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91.
Long-term growth and yield effects of respacing natural regeneration of Sitka spruce in Britain 总被引:2,自引:0,他引:2
Stands of Sitka spruce (Picea sitchensis (Bong.) Carr.) originating from natural regeneration can be extremely dense with high mortality, poor growth form and low volume production. Although costly, respacing (pre-commercial thinning) can reduce resource competition for the remaining trees, altering the final crop produced. Three experiments were established to examine the effect of respacing 1–2 m tall trees to different target densities. The impact on stand growth and yield was measured 11–17 years after respacing, and the longer-term impact was modelled to year 50. Unrespaced control treatments self-thinned at a similar and constant rate at two sites. At the third, extremely high initial density resulted in a higher rate of self-thinning and lower density after 11 years. Wider respacing treatments resulted in larger mean tree diameter, but there was no significant effect of respacing on stand volume 11–17 years after respacing; greater diameter growth did not compensate for low tree number. Results indicate a volume penalty associated with delaying respacing until trees were 4 m tall, but this treatment was unreplicated. Modelled stand volume in year 50 was higher for the 2.6 m × 2.6 m respacing treatment than for the 1.8 m × 1.8 m, 2.1 m × 2.1 m or 3.3 m × 3.3 m treatments. However, open-grown conditions may reduce timber quality compared to closer spacing treatments. The results are presented using a stand density management diagram for Sitka spruce growing in Canada and support recent suggestions that British stands have a shallower size–density relationship than Canadian stands. 相似文献
92.
A comparative review of fisheries management experiences in the European Union and in other countries worldwide: Iceland,Australia, and New Zealand 下载免费PDF全文
Paul Marchal Jesper Levring Andersen Martin Aranda Mike Fitzpatrick Leyre Goti Olivier Guyader Gunnar Haraldsson Aaron Hatcher Troels Jacob Hegland Pascal Le Floc'h Claire Macher Loretta Malvarosa Christos D Maravelias Simon Mardle Arantza Murillas J Rasmus Nielsen Rosaria Sabatella Anthony D M Smith Kevin Stokes Thomas Thoegersen Clara Ulrich 《Fish and Fisheries》2016,17(3):803-824
This study compares the details and performance of fisheries management between the EU and a selection of other countries worldwide: Iceland, New Zealand, and Australia, which are considered in many respects to be among the most advanced in the world in fisheries management. Fisheries management in the EU, Iceland, Australia, and New Zealand has developed following different paths, despite being based on similar instruments and principles. Iceland, Australia, and New Zealand have been at the forefront of developing management practices such as stakeholder involvement, legally binding management targets (Australia, New Zealand), individual transferable quotas, and discard bans (Iceland, New Zealand). The EU has since the beginning of the 21st century taken significant steps to better involve stakeholders and establish quantitative targets through management plans, and a landing obligation is gradually being implemented from 2015 onward. The management of domestic fisheries resources in Australia, New Zealand, and Iceland has, overall, performed better than in the EU, in terms of conservation and economic efficiency. It should, however, be stressed that, compared to Australia, New Zealand, and Iceland, (i) initial over‐capacity was more of an issue in the EU when management measures became legally binding and also that (ii) EU has been progressive in developing common enforcement standards, on stocks shared by sovereign nations. The situation of EU fisheries has substantially improved over the period 2004–2013 in the northeast Atlantic, with fishery status getting close to that in the other jurisdictions, but the lack of recovery for Mediterranean fish stocks remains a concern. 相似文献
93.
Petrakis PV Agiomyrgianaki A Christophoridou S Spyros A Dais P 《Journal of agricultural and food chemistry》2008,56(9):3200-3207
This work deals with the prediction of the geographical origin of monovarietal virgin olive oil (cv. Koroneiki) samples from three regions of southern Greece, namely, Peloponnesus, Crete, and Zakynthos, and collected in five harvesting years (2001-2006). All samples were chemically analyzed by means of 1H and 31P NMR spectroscopy and characterized according to their content in fatty acids, phenolics, diacylglycerols, total free sterols, free acidity, and iodine number. Biostatistical analysis showed that the fruiting pattern of the olive tree complicates the geographical separation of oil samples and the selection of significant chemical compounds. In this way the inclusion of the harvesting year improved the classification of samples, but increased the dimensionality of the data. Discriminant analysis showed that the geographical prediction at the level of three regions is very high (87%) and becomes (74%) when we pass to the thinner level of six sites (Chania, Sitia, and Heraklion in Crete; Lakonia and Messinia in Peloponnesus; Zakynthos). The use of classification and binary trees made possible the construction of a geographical prediction algorithm for unknown samples in a self-improvement fashion, which can be readily extended to other varieties and areas. 相似文献
94.
