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CLINQUART, A., C. BRUNDSEAUX, I. DUFRASNE, L. ISTASSE, and D. MICOL. "Utilisation des matières grasses chez les bovins à l’engraissement." INRAE Productions Animales 8, no. 1 (February 21, 1995): 29–42. http://dx.doi.org/10.20870/productions-animales.1995.8.1.4102.
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L’incorporation de matière grasse dans les rations d’engraissement de bovins est une technique courante. Différents buts sont poursuivis : augmenter la teneur en énergie de la ration, faciliter la finition des animaux ou manipuler la teneur en acides gras insaturés de la graisse. L’incorporation des matières grasses se fait sous forme de graisses purifiées d’origine végétale ou animale ou sous forme de graines ou de fèves oléagineuses. Généralement, ces dernières subissent des traitements technologiques, avec comme conséquence, par exemple, une augmentation des acides gras à chaîne plus courte et saturés. Vu l’origine extrêmement variée des graisses utilisées, les effets observés chez les animaux sont parfois divergents.
L’utilisation de graisses dans des rations d’engraissement a tendance à réduire l’intensité des fermentations dans le rumen et à les orienter vers une production plus importante d’acide propionique. Les données de la littérature indiquent que l’incorporation de matière grasse a tendance à réduire la digestibilité apparente de la matière sèche et de la matière organique et à augmenter la digestibilité de l’extrait éthéré.
Les principaux effets sur les performances zootechniques sont une réduction de la durée d’engraissement, une augmentation des gains de poids, une réduction des ingestions, et par conséquent une amélioration de l’indice de consommation. Les auteurs signalent généralement une augmentation du poids des carcasses et du rendement à l’abattage. Les carcasses sont souvent plus grasses. La composition chimique de la viande et celle du muscle, c’est-à-dire de la viande maigre, ne semblent pas être modifiées. La supplémentation avec des graisses d’origine animale entraîne une diminution plus ou moins importante de la proportion des acides gras insaturés. A l’opposé, l’utilisation des graisses d’origine végétale se caractérise par une augmentation de la proportion des acides gras insaturés.
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BAS, P., and D. SAUVANT. "Variations de la composition des dépôts lipidiques chez les bovins." INRAE Productions Animales 14, no. 5 (December 19, 2001): 311–22. http://dx.doi.org/10.20870/productions-animales.2001.14.5.3755.
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La teneur et le profil des acides gras (AG) des dépôts adipeux et des muscles influencent la qualité de la viande. Les principales causes de variation de la composition des lipides de ces dépôts ont été étudiées chez les bovins par méta-analyse des données publiées. Le taux de lipides intramusculaires est influencé par le génotype et par le niveau d’ingestion d’énergie. L’accroissement des teneurs en lipides intramusculaires est presque exclusivement constitué de triglycérides (TG). La teneur en phospholipides (PL) varie peu pour un type de muscle donné. Les TG sont plus riches en AG monoinsaturés (AGMI) et en AG saturés (AGS) (TG / PL = 1,9 - 1,3 - 4,5 - 1,2 et 1,1 pour les AGMI - AGS - C14:0 - C16:0 et C18:0, respectivement) mais plus pauvres en AG polyinsaturés (TG / PL : environ 1/15 pour les AGPI) que les PL. Avec des rations contenant des aliments concentrés non supplémentés en matières grasses, les dépôts adipeux et les muscles présentent des teneurs plus faibles en C18:0 et en C18:3 mais plus élevées en C18:1 qu’avec des rations constituées uniquement de fourrage. En outre, dans les lipides intramusculaires, le rapport des AGPI n-6/n-3 est plus élevé avec des aliments concentrés qu’avec du fourrage. Excepté les huiles de palme et les graines de coton, les matières grasses végétales réduisent les teneurs en AGS dans les dépôts adipeux par rapport aux matières grasses d’origine animale. Les graines de lin et de carthame induisent les teneurs en AGPI les plus élevées dans les dépôts adipeux et le lin induit les teneurs les plus élevées en C18:3 dans les muscles. Dans les muscles, les teneurs en C18:2 sont peu influencées par la nature de la matière grasse ajoutée à la ration lorsque celle-ci n’est pas protégée. Les huiles de poisson diminuent les teneurs en C18:0 des muscles et augmentent les teneurs en AGPI à longue chaîne de la série n-3. Une supplémentation de la ration en matières grasses a un effet différent sur la composition en acides gras des triglycérides et des phospholipides des muscles selon la proportion relative des différentes classes de lipides.
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Ludwig, J., and D. Tongway. "Clearing savannas for use as rangelands in Queensland: altered landscapes and water-erosion processes." Rangeland Journal 24, no. 1 (2002): 83. http://dx.doi.org/10.1071/rj02004.
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This paper presents a framework and some examples of how tree clearing alters landscapes (vegetation structure and faunal habitat) and processes (run-off and soil erosion) for eucalypt savannas in Queensland. Unaltered savannas have a tree-layer and a well-covered ground-layer of perennial grasses, and they provide habitats favoured by a variety of open woodland birds, reptiles and small mammals. Because unaltered savannas have a high ground-cover, they have low rates of run-off and erosion. When savannas are chained, but otherwise unaltered, trees rapidly regrow and increase in canopy cover. The exotic buffel grass often establishes in chained regrowth (especially if grazed), although the cover of native grasses such as black speargrass remains high (unless heavily grazed). We found that open woodland birds declined on these chained regrowth sites, except for the Weebill, which increased in abundance. When savannas are cleared of trees and woody debris and developed as improved pasture systems, both exotic and native perennial grass increased in cover. However, open woodland fauna abundance declined whereas grassland fauna such as the Red-backed Fairy-wren and the House Mouse increased in abundance. If these pasture sites are heavily utilised by livestock so that ground-cover is reduced, rates of run-off and soil loss are likely to rapidly increase, especially as cover declines below 40%. These run-off and erosion findings suggest that the manner in which savanna landscapes are cleared and subsequently used will have flow-on effects at catchment scales.
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Chappe, P., A. Mourey, and J. Manem. "La microflore de boues aérobies acclimatées à des teneurs élevées en graisse." Revue des sciences de l'eau 7, no. 4 (April 12, 2005): 395–404. http://dx.doi.org/10.7202/705208ar.
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Le travail présenté dans cet article a pour but d'isoler les principaux micro-organismes impliqués dans la biodégradation des lipides concentrés dans des réacteurs spécifiques de stations d'épuration des eaux et d'étudier leur action sur ce type de substrat. La microflore d'une boue activée « classique » est comparée à celle de boues acclimatées à des teneurs élevées en lipides selon un nouveau procédé « BIOMASTER® G ». Cela montre un enrichissement en bactéries fortement lipolytiques dans le système à l'équilibre. En effet, la boue activée « classique » ne contient aucun microorganisme fortement lipolytique alors qu'à partir de la boue acclimatée du même site on a pu en isoler, Acinetobacter calcoaceticus et Pseudomonas putida étant les constituants les plus actifs. L'utilisation de bioadditifs du commerce pour l'ensemencement des pilotes au lancement du système ne semble pas apporter d'avantages décisifs puisqu'on ne retrouve pas à l'équilibre les micro-organismes contenus dans ces bioadditifs. Par contre, d'autres microorganismes à pouvoir lipolytique élevé sont détectés tels que Pseudomonas sp., Aeromonas hydrophila et Staphylococcus sp . Le genre Pseudomonas est par ailleurs presque toujours rencontré quelle que soit la boue acclimatée examinée. De même, on peut noter la quasi absence de bactéries Gram positif. Tous les isolats Gram négatif dégradent plus ou moins les acides gras de longueur de chaîne variée. Le seul isolat Gram positif est inhibé ou même tué par les acides gras à chaîne moyenne ou courte et cela peut contribuer à la pauvreté en bactéries Gram positif dans les boues acclimatées. Les genres principaux que nous avons rencontrés, Pseudomonas, Acinetobacter et Aeromonas, sont capables d'assurer à la fois la lipolyse (libération des acides gras) et l'oxydation subséquente des acides gras. L'enrichissement naturel de la microflore lipolytique des boues activées dans le procédé aboutit à une microflore acclimatée capable d'assurer la biodégradation complète des lipides.
