Aspect differences in an unimproved hill country pasture

Abstract

A number of climatic variables were monitored on N, S, E, and W aspects of a hill in the foothills of the southern Ruahine Range, New Zealand, over a 12-mo. period. Wind speed values were consistently higher on the N aspect than on the W, E, and S aspects. Differences in net radiation between the N and S aspects were largest during the winter and smallest during the summer months. All evapotranspiration values calculated were larger for the N than for the S aspect. Soil moisture tension differences were not detected during winter, but during the remainder of the year soil of the N aspect had the highest moisture tension and that of the S aspect the lowest. Rainfall differences among aspects were difficult to detect because of the effects of wind on rain gauge catch. Differences among aspects in average monthly 40 mm air temperature were not apparent. However, large differences in the average monthly 40 mm soil temperature of the various aspects were detected. During the Jan.-Aug. period the N aspect was warmest and the S aspect coolest, but for the remainder of the year the E aspect was warmest. The interrelationships of some of the above variables are discussed. The significance of wind in the hill pasture environment is probably underestimated.