Key to the Trees and Shrubs of Black Mtn, Mt Ainslie and Mt Majura based on Vegetative Characters
Laurence G. Adams
Black Mountain Reserve on the one hand and Mount Ainslie/Mount Majura Reserve on the other are, geologically speaking, of very different age and material. Black Mtn is entirely derived from sedimentary rocks, mainly fine-grained quartz sandstone (Black Mtn Sandstone - Lower Silurian) with a smaller area on the western and northern side of even older shales and siltstones (Pittman Formation -Middle Ordovician). The Ainslie-Majura ridge, by contrast, is of younger acidic volcanics (Ainslie Volcanics - Middle Silurian [not Lower Devonian as previously thought]). Detailed descriptions of the respective geology can be found in R.S.Abell: "Geology of the Canberra 1:100,000 Sheet Area." - BMR Bulletin 233 (1991).
Despite this very different geology, both reserves carry a generally similar vegetation, the climax community being dry sclerophyll forest and woodland, in the main dominated by Eucalyptus rossii, E. mannifera and E. macrorhyncha. The only significant difference in canopy species is the far greater amount of E. melliodora, E. bridgesiana and E. blakelyi on Ainslie/Majura, predominantly on the lower slopes, reflecting the larger areas of deeper soils within the reserve compared with Black Mtn. One other distinction is that Casuarina verticillata is unaccountably common in the former but very rare in the latter. On the other hand Black Mtn has a significantly richer shrub and herbaceous flora, no doubt correlated with soils derived from the sandstone. Each has at least one native tree species not found in the other: Callitris (Black Mtn, a small colony on the western side), and Brachychiton (Mt Majura, purported to have been originally planted, but now thoroughly naturalised).
Both reserves had been subjected to considerable interference since European settlement in the area, mainly from stock grazing, burning and timber harvesting; it is probably unlikely however that, overall, the respective native floristic compositions have been significantly altered except in proportions of individuals of species present. The most obvious change to the casual observer is, of course, the presence of exotic trees, shrubs and weedy herbs; the latter, in particular, becoming dominant over small areas to the exclusion of almost all native species.
Although the Key has been written exclusively around the flora of the two reserves, it will be found to have relevance to most of the indigenous woody flora of Canberra's Nature Park system. The taxa treated are those that have been recorded up to the time of writing. A name that has been used in a leading work in the last 35 years (e.g. Burbidge & Gray: Flora of the ACT) but currently reduced to synonymy is given (in parentheses) immediately after the accepted name.
The few deciduous species represented (all introduced) were thought not significant enough to warrant keying out in any other than their full-leaf condition.
Throughout this work all main foliar structures are, for the sake of convenience, treated as leaves or leaflets even though, in the case of certain Acacia spp., the 'leaves' are actually phyllodes. Refer to the glossary for definitions of all other terminology used. In the few instances where supplementary flower and fruit characters have been utilized they are always given last [in square brackets].
Certain herbaceous species may on occasion cause difficulty by becoming "woody" and shrub-like when fully grown, and in some instances may even briefly resume growth from aerial stems that have survived the winter. The number of species that have this tendency is very small, and they are fairly readily distinguished in the field from true shrubs by the presence of dead stems from the previous year; they have been ignored for the purposes of this Key.
As an additional aid, a month is given in parentheses, ie. (Nov), immediately following each lead; this represents the earliest month in a normal year in which one could be reasonably sure of finding the taxon in flower. However, depending on seasonal weather variation, time of flowering can fluctuate by up to a month, so this figure should be taken as a rough guide only.
If difficulty is found in reaching a positive identification for a plant, the reason could be that the user has found a taxon previously unrecorded for the area; or possibly the Key itself has not taken sufficient account of the occurrence of aberrant features. Notice of any new records, problems or errors encountered would be gratefully received by the author.
The only tools required are an 8x–10x hand-lens and a metric rule.