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Hamilton, Natalia P., Stephanie G. Yelenik, Tara D. Durboraw, Robert D. Cox, and Nathan S. Gill. "Understanding Grass Invasion, Fire Severity, and Acacia koa Regeneration for Forest Restoration in Hawaiʻi Volcanoes National Park." Land 10, no. 9 (September 10, 2021): 962. http://dx.doi.org/10.3390/land10090962.
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With invasive grasses increasing wildfire occurrence worldwide, a better understanding of the relationships between native plants, fire, and invasive grass is needed to help restoration plans facilitate ecosystem resilience. Invasive grasses are particularly problematic for altering fire regimes in the tropics, yet in Hawaiʻi, restoration sites are often planted with monocultures of the native tree Acacia koa, which can promote grass growth via nitrogen fixation. This, combined with the difficulty of estimating pre-fire grass cover under thick canopies, complicates attempts to restore Hawaiian ecosystems. We studied the 2018 Keauhou Ranch Fire in Hawaiʻi to investigate three questions: (1) at what level of precision can pre-fire grass cover be accurately estimated from oblique aerial photos? (2) how are post-fire A. koa regeneration densities affected by fire severity? and (3) how are post-fire A. koa regeneration densities affected by pre-fire grass cover and its interaction with fire severity? We collected burn severity and post-fire regeneration data from 30 transects stratified across mid-elevation woodland, montane woodland, and montane shrubland communities. We evaluated visual estimates of pre-fire grass cover from oblique aerial imagery with quantitative in situ data from 60 unburned transects of the same cover types. Pre-fire estimates of grass cover categories were 67% accurate in montane woodland (n = 9) and 100% accurate in montane shrubland (n = 11), but only 20% accurate in mid-elevation woodland (n = 10). In montane woodlands with low pre-fire tree densities, A. koa regeneration densities were higher with increased fire severity, but this trend reversed when pre-fire tree densities were high. We detected no effect of pre-fire grass cover, nor its interaction with fire severity, on A. koa regeneration density. This indicates that restoration through the planting of A. koa may be successful in promoting fire-resilient A. koa forest, although there are potential issues to consider regarding the effects that A. koa’s grass promotion may have on other species within the ecosystem.
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LUCAS, A., S. HULIN, V. MICHEL, C. AGABRIEL, J. F. CHAMBA, E. ROCK, and J. B. COULON. "Relations entre les conditions de production du lait et les teneurs en composés d’intérêt nutritionnel dans le fromage : étude en conditions réelles de production." INRAE Productions Animales 19, no. 1 (March 12, 2006): 15–28. http://dx.doi.org/10.20870/productions-animales.2006.19.1.3477.
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Les relations entre les conditions de production du lait et les teneurs en composés d’intérêt nutritionnel de fromages fermiers au lait de vache ou de chèvre ont été étudiées en conditions réelles de production au sein de 4 filières fromagères (Abondance, Tomme de Savoie, Salers/Cantal et Rocamadour). Au total, 432 fromages, dont 306 au lait de vache et 126 au lait de chèvre, produits tout au long de l’année par 74 producteurs fermiers ont été analysés. Dans un premier temps, les effets respectifs des conditions de production du lait et de la transformation fromagère sur la variabilité de composition du fromage ont été quantifiés. Dans un second temps, les relations entre la composition du fromage et les conditions de production du lait, préalablement identifiées au moyen d’enquêtes, ont été étudiées. Le fromage fermier se caractérise par une grande variabilité de composition qui dépend majoritairement de la transformation fromagère pour la vitamine B9 et les minéraux et des conditions de production du lait pour les acides gras (AG), les vitamines A et E et les caroténoïdes. L’espèce animale explique une grande partie de la variabilité en certains AG et en β-carotène dans le fromage. Les teneurs en micronutriments liposolubles et le potentiel antioxydant du fromage dépendent principalement de la nature de la ration fourragère (pâturage vs fourrages conservés) quelle que soit l’espèce animale. Les rations à base de pâturage sont associées à des teneurs en caroténoïdes et en vitamines A et E et à un potentiel antioxydant dans le fromage plus importants. En revanche, les facteurs de variation du profil en AG du fromage ont différé dans cette étude entre les vaches et les chèvres. Pour les fromages au lait de vache, il dépend principalement de la nature de la ration fourragère (pâturage vs fourrages conservés). Les fromages associés au pâturage sont plus riches en AG saturés et insaturés à longue chaîne (≥ C18) et plus pauvres en AG saturés à courte et moyenne chaîne (C6:0 à C16:0). Le profil en AG du fromage au lait de chèvre dépend principalement de la proportion de matières grasses apportées par les concentrés dans la ration, du stade de lactation des animaux et dans une moindre mesure de la présence ou non de lin dans les concentrés. Ce fromage est plus riche en AG à longue chaîne et plus pauvre en AG saturés à courte et moyenne chaîne lorsque la proportion de matières grasses apportées par les concentrés est plus importante, les concentrés contiennent du lin et les animaux sont en début de lactation. En conclusion, ce travail a permis de collecter des données représentatives et détaillées sur les caractéristiques nutritionnelles de différentes variétés fromagères et de hiérarchiser les effets des principaux facteurs de production responsables de la variabilité de composition du fromage.
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Ragot, Bernadette. "Les bonnes matières grasses qui protègent chacune de nos cellules." Hegel N° 3, no. 3 (2017): 211. http://dx.doi.org/10.4267/2042/62696.
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DOREAU, M., and Y. CHILLIARD. "Influence d’une supplémentation de la ration en lipides sur la qualité du lait chez la vache." INRAE Productions Animales 5, no. 2 (February 28, 1992): 103–11. http://dx.doi.org/10.20870/productions-animales.1992.5.2.4224.
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L’enrichissement en matières grasses des rations est couramment pratiqué pour les vaches laitières fortes productrices. L’une des conséquences les plus fréquentes est la diminution de la teneur en protéines, et plus particulièrement en caséines du lait. Les causes en sont encore mal connues. Une partie de cet effet est liée à la dilution des protéines dans un volume accru de lait, car la sécrétion totale de protéines n’est que peu affectée. La diminution du taux protéique est beaucoup plus modérée au début de la lactation, où l’effet positif sur la production laitière est moins net, qu’après le pic de production. L’incorporation de matières grasses dans les rations a un effet très variable sur le taux butyreux, qui dépend du bilan entre l’augmentation des acides gras longs d’origine alimentaire et la réduction de la synthèse mammaire des acides gras à chaîne courte ou moyenne. La teneur en acides gras polyinsaturés dans le lait n’est presque jamais fortement modifiée, en raison de l’hydrogénation des lipides alimentaires dans le rumen. Seule la technique d’encapsulation des lipides dans une coque de protéines tannées protège les lipides alimentaires de l’hydrogénation ruminale. Certains types de suppléments lipidiques entraînent une détérioration de la valeur organoleptique des produits laitiers, en particulier par oxydation et rancissement.
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BAUCHART, D., D. DURAND, D. GRUFFAT-MOUTY, C. PIOT, B. GRAULET, Y. CHILLIARD, and J. F. HOCQUETTE. "Transport sanguin et métabolisme tissulaire des lipides chez le veau de boucherie. Effets du remplacement du suif par de l’huile de coprah dans l’aliment d’allaitement." INRAE Productions Animales 12, no. 4 (September 1, 1999): 273–85. http://dx.doi.org/10.20870/productions-animales.1999.12.4.3888.
