Pittosporum invasion front emerges from a eucalyptus forest . . . .

. . . . and leaves us with a pittiful landscape!

THE INVASION

of the

DANDENONG RANGES

by

SWEET PITTOSPORUM

(Pittosporum undulatum)

AND THE WIDER IMPLICATIONS

Low light - no understory - no shrubs - no ferns - no grasses - no orchids - and no eucalyptus seedlings!!

In short: “In 300 years, there will be no eucalyptus, or any other trees, in the Dandenongs, except perhaps, some regnans in deep valleys of the

Sherbrooke Forest plus a few old giants - pittosporum will have prevailed -

- UNLESS WE DO SOMETHING - NOW!”.

Prepared by Jeff Walker, Convenor, StopPitt (V4.15) Dedicated to the control of Pittosporum invasions

Contact: stoppitt@internode.on.net

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PART 1: The Science - Biology and Distribution

1. Introduction Seventy years ago, there was just ONE pittosporum tree in the entire village of Menzies Creek, situated in the Dandenong Ranges, 50 km east of Melbourne. Now, on a block of remnant eucalyptus forest, which had been cleared every year until 2009, 6,000 seedlings per hectare became established in the following two seasons. On the adjacent blocks of similar remnant forest, which had not been cleared - or subject to bushfires - for 30 years, 4-6,000 pittosporum saplings and young trees are now established. There are up to 120,000 seedlings/ha in the nearby bed of Menzies Creek and tree-ferns have been choked. There are no eucalyptus seedlings under the combined eucalyptus/pittosporum canopy. This means that when the existing eucalyptus trees mature and die, our present diverse eucalyptus ecosystem will be replaced with the mono-cultural pittosporum ecosystem.

Does this concern you - should we prevent it happening?

2. Evolution and Spread of Sweet Pittosporum It is believed that pittosporum undulatum evolved in the cool mountain forests of south east Queensland and then gradually migrated southwards along the east coast, across the cool valleys which radiated out from the Great Dividing Range, eventually reaching East Gippsland in Victoria. It then spread westwards more recently, following European habitation, generally south of the Dividing Range, to Melbourne suburbia, the Surf Coast, the Otways and Glenelg; it has now crossed South Australia and has reached the South West of Western Australia - see Figure 9 (Victoria) and 10 (Australia) on page 7.

The migrations from East Gippsland to Western Australia were probably facilitated by its commercialisation as an attractive garden plant - by virtue of its pleasant scent and attractive bunches of large orange berries. The seeds of these berries were then distributed by animal and avian vectors - particularly the introduced blackbird,

Notes: 1. The common name of Pittosporum undulatum, Sweet pittosporum, is used throughout this document.

2. Its fruiting body is a ‘capsule’ but the more common term of ‘berry’ is used in this document. 3. This document is based on Gleadow and Walker: The Invasion of Pittosporum undulatum in the Dandenong

Ranges, Victoria. Realising predictions about rates and impact. Plant Protection Quarterly 29(3), 2014. 4. Contact address: stoppitt@internode.on.net (website under development).

Figure 1: Sweet pittosporum seedlings (6,000/ha) in a remnant eucalyptus forest at the Menzies Creek study site, which developed during two seasons on land which had been previously cleared every year - in front of a wall of saplings and young trees which had developed in forest which had not been cleared, or subjected to bushfires, for 30 years (4-6,000/ha). This site is located 200 m from the site of the original tree planted in Menzies Creek about 1925.

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Turdus merula. It has now “Escaped the Garden Fence” and has become a problem in peri-urban areas surrounding Melbourne and Sydney as well as other regional towns and villages. It is now invading nearby remnant forests and State and National Forests. Internationally, it has invaded the Green Mountain Range in Jamaica and occupies 60% of the Azores. It is a nuisance in the Canary Islands, South Africa, New Zealand, Hawaii and California. It became a noxious weed on Lord Howe Island but under New South Wales legislation it has now been eliminated - see Figure 11, International Distribution, on page 7.

