An expedition to Chile andArgentina was made with the main purpose of collecting representative samples of the genetic variability of the species Hordeum chilense Roem. et Schult. During the field trips 55 populations of H. chilense and 45 populations of other Hordeum species were collected. The habitats where the species were growing were analyzed.

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This work is the product of a long process that tried to approximate the principia involved in sustainable agriculture in an attempt to analyze it. We believe that these principia are crucial for the systematic, rigorous, and consistent development of sustainable agriculture. The unifying concepts of agriculture sustainability are classifi ed into seven fundamental principles: (i) there is a hierarchy in decision-making with respect to human actions on the landscape and environment; (ii) human impact on the land should be analyzed from different perspectives (local, global, anthropocentric, and ecocentric); (iii) the carrying capacity in an agrarian context is crucial to ecosystem management and design; (iv) humans arrange nature with little consideration of its own natural organization; (v) land-use planning and design are subordinate to the order determinants that occur in a particular situation; (vi) cultural landscape is a result of humans' actions on the land; and, (vii) the concepts of agriculture and rurality lack a territorial connotation, unlike farm and comarca (a region connected through a common local market). Finally, agriculture sustainability should be addressed from various focal points, with a focus on nature and culture as its main determinants.

Highlight: Phenological development of aboveground portions of shadscale and winterfat was observed for 7 years in Curlew Valley, Utah, and graphically related to patterns of precipitation and temperature. The considerable variation in year-to-year phenology should be noted by those taking data in other basic and applied studies. Preset dates for livestock management actions that ignore yearly phenological differences could result, in some years, in the plants being used during phenological states that are susceptible to damage by browsing. Seed set cannot be counted on every year, complicating one of the assumptions of rest-rotation grazing. Explanations of various rangeland plant phenomena often require an understanding of the phenological course of development of the organisms under study. For example, transpiration rates of desert plants are only partially explained by soil moisture depletion. Loss of ephemeral leaves sharply cuts transpiration losses by cold-winter desert shrubs during summer drought (Moore et al. 1972). Productivities are often inferred from what are thought to be peak standing crops (Holmgren and Brewster 1972). However, if the periods of growth were better defined, one could more accurately gauge when peak standing crop occurs. Nutritive values also vary with phenological stages. Sampling of materials on a preset date for several years may result in collection of materials in radically different phenological stages. Management plans are dependent on plant development. Desert ranges are best suited for livestock utilization during the dormant periods. Although desert plants commonly provide more palatable and nutritious forage during their periods of growth, the plants can withstand much less grazing pressure and have high mortality rates if grazed at that time (Cook 1971). If phenological patterns and their likely variations due to climatic differences were more completely known, we could better adjust livestock use to avoid excessive damage by grazing. Although some data are available on the phenology of the aboveground growth of cold winter desert and semidesert species, particularly sagebrushes, (Morton and Hull 1975) only Authors are professor and former Rockefeller Foundation graduate fellow, respectively,

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