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Cet article décrit le transport sanguin et le métabolisme tissulaire des lipides chez le veau de boucherie recevant un aliment d’allaitement à base d’huile de coprah (riche en acides gras à chaîne moyenne) ou de suif (riche en acides gras longs saturés et insaturés). L’huile de coprah élève fortement la lipémie, notamment les teneurs en cholestérol et en phospholipides. Ses acides gras de type C12:0 et C14:0 sont transportés sélectivement dans les lipoprotéines riches en triglycérides (38 %) ou en cholestérol (44 %).Dans le foie, le captage des acides gras de l’huile de coprah entraîne une stéatose hépatique marquée, due à une teneur accrue en triglycérides (×18). Ceci s’expliquerait à la fois par une élongation des produits de l’oxydation des acides gras à chaîne moyenne (C12:0), par une oxydation plus faible et une estérification en triglycérides accrue des acides gras longs (C18:1n-9) et par une capacité de sécrétion des triglycérides faible et peu modulée. Le potentiel d’oxydation des acides gras dans les tissus musculaires et le potentiel lipogénique du tissu adipeux périrénal ne sont pas influencés par les acides gras alimentaires. En revanche, la composition en acides gras des tissus musculaires et adipeux est fortement marquée avec le régime coprah par l’accumulation du C12:0 et surtout du C14:0 (au détriment du C18:1 n-9) conduisant à élever le degré de saturation des acides gras des lipides de dépôt. En conclusion, l’emploi de l’huile de coprah comme seule source de matières grasses alimentaires n’est pas recommandée chez le veau de boucherie en raison de l’altération du métabolisme du foie (stéatose), de l’absence d’amélioration des performances de croissance et de la dépréciation de la qualité diététique de la viande pour le consommateur par le dépôt accru d’acides gras saturés à propriétés athérogènes.
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Singh, M., T. Durali, and A. J. Cowieson. "Use of n-alkanes for determination of Kikuyu grass (Pennisetum clandestinum) intake in free-range broilers." Animal Production Science 56, no. 7 (2016): 1152. http://dx.doi.org/10.1071/an14778.
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N-alkanes, long-chained saturated hydrocarbons occurring in plant cuticles, were used for estimating grass intake in fast-growing, free-range broilers. A total of 1440 as hatched mixed sex Cobb 500 broilers were equally divided between one of four experimental treatments in a 2 by 2 factorial arrangement involving conventional (barn) or free-range (barn and range access) production systems and diets (crude protein: 21%, metabolisable energy: 13 MJ/K) with or without in-feed antibiotic (Zinc Bacitracin: Albac® G 150 antibiotic feed premix, Pfizer Australia Pty Ltd, Sydney, NSW, Australia). Day-old chicks were randomly allocated to 48 pens (12 replicates/treatment) with 30 birds in each pen. Chicks were assigned to treatment diets on Day 1 while free-range access was available to birds from Day 21 onwards. Alkane concentrations in litter were measured and compared with alkane profiles of the intake components (grass, diet pellets and woodchip). Correction for incomplete recovery followed by estimation using a non-negative least square procedure resulted in calculation of total grass intake from the range area. Kikuyu grass consumption was estimated to be 13.5–14.7% of total ‘as-fed’ intake, equating to 6.34–6.78 g of grass per bird per hour of range access in this study. Taking into account grass consumption, this resulted in a significant increase in feed intake by 8.7–8.9% (P < 0.01) and feed conversion ratio from 2.30 to 2.54 points (P < 0.01). It can be concluded that broilers reared under free-range conditions eat a substantial quantity of grass. However, the nutrient profile of grass is not complementary to the formulated ration and its consumption is likely to lead to an array of nutritional changes for the bird, thus affecting performance.
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deBortoli, Leah A., Bradley D. Pinno, M. Derek MacKenzie, and Edith H. Y. Li. "Plant community composition and tree seedling establishment in response to seeding and weeding treatments on different reclamation cover soils." Canadian Journal of Forest Research 49, no. 7 (July 2019): 836–43. http://dx.doi.org/10.1139/cjfr-2018-0363.
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The majority of plant diversity in North American boreal forests is comprised of understory plant communities undergoing continuous interspecific competition. Anthropogenic activities, particularly surface mining, have introduced higher severity disturbances that not only remove vegetation, but also modify soil. During reclamation, soils used to cap overburden materials have inhibited native plant growth and increased weed invasion. This study aimed to examine the effectiveness of seeding and weeding treatments for promoting the establishment of native understory plant communities, as well as a common deciduous tree species, on three different reclamation cover soils (forest floor – mineral mix, peat–mineral mix, and transitional). The broadcasting of a native forb seed mix was not successful on any of the cover soils, whereas weeding affected each cover soil differently. With weeding, the forest floor – mineral mix and transitional cover soils experienced a decrease in the relative abundance of introduced forbs and an increase in the relative abundance of graminoids. The increase in graminoid cover on the forest floor – mineral mix was mostly attributed to the expansion of Calamagrostis canadensis (Michx.) P. Beauv. Overall, weeding effectively eliminated introduced plant species, allowing competitive native grasses to establish. However, weeding may have unintentionally hindered the development of a native understory plant community via the over-establishment of grass on reclamation sites.
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WEIGL, PETER D., and TRAVIS W. KNOWLES. "Megaherbivores and Southern Appalachian Grass Balds." Growth and Change 26, no. 3 (July 1995): 365–82. http://dx.doi.org/10.1111/j.1468-2257.1995.tb00176.x.
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Lieffers, Victor J., S. Ellen Macdonald, and Edward H. Hogg. "Ecology of and control strategies for Calamagrostiscanadensis in boreal forest sites." Canadian Journal of Forest Research 23, no. 10 (October 1, 1993): 2070–77. http://dx.doi.org/10.1139/x93-258.
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Calamagrostiscanadensis (Michx.) Beauv. is a widely distributed rhizomatous grass that can seriously inhibit growth of white spruce (Piceaglauca (Moench) Voss) seedlings in the boreal forests of North America. We review the dynamics of this grass during four successional stages: the colonization of disturbed sites; dominance of the site by the grass a few years after disturbance; gradual loss of dominance with overstory development; and maintenance of the grass at low levels in the understory of the mature forest. We also describe C. canadensis in relation to recruitment from clonal growth and seed, environmental conditions for growth, the effects of grass litter buildup on conifer seedling microclimate, and overall competitive abilities. Control strategies for C. canadensis are as follows. If the grass is found in nearly every square metre in the understory prior to logging, there will be rapid spread when the stand is clear-cut unless clones are killed using herbicides or a deep burn. Large spruce seedlings, planted on large soil scalps or mounds, coupled with release by way of herbicides or sheep grazing, may be necessary for plantation establishment under conditions of encroachment by C. canadensis. Alternatively, the shade provided by a partial canopy may inhibit the grass sufficiently to allow spruce seedlings to establish. If grass is not abundant in the understory, we recommend (i) minimizing forest floor disturbance to reduce sites for grass seedling colonization or (ii) a slash burn with the hope of encouraging colonization by herbaceous species that have less impact on conifer seedlings.
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Evett, Rand R., Ernesto Franco-Vizcaino, and Scott L. Stephens. "Phytolith evidence for the absence of a prehistoric grass understory in a Jeffrey pine – mixed conifer forest in the Sierra San Pedro Mártir, Mexico." Canadian Journal of Forest Research 37, no. 2 (February 2007): 306–17. http://dx.doi.org/10.1139/x06-240.
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Phytolith analysis was applied to several sites in a Jeffrey pine ( Pinus jeffreyi Grev. & Balf.) – mixed conifer forest in the Sierra San Pedro Mártir, Baja California, Mexico, to explore the hypothesis that the introduction of livestock in the late 18th century led to overgrazing of a prehistoric grass understory, resulting in changes to the prehistoric fire regime observed in the tree-ring fire-scar record. Stable soils in regions with extensive prehistoric grass cover retain a high concentration of total phytoliths and high percentage of grass phytoliths, regardless of historic vegetation changes. Phytoliths extracted from soil samples collected from several sites in the Sierra San Pedro Mártir revealed total phytolith concentrations in forest soils were generally <0.5% by mass, with most <0.1%, whereas grass phytoliths were generally <10% of the total, values consistent with the interpretation of a forest with sparse grass cover in the understory. Phytolith evidence suggests that there was minimal grass available for grazing in prehistoric Sierra San Pedro Mártir forests; overgrazing a grass understory was probably not a major driver of changes in the prehistoric fire regime.
