Black Mountain
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Black Mountain A NATURAL HISTORY OF A CANBERRA ICON 2 Vegetation Black Mountain A NATURAL HISTORY OF A CANBERRA ICON 3 3 Vegetation Context Canberra – and thus Black Mountain – lies within the Southern Tablelands of New South Wales, which in general means cold winters, hot summers and moderate rainfall occurring all year round. More specifically, the adjacent weather station at the Australian National Botanic Gardens, which has operated since 1968, gives an average annual rainfall over that time of 688 mm, with extremes of 328 mm in 1982 and 1033 mm in 1974. There is no real wet or dry season; the driest month is June (47.8 mm mean) and the wettest is November (77.9 mm mean). The nearest long-term temperature records are from the Canberra Airport, 8.5 kilometres to the east; here the mean annual maxima and minima are 19.70C and 6.50C. The coldest average nights are in July (mean minimum -0.10C) and the hottest average days are in January (mean maximum 280C). Over the recording period (1939 to 2010) the temperature ranged over an impressive 520C (from 420C to -100C), but in most years the range has historically been about 400C. Table 3.1 Black Mountain’s Climate Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Annual Mean rainfall (mm) at the Australian National Botanic Gardens (1968–2018) 64.0 63.6 55.6 49.9 45.4 47.8 50.8 54.5 61.8 63.8 77.9 59.7 688 Mean maximum temperate (0C) at Canberra Airport (1939–2018) 28.2 27.2 24.6 20.1 15.6 12.4 11.5 13.2 16.4 19.7 23.1 26.3 19.9 Mean minimum temperate (0C) at Canberra Airport (1939–2018) 13.2 13.1 10.7 6.6 3 1 -0.1 0.9 3.2 6.1 8.9 11.5 6.5 4 Vegetation At a regional level these are the factors Plant Patterns of which determine the maximum biomass of vegetation which is possible, likely plant Black Mountain growth forms and plant species richness. There have been various attempts to At finer scales – say on Black Mountain define Australian vegetation types and itself – the geology, slope and aspect (the structures. One highly respected one direction of the slope) determine local is that of Professor Raymond Specht in microclimates and soil conditions, and it 1981; by that definition Black Mountain is is these which ultimately determine the dominated by Open Forest. This is a pretty actual plant species composition. Onto this broad definition, as we might expect from must be added the locally unique further a continent-wide system. More recently, complicating factors of disturbances David Keith of the NSW National Parks which may arise from fire, drought, storms, and Wildlife Service, now the Department human clearing, weeds, feral animals of Environment and Conservation, or diseases. produced a more finely-tuned model for NSW and the ACT. By his model Black All these disturbance factors have had Mountain represents Southern Tablelands an impact on Black Mountain in the last Dry Sclerophyll Forests, characterised century or so, and include the impacts by Eucalyptus trees less than 20 metres of severe drought (1965), storm (2007), high, including species of scribbly gums, Phytophthora dieback (after a wet summer peppermints and stringybarks. in 1969-70), thinning and firewood The shrubby understoreys have relatively collection (into the 1960s and over much of few species, which are dominated by the mountain except for the steepest and scattered wattles, peas and heaths highest slopes) and clearing (small areas interspersed with open spaces supporting on the lower eastern and southern slopes tussock grasses. This is a pretty fair in the late 19th century). In each case the description of the Black Mountain forests. affected areas recovered in time, or are However it’s important to note that the still doing so. The impacts of weeds are Southern Tablelands Dry Sclerophyll discussed later in this chapter, and of feral Forests are found in a broad swathe on the animals and fire in chapters four and six. drier western slopes of the Great Dividing Veg. type 1: Red Stringybark – Scribbly Gum open Veg. type 2a: Scribbly Gum – Red Stringybark forest with a Red-anthered Wallaby Grass ground (large stem sizes) open forest with a Red-anthered layer. Wallaby Grass ground layer. Black Mountain A NATURAL HISTORY OF A CANBERRA ICON 5 Table 3.2 Vegetation Types of Black Mountain (adapted from Peter Coyne) Type Structure Dominant species Main occurrence and notes 1 Open Forest Red Stringybark (Eucalyptus Grows on cooler, moister macrorhyncha) and Scribbly south-facing slopes of Gum (E. rossii), with some Brittle 150–300. Gum (E. mannifera), Broad-leaved Peppermint (E. dives) and Apple Box (E. bridgesiana). 2a Open Forest Scribbly Gum and Red Stringybark Northerly slopes. (large stem sizes), with some Red Box (E. polyanthemos). 