Investigating the Distribution of Acacia Longifolia Ssp. Sophorae in South

30 Plant Protection Quarterly Vol.21(1) 2006 and Paull 2000, Mitchell and Wilson 2005). Yet despite the probable impacts, relative- Investigating the distribution of Acacia longifolia ssp. ly little is known about the inland invasion of coast wattle in south-west Victoria, sophorae in south-west Victoria using satellite remote including the current extent of invasion and factors involved in the invasion proc- sensing and GIS ess. It is diffi cult to assess the threat of the species and develop appropriate manage- A B C A Jennifer Emeny , Gordon Duff , Dianne Simmons and Anne Wallis ment strategies without such information. A School of Ecology and Environment, Deakin University, PO Box 423, Field assessment of coast wattle in south- Warrnambool, Victoria 3280, Australia. west Victoria has been made diffi cult by B CRC for Tropical Savannas Management, Charles Darwin University, the extent and remoteness of vegetation in Darwin, Northern Territory 0909, Australia. the region (Baldock et al. 1995 b). C School of Ecology and Environment, Deakin University, 221 Burwood There has been considerable interest in Highway, Burwood, Victoria 3125, Australia. the use of geospatial technologies in environmental weed management. Of particular interest is the potential use of remote sensing for mapping weed distribution (e.g. Everitt et al. 1991, 1992, 1999, 2001, Pitt and Miller 1988, Ullah et al. 1989a,b, Summary 1997, Costello et al. 2000, Mullet 2001). In Everitt and Escobar 1996, Frazier 1998, Mapping and analysis of the distribution Victoria, most coastal and near-coastal re- Bulman 2000, Crossman and Kochergen of environmental weeds is an important serves now contain at least one Australian 2002, Underwood et al. 2003, van Klinken component of strategic weed manage- plant species which has become invasive 2005, Lass et al. 2005, Fuller 2005, Emeny ment. Such information is particularly beyond its traditional range (Burrell 1981, et al. 2005), and GIS for weed distribution important in managing ‘native invaders’, Molnar et al. 1989, Bennett 1994, McMahon analysis (e.g. Lass and Callihan 1993, Kerr where invasion characteristics must be et al. 1996, Parks Victoria 1998, 1999, 2001, and Westbrooke 1996, Wilcock and West- clearly understood prior to any manage- Coutts 2001, McMahon and Brighton 2002). brook 1996, Siderov and Ainsworth 2004). ment action being taken. This paper re- In most cases, the current impact, extent, Where successfully applied, remote sens- ports on an investigation of the current spread over time, and factors promoting ing can provide a large-scale, cost-effective distribution of the native invader Acacia invasions remain largely unknown. Yet a and repeatable alternative to traditional longifolia ssp. sophorae (Labill.) Court clear understanding of invasion charac- fi eld-based mapping (Frazier 1998), and (coast wattle) in south-west Victoria, us- teristics is required for ‘native weeds’, as GIS can be used to investigate spatial rela- ing remote sensing and Geographic In- management actions require stronger jus- tionships between weed distribution and formation Systems (GIS). Coast wattle tifi cation than for most exotic weeds (Rose environmental/cultural factors (Kerr and was successfully mapped from Landsat 1997, Mullet 2001, Howell 2003). Accord- Westbrooke 1996, Wilcock and Westbrooke ETM imagery using a supervised clas- ingly, the threat of a species must be dem- 1996). However, whilst mapping and sifi cation procedure, with 82% of coast onstrated on a case-by-case basis. analysis of weeds has been undertaken wattle shown on the map accurately de- Acacia longifolia ssp. sophorae (Labill.) independently using these technologies, picting coast wattle on the ground. An es- Court (coast wattle) is recognized as one integration of the two is less common. Al- timated 11 448 ha were classifi ed as sup- of the more serious native invaders in though weed distribution maps produced porting coast wattle, representing 12% Australia (Carr 2001), and is invasive both from remotely sensed data are useful in of native vegetation in the study area. A within and beyond its original biogeo- their own right, analysis of distribution more detailed GIS analysis in the Lower graphical range (Groves 2001). In south- patterns is limited to visual assessment. Glenelg National Park revealed coast west Victoria, coast wattle has spread Likewise, whilst GIS is often used to ana- wattle has invaded a limited number of extensively over the past 40 years, from lyse weed distribution data collected in vegetation types, and is more prevalent coastal foredune vegetation into inland the fi eld, its application is limited by the close to roads and within management vegetation types. Studies in the region coverage and accuracy of the data, which zones associated with disturbance. The (McMahon et al. 1996, Clay and Schneider can be biased by site accessibility (Kerr and current regional extent of the species 2000, Rees and Paull 2000, Mitchell and Westbrooke 1996). By integrating the two, means widespread control is unlikely; Wilson 2005) and elsewhere in southeast- the utility of remotely sensed distribution hence the immediate focus should be ern Australia (Costello et al. 2000) have maps could be