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Sene, Birama, Fallou Sarr, Diegane Diouf, Amadou Kane, and Djibril Traore. "Étude de la composition minérale et des teneurs en protéines et en matières grasses de huit variétés de sésame (Sesamum indicum L.) introduites au Sénégal pour un criblage variétal." OCL 25, no. 6 (August 29, 2018): A601. http://dx.doi.org/10.1051/ocl/2018045.
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Huit variétés de sésame (EF153, EF147, LC162, LC164, HB168, 32-15, 38-1-7 et Birkan) qui, selon le Centre d’Étude Régional pour l’Amélioration de l’Adaptation à la Sécheresse (CERAAS), sont les mieux appréciées sur le plan agro-morphologique, ont fait l’objet de cette étude. Les teneurs en protéines, en matières grasses et en éléments minéraux de chacune d’elles ont été déterminées. L’étude des éléments minéraux a porté sur le calcium, le phosphore, le magnésium, le fer et le zinc. Les résultats ont montré que, pour les huit variétés de sésame étudiées, les teneurs en protéines varient de 22,59 % à 29,37 % tandis que celles en matières grasses s’établissent dans une fourchette de 48,65 % à 52,45 %. L’étude montre aussi que toutes les variétés sont riches en éléments minéraux. Cependant, le calcium demeure l’élément le plus important dans toutes les variétés étudiées, suivi du phosphore, du magnésium, du fer et du zinc. Les meilleures teneurs minérales obtenues, pour tous les minéraux étudiés, sont avec la variété 38-1-7 : magnésium 455,04 mg/100 g ; phosphore 711,17 mg/100 g ; calcium 973,22 mg/100 g de ; fer 10,86 mg/100 g et le zinc 7,88 mg/100 g. L’étude statistique des teneurs en protéines, en matières grasses et en composition minérale des variétés a permis d’identifier trois variétés plus appréciées, mais aussi d’indiquer leurs domaines potentiels d’utilisation. Ainsi, les variétés LC162 et 38-1-7 pourraient être utilisées respectivement comme additifs en protéines et en éléments minéraux dans les aliments destinés aux enfants. Quant à la variété EF147, elle pourrait être recommandée pour la consommation d’huile.
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Rivard, Paul G., Paul M. Woodard, and Richard L. Rothwell. "The effect of water table depth on white spruce (Piceaglauca) seedling growth in association with the marsh reed grass (Calamagrostiscanadensis) on wet mineral soil." Canadian Journal of Forest Research 20, no. 10 (October 1, 1990): 1553–58. http://dx.doi.org/10.1139/x90-207.
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The effect of water table depth (10, 20, and 40 cm) in association with marsh reed grass (CalamagrostisCanadensis (Michx.) Beauv.) on white spruce (Piceaglauca (Moench) Voss) 2 + 0 seedling survival and growth was tested over a 5-month period. All spruce seedlings grown alone survived, whereas, 16.7% of the trees died when grown with reed grass. The root weight and total weight of spruce seedlings and marsh reed grass were significantly affected by the water table depth. The weight of both components increased as the water table decreased. Over 80% of the roots by weight for both species were found in the upper 10 cm of the soil profile regardless of water table depth. The presence of marsh reed grass significantly affected the growth of spruce seedlings. The nutrient concentration of the white spruce foliage was significantly affected by water table depths and the presence of grass.
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Barbehenn, Raymond V., Zhong Chen, David N. Karowe, and Angela Spickard. "C3 grasses have higher nutritional quality than C4 grasses under ambient and elevated atmospheric CO2." Global Change Biology 10, no. 9 (September 2004): 1565–75. http://dx.doi.org/10.1111/j.1365-2486.2004.00833.x.
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Liu, Q., P. Loganathan, M. J. Hedley, and M. F. Skinner. "Root processes influencing phosphorus availability in volcanic soils under young Pinus radiata plantations." Canadian Journal of Forest Research 36, no. 8 (August 1, 2006): 1913–20. http://dx.doi.org/10.1139/x06-083.
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Phosphorus (P) availability was investigated in rhizosphere soils under 4- to 5-year-old, second-rotation Pinus radiata D. Don and understorey grass (browntop, Agrostis capillaris L.) in two P-deficient Andosols (a Pumice Soil and an Allophanic Soil). Pinus radiata rhizosphere had more soil organic matter, greater mycorrhizal hyphal length density, higher acid phosphatase activity, and more concentrated dissolved organic carbon than bulk soil or the rhizosphere of grass species in one or both soils. Concentrations of resin P and organic P in the P. radiata rhizosphere were higher than those in the grass rhizosphere and bulk soils, suggesting that P. radiata rhizosphere processes have a greater potential to accumulate organic P and mobilize soil P than understorey grass rhizosphere processes. This effect was less marked in the Allophanic Soil than in the Pumice Soil, probably because of the higher P-fixing capacity and lower plant-available P concentrations in the Allophanic Soil.
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Kolb, T. E., T. W. Bowersox, and L. H. McCormick. "Influences of light intensity on weed-induced stresses of tree seedlings." Canadian Journal of Forest Research 20, no. 5 (May 1, 1990): 503–7. http://dx.doi.org/10.1139/x90-066.
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Growth of northern red oak (Quercusrubra L.), white ash (Fraxinusamericana L.), and white pine (Pinusstrobus L.) seedlings was evaluated for 2 years after germination in 12 environments that consisted of four levels of herbaceous interference (fern, fern free, grass, grass free) crossed with three levels of light intensity (100, 45, and 20% full sun), at two clear-cuts in central Pennsylvania. Grass and fern interference reduced soil moisture content and reduced height or diameter growth of all species. Shading ameliorated soil moisture, reduced herbaceous growth, generally reduced growth of all tree species in interference-free environments, and had no effect on growth of any tree species in fern and grass environments. Reduction in growth due to herbaceous interference was lower for northern red oak and white pine than for white ash, while shading had similar effects on growth of all species. Results suggest that stresses induced by shading alone have little short-term effect on the establishment of these species under conditions of heavy herbaceous interference.
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Anderson, Hal E. "Moisture diffusivity and response time in fine forest fuels." Canadian Journal of Forest Research 20, no. 3 (March 1, 1990): 315–25. http://dx.doi.org/10.1139/x90-046.
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Fine forest fuels, such as grasses, hardwood leaves, and conifer needles, vary greatly in response times and mean moisture diffusion coefficients when exposed to desorption and adsorption conditions. Results are reported for tests made with recently dead and weathered dead fine forest fuels and small woody samples. Test conditions were 26.7 °C (80°F) with changes in relative humidity from 90 to 20% and back, in an environmental chamber. Moisture diffusivities of fine forest fuels were found to be smaller than diffusivities of woody samples. The diffusivities of the foliage and grass fuels tested ranged from near 1.0 × 10−10 to 1.0 × 10−8 cm2/s, whereas the woody fuels ranged from 1.5 × 10−7 to3.0 × 10−5 cm2/s. Weathered fine fuels had faster response times and higher diffusivities than recently cast materials. Adsorption response times were longer and diffusivities lower than for fuels in desorption. Response times of various recently dead fine fuels ranged from 0.2 to 37 h and weathered fuels from 0.5 to 10 h. Therefore, specific fuel types need to be tested to assign more precise response times. Under the drying conditions of 26.7 °C and 20% relative humidity, fine forest fuels had lower diffusivities and longer response times than anticipated in the United States National Fire Danger Rating System. As a result, predicted fire danger during or after a weather change may be overestimated because fuels are responding more slowly than anticipated. Equations are presented for making first estimates of response time and (or) diffusivity if certain physical properties are known: surface area-to-volume ratio, packing ratio, and bed depth.
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White, Stuart. "Grass páramo as hunter-gatherer landscape." Holocene 23, no. 6 (February 19, 2013): 898–915. http://dx.doi.org/10.1177/0959683612471987.