Thomas R. Carruthers Quang C. Huynh Adrian R. Hordyk David Newman Anthony D. M. Smith Keith J. Sainsbury Kevin Stokes Alexander Morison David Agnew Ana Parma Ignacio Sobrino Catherine Longo 《Fish and Fisheries》2023,24(2):279-296
Fisheries managers are in need of quantitative tools to inform decisions regarding selection of robust management practices, prioritising research gaps and stocks to focus on, particularly where there are limited resources or data. To support these decisions, the use of Management Strategy Evaluation (MSE), that is, closed loop simulation-testing of management procedures, is widely regarded as best practice. However, applying MSE is time- and computationally intensive, and requires highly skilled expertise and processes for stakeholder input and peer review. For data- and capacity-limited fisheries, MSE may be particularly challenging to implement. Yet, these are the contexts where it is most critical to test assumptions, evaluate the implications of all sources of uncertainty and identify the most informative data sources. To facilitate wider use of MSE, the Method Evaluation and Risk Assessment (MERA) framework was developed as an accessible online interface, with quick processing time, focused on generic data-limited management procedures, but allowing progression to tailored and more data-rich methods. The framework links a quantitative questionnaire and data input standard to a flexible operating model with optional customisation via command line access to the back-end open-source R libraries. Here, we illustrate a case study application of MERA for the bocinegro (Pagrus pagrus, Sparidae) fishery in the Gulf of Cadiz, where in conjunction with fishery stakeholders, a custom management procedure was developed and tested and key research gaps and data collection priorities were identified. We discuss implications for wider use of MSE in various contexts, including eco-certification and fishery improvement projects. 相似文献
95.
The arrangement of a plant's roots in the soil determines the ability of the plant to resist uprooting. We have investigated the influence of root morphology on anchorage using simple patterns of root systems and numerical simulation. The form and mechanical properties of roots were derived from results found in the literature. Major parameters determining soil characteristics, root patterns and strength were varied so that their influence could be evaluated. The design of the experimental method we used generated an optimal number of configurations of different root systems, the tensile resistances of which were calculated by two‐dimensional finite element analysis. We could quantify the influence of specific parameters, e.g. branching angle, number of lateral roots and soil cohesion, as well as global parameters such as total contact area, basal diameter and volume of the whole root system. We found that the number of roots and the diameter of roots were major components affecting the resistance to uprooting. The combination of topology and biomass explained 70% of the variation of tensile resistance. 相似文献
96.
Effects of vegetation type on soil resistance to erosion: Relationship between aggregate stability and shear strength 总被引:5,自引:0,他引:5
M. Fattet Y. Fu M. Ghestem W. Ma M. Foulonneau J. Nespoulous Y. Le Bissonnais A. Stokes 《CATENA》2011
Soil water erosion and shallow landslides depend on aggregate stability and soil shear strength. We investigated the effect of vegetation on both soil aggregate stability and shear strength (through direct shear tests) in former croplands converted to vegetated erosion protection areas within the context of China's sloping land conversion programme. Four treatments were analysed in plots comprised of (i) 4 year old crop trees, Vernicia fordii, where understory vegetation was removed; (ii) V. fordii and the dominant understory species Artemisia codonocephala; (iii) only A. codonocephala and (iv) no vegetation. Soil samples were taken at depths of 0–5 cm and 45–50 cm. Root length density (RLD) in five diameter classes was measured, soil organic carbon (SOC), hot water extractable carbon (HWEC), texture and Fe and Al oxides were also measured. We found that mean weight diameter after slow wetting (MWDSW) in the A-horizon, was significantly greater (0.94–1.01 mm) when A. codonocephala was present compared to plots without A. codonocephala (0.57–0.59 mm). SOC and RLD in the smallest diameter class (< 0.5 mm), were the variables which best explained variability in MWDSW. A significant positive linear relationship existed between MWDSW and soil cohesion but not with internal angle of friction. As herbaceous vegetation was more efficient than trees in improving aggregate stability, this result suggests that the mechanisms involved include modifications of the cohesive forces between soil particles adjacent to plant roots and located in the enriched in SOC rhizosphere, thus also affecting shear strength of the corresponding soil volume. Thus, vegetation stabilised soil under different hierarchical levels of aggregate organisation, i.e. intra- and inter-aggregate. Our results have implications for the efficacy of techniques used in land conversion programs dedicated to control of soil erosion and shallow landslides. We suggest that mixtures of different plant functional types would improve soil conservation on slopes, by reducing both surface water erosion and shallow substrate mass movement. Planting trees for cropping or logging, and removing understory vegetation is most likely detrimental to soil conservation. 相似文献
97.
