Historically, riparian vegetation has been defined as vegetation rooted at the water's edge (Campbell and Franklin 1979). Quite often, however, the stream influences vegetation in many ways and well beyond the water line. In lotic systems, the stream is not only responsible for increased water availability, but also for the soil deposition, unique microclimate, increased productivity, and the many consequential, self-perpetuating biotic factors associated with riparian zones. These factors all contribute in the formation of a unique assemblage of plant communities quite distinct from upland communities surrounding the riparian zone. Therefore, along streambanks, other lotic systems, and even ephemeral drainages, riparian ecosystems could best be defined as those assemblages of plant, animal, and aquatic communities whose presence can be either directly or indirectly attributed to factors that are stream-induced or related (Kauffman 1982). Riparian zones can vary considerably in size and vegetation complexity because of the many combinations that can be created between water sources and physical characteristics of a site (Odum 1971, Platts 1979, Swanson et al. 1982). Such characteristics, include gradient, aspect, topography, soil type of streambottom, water quality, elevation, and plant community (Odum 1971). However, riparian zones, particularly those bordering streams or rivers, have several characteristics in common. They are ecotonal, with high edge to area ratios (Odum 1978). As functional ecosystems they are very open with large energy, nutrient, and biotic interchanges with aquatic systems on the inner margin (Cummins 1974, Odum 1978, Sedel et al. 1974) and upland terrestrial ecosystems on the other margin (Odum 1978). Thomas et al. (1979) stated that all riparian zones within managed rangelands of the western United States have the following in common: (1) they create well-defined habitat zones within the much drier surrounding areas; (2) they make up a minor proportion of the overall area; (3) they are generally more productive in terms of biomass-plant and animal-than the remainder of the area; and (4) they are a critical source of diversity within rangelands. Both density and diversity of species tends to be higher at the

State-and-transition models hold great potential to aid in understanding rangeland ecosystems' response to natural and/or management-induced disturbances by providing a framework for organizing current understanding of potential ecosystem dynamics. Many conceptual state-and-transition models have been developed, however, the ecological interpretation of the model's primary components, states, transitions, and thresholds, has varied due to a lack of universally accepted definitions. The lack of consistency in definitions has led to confusion and criticism indicating the need for further development and refinement of the theory and associated models. We present an extensive review of current literature and conceptual models and point out the inconsistencies in the application of nonequilibrium ecology concepts. The importance of ecosystem stability as defined by the resistance and resilience of plant communities to disturbance is discussed as an important concept relative to state-and-transition modeling. Finally, we propose a set of concise definitions for state-and-transition model components and we present a conceptual model of state/transition/threshold relationships that are determined by the resilience and resistance of the ecosystems' primary ecological processes. This model provides a framework for development of process-based state-and-transition models for management and research. ResumenLos modelos de estados-y-transicion presentan un gran potencial para ayudar a entender la respuesta de los ecosistemas de pastizal a los disturbios naturales y/o inducidos por el manejo al proveer una estructura para organzzar el conocimiento presente de las dinamicas del potential del ecosistema. Muchos modelos conceptuales de estados-y-transicion han sido desarrollados, sin embargo, la interpretacion ecologica de los componentes principales del modelo: estados, transiciones y umbrales han variado debido a la carencia de definiciones universalmente aceptadas. La falta de consistencia en las definiciones ha conducido a confusion y critica indicando la necesidad de un mayor desarrollo y refinamiento de la teoria y los modelos asociados. Nosotros presentamos una revision extensiva de la literatura actual y modelos conceptuales y puntualizamos las inconsistencias en la aplicacion de los conceptos de la ecologia de no equilibrio. La importancia de la estabilidad del ecosistema, detinida como la resistencia y resilencia de las comunidades vegetales a los disturbios, se discute como un concepto importante relativo al modelaje de estados-y-transicion. Finalmente, proponemos un grupo de definiciones concisas para los componentes del modelo de estados-y-transicion y presentamos un modelo conceptual de las relaciones de estados/transiciones/umbrales que estan determinadas por la resilensia y resistencia de los principales procesos ecologicos del ecosistema. Este modelo provee un marco para el desarrollo de modelos de estados-y-transicion basados en procesos para manejo a investigacion.1986, Tausch et al. 1993). After 50 y...

Environmental and topographic parameters on a mountainous forested range were analyzed to establish causes of cattle behavioral responses. Distinct home range groups of cattle were identified through examination of quality and patterns of forage use, cattle distribution, herd social structure, and cattle activities. The home range of one group encompassed only upland areas. Water and vegetation type were important parameters in determining area and degree of use. Vertical distance above water was the most important factor in determining vegetation utilization on moderately steep slopes. Time after sunrise and relative humidity factors were key factors in determining kind and timing of cattle activity. Cattle have been grazing forested ranges in western United States for more than 125 years (United States Senate 1936). Grazing units on the forests have been fenced, restricting livestock to given areas. Fencing placed definite limits on forage and often increased animal concentration on key vegetation types. Some vegetation types were over-utilized while others were left ungrazed. As the demand for more and varied uses of mountain land areas increases, it becomes important to enhance livestock distribution, alleviating concentration problems and minimizing real or potential conflicts with other resource uses. Detailed information assessing the pattern of livestock use, the types and amounts of forage consumed, and livestock distribution is required. This is only baseline information; in order to apply it, one must know the cause and the mechanism of each parameter. Determining causes for observed actions of cattle overlaps range management and applied behavioral sciences. External physical and biotic influences interact with the animal's innate behavioral complex to produce a given response. Measurement of influencing parameters must be matched with the animal response and examined to establish the cause and effect relationship. Distance from water, topography, temperature, humidity, and forage availability have been rated as important parameters in modifying animal behavior. Herd structure is a behavioral factor which could have considerable influence on grazing patterns and forage use. Many researchers have observed a given event and assessed the impact on vegetation, but those observations were often not analyzed in terms of what caused the event. This research was designed to quantitatively define the influences of topography, environment and biotic factors on cattle distribution and grazing habits. Cattle behavioral responses to external factors were described by regression relationships.

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CC-1065 (NSC 298223) is a potent new antitumor antibiotic with a unique structure produced by Streptomyces zelensis. Improved production, isolation, and assay methods are described along with physico-chemical properties and antitumor activity. Screening for soil cultures producing agents displaying both cytotoxic activity against L1210 cells in culture and in vivo activity against P388 leukemia in mice afforded a culture, Streptomyces zelensis, producing a new, potent antitumor antibiotic, CC-1065. Its production, in vitro biological activity, microbiological assays, and taxonomy have already been described1) ; a preliminary communication announced the structure2) shown in Fig. 1. Details of the structure determination have recently been described3). A molecular model of CC-1065 displayed a remarkable curvature, shape,