3. The Menzies Creek Story That single tree in Menzies Creek was planted in about 1925, when its eucalyptus forests were being cleared and developed for farming. One property owner planted a female tree, probably purchased from the only nearby nursery at the time, in Selby. The Menzies Creek area is subject to periodic bushfires and since sweet pittosporum is sensitive to fire it seems likely that it did not begin to spread until after effective fire control and management programmes were adopted in the 1960’s. The oldest pittosporum tree in Menzies Creek is about 55 years old, indicating that it was established in about 1960. The next cohort of trees is only about 30 years old, which suggests that the recent invasion commenced after the last bushfire in 1982. It has now spread about 7 km south of Menzies Creek, through remnant eucalyptus forest and peppermint gum scrubland, to just beyond Cardinia Dam. It did not spread northwards across open farmland, which probably offered a less attractive habitat for blackbirds or foxes.

That Menzies Creek experience, referred to above, led to a ‘Citizen Science’ programme with Grade 6 classes at the nearby Menzies Creek Primary School and these studies generated valuable data about the growth and development characteristics of pittosporum. This information provided the ability to determine the approximate age of trees, simply by measuring their circumference. Then, by knowing the age distribution of trees across a population, the direction of an invasion could be determined, assuming that the youngest trees in the population are at its front.

4. The Invasion Rate From those age data it was possible to establish a timeline for the invasion. Its front has progressed some 7km from Menzies Creek in 90 years (1925 to 2015), so the nominal invasion rate is about 80m/yr. If that invasion has been interrupted by periodic bushfires, then it would have progressed at a somewhat higher rate between bushfire events. Since the last bushfire was in 1982, that front would have moved 7 km in about 30 years, which indicates a rate of about 230 m/yr. However, In this document, the rate of 80 m/yr is adopted; this will be checked for other environments and locations in due course. There is only one other study in the World which has provided a comparative rate; 30 m/yr in the Blue Range of Jamaica. However, that was determined over a very short 5 year period in a somewhat different environment to that of the Dandenong Ranges.

5. Shire of Yarra Ranges Weed Distribution Data The Shire of Yarra Ranges undertook a comprehensive audit of the distribution of significant weeds in the public reserves and roadsides for which it is responsible, with the support of Grants to the Urban Fringe Weed Management Initiative (UFWMI). Sweet pittosporum is the second most frequent weed, after blackberry, being present on 50% of all reserves (Figure 3). This audit showed that our Dandenong Ranges are virtually surrounded by invading pittos-porum fronts; the eastern and western fronts being only 4 km apart. No data are available for those areas

Figure 2: Sweet Pittosporum invasion from Menzies Creek passes Cardinia Dam

Figure 3: Weed species present on Bushland Reserves

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under the control of Knox City and Cardinia Shire, while more information through UFWMI along the eastern sector from Mount Evelyn to Silvan and across Monbulk to The Patch would complete the audit and provide a better understanding of the issue. This situation is shown by Figure 4 opposite. It emphasises the hot-spots around the urban fringe, which, like the Menzies Creek example, appear to be associated with the location of early nurseries. While these data only refer to public land, it is known that such populations are continuous across neighbouring private properties. It is also known that the catchment surrounding Silvan dam for which Melbourne Water is the responsible authority, also carries a heavy population.

6. Closure of Pittosporum Invasion Fronts If the invasion rate is 80 metres (or more) per year and those invasion fronts are about 4 km apart, they will meet and close in 25 years - or less. Once closure occurs the canopies will then coalesce and the subsequent reduction in sunlight would reduce plant diversity to virtually zero (as depicted on the front cover). Eucalyptus seedlings would be inhibited and maturing eucalypts would not be replaced. Small populations may persist deep in Sherbrooke Forest and a few ‘giants’ may remain, but in say, 300 years, we would eventually end up with a monoculture of sweet pittosporum - unless effective control programmes are put in place, as soon as possible, to prevent this happening.

7. Not a Darwinian Situation Some critics have questioned any need to control sweet pittosporum since it is ‘native’ and they consider that the situation is simply evolutionary. However, it can be confidently stated that Darwinian theory did not contemplate a role for commercial nurseries in the evolution (and distribution) of a species!

