Palm Trees Investigation Canary Island

ABN 42 054 177 614

Preliminary investigation into the cause of crown damage in Canary Island Palm (Phoenix canariensis)

at Catani Gardens, St. Kilda

prepared by

Bryan Walters Ecoplan Australia Pty Ltd

wildlife and environmental expertise

prepared for

Ann Cremean City of Port Phillip

May 2006

Damage to Canary Island Palms, Catani Gardens EcoplanAustralia Pty Ltd

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City of Port Phillip

Ann Cremean Open Space Planner City of Port Phillip Phone 9209 6657 Email: [email protected]

Ecoplan Australia Pty Ltd ABN 42 054 177 614

Melbourne Office: Bryan Walters PO Box 580, Hurstbridge Vic., 3099 Phone/fax 03 9714 8622 Email: [email protected]

Portland Office: John Hill PO Box 239, Portland Vic 3305 Phone 03 55 235 111 Email: [email protected]

The ideas, techniques and strategies outlined in this report remain the intellectual property of Ecoplan Australia Pty Ltd and are provided for use solely by the client. Any use outside this designated purpose, including the publishing of material, must only be carried out with the written consent of Ecoplan Australia Pty Ltd.


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Background Routine inspections of the Canary Island Palm (Phoenix canariensis) by maintenance staff and arborists at the Catani Gardens, St Kilda revealed animal damage to the emergent shoots of the crowns of the trees. Both the Black Rat (Rattus rattus) and the Common Brushtail Possum (Trichosurus vulpecula) are known to inhabit the tree crowns and the damage was attributed to one or both of these species. An additional environmental issue, the identification of Palm Wilt fungus (Fusarium oxysporum f. sp. canariensis) within the City of Port Phillip’s precincts and suggested in guideline literature (Smith et al. 2004), raised concerns that the mammals may be implicated in the spread of this fatal disease of Palms. Such was the concern that Council responded immediately by isolating each Palm with a sheet-metal collar around each trunk following the practice of tree-guarding in pubic gardens throughout Melbourne. The collar is designed to stop animals returning to the crown of the tree following their descent to the ground. This action invoked an immediate response from residents, constituents and agents associated with the animal liberation movement, resulting in the immediate removal of forty-two of the bands. An anecdotal account by a local resident suggested that all guards were removed by ‘civic’ action within twenty-four hours of their establishment. Two tree-guards, these on young Palms, remain. Adverse press and constituent reaction followed. Aim The aim of this study is to identify the cause or causes of damage to Canary Island Palms at Catani Gardens, St Kilda.

The brief:

Record the numbers and species of animals at Catani Gardens, St Kilda Foreshore. Collect data on the type of vegetation possums and or rats are using (including the 102 Palms on site) Collect data on damage to Palms or other vegetation incurred by possums Collect data on human interactions with animals at Catani Gardens as observed on site visits only. Provide advice regarding appropriate responses Council may take to manage the wildlife issues at the Catani Gardens if this proves to be the case.

In the long-term, the City of Port Phillip aims to develop an integrated management strategy for the ongoing care of the Catani Gardens.


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Study site The Gardens were designed by Carlo Catani and constructed between 1911 and 1920. Catani Gardens were gazetted in 1999 for inclusion in the Victorian Heritage Register, (H1805 Heritage Victoria). The registration includes paths, plants, avenues of trees. Permits are required from Heritage Victoria for new buildings, and the pruning and loping of trees. The Heritage listing requires the ongoing care and maintenance of the Palm trees by City of Port Phillip. The gardens are manicured grass with colonnades of Canary Palms (Phoenix canariensis) planted along each side of formal paths. The northern margin of the Gardens along Beaconsfield Parade to Fitzroy Street is planted with a single row of Skyduster Palms (Washingtonia robusta?). Inclusive plantings, now mature trees, of representatives of northern hemisphere trees such as Sequoia, and Cupressus, add slightly to the diversity. A few representatives of southern hemisphere trees such as Angophora and Laugnaria patersonii (Norfolk Island Hibiscus) complete the mix. Approximately nineteen trees compliment the 102 Palms. Beaconsfield Parade, and Jacka Boulevard form vehicular boundaries, both being heavily trafficked. Vehicular access along the southern (foreshore) side provides access to the Yacht Squadron buildings car park. This access allows circumnavigation of the Gardens by vehicles, although traffic along the southern access is light and slow. A low bluestone wall defines the southern or sea-side of the gardens. Along the sea-wall, the introduced Mirror-bush (Coprosma repens) and Golden Californian Privet (Ligustrum ovalifolium) combine to form a more-or-less continuous shrubby canopy between one and 2.1 metres tall. Methods A cursory inspection on Monday April 23 was made to identify potential influences at the site such as animals coming to the gardens from external sites, evidence of hand-feeding, potential disruptive events and the like. A count strategy based on the potential visibility of all possums was prepared. Three observers were allocated approximately one third of the Gardens area. The western end, named on the map as the Northern Lawn, was divided into two parts, the more easterly designated as the ‘central section’ for the census. The Central Lawn, Yacht Squadron Lawn and Pier Lawn were designated as the ‘eastern section’ in the census. The divisions were made so that each observer had approximately the same area to assess. Each observer was asked to walk past each tree of their area and sweep the canopy and ground with a spotlight, counting possums cumulatively each half hour. Observers were also asked to record the presence of any other animal (Flying fox, rat, bat, domestic dog etc). Observers were to record any human-possum interactions. It was expected that four counts might be made between the hours of 7 30 pm and 9:30 pm, thus repeating the assessment.


