Predicting pasture production under poplars using canopy closure images

Abstract

Poplar trees serve a wide variety of purposes on New Zealand farms. Their high growth rate and ability to establish from poles make them a very suitable tree species for soil conservation plantings on erosion-prone hill pastures. The impact that such plantings have on understorey pasture production as the tree canopy develops in size was determined by measuring pasture dry matter (DM) production on three North Island sheep and beef hill farms. Poplars markedly reduced annual pasture production by up to 50% at high canopy closure. To maintain pasture production at 65-75% of uneroded open pasture, poplar canopy closure should not exceed 50%. However, it must be emphasised that the loss in production through soil erosion (e.g. slips or earthflows) without poplars can be even greater, more permanent, and much more unpredictable. Keywords: Populus, soil erosion, agroforestry, digital images, canopy closure, understorey pasture