Guidelines and Field Methodology for Vegetation Survey and Mapping

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SECTION A: GUIDELINES Historically the NT adopted the first approach by using aerial photography and more recently satellite imagery for interpretation. Aerial photography involves stereoscopic interpretation of patterns on contact prints and then transferred to a geo-referenced digital base such as topographic maps. Aerial photography provides reasonable resolution, although is expensive. More recently digital aerial photography with on screen digitising and attribution has been used in conjunction with traditional stereoscopy methods. The process of scanning, geo-rectifying and generating mosaics to produce the digital aerial photography is time consuming. Fortunately future aerial photography will be flown digitally and geo-referenced to some degree. Software allowing 3D vision is available for on screen digitising, however is expensive. As an alternative, contact prints (stereo pairs) and a stereoscope are used to delineate unique mapping areas then digitised on screen using a Geographic Information System (GIS). This is a tedious and time consuming process. If aerial photography is the interpretive base, the oldest available is recommended to provide information on vegetation prior to clearing or modification. Pre-clearing and present vegetation can be mapped and updated with recent satellite imagery or land clearing data. The use of old aerial photography will depend on the purpose of a vegetation survey. The disadvantage of using old photography may potentially limit field navigation and site location. Innovative interpretive materials (i.e. high resolution satellite imagery) are becoming increasingly available. Some possess comparable resolutions to aerial photography (eg. SPOT5, QuickBird, IKONOS, ASTER, ALOS) and will potentially replace traditional aerial photography methods in the future. Higher powered computers combined with enhanced GIS specifications and the increasing integration of GIS with remote sensing has made computer based mapping more efficient. These methods still only provide a ‘pattern’ and require considerable ground-truthing. Ancillary data such as Digital Elevation Models (DEM) and Normalised Difference Vegetation Index (NDVI) can assist in mapping and field survey components; they can also be used for modelling. 4.3 Defining Map Units The essential purpose of the mapping phase is to define unique mapping units, which are definable on the interpretive materials (by texture, colour, tone, canopy spacing, spectral signature etc), are a repeating unit /pattern across the mapped area, and which correlate to a greater or lesser degree with something tangible in the real world (i.e. a homogeneous vegetation community or a classification of that vegetation community). The boundaries marked should identify apparent changes in the vegetation communities. Each map unit/polygon is assigned a preliminary map unit code prior to field survey and reevaluated and attributed following field survey, analysis and classification of field data. Boundaries should also be checked in the field for attribute and spatial accuracy. Various protocols and specific formula exist for a minimum map unit size. Generally whatever correlates to an area larger than two by two millimetres on interpretive material is acceptable (eg. two by two millimetres on 1:50 000 aerial photography equates to 100 by 100 metres or one hectare on the ground; Table 3). Northern Territory Guidelines and Field Methodology for Vegetation Survey and Mapping 8
SECTION A: GUIDELINES Table 3. Data resolution at various scales. Description Size on Map 1:25 000 1:50 000 1:100 000 1:250 000 1:1 000 000 Surface area of the smallest mapped feature Minimal area width for linear features 1mm wide (on the ground) 2 x 2 mm 0.25 ha 1.0 ha 4 ha 25 ha 400 ha or 4 km 2 1 mm 25 m 50 m 100 m 250 m 1 km Source: Neldner and Butler (in prep) 4.4 Mosaics Mosaic map units incorporate more than one vegetation community within a map unit boundary. Mosaics should be noted during the interpretation phase and were possible a percent proportion subscribed to each component vegetation community within the one map unit boundary. If the mosaic components are too small to map, or they are not feasible to map even as mosaics, they should still be assessed in the field and described in the survey report. For example, Queensland mapping is attributed with a code to provide a floristic association (i.e. NVIS Information Hierarchy Level VI - Sub-association; refer to Chapter 5.1) and the proportion it occupies in each map unit. Each polygon is therefore individually assessed as opposed to identifying similar unique mapping areas and vegetation groupings as done in the NT. Map polygons are labelled with the dominant vegetation community. Spatially smaller units within the polygon boundary are referred to in the survey report. The NVIS framework allows for mosaic mapping units (ESCAVI, 2003; refer to Chapter 5.0). 