Tree guards and weed mats in a dry shrubland restoration in New Zealand

Abstract

Associated with restoration of 150 ha of native plant communities within a highly exposed low rainfall landscape, we evaluated whether the benefits of tree guards and weed mats justified a doubling of planting costs. One-year-old nursery-grown specimens of Kānuka (Kunzea serotina) and Pomaderris (Pomaderris amoena) were planted with and without polythene and rigid plastic tree guards, and weed mats, then monitored for 12 months. Herbivory was reduced with both types of tree guard by 10–35%, but mortality was largely caused by desiccation. Polythene tree guards provided the best protection, buffering extremes of ambient and soil temperature in summer but with no effect on soil temperature in winter. Weed mat addition reduced soil temperature fluctuation further in winter; a moss turf mat was best. Both mulch and moss weed mats reduced soil temperature in summer and raised soil moisture in winter. We showed that tree guards could save at least NZ$ 70 k/ha, but this is likely to vary with plant species traits and site conditions.