Deciduous or evergreen: Does it make a difference to understorey pasture yield and riparian zone management?

Abstract

This paper uses data from an artificial shade trial to compare the impacts of shade duration on pasture production with deciduous and evergreen tree species. Results indicated that light quantity was not the only main limiting factor in understorey pasture yield. At low levels of shade (<40%), pasture relative yields under the nitrogen-fixing tree, Acacia melanoxylon, were greater than relative yields under corresponding levels of artificial shade. We concluded that when comparing tree understorey pasture yields, the variation between tree species was greater than the variation between deciduous and evergreen tree groups. For a deciduous tree species to be effective in mitigating pasture yield during the leaf-free period, they must be leaf-free for longer than 4 months. Additionally, in riparian zone plantings the amount of shading required to reduce water temperatures to desired levels for invertebrate stream life is too high to maintain pasture cover. Selection and management of appropriate tree species to reduce shading intensities is required to maintain adequate understorey pasture yield and density. Further work on deciduous tree species is required to further understand the interactions between understorey pasture yield, duration of shade and tree species. Keywords: Acacia melanoxylon, agroforestry, artificial shade, Eucalyptus nitens, light, Poplar spp.