8. The Gender of Sweet Pittosporum Sweet Pittosporum is a dioecious species and the Citizen Science research at Menzies Creek found that when its flowers are first formed in late winter, they exhibit a M:F sex ratio of about 60:40. However, by the time fruit is formed the ratio changes to about 70:30 and six months later, when the fruit is maturing, that ratio declines even further toward 75:25; it is not known what drives that attrition. This finding was confirmed by Shire of Yarra Ranges internal research.

9. Fecundity and the Concept of Matriarchs That same research reports that the fruit load of ‘female’ pittosporum trees can be categorised as Heavy, Medium or Light, and that the number of berries declines by the time they reach maturity in late autumn, some in the light category even rotting. This attrition may explain the change in the gender ratio mentioned above - but more research is required to resolve the issue. Figure 4 below depicts a typical fruit load in the heavy category. This image was obtained from one of two trees in Menzies Creek which are described as Matriarchs (Figure 5); it has been aged at 56 years and is a daughter of the original tree planted in 1925 about 300m to its north. These two Matriarchs are the only specimens growing in Menzies Creek - in a cohort of thousands of trees. While the concept of Matriarchs is

Pittosporum

undulatum

Figure 4: A heavy load of berries carried by a typical matriarch tree.

This MATRIARCH is 56 years old, 8m high and 17m wide. There are only 2 such trees in the MZK population of thousands - why?

Concept of Matriarchs

Figure 5: This tree, since poisoned, was a 56 year old ‘Matriarch’, 8 metres high and 17 metres in diameter; it was one of only two such trees in the Menzies Creek population of thousands. After it died, a dense population of English violets, forget-me-not and common farm weeds (below) recovered the previously barren area under its canopy, indicating that shading was responsible for the loss of diversity under its canopy rather than alleleopathy.

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More data required.

UWFMI?

More data? (Knox City)

More data required.

UWFMI?

Figure 6: Distribution of Sweet Pittosporum throughout the Dandenong Ranges, 2010 -2014

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attractive, these two trees may simply be the survivors from earlier generations, the other members of their cohorts being burned in bushfires or removed by the neighbouring farmers. 10. Lack of Diversity under Pittosporum trees - Shading or Alleleopathy It has been postulated that Sweet Pittosporum is alleleopathic, i.e., its leaves secrete a chemical which is leached into the soil and inhibits the germination of competitive species; many experiments have been conducted to identify the class of chemical or chemicals involved, without success. Recent research appears to have resolved this issue; it is the shading effect of its dense canopy which causes the loss of diversity. Three months after the 56 year old matriarch depicted in Figure 6 was poisoned, a dense population of weeds developed, typical of those which grow on cultivated farmland which it borders. Similar evidence was found at the nearby Menzies Creek School Study Site, where trees were removed and the previously barren area under the trees has now been repopulated by native plants and grasses common to its damp forest environment. Just as sunlight is restricted under dense pittosporum canopies, It also seems likely that rainfall is also restricted, being channelled down the limbs and trunks of the trees, rather than being distributed uniformly under those canopies.

11. Habitat for the Powerful Owl The key habitat for adult Powerful Owls (Figure 7) is large hollow branches of dead eucalyptus trees but it is reported that sweet pittosporum is favoured by fledglings. Hence the control of pittosporum is not favoured by those who believe that this would remove habitat. This is not considered to be a valid impediment to controlling pittosporum, since less than half of any population would need to be removed. The remaining male trees would provide adequate habitat for another 30 to 50 years until they mature and die. During that long period, the Powerful Owl would have adequate time to adapt to the gradual reduction in pittosporum habitat and return to the blackwood (Acacia melanoxylon ) trees it inhabited before the pittosporum invasion. Blackwoods are a endemic species in forests invaded by pittosporum and it is an early coloniser of areas cleared of pittosporum; it grows up to 20m tall (Figure 8), providing a much greater volume of habitat per tree than does pittosporum. Where its numbers have been depressed after a long occupation by pittosporum, seedlings could be planted so that they would be well advanced by the time the Powerful Owl fledglings would need them. Blackwood is a strong native species and its seedlings have a high survival rate, however in particularly dry seasons, monitoring would be required and supplementary watering may be indicated.

