Black Mountain a NATURAL HISTORY of a CANBERRA ICON 3
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Black Mountain A NATURAL HISTORY OF A CANBERRA ICON 3 2 Black Mountain: a natural history of a Canberra icon 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 At a regional level these are the factors which determine the maximum biomass of vegetation which is possible, likely plant growth forms and plant species richness. At finer scales – say on Black Mountain itself – the geology, slope and aspect (the direction of the slope) determine local microclimates and soil conditions, and it is these which ultimately determine the actual plant species composition. Onto this must be added the locally unique further complicating factors of disturbances which may arise from fire, drought, storms, human clearing, weeds, feral animals or diseases. Black Mountain: a natural history of a Canberra icon 3 Veg. type 1: Red Stringybark – Scribbly Gum open Veg. type 2a: Scribbly Gum – Red Stringybark (large forest with a Red-anthered Wallaby Grass ground layer. stem sizes) open forest with a Red-anthered Wallaby Grass ground layer. 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. All these disturbance factors have had Plant Patterns of an impact on Black Mountain in the last century or so, and include the impacts Black Mountain of severe drought (1965), storm (2007), There have been various attempts to Phytophthora dieback (after a wet define Australian vegetation types and summer in 1969-70), thinning and firewood structures. One highly respected one collection (into the 1960s and over much of is that of Professor Raymond Specht in the mountain except for the steepest and 1981; by that definition Black Mountain is highest slopes) and clearing (small areas dominated by Open Forest. This is a pretty on the lower eastern and southern slopes broad definition, as we might expect from in the late 19th century). In each case the a continent-wide system. More recently, affected areas recovered in time, or are David Keith of the NSW National Parks still doing so. The impacts of weeds are and Wildlife Service, now the Department discussed later in this chapter, and of feral of Environment and Conservation, animals and fire in chapters four and six. produced a more finely-tuned model for 4 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. Veg. type 5: Grassland of native herbs formed where Veg. type 6: Grassland of introduced herbs formed the Eucalyptus trees have been cleared from grassy where Red Stringybark, Scribbly Gum open forest woodland. has been cleared. NSW and the ACT. By his model Black drier western slopes of the Great Dividing Mountain represents Southern Tablelands Range south from Mudgee to the Murray Dry Sclerophyll Forests, characterised (and into Victoria); Black Mountain is a by Eucalyptus trees less than 20 metres good—and accessible—example of the high, including species of scribbly gums, vegetation type, but is certainly not unique. peppermints and stringybarks. The shrubby understoreys have relatively In 1969 Peter Coyne, then an Honours few species, which are dominated by Student at the Australian National scattered wattles, peas and heaths University, used aerial photography and interspersed with open spaces supporting ground transects to describe and map tussock grasses. This is a pretty fair vegetation types on Black Mountain based description of the Black Mountain forests. on the number and diameter of tree stems However it’s important to note that the 1.2 metres above ground level. In this way Southern Tablelands Dry Sclerophyll he described four Open Forest structures Forests are found in a broad swathe on the (subdividing one of them) plus one 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 Gum south-facing slopes of (E. rossii), with some Brittle Gum 150–300. (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 areas (small stem sizes), with some Brittle and also on steep slopes Gum, Broad-leaved Peppermint west of the summit. and Yellow Box (E. melliodora) 3 Open Forest Red Box, with some Red Stringybark, Found on dry exposed Scribbly Gum, Brittle Gum and north-west to west-facing Blakely’s Red Gum (E. blakelyi). slopes. 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 (new) Grassland Introduced grasses and herbs. South-eastern slopes below ANBG viewing platform. Woodland structure as shown in Table 3.2. Red Stringybark and Scribbly Gum but He went on to propose a management while both species can be found on both plan for the mountain—pioneering stuff sheltered southern and exposed northern in those days. While the thesis has never slopes, the stringybark strongly prefers the been published, it remains the best sheltered situations and the gum the drier description of the area’s vegetation types. sides. This corresponds to their respective tolerances to higher temperatures and Vegetation types 1 and 2 have the same water stress as revealed in laboratory two dominant species but the reversed experiments. Of the four other main order indicates a reversal in their relative eucalypt species in the forest, only Red Box dominance. Type 2 has two subtypes that prefers the northern slopes, while Brittle are essentially restricted to northerly slopes, Gum, Broad-leaved Peppermint and Apple but extend over the crests of east-west Box favour the more sheltered aspects and/ spurs onto the upper southerly slopes. or gentler slopes. Types 1-3 dominate the Black Mountain Vegetation Type 4, dominated by forests; a walk around the Forest Loop, Broad-leaved Peppermint, occurs as which circumnavigates the mountain a a pure stand on a very steep shady little below the summit, is an excellent south-facing slope above Lake Burley introduction to them and illustrates nicely Griffin. Elsewhere on the mountain this the changes with aspect. In summary, the species occurs as scattered trees along most abundant trees on the mountain are some creek lines on the lower slopes. 6 Vegetation Vegetation Type 5, dominated by Blakely’s Rosemary this text is added in order to Red Gum and Yellow Box, is the only fill space - we will figure out the layout woodland type on Black Mountain. On once we have final text - but this just to the lower south west side of the reserve get a sense of overall style. At first glance, (which Coyne excluded from his study) other than the Type 5 woodland, the tree- it grades into grassland which was formed defined vegetation types seem not to when the original grassy woodland be strongly reflected in the understorey. vegetation in an area known as Smith’s The shrub layer is dominated throughout Paddock was cleared for grazing. Almost by Narrow-leaved Bitterpea (Daviesia none of this grassy woodland is left intact mimosoides). within Black Mountain Nature Reserve. erb layer by the large tussocks of An area on the south-east side of the Red-anther Wallaby Grass (Rytidosperma mountain, also excluded by Coyne and pallidum). However there are preferences now located in the ANBG’s southern here too. Overall the Narrow-leaved annex and called the Bushland Precinct, Bitterpea grows preferentially on the is grassland (Veg. type 6) resulting from southern aspect, as do the other relatively Red Stringybark, Scribbly Gum open forest common shrubs Prickly Broom Heath being clearing for grazing.