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Wragg, Peter D. "Holocene book review: Grasses and grassland ecology." Holocene 19, no. 7 (October 23, 2009): 1101–2. http://dx.doi.org/10.1177/0959683609341419.
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Cole, Elizabeth C., and Michael Newton. "Nutrient, moisture, and light relations in 5-year-old Douglas-fir plantations under variable competition." Canadian Journal of Forest Research 16, no. 4 (August 1, 1986): 727–32. http://dx.doi.org/10.1139/x86-130.
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Competition for soil nutrients, moisture, and light was examined in 5-year-old plantations of young coastal Douglas-fir (Pseudotsugamenziesii (Mirb.) Franco var. menziesii) growing at 17- to 123-cm spacings, alone or with either of two competitors, grass (Elymus spp. and Agrostistenuis L.) or red alder (Alnusrubra Bong.), on three different site types in the Oregon Coast Range. Douglas-fir foliar nitrogen concentration and total and available soil nitrogen did not differ significantly by competitor species; however, foliar phosphorus was higher in the grass treatments. Both foliar nitrogen and phosphorus concentrations were significantly lower at high planting densities. Predawn moisture stress varied with site, competitor, and density, the lowest stresses occurring at low densities where Douglas-fir was growing alone. Canopy light penetration varied with competitor, density, and height above ground, the lowest values occurring under the red alder canopy. Grass competed with Douglas-fir seedlings primarily for moisture until crown closure eliminated the grass. Nodulated red alder did not increase soil or Douglas-fir foliar nitrogen on any site or at any density, but competition from red alder trees reduced available light and moisture for Douglas-fir. Regardless of competitor type, high density resulted in increased demands on resources.
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Margolis, H. A., and R. H. Waring. "Carbon and nitrogen allocation patterns of Douglas-fir seedlings fertilized with nitrogen in autumn. II. Field performance." Canadian Journal of Forest Research 16, no. 5 (October 1, 1986): 903–9. http://dx.doi.org/10.1139/x86-161.
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October-fertilized and unfertilized 2-0 Douglas-fir (Pseudotsugamenziesii (Mirb.) Franco) seedlings were outplanted the following February. Half of each planting block was seeded with grass to induce water stress during the typical summer drought. Sucrose was applied to soil around each seedling to limit availability of nitrogen to tree roots. Fertilized seedlings broke bud 9–10 days earlier, produced more shoot growth, and, as shown in later harvests, had higher relative growth rates than unfertilized seedlings. However, initial differences in growth response were due primarily to the earlier budbreak. Seedlings growing with grass had predawn water potentials of −1.5 MPa by early August; by September 3, unfertilized seedlings growing with grass were significantly more stressed than any others. Although free amino acid and total nitrogen concentrations were higher in fertilized than unfertilized seedlings when planted, they became equal by the end of one growing season. However, fertilized seedlings contained more free amino acids and nitrogen because of their greater size. Grass competition affected both seedling nitrogen and carbohydrate chemistry. After one growing season, fertilized seedlings had greater height increment, shoot growth, leaf area, relative growth rate, and production per unit nitrogen. Although autumn fertilization benefited these Douglas-fir seedlings, negative effects could result from carbohydrate depletion because of increased respiration or from frost damage because of earlier budbreak.
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Kwit, Charles, and Beverly Collins. "Native Grasses as a Management Alternative on Vegetated Closure Caps." Environmental Management 41, no. 6 (February 20, 2008): 929–36. http://dx.doi.org/10.1007/s00267-008-9090-x.
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Woodburn, Terri L., William C. Johnson, Joseph A. Mason, Steven R. Bozarth, and Alan F. Halfen. "Vegetation dynamics during the Pleistocene–Holocene transition in the central Great Plains, USA." Holocene 27, no. 1 (July 28, 2016): 155–63. http://dx.doi.org/10.1177/0959683616652710.
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The Holocene–Pleistocene transition in the upland loess-mantled regions of the central Great Plains is punctuated by the Brady Soil, which separates the late-Pleistocene Peoria Loess and the Holocene Bignell Loess. Previous research on the Brady Soil at the Old Wauneta Roadcut site in Southwestern Nebraska has produced paleoenvironmental information based on well-constrained luminescence and radiocarbon ages, stable carbon isotope data, and chemical and physical data. While the research indicated high effective moisture during formation of the Brady Soil and a shift to warm-season C4 vegetation from the cool-season C3-dominated vegetation of the Peoria Loess, those data do not provide any detail as to plant community composition and significant underlying climatic inferences. Assemblages of phytoliths and other biosilicates extracted from the Brady Soil provide specific information on vegetation communities and indicate shifts of plant taxa comprising these assemblages. Short-cell phytolith count data reveal a shift from dominance of Pooideae (C3) grasses, with relatively large numbers of arboreal dicot spheres and a few Cyperaceae (sedge) present in a savannah or open woodland in the Bølling-Allerød, to a mixed, open Chloridoideae (C4) and Pooideae (C3) grassland in the early-Holocene. Stipa-type Pooideae, a cool-season grass preferring drier soil conditions, marks the onset of the Younger Dryas. Large-cell phytoliths such as long cells, bulliforms, and trichomes, provided further definition of the climate history. This comprehensive biosilicate study of the Brady Soil has provided a more detailed paleoclimatic reconstruction than that generated with bulk sediment-derived δ13C data, or even with short-cell phytolith data alone.
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Cole, Elizabeth C., and Michael Newton. "Fifth-year responses of Douglas-fir to crowding and nonconiferous competition." Canadian Journal of Forest Research 17, no. 2 (February 1, 1987): 181–86. http://dx.doi.org/10.1139/x87-031.
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Growth responses from crowding and interspecific competition were examined in 5-year-old plantations of Douglas-fir (Pseudotsugamenziesii (Mirb.) Franco var. menziesii) spaced 17 to 123 cm apart, alone or with either grass or red alder (Alnusrubra Bong.) on three site types in the Oregon Coast Range. Grass and red alder competition and crowding adversely affected growth and standing biomass on a per tree basis. Basal area per hectare and volume per hectare were higher at high densities but these relations are expected to change with time as the larger trees at low densities form fully stocked stands. Grass competition showed greatest effects on growth at the driest site. Although the presence of red alder decreased growth on all sites, the effect was most significant at the coastal site where light is most limiting and moisture is least limiting. If the production of maximum tree size is the primary objective, then low stocking with control of competing vegetation will produce larger trees faster than will other management alternatives.
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Mworia-Maitima, Joseph. "Prehistoric fires and land-cover change in western Kenya: evidences from pollen, charcoal, grass cuticles and grass phytoliths." Holocene 7, no. 4 (December 1997): 409–17. http://dx.doi.org/10.1177/095968369700700404.
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Tuenter, E., S. L. Weber, F. J. Hilgen, and L. J. Lourens. "Simulating sub-Milankovitch climate variations associated with vegetation dynamics." Climate of the Past 3, no. 1 (March 22, 2007): 169–80. http://dx.doi.org/10.5194/cp-3-169-2007.
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Abstract. Climate variability at sub-Milankovitch periods (between 2 and 15 kyr) is studied in a set of transient simulations with a coupled atmosphere/ocean/vegetation model of intermediate complexity (CLIMBER-2). Focus is on the region influenced by the African and Asian summer monsoon. Pronounced variations at periods of about 10 kyr (Asia and Africa) and about 5 kyr (Asia) are found in the monsoonal runoff in response to the precessional forcing. In the model this is due to the following mechanism. For low summer insolation (precession maximum) precipitation is low and desert expands at the expense of grass, while for high insolation (precession minimum) precipitation is high and the tree fraction increases also reducing the grass fraction. This induces sub-Milankovitch variations in the grass fraction and associated variations in the water holding capacity of the soil. The runoff does not exhibit sub-Milankovitch variability when vegetation is kept fixed. High-latitude vegetation also exhibits sub-Milankovitch variability under both obliquity and precessional forcing. We thus hypothesize that sub-Milankovitch variability can occur due to the dynamic response of the vegetation. However, this mechanism should be further tested with more sophisticated climate/vegetation models.