12. Beyond the Dandenong Ranges The above analysis is derived from the recent ‘Community Science’ programme at the Menzies Creek Primary School. While its data were collected in the Dandenong Ranges, its findings are likely to apply across the wide range of pittosporum populations which occur throughout Southern Victoria; only the rates of invasion in different locations may change. Figures 9, 10 and 11 opposite, present the current distribution for Victoria, Australia and the World, respectively.

13. Further Research To refine control measures and to use funds as effectively as possible, we need a better knowledge of its biology and genetics. Associate Professor Roslyn Gleadow (Monash University), who led the early research into the nature of pittosporum during the 1980’s, and predicted the invasion outcome described in this document, has

Figure 7: A Powerful Owl - with possum in hand.

Figure 8: 20 metre high Blackwood tree in Clematis, Victoria.

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Widely planted: Naturalized in many regions

★

★

★

★

★

★

★

★

★

★

Bermuda

JamaicaHawai’i

California

South Africa

Azores

Canary Is

Norfolk Is★

New Caledonia

LordHowe Is★

★★

★★

★

Figure 11: World Distribution of Pittosporum undulatum

indicated that Monash University would raise a Ph.D. programme immediately, if funding of $25,000 annually for three years, for a Research Fellowship was available.

Genetics. A clear understanding of the genetics of this

invasive species is urgent. The variant which

evolved and spread south to East Gippsland

before European settlement does not appear

to be as invasive as the variant which has

invaded the Dandenongs, the Sydney urban

fringe, Lord Howe Island, Jamaica, Azores,

Hawaii, California and South Africa.

In Menzies Creek, there are at least four

phenotypes of this invasive strain of pittos-

porum. It is not known whether one or more

of them are aggressive mutants of the East

Gippsland genotype, or whether periodic

bushfires have controlled the spread of the

original variant from East Gippsland or even

whether environmental variation is involved.

Ideally, that programme should take on an

International breadth and include samples

from all known International invasion sites.

Australia probably has an obligation to those

Nations which have been invaded by our

native invasive weed, and owe them some

measure of assistance (even if it is just

intellectual knowledge) to help control it. We

can escape any measure of blame for their

plight, as we really did not know how

invasive it might become in our own

environment, let alone in the various

environments Internationally. Professor

Roslyn Gleadow did issue such predictions in

the 1980’s but their impact did not rise

above other priorities of that time.

Compared with the cost of control (§16) throughout Australia and the rest of the

World, an allocation of $75,000 for this

Research Fellowship would be minor.

Atlas of living Australia:Current distribution of P. undulatum

http://bie.ala.org.au/species/Pittosporum+undulatum

Figure 10: Current distribution of Pittosporum undulatum in Australia

Atlas of living Australia http://bie.ala.org.au/species/Pittosporum+undulatum

Figure 9: Present Distribution of Sweet Pittosporum, Pittosporum undulatum, in Victoria

The infestations shown on this map are derived from the Flora Information System (FIS 2004) and the Integrated Post Management System (IPMS 2004). They are not meant to display a complete statewide inventory for this species. There are areas, however, where this species may be present

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PART 2: Control

14. Control Measures The material presented above indicates an obvious strategy to control this invasive weed species. Since it has now been determined that there are no alleleopathic chemicals in pittosporum undulatum, it is safe to use its dead material as mulch.

Remove all female trees (those carrying berries), i.e., about 25 to 30% of a population. Remove some of the remaining male trees where their density is assessed as excessive and where it provides habitat for the Powerful Owl. The more efficient use of equipment, labour and finance would guide the decision on their residual density. That residual density of male trees should allow for the trees to grow to their mature size at 40 to 50 years of age, when it may be about 15 - 20 m diameter. The areas beneath the canopies of each tree would lack diversity and be covered by leaf litter (about 200 kg/ha/yr). If a similar space is allowed between trees, the residual tree density would be in the range of 25 to 40 trees per hectare. Powerful Owl Habitat. Since the residual male trees would die at 40-60 years of age, regrowth of blackwoods should be monitored and if assessed to be inadequate, seedlings should be planted - in which case their survival must be monitored (watering during early dry seasons may be necessary).