increased by quantitative on preventing further spread into areas suggested coast wattle can have signifi - analysis within a GIS, and GIS analysis where it is currently absent. Landsat im- cant impacts on biodiversity and faunal could benefi t from the complete coverage agery also proved to be a successful tool habitat. McMahon et al. (1996) recorded of a study area using remote sensing. for mapping large scale coast wattle dis- an average loss in plant diversity of 60% This paper reports on an investigation tribution, and could be used in long-term 10 to 15 years after coast wattle invasion of the current distribution of coast wattle monitoring of the species. in coastal heathland in south-west Victo- in south-west Victoria using a combination ria, which is supported by recent fi ndings of remote sensing and GIS. The investiga- Introduction by Mitchell and Wilson (2005). Similarly, tion had two primary objectives. The fi rst Over the last two decades there has been Costello et al. (2000) recorded an average objective was to map the current distribu- increasing recognition that some Austral- decline in plant diversity of 36% just 10 tion of coast wattle in south-west Victoria ian plants can behave as environmental years after coast wattle invasion in coastal using satellite imagery. Race and Rollings weeds beyond their original range (Carr grasslands of New South Wales, increas- (1992) have successfully mapped coast et al. 1992, Rose 1997, Carr 2001, Groves ing to 76% after 20 years. Further studies wattle from Landsat imagery at a spatial 2001, Keighery 2002), and that impacts of in coastal heathland of south-west Victoria scale of 31 km2 in coastal vegetation in these species can equal that of any exotic have demonstrated negative impacts on the region. This study aimed to determine weed (Mullet and Simmons 1995, Mc- ant diversity (Clay and Schneider 2000) whether Landsat imagery could be used Mahon et al. 1996, Rose and Fairweather and loss of suitable mammal habitat (Rees to map coast wattle over a much larger Plant Protection Quarterly Vol.21(1) 2006 31 spatial extent and range of environments. The use of Landsat imagery as a mapping and monitoring tool for coast wattle is also discussed. The second objective was to analyse the distribution of coast wattle in the Lower Glenelg National Park using GIS. The park was of particular interest due to its size (27 300 ha), conservation �� status, and concern about rapid prolif- eration of coast wattle in recent decades. � �� Two broad vegetation types occur in the �� park, heathy woodland and lowland forest (Parks Victoria 2000), which are further divided into a number of Ecological Veg- etation Classes (EVCs). The total area and spatial arrangement of coast wattle in the park are currently unknown. Hence four basic patterns of distribution were inves- �� tigated: the total area, and the distribution �� according to management zones, proximity to roads, and EVC. By increasing our �� understanding of the current distribution �� of coast wattle in south-west Victoria, management of the species can be better informed and a baseline established for future monitoring. �� Methods Study area The study area for the mapping exercise was a 60 × 60 km section of south-west �� Victoria (Figure 1), chosen to cover the dis- �� tribution of coast wattle in the region. The �� pre-European distribution of coast wattle in this area is unknown. However historic distributions are believed to have been re- � stricted to the narrow foredune zone along �� the coast (Baldock et al. 1995a). �� A number of parks and reserves occur within the study area. The Lower Glenelg �� National Park is the largest set aside primarily for conservation (Figure 1). The second component of the study focused on the Lower Glenelg National Park only, � � �� where the spatial distribution of coast wattle was analysed in greater detail. �� Mapping coast wattle distribution in south-west Victoria using satellite Figure 1. Study area, showing the 60 × 60 km area used for the regional imagery mapping exercise, and the Lower Glenelg National Park, which was the The fi rst step in the investigation was to focus of further distribution analysis. establish the current distribution of coast wattle in south-west Victoria. Satellite imagery was chosen for the mapping exercise due to the extent of the region, which Image selection and preparation Land- panchromatic band (band eight) were ex- made fi eld-based mapping or mapping sat Enhanced Thematic Mapper 7 was cluded as these were of different spatial from aerial photographs impractical and chosen as the imagery source due to its resolution. cost-prohibitive. availability, its cost-effectiveness for the Geometrically corrected Landsat quar- Mapping of coast wattle from satellite study area size, and the previous success ter scenes were obtained on August 3rd imagery followed standard image classi- of coast wattle mapping by Race and Roll- 2001 and January 10th 2002. These cor- fi cation procedures, including: image se- ings (1992). Landsat 7 imagery consists responded with the period immediately lection and pre-processing; unsupervised of eight spectral bands, including seven prior to fl owering of coast wattle and the classifi cation to identify spectrally distinct thematic bands and one panchromatic post-fl