The derivation of climate surfaces for New Zealand, and their application to the bioclimatic analysis of the distribution of kauri (Agathis australis)

Abstract

Modelling techniques based on Laplacian smoothing splines were used to derive climate trend surfaces for each of four parameters: monthly mean rainfall, minimum temperature, maximum temperature and solar radiation. The use of analytical procedures, based on the program BIOCLIM, are described; these allow the estimation of climate parameters at individual locations from the trend surfaces. These techniques were used to analyse the geographic distribution of kauri with respect to contemporary climate. For each location where kauri has been recorded, an estimate was made of various climate parameters, which by summation allowed the derivation of a ‘climate profile’. This profile may be considered a multivariate definition of the climatic regime within which the species now grows. To analyse the role of climate in determining the geographic distribution of kauri, each location in a North Island database was tested against the profile, to assess whether it could support kauri growth. There was a close correspondence between the actual and predicted distribution, which supports the hypothesis that climate determines the southern limit of kauri. There was also a suggestion that, towards the southern limit of kauri, edaphic factors may become more important, and interact with climate to control the specific locations where kauri grows.