Pine needle consumption and bark stripping by sheep grazing annual pastures in young stands of widely spaced Pinus radiata and P. pinaster

Abstract

The consumption of the pine needles and the stripping of bark by sheep grazing annual pastures in three open stands of P. radiata and one of P. pinaster were measured. The P. radiata were four years old and the densities were 250, 500 and 750 trees ha^-1. The P. pinaster included two, three and four year-old trees and the density was 440 trees ha⁻¹.

Needles were eaten immediately after the sheep were admitted and this continued throughout the year. Within ten weeks of the start of winter grazing, sheep stocked at 7–10 ha⁻¹ had eaten about half of the accessible needles on both species where densities were less than500 trees ha⁻¹. The estimated consumption was about 260 g sheep⁻¹ day⁻¹ for the P. radiata. Bark stripping then commenced and continued throughout spring and summer on most plots. In some plots at low tree density, bark was stripped from more than 35% of the trees. In denser stands, needle consumption per tree was less and bark was stripped from less than 5% of the trees.

Bark damage was most common on the smaller trees, and severity of stripping was negatively correlated with tree size. Of all the trees with bark damage, 22% of the P. pinaster and 14% of the P. radiata had more than half of the stem circumference stripped. A number of these will probably suffer both stem distortion and growth retardation, and some may die.

Methods of reducing the incidence of bark damage are discussed.