Growth of radiate pine (Pinus radiata D. Don) as influenced by understory species in a silvopastoral system in New Zealand

Abstract

The success of silvopastoral systems depends to a large extent on the type of understory species used under particular site conditions. The effects of understory management on tree growth characteristics were investigated in an eight-year period in a silvopastoral agroforestry experiment in Canterbury, New Zealand. The period studied was from establishment (1990) to year eight (1998). The experiment included six understory treatments: 1) bare ground, 2) Maru phalaris (Phalaris aquatica L. cv. ‘Maru’) + clovers (Trifolium spp.), 3) Wana cocksfoot (Dactylis glomerata L. cv. ‘Wana’) + clovers, 4) Yatsyn perennial ryegrass (Lolium perenne L. cv. ‘Yatsyn’) + clovers, 5) Yatsyn perennial ryegrass, and 6) WL320 lucerne (Medicago sativa L. cv. ‘WL320’) and five radiata pine (Pinus radiata D. Don) genotypes. showed that tree height growth was mainly controlled by the genetic differences (genotypes) and was affected by understory competition to a lesser degree. Diameter growth was also affected by genetic differences and was significantly reduced by understory competition starting in year two. At the end of the eight-year period, diameter, basal area, and volume index in the most competitive understory treatment (lucerne) was only 81, 66, and 64% of that in the control (bare ground). Stem form and quality characteristics were also dependent on understory and genotype treatments, indicating the need for treatment specific evaluation when developing silvicultural prescriptions.