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Tuenter, E., S. L. Weber, F. J. Hilgen, and L. J. Lourens. "Simulating sub-Milankovitch climate variations associated with vegetation dynamics." Climate of the Past Discussions 2, no. 5 (September 11, 2006): 745–69. http://dx.doi.org/10.5194/cpd-2-745-2006.
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Abstract. Climate variability at sub-Milankovitch periods (between 2 and 15 kyr) is studied in a set of transient simulations with a coupled atmosphere/ocean/vegetation model of intermediate complexity (Climber-2). Focus is on the region influenced by the African and Asian summer monsoon. Pronounced variations at sub-Milankovitch periods of about 10 kyr (Asia and Africa) and about 5 kyr (Asia) are found in the monsoonal runoff in response to the precessional forcing. This is caused by the dynamic response of the vegetation. For low summer insolation (precession maximum) precipitation is low and desert expands at the expense of grass, while for high insolation (precession minimum) precipitation is high and the tree fraction increases thus reducing the grass fraction. This induces sub-Milankovitch variations in the grass fraction and associated variations in the water holding capacity of the soil. No sub-Milankovitch variability occurs in the runoff when vegetation is kept fixed. The high-latitude vegetation coverage also exhibits sub-Milankovitch variability under both obliquity as well as precessional forcing. We hypothesize that sub-Milankovitch variations found in terrestrial and marine records are related to variations in vegetation, soil characteristics and runoff influencing ocean salinity and circulation.
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Mason, Euan G. "Interactions between influences of genotype and grass competition on growth and wood stiffness of juvenile radiata pine in a summer-dry environment." Canadian Journal of Forest Research 36, no. 10 (October 1, 2006): 2454–63. http://dx.doi.org/10.1139/x06-098.
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Clones of radiata pine (Pinus radiata D. Don) were established in two experiments on two contrasting pasture sites in Canterbury, New Zealand, with four levels of competition from grass as main plots within each experiment. Control was extended over the first 5 years at one site, whereas grass at the other site was controlled by a single herbicidal spray immediately after planting. At the latter site, 1 m diameter spots cleared with herbicide were compared with the same size spot created using a woven mat. Grass competition added up to 3 years to a rotation, and the gain from control was correlated with spot size. Competition control was most critical during the first year after planting. Trees grown within spots cleared by mats grew more slowly than those in weed-free spots cleared with herbicide. Green dynamic modulus of elasticity was related to genotype and increased with both slenderness and higher levels of pruning. Significant interactions between genotype and level of competition were observed for growth, indicating that choice of genotype can be a useful way of coping with pasture competition if managers wish to reduce the use of herbicides.
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COULON, J. B., and A. PRIOLO. "La qualité sensorielle des produits laitiers et de la viande dépend des fourrages consommés par les animaux." INRAE Productions Animales 15, no. 5 (December 15, 2002): 333–42. http://dx.doi.org/10.20870/productions-animales.2002.15.5.3712.
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La nature des fourrages ingérés par les ruminants est un des facteurs de variation de la qualité sensorielle des produits laitiers et de la viande. L’effet de ce facteur a été récemment mis en évidence, en particulier dans le cadre des produits d’Appelation d’Origine Contrôlée, pour lesquels l’alimentation des animaux constitue un élément important de liaison au terroir.
Sur les fromages, la conservation de l’herbe sous forme d’ensilage ne semble pas entraîner, lorsqu’elle est réalisée dans de bonnes conditions, de modifications importantes des caractéristiques sensorielles, exception faite de la couleur, plus jaune avec l’ensilage. Les régimes à base d’herbe pâturée conduisent à des fromages dont la couleur, le goût et l’odeur sont plus intenses que ceux issus d’une alimentation hivernale à base d’herbe conservée sous forme de foin et d’ensilage. La composition botanique de l’herbe modifie aussi les caractéristiques sensorielles des fromages. Les écarts les plus importants concernent la texture et sont obtenus sur des fromages à pâte pressée cuite lorsque les vaches pâturent des prairies très diversifiées.
Ces différences sensorielles peuvent être dues à des constituants du lait directement issus de l’alimentation. C’est le cas des carotènes, responsables de la couleur jaune des produits laitiers, et qui sont présents en grande quantité dans les fourrages verts. Elles peuvent aussi être liées à des constituants du lait produit par l’animal de manière différentielle selon l’alimentation offerte. C’est le cas de la teneur en plasmine du lait ou de la composition de ses matières grasses, qui peuvent modifier la texture du fromage.
La viande des animaux finis à l’herbe est plus sombre et moins tendre que celle des animaux finis avec des régimes riches en concentrés. Cet effet pourrait être lié d’une part à une modification du pH ultime de la viande (pour la couleur), mais aussi à l’âge à l’abattage (plus avancé avec les régimes à base d’herbe), à l’état d’engraissement des carcasses et à la teneur en gras intramusculaire (plus élevés avec les régimes riches en concentrés), qui peuvent modifier à la fois la couleur et la tendreté des viandes. L’alimentation à l’herbe influence aussi la flaveur de la viande. Cet effet serait lié d’une part à l’interaction entre les acides gras à chaînes ramifiées (considérés comme responsables de la flaveur caractéristique de la viande ovine) et le scatole (issu de la dégradation du tryptophane) qui renforcerait la perception sensorielle des acides gras à chaînes ramifiées, et d’autre part à la teneur en acide linolénique. Les produits d’oxydation de cet acide sont en effet associés aux flaveurs spécifiques de la viande.
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Silva, Leonardo Xavier da, and Carla Weiss. "O AMBIENTE INSTITUCIONAL FORMAL E OS RUMOS DA CADEIA AGROINDUSTRIAL DO TABACO NO RIO GRANDE DO SUL." RDE - Revista de Desenvolvimento Econômico 1, no. 39 (April 2015): 872. http://dx.doi.org/10.21452/rde.v17i32.4199.
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Este artigo busca analisar a cadeia agroindustrial do tabaco no Rio Grande do Sul, seu ambiente institucional formal e as principais ações e medidas adotadas pelo Brasil após a ratificação a Convenção-Quadro para Controle do Tabaco (CQCT) em 2005. Em ter
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Barker, Hilary L., Denise Smith, Glen Stanosz, and Richard L. Lindroth. "Host genetics and environment shape fungal pathogen incidence on a foundation forest tree species, Populus tremuloides." Canadian Journal of Forest Research 46, no. 9 (September 2016): 1167–72. http://dx.doi.org/10.1139/cjfr-2016-0116.
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Diseases can markedly alter the ecological and economic value of poplars. To better understand poplar–pathogen interactions, we investigated the independent and interactive effects of tree genotype, soil nutrient limitation, and interspecific competition on incidence of powdery mildew (caused by the fungal obligate pathogen Erysiphe adunca (Wallr.) Fr., 1829) in a foundation tree species, trembling aspen (Populus tremuloides Michx.). We established a common garden of potted aspen saplings, incorporating five tree genotypes, two levels of soil nutrients (low and high), and two levels of competition (with and without grass). We then surveyed natural incidence of powdery mildew and aspen vigor (i.e., growth). Incidence of powdery mildew varied among aspen genotypes, and variance in incidence shifted among environments in which the trees were grown. Added soil nutrients increased powdery mildew incidence on aspen, whereas grass competition had the opposite effect. Interestingly, grass competition either enhanced or dampened the variance in incidence of powdery mildew among tree genotypes, depending on soil nutrient levels. In addition, powdery mildew incidence was positively related to tree vigor. Our findings reveal strong genetic, environmental, and genetic×environmental effects of disease on a foundation tree species and that particular environments can either enhance or diminish variation in responses among tree genotypes.
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Behrmann, Jan H. "Coeval shearing of eclogites and low-grade metasediments: petrofabrics in a possible Eo-Alpine subduction channel (Schobergruppe, Austria)." Neues Jahrbuch für Geologie und Paläontologie - Abhandlungen 230, no. 2-3 (December 12, 2003): 299–318. http://dx.doi.org/10.1127/njgpa/230/2003/299.
