Showing papers in "Journal of Applied Ecology in 1966"

A method of estimating the total length of root in a sample

Abstract: Research in many fields of plant ecology could be helped by quicker and more satisfactory methods of determining the amount of root in a volume of soil. Most quantitative studies of roots have used weight as the means of assessing the amount of root; but it is generally accepted that the capacity to take up water and salts is usually more closely related to the surface area or total length of the root system than to its weight. Interest in root length has been stimulated by papers by Gardner (1960, 1964) and Cowan (1965) dealing with water uptake from soil, in which length of root per unit volume of soil is an important parameter. The main difficulties indetermining root length arise from the great lengths which can occur in even small volumes of soil. Some root densities which have been reported for plants growing outdoors are: 364-3434 m of root per litre of soil under grass swards (data of Pavlychenko quoted by Troughton 1957), 66-548 m/l under Graminae (Dittmer 1938), up to 21 m/l under coffee trees (Nutman 1934), up to 18 m/l under sugar-cane (Evans 1938). Thus, even if it is practicable to use soil samples as small as 041 1., direct measurement of the roots may take a long time. Indirect methods have been used: for instance, measuring root diameters and then determining root volume (Evans 1938); or measuring the length of a small portion of the root sample, then weighing this portion and the remainder. However, these methods are often inaccurate because of variations in the ratios volume: length and weight: length. This paper describes a new method of estimating the total length of root in a sample, the line intersection method. I believe that it will in many circumstances prove more satisfactory than any existing method.

Behavioural pathology in fish; a qnastitatíre study of sublethal pesticide toxicatíon.

Abstract: The continued increase in use of the persistent pesticides over the last decade is well documented. Their widespread application in the control of disease-carrying and agriculturally important arthropods and other invertebrates has resulted in thousands of millions of kilograms of these materials being introduced into the environment. During 1962, in the United States alone, 177 800 000 kg of insecticides were used. Herbicides and fungicides were also applied in great quantity; according to Thimann (1964) the amounts of these totalled about half that for insecticides. Since the trend is for increased consumption, the total quantities released into the environment in 1965 will be substantially higher. Some of the effects of these pesticides are known and well documented. The relative sensitivity of a variety of living systems to lethal concentrations has been studied in some detail (Doudoroff, Katz & Tarzwell 1953; Sawyer 1959; Pickering, Henderson & Lemke 1962). Less attention has been paid to physiological effects, and little is yet known of the ecological consequences of pesticides in natural water supplies, despite some excellent studies of the problem (Harrington & Bidlingmayer 1958; Prevost 1960; Cope 1961). Even allowing for these recent gains, surprisingly little is yet known regarding the biological effects of pesticides. For example, in spite of the near-ubiquitous use of the organochlorine compounds for almost 20 years, their biochemical mode(s?) of action remains obscure. Recently O'Brien & Matsumura (1964) advanced a new hypothesis for the mode of action of DDT, attempting to reconcile the high level of toxicity of organochlorine compounds with their extreme resistance to biochemical degradation. Whether or not this new and interesting hypothesis proves correct, the significant fact remains that for years we have been introducing vast quantities of these compounds into the environment without knowing in detail the nature of their biological properties. We have tended to assume, when questions of potential danger to living systems are raised, that the toxic properties of pesticides are limited to those effects which are already well known through previous experimentation or trial-and-error activities. The many-faceted problems of pesticide-altered ecosystems are even more complex. A review of the recent and current research on both field and laboratory aspects of microchemical contaminants makes one point very evident: we are today still working largely in an unknown and complex realm, our efforts dominated by the search for suitable means of measuring the effects which these compounds have on living systems. This search is the necessary first step. It is now clear that only after we have devised thoroughly adequate methods of measurement, capable of detecting physiological, behavioural and ecological changes due to sublethal concentrations of pesticides and other biocides, shall we be able properly to evaluate their impact on ourselves and our environment.

Ecology and the industrial society

Abstract: A review is presented of a book which contains material presented at a symposium entitled Ecology and the Industrial Society. The symposium was held April 13-16, 1964 at the University College of Swansea, in Wales. Aspects of air pollution were discussed with emphasis on coal smoke, smelter smoke, photochemical smog and fluorides in the atmosphere. Problems involving stream pollution were also assessed. Much information is included on general ecology.

Soil animals as vectors of organochlorine insecticides for ground-feeding birds

Abstract: The uptake of small sublethal doses of organochlorine pesticides by birds appears now to be quite a common phenomenon, but the pathways have been, for the most part, little examined. This paper discusses some of the ecological factors affecting the uptake and passage of organochlorine compounds in terrestrial ecosystems with particular reference to soil animals and ground-feeding birds such as the Robin (Erithacus rubecula), Skylark (Alauda arvensis), Lapwing (Vanellus vanellus), Starling (Sturnus vulgaris), thrushes (Turdus spp.) and corvids (Corvus spp.) for which animals form a large fraction of the diet. Blackbird (Turdus merula) and the Kestrel (Falco tinnunculus), both of which take large numbers of invertebrates, though the Blackbird is an omnivore with a partiality for fruit and the Kestrel a raptor feeding largely on small mammals. The ppm intervals chosen follow approximately a log scale which is rounded to the nearest convenient figures. The two species cannot be compared in detail since liver alone was used for analysis of the Kestrels and mixed viscera, which consisted of liver, heart and spleen (and possibly gut in some instances), in the Blackbirds. Both species came from a large number of counties but as the birds were generally found dead and the cause of death unknown neither set can be assumed to be a fair sample of the population. However, several features can be deduced. First, that both species had picked up residues of all the common organochlor- ine pesticides used in this country and secondly, apparently in contrast to the American situation, dieldrin and heptachlor epoxide residues are commonly present. DDT itself features very insignificantly but the preponderance of DDE indicates a large original DDT source. The relatively high amounts of heptachlor epoxide and low amounts of BHC contrast with the annual depositions of these compounds (see Strickland 1965) and reflect probably the biased nature of the samples as well as the known properties of relative persistence of these compounds in biological tissues.

Shelterbelts and Windbreaks.

Abstract: Shelterbelts and windbreaks , Shelterbelts and windbreaks , مرکز فناوری اطلاعات و اطلاع رسانی کشاورزی