Habitat discussion

The nutrients in the soil and therefore in the vegetation and the availability of water and its quality determine an area’s suitability as habitat for arboreal folivores such as ringtail possums. (Kanowski,  2004) The quantity of food resources, the variability of nutrient levels in the foliage and their toxicity then determine its carrying capacity.

As ringtails need to eat a certain quantity of food per day but will not eat leaves that contain toxic compounds exceeding a certain limit, carrying capacity can theoretically be estimated from the number of palatable trees in the area. (Tyndale-Biscoe, 2005, Lawler et al, 2000)
As our general knowledge about these issues is still highly limited, we are unable to test the trees of an envisioned translocation site for suitability or of an occupied site under development pressure in order to evaluate its habitat values and to put protective measures in place in accordance with those values.

Also, our knowledge about the metabolism and digestive physiology of marsupials has increased drastically over the past few decades but there still remain large gaps in our knowledge of specific nutrient requirements of most species of marsupials (Hume, 2006) and definitely of our western ringtail possum. Neither reintroduction programs nor habitat restorations are likely to succeed without this knowledge.  
At least an assessment of nitrogen levels in the foliage, which have been most highly correlated with ringtail abundance and survival in past studies, should be given priority when translocating animals.

As far as I know, no research project in relation to food availability, quality and composition is on the horizon.
There is clearly a correlation between soil chemistry,  communities of microrrhizal fungi , which might be destroyed in fires , and peppermint trees. However, again I was unable to find any investigations into this issue.
The soil in our backyards has higher nitrogen levels through fertilisation and watering which leads to higher foliar nitrogen levels and lower levels of toxic compounds. 
However, our backyards are shrinking as habitat areas and anthropogenic dangers and predation by pets are high.
The additional nutrients through fertilising favour exotic species which can then overgrow/replace natives and are a potential driver for weed invasion which can again cause decline in abundance and diversity of native species. Also, natives are unable to down-regulate phosphorus levels (Thomson and Leishman, 2004) which are usually extremely elevated when fertilised.
The extended fertilisation of soils potentially alters the structure of natural plant communities and can in fact exacerbate pathogen emergence and transmission. (Bradshaw, 2017)

Some garden plants introduced to Australia have turned into invasive weeds (e.g. Brazilian Pepper) and they are most abundant and thrive particularly well in highly modified landscapes.
In some cases, such as Acacia saligna, opinions what are weeds are greatly divided. A. saligna is valued as ringtail food by carers, while horticulturalists usually condemn it as invasive and unsuitable for suburban backyards.   

The best available habitat for western ringtails can clearly be found in the urban and peri-urban areas around Busselton/Dunsborough and East Augusta.
However, there is no tree preservation policy in place to protect this valuable resource. A planned habitat protection plan and scheme amendment prepared by the (then) Shire of Busselton mutated into such a blatant ‘development protection plan’ that the WAPC put a stop to it. Instead of salvaging the work that had gone into it and amending, it all vanished.  

The most pressing issue in urban/peri-urban environments would be to implement controls on tree clearing and enforce the retention  of undisturbed habitat with an abundance of mature trees – in particular peppermint - providing adequate foliage and hollows.
New subdivisions/residential areas need to be developed in stages over a number of years.  A planting program of ‘advanced’ trees on housing lots and roadside verges should be started even prior to the sale of the land.
However, currently there seems to be no compliance monitoring  even if some conditions are put in place. The example set by the City of Busselton (CoB) is also usually a bad one.

When mature trees are retained, the soil is often so severely compacted that the tree will not survive in the long term. Our narrow verges can barely accommodate decent sized trees. There are engineering solutions such as tree root vault systems which allow roots to spread out without damaging pavement. Why are they not even considered?
There is a clear infrastructure boom going on in the South West but designing roads and public spaces in a way that will still accommodate trees when they have reached maturity seems to be in the ‘too hard basket’. 


