The relationship between site factors and white ash (Fraxinus americana L.) decline in Massachusetts     

H. Woodcock  W.A. Patterson III  K.M. Davies Jr. 《Forest Ecology and Management》1993,60(3-4):271-290

Forest inventory records incorporating individual tree data are an important source of information about the extent and severity of past rates of forest decline, thus providing a temporal perspective for contemporary observations. We demonstrate the potential of this approach by using continuous forest inventory (CFI) data to reconstruct the extent, severity, pattern of development and site-factor associations for white ash decline in Massachusetts. White ash (Fraxinus americana L.) increased in basal area on Massachusetts CFI plots at about 1.5% per year from 1962 to 1979. Ash decline is, however, locally severe. Plot decline status was estimated, based on vigor rating, and growth and mortality rates of white ash. Plots with a mean change in basal area per year of −0.5% and/or with a mean vigor rating of 2.0 (on a scale of 0–4) were classified as ‘decline’. Using these criteria, 20% of the 82 CFI plots with 10% total basal area of white ash in 1962 were classified as ‘decline’ in both 1979 and 1991. These results suggest that statewide there has been no net loss of ash basal area since 1962. The total forest area affected by ash decline has not increased in the past decade.

Analyses of the CFI data indicate that decline was most prevalent on mesic sites, high on the landscape and/or on steep slopes. Such sites are potentially subject to large fluctuations in soil moisture availability during drought periods. Relationships identified between the prevalence of ash decline and site factors were further evaluated within a 2 ha intensived study site in the center of a 13 ha white ash stand affected by ash decline in 1990. Decline was heterogeneously distributed within the stand, with declining trees most frequent on the ‘decline-prone’ site-type identified through CFI plot analyses.  相似文献   

The validity of the use of SEM/EDAX as a tool for the detection of UF resin penetration into wood cell walls in particleboard     

A. J. Bolton  J. M. Dinwoodie  D. A. Davies 《Wood Science and Technology》1988,22(4):345-356

Summary The interpretation of data from scanning electron microscopy (SEM) combined with energy dispersive analysis of X-rays (EDAX) is dependent on the size of the excitation volume, the magnitude of which for organic materials such as wood has been little studied. From the analysis of a model system comprised of a thin layer of gold sandwiched between two layers of an epoxy plastic, it was shown that about 90% of all excitations arise from a volume about 6 m wide and 4 m deep. However, these dimensions vary with the orientation of the gold relative to the specimen surface, and the specimen tilt. Theoretical predictions based on these data support, but not conclusively, the previously published SEM/EDAX evidence of the penetration of urea formaldehyde resins into the wood cell wall in particleboard manufacture.This paper was written while A. J. Bolton was Heritage Visiting Scientist at the Forest Products Laboratory, U.S. Department of Agriculture, and Visiting Professor at the Department of Forestry, University of Wisconsin, both at Madison, Wisconsin, U.S.A. This support is gratefully acknowledged. The authors would also like to acknowledge the assistance of E. Edwards in machining the SEM specimens  相似文献   

A longitudinal observational study of Salmonella shedding patterns by commercial turkeys during rearing and fattening,showing limitations of some control measures     

V.K. Morris  J.J. Carrique-Mas  D. Mueller-Doblies  R.H. Davies  A.D. Wales  V.M. Allen 《British poultry science》2015,56(1):48-57

1. The onset and progression of Salmonella infections was investigated in commercial turkey flocks from placement at 1 d old until slaughter in “brood and move” systems using a longitudinal observational approach based on faeces and environmental sampling with subsequent culture of Salmonella.

2. Persistent Salmonella Newport contamination was found within rearing houses and on their external concrete aprons after cleaning and disinfection between crops of heavily shedding young birds.

3. Salmonella shedding was often detected by 5 d of age and the frequency of positive samples peaked at 14–35 d. Thereafter Salmonella isolations declined, especially in the later (fattening) stages. Samples were still Salmonella-positive at low prevalence in half of the intensively sampled houses at slaughter age.

4. A number of management interventions to combat Salmonella infection of flocks, including sourcing policy, competitive exclusion cultures and cleaning and disinfection, were inadequate to prevent flock infection, although improved disinfection on one unit was associated with a delay in the onset of flock infection.