15. Control Methods Identify Female Trees Female trees are readily identified between early spring and mid-winter by the presence or absence of berries. Where the berry load is medium or light, it is necessary to appraise the tree on their northern side, which receives stronger sunlight than the southern side, where berries are often absent. These trees could be identified by volunteers during this extended period so that they may be treated removed at other times of the year when berries are absent. Drill and Fill - leave dead trees standing; - if aesthetics offend the community, fell dead trees after a period and leave in situ or burn. Cut and Paste - chip trees on site (wheeled or tracked chipping machines) and spread chips over cleared areas; - remove trees and chip off-site; stockpile chips in mulch heaps for the use of local communities. - remove trees from site, store until ‘dry’ and burn when and where permissible. CONTRACTORS while different contractors have their own preferred methods for control there are probably opportunities for more innovation so that scarce funds might be used more effectively. The combination of contractors and volunteer groups would optimise the use of scarce funds. FIRE. While the flammability of Pittosporum is not well documented, it is sensitive to high temperature fires, so hot fire is an effective control measure; such hot bushfires were largely responsible for controlling it across Victoria before bushfire management improved after the 1980’s. However, it is impractical in many peri-urban locations which it has now invaded, as small controlled fires do not burn at sufficiently high temperatures to totally destroy pittosporum and follow up weeding or treatment would be necessary. Fire would not be appropriate in Powerful Owl habitat. Biological. At present there is no known disease of this native species, so this avenue for control remains open; the often observed ‘terminal tip leaf curl’ in early spring appears to be temporary.

16. An Estimated Cost of Control The control of Pittosporum is a long term project and carries a significant cost. Contractors estimate that the cost of removing it is about $5,000, $7,500 or $12,000 per hectare, for light, medium and heavy populations, respectively. These cost estimates equate, approximately, to the 0-5, 5-25 or 25-75 percent coverage shown by Figure 9 for the reserves and roadsides so far surveyed by the Shire of Yarra Ranges in the Dandenong Ranges. Hence, the aggregate cost of removing all pittosporum trees from just those populations shown by Figure 8, is estimated to be about two million dollars. If only the female trees, and some of the male trees in heavily affected areas are removed, this cost would be less. However, this figure only depicts populations on public land, so the cost of control on adjacent private land may be similar.

Any control strategy is likely to be spread across several years, so during this period, with an invasion rate of about 80 metres/year, the areas of populations will expand and their densities will increase. Hence, it would

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be expedient to invest as heavily as possible in the short term, thereby containing those expansions and the thickening of stands, and minimising the overall cost of control in the long term.

These estimated costs only refer to the Dandenong Ranges situation. If all the other invasions throughout Victoria and elsewhere, as shown by Figures 9 and 10 are considered, the aggregate cost of control will be very much higher. 17. Sociology and Education The issue of pittosporum removal is contentious in some communities, particularly in those which provide habitat for the Powerful Owl, as well as, quite simply, with those in suburbia who ‘like’ the species and have never given a thought to its invasive characteristics beyond their garden fences and the role of blackbirds in that invasion.

When the owners of properties which have been invaded by pittosporum, or who reside near public lands which have been invaded, are interviewed, and the above characteristics explained on a one to one basis, they generally understand the situation quite quickly and agree that control measures should be introduced. Residents near heavily invaded locations ‘hate’ the species and want it removed. Many respond with a wish to join a community group to control it ‘immediately’.

If private land is involved, the owners balk at the cost of its removal. Such landholders are ‘blameless’ for this pittosporum invasion as it developed insidiously and incrementally; its characteristics were not generally understood and it was never declared to be noxious, so landholders were never obliged to remove it. It is classified simply as an ‘invasive weed’. These landholders respond to scientific information and appear to be a rich source of volunteers for community based control programmes; their combination with ‘reasonable’ contractors, supported by adequate Government grants, appears to be the most cost effective system to address this issue.