When trees were cleared for yet another parking lot in Busselton, the very last still standing contained a female ringtail possum with offspring.  Due to pre-clearing surveys this was well known to the fauna spotter, who had already captured 2 and herded 2 more ringtails out of the danger zone.
However, then a community person spotted those animals in the tree and the trouble started.
The fauna spotter’s job was to ensure the safety of the animals during the demolition of their habitat. The community people and the reps of the local wildlife care organisation wanted exactly the same but the situation still escalated. The next day the animals were finally ‘rescued’ with the help of a tree lopper with cherry picker, taken to a vet, then to a carer overnight and released into the closest tree.
In my personal view, this incidence highlights the problem with the process – there is no mitigation for removal of important habitat trees.
Despair about the loss of mature peppermint trees resulted in anger aimed at the fauna spotter who was obviously seen as representing the developer and therefore  the destruction. However fighting each other will not change the protocol and will not stop removal of more trees.
Those that approve destruction and disguise the negative outcome by having some pseudo-mitigation measures in place, should have to accept responsibility. (also see:  Threatening process: 'Pseudo-mitigation')

dead treesforeshore treeSome trees seem to 'just die' and no explanation can be given why as all other trees in that patch seem to be doing well. This seems to happen particularly often at the foreshore when those trees limit ocean views.






pruned under power linesPruning practices by various government bodies and Western Power mostly leave vegetation in a state that it is not of any use to ringtails. Peppermints are also often placed under powerlines and then pruned to death before they reach any maturity.Why plant those trees under power lines to then prune them in a way that they are not only ugly but completely useless for ringtail possums and even potentially dangerous (leaning to one side)?

plantingsThe CoB is running several tree planting projects – but does their registry show how many of those trees are immediately removed again because people do not want them?
Trees are planted next to a pedestrian walkway and when they have reached a height that would make them useful for possums, they are pruned heavily so that they do not interfere with the path.  

Planting days organised by the City or other government-related entities rarely ever lead to true ringtail habitat. Often, the saplings are not watered, the plastic bags stay on during heat waves and the plants ‘cook’, and the areas are hardly ever monitored for plant survival. A feel-good exercise for people with no long-term outcome will not feed a single possum!

foreshore habitat

As usually structural features of a tree species including their maturity are of importance to fauna , not just the presence of the species, we need to reconsider the idea of ‘replacing’ valuable habitat trees with larger numbers of new plantings as we might replace habitat with ‘just trees’ of little or no value.

Public land is for dual use (people and wildlife) but mainly for the enjoyment of people and their pets.
Even in areas with high numbers of ringtails, there are no caveats on cats in place either banning them or enforcing the requirement to keep them inside. 

Urban remnants often have larger, older peppermint trees than woodland remnants but if they are not under threat from development, they seem the most vulnerable to our changing climate and accordingly are affected most by severe tree decline. Even after the good wet seasons 2016/2017 particularly old trees seem to still be dying in high numbers.

If we engage in landscape restoration/enhancement efforts at all, we rarely do it in a way that our landscapes become less suitable for predators and more hospitable for native wildlife. (Graham et al, 2012)
pruning heavilyHowever, many features that make a habitat safer for wildlife (e.g. good understorey) clash with our human need for safety.
The City’s fire protection requirements follow a  ‘one size fits all’ protocol and amount to a scare campaign (high fines) so that people tend to clear or prune more than necessary.  

Even vegetation verging on the roadside and drainage system can support similar good densities of western ringtail possums if  there are peppermint trees and other palatable food sources.
Narrow, linear patches might however become ecological traps for native fauna because of increased predator activity. This could even be an argument against corridors, which are vital for the facilitation of movement but rarely are wide enough to be habitat themselves.  

Areas with high edge to area ratios are never good habitats, not even with appropriate maintenance and conservation methods as stated in local research. (Harring-Harris, 2014)
I cannot imagine which maintenance and conservation methods she can envision that could make dangerous road sites acceptable habitat. However, I completely agree that it is important to protect whatever eatable tree is left in those highly modified, hostile but comparatively densely populated areas.

Outside the urban/peri-urban context, the situation is not any better.
Parking for a boat ramp in Dunsborough was deemed more important than the endangered species occupying the area to be cleared.

Mountain  bike trails through the last bush areas such as Meelup, Bramley and a national park in Albany will give people enjoyment, however it will also fragment habitat.
26 km of walking/mountain biking  trail deject Bramley and it is earmarked ‘as a high priority for future trail development’ (King, 2016) – probably the main reason why there has basically no fox baiting happened in the park.
National parks and reserves are now mainly for people; wildlife, undisturbed mature is at best an added bonus, but no necessity.