owering/seed production phase, land cover categories; supervised classi- band. Bands one to fi ve and seven were respectively. Images were acquired on fi cation, and; a classifi cation accuracy as- used in the image analysis, spanning the more than one date as several weed map- sessment. All image analysis was under- visible, near infrared and middle infrared ping studies have found time of year to taken in ER Mapper 6.3 (Earth Resource regions of the electromagnetic spectrum, infl uence weed detectability (Everitt and Mapping Ltd 2002). with an approximate ground resolution Escobar 1996). Cloud-free imagery was of 30 m. The thermal band (band six) and not available during the peak fl owering 32 Plant Protection Quarterly Vol.21(1) 2006 period of late August to early September. the study area to account for variability format, then clipped to the extent of the Images from previous fl owering periods in land cover refl ectance that can occur park boundary. The XTools ArcView ex- were not considered appropriate due to across geographic space. tension (Oregon Department of Forestry the length of time between image acquisi- The spectral signatures of coast wattle, 2001) was used to calculate the total area of tion and collection of ground-truth data. heathland and woodland were compared coast wattle and other land cover classes. Prior to analysis the images were clipped using line graphs and scattergrams to in- The proportion of coast wattle to coast to the 60 × 60 km study area, and a stand- dicate whether the classes were spectrally wattle-free land cover was then calculated ard contrast stretch applied to enhance the distinct and therefore likely to be distin- within each management zone in the park. display of the image. guishable in the supervised classifi cation. The Lower Glenelg National Park is di- The supervised classifi cation procedure vided into four management zones: zone Image analysis and production of coast was then run using the maximum likeli- one; two; three, and; ‘reference areas’. wattle distribution map Supervised clas- hood classifi er. Based on similarity of spec- These zones represent a gradient of hu- sifi cation was used as the primary image tral signature, each pixel was classifi ed man disturbances ranging from minimal analysis technique for mapping coast wat- into a single land cover class to form an in the reference zones through to relatively tle. Supervised classifi cation uses the spec- overall land cover map. The total area of high in zone three (Table 1). tral properties of pre-defi ned land-cover coast wattle and coast wattle-free vegeta- To examine the spatial relationship categories to classify each pixel in an im- tion was then calculated, and the classifi ed between coast wattle and proximity to age into one of these categories, forming a image exported to ArcView 3.3 (Environ- roads, a buffer tool was used to create land cover map (Richards and Jia 1999). mental Systems Research Institute 2002) 50 m buffers extending out either side of Fifteen land cover categories were cho- for fi nal map production and assessment roads in the park to the maximum possible sen for inclusion in the supervised clas- of classifi cation accuracy. distance of 2300m. The total area of coast sification, based on field observations, wattle in each buffer was calculated using existing maps and the results of an un- Accuracy assessment of the distribution XTools, and the proportion of coast wat- supervised classifi cation, which was used map Map accuracy was estimated using tle in each buffer plotted against distance to identify land categories with clearly the method described by Congalton (1991), from road. Finally, the total area of coast distinct spectral signatures (Emeny 2002). which compares classifi cation results with wattle within each EVC was calculated us- The land categories of primary interest the ‘true’ land cover type on the ground ing the ArcView Spatial Analyst extension in the study were those containing coast at a number of locations (reference data). (Environmental Systems Research Insti- wattle (labelled ‘coast wattle’) and native Reference data were collected primarily in tute, 2000). vegetation free of coast wattle. Native veg- the fi eld using the GPS, located according etation free of coast wattle was divided to a stratifi ed random sampling strategy Results into ‘heathland’, ‘woodland’ and ‘burnt’ (Congalton 1988). Aerial photos and exist- Mapping coast wattle distribution (of any type) as these were too spectrally ing maps were used to collect reference in south-west Victoria using satellite distinct to include as a single category. data for heathland and water categories imagery The remaining eleven land categories which were inaccessible in the fi eld. Whilst Inspection of spectral signatures created (e.g. water, pine plantations, urban etc.) it is ideal to collect a minimum of 50 refer- from the mean refl ectance values of the will be grouped as ‘other’ from this point ence points per land cover category, more training areas revealed that coast wattle for brevity. The ‘coast wattle’ category in- or less can be collected according to the was spectrally distinct from all other land corporated coast wattle presence in any relative importance and spectral variabil- cover classes in the January image. Dis- environment, as