The ecology and ethnobotany of karaka (Corynocarpus Laevigatus)

Abstract

Historically there has been considerable debate over the origin of karaka ( Corynocarpus laevigatus J.R. et G. Forst.) in New Zealand. In contrast, the extent and importance of prehistoric arboriculture in New Zealand has received little attention in the literature. This study reviews the ecology and ethnobotany of karaka and investigates its cultural and natural biogeography.

Maori migration traditions frequently state that karaka was introduced to New Zealand. However, molecular evidence and finds of fossil seeds of late Oligocene age show that karaka is endemic to New Zealand. Therefore, Maori traditions probably relate to the translocation and cultivation of karaka within the New Zealand region, for which there is abundant anecdotal evidence. Karaka fruits were a valuable addition to the Maori diet and were likely to have functioned as a replacement for traditional Polynesian tree crops. The preparation of karaka seeds also had Polynesian precedents and entailed a rigorous regime of steaming and soaking to rid the kernel of its toxic elements. There is data to suggest selection for fruit size and/or nutritional value in cultivated karaka populations.

A database of karaka distribution was compiled and populations classified as 'cultural' or 'unknown' on the basis of spatial association with archaeological sites. Groves classed as cultural were assumed to be cultivated or translocated by pre-historic Maori. Lack of effective seed dispersal by birds and the longevity of the trees, mean that the contemporary distribution of karaka provides a reasonable template for the extent of its prehistoric translocation and cultivation within New Zealand.

Karaka has a distinct cultural and natural biogeography. The greatest overlap between cultural and unknown trees occurred in the northern North Island while the majority of trees in the lower North Island, and all trees in the South Island were classed as cultural. Prior to the arrival of Polynesians in New Zealand, karaka was probably restricted in distribution to the Northland/Auckland region. Its natural range was then extended by human translocation and cultivation to the lower North Island, South Island, Kermadec Islands, Chatham Islands and many other in-shore islands off New Zealand.

Climate variables were fitted to the distribution data and discriminant analysis used to further test the classification of karaka into cultural and unknown populations. Significant differences were found in climatic parameters between groups. Cultural karaka were found in environments with greater solar radiation seasonality, higher evaporative demands and greater soil moisture deficits than unknown karaka. The climate profile of karaka was closer to that of other tree species currently restricted to the northern North Island than with more widely distributed species. Furthermore, the climate profile and location of cultural karaka is biased towards the same environmental correlates of pa and pit site locations, further indicating that karaka was a cultivated tree crop.

The extensive translocation of karaka by Maori means that it has the potential, with the application of molecular methods, to serve as a marker for prehistoric settlement and mobility. Preliminary work was begun on this aspect and a predictive model is presented of the possible relationships within and between populations of karaka.