Workshop Notes Perth Region Plant Biodiversity Project Jarrah Forest Reference Sites of the Perth Metropolitan Area: the Norther
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Workshop Notes Perth Region Plant Biodiversity Project Jarrah Forest Reference Sites of the Perth Metropolitan Area: The Northern Transect Shaun Molloy November 2007 - 1 - Introduction Bush Forever is a 10 year strategic plan instigated by the Western Australian Government in conjunction with the general community and appropriate Local Government organisations to protect some 51,200 hectares of regionally significant bushland in 287 Bush Forever Sites, representing, where achievable, a target of at least 10 percent of each of the original 26 vegetation complexes of the Swan Coastal Plain portion of the Perth Metropolitan Region. Subsequent to Bush Forever, the Perth Biodiversity Project identified the need to catalogue and describe a series reference sites to facilitate consistency in the assessment of local natural areas and to further enhance the capacity of relevant people to undertake site recording tasks. To this end 40 reference sites were established based on Bush Forever on the Swan Coastal Plain part of the Perth Metropolitan Region (PMR) as part of the Perth Region Plant Biodiversity Project (PRPBP), a collaborative project between the WA Local Government Association’s Perth Biodiversity Project and the Department of Environment and Conservation. The PRPBP recognises a need to provide a fuller appreciation of the diversity of native vegetation found within the PMR. To that end, it was decided to establish reference sites within, or in close proximity to, Darling Plateau part of the PMR. It is proposed that these reference sites are established so as to represent major variations found in the plant communities found within this area. The purpose of this document is to provide information applicable to the management of Bushland within the PMR part of the Jarrah Forest, and to describe the reasoning for selecting the sites used in the PRPBP Jarrah Forest Reference Sites. Jarrah Forest The Jarrah Forest Interim Biogeographical Regionalisation of Australia (IBRA) region covers an area of approximately 5.4 million hectares stretching from the Shire of Chittering in the north to near Albany in the south (Commonwealth of Australia 2001), although smaller outlying populations of Jarrah (Eucalyptus marginata) occur outside of the Jarrah Forest Region extending into the Wheatbelt and Swan IBRA regions. Jarrah forest itself, generally occurs on the duricrusted plateau of the Yilgarn Craton and is characterised by Jarrah- Marri (Corymbia calophylla) woodlands on laterite gravels, bordered by Wandoo (Eucalyptus wandoo)- Marri woodlands on clayey soils to the east, Darling Scarp shrublands to the west and Karri (Eucalyptus diversicolor) forests to the south. Within this region are areas of eluvial (wind deposited minerals) and alluvial (water deposited) landforms support diverse shrublands. In areas of Mesozoic (248-65 mya) sediments, Jarrah forests occur in a mosaic with a variety of species- rich shrublands. The climate of the Jarrah Forest region is described as warm and Mediterranean. Rainfall varies from 1,200 mm in Serpentine and the lower south west to 500 mm in the east most of which falls between June and September (May and McKenzie 2003). - 2 - Unlike most of the world’s hardwood forest trees, Jarrah occurs as an almost pure stand within the Jarrah Forest region (although outlying populations are usually far less homogenous in structure). Few other trees grow in association with Jarrah, and those that do have specialized requirements and/or prefer soils other than pure laterite. Marri, Wandoo and Powderbark Wandoo (Eucalyptus accedens) prefer clayey soils, Bullich (Eucalyptus megacarpa) preferring wetter sandy duplex soils on valley floors, Flooded gum (Eucalyptus rudis), Blackbutt (Eucalyptus patens), and Melaleuca rhaphiophylla are generally associated with water courses, Melaleuca preissii and Swamp Banksia (Banksia littoralis) being associated with swamps, and Rock Sheoak (Allocasuarina huegeliana) being mainly associated with granite outcrops (Erickson et al 1973). Most other trees that grow in association with Jarrah usually form a second story or are found in small isolated stands. Foremost amongst these are Allocasuarina fraseriana and proteaceous species such as; Banksia grandis, Persoonia longifolia, Persoonia elliptica, Dryandra sessilis and in some areas Banksia menziesii, Banksia attenuata and Banksia prionotes. Beneath the relatively homogenous canopy of the Jarrah Forest there is often found deceptively diverse shrub and herbaceous understorey layers (Erickson et al 1973). These layers can vary from near monocultures in composition to highly diverse understorey mosaics. This diversity of structural units