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Sandel, Brody, and Emily M. Dangremond. "Climate change and the invasion of California by grasses." Global Change Biology 18, no. 1 (July 13, 2011): 277–89. http://dx.doi.org/10.1111/j.1365-2486.2011.02480.x.
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Moravek, Silvie, Jon Luly, John Grindrod, and Russell Fairfax. "The origin of grassy balds in the Bunya Mountains, southeastern Queensland, Australia." Holocene 23, no. 2 (November 9, 2012): 305–15. http://dx.doi.org/10.1177/0959683612460792.
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Montane grasslands, or grassy balds, are enigmatic features of mountains worldwide. Their origins are often obscure. Pollen, phytolith and charcoal analysis of Dandabah Swamp in the Bunya Mountains in southeastern Queensland, Australia suggest that there, grassy balds comprise a relict vegetation maintained in the face of postglacial tree invasion by fire. The balds are not the product of edaphic phenomena or natural or anthropogenic cataclysms and will require intensive management efforts to be conserved in a world of increased woodiness, rising atmospheric CO2 and changing climate.
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Baker, Patrick J., Andrew P. Robinson, and John J. Ewel. "Sudden and sustained response of Acacia koa crop trees to crown release in stagnant stands." Canadian Journal of Forest Research 38, no. 4 (April 2008): 656–66. http://dx.doi.org/10.1139/x07-137.
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We examined the growth response of Acacia koa Gray (koa) in dense (10 000 trees/ha), ~25-year-old, second-growth stands on Hawai‘i to crown release (thinning) and grass control. Koa diameter increment increased within 2 months of thinning across the range of residual densities (200–900 trees/ha). After 3 years, diameter increment in the most intense thinning treatment was 180% greater than in the control treatment (1.4 vs. 0.5 cm/year); in the least intense thinning treatment diameter increment was 100% greater than the control (1.0 vs. 0.5 cm/year). Koa’s growth response was independent of all measures of tree size (diameter at breast height, height, and leaf area) across the range of tree sizes sampled. A grass control treatment to determine if reduced competition for soil water would improve koa growth showed no improvement in growth response. Koa phyllode δ13C values, which represent an integrated measure of tree water status, showed no evidence of tree water stress (mean δ13C = –28.3‰) and were not significantly different between the grass removal and control treatments. These results demonstrate that koa is capable of responding quickly and positively to crown release despite years of suppressed growth and suggest that landowners interested in managing koa forests may have considerable flexibility in the timing and application of thinning treatments to koa stands.
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Man, Cosmin D., Philip G. Comeau, and Douglas G. Pitt. "Competitive effects of woody and herbaceous vegetation in a young boreal mixedwood stand." Canadian Journal of Forest Research 38, no. 7 (July 2008): 1817–28. http://dx.doi.org/10.1139/x08-032.
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The influence of aspen ( Populus tremuloides Michx.) and herbaceous (forb and grass) vegetation on resource availability and white spruce ( Picea glauca (Moench) Voss) growth were examined as part of a long-term experiment established in 2002 near Whitecourt, Alberta, Canada. During the 2005 growing season, we examined the effects of herbicide treatments designed to control only woody (triclopyr ester) or both woody and herbaceous (glyphosate) vegetation on leaf area index (LAI) of both the woody and herbaceous components and relationships among LAI and light, soil moisture, air temperature, soil temperature, nitrogen availability, and spruce growth. Treatments reduced LAI and increased light, soil nitrogen availability, and white spruce growth. There were no apparent effects of the treatments on soil moisture in 2005. Both the woody and herb–grass layers appear to be competing for light and soil nitrogen in this young plantation. Controlling only woody vegetation resulted in an increase in herbaceous and total LAI (dominated by the grass Calamagrostis canadensis (Michx.) Beauv.). Spot treatment, involving control of vegetation within a 2 m radius of spruce seedlings while leaving 1 m of untreated ground between treated spots, may be a promising alternative to classical broadcast treatments for establishing spruce in a mixedwood stand. Spot treatments provided good growing conditions and reduced exposure of spruce seedlings to summer and winter frost injury during the first 3 years after planting.
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Bremond, Laurent, Anne Alexandre, Matthew J. Wooller, Christelle Hély, David Williamson, Peter A. Schäfer, Amos Majule, and Joël Guiot. "Phytolith indices as proxies of grass subfamilies on East African tropical mountains." Global and Planetary Change 61, no. 3-4 (April 2008): 209–24. http://dx.doi.org/10.1016/j.gloplacha.2007.08.016.
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Fisher, James T., Gregory A. Fancher, and Earl F. Aldon. "Factors affecting establishment of one-seed juniper (Juniperusmonosperma) on surface-mined lands in New Mexico." Canadian Journal of Forest Research 20, no. 7 (July 1, 1990): 880–86. http://dx.doi.org/10.1139/x90-118.
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Containerized one-seed juniper (Juniperusmonosperma (Engelm.) Sarg.) were planted on two northern New Mexico mine spoils to evaluate effects of establishment methods and postplanting site conditions on seedling survival and growth. Establishment factors included planting date, mulch, fertilizer regimes, and seedling protection. Wood chip mulch and animal protection provided by rigid plastic mesh tubes or plastic netting improved juniper survival, growth, or both, depending on the study. The forms and rates of fertilizers tested provided no benefits and sometimes decreased survival. Juniper fertilization at planting stimulated the growth of reseeded grass and resulted in greater competition. Perennial weeds that invaded a mechanically cleared planting site also reduced juniper growth and survival. Results point to the need to consider the adverse effects associated with fertilization, time of planting, and order of grass and juniper revegetation.
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Breman, Elinor, Lindsey Gillson, and Kathy Willis. "How fire and climate shaped grass-dominated vegetation and forest mosaics in northern South Africa during past millennia." Holocene 22, no. 12 (April 21, 2011): 1427–39. http://dx.doi.org/10.1177/0959683611400196.
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Grassland and savanna are globally important ecosystems, both ecologically and economically. These grass-dominated systems are at risk from current and future climate change and increasing anthropogenic impact. Key questions for understanding the resilience and variability of grass-dominated ecosystems under current and future environmental conditions include: How have these systems responded to climate change and disturbance in the past? What are the principal driving agents responsible for their present-day composition and distribution? Do the palaeoecological data provide evidence for feedbacks between climate, fire and anthropogenic activities? In this study, the temporal dynamics of grassland, savanna and forest in the summer rainfall region of northern South Africa were reconstructed for the last ~6500 years. Palaeoecological techniques used include analyses of fossil pollen, charcoal and stable isotopes. Data from two sites located at the present-day grassland-savanna ecotone in Mpumalanga province of South Africa are reported. Results indicate that a mosaic of grassland, savanna and Podocarpus forest occupied the landscape throughout the late Holocene, with grassland and forest dominating higher altitudes, and savanna and forest lower altitudes. Podocarpus forest retreated and grass-dominated vegetation expanded its range around 1800 cal. yr BP at the lower altitude site (Lowveld) and 600 cal. yr BP at the higher altitude site (Highveld), representing a change from a stable state forest savanna/grassland mosaic to an increasingly grass-dominated system. Climatic stress, changes in fire regime and anthropogenic impact led to the vegetation transitions recorded, and resulted in changes in water and nutrient cycles. In an increasingly warm world, with fluctuating water availability and heightened anthropogenic use of natural resources, the future of grass-dominated ecosystems appears far from stable.
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Trulls, HE, ML Ortiz, A. Zach, JA Picot, and JC Brem. "RUMEN DEGRADATION OF DRY MATTER OF CHANÉ GRASS (Paspalum guenoarum) IN GOATS IN DIFFERENT SEASONS OF THE YEAR." Compendio de Ciencias Veterinarias 8, no. 2 (December 30, 2018): 31–35. http://dx.doi.org/10.18004/compend.cienc.vet.2018.08.02.31-35.
