Tiritiri Matangi Island: what if nothing had been done?

Forty years since the cessation of grazing on Tiritiri Matangi, the island has been transformed by a restoration programme. However, a big question remained: What the island would have looked like if restoration had not occurred? This study addresses that question. Some sections of the island were deliberately not restored and allowed to regenerate naturally to provide a reference point for the changes brought about by direct intervention. In one area a transect of plots was available in which species composition and frequency information had been measured in a pre-restoration state. A comparison, almost 30 years later, showed that many previously dominant pasture grasses had been lost, and replaced by native grassland dominated by Microlena stipoides. Also, native shrubs and small trees absent from the pasture grassland in 1979 were now present, although in low abundance. Overall this study shows that in this environment, even 40 years after the cessation of grazing, the succession to woody vegetation is slow. It may be another 40 years before woody vegetation dominates the area. This demonstrates that active restoration of the island greatly accelerated the development of forest over natural regeneration, and this has undoubtedly allowed the rapid expansion of many otherwise very restricted bird species.