Herbert C. Hanson

The concept of climax in arctic and alpine vegetation

TYpEs oF GRADIENTS ............................................................................ 130 RELATIONSHIP OF COMMUNITIES TO HABITATS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 132 UNIT OF STUDY ............................................................................................ 133 CHANOES ........................................................................................................ 13 5 T~ES OF CHANOE REPLACEMENT CHANGE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 136 INTERCOMMUNITY CYCLE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 138 DmECTIONAL CHANOE ................................................................ 139 FLUCTUATION CHANGE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 143 CHANGES IN SPACE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 146 RATE OF CHANGE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 147 CRITIQUE OF CONCEPTS ................................................................................ 148 C~OE CHARACTERISTIC OF STEADY-STATE COMMUNITZ ................ 149 CRITERIA OF CLIMAX ............................................................................ 149 RBVmW OF CLIMAX CONCEPTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 150 REvmw OF SUCCESSION CONCEPTS .................................................... 154 REVIEW OF CLASSIFICATION SYSTEMS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 157 REVIEW OF ARCTIC AND ALPINE STUDIES ........................................ 158 SUMMARY ..................................................................................................... 179 LIT~ATUaE CITED ........................................................................................ 181

Ecology of the Grassland

ConclusionThis paper has been limited chiefly to a discussion of the nature of the characteristics that are classified under the category of floristics and structure of the community. Methods of studying these characteristics and applications of the methods in grassland research have been described and evaluated. The four other categories of community characteristics, namely, environmental relations, geographic distribution, plant succession and processes involved, and classification are not considered in detail.The choice of characteristics to measure and the methods to employ depend primarily upon the purpose of the study and secondarily upon the time, equipment, assistance,etc., that can be made available. For a full understanding of a community all the characteristics must be studied.Grassland ecology will be advanced by careful consideration of all basic principles and characteristics of vegetation and by the use of methods that have yielded results or by the development of new methods.

Ecology of the grassland. II.

SummaryDuring the past decade or so increasing attention has been given to refinements in methods and procedures in the study of grassland communities and to more complete characterizations of communities. Advances have been made toward standardization, but it is premature at the present stage of development of grassland ecology to expect rigid formulations of research procedures. It is evident in recent publications that the trend is toward selection and further refinement of methods which will measure as objectively as possible the characteristics that are most significant in a particular investigation. For a complete analysis and description, all characteristics of the community require study.

Ecology in Agriculture

The major emphasis in ecological research, by ecologists, has been on native or wild plants and animals and not on cultivated plants and domesticated animals. Human ecology has also been largely untouched by ecologists. Scientists in other fields such as agronomy, horticulture, pathology, geography, sociology, and economics have not only been making increasing use of ecological concepts and procedures, but have been urging ecologists to broaden the scope of their investigations and teaching, so as to include the whole gamut of life in relation to the environment. The value of men who have been well trained in ecological technique and thinking has been long appreciated in forestry and range management, but now the call for help is coming from numerous additional fields. I am not advocating any diminution of interest and activity by ecologists in native plants and animals. We need to study these organisms under natural conditions much more than we have in the past in order to secure an adequate fund of basic information to use in planning improved relationships of people to the land. A few examples will be described to illustrate the need for ecologists to conduct research in crop plants. At a recent conference of scientists and representatives of industry to consider ways and means to increase domestic production of flaxseed and to improve the quality of the oil, a prominent plant pathologist emphasized the need for a comprehensive study of the ecology of the flax plant. While much research has been done to improve varieties by breeding to control diseases, and to maintain yields by good agronomic practices, only a small start has been made in determining the relationships of the flax plant to soil and climatic conditions. Since one of the chief hazards in growing flax is its high degree of sensitiveness to changes in environmental conditions and since it is an important crop, not raised in sufficient quantity in the United States to supply the demand, it furnishes excellent material for the ecologist interested in plant-weather-soil relationships. It also furnishes a good op-

Characteristics of the Stipa Comata-Bouteloua Gracilis-Bouteloua Curtipendula Association in Northern Colorado

1. The effects of mold in the cultures of Tenebrio molitor on pupal and adult weights are given, and these weights are compared with weights of pupal and adult beetles reared in normal cultures without mold. 2. The results of a few observations are given of the interactions among the several grain inhabitants that may occur with Tenebrio molitor: the flour beetles of the genus Tribolium, the flour moth Ephestia, and mites of the genus Acarus. Of these, Tribolium appears to be more detrimental to populations of Tenebrio, but the mites show the greatest fluctuations in population density. 3. Analyses of the reactions of Tenebrio larvae and adults to various conditions of light, dark, and the presence of the insecticide paradichlorobenzene (PDB) are given. Various combinations of these conditions indicate that the apparently inherent photonegativity of the species is a stronger directing force in the behavior and orientation of Tenebria than is its negativity to the lethal chemical PDB. 4. Humidity experiments showed that the animal does not usually aggregate in the dark, but under various conditions of light, dark, moisture and dryness, aggregations were seen to form as negative responses. 5. Observations of the widespread phenomenon of letisimulation (death feigning) are described. The adults are more inclined to exhibit this behavior than are the larvae or pupae. 6. The tendency of Tenebrio to acclimate to unnatural circumstances has been described. This was shown in the responses to light intensity, poisonous chemicals, and mechanical stimulation by handling.

Principles concerned in the formation and classification of communities

ECOLOGICAL SUCCESS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 0 GROUPING OF SPECIES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 2 ANALYSIS AND DESCRIPTION OF STANDS AND COMMUNITY TYPES ..... . . . 101 CLASSIFICATION OF COMMUNITIES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 105 SUMMARY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 116 LITE~TtmE CITED . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117