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Grazing Conditions (grazing + condition)
Selected AbstractsSeedling recruitment dynamics of forage and weed species under continuous and rotational sheep grazing in a temperate New Zealand pastureGRASS & FORAGE SCIENCE, Issue 2 2005G. R. Edwards Abstract Understanding the grazing conditions under which plant populations are limited by seed availability (seed limitation) is important for devising management schemes that aim to manipulate the establishment of weed and forage species. Seeds of three weed species (Cirsium arvense, C. vulgare and Rumex obtusifolius) and five forage species (Lolium perenne, Lotus uliginosus syn. L. pedunculatus, Paspalum dilatatum, Plantago lanceolata and Trifolium repens) were broadcast sown into L. perenne,T. repens pastures in Manawatu, New Zealand and five sheep-grazing and two slug-grazing (with and without molluscicide) treatments were imposed in a split-plot design. Of the five sheep-grazing treatments, four compared continuous grazing with rotational grazing at intervals of 12, 24 and 36 d in spring, with all four grazed under a common rotation for the remainder of the year. The fifth treatment was continuous grazing all year. Seed sowing increased seedling emergence of C. vulgare, L. perenne, P. lanceolata, R. obtusifolius and T. repens under all sheep- and slug-grazing treatments, with differences in seedling densities persisting for at least 21 months. Seed sowing did not increase seedling densities of C. arvense, L. uliginosus or P. dilatatum. The effects of sheep-grazing management on seedling emergence and survival were uncoupled. For the five seed-limited species, seedling emergence was greater on pastures that were rotationally grazed during spring compared with those that were continuously grazed. However, seedling survival was lower in pastures grazed rotationally during summer, autumn and winter, so that after 21 months seedling numbers were greater on plots that were continuously grazed all year. Exclusion of slugs increased seedling recruitment of T. repens but had no impact on the other species. As weed and forage species responded in a similar way to sheep-grazing management (increased under continuous, decreased under rotational), it is unlikely that the goals of reducing weed invasions and enhancing forage species establishment could be carried out concurrently in established pastures with the same management. [source] Relation between Holstein bulls' proofs for milk in USA and the survival and body weights up to 18 months of their F1 zebu progeny in VenezuelaJOURNAL OF ANIMAL BREEDING AND GENETICS, Issue 3 2003J. R. Pacheco Summary The purpose of the study was to determine the relation between Holstein bulls' proofs for milk in USA, and the survival and body weights of their F1 progeny under lowland grazing conditions in Venezuela. Semen was selected from sires with the highest proofs available locally (class H, n = 23) or with proofs close to the breed average (class A, n = 18). Mean proofs were 934 kg (H) and 237 kg (A), respectively, when semen was purchased (1989,93), falling to 204 and ,386 kg when updated in 2001. Dams were Brahman-type zebus on seven farms, raising the F1 progeny (n = 866) on native or cultivated pasture with only mineral supplements. Records of survival to 8 and 18 months and weights at birth, 8 and 18 months of age were analysed using linear models. Sire class had no effect on survival or weight at birth, but H progeny were slightly heavier than A progeny at 8 (4.0%, p = 0.06) and 18 months (2.6%, p < 0.05). The interaction class × farm was only significant for survival, with H progeny equal or superior to A groups on six farms. The effect of sire within class was highly significant for survival to 8 months and weight at 18 months. Rank correlations using sires' milk proofs and F1 progeny weights and survival were not significant. It was concluded that the use of Holstein bulls with high milk proofs may lead to slightly higher 18-month weights in their F1 progeny in tropical grazing systems, covering the additional cost of H semen, but that sire evaluation for weight gain and progeny survival rates may be justified under these conditions. Zusammenfassung Beziehungen zwischen den Zuchtwerten für Milch von Holstein-Bullen in den USA und dem Überleben und dem Körpergewicht bis zu 18 Monaten ihrer F1-Zebu-Nachkommen in Venezuela Der Zweck dieser Studie war die Ermittlung der Beziehungen zwischen den Milch-Zuchtwerten von Holstein-Bullen in den USA und dem Überleben und dem Körpergewicht von F1-Nachkommen unter den Weidebedingungen des Flachlandes in Venezuela. Ausgewählt wurde das Sperma von lokal verfügbaren Bullen mit den höchsten Zuchtwerten (Klasse H, n = 23) oder mit Zuchtwerten, die eng am Populationsdurchschnitt (Klasse A, n = 18) lagen. Beim Erwerb des Spermas (1989,1993) betrugen die mittleren Zuchtwerte 934 kg (H) beziehungsweise 237 kg (A), die bei der Neubewertung 2001 auf 204 kg und ,386 kg abfielen. Die Kühe waren Zebus im Brahman-Typ von sieben Farmen, die die F1-Nachkommen (n = 866) auf natürlichen oder kultivierten Weiden nur mit zusätzlichem Mineralfutter aufzogen. Das Überleben mit acht und 18 Monaten und das Gewicht bei der Geburt, mit acht und mit 18 Monaten wurde mittels linearer Modelle analysiert. Die Bullenklasse zeigte keinen Effekt auf das Überleben und das Geburtsgewicht, aber die H-Nachkommen waren mit acht (4%, p = 0,06) und 18 Monaten (2,6%, p < 0,05) etwas schwerer als die A-Nachkommen. Die Interaktion "Klasse × Farm" war nur für das Überleben signifikant, mit H-Nachkommen gleich oder besser als die A-Gruppen auf sechs Farmen. Der Effekt des Vaters innerhalb der Klasse war hochsignifikant für das Überleben der ersten acht Monate und das Gewicht mit 18 Monaten. Rang-Korrelationen mit den Milch-Zuchtwerten der Bullen und den Gewichten und