160 Frank et al.: Street Tree Population of Greater Melbourne Table 3. Origin of species. Origin Exotic broadleaf Australian native broadleaf Exotic conifer Australian native conifer Totals Number of taxa 600 439 75 12 1,126 Table 5. Major tree genera based on species/variety diversity. Percentage 53 39 7 1 100 largest number of taxa with 141 (13%) and also the largest percentage of individuals (also 13%). This figure does not include Corymbia spp., which were, until relatively recently, part of the genus Eucalyptus. Corymbia spp. contributes an- other nine taxa and a further 37,394 trees (4% of total plants). There were other Australian native tree taxa that contrib- uted significant numbers to the total tree population. For ex- ample, only three Melaleuca species were found: bracelet Table 4. Rank order of families with more than 100 individuals. No. of Family Myrtaceae Rosaceae Oleaceae Platanaceae Mimosaceae Proteaceae Fagaceae Ulmaceae Pittosporaceae Malvaceae Cupressaceae Meliaceae Casuarinaceae Aceraceae Fabaceae Apocynaceae Caesalpiniaceae Lauraceae Salicaceae Bignoniaceae Moraceae Pinaceae Anacardiaceae Sterculiaceae Arecaceae Lythraceae Sapindaceae Totals genera 28 15 7 1 3 13 4 3 4 7 Hamamelidaceae 3 Betulaceae 2 8 2 2 1 20 2 6 3 2 4 3 7 5 2 13 1 4 Percentage total genus 8.4 4.5 2.1 0.3 0.9 3.9 1.2 0.9 1.2 2.1 0.9 0.6 2.4 0.6 0.6 0.3 6.0 0.6 1.8 0.9 0.6 1.2 0.9 2.1 1.5 0.6 3.9 0.3 1.2 175 52.50 ©2006 International Society of Arboriculture Number of individuals 467,282 110,712 41,156 40,728 30,126 24,501 23,692 19,890 15,101 14,044 12,991 12,679 10,350 10,085 9,026 6,963 6,087 4,804 4,598 4,446 4,324 3,755 2,907 2,324 2,053 2,032 1,933 1,613 1,007 891,209 Percentage total individuals 52.0 12.3 4.6 4.5 3.3 2.7 2.6 2.2 1.7 1.6 1.4 1.4 1.2 1.1 1.0 0.8 0.7 0.5 0.5 0.5 0.5 0.4 0.3 0.3 0.2 0.2 0.2 0.2 0.1 99.00 Genus Melaleuca spp. Grevillea spp. Prunus spp. Callistemon spp. Acer spp. Quercus spp. Hakea spp. Fraxinus spp. Cupressus spp. Malus spp. Totals Number of taxa/cultivars Eucalyptus spp. 141 Acacia spp. 49 30 30 26 21 20 18 17 13 13 13 391 Percentage of taxa 13 4 3 3 2 2 2 2 2 1 1 1 36 Number of individuals 121,320 29,895 103,456 6,651 86,227 78,100 6,963 23,436 14,698 36,502 4,978 3,453 515,679 honey myrtle (Melaleuca armillaris Gaertn. Sm.), snow-in- summer (M. linariifolia Sm.), and prickly-leaf paperbark (M. styphelioides Sm.), but these three taxa contribute 10% of the total plants. Lophostemon is represented by only two taxa (Queensland brush box and its variegated variant), but com- prised 7% of total plants and it was the most common street tree taxon in the surveyed population. Considering the importance of Australian native tree taxa within the street landscapes of Melbourne, it is interesting to note that very little genetic improvement or other selection research has been undertaken on this material. The majority of native taxa used in street tree planting are propagated from seed with clonal propagation only common in the genera Agonis, Callistemon, Acmena, and Syzygium. This situation is in contrast to that of exotic deciduous taxa where, according to recent nursery supply lists, the vast majority of new tree introductions into Australia for the purpose of street tree planting are virtually all cultivars, many with plant-breeding rights (PBR) protection and most from North America. This suggests potential for improvement and for the identification and propagation of clonal material of native species for this market, but the small size of the potential market and the fact that many Australian trees are difficult to propagate asexually are impediments to this. Potential contenders for improvement are Queensland brush box, spotted gum, red ironbark, yellow gum, smooth- barked apple (Angophora costata [Gaertn.] Britt.), Wal- langara white gum (Eucalyptus scoparia Maiden), and ka- Table 6. Number and percentage of tree taxon foliage types. Foliage Evergreen Deciduous Total 788 324 Percentage 71 29
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