Nafsika Karakatsouli Sofronios E. Papoutsoglou Gianluca Pizzonia Georgios Tsatsos Aristeidis Tsopelakos Stella Chadio Dimitris Kalogiannis Christina Dalla Alexia Polissidis Zeta Papadopoulou-Daifoti 《Aquacultural Engineering》2007,36(3):302-309
Previously reported data clearly indicate that depending on species, ambient light spectrum can affect fish growth, physiology, behaviour, reproduction, etc. Since light spectrum can be easily controlled in intensive indoor fish farming facilities, the present study aimed to investigate the effects of coloured light on growth performance (body weight, growth rate, food utilization, carcass composition, etc.) and physiological status (blood and plasma parameters, brain neurotransmitters, tissue fatty acid composition, etc.) of two widely reared fish species, gilthead seabream Sparus aurata and rainbow trout Oncorhynchus mykiss. For this purpose, 240 specimens of S. aurata (29.8 ± 0.13 g) and 60 specimens of O. mykiss (71.4 ± 0.30 g) were exposed to white (full-spectrum, fluorescent lamps), red (605 nm) and blue (480 nm) light (lamps covered with appropriate filters) for 11 weeks under recirculating water systems. Blue light had a significantly negative impact on O. mykiss growth performance accompanied with reduced liver total lipids and plasma glucose and increased brain serotonergic and dopaminergic activity. In the case of S. aurata, red light significantly increased brain dopaminergic activity, while a tendency towards reduced growth was also observed. Since these results indicated the establishment of stressful conditions, O. mykiss and S. aurata should not be reared under blue and red light, respectively. For each species, the effect of the remaining light colours tested, was not clearly differentiated so that an appropriate light spectrum for the most efficient farming of O. mykiss and S. aurata could not be suggested, at least for the time period examined. Nevertheless, present results suggest that light colour should be regarded as a rearing factor worth to be further investigated, especially when recirculating systems are concerned. 相似文献
98.
S R Stokes A L Goetsch H H Nejad G Murphy A L Jones S Mashburn K W Beers Z B Johnson E L Piper 《Journal of animal science》1988,66(1):204-212
Effects of supplemental Bermuda grass hay (BG) or ground corn on intake, digestion and performance of cattle consuming endophyte-infected fescue (I) were studied. In Exp. 1, a Latin square study, five growing Holstein steers (158.1 kg) consumed I ad libitum and were offered 0, .3, .6, .9 or 1.2% body weight (BW) of BG daily. Total dry matter (DM) intake rose linearly (P less than .05) with increasing BG, although intake was numerically similar with .6, .9 and 1.2% BW of BG. Digestibility was constant with diet (P greater than .10). Six growing Holstein steers used in Exp. 2, a Latin square with a 2 x 3 factorial arrangement of treatments, ingested I or noninfected (NI) fescue hay ad libitum with 0, .5 or 1.0% BW of ground corn. Total DM intake increased linearly as the level of corn rose (P less than .05). Total intake with I increased more with the first than with the second addition of corn, and the opposite occurred with NI (interaction between fescue infection and the quadratic effect of corn level, P less than .10). Organic matter digested (g/d) was greater for NI than for I and rose linearly with increasing corn ingestion (P less than .05). Ninety-six crossbred beef heifers and steers (184.2 kg avg initial live weight) were used in a 77-d fall grazing experiment (Exp. 3) with a 2 x 3 factorial treatment arrangement. Cattle grazed I or NI paddocks and were given no supplement or .34% BW of BG or .65% BW of ground corn on a daily basis (DM).(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献
99.
J L Fitzpatrick M Bailey D A Harbour C R Stokes 《Veterinary immunology and immunopathology》1992,34(3-4):245-257
Adult ponies which were fed ovalbumin (OVA) daily for 2 weeks had significantly greater serum anti-OVA IgG (P = 0.001) and antigen specific lymphocyte responses (P = 0.031) after intramuscular injection with OVA given with saponin than control ponies which had not been fed the antigen. This suggests that, despite the lack of evidence of B- or T-cell activation in peripheral blood during the period of OVA feeding, the animals were primed for an active secondary immune response. Adult ponies were challenged with equine rotavirus, strain H-2, but no statistically significant differences were found in serum IgG-associated antibody responses or antigen-specific lymphocyte responses between the rotavirus-challenged group and the control group, either following rotavirus challenge or intramuscular injection of rotavirus antigen given with saponin. Our findings, that feeding the non-replicating protein antigen OVA appeared to prime for an increased immune response rather than inducing oral tolerance, may be of relevance to future studies on the way the equine gastrointestinal tract handles usually harmless antigens. 相似文献
100.
J L Fitzpatrick P J Cripps A W Hill P W Bland C R Stokes 《Veterinary immunology and immunopathology》1992,32(1-2):13-23
The distribution of major histocompatibility complex (MHC) class II positive cells within the connective tissue and the epithelium of the involuted bovine mammary gland has been determined. The effect of intramammary administration of the antigens ovalbumin and formalin killed Streptococcus uberis on the distribution pattern has also been investigated. Infusion of formalin killed S. uberis increased cellular expression of class II antigens when compared with quarters either infused with ovalbumin, not infused at all, or from which minor pathogens had been isolated. The increased expression occurred particularly in the area of the gland cistern-secretory tissue junction. 相似文献