Post-fire recovery of a dryland forest remnant in the Wither Hills, Marlborough

Fire is a major threat to remnant native woody vegetation in dry, lowland New Zealand. This is because the woody flora lacks specific adaptations to survive fire, and seedling regeneration is constrained by summer drought, limited native seed rain and intense competition from non-native grasses that are often favoured by fire. In December 2000, a fire burnt a 41 ha remnant of mature Kunzea robusta (Myrtaceae) forest in the Wither Hills, Marlborough, a dry region with little remaining native woody vegetation. Shortly after the fire the area was fenced to exclude grazing animals and oversown with pasture species to stabilise the soil. A study was then initiated in June 2001 to determine the rate and direction of native forest recovery using 15 randomly located monitoring plots. Plots were re-measured in summer 2001, 2002, 2003 and 2015. Additional strategically located plots monitored the survival and re-growth of burnt individuals of Kunzea robusta, Sophora prostrata (Fabaceae) and Clematis quadribracteolata (Ranunculaceae). In spite of the dry climate, limited seed rain, oversowing and absence of grazing, woody biomass has started to recover after fire in the Wither Hills – but slowly as non-native grasses are overwhelmingly dominant. After 15 years, woody biomass and cover are less than 5% of the original estimate for the area. However, while fire-damaged Kunzea mostly died, Sophora and Clematis individuals have recovered through resprouting. Our study site is typical of many dryland areas in New Zealand in which native biodiversity is part of a productive landscape and is under threat from fire, weeds and grazing. It is inevitable that a proportion of dryland reserves will be burnt each decade and our results underscore the need for conservation planning to incorporate fire and for experimental investigations to assist with accelerating native vegetation recovery.