Effect of cattle grazing and seedling size on the establishment of Araucaria cunninghamii in a silvo-pastoral system in northeast Australia

Abstract

A study was undertaken to assess the effect of tree age at which grazing commenced and seedling size on the establishment of Araucaria cunninghamii (hoop pine) trees in a silvo-pastoral system on the Atherton Tablelands of northeast Australia. Grazing with dairy cattle commenced at three ages after tree planting: (1) 2 weeks; (2) 6 months and (3) 18 months. Seedlings of two size classes, small (15cm tall and 18 months old) and large (45cm tall and 27 months old), were used. Trees were measured for survival and height, and assessed for physical damage and development of multi-stems at ages 6, 12 and 24 months. Results showed that tree survival and height did not differ significantly with age at which grazing commenced and that grazing did not cause unacceptable mortality, damage or reduction in height growth of A. cunninghamii. The lack of cattle impact was mainly because A. cunninghamii has a special morphological feature, prickly needles, which discourages cattle from physical contact. Although tree height of A. cunninghamii varied significantly between the two seedling sizes, the difference became smaller as the trees grew. It is suggested that for the establishment of A. cunninghamii in silvo-pastoral systems, grazing can be allowed almost immediately after tree planting, providing an appropriate stocking rate is used. There are no apparent advantages in using larger, compared with smaller, seedlings.