Experimental investigations of the effects of takahe and deer grazing on Chionochloa pallens grassland, Fiordland, New Zealand.
Abstract
An experiment was carried out in 1978-86 to study the individual and combined simulated grazing effects on C. pallens tussocks of takahe (Notornis mantelli) which eat only the succulent basal butt of the tiller, and red deer (Cervus elaphus) which eat the leaf blades. Chemical and morphological changes induced in tussocks by cutting were monitored. After 8.5 years of cutting, plant biomass and carbohydrate concn were determined. Effects of a combination of cutting (halfway up the blade, or at the sheath-blade junction) and pulling out tillers (25-100%) were determined. The combined effect of cutting and takahe feeding induced a long-term decline in tussock biomass. After 8.5 years of cutting a 64% reduction in biomass compared with controls was observed. Tussocks were estimated to require 20 years to recover, even without further grazing. Pulling 25 and 50% of tillers caused no decline in tillering rates, whereas cutting tillers at the sheath-blade junction did. Deer control and takahe recovery was investigated. Continued deer control is recommended to avoid habitat degradation by grazing which is more rapid than recovery time.