is, in many cases, as much due to disturbance history as it is to variations in climate and geology. There are 3850 current, native flora taxa listed on Florabase (WA Herbarium 1998-) within the Jarrah Forest IBRA region. The western edge of the Darling Range is called the Darling Scarp. This is the surface expression of an extensive geological structure known as the Darling fault. The scarp rises steeply to more than 200 meters above sea level, where it flattens out to form the Darling Plateau (Copp 2001). Patterns in the vegetation structure and floristic associations have long been attributed to the influences of the environment, which is evident at the environmental extremes presented by the Darling Scarp. The vegetation of the Scarp forms a variety of structural units varying from open woodlands of Jarrah, Marri, Wandoo, Darling Range Ghost Gum (Eucalyptus laeliae) and Rock Sheoak (Allocasuarina huegeliana), through to herbaceous lithic complexes and extensive shrublands, which, in the northern part of the Scarp, (including the section of the Darling Scarp included in the Perth Metropolitan Region) have been described by Markey (1997)as a series of 13 Floristic Community Types within 3 Super Groups. Six hundred and eighty nine taxa have been documented within the Northern Darling Scarp (Markey 1997). - 3 - Northern Jarrah Forest Reference Sites John Forrest National Park - PRPBP Jarrah Forest Reference Site 1 (JF1) John Forest National Park is approximately 20km due east of Perth within two local government areas; the City of Swan, and the Shire of Mundaring. It is managed by the Department of Environment and Conservation and includes a large section of the Darling Scarp and adjoining Jarrah Forest covering an area of 2,676 hectares within which the following vegetation complexes can be found; Forrestfield (FO), Darling scarp (DS), Helena (He2), Yarragil 2 (Yg2) and Dwellingup 2 (D2) (Havel and Mattiske 2000) (see JF1 Map 1 att.). The reference point selected (JFor1 see Map JF2 att.) was towards the top of the Darling Scarp on the Toodyay Rd within the locality of Swan View in the City of Swan (JFor1 reference site description att.). During the 2006-7 summer bushfires severely burnt much of the Northern PMR Darling Scarp. Because of the physical nature of the Scarp this area is very prone to bushfires ignited through natural causes such as lightening strike and (too often) through arson. For this reason much of the Scarp in this area is noticeably impacted through high intensity and high frequency (usually 3 year approx interval) fires. To the south of Toodyay Rd. at JFor1 there is a highly diverse shrubland which is in (generally) Very Good condition. This area has not been burnt for 5-7 years (estimated), has little weed intrusion, includes a diverse selection of species indicative of its floristic community type (Supergroup 1, FCT2, Southern granite shrublands and woodlands) (Markey 1997), and adjoins many structural units unique to this vegetation complex, including lithic complex, drainage line and Marri, Jarrah and Wandoo Open Woodland. To the north of Toodyay Rd. at the reference site there is a clear vista over a large area of the Scarp within in which a large selection of vegetation structural units are visible. These units form an easily viewed representational landscape ranging from Dwellingup through Darling Scarp to Forrestfield vegetation complexes on the Swan Coastal Plain. Unfortunately much of this area was burnt during the 2006-7 bushfires (Molloy 2007). However, if allowed to regenerate, monitoring the gradual recovery of this site will reveal much about; the vegetation structural units of the Darling Scarp Vegetation Complex, the impacts of a high intensity high frequency fire regime on this Vegetation Complex, and the natural mechanisms and disturbance opportunist species that will facilitate this recovery. In general this site (both north and south of Toodyay Rd.) complies very well with the representational landscape provided by Havel and Mattiske (2000) in Appendix 257 (att.) and as such provides a convenient opportunity to introduce participants to the flora and geology of the Darling Scarp. This landscape conforms well to that represented in Havel and Mattiske (2000) appendix D257. A site description summarising the known values of the site is attached. Reserve 2145/ Percy Cullen Oval - PRPBP Jarrah Forest Reference Site 2 (JF2) - 4 - This is a 26 hectare reserve situated just west of the locality of Gidgegannup within, and managed by, the City of Swan. This site contains good representations of the landscape and flora of two vegetation complexes; these being Yarragil 1 and Dwellingup 2 (Havel and Mattiske 2000). Two reference points have been selected in this reference site using quadrats previously established as part of a comprehensive survey of this reserve (Bennett