2b Open Forest Scribbly Gum and Red Stringybark Gentle northern slope (small stem sizes), with some Brittle areas and also on steep Gum, Broad-leaved Peppermint slopes west of the summit. and Yellow Box (E. melliodora) 3 Open Forest Red Box, with some Red Found on dry exposed Stringybark, Scribbly Gum, Brittle north-west to west-facing Gum and Blakely’s Red Gum slopes. (E. blakelyi). 4 Open Forest Broad-leaved Peppermint. South-facing slopes. 5 Woodland Blakely’s Red Gum and Yellow Box. Broad depressions marking drainage lines at altitudes below 640 metres. 6 Grassland Introduced grasses and herbs. South-eastern slopes (new) below ANBG viewing platform. Veg. type 2b: Scribbly Gum – Red Stringybark (small Veg. type 3: Red Box open forest with a low shrub stem sizes) and a sparse low shrub layer. layer of Silver Teatree. 6 Vegetation Veg. type 4: Broad-leaved Peppermint open forest Veg. type 5: Woodland with a large old-growth with scattered Burgan shrubs. Apple Box tree and a Burgan shrub layer. Range south from Mudgee to the Murray which circumnavigates the mountain a (and into Victoria); Black Mountain is little below the summit, is an excellent a good—and accessible—example of introduction to them and illustrates nicely the vegetation type, but is certainly not the changes with aspect. In summary, the unique. most abundant trees on the mountain are Red Stringybark and Scribbly Gum but In 1969 Peter Coyne, then an Honours while both species can be found on both Student at the Australian National sheltered southern and exposed northern University, used aerial photography and slopes, the stringybark strongly prefers the ground transects to describe and map sheltered situations and the gum the drier vegetation types on Black Mountain based sides. This corresponds to their respective on the number and diameter of tree stems tolerances to higher temperatures and 1.2 metres above ground level. In this way water stress as revealed in laboratory he described four Open Forest structures experiments. Of the four other main (subdividing one of them) plus one eucalypt species in the forest, only Red Box Woodland structure as shown in Table 3.2. prefers the northern slopes, while Brittle He went on to propose a management plan Gum, Broad-leaved Peppermint and Apple for the mountain—pioneering stuff in Box favour the more sheltered aspects and/ those days. While the thesis has never been or gentler slopes. published, it remains the best description of the area’s vegetation types. Vegetation Type 4, dominated by Broad-leaved Peppermint, occurs as a pure Vegetation types 1 and 2 have the same stand on a very steep shady south-facing two dominant species but the reversed slope above Lake Burley Griffin. Elsewhere order indicates a reversal in their relative on the mountain this species occurs as dominance. Type 2 has two subtypes that scattered trees along some creek lines on are essentially restricted to northerly slopes, the lower slopes. but extend over the crests of east-west spurs onto the upper southerly slopes. Vegetation Type 5, dominated by Blakely’s Red Gum and Yellow Box, is the only Types 1-3 dominate the Black Mountain woodland type on Black Mountain. On forests; a walk around the Forest Loop, the lower south west side of the reserve Black Mountain A NATURAL HISTORY OF A CANBERRA ICON 7 Veg. type 5: Grassland of native herbs formed Veg. type 6: Grassland of introduced herbs formed where the Eucalyptus trees have been cleared where Red Stringybark, Scribbly Gum open forest from grassy woodland. has been cleared. (which Coyne excluded from his study) Spurge (Phyllanthus hirtellus), Small-leaved it grades into grassland which was formed Parrot-Pea (Dillwynia phylicoides), Bushy when the original grassy woodland Needlewood (Hakea decurrens), and vegetation in an area known as Smith’s Ivy Goodenia (Goodenia hederacea) are Paddock was cleared for grazing. Almost more likely to be found on the hotter none of this grassy woodland is left intact north-facing slopes. On sheltered southern within Black Mountain Nature Reserve. aspects the Red-anther Wallaby Grass An area on the south-east side of the is joined by the smaller tussocks of mountain, also excluded by Coyne and Common Snow Grass (Poa sieberiana) and now located in the ANBG’s southern on some of the most exposed northern annex and called the Bushland Precinct, aspects in the north-west corner of is grassland (Veg. type 6) resulting from the mountain, it is replaced by Narrow Red Stringybark, Scribbly Gum open forest Swordsedge (Lepidosperma gunnii). There being clearing for grazing. is more on the component species of the Black Mountain forests in chapter 4. At first glance, other than the Type 5 woodland, the tree-defined vegetation types seem not to be strongly reflected in the understorey.