4.5 Accuracy Assessment On completion of a survey, the final mapping units should be assessed for reliability and accuracy. Maps should also be validated for spatial and attribute accuracy. Spatial accuracy refers to the accuracy of a map in terms of real world coordinates (georeferencing) usually measured in metres. It is applied to the entire map and individual polygon boundaries. Spatial accuracy can be assessed using global positioning system (GPS) ground control points or by comparison with geo-referenced GIS coverage’s (eg. satellite imagery, cadastral boundaries, digital topographic maps). Spatial accuracy can be corrected or improved with a selected geo-referenced base using GIS. Attribute accuracy is an estimate of how accurately vegetation communities have been depicted within map units. The process requires ground-truthing; a simple method is to select one hundred sites on a stratified random basis covering the survey area and individual vegetation communities. The sites are visited and evaluated to determine the correspondence with the assigned vegetation community. Accuracy can be measured as an overall percentage. Depending on scale, a map is rarely 100% correct at any given site location. For more detail refer to the Australian Soil and Land Survey Handbook: Guidelines for Conducting Surveys ‘Blue Book’ (Gunn et al., 1988). Northern Territory Guidelines and Field Methodology for Vegetation Survey and Mapping 9
Page 1: DEPARTMENT OF NATURAL RESOURCES,ENV
Page 4 and 5: PREFACE This document describes the
Page 6 and 7: CONTENTS PREFACE ..................
Page 8 and 9: GLOSSARY...........................
Page 10 and 11: ACRONYMS ANZLIC BRS DEH DEM DVT ERI
Page 13 and 14: SECTION A: GUIDELINES 1.0 INTRODUCT
Page 15 and 16: SECTION A: GUIDELINES 3.0 PRINCIPLE
Page 17 and 18: SECTION A: GUIDELINES Currently, th
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Page 23 and 24: SECTION A: GUIDELINES Table 4. The
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Page 27 and 28: SECTION A: GUIDELINES The structura
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Page 31 and 32: SECTION A: GUIDELINES Resource Asse
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Page 35 and 36: SECTION A: GUIDELINES 9.0 FUTURE DE
Page 37 and 38: SECTION A: GUIDELINES Satellite pla
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Page 45 and 46: SECTION B: FIELD METHODOLOGY 2.2 Si
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Page 59 and 60: SECTION B: FIELD METHODOLOGY 5.1 Ha
Page 61 and 62: SECTION B: FIELD METHODOLOGY Soil d
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Page 65 and 66: SECTION B: FIELD METHODOLOGY Broad
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Page 69 and 70: GLOSSARY CSR Datum Distribution Div
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GLOSSARY Overstorey Physiognomy Pla
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REFERENCES REFERENCES Abed, T. & St
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REFERENCES Meagher, D. (1991) The M
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APPENDICES
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APPENDICES APPENDIX 2: Overview of
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APPENDICES APPENDIX 4: Height Class
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APPENDICES TUSSOCK GRASS Closed Tus
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APPENDICES APPENDIX 6 (continued) D
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APPENDICES APPENDIX 6 (continued) G
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APPENDICES APPENDIX 8: Preliminary
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APPENDICES APPENDIX 10: Definitive
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Disturbance, Succession, adjoining
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APPENDICES APPENDIX 11: IUCN Red Li
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APPENDICES APPENDIX 13: NT Weeds Da
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APPENDICES APPENDIX 14 (continued)
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APPENDICES APPENDIX 16: Field Data
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APPENDICES APPENDIX 17: Field Data
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APPENDICES APPENDIX 17 (continued)
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APPENDICES APPENDIX 19: NT Site Pro
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