Twelfth Australian Weeds Conference

SOME CHARACTERISTICS OF A NATIVE ENVIRONMENTAL WEED: UNDULATUM Trudi L. Mullett School of Ecology and Environment, Deakin University, 662 Blackburn Road, Clayton, Vic. 3168 (Current Address: PO Box 160, Murchison, Vic. 3610)

Abstract Invading populations of Pittosporum features that make invasive populations of P. undulatum undulatum Vent. (Sweet Pittosporum) impact on the so difficult to manage in invaded remnant vegetation. floristic and structural composition of invaded The abundant winter fruit crops produced by ornamen- communities. This plastic, adaptable species is able to tal plantings and established populations of P. colonise a range of environments and is arguably the undulatum attract a suite of generalist avian frugivores most successful native weed in south east . including Pied Currawongs (Strepera graculina), Eu- Abundant P. undulatum fruit crops attract a suite of ropean Blackbirds (Turdus merula), Satin Bowerbirds generalist, opportunistic frugivores and seed (Ptilonrhynchus violaceus) Silvereyes (Zosterops lat- germinability is high in natural and invaded habitats. eralis) and Red whiskered Bulbuls (Pycnonotus The continued invasion of P. undulatum in remnant jocosus) (Cooper 1959, Gleadow 1982, Emison et al. vegetation is further facilitated by fundamental changes 1987, Buchanan 1989, Barker and Vestjans 1990, in natural fire regimes. Mullett 1996). Impacts associated with P. undulatum invasion vary in The establishment of P. undulatum individuals is gen- different habitats and are most obvious in dry erally restricted to the base of mature trees as these sclerophyll forest. Changes in the composition of in- offer perching sites for frugivorous dispersers, which digenous species are evident with incremental increases defecate or regurgitate undigested seeds whilst perch- in P. undulatum cover-abundance. Considerable de- ing. The clumps of P. undulatum which develop act as clines in indigenous species richness have been re- a focus for further avian activity and thus for further corded at some invaded sites. The floristic and struc- seed dispersal (Mullett and Simmons 1995). The proc- tural simplification associated with P. undulatum in- ess of clump enlargement perpetuates and as these vasion reduces the diversity of habitat resources and clumps coalesce virtual monospecific stands of P. ultimately diminishes the biodiversity values of invaded undulatum develop (Richardson and Brink 1985, sites. Mullett 1996). INTRODUCTION P. undulatum invasion is particularly severe in dry Pittosporum undulatum Vent. (Sweet Pittosporum) is sclerophyll forest remnants where natural fire regimes a densely foliaged tree native to the wet forests of south have been altered. The suppression of natural fire re- east Australia that functions as an environmental weed gimes facilitates the invasion of some fire sensitive in habitats outside its natural range (Mullett 1996). In- invaders including P. undulatum, further compound- creasingly, some populations of P. undulatum occur- ing the displacement of fire adapted species. ring within the species natural range are also expand- Increasing cover-abundance of P. undulatum modifies ing their distribution and local densities in response to the floristic composition, structure and some functional altered ecological conditions (Rose and Fairweather elements of invaded communities and ultimately di- 1997). minishes the biodiversity values of invaded sites P. undulatum has been widely planted throughout Aus- (Mullett and Simmons 1995, Mullett 1996). P. tralia and some locations overseas for ornamental, undulatum is capable of invading a range of habitat hedge and windbreak purposes (Cooper 1956). Early types and is recognised as one of Victoria’s most seri- botanists (Maiden 1889) and gardening experts ous environmental weed species (Carr et al. 1992). (Oakman 1964) enthusiastically advocated planting of Invasion of P. undulatum into habitats outside its natu- P. undulatum for its ornamental qualities and its adapt- ral range has been listed as a ‘potentially threatening ability to a range of climatic and edaphic conditions. process’ under Schedule Three of the Victorian Flora Ironically, the same adaptive and hardy features that and Fauna Guarantee Act 1988 (Scientific Advisory so enthused early proponents of this species are now Committee 1994). regarded by conservation managers as the very