initial investigations indi- ity of a class (Congalton 1991). Between 28 tinction between coast wattle and wood- cated that separating coast wattle presence and 265 reference points were collected for land or heathland was greatest in the according to its environment increased each category (total of 1086 points), with a near- and middle-infrared regions of the mis-classifi cation errors. positive bias towards the most important spectrum, in bands four, fi ve and seven Training areas were identifi ed on the categories of coast wattle, heathland and (Figure 2). Coast wattle was more spectral- image to develop a spectral signature for woodland. These were compared to clas- ly distinct from heathland than woodland. each land cover category. These areas were sifi cation results and entered into an error In the August image, coast wattle was not selected on the basis of being relatively ho- matrix to calculate overall accuracy, us- sufficiently distinct from heathland or mogenous and representative of the land er’s accuracies and producer’s accuracies woodland (Figure 3). Initial attempts at cover category of interest. Coast wattle (Congalton 1991). The ‘Kappa Coeffi cient’ undertaking a supervised classifi cation of training areas were selected on the basis of was also calculated, a standard method this image confi rmed this; hence it was ex- having greater than or equal to 70% coast for estimating the degree of accuracy cluded from further analysis. wattle cover, which was assessed visu- achieved above chance alone (Monserud The supervised classification of the ally following calibration in the fi eld us- and Leemans 1992). January image resulted in 11 448 ha clas- ing line-intercept transects (Krebbs 1999). sifi ed as coast wattle, 67 369 ha as coast Training area locations were identifi ed in Analysis of coast wattle distribution in wattle-free woodland, and 8869 ha of coast the fi eld using a Trimble Geographic Posi- the Lower Glenelg National Park wattle-free heathland. A further 9364 ha tioning System (GPS) then transferred to The second component of the investiga- were classifi ed as burnt vegetation, and ER Mapper. Field identifi cation was con- tion aimed to analyse the pattern of coast 143 872 ha as all other land cover types. ducted close to the time of image acqui- wattle distribution in the Lower Glenelg Overall, 12% of native vegetation in the sition to minimize errors associated with National Park. Four distribution param- study area was classifi ed as currently sup- land cover change. For the inaccessible eters were quantifi ed: the total area; dis- porting coast wattle. land cover types of heathland and water tribution according to park management The regional distribution map created (incorporated in the ‘other’ category), aer- zones; distribution in relation to roads, from the classifi cation indicated that coast ial photographs and existing maps were and; distribution within different EVCs. wattle is present in virtually all vegetation used to select suitable training sites. A to- Analyses were undertaken using ArcView reserves within the study area, including tal of 408 training areas were used, with 3.3. those as far as 15 kilometres inland. In an average of 27 per category (due to the To estimate the total area occupied by many instances even the verges of pine large study area). The training areas were coast wattle in the park, the distribution plantations and cleared roadsides contain distributed as evenly as possible across map was converted from raster to vector coast wattle. Both visual inspection of the Plant Protection Quarterly Vol.21(1) 2006 33 Table 1. Description of management zones in the Lower Glenelg National Park, including conservation values and management prescriptions (adapted from Department of Conservation and Environment (1991)). There is an increase in the degree of human infl uence from zone 1 and the reference areas through to zone 3. Feature Zone 1/reference areas Zone 2 Zone 3 Conservation values Highly signifi cant conservation Includes ecological systems Known conservation values not area or reference area and vegetation types not well threatened or are adequately represented in park and areas protected of landscape/ archaeological signifi cance Recreation/ facilities Essentially unmodifi ed, Natural appearing settings, Natural appearing settings, frequency of contact very low, moderate frequency of contact but may have noticeable facilities absent on roads (low to moderate modifi cations, high to moderate elsewhere), facilities simple and frequency of contact, facilities isolated may be complex and cater for large numbers Fragmentation/ Minimum 800 ha, width 2 km, No size criteria, low use roads No size criteria, access by public roads/ surrounding minimum 500 m from public acceptable roads land use roads, pine plantations or private land, management tracks rare and of minimum standard Management actions Primarily off-site controls Site controls subtle Controls obvious but in harmony with the environment Prescribed burning For vegetation or habitat For protection within defi ned For protection within defi ned management only fi re breaks, and for vegetation or zones, other protection measures habitat management as required near visitor sites and main roads, and for vegetation or habitat management as required

