A vanished ecosystem: Sophora microphylla (Kōwhai) dominated forest recorded in mid-late Holocene rock shelters in Central Otago, New Zealand

Abstract

When European settlers first arrived in Central Otago, New Zealand, in the 1850s, they found much of the region to be semi-arid, rocky, and treeless – at least partly due to fires after the arrival of Polynesians in the late thirteenth century or early fourteenth century. The condition of the vegetation rapidly deteriorated with the European introduction of grazing mammals (including sheep and rabbits), leading to a situation now, where it is difficult to understand what the ‘original’ vegetation was. However, rock overhangs (termed ‘shelters’ in this paper) accumulated dried vegetation in the prehuman mid-late Holocene. Much of this material appears to have been transported into the shelters as roosting material by the extinct giant moa birds. This record of dried vegetation, and sometimes the coprolites scattered through it, is therefore an important source of information about the pre-human vegetation, as well as the diet of the moa. The present study analyses samples of mid-late Holocene dried leaf material from 115 rock shelters, identifying the taxa on the basis of epidermal details of the leaf cuticle. Based on it being the only large tree in the area now, and the nearly ubiquitous presence of its leaves in the shelters, the most important plant in the area is considered to have been Sophora microphylla. Based on the size of old, relict, ‘champion’, trees in the area now, it likely formed a forest with a continuous, but low (perhaps 14 m) and open canopy over the study area. Other trees which were present and are entirely absent (or almost so) from the area now include Pittosporum tenuifolium and Pseudopanax ferox. They suggest more closed canopy forest, perhaps in more localized areas, but were subordinate to Sophora. However, other common plants included Carmichaelia, Rubus, and Hebe lycopodioides that are more suggestive of lower, open vegetation. There is no indication of a conifer component or of ‘wetter’ forest trees such as Nothofagus and Griselinia. Cuticle within the largest associated coprolites indicate that moa (Aves, Dinornithiformes) was ingesting a similar range of plants as the shelter material. Of particular interest is that moa clearly ate Sophora microphylla, the first evidence for this. Together these data suggest a Central Otago ecosystem where a low Sophora microphylla forest predominated and was utilized and perhaps maintained by moa. POLE: VANISHED-ECOSYSTEM 2 Mike Pole. Queensland Herbarium, Brisbane Botanic Gardens Mt Coot-tha, Mt Coot-tha Rd, Toowong, Australia murihiku@yahoo.com