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The effect of mesh covers on the survival and growth of Crassostrea gigas Thunberg grown on the sea bed     

P.R. Walne  G. Davies 《Aquaculture (Amsterdam, Netherlands)》1977,11(4):313-321

Growth and mortality were measured in samples of Crassostrea gigas planted in trays on the beach at 4.5, 7.5 and 20% exposure. The oysters were graded by live weight into < 1, 1 2, 3–4, 5 6 and 8–10-g groups at planting. Three levels of protection were provided: none, 36-mm and 12.5-mm mesh. Five separate trials of 41–108 days covered about a year.Mortality decreased with increasing size of oyster at planting and with increasing degree of cover. On average, oysters of < 1 g and without cover showed 50% survival over 30 days, while oysters of 3–4 g protected with a 12.5-mm mesh showed 97% survival. Neither seasonal variation in survival nor variation related to exposure was detected. Unprotected oysters grew to a smaller size than protected oysters and those at 20% exposure grew less than those at 7.5 or 4.5% exposure. It is probable that the two sizes of mesh provided protection against interference and predation by the shore crab Carcinus maenas.The combined results of the trials indicated that the standing stock at the end of about 6 months, which included the summer, obtained from laying 100, 0.6 g oysters at 4.5% exposure would be 564 g and 99 g with 12.5-mm mesh and no protection, respectively.  相似文献   

Influence of multiple amino acid supplementation on the performance of rainbow trout, Oncorhynchus mykiss (Walbaum), fed soya based diets   总被引：1，自引：0，他引：1  

S J Davies  P C Morris 《Aquaculture Research》1997,28(1):65-74

Using rainbow trout, Oncorhynchus mykiss (Walbaum), of approximately 50 g, a 63 day feeding trial was undertaken to evaluate the efficacy of individual and multiple amino acid supplements in diets where soyabean meal was used as the principle protein source. Iso-nitrogenous diets (45% crude protein) were formulated where the control diet (F) contained fishmeal as the reference protein and a solvent extracted soyabean meal (S) replaced approximately 66% of this protein source. The soyabean containing diets were then supplemented with crystalline amino acids thus; methionine only, dual supplemented with two methionine and lysine levels and finally, a supplement comprising methionine, lysine, tryptophan, threonine, arginine and histidine. The results showed that soyabean meal (SBM) was inferior to the reference protein when SBM was used to replace 66% of the fishmeal and that no significant restoration in growth, feed efficiency and apparent net protein utilization was obtained by either methionine only or dual methionine and lysine supplementation. However, by comparison with the fish fed the unsupplemented, single and dual supplemented diets, multiple amino acid incorporation was associated with significantly improved percentage weight gain, specific growth rate and marginal improvements in apparent net protein utilization. However, performance was not equal to that of the fish fed the fishmeal based control diet. The results are discussed with respect to the level of each of the essential amino acids (EAA) as a proportion of the total EAAs (A/E index) of test diets by reference to the whole body tissue amino acid profile of rainbow trout.  相似文献   

Inclusion of a commercial poultry by-product meal as a protein replacement of fish meal in practical diets for African catfish Clarias gariepinus (Burchell 1822)     

A A Abdel-Warith  P M Russell  & S J Davies 《Aquaculture Research》2001,32(S1):296-305

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The effect of vitamin E on the serum complement activity of the rainbow trout, Oncorhynchus mykiss (Walbaum)     

J. Pearce  J.E. Harris  & S.J. Davies 《Aquaculture Nutrition》2003,9(5):337-340

Rainbow trout were fed three experimental diets with varying levels of vitamin E (α‐tocopherol) supplementation (0, 100 and 1000 mg kg^?1 diet), and the effects of feeding these diets on serum spontaneous haemolytic activity and classical complement activity were investigated. Hepatic α‐tocopherol levels reflected the dietary intake of the vitamin. Fish fed the diet deficient in vitamin E showed reduced growth and increased mortality. Their hepatosomatic index and erythrocyte fragility was significantly higher than both the supplemented groups and haematocrit, and complement activity were all significantly lower. There appeared to be some enhancement of serum complement activity correlated with increased dietary supplementation with vitamin E but the benefits of supplementation at levels above those currently recommended were not established.  相似文献   

Conservation and management of the rivers of the Kruger National Park: Suggested methods for calculating instream flow needs     

Jay O'Keeffe  Bryan Davies 《水产资源保护:海洋与淡水生态系统》1991,1(1):55-71

1. Six major river systems flow west to east across the Kruger National Park (South Africa). All arise outside the western boundary of the KNP, and are outside the jurisdiction of the Park authorities. 2. Growing human populations to the west of the Park are placing increasing demands on the water resources of these rivers, and a variety of artificial changes threaten the ecological integrity of the rivers. 3. As a result, the Luvuvhu and Letaba Rivers to the north no longer have a perennial flow, while the flow of the Crocodile River on the southern boundary of the Park has been regulated to a more constant regime due to irrigation demands. The Letaba, Olifants, and Crocodile Rivers all receive diverse pollutants. The Sabie River, at present the least disturbed system, and biologically the most diverse in South Africa, is threatened with multiple regulation within the next five years. 4. The paper describes the development of initial protocols for the assessment of instream flow needs for the Luvuvhu and Sabie Rivers. These methods require an extension of existing methods developed in the USA to ensure the maintenance of ecological processes, rather than the maintenance of single target species. 5. Two methods are described: one that identifies the consumptive and non-consumptive water requirements of the rivers, adding all consumptive to the limiting non-consumptive quantity to give a base-flow requirement. 6. A second method uses a conservation status model to assess the ecological consequences of flow reductions generated through a hydrological model, in response to different impoundment conditions. 7. Both methods are successful in appropriate circumstances, but we conclude that the proposed impoundment and agricultural development of the Sabie River, in particular, is an inappropriate use of this unique resource, and that the catchment would be more advantageously developed for tourism, recreation, and nature conservation.  相似文献   