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Map 1. The study site: Catani Gardens, St Kilda

Map supplied by City of Port Phillip


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A fundamental assumption was made from work by Pietch (1995), that possums would be more-or-less sedentary, remaining within a home territory of up to 120 metres diameter. A second assumption was that all possums would descend to the ground during the course of the evening. Results Table 1. Counts of mammals at Catani Gardens April 27, 2006 Palms Other

trees Possums 7:30 pm

Possums 9 pm

Rats 7:30 pm

Rats 9 pm

Observer West 33 1 16 18 1 4 Observer Central 49

(9*) 8 44 48 4 3

Observer East 21 (10*)

12 14 17 3 0

Total 74 78 8 7 *Washingtonia The population count for Common Brushtail Possum was 78.5 +/- 4.5. The number of Black Rat observed was 7.5 +/- 0.5 Premeditated interactions occurred between the possums and three human couples, possums, rats and one middle-aged human male. This took the form of feeding (bread), petting and observation. No other mammalian species were observed. Discussion Cursory inspection The cursory inspection on April 23 serendipitously identified potential territory partitioning. By 10 pm Common Brushtail Possum (Trichosurus vulpecula) were observed generally sitting or grazing on the grass of the Gardens. Many of the animals were equidistant and close to the curbing of Beaconsfield Parade. They were also observed on the open grass and near the sea-wall. They formed an evenly spaced ‘network’. No agonistic behaviour was observed. Using the presence of an active sternal gland as an identifying feature, it was noted that many animals that were examined (16 of 28 observed) were male. This observation led to an assumption that the animals were reinforcing territory boundaries at this time and, if tested, animals may indicate their core tree. The test was to approach a particular possum to within one metre and utter a territorial call. The possum would then retreat the base of the next tree and would turn to reinvestigate the threat. If repeated the possum would then retreat to a tree that it would unhesitatingly ascend. This was taken as the core tree of the possum’s territory. Measuring from the edge of the territory – from where the possum was encountered at the road edge, to the core tree was 32 metres (60 metre diameter). This was smaller than territories (120 m) recorded by Pietch (1995).


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From these simple and incomplete observations and the number of dispersed possums it was deduced that approximately thirty defended possum territories were likely to exist within the Gardens. The counts Possums descended from the trees en masse. All possums observed were the Common Brushtail Possum. The time of emergence was between 7:05 pm and 7:20 pm. This was about one to one and a half hours earlier than animals in the wild at this time of year. Most possums descended immediately to the ground, but a number remained on tree trunks for a few minutes. The first count was easily achieved by 7:30 pm as possums remained still and close to their refuge tree. They showed no fear of observers and some individuals approached observers. One backyoung was observed in the eastern section of the Gardens, this was the only backyoung seen. Scans of the tree crowns revealed the movements of the Black Rat (Rattus rattus). Some rats descended from the Palm trees and waited on or near their trunks. One particular Palm surrounded by three bench seats, had three rats in the crown. No possums were observed using the tree. At 7:30 pm one human couple approached the possums and fed them with bread pieces from a bag. The possums gathered about, taking bread on an individual basis. In another part of the Gardens a male resident also fed the possums. He sat on a bench with the possums gathered about. Some climbed the bench and sat by his shoulders, pulling at his clothes for their share of the bread. He patiently fed them, selecting individuals to stroke. Three rats capitalized on the handout, scavenging beneath the seat for dropped morsels. Occasionally they would stand bipedally to await the next scrap. The man was untroubled by their presence. Now the possums were clustered around the humans at two or three locations. Their movements were focused on the humans but there were constant small movements within the group. Counting became difficult because of the grouping and movement. A count at 8 pm was abandoned. When all the bread was consumed the possums spread out, some eating grass, some preening or interacting with others. A second count was initiated at 8:30 pm finishing at 9 pm. The two count figures varied little and a mean possum count of 78.5 +/- 4.5 was established. After 9 pm possums began to climb trees, leaving mostly large males on the ground. Some agonistic behaviour was noticed at this time. The behaviour of the possums was not consistent with that of their wild counterparts who exhibit foraging and social behaviour throughout the night, mostly in trees. Decent to the ground and searching for incidental food items such as insects is a common behaviour of Brushtail possums in the wild, as is occasional grass eating. It appeared that the behaviour of the possums at Catani Gardens was altered by human presence, the habituation to human presence and the free-feeding associated with this presence. It was not possible to observe the activities of possums after they returned to Palms.


