Lincoln University Digital Thesis Copyright Statement The digital copy of this thesis is protected by the Copyright Act 1994 (New Zealand). This thesis may be consulted by you, provided you comply with the provisions of the Act and the following conditions of use: you will use the copy only for the purposes of research or private study you will recognise the author's right to be identified as the author of the thesis and due acknowledgement will be made to the author where appropriate you will obtain the author's permission before publishing any material from the thesis. APPLYING A LAND SYSTEMS APPROACH TO DESCRIBE AND PARTITION SOIL AND FOREST VARIABILITY, SOUTHERN MAMAKU PLATEAU, PART OF KINLEITH FOREST, NEW ZEALAND A thesis submitted in partial fulfilment of the requirements for the Degree of Doctor of Philosophy at Lincoln University By Reece B. Hill Lincoln University 1999 Abstract of a thesis submitted in partial fulfilment of the requirements for the Degree of Doctor of Philosophy APPLYING A LAND SYSTEMS APPROACH TO DESCRIBE AND PARTITION SOIL AND FOREST VARIABILITY, SOUTHERN MAMAKU PLATEAU, PART OF KINLEITH FOREST, NEW ZEALAND By Reece Blackburn Hill Kinleith Forest is a P. radiata dominated plantation forest situated on the edge of the Taupo Volcanic Zone in the central North Island, New Zealand. Approximately 35000 ha of the forest is situated on the southern Mamaku Plateau. The aim of this study was to determine the spatial structure of soil variability and integrate an analysis of the growth, productivity and nutrient variables for P. radiata to ascertain the detail of soil information appropriate for plantation forestry. A land systems approach, using generic and specific soil-landscape models and hierarchical landscape analysis, provides the framework for soil mapping. The approach is scale-flexible and lends itself to implementation of site specific forest soil, nutrient and health management practices. The southern Mamaku Plateau consists of five superimposed Late Quaternary welded ignimbrites with the Mamaku Ignimbrite (c. 220 ± 10 ka) being the uppermost. Aeolian coverbeds consisting of predominantly loess and rhyolitic tephras mantle erosional surfaces formed in ignimbrite bedrock. Four episodes of strath cutting and valley incision into ignimbrite are recognised from the sequence of overlying loess and tephra coverbeds. The basal loess and/or tephra on the erosion surfaces denoting the cessation of each episode of strath cutting and valley incision are: (a) pre-Rotoehu loess, (b) pre-Kawakawa loess, (c) Rotorua Tephra, and (d) Taupo Ignimbrite. The four episodes of strath cutting and valley incision can be synthesised into five topographically recognised stages of landform evolution. Landform evolution stage (I) is represented on the upper Mamaku terrain and stage (V) on the lower Mamaku terrain. In a revised coverbed distribution model the oldest coverbed sequence is recognised on hill and terrace land components on the upper and lower Mamaku terrain. The coverbed stratigraphy together with its soil stratigraphic interpretation and soil-landform relationships has been used to map nine land systems. Soil-landscape relationships and forest variability are described and analysed within the U3 complex land system. The U3 complex land system comprises Oruanui and Mamaku simple land systems, each with a ii common recurring pattern of hillock, ridge, flat and ravine land components, situated on the upper Mamaku terrain. Soil and regolith variables were partitioned at progressively finer levels of hierarchical landscape subdivision to ascertain spatial variability structure. Taupo Ignimbrite thickness, topographically controlled over short range (lOs of metres), and a rainfall (leaching) gradient over a longer range (lOOOs of metres) were identified as the main factors controlling soil variability. Land components within simple land systems effectively represented the variability. Simple and composite soils formed in Taupo Ignimbrite veneer deposits over yellowish-brown beds (collectively <2.5 m thick) dominate the U3 complex land system, with soils showing varying expression of podzolisation. The structure of spatial variabili~y of foliar nutrient concentration differs between foliar nutrients N, P, Mg, K and B. Complex land system for foliar N, P, Mg and K, and simple land system for foliar B were appropriate grainsize for amelioration purposes. Within U3, foliar P was deficient and foliar Mg was marginal with a high probability of deficiency. Forest productivity was measured using site index, basal area index and volume index. Basal area index was the most effective indicator of forest productivity variability. Spatial variability was best partitioned by land components. Spatial variability of