Phytogeography and climate analysis of Nothofagus subgenus Brassospora in New Guinea and New Caledonia

Nothofagus subgenus Brassospora now occurs only in New Guinea and New Caledonia, but is well known from fossil deposits of South America, New Zealand, Antarctica and Australia. It is commonly used for palaeoclimatic interpretation, but the climate characteristics of the extant species have not been described. In this paper we used the climatic estimation software, BIOCLIM, to derive a climate profile of 24 variables for each of the 14 species of Nothofagus native to New Guinea, and lapse rates and isohyet maps to describe the annual mean temperature and rainfall range of the five species native to New Caledonia. The New Guinea species occur at annual mean temperatures ranging from 10.6 to 23.5°C, with annual precipitation of 1762-7733 mm. The first three axes of a principal components analysis explained 85% of the total variation, the first axis comprising temperature variables, the second comprising precipitation range and precipitation of the wet season, and the third axis comprising dry-season precipitation and annual and diurnal temperature range. Some species had distinct combinations of positions along these component axes, indicating clear niche differentiation with respect to climate. The New Caledonian species occur at annual mean temperatures of 14.5-23.5°C, and annual precipitation of c. 1500-3500 mm. Although there was no significant difference in annual mean temperature and precipitation between the New Guinea and New Caledonian species, comparison of median values across species suggests specialisation of most New Caledonian species towards slightly drier conditions than the New Guinea species that occur at similarly high annual mean temperatures. Use of subgenus Brassospora to interpret palaeoclimates should take into account the variation in climate experienced across the range of extant species