classiﬁ cation results and ground obser- Analysis of coast wattle distribution in � ��

� ��

vations suggest that remnant vegetation the Lower Glenelg National Park � ��

� ��

with a high edge to area ratio has a greater Overall extent of coast wattle in the � �� proportion of area occupied by coast wat- � park—Coast wattle distribution within � �� tle than larger reserves and, around the the Lower Glenelg National Park is shown � ��

� ��

boundary of the Lower Glenelg National in Figure 4. The current distribution of the � � �� Park, edges adjacent to pine plantations species appears to be conﬁ ned largely to � ��

are invaded more often than those adja- the central and southern sections of the � �� cent to other native vegetation or agricul- park, predominantly close to boundary �� tural land. edges. The far western and eastern sec- �� According to the accuracy assessment, tions of the park are relatively free of coast an overall classifi cation accuracy of 81% wattle. Figure 2. Spectral signatures of coast was achieved for the January image. The Table 3 shows the relative proportions wattle, woodland and heathland Kappa Coeffi cient was 0.78, indicating that of coast wattle and other cover classes in the January 2002 Landsat image. the classifi cation was 78% better than could within the Lower Glenelg National Park. Coast wattle is spectrally distinct be achieved by chance alone. An error ma- Despite appearing to cover a large area, from both heathland and woodland. trix including only coast wattle and coast coast wattle-invaded vegetation was wattle-free vegetation types is shown in found to make up only 7% (1963 ha) of Table 2. The user’s accuracy for coast wat- the park. In comparison, heathland and � ��

tle, which is a measure of the percentage woodland free from coast wattle made up � �� of coast wattle shown on the image that is 64% and 19% respectively. � ��

� �� actually coast wattle on the ground, was � ��

calculated at 82%. The producer’s accu- Distribution of coast wattle according to � �� racy, a measure of the percentage of coast management zones The proportion of � ��

� ��

wattle on the ground actually shown as coast wattle to coast wattle-free vegetation �

� �� coast wattle in the image, was 71%. These was found to vary considerably between � � �� accuracies are comparable to the results of management zones in the park. The pro- � � � � � � � other Australian weed mapping studies portion of coast wattle-invaded vegetation �� using remote sensing (e.g. Frazier 1998, in each of the zone was: Reference Areas Abbott et al. 1999, Crossman and Kocher- (<1%); Zone 1 (4%); Zone 2 (10%), and; Figure 3. Spectral signatures gen 2002) and were considered acceptable Zone 3 (28%). An increase in the propor- of coast wattle, woodland and for continuation to the next stage of analy- tion of coast wattle per zone was found heathland in the August 2001 sis using GIS. to coincide with the increase in the inten- Landsat image. Coast wattle is not sity of human disturbances used to defi ne spectrally distinct from heathland these zones (as outlined in Table 1). or woodland. 34 Plant Protection Quarterly Vol.21(1) 2006 Table 2. Error matrix for the classifi cation of the January 2002 Landsat Distribution of coast wattle within Eco- image, showing only coast wattle and coast wattle-free heathland and logical Vegetation Classes GIS calcula- woodland. ‘Other’ refers to all other categories in the classifi cation. tions highlighted that some Ecological Diagonal values shown in bold represent correctly classifi ed data. Vegetation Classes are more vulnerable to invasion by coast wattle than others. As Reference data can be seen in Table 4, 48% of the area clas- Coast wattle Heathland Woodland Other Total sifi ed as coast wattle in the Lower Glenelg National Park occurred in a single Ecologi- Coast wattle 188 1 28 11 228 cal Vegetation Class (EVC), damp sands Heathland 0 43 0 5 48 herb-rich woodland (EVC 3). Approxi- mately 85% occurred in just four EVCs: data Woodland 36 6 148 10 200 damp sands herb-rich woodland (EVC 3),

Classiﬁ cation Classiﬁ Other 41 1 3 herb-rich heathy woodland (EVC 179), and two mosaic EVCs which included damp Total 265 51 179 sands herb-rich woodland (EVCs 881 and Producer’s Accuracy 71% 84% 83% 740) (Table 4). In addition to having the highest total area of coast wattle invasion, User’s Accuracy 82% 90% 74% these EVCs also tended to have the highest proportion of their area invaded when taking into consideration the area occupied by different EVCs (Table 4). EVCs with a relatively low proportion and total area of coast wattle invasion included forest EVCs (EVC numbers 16 and 23), heathland EVCs (6 and 8), heathy � woodland EVCs (48, 737 and 793), shrubland EVCs (675 and 133), and freshwater marshes (200 and 681).