Woodland remnants tend to have low carrying capacity and are under a myriad of pressures.  Without reliable canopy growth flush western ringtail possums will lack the body condition to withstand predation pressure and will not breed well enough to safeguard the viability of the population.

In summary, we need  far reaching protective measures for all still healthy western ringtail possum habitat patches and this must be put in place urgently.
Already, under the EPBC Act, there is a national critical habitat register in place and the federal government can identify land critical to the survival of a species.
However, under the current law it seems only possible to register and protect habitat on commonwealth land. The most valuable western ringtail possum habitat is unfortunately not on commonwealth or state owned conservation estate, but on private land.

Case study 1
Upgrade of a drain
Alongside drains and other water courses, peppermints are usually well used by ringtails, which prompts a referral  under the EPBC Act.

Simultaneously with scrutinising whether ringtail decline warrants a conservatoin listing upgrade to ‘critically endangered’ the agency investigating referrals under the EPBC Act utilised highly outdated literature for their assessmentof this case that might have applied when the animal was just vulnerable. They seemed to not even realise that there was now a federal recovery plan (2017).

Reasoning that the development will not have a significant impact as it will not endanger the species as such is as common now as it is flawed as no single development will ever cause a species extinction. There is no doubt that hundreds of developments that are assessed in isolation will, though.

However in this case, prior to the drain upgrade works a program aiming at removing highly invasive Brazilian/Japanese pepper trees started. To do this, heavy machinery needed access and large tracks of understorey were cleared -  and while they were at it, peppermints were pruned heavily, whole stems removed and connecting canopy disrupted. A peppermint with a drey was isolated, but trees overhanging the drain and a lot of dead wood were left. This all did not even require a clearing permit!


A survey the night after the works, which I am tempted  to call vandalism, revealed 13 resident animals including 3 active breeders with offspring. At a repeat survey 2 months later only 5 ringtails were spotted in the same area with only 1 active breeder.

drainProfessional pruning or vandalism?




The EPBC assessment might well be correct now. The damage to the breeding colony has been done well before any upgrade work would start.


Case study 2
Eastern Link Project
The highest ringtail densities can be found in the urban environment even though the habitat does not always look healthy. Old, not very sightly trees are either (conveniently) declared a public safety risk or a fire risk and removed.
In this case, the vegetation comprising of very mature trees alongside the river were classified as completely degraded, however the largest amount of ringtail scats can be found underneath the oldest trees which shows their high value as a food source.

We remove all understorey and clear to create parkland for the use of people that can be easily mowed using big machinery.  However, we then declare the area ‘completely degraded’ as it is ‘parkland cleared’ and conclude that it is therefore worthless and can be removed for the establishment of infrastructure (a bridge and road in this case).
Understorey is important and often life-saving for ringtail possums, but connective canopy cover is even more important for an arboreal species and canopy connectivity in this patch is quite adequate.

Even though an animal listed as ‘critically endangered’ is the main loser in this project, no dedicated survey was commissioned and the reconnaissance survey that included ringtails was done at the time of the year when numbers are always at the lowest. Only the trees to be removed were surveyed as if the animals lived statically in the one tree they were observed in. Environmental consultants know about home ranges and the importance of breeding home ranges but that was obviously not included in their brief.

A count of 2 and 3 animals gave the impression that the habitat was not of any value for the species. 3 counts in summer however revealed up to 22 animals in the affected area.
The significance of the wildlife corridor has been acknowledged and a rope bridge might be established, but no specifics are given. However, the real issue here is the ensuing food shortage for the colony, which cannot be addressed in the short term.

There are other possible solutions to the traffic issue that prompted the project’s development and even our former (first) mayor publicly called the project ‘environmental vandalism’.

I had to agree with MLC Steven Thomas who said in our local newspaper that the EPA tends to just tick projects off – because that is exactly what they did here.
However, the proposal was declared a ‘controlled action’ under the EPBC Act and there will be some conditions. Also, miraculously the number of peppermint trees to be cleared has significantly decreased. Nobody knows which trees will be spared and how this will change the proposal though.
The council has now decided to defer the project for 6 months to allow for further community consultation. Unfortunately the most outspoken opponents of the development have only ‘hijacked it’ for their own, equally if not more damaging preferences. If Eastern Link does not happen, they think the way is cleared for another road to be built that would impact a Ramsar listed wetland.

threats introduction