dem Überleben der F1-Nachkommen waren nicht signifikant. Die Verwendung von Holstein-Bullen mit hohen Zuchtwerten für Milch kann zu einer leichten Erhöhung des Gewicht der F1-Nachkommen mit 18 Monaten in tropischen Weidesystemen führen, welche die zusätzlichen Kosten des H-Spermas abdeckt, aber die Bewertung der Bullen hinsichtlich Gewichtszunahme und Überlebensrate der Nachkommen müsste unter diesen Bedingungen berichtigt werden. [source] A community-level test of the leaf-height-seed ecology strategy scheme in relation to grazing conditionsJOURNAL OF VEGETATION SCIENCE, Issue 3 2009Carly Golodets Abstract Question: Is the assumption of trait independence implied in Westoby's (1998) leaf-height-seed (LHS) ecology strategy scheme upheld in a Mediterranean grazing system dominated by annuals? Is the LHS approach applicable at the community level? Location: Northern Israel. Methods: LHS traits (specific leaf area [SLA], plant height and seed mass), and additional leaf traits (leaf dry matter content [LDMC], leaf area, and leaf content of nitrogen [LNC], carbon [LCC], and phosphorus [LPC]), were analyzed at the species and community levels. Treatments included manipulations of grazing intensity (moderate and heavy) and protection from grazing. We focused on species comprising 80% of biomass over all treatments, assuming that these species drive trait relationships and ecosystem processes. Results: At the species level, SLA and seed mass were negatively correlated, and plant height was positively correlated to LCC. SLA, seed mass, and LPC increased with protection from grazing. At the community level, redundancy analysis revealed one principal gradient of variation: SLA, correlated to grazing, versus seed mass and plant height, associated with protection from grazing. We divided community functional parameters into two groups according to grazing response: (1) plant height, seed mass, LDMC, and LCC, associated with protection from grazing, and (2) SLA, associated with grazing. Conclusions: The assumption of independence between LHS traits was not upheld at the species level in this Mediterranean grazing system. At the community level, the LHS approach captured most of the variation associated with protection from grazing, reflecting changes in dominance within the plant community. [source] Impacts of differential consumption by the grazing fish, Plecoglossus altivelis, on the benthic algal composition in the Chikuma River, JapanPHYCOLOGICAL RESEARCH, Issue 2 2006Shin-ichiro Abe SUMMARY Grazing effects of ayu, Plecoglossus altivelis Temminck et Schegel, on the benthic algal assemblages were investigated in the Chikuma River, Japan. Comparison of the algal composition on boulders with and without intensively grazed patches indicated that fish grazing decreased the abundance of diatoms and prostrate filamentous cyanobacteria and caused upright filamentous cyanobacteria to predominate. Differential consumption by ayu was estimated by comparing the relative abundance of algae in the stomach contents of ayu and that in the algal assemblages within the grazed patches. The results showed that ayu consumed the prostrate filamentous cyanobacteria proportionally to their abundance, whereas they ingested diatoms and the upright filamentous cyanobacteria in a larger and lower quantity, respectively, than that expected from their abundance. Differential consumption would involve the change in the algal composition toward the predominance of upright filamentous cyanobacteria under fish grazing conditions. [source] Intraspecific changes in plant morphology, associated with grazing, and effects on litter quality, carbon and nutrient dynamics during decompositionAUSTRAL ECOLOGY, Issue 1 2006MARÍA SEMMARTIN Abstract: Continuous biomass removal by grazing usually changes the resource allocation pattern of plants. These changes often increase resistance to tissue removal and produce individuals with different morphometric traits, such as root to shoot or blade to sheath ratios. Shifts in morphometric traits, in turn, may alter nutrient cycling through changes in the average quality of litter that decomposes in soil. Previous work has shown that Paspalum dilatatum, a native grass from the Pampas grasslands, which inhabits a vast area and supports a wide range of grazing conditions, increases its blade to sheath ratio under continuous grazing with respect to ungrazed conditions. Here, we explored the consequences of these changes apparently associated with grazing regime on litter quality and nutrient dynamics during litter breakdown in soil. We separately analysed litter quality of blades and sheaths of P. dilatatum and determined under controlled conditions their decomposition and nutrient release kinetics over a maximum period of 1 year. We also studied the mineral nitrogen contents in soil amended with each litter type. Blade quality was significantly higher than sheath quality, nitrogen concentrations of blades and sheaths were approximately 1% and 0.6%, respectively, and lignin to nitrogen ratios were approximately 5 and 11 for blades and sheaths, respectively. Phosphorus concentration, however, was similar in both litter types. Blades decomposed 10% faster than sheaths, released 20% more nitrogen and released 15% more phosphorus than sheaths during the last half of the incubation period. During the first 3 months, the soil nitrogen content of litter-amended incubations indicated immobilization with respect to non-amended control; however, later blade incubations mineralized nitrogen, whereas sheath incubations continued immobilizing it. Results revealed that grazing potentially accelerates nutrient cycling during decomposition by increasing the blade to sheath ratio of P. dilatatum individuals, and suggest that this may be an important mechanism underlying grazing impact on nutrient cycling. [source] | |||||||||||||