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Warren, Stuart L., Walter A. Skroch, and L. Eric Hinesley. "Effect of root competition and nitrogen on growth and mineral content of Abiesfraseri." Canadian Journal of Forest Research 17, no. 9 (September 1, 1987): 1092–99. http://dx.doi.org/10.1139/x87-167.
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Three-year-old (3 + 0) Fraser fir seedlings (Abiesfraseri (Pursh) Poir.) were grown in a controlled-environment chamber under four N regimes, with and without root competition from orchard grass (Dactylisglomerata L.) or white clover (Trifoliumrepens L.). New shoot, stem, and root growth of Fraser fir were harvested 30, 60, and 90 days after budbreak. In the absence of root competition, dry weight and N content increased in a significant curvilinear manner with increasing N. With root competition, dry weight decreased linearly with increasing N, while N content increased linearly with increasing N levels. Responses of P and K content varied with seedling part. Cal content was not affected by root competition, while Mg content decreased in all seedling parts for trees grown with root competition. Orchard grass decreased growth and nutrient accumulation more than white clover.
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Vose, James M., and Wayne T. Swank. "Site preparation burning to improve southern Appalachian pine–hardwood stands: aboveground biomass, forest floor mass, and nitrogen and carbon pools." Canadian Journal of Forest Research 23, no. 10 (October 1, 1993): 2255–62. http://dx.doi.org/10.1139/x93-279.
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On three sites in the southern Appalachians, stands characterized by sparse overstories and dense Kalmialatifolia L. shrub layers were felled in early summer and burned in early fall. Amounts of aboveground vegetation and forest floor mass, nitrogen (N), and carbon (C) were measured before and after treatment by sampling wood, foliage, herbs, grasses, and forest floor (Oi and Oe + Oa layers). Burning decreased woody mass by 48 to 60% across the three sites. The most intense burn reduced mass from 180 to 70 Mg•ha−1, and N and C losses were 300 kg•ha−1 and 52 Mg•ha−1, respectively. Significant losses of mass, N, and C occurred in the Oi layer, but not in the Oe + Oa layer. Foliage, herbs, and grasses were totally consumed by the fires. Total aboveground N losses across sites ranged from 193 to 480 kg•ha−1. These losses may be significant because N availability is low on these sites. Variations in patterns of mass, N, and C consumption were related to differences in amounts, types, size distributions, and moisture contents of fuels.
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Milesi, Cristina, Steven W. Running, Christopher D. Elvidge, John B. Dietz, Benjamin T. Tuttle, and Ramakrishna R. Nemani. "Mapping and Modeling the Biogeochemical Cycling of Turf Grasses in the United States." Environmental Management 36, no. 3 (July 27, 2005): 426–38. http://dx.doi.org/10.1007/s00267-004-0316-2.
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Liu, Yaning, M. Yousuff Hussaini, and Giray Ökten. "Global sensitivity analysis for the Rothermel model based on high-dimensional model representation." Canadian Journal of Forest Research 45, no. 11 (November 2015): 1474–79. http://dx.doi.org/10.1139/cjfr-2015-0148.
Full textAbstract:
Rothermel’s wildland surface fire spread model is widely used in North America. The model outputs depend on a number of input parameters, which can be broadly categorized as fuel model, fuel moisture, terrain, and wind parameters. Due to the inevitable presence of uncertainty in the input parameters, knowing the sensitivity of the model output to a given input parameter can be very useful for understanding and controlling the sources of parametric uncertainty. Instead of obtaining the local sensitivity indices, we perform a global sensitivity analysis that considers the synchronous changes of parameters in their respective ranges. The global sensitivity indices corresponding to different parameter groups are computed by constructing the truncated ANOVA – high dimensional model representation for the model outputs with a polynomial expansion approach. We apply global sensitivity analysis to six standard fuel models, namely short grass, tall grass, chaparral, hardwood litter, timber, and light logging slash. Our sensitivity results show similarities, as well as differences, between fuel models. For example, the sensitivities of the input parameters, i.e., fuel depth, low heat content, and wind, are large in all fuel models and as high as 85% of the total model variance in the fuel model light logging slash. On the other hand, the fuel depth explains around 40% of the total variance in the fuel model light logging slash but only 12% of the total variance in the fuel model short grass. The quantification of the importance of parameters across fuel models helps identify the parameters for which additional resources should be used to lower their uncertainty, leading to effective fire management.
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Shropshire, Christy, Robert G. Wagner, F. Wayne Bell, and Clarence J. Swanton. "Light attenuation by early successional plants of the boreal forest." Canadian Journal of Forest Research 31, no. 5 (May 1, 2001): 812–23. http://dx.doi.org/10.1139/x01-006.
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The influence of eight early successional plant species from the boreal forest on photosynthetically active radiation (PAR) were compared using a controlled plant competition study. Four woody (green alder, Alnus crispa (Ait.) Pursh; upland willow, Salix humilis Marsh.; white birch, Betula papyrifera Marsh.; wild red raspberry, Rubus idaeus L.) and four herbaceous (eastern bracken fern, Pteridium aquilinum L.; bluejoint grass, Calamagrostis canadensis Michx.; large-leaved aster, Aster macrophyllus L.; fireweed, Epilobium angustifolium L.) plant species were studied using an additive density experiment with jack pine (Pinus banksiana Lamb.) seedlings. The transmission of PAR through the plant canopies was measured using a line quantum sensor under six plant density treatments at the time of maximum canopy development each year. Four measures of plant abundance (planting density, actual density, projected leaf area index, and crown cover) were evaluated for their ability to predict PAR transmission through the plant canopies. Visual estimates of crown cover provided the best models each year. Vertical profiles of PAR transmission were used to compare the canopy structure among plant species and were used to refine the models. During the second growing season, increasing crown cover of bluejoint grass and large-leaved aster had the largest influence on PAR. In the third season, green alder, upland willow, and white birch (along with bluejoint grass and fireweed at the jack pine crown level) had the greatest influence on PAR. PAR measurements taken from a nearby forest for several of the plant species indicate that the models developed from our controlled experiment are reasonably applicable to naturally occurring plant populations.
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Handiani, D., A. Paul, M. Prange, U. Merkel, L. Dupont, and X. Zhang. "Tropical vegetation response to Heinrich Event 1 as simulated with the UVic ESCM and CCSM3." Climate of the Past 9, no. 4 (July 31, 2013): 1683–96. http://dx.doi.org/10.5194/cp-9-1683-2013.
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Abstract. We investigated changes in tropical climate and vegetation cover associated with abrupt climate change during Heinrich Event 1 (HE1, ca. 17.5 ka BP) using two different global climate models: the University of Victoria Earth System-Climate Model (UVic ESCM) and the Community Climate System Model version 3 (CCSM3). Tropical South American and African pollen records suggest that the cooling of the North Atlantic Ocean during HE1 influenced the tropics through a southward shift of the rain belt. In this study, we simulated the HE1 by applying a freshwater perturbation to the North Atlantic Ocean. The resulting slowdown of the Atlantic Meridional Overturning Circulation was followed by a temperature seesaw between the Northern and Southern Hemispheres, as well as a southward shift of the tropical rain belt. The shift and the response pattern of the tropical vegetation around the Atlantic Ocean were more pronounced in the CCSM3 than in the UVic ESCM simulation. For tropical South America, opposite changes in tree and grass cover were modeled around 10° S in the CCSM3 but not in the UVic ESCM. In tropical Africa, the grass cover increased and the tree cover decreased around 15° N in the UVic ESCM and around 10° N in the CCSM3. In the CCSM3 model, the tree and grass cover in tropical Southeast Asia responded to the abrupt climate change during the HE1, which could not be found in the UVic ESCM. The biome distributions derived from both models corroborate findings from pollen records in southwestern and equatorial western Africa as well as northeastern Brazil.
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Bernal, Blanca, J. Patrick Megonigal, and Thomas J. Mozdzer. "An invasive wetland grass primes deep soil carbon pools." Global Change Biology 23, no. 5 (November 17, 2016): 2104–16. http://dx.doi.org/10.1111/gcb.13539.
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