Palaeoecological insights for the conservation of aquatic ecosystems in dryland environments: A case study of the Verlorenvlei system,South Africa     

Andrew J. Baxter  Bryan R. Davies 《水产资源保护:海洋与淡水生态系统》1994,4(3):255-271

Verlorenvlei, a dryland aquatic ecosystem in South Africa, has been identified as having enormous conservation importance. Although the system has Ramsar status and is widely regarded as being in ‘pristine' condition, neither statutory control nor any form of management is currently in existence. Based on the analysis of fossil pollen derived from the sediments of Verlorenvlei, a sequence of rapid changes within the riparian and aquatic vegetation is identified. Synchronous changes in the rate of sedimentation suggest a threefold increase in annual sediment deposition since the mid-18th century—the onset of colonial settlement. The pollen spectra prior to the arrival of colonial settlers suggest that abundant Poaceae (grasses) and rooted aquatic plants dominated the vegetation of the site. Radical changes in the pollen record become evident after the time of European colonization. Aquatic vegetation, including Gentianaceae (water lilies) and Potamogetonaceae, show a marked decrease while riparian vegetation, particularly reed elements such as Cyperaceae, Typhaceae and Juncaceae, are seen to increase progressively. Terrestrial pollen indicators reveal an expansion in the vegetation of classic disturbance indicators such as Asteraceae, Oxalidaceae and Scrophulariaceae. As the wetland has already endured rapid ecological adjustments in the face of colonial (and more recent) occupation of the broader landscape, it cannot be regarded as being in a ‘pristine’ state. Indeed, Verlorenvlei is interpreted as having reached a state of ‘transitional’ ecological equilibrium in which it continues to endure a number of rapid ecological changes; nonetheless, it is still worthy of conservation and management, not least because of its role as a strategic wetland in a dryland environment. Failing the timely implementation of remedial action in the form of an integrated conservation and management plan, Verlorenvlei appears destined to become irreversibly altered. Dryland aquatic ecosystems are vital aquatic resources in so called ‘Third World’ regions of the world yet, paradoxically, scientific research on, and the conservation of, these environments in the Southern Hemisphere are rare by comparison to wetland environments in the northern temperate zones. Although many dryland aquatic systems may already be altered, most are worthy of urgent management and conservation action, bearing in mind the fundamental question: ‘What is it that we wish to conserve?’. A number of recommendations for the management of dryland aquatic ecosystems such as Verlorenvlei are listed.  相似文献   

Machine learning highlights the importance of primary and secondary production in determining habitat for marine fish and macroinvertebrates     

Kevin D. Friedland  Michelle Bachman  Andrew Davies  Romain Frelat  M. Conor McManus  Ryan Morse  Bradley A. Pickens  Szymon Smoliński  Kisei Tanaka 《水产资源保护:海洋与淡水生态系统》2021,31(6):1482-1498

1. Species distribution models for marine organisms are increasingly used for a range of applications, including spatial planning, conservation, and fisheries management. These models have been constructed using a variety of mathematical forms and drawing on both physical and biological independent variables; however, what might be called first-generation models have mainly followed the form of linear models, or smoothing splines, informed by data collected in the context of fish surveys.
2. The performance of different classes of variables were tested in a series of species occurrence models built with machine learning methods, specifically evaluating the potential contribution of lower trophic level data. Random forest models were fitted based on the classification of the absence/presence for fish and macroinvertebrates surveyed on the US Northeast Continental Shelf.
3. The potential variables included physical, primary production, secondary production, and terrain variables. For accepted model fits, six variable importance measures were computed, which collectively showed that physical and secondary production variables make the greatest contribution across all models. In contrast, terrain variables made the least contribution to these models.
4. Multivariable analyses that account for all performance measures reinforce the role of water depth and temperature in defining species presence and absence; however, chlorophyll concentration and some specific zooplankton taxa, such as Metridia lucens and Paracalanus parvus, also make important contributions with strong seasonal variations.
5. Our results suggest that lower trophic level variables, if available, are valuable in the creation of species distribution models for marine organisms.

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