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Human interactions Two couples, a young male jogger, and a single middle-aged resident were interviewed some time after they were observed interacting in some way with the possums. Nationalities were New Zealand, Scandanavian, American, and Australian. The couples were young, about 20 to 25 years. One couple were travelers interested in any form of Australian wildlife. This couple offered tidbits to the possums. One couple had commenced to visit the possums nightly as a mutual experiential exercise. They were feeding out bread. “We don’t know what they eat but we have fed them bread for three nights and they seem ok with it”. The middle-aged male resident had been feeding the possums each night for five years. He fed mainly bread but occasionally supplemented the food with fruit. He had formed strong bonds with the possums encapsulated in his statement that ‘It is a kind of therapy coming here with these animals. They are so gentle. You forget all your troubles of the day’. The man knew of the efforts of the Council and of the sentiments of the residents. He was vexed by the events of the recent past and was cautiously reactionary to any future changes that might be wrought. Death and injury One dead possum was observed killed, presumably by vehicle impact, on Beaconsfield Parade (P Robertson, Wildlife Profiles, pers.com.) on the morning of April 26. During the census one male possum was observed (BW) with a skinned centre-section of its tail. The injury was consistent with an attack by a dog. Dogs were observed off leash on April 23 before possum emergence. No dogs were observed during the census. Generally, responsible dog-ownership prevails in most parks and gardens and injury by dogs is regarded as low, although a small number of adverse interactions continually occur. An anecdotal account by a local resident was that a particular dog-owner during summer months allowed his two dogs to harass possums. Occasional aggravation of possums by youths occurred according to the same resident. These sorts of incidents are consistent with observations in other city parks and gardens (Walters 1997). Visible injuries and perceived distress form the basis of concern by welfarists when possums are displaced from tree, building or refugia. Although natural dispersal of possums from natal dens through antagonism of young by cohorts (Tindale-Biscoe 1973), and the consequent mortality that follows, appears not to be considered by animal welfarists as the controlling mechanism for possum populations. Tree preferences The possums descended from two types of tree. The Canary Island Palms provided most of the refuge. No possums were seen descending or climbing the Skydusters (Washingtonia robusta). No possums were seen in the Ficus spp., although they are known to use hollow-bearing Ficus in the Fitzroy Gardens (Walters 1997). The Ficus was examined for browse but none was seen.


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Seasonally (late summer), Ficus fruits nearly ripen at this latitude. At this time possums are known to feed on them. No possums were observed in the single Sequoia or the Smooth-barked Apple-Gum (Angophora costata). However approximately sixteen possums were observed descending from four Cypress (Cupressus spp.) in the central section of the Gardens. The matted crowns of the Cypress provided sound, all-year refuge. Three possums were found browsing Mirrorbush (Coprosma repens) and Norfolk Island Hibscus (Laganaria pattersonii) along the sea-wall. The Coprosma was repeatedly eaten and obvious feeding sites were visible where constantly browsed branches had reacted with the growth of a clubby overwood. From these knobbled branches, new shoots emerged in profusion. It was these shoots that the possums repeatedly visited for sustainance. The browsers were all young animals. They appeared to be using the cover as daytime refuge as well as a food source. The appearance of young animals at the margins of the habitat is consistent with possum behavior, where young are driven from secure refugia at the time of their maturity to the margins of the protective environment. Rat movements Rat movements were not confined to the trees, but were largely so. Not all rats observed appeared on the ground, at least during the census. One rat, showing the effects of a poison (anticoagulant) was seen to move from pavement to grass and while observed, disappeared into a storm-water grate and pipe. The presence of the rat indicated that access between the built environment and the Gardens was relatively direct. Rats were also observed along the sea-wall vegetation. It was assumed that they emerged from hollows beneath the stone-work as it was some distance to buildings. The presence of rats in the built environment is usually underestimated and numerous sites existed along the waterfront for their protection. The central issues Tree damage: What is the role of animals in the spread of Fusarium wilt? The issue of Fusarium Wilt is, in the authors view, clouding the issue. The chlamydospores of Fusarium can be airborne or transported by a number of vectors such as contaminated soil, machinery and water. The known outbreaks in Victoria are disjunct and indicate vectors other than animals. If animals are a vector, a more suitable one is the Grey-headed Flying-fox (Pterops poliocephalus), a long-range visitor to many trees in one night. Possum movements are relatively slight. Displaced young will move until they can find safe refuge or die within 6 weeks (Peitch 1995) in the attempt. Even if waves of dispersing young were successful it would take a number of generations for animals to carry spores from one environment to another at some distance. With all territories appearing to be full at the Catani Gardens, most of the dispersal of possums would be outward.


