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Soil intactness assessment of the Waikato region: 2003

Report: TR 2003/14
Author: Dr Douglas Hicks, Ecological Research Associates

Abstract

Waikato Regional Council commissioned a survey to assess soil intactness (soil disturbance and bare soil) in the Waikato region using a point sampling assessment of aerial photographs flown in 2002.

The survey and a final report were completed by September 2003. In August 2005 additional analysis of bare ground was carried out using an improved cluster sampling technique. The survey developed an innovative method to interpret orthophotos (aerial photographs rectified to fit a map grid) on-screen using a Geographic Information System (GIS) with direct entry of data to a GIS-linked database.

The survey estimates soil disturbance and bare soil from land use activities and natural erosion processes across the region. Additionally, measures of bare soil under naturally occurring and planted primary and secondary vegetation cover (including soil conservation) indicate land use pressures and responses to soil intactness.

The point sample is sufficiently representative to draw conclusions about soil intactness/disturbance region wide, for land uses within the region and for large subdivisions of the region such as districts. An additional analysis has been carried out for the Coromandel catchment management zone. This has enabled a procedure to be worked out for future sub-regional analyses. The results furnish some useful examples of what can be extracted from such surveys.

Soil Intactness Assessment of the Waikato Region: 2003
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Table of contents

Acknowledgements i
Executive summary iii
1 Introduction 11
1.1 Background 11
1.2 Brief 11
1.3 Survey design 12
1.4 What has been recorded 13
1.5 Data storage, statistical analysis and data presentation 16
1.6 Survey concepts 17
2 Survey results - soil intactness and disturbance 19
3 Survey results - land use impacts on soil 19
4 Survey results - secondary vegetation 26
5 Survey results - vegetative soil conservation measures 32
6 Conclusions about state of the Waikato's soil 39
Technical conclusions about survey method 44
  Use of orthophotos 44
  Representativeness of results 44
  Photo-interpretation error 45
  Calibration of data for sample point size and cluster analysis of bare soil 45
  Procedure for extracting regional subsets 45
References 47
Appendix I: Field check of randomly selected sample points 49
  Type of disturbance 50
  Landform 50
  Overall comments on photo-interpretation error 50
Appendix II: Calibration of data for sample point size 52
Appendix III: Cluster analysis of fresh soil disturbance under various soil conservation covers 56
Appendix IV: Procedure for extracting regional sub-sets 59