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This paper reports on some aspects of a larger study of in the germinability of P. undulatum seeds. This result P. undulatum ecology in south east Australia. also provides a relative measure of the dispersal po- tential of Pied Currawongs, which preferentially se- METHODS lect pre-dehiscent P. undulatum fruits for consump- Leaf morphology attributes were measured on fifty tion. Seeds extracted from Pied Currawong pellets and leaves sampled from 26 populations of P. undulatum Blackbird scats displayed high germinability (91.8% in south east Australia. Multivariate analyses were and 95.8% respectively), and were not significantly employed to assess the level of morphological varia- different from fresh P. undulatum seed (97.2% tion within and between populations and to investi- germinability). gate patterns of variation related to geographic and P. undulatum invasion patterns and impacts The climatic parameters. impacts of increasing cover-abundance of P, undulatum Germination trials were conducted on P. undulatum on species richness are most pronounced in the cen- seeds extracted from pre- and post-dehiscent fruits tres of radiating P. undulatum clumps. P. undulatum collected from natural and invasive populations invasion patterns and impacts were measured in sev- throughout Victoria. The germinability of P. undulatum eral natural and invaded sites however only data from seeds recovered from Blackbird scats and pellets re- one site, an invaded heathy woodland remnant on the gurgitated by Pied Currawongs were also assessed. Mornington Peninsula, Victoria, are presented. At this site, increasing cover-abundance of P. undulatum was Vegetation surveys were conducted in natural and in- significantly negatively correlated with species rich- vasive populations of P. undulatum in south east Aus- ness (r = -0.49, P <0.001) and the cover-abundance of tralia to investigate the ecological role of P. undulatum species (r = -0.68, P <0.001). Incremen- across a range of habitats. At each site, species rich- tal increases in P. undulatum cover-abundance have a ness and the cover-abundance of vascular were demonstrable impact on species richness (Figure 1). recorded in 3 × 3m quadrats along 33m north-south and east-west orientated transects located through five Where P. undulatum cover-abundance levels exceed P. undulatum ‘clumps’. 20%, the competition and shading effects imposed are critical enough to exert a negative influence on some RESULTS species. Species richness declines from a mean of 15 Geographic variation in leaf morphology P. undulatum species per quadrat where P. undulatum cover-abun- leaf morphology attributes varied significantly dance is less than 20% to an average of four species in (ANOVA, all P < 0.001) across 26 populations sam- quadrats where P. undulatum cover-abundance exceeds pled in south east Australia. Leaf dimensional charac- 90%. ters (lamina length, width and distance from leaf base DISCUSSION to widest point) were significantly negatively corre- lated (all P <0.05) with altitude. Mean lamina width P. undulatum is able to adapt its phenotypic expres- was also significantly negatively correlated with lati- sion to a range of environments and environmental tude (r = -0.51, P <0.01). No clear patterns of morpho- conditions. For a species thought to have evolved in logical variation along temperature and rainfall gradi- or near wet forests it adapts extremely well to invaded ents were evident although coarse aggregations of coastal and dry forest environments. The successful populations sampled in northern New South Wales and invasion of a diverse range of vegetation complexes in South Australia were revealed through cluster analy- on other continents and islands throughout the tem- sis. The pattern of variation within and between perate, sub-tropical and tropical zones (Cooper 1956; populations sampled in Victoria was particularly com- Goodland and Healey 1996) is further evidence of the plex. species adaptability and broad ecological amplitude. Phenotypic plasticity and adaptability may compen- Dispersal and germination P. undulatum seed col- sate for low levels of genetic diversity within and be- lected from natural and invaded populations displayed tween populations of P. undulatum (Orso 1994) and high germinability. No significant differences were will facilitate further range expansion of this species recorded in the germinability of P. undulatum seeds across a range of habitats and climate regions. extracted from pre- and post-dehiscent fruits in five of the six populations sampled. This suggests that site The P. undulatum dispersal syndrome has been al- differences may be more important than fruit maturity tered in several ways since European settlement. The

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25 between invasive fleshy-fruited spe- cies such as P. undulatum and adap- tive dispersal agents. Increased nestling predation is one 20 reported consequence of changes in the distribution, abundance and sea- sonal migration patterns of Pied 15 Currawongs in the Armidale (Bass 1996) and Canberra (Lenz 1990) re- gions.

10 Disruption to the dispersal syn- dromes of native fleshy-fruited plants and frugivorous vertebrates may be an additional consequence and is 5

Mean species richness (±SD) worthy of further investigation. The decline in species richness associated with increasing cover-abundance of 0 P. undulatum is attributed to reduced +123456789light infiltration and subsequent changes in microclimatic conditions, P. undulatum cover-abundance the influence of allopathic properties and other competition factors Figure 1. A decline in mean species richness with increasing cover- (Gleadow and Ashton 1981, Mullett abundance of P. undulatum was recorded in 105, 3 × 3 m quadrats sampled and Simmons 1995). at Woods Reserve, an invaded heathy woodland remnant on the Mornington Invading populations of P. Peninsula, Victoria. P. undulatum cover-abundance categories are: + = undulatum reduce the floristic and <10%, 1 = 10-19%, 2 = 20-29%, 3 = 30-39%, 4 = 40-49%, 5 = 50-59%, 6 structural diversity of invaded sites = 60-69%, 7 = 70-79%, 8 = 80-89%, 9 = >90% and may facilitate a successional shift towards mesic species that further introduction and subsequent invasion of P. undulatum disrupts functional processes such as natural fire re- into habitats outside its natural ecological range brings gimes (Mullett and Simmons 1995). The impacts of the species into contact with a ‘novel’ assemblage of the floristic and structural simplification associated frugivores and potential dispersal agents. The addition with P. undulatum invasion on faunal assemblages are of introduced frugivores (i.e. Blackbirds and Red unknown, but presumably substantial. whiskered Bulbuls), throughout the natural and inva- The adaptive attributes of P. undulatum contribute to sive range of P. undulatum in south east Australia also its value as a pioneer species in wet forest communi- constitutes a fundamental change in the dispersal po- ties and to this end, P. undulatum is often advocated tential of P. undulatum. The increased distribution and and used in revegetation programs in New South Wales abundance of some native dispersal agents, (i.e. Pied and south east Victoria. The ecological conditions and Currawongs) further modifies the P. undulatum dis- constraints with which the species evolved in these persal regime. Regional declines in the distribution and habitats, even within the species apparent natural range, abundance of some P. undulatum seed predators, such have been so fundamentally altered that the use of P. as King Parrots (Alisterus scapularis) in the Strzelecki undulatum in revegetation programs may be question- Ranges, Victoria (Emison et al. 1987), may also rep- able in some cases. This is especially true in the con- resent a change in the dispersal potential of P. text of its proven invasiveness in other habitats. undulatum that can be considered novel in an ecologi- cal and evolutionary sense. In addition to increased dispersal potential, secondary impacts on the invaded community may result from mutualistic relationships

