DOI: 10.15493/sarva.bgis.10000105
title: STEP - Vegetation

description: Vegetation types within the STEP planning domain. The final vegetation map for the STEP planning domain comprised two sections: (i) Thicket vegetation (mapped in the field by the Biological Survey team , see Vlok, J.H.J. and Euston-Brown, D.I.W. 2002. The patterns within, and the ecological processes that sustain, the subtropical thicket vegetation in the planning domain for the Subtropical Thicket Ecosystem Planning (STEP) project. TERU Report 40: 142pp), and (ii) non-thicket vegetation (mapped as a desktop exercise from CAPE Project and the vegetation map produced by the National Botanical Institute). (i) Thicket vegetation - 112 thicket types were identified and mapped for the STEP project by in Vlok and Euston-Brown (2002). These included 34 solid thicket vegetation types, and 78 mosaic thicket vegetation types. This map covered the entire STEP planning domain, and therefore included non-thicket vegetation types, but these were very broadly (coarsely) defined. The 112 thicket types from this map remained unchanged in the final STEP vegetation map (with three exceptions, see Table 7 - coastal vegetation). The broad definitions of non-thicket vegetation types were used simply as a guide for the further delineation and coding of non-thicket types in the final vegetation map. (ii) Non-thicket vegetation - 55 non-thicket vegetation types were defined and delineated as a desktop exercise using two sources of information (see map below). In the west, the Broad Habitat Units (BHUs) defined by Cowling and Heijnis (2001) for the CAPE Project were used (1:250 000 scale). In the east, the vegetation types compiled by Dr M. Rutherford, National Botanical Institute (NBI - preliminary map) were used (mixed scales). Additional non-thicket vegetation boundaries mapped by the Biological Survey team were also used places where they were in sufficiently fine detail. The three water types mapped by the team remained unchanged and were incorporated directly in the final STEP vegetation map. The 58 non-thicket types referred to in this document refer to the 55 vegetation types and the three water types. Purpose: Created for the Subtropical Thicket Ecosystem Planning Project. Method of capture/Lineage: (See Lombard et al. 2003) Vegetation polygons were delineated in the field by the Biological Survey team onto fifty-five Landsat TM images which were plotted by the Institute for Soil, Climate and Water on paper at 1:100,000 scale, in Gauss Conform Projection, Central Meridian 20 - 29 East, Clarke 1880 Spheroid. To assist with the definition of the vegetation polygons, geology (1:1 000 000) and homogeneous climate zones (Dent et al. 1990) were plotted as clear overlays at 1:250 000 scale (by Lombard, Wolf and Cole), to enable the Biological Survey team to view them over the Surveyor General 1:250 000 topo-cadastral map sheets. A unique ID number was assigned to each vegetation polygon at the time of field delineation. The unique ID numbers were then entered into an Excel spread sheet along with the description for each vegetation polygon (Vlok and Euston-Brown 2002, Appendix 3). The vegetation polygons were digitized on a GTCO Super LII Plus- A0 digitizing tablet using ArcView GIS 3.2a (ESRI) at the same projection as each 1:100 000 satellite image. Unique ID numbers were captured as points and imported into the final vegetation polygon GIS map. Maps were registered for digitizing using existing tick points on the 1:100 000 images. Once the line digitizing was complete the final polygon file was built using ArcInfo 7.2.1 (ESRI) in Albers Equal Area projection (Appendix 1). Additional vegetation polygon descriptions were imported into the final polygon file from the Excel spread sheet using the unique ID as the link field. 112 Thicket vegetation units were defined using a concatenation of a number of database fields, and a unique name was assigned to each unit by the Biological Survey team (Vlok and Euston-Brown 2002, Appendix 3). (ii) Non-thicket vegetation Western Area Broad Habitat Units (BHUs) from the CAPE project The CAPE BHU map was delineated for the CAPE project and is fully described in Cowling and Heijnis (2001). It was used as the primary layer for delineating and coding the non-thicket vegetation types in the western half of the planning domain, where the STEP planning domain and the CAPE planning domain overlap. The decision to use the BHU map for the western planning domain, instead of using the NBI vegetation map, was made after careful consideration of the two options by R. Cowling, J. Vlok and A. Lombard. From a botanical perspective, the very fine subdivisions of non-thicket vegetation types in the preliminary NBI map were often based on underlying geology, and these subdivisions were not considered appropriate for the final STEP vegetation map. From a technical (GIS) perspective, the NBI map consisted of the 112 thicket types from the STEP thicket map overlaid on the underlying NBI vegetation base map, and this had created many sliver polygons along the edges of the 112 thicket polygons. The BHU definitions, however, seamed more neatly into the STEP thicket map and were considered more appropriate for the western part of the STEP planning domain. The integration of the BHU map into the STEP thicket map was performed as a desktop exercise by R. Cowling and A. Lombard. The problems encountered with the NBI vegetation map in this western part were less pronounced in the eastern part. Eastern Area National Botanical Institute (NBI) preliminary vegetation map This map was received from the NBI at the end of August 2002, and was in a preparation stage. It was used as the primary layer for delineating and coding the non-thicket vegetation types in the eastern half of the planning domain. The integration of this map into the STEP thicket map was performed as a desktop exercise by J. Vlok and A. Lombard. Forest patches A forest map was received from the National Botanical Institute, consisting of four forest types (extant areas only, Table 6). For the final STEP vegetation map, these forest boundaries were ignored where they fell under STEP thicket vegetation types (solid or mosaic). Where they fell outside of thicket, they were assigned to four final STEP forest types defined in Table 6. The final STEP vegetation map included the following four forest types: (i) Knysna Afromontane Forest and (ii) Alexandria Indian Ocean Forest (both names were derived from the BHU map) and (iii) Amatole Afromontane Forest and (iv) Zuurberg Afromontane Forest (both newly defined names for STEP). Completeness: The final STEP layer is as complete as is currently possible. Supplemental Information: Lombard, A.T., Wolf, T. and Cole, N. 2003. GIS coverages and spatial analyses for the Subtropical Thicket Ecosystem Planning (STEP) Project. TERU Report 42: 78 pp, Appendix 78 pp. Vlok, J.H.J. and Euston-Brown, D.I.W. 2002. The patterns within, and the ecological processes that sustain, the subtropical thicket vegetation in the planning domain for the Subtropical Thicket Ecosystem Planning (STEP) project. TERU Report 40: 142pp. http://zoo.upe.ac.za/step http://cpu.uwc.ac.za