasing environmental stress. Although developed ...across a variety of ecosystems, the SGH's relevance to the dynamic tree—grass systems of global savannas remains unclear. Here, we present a meta-analysis of empirical studies to explore emergent patterns of tree—grass relationships in global savannas in the context of the SGH. 2. We quantified the net effect of trees on understorey grass production relative to production away from tree canopies along a rainfall gradient in tropical and temperate savannas and compared these findings to the predictions of the SGH. We also analysed soil and plant nutrient concentrations in subcanopy and open-grassland areas to investigate the potential role of nutrients in determining grass production in the presence and absence of trees. 3. Our meta-analysis revealed a shift from net competitive to net facilitative effects of trees on subcanopy grass production with decreasing annual precipitation, consistent with the SGH. We also found a significant difference between sites from Africa and North America, suggesting differences in tree—grass interactions in the savannas of tropical and temperate regions. 4. Nutrient analyses indicate no change in nutrient ratios along the rainfall gradient, but consistent nutrient enrichment under tree canopies. 5. Synthesis. Our results help to resolve questions about the SGH in semi-arid systems, demonstrating that in mixed tree—grass systems, trees facilitate grass growth in drier regions and suppress grass growth in wetter regions. Relationships differ, however, between African and North American sites representing tropical and temperate bioclimates, respectively. The results of this meta-analysis advance our understanding of tree—grass interactions in savannas and contribute a valuable data set to the developing theory behind the SGH.
Grasses and grasslands are of increasing interest to conservationists, biologists, and gardeners. There are more than 300 species of native California grasses and they are found in almost every ...climate—from cool, wet forests to hot, dry deserts. Native grasses are also important to land restoration as they improve soil quality, increase water infiltration, and recycle nutrients. Their deep roots can tap soil water, which allows them to stay green year-round and to act as fire buffers around residences. Native grasses also provide vital habitat for many species of insects, birds, reptiles, and mammals. Despite their importance, grasslands remain one of the most underprotected of California's vegetation types, and native grasslands have undergone the greatest percentage loss of any habitat type in the state. Grasses are also among the most difficult plants to identify. Organized alphabetically, Field Guide to Grasses of California covers common native and naturalized grasses and, to help identify them, also features over 180 color illustrations.
Background IgE sensitization against grass pollen is a cause of seasonal allergic rhinitis. Objective We sought to investigate the evolution at the molecular level and the preclinical predictive ...value of IgE responses against grass pollen. Methods The German Multicentre Allergy Study examined a birth cohort born in 1990. A questionnaire was administered yearly, and blood samples were collected at 1, 2, 3, 5, 6, 7, 10, and 13 years of age. Grass pollen–related seasonal allergic rhinitis (SARg) was diagnosed according to nasal symptoms in June/July. Serum IgE antibodies to Phleum pratense extract and 8 P pratense molecules were tested with immune-enzymatic singleplex and multiplex assays, respectively. Results One hundred seventy-seven of the 820 examined children had SARg. A weak monomolecular/oligomolecular IgE response to P pratense was observed very frequently before SARg onset. These initial IgE responses increased in concentration and molecular complexity during the preclinical and clinical process. A typical progression of IgE sensitization was observed: Phl p 1 (initiator in >75% of cases); then Phl p 4 and Phl p 5; then Phl p 2, Phl p 6, and Phl p 11; and then Phl p 12 and Phl p 7. At age 3 years, IgE sensitization predicted SARg by age 12 years (positive predictive value, 68% 95% CI, 50% to 82%; negative predictive value, 84% 95% CI, 80% to 87%). At this preclinical prediction time, the number of recognized molecules and the serum levels of IgE to P pratense were significantly lower than at 3 or more years after SARg onset. Conclusions The IgE response against grass pollen molecules can start years before disease onset as a weak monosensitization or oligosensitization phenomenon. It can increase in serum concentration and complexity through a “molecular spreading” process during preclinical and early clinical disease stages. Testing IgE sensitization at a preclinical stage facilitates prediction of seasonal allergic rhinitis at its molecular monosensitization or oligosensitization stage.
Aim
Little is known about the distribution of grasses throughout Australia. Using endemism as a basis for understanding biogeographical distributions, we hypothesised that contemporary species ...richness would be the result of environmental factors and dynamic ecological interactions spanning more than 25 Ma.
Location
Australia.
Taxon
Grasses.
Methods
We mapped the distribution of all Australian grass species and modelled climatic and landscape correlates according to photosynthetic type (C3 or C4), endemism, age in Australia, phylogenetic lineage and traits linked to dominance, using height as a proxy. Age classes comprised ‘Ancient’ (Gondwanan), and three others related to migration during the Sunda‐Sahul Interchange (SSI): Early, Mid or Recent. In some analyses, ‘Ancient’, ‘Early SSI’ and ‘Mid SSI’ were combined into ‘Pre‐Recent SSI’.
Results
Overall, species richness of C4 grasses increased with warmer mean annual temperatures, while richness of C3 grasses was higher in cooler areas. Recent SSI species had strong associations with summer rains and were dominant in the continent's northeast, with Pre‐Recent SSI species concentrated in the southeast, a pattern largely reflecting photosynthetic type (C4 and C3 respectively). Endemic and shared species distribution patterns support a migration sequence in which most C3 Pooideae and Panicoideae genera arrived in Australia before the Pliocene aridifications, followed by C4 Chloridoideae as aridification increased, with C4 Andropogoneae immigrating most recently across Lake Carpentaria's open habitats in the later Pleistocene. Recent SSI shared species were significantly taller than Pre‐Recent SSI endemic grasses.
Main Conclusions
The few grasses present in Australia before the Pliocene grew in cooler areas. The influx of taller Recent SSI grasses contributed to dramatic environmental changes—including creation of the northern savannas—with repercussions for resident taxa. Contemporary methods of fuel management could be promoting invasion by grass, thereby jeopardising the conditions suited to ancient taxa and threatening the region's evolutionary history.
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