Kauri-climate relationships revisited

Abstract

This thesis re-examines the relationship between climate forcing and kauri growth to inform future climate reconstruction. Dendroclimatological research using kauri has identified the suitability of kauri for climate reconstruction, particularly ENSO, and a 4500-year tree ring chronology has been built from modern, archaeological and sub-fossil material. However, there are still uncertainties regarding aspects of the kauri-climate relationship, including possible sub-regional differences and the effect of sensitivity to environmental gradients on the climate signal, which constrain use of the multi-millennial chronology for climate reconstruction. These issues are addressed by: 1) investigating the site-specific kauri growth response to determine if there are additional, unidentified climate variables affecting growth. 2) Investigating the growth response to climate for various locations and site characteristics to determine if there are differences in climate signal through the kauri network. 3) Determining the effect of regional scale forcing mechanisms on the kauri growth response, other than ENSO, such as the Southern Annular Mode (SAM) and the Inter-decadal Pacific Oscillation (IPO). 4) Determining the influence of soil moisture on kauri growth to address the potential difference in climate signal of modern and swamp kauri, using the Waitakere Dam, Auckland, as an (imperfect) swamp kauri analogue. The kauri growth response to a range of climate variables and climate drivers was investigated using response function analysis to determine the nature of the relationship and if any additional information could be obtained. Additionally, this response was tested using sub-master chronologies based on geographical location, elevation and soil moisture to determine if there were differences in climate response through the kauri network. The key findings of this research are: 1) a stronger relationship with climate for kauri on the east coast of the upper North Island, than kauri on the west coast. 2) A weaker response of kauri at higher elevations (>400 m). 3) A general positive relationship between kauri growth and the IPO, however lack of a clear climate pattern between kauri growth and the SAM. 4) The impact of soil moisture on kauri growth is not significant, suggesting kauri are resilient to high levels of soil moisture and grow well in a range of environmental conditions. Keywords: Kauri (Agathis australis), dendroclimatology, Southern Annular Mode, Inter-decadal Pacific Oscillation, soil moisture, Waitakere Dam.