Holocene forest fires in the upper Clutha district, Otago, New Zealand

Abstract

Surveyors’ maps and descriptions show that the extent of tall forest in the upper Clutha dis trict was almost the same at the beginning of Euro pean settlement in the 1850s as it is today. Since the 1850s fires in non-forest vegetation have burnt up to forest boundaries, but in the one locality where a large block of Nothofagus forest was burnt (about 1891), succession towards podocarp woodland is now advanced. Totara (Podocarpus hallii) logs were abundant on mountain sides down-valley from ex isting forests at the time of European settlement. Radiocabon dates range between 730 and 1200 yr BP, with the younger dates likely to be closest to the time of destruction of the trees. Charcoal occurs on slopes where soil movement after fire has led to burial and preservation, and in alluvial fans and ter races. It is most frequent between altitudes of 300 and 1000 m, and depths of 20–40 cm. None was found where annual precipitation exceeds 3600 mm, very little where it is less than 450 mm, and none within existing forest except close to margins. Frag merits were identified as angiosperm or podocarp. Nothofagus and six Other angiospem genera were confident1y distinguished. Six species of podocarp were separated, though usually as probable rather than definitive identifications; most were identified as Phyllocladus alpinus, but Prumnopitys taxifolia, Halocarpus, and Podocarpus also occur. Podocarp charcoal is widely distributed though the district, usually dispersed through the subsoil, and ranges in age from 860 to 8490 years BP. Nothofagus char coal is most abundant near surviving Nothofagus stands, often as substantial pockets. One sample was dated at 3830 years BP, whereas the remainder date at 1620 years BP or younger. Charcoal of Kunzea ericoides andor Leptospermum scoparium, which usually grow as fire-induced stands, dated to as old as 3420 years. Charcoal and totara logs dated be tween 430 and 860 years BP, together with abundant undated material with similar stratigraphy, indicate burning within the Period of Maori Presence. © 2001 Taylor & Francis Group, LLC.