Discussion The results of this investigation confi rm �� the anecdotal estimate reported by Mc- �� Mahon et al. (1996) that coast wattle now occurs across more than 10 000 ha of na- �� tive vegetation in south-west Victoria. It appears that coast wattle is now a signifi - � � �� cant component of native vegetation in the region, and has spread considerably in recent decades. This is particularly evident in the Lower Glenelg National Park. It is believed that as an early dune colonizer, Figure 4. Coast wattle distribution in the Lower Glenelg National Park the species did not originally occur in the according to the supervised classifi cation of the January 2002 image. park. Even prior to the 1970s coast wattle was sparse in what is now the National Park, occurring over no more than a few hundred hectares (Baldock et al. 1995b). Table 3. Proportions of different land cover classes in the Lower Glenelg This study estimates that almost 2000 ha of National Park according to the supervised classifi cation of the January 2002 the park are now occupied by coast wattle, Landsat image. representing a signifi cant expansion in the species’ range. Land cover class Area classifi ed as Proportion of total park area Examination of distribution patterns land cover class (%) in the Lower Glenelg National Park in- (ha) dicates that coast wattle invasion has not Woodland 16 685 64 been uniform, tending to be concentrated Heathland 4 943 19 in particular areas. This patchiness may refl ect the particular environmental or dis- Coast wattle 1 963 7 turbance factors required to create a suit- Burnt vegetation 1 366 5 able environment for invasion (provided a Other 1 287 5 ready supply of propagules). The present study quantifi ed some basic distribution Total 26 244 patterns according to units relevant to management, and suggests hypotheses for further testing. Distribution of coast wattle in relation to roads. Beyond 1000 m from roads, coast It appears that coast wattle is not in- roads Coast wattle presence was found wattle presence was negligible (Figure 5). vading all vegetation types in the Lower to decrease signifi cantly with increasing The results also indicated however that oc- Glenelg National Park, but is concentrat- distance from roads in the park (Figure 5). casionally coast wattle can occur at some ed mainly in the herb-rich woodlands. Of the total area classifi ed as coast wattle distance from roads. Damp-sands herb-rich woodland has a in the park, 86% occurred within 500 m of particularly high degree of invasion (25% Plant Protection Quarterly Vol.21(1) 2006 35 of the total EVC, and 48% of total coast � wattle distribution in the park), and is the

� ��

� second most extensive vegetation type in � � � the park. Conversely, there is relatively

� ��

� little coast wattle in forest and heathland

� areas, which also cover a considerable pro- � ��

� portion of the park. These results are con- � � � sistent with roadside observations by Bal- � �

� � � dock et al. (1995b). Previous observations �

� have found coast wattle to be more proliﬁ c � �

� � in high light environments (Baldock et al. �

� 1995a), and on sandy soils, and rarely on � � � �

� dark clay, peat or waterlogged soils (Ste- �

� vens 1983, Tame 1992, Costermans 2000). � � � � � The herb-rich woodlands in which coast �

� wattle is most prevalent tend to be fairly � � open, with relatively sparse canopy cover, � � � �� low to moderate shrub cover, and occur on either sandy or loamy soils. Those EVCs �� where coast wattle invasion has been low generally have higher tree or shrub cover Figure 5. Relationship between proximity to roads and coast wattle than the herb-rich woodlands, and many occurrence in the Lower Glenelg National Park. Coast wattle is shown as a occur on heavy or waterlogged soils (e.g. proportion of 50 m buffers extending out from roads.