foliar nutrients and forest productivity indices were not structured in the same way, indicating a weak correlation between foliar nutrient variables and forest productivity. The relationships between P. radiata and soil chemical properties were established by a pot trial for soils on the flats within U3. Principal Component Analysis (PCA) identified the main effects on P. radiata shoot growth and nutrient uptake as nutrient availability, P sorption and Mg inhibition. Podzolisation, although evident in the soil morphology, was not shown to significantly influence shoot variables. Shoot dry weight and height were significantly greater for seedlings grown in A horizons compared to seedlings grown in the Bw and BC horizons in Taupo Ignimbrite and buried Bw horizons in yellowish-brown beds. The nutrient availability effect was most apparent in A horizons, while the Mg inhibiting effect and P sorption effect were responsible for limiting shoot growth in the Taupo Ignimbrite and yellowish-brown beds respectively. A nutrient availability index (NAI), developed from the pot trial and soil horizon stratigraphy, was calculated for hillock and flat land components in the Oruanui and Mamaku land systems. Poor correlation between NAI and site productivity (basal area index) reaffirmed the influence of non-soil related factors on forest productivity variability. iii The land systems approach effectively partitioned soil and forest spatial variability at different levels of resolution. However, soil and soil-induced forest variability are not strong because of the homogenising effects of widespread aeolian (including pyroclastic) coverbeds. Implementing a scale-flexible mapping approach, such as land systems, would provide a basis for improved inventory data collection, and management of forest soils, nutrients and health in Kinleith Forest. Keywords: soil variability, soil-landscape models, aeolian coverbeds, rhyolitic tephras, loess, Taupo Ignimbrite, strath cutting, landform evolution, land components, land systems, composite soils, foliar nutrient concentration, forest productivity, nutrient availability, forest soils. iv ACKNO~DGEMENTS It is fitting that this expression of gratitude is my final task because I have continued to receive support and encouragement until this time. The opportunity to work with my supervisors, and build on their experience, has made me realise that it is their inspiration and dedication that feeds my own fascination with soils and the landscape. My most sincere thanks go to my supervisor, Peter Almond for his patience and for the many long discussions, which at times left my head a little sore but a lot more knowledgeable. I feel privileged to have worked with Peter throughout this study and I feel we can both be proud of the end result. Thank you to my co-supervisor, Phil Tonkin. I have always admired Phil's dedication to his work, his willingness to share his knowledge has set me in good steed. I am also very grateful to my external supervisor, Tim Payn. My fieldwork required me to spend 1 Y2 years away from home. During this time Tim has not only helped as a supervisor but together with Barbara and family, have provided me with a second home. Further thanks go to associate supervisors John Adams and more recently Chris Frampton who has provided tremendous support with the statistical analyses. I have learnt a great deal in a very short time, thanks! I would like to acknowledge the support of Forest Research (previously FRI), Carter Holt Harvey Forests Limited and Lincoln University, who jointly established and funded . my study. I am also very grateful to Tony Fenton and Tony Petch at Environment Waikato not only for financial support through 1999, but for providing me with employment. I appreciated the friendly work environment at Forest Research, Rototrua. Particular thanks go to: Barbara Hock and team 'for their GIS assistance; the Soils team for providing forest nutrient information and soil and plant analyses; and Mark Kimberly and Judy Hayes for helping me decipher all the tree data I collected. Thank you to the Carter Holt Forests staff in Tokoroa, especially Scotty Downs and Peter Thompson (who organised vehicles, office space and field requirements) and Andy Haywood (for calculating the forest growth data). My numerous Tokoroa flatmates (Melissa and Finbar, Steph, Diana, and Marion) also deserve a mention. I also thank Wim Rijkse and David Lowe for their valuable advice and discussion. v Thank you to all those in the Soil and Physical Sciences Group for your companionship. Colin, thank you for your proof-reading and editing inputs and Leanne for the soil analysis. A big thank you to my post-grad friends, past and present, especially those on the night shift. I have enjoyed your company