In some jurisdictions it cannot be sold in nurseries, yet in East Gippsland, where its invasiveness is less pronounced than in the peri-urban areas surrounding suburbia, it is still being used as a species for environmental erosion control; plants are still sourced from local nurseries and no emphasis is placed on the planting of only male plants, so a future control problem, and additional cost, is being created in those situations.

Sufficient knowledge to control pittosporum has only developed during the last three years so it is now time to apply it. While more research is still necessary to refine that knowledge, we have a sufficient understanding of the issues involved to develop effective control programmes now.

In due course, it will be necessary to legislate the reclassification of the weed status of sweet pittosporum.

In the meantime, a continuing source of Government funding, a professional education programme through community meetings with general and social media releases, combined with ‘work on the ground’, would achieve excellent and early results. An informative documentary film would also assist. 18. Census and Mapping It is necessary that the distribution of sweet pittosporum is better understood and the simplest initial approach would be to know where the oldest trees are located. A competition among school children, with a prize of say $1-2,000 to the winning school, would be the most cost effective means of collecting that information. Such a competition could be tested in the Shire of Yarra Ranges in 2015 and throughout affected municipalities in Victoria, during 2016. That strategy would reveal the broad structure of the distribution for a very low cost and indicate where supplementary information is needed.

Limited mapping of individual populations would be necessary to estimate the cost of their control and assist with reporting the effectiveness of various control measures.

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19. StopPitt* StopPitt is an emerging community based organisation, focused on the control of sweet pittosporum. Its need and concept developed from the recent Citizen Science programme at Menzies Creek Primary School, which revealed the enormity of this pittosporum invasion and confirmed the prediction of the earlier research by Associate Professor Roslyn Gleadow, then at the University of Melbourne, now at Monash.

StopPitt is a member of the Community Weeds Association of the Dandenongs (CWAD) and of the Southern Ranges Environment Association (SREA). In the short term it will concentrate its efforts on the Dandenong Ranges area. Since there are several serious invasion sites around the Dandenong Ranges (Figure 6, page 5) and numerous members of the community are interested in involvement, Chapters may be necessary in several locations.

The outcome of this programme in the Dandenong Ranges will then generate a model for adoption in neighbouring areas, and ultimately throughout Victoria, reappraising the model as required. The methodology and knowledge developed in this programme is likely to be useful to control invasions in other States. At some point in this work, Australia should ask the appropriate UN body to issue an alert for Pittosporum undulatum.

It is currently planned to organise a Local Forum with the Shire of Yarra Ranges late in 2015 or in 2016, while Monash University is interested in an International Symposium in due course.

20. Acknowledgements The Principal and Staff of the Menzies Creek Primary School.

Associate Professor Roslyn Gleadow, Monash University. Dr Craig Nitschke, Forest and Ecosystem Science, University of Melbourne. Paul Smitka, Weeds Officer for the Shire of Yarra Ranges, and his fellow officers collectively, for their trail blazing initiatives in the collection and mapping of vast amounts of environment and weeds data. UFWMI (Urban Fringe Weed Management Initiative) for partial funding of the above programme. Ms Hilary Miller, for the use of her pittosporum invaded land for several years. N and D Jonker for the provision of pittosporum trees and saplings for data collection. My wife; without her forbearance, the knowledge reflected in this document would not exist. Serendipity for placing me twice in the same location in Menzies Creek, 70 years apart; that my sister and niece had never needed to sell their block of land and had kept it cleared until 2009, after which 6,000 seedlings per hectare became established in two seasons; that appropriate scientific training allowed me to recognise that a significant issue existed; and that Professor Roslyn Gleadow had researched the issue 30 years earlier.

*This name was coined by the 2012 cohort of Grade 6 students at Menzies Creek Primary School in the first year of the

Citizen Science project. One smart lad suggested ‘PittOff’ - with a lithp - of course! ____________________________________________________________________

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Notes:

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Sweet Pittosporum (Pittosporum undulatum) is taking over the Warburton Trail Reserve in Mt Evelyn

- and - has turned the roadsides of Mornington Peninsular into chasms

of ‘pitto’, denying views across the beautiful countryside.