Table 4. Area of coast wattle according to Ecological Vegetation Class in the Lower Glenelg National Park, including the proportion of EVC invaded, total area of coast wattle, and proportion of coast wattle in the park. EVC EVC Description Proportion of Total area of Total area of Proportion No. EVC invaded EVC in park coast wattle in of total coast by coast wattle (ha) EVC wattle in park (%) (ha) (%) 3 Damp sands herb-rich woodlandAB 25 3535 914 48 179 Herb-rich heathy woodland 15 859 128 7 740 Damp sands herb-rich woodland/ heathy 13 974 126 7 woodland/ sand heathland 881 Damp sands herb-rich woodland/ heathy 12 3490 428 23 woodland 669 Escarpment shrubland/ damp sands herb-rich 9 272 24 1 woodland/ riparian woodland 725 Damp sands herb-rich woodland/ riparian 8 389 31 2 woodland/ swamp scrub 23 Herb-rich foothill forestAB 6 232 14 1 191 Riparian scrub 5 323 15 1 645 Wet heathland/ heathy woodland 4 2821 101 5 675 Escarpment shrubland/ damp sands herb-rich 4 46 2 <1 woodland/ swamp scrub 737 Heathy woodland/ limestone woodland 2 1953 48 3 16 Lowland forest <1 3712 34 2 8 Wet heathland <1 3454 10 1 48 Heathy woodland <1 2499 9 <1 200 Shallow freshwater marshAB <1 29 <1 <1 681 Deep freshwater marshB 0 5 0 0 6 Sand heathland 0 39 0 0 133 Limestone pomaderris shrubland 0 60 0 0 793 Damp heathy woodlandA 0 340 0 0 A Threatened in Glenelg Plains Bioregion (encompassing the western section of the Lower Glenelg National Park) B Threatened in Victorian Volcanic Plains Bioregion (encompassing the eastern section of the Lower Glenelg National Park) 36 Plant Protection Quarterly Vol.21(1) 2006 wet heathlands and damp heathy wood- McMahon et al. (1996) and Costello et al. (Bulman 2000). To be useful in practice, land). (2000). The variation in coast wattle distri- mapping techniques need to be robust and Coast wattle is not typically a compo- bution according to vegetation type sug- repeatable, preferably across sites of vary- nent of these inland woodland vegetation gests that environmental factors in part ing scales and environmental conditions. types, and has only invaded in recent dec- determine susceptibility to invasion by This is essential if the technique is to be ades. Parendes and Jones (2000) suggest coast wattle. It appears that a combination useful in ongoing monitoring, which is of- that invasion of a species into a new envi- of disturbance and environmental factors ten stated as a primary objective in weed ronment occurs when a previous barrier to may determine its inland distribution. mapping trials (Emeny et al. 2005). invasion is removed. The initial and ongo- The invasion of EVCs typically open The overall mapping accuracy and ac- ing causes for the invasion of coast wat- in structure with relatively low shrub curacy of mapping coast wattle in this tle into the Lower Glenelg National Park cover suggests that signifi cant structural study was slightly lower than that re- and surrounding region are poorly under- and compositional change may be taking ported by Race and Rollings (1992). This stood. However, they are often attributed place. Damp-sands herb-rich woodland is is probably due to the much larger study to anthropogenic disturbances or a change currently classifi ed as ‘vulnerable’ (i.e. 10 area and range of environments in the to pre-European disturbance regimes, par- to 30% pre-European extent remains) in present study, which tends to increase ticularly fi re and grazing (McMahon et al. the regions in which the Lower Glenelg spectral variability within individual land 1996, Baldock et al. 1995b, Costello et al. National Park falls (Glenelg Hopkins classes. Mapping accuracy at the region- 2000). GIS analysis in this study revealed Catchment Management Authority 2000). al scale might be improved by mapping an increase in coast wattle prevalence in The degree of coast wattle invasion in this coast wattle separately within different areas with higher levels of human infl u- EVC should therefore be of considerable vegetation types or smaller geographical ence, such as vegetation close to roads and concern, and be prioritized in any man- units, to decrease the effect of spatial vari- management zones with higher levels of agement programs. ability. However, for the purpose of this human access and management control. study, which was to provide a relatively The increase in coast wattle with proxim- The effectiveness of Landsat imagery for rapid assessment of coast wattle distribu- ity to roads in the Lower Glenelg National mapping and monitoring coast wattle tion across a large area, the accuracy was Park supports similar observations by Landsat imagery proved to be a success- considered adequate. Baldock et al. (1995b). The increased light, ful means of mapping coast wattle at The distribution map produced in this space and soil disturbance typical of road- the regional scale in south-west Victoria, study provides a baseline for future moni- sides is likely to allow establishment by comparing well to the accuracy of other toring of coast wattle spread in south-west coast wattle, which is an early-dune colo- weed mapping attempts (e.g. Frazier Victoria. Landsat imagery has proven to be nizer. This effect may be amplifi ed when 1998, Crossman and Kochergen 2002, Un- a repeatable and relatively robust means a road is adjacent to a land use in which derwood et al. 2003). As with a number for mapping coast wattle, and is currently regular disturbance occurs. Although not of other studies where a single species is the only feasible means for mapping the quantifi ed, visual inspection of classifi ca- mapped from remotely sensed imagery species at the regional scale. By undertak- tion results of coast wattle distribution at (Everitt and Deloach 1990, Everitt et al. ing an accuracy assessment, an estimate the boundary of the Lower Glenelg Na- 1991, Everitt et al. 1992), successful map- of the reliability of distribution maps can tional Park indicated that sections adjacent ping of coast wattle was found to depend also be gauged. The relative coarseness to pine plantations (which have regular on time of year and corresponding phe- of Landsat imagery limits detection of disturbance during establishment, harvest nological stage. In this case, coast wat- coast wattle to mature plants and larger and road maintenance) were more likely tle was successfully mapped during the stands of the species. It is recommended to be invaded than those adjacent to graz- post-fl owering, seed production phase of that regional-scale mapping from satellite ing land or other native vegetation. mid-January, but