Addition series field experiments were conducted near Moscow, ID, in 1987 and 1988 to determine the relative aggressiveness of spring barley and wild oat and to determine the effect of barley and wild oat density and proportion on barley grain yield and wild oat seed rain. Regression analysis was used to describe the relationship of the aboveground biomass and grain yield to species density. Barley was more aggressive than wild oat. Barley biomass was affected most by intraspecific competition, while wild oat biomass was affected most by interspecific competition. Barley aggressiveness changed little throughout the growing season. Wild oat aggressiveness varied but was always less than barley aggressiveness. Increasing wild oat density had a negative, asymptotic-type effect on barley grain yield at all barley densities. However, the effect of wild oat was greatest at the lower density of barley. Increasing barley density decreased wild oat seed rain.

A 136-m-long drill core of sediments was recovered from tropical high-altitude Lake Titicaca, Bolivia-Peru, enabling a reconstruction of past climate that spans four cycles of regional glacial advance and retreat and that is estimated to extend continuously over the last 370,000 yr. Within the errors of the age model, the periods of regional glacial advance and retreat are concordant respectively with global glacial and interglacial stages. Periods of ice advance in the southern tropical Andes generally were periods of positive water balance, as evidenced by deeper and fresher conditions in Lake Titicaca. Conversely, reduced glaciation occurred during periods of negative water balance and shallow closed-basin conditions in the lake. The apparent coincidence of positive water balance of Lake Titicaca and glacial growth in the adjacent Andes with Northern Hemisphere ice sheet expansion implies that regional water balance and glacial mass balance are strongly influenced by global-scale temperature changes, as well as by precessional forcing of the South American summer monsoon.