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The potential vector of rats remains conjectural. The number of rats observed was eight. It is likely that not all rats in the canopy were seen, but the count indicated comparatively low numbers and this was consistent with other observations such as the low number (2) during free-feeding. Wilt has been detected within City of Port Phillip precincts. Changes to maintenance practices such as the washing down of machinery and the like are in place to minimize the spread of the pathogen by human agency. The principle and immediate issue in Catani Gardens is the physical damage to the emergent rachis of the Palms. Without new shoots the Palms will ultimately die. With constant physical damage to the apex of the trees, a micro-environment is created that is suitable for pathogen invasion, should the pathogen arrive. Differentiation of the perceived problem Is it rats, possums or both? Without establishing complex technical equipment in tree crowns such as automatic cameras and the like to record browsing or otherwise of tree crowns, the contribution of crown damage may be made by differential exclusion of the two species thought to be implicated. This may be achieved by the fitting of specialized tree bands that are fitted with a one-way gate that allows passage of both rats and possums, but only the return of possums. In this way, three trees can be selected, one allowing normal entry of both rats and possums, one excluding rats and one excluding both. The number of replicates will depend on external factors such as acceptance by constituents and finances. The damage or recovery of the trees can be monitored over three months or so by periodically photographing the emergent shoots of the crowns of the selected trees and comparing the result. The welfare of possums The concern of animal welfarists is limiting both the data gathering and the degrees of freedom for potential solutions. If an animal proves to be eating and damaging the crowns of the trees that support them it would seem self-evident that intervention will be needed to ensure the long-term survival of possums at the site. Under existing legislation, the City of Port Phillip is obliged to care for the Heritage trees in their charge. The antagonism to tree-guards means that any fitting of these to either gather data or control access by possums will need to be done at a point high above the ground (limited human access), thus increasing the potential for possums to fall from height when negotiating a tree-guard. The specialized tree-guard (nominally called the ‘Wildvet Gate’) incorporates a ladder that allows the safe passage of climbing animals and may be suitable at height.


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This tree guard will need testing and acceptance before it can be deployed. The inherent asset of wildlife in the Gardens The Catani Gardens, situated at the hub of StKilda, attracts numerous interstate and overseas visitors. For many of them the chance of seeing Australian wildlife close-up is irresistible. For residents and casual visitors the presence of possums is seen as part of the natural world that signifies a state of harmony and wellbeing in the open-space and gardens that support them. For others, the unfailing presence of the possums gives meaning to their daily lives. The possums appear to be an integral asset of the Gardens and of the St Kilda precinct. Recommendations A record of crown damage to Palm trees is to be constructed. The record is to take the form of dated photographs of the crown (apical meristems) or the emerging rachis spikes of selected Palms at monthly intervals. The trial of a differential gate (‘Wildvet Gate’) is recommended to ascertain the contribution of damage by both rats and possums. Acknowledgments

I would like to thank Dr. Peter Robertson of Wildlife Profiles and Dr. Wouter van Dongen of Chirnside Park for their assistance in the field.

References

Pietch R S. 1995. The ecology and translocation of urban Common Brushtail Possums. Thesis for the Masters of Applied Science. Deakin University, Rusden Campus, Melborne. Tyndale-Biscoe H. 1973. Life of Marsupials. Edward Arnold Limited, London. Walters B. 1995. Management strategies for possums in the Fitzroy and Treasury Gardens, Melbourne. Unpublished report to the City of Melbourne. Ecoplan Australia Pty Ltd, Hurstbridge, Melbourne. Walters B. 1997. Management strategies for possums in the St. Kilda Gardens, Melbourne. Unpublished report to the City of Port Phillip. Ecoplan Australia Pty Ltd. Hurstbridge, Melbourne.

Documents

Palm Trees Investigation Canary Island