not during the pre-fl ow- imagery be considered as a component of The increase in coast wattle with a ering phase of early August. The success- long-term coast wattle monitoring, along- general increase in disturbance in man- ful mapping of coast wattle by Race and side ground observations used to assess agement zones may refl ect the infl uence Rollings (1992) was also during the post- densities and detect recent invasions into of a complex range of factors associated flowering phase (February). Although new areas. with disturbance. When considering the coast wattle detection was not assessed distribution of coast wattle within man- during peak fl owering, it is unlikely that Conclusion agement zones, it is apparent that a gra- more accurate result would be achieved By integrating satellite remote sensing and dient from low occurrence to relatively using a single image due to the extended GIS technologies, the current distribution high occurrence occurs from the Refer- period over which individual coast wat- of coast wattle in south-west Victoria has ence Areas and Zone 1 through to Zone tle plants come in and out of fl ower (July been established, and some basic distri- 3. The human disturbance factors used to to November) and as such, it is doubtful bution patterns identifi ed in the Lower determine management zones vary along that all coast wattle infestations would be Glenelg National Park. When compared to a similar gradient. For example, the level detectable in one image. However, further pre-1960 anecdotal estimates, the present of fragmentation, proximity to roads, rec- investigation during the fl owering period, extent of the species suggests a rapid ex- reational use and level of management possibly using multiple images, would be pansion of range inland. Analysis of coast control all increase from the Reference Ar- worthwhile. wattle patterns in the Lower Glenelg Na- eas and Zone 1 to Zone 3 (see Table 1). It An important outcome of this study is tional Park indicates this invasion has not is also likely that prior disturbances such that it confi rms the repeatability of Land- been uniform, and is at this stage restricted as logging and grazing would have in- sat imagery as a tool for mapping coast to a limited number of vegetation types. creased in intensity according to a similar wattle, with the success of this and the There is also some evidence that coast wat- trend, as a function of proximity to roads. previous study in the same region by tle invasion may be associated with an- Further analysis is required to determine Race and Rollings (1992). There have been thropogenic disturbances; however, GIS the relative importance of various envi- relatively few Australian examples where analysis in the study considered only a ronmental and disturbance factors in ex- environmental weeds have been mapped small number of factors potentially asso- plaining the current distribution of coast using satellite remote sensing (Crossman ciated with coast wattle distribution. The wattle, including the role of changes to and Kochergen 2002), and even fewer senior author of this paper is continuing fi re and grazing regimes as suggested by examples of successful repeat mapping this study by further investigating the Plant Protection Quarterly Vol.21(1) 2006 37 relative importance of various factors remote sensing to weed mapping just and Technology, Deakin University. in explaining current distribution, and ‘S-pie in the Sky’? Plant Protection Quar- Emeny, J., Simmons, D. and Wallis, A. whether factors such as vegetation type terly 15, 127-32. (2005). Using geospatial technologies and disturbance history interact to in- Burrell, J.P. (1981). Invasion of coastal to map and monitor environmen- crease likelihood of invasion. heaths of Victoria by Leptospermum lae- tal weeds. Proceedings of the Second The current extent of coast wattle in the vigatum (J.Gaertn.) F.Muell. Australian Victorian Weed Conference, pp. 56-62 region means widespread control is not Journal of Botany 29, 747-64. (Weed Society of Victoria, Frankston). feasible in the short term. Management Carr, G.W. (2001). Australian plants as Environmental Systems Research Institute should focus on prevention of further weeds in Victoria. Plant Protection Quar- (2000). Spatial Analyst for Arcview. En- coast wattle spread into environmentally terly 16, 124-5. vironmental Systems Research Insti- signifi cant areas from which it is currently Carr, G.W., Yugovic, J.V. and Robinson, tute, Redlands, California. absent, and close monitoring of further K.E. (1992). ‘Environmental weed in- Environmental Systems Research Institute spread. Of particular concern should vasions in Victoria: conservation and (2002). ArcView 3.3. Environmental be prevention of further spread within management implications’, p. 5. (De- Systems Research Institute, Redlands, damp-sands herb-rich woodland, which partment of Conservation and Environ- California. is regionally vulnerable and already sig- ment and Ecological Horticulture Pty. Everitt, J.H., Alaniz, M.A., Escobar, D.E. nifi cantly invaded by coast wattle. The Ltd., Melbourne) and Davis, M.R. (1992). Using remote regional distribution map created in this Clay, R.E. and Schneider, K.E. (2000). The sensing to distinguish common (Isoco- investigation provides both a baseline for ant (Hymenoptera: Formicidae) fauna ma coronopifolia) and Drummond gold- monitoring future spread of the species, of coastal heath in south-west Victoria: enweed (Isocoma drummondii). 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Geocarto Interna- error matrices for assessing the accu- tional 11, 63-80. Acknowledgements racy of maps generated from remotely Everitt, J.H., Escobar, D.E., Alaniz, M.A. The authors wish to acknowledge fund- sensed data. Photogrammetric Engineer- and Davis, M.R. (1991). Light refl ect- ing provided by the Australian Research ing and Remote Sensing 54, 593-600. ance characteristics and video remote Council and Parks Victoria for this project, Congalton, R. (1991). A review of assess- sensing of pricklypear. Journal of Range which was carried out as part of an Hon- ing the accuracy of classifi cations of Management 44, 587-92. ours Degree at Deakin University by the remotely sensed data. Remote Sensing of Everitt, J.H., Yang, C., Escobar, D.E., Web- fi rst author. Thanks also to Parks Victoria Environment 37, 35-46. ster, C.F., Lonard, R.I. and Davis, M.R. staff for their advice, particularly David Costello, D.A., Lunt, I.D. and Williams, J.E. (1999). 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