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ACKNOWLEDGMENTS Goodland, T. and Healey, J.R. (1996). ‘The invasion of Jamaican montane rainforests by the Australian tree This research was supported by an Australian Post- Pittosporum undulatum. (School of Agricultural and graduate Research Award and funding provided by the Forest Sciences, University of Wales, Bangor, CRC for Weed Management Systems and Deakin Uni- United Kingdom). versity. I would like to thank Dianne Simmons, Paul Ryan and Roger Ashburner for helpful comments on Lenz, M. (1990). The Pied Currawong in urban Can- the manuscript. berra: Friend or foe? Canberra Bird Notes 15, 2-9. REFERENCES Maiden, J. H. (1889). ‘The Useful Native Plants of Australia (including Tasmania).’ (1975 facsimile re- Barker, R.D. and Vestjans, W.J.M. (1990). ‘The Food production). (Compendium, Victoria). of Australian Birds Volume II. Passerines.’ (CSIRO, Melbourne). Mullett, T. and Simmons, D. (1995). The ecological impacts of Sweet Pittosporum (Pittosporum Bass, D.A. (1996). Pied Currawongs and invading undulatum Vent.) in dry sclerophyll forest commu- ornamentals: what’s happening in northern New nities, Victoria. Plant Protection Quarterly 10, South Wales. In ‘Proceedings of the 11th Austral- 131-8. ian Weeds Conference, Melbourne,’ ed. R.C.H. Shepherd, pp. 362-65. (Weed Science Society of Mullett, T.L. (1996). Ecological aspects of the environ- Victoria Inc., Victoria). mental weed Sweet Pittosporum (Pittosporum undulatum Vent.): Implications for control and man- Buchanan, R.A. (1989). Pied Currawongs (Strepera agement. In ‘Proceedings of the 11th Australian graculina): their diet, and role in weed dispersal in Weeds Conference, Melbourne,’ ed. R. C. H. Shep- suburban Sydney, New South Wales. Proceedings herd, pp. 489-92. (Weed Science Society of Victo- of the Linnaean Society of New South Wales 11 I, ria Inc., Victoria). 241-55. Oakman, H. (1964). The as street trees. Carr, G.W., Yugovic, J.V. and Robinson, K.E. (1992). Australian Plants 3, 30-1. ‘Environmental Weed Invasions in Victoria: Con- servation and Management Implications.’ (Depart- Orso, F.I. (1994). ‘Genetic variation and breeding sys- ment of Conservation and Natural Resources and tem analysis of Pittosporum undulatum Vent. Ecological Horticulture, Victoria). ().’ B.Sc. Honours Thesis. (School of Genetics and Human Variation, La Trobe Uni- Cooper, R.C. (1956). The Australian and New Zealand versity, Victoria). species of Pittosporum. Annals of the Missouri Bo- tanical Garden 43, 87- 188. Richardson, D.M. and Brink, M.P. (1985). Notes on Pittosporum undulatum in the south western Cape. Cooper, R.P. (1959). Birds feeding on Pittosporum Veld and Flora 71, 75-7. seeds. Emu 59, 60-1. Rose, S. and Fairweather, P.G. (1997). Changes in Emison, W.B., Beardsell, C.M., Norman, F.I., Loyn, R. floristic composition of urban bushland invade by H. and Bennett, S. C. (1987). ‘Atlas of Victorian Pittosporum undulatum in northern Sydney Aus- Birds.’ (Department of Conservation, Forests and tralia. Australian Journal of Botany 45, 123-49. Lands and the Royal Australasian Ornithologists Union, Victoria). Scientific Advisory Committee, (1994). ‘The spread of Pittosporum undulatum in areas outside its natural Gleadow, R. M. and Ashton, D. H. (1981). Invasion by range (Potentially Threatening Process) Final rec- Pittosporum undulatum of the forests of central ommendation on a nomination for listing.’ (Flora Victoria. I. Invasion patterns and plant morphol- and Fauna Branch, Department of Conservation and ogy. Australian Journal of Botany 29, 705-20. Natural Resources, Victoria). Gleadow, R.M. (1982). Invasion by Pittosporum undulatum of the forests of central Victoria. II. Dis- persal, germination and establishment. Australian Journal of Botany 30, 185-98.

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