It never rains but it pours

River Red Gum (Eucalyptus camaldulensis) experiencing extended inundation

Trees have evolved to occupy a wide range of environmental niches and while a minority of species have adapted to succeed in sporadically or permanently flooded areas most are not well equipped to deal with waterlogged soils.

Different species and individual trees have developed a range of flood tolerance levels but it is difficult to predict how long a tree can tolerate waterlogged soils. In part, the duration and timing of the water-logging event, the complexity of the soil as well as individual tree characteristics all affect the outcome for the tree.

Waterlogged or saturated soils are those where the voids between the soil particles are entirely filled with water and occur when water enters soil faster than it can drain away under gravity.  The duration of a water-logging event is influenced by the rate of water input and the rate of outflow or drainage. Topography will influence lateral flow; however soil structure and texture is critical in influencing vertical drainage.

Soil is made up of solid material, accounting for around 40-60% of the soil by volume, and the spaces between or pores. Soil texture determines pore size, while soil structure influences the inter connectivity of the pores. The ease with which water passes from pore to pore is referred to as hydraulic conductivity.  Small pore size and poor connectivity, such as occurs in clay soils, will drain slower than sandy soils which although having lower porosity than clay soils have larger pores that are efficient in the movement of water and air.

The immediate effect of waterlogging is to significantly reduce the movement of oxygen from the atmosphere to the soil and the root surface where it is used for respiration.   A lack of oxygen is the principle cause of injury to roots and other parts of the tree.  Oxygen depletion in waterlogged soils occurs rapidly.  The maximum amount of dissolved oxygen in still water is a little over 3% of that in a similar volume of air.   Available oxygen is quickly used by respiring roots and aerobic microorganisms creating an oxygen depleted or anaerobic environment.

Oxygen deprived or anaerobic soils lead to the production and accumulation of, gases such as carbon dioxide, ethylene, methane, hydrogen, nitrogen, sulfur and cyanogenic compounds, some of which are toxic to trees influencing plant growth and function.  The soil ecology is altered as anaerobic soil organisms replace aerobic organisms.  Soil pH becomes increasingly acidic influencing nutrient availability.  Anaerobic organisms, primarily bacteria alter soil chemistry and cause de-nitrification and reductions in manganese, iron and sulfur.

Waterlogging can be fatal to trees. Mature, well-established trees are generally more tolerant of waterlogging than senescent trees or seedlings of the same species.  Healthy trees are generally able to withstand periods of waterlogging better than trees that were already under stress. Waterlogging during periods of growth tends to be more harmful than during period of plant dormancy.

Signs of waterlogging include the yellowing or paleness and mottling of older leaves.  Growth is stunted and internodal extension may cease.  Wilting of young shoots and leaves may occur and brittle green leaves present.  Premature senescence and abscission of leaves (older leaves first) can occur. Fibrous root death occurs and the death of small ephemeral woody roots may follow.  The dead roots become blackened and the bark may peel away.  Prolonged waterlogging can result in root decay rendering trees susceptible to wind-throw.  Notably the anaerobic decay of organic material including dead roots in waterlogged soil creates a characteristic sour sulfurous smell.

Waterlogging alters the biochemical functioning of trees, impairing defense mechanisms and increasing the potential for trees to succumb to attack from opportunistic pests and diseases. Soil-borne fungal diseases that tolerate low soil oxygen levels include Phytophthora spp. and Pythium spp.

Following periods of extended waterlogging, tree management should aim to enhance tree vigor whilst avoiding further stress. The addition of a light dose of nitrogen, potassium and phosphorous can assist, though the addition of micronutrients should generally be avoided.  Pruning that removes live foliage or foliage-bearing branches should be avoided to conserve the trees energy supplies and photosynthetic potential and capacity.  Mulching may encourage the return of aerobic micro and macro soil organisms improving nutrient cycling.

Knowing your site conditions and if the area may be prone to periodic inundation or extended waterlogged, will allow appropriate plant selection to suit the location.  Some ornamental Australian native tree species tolerant of temporary inundation include some of the Bottlebrush (Callistemon viminalis, C. ‘Harkness’ and C. ‘Kings Park Special’), Argyle Apple (Eucalyptus cinerea), Plunkett Mallee (Eucalyptus curtisii), Spotted Gum (Corymbia maculata), and Water Gum (Tristaniopsis laurina).  Some exotic trees include the River Birch (Betula nigra), Black Tupelo (Nyssa sylvatica), Dawn Redwood (Metasequoia glyptostroboides) and Callery Pear varieties (Pyrus calleryana var.).

As arborists, we know the importance of identifying when trees become unsafe to nearby properties and people, but we also recognise the aesthetic value a beautiful tree can add to a landscape. Often, the first response of a property owner to a hazardous tree is to have it removed. However, removing the tree would not only be a costly exercise, but could also be a waste when there may be other ways to save it and reduce its risk potential.

The Logical Tree Management (LTM) crew found this was the case recently when working at a local high school. A large Spotted Gum (Corymbia maculata) on a sports ground boundary was found to have poor structural form, mainly due to several major co-dominant stems with extremely narrow attachment angles. These types of stems are weakly attached and often become prone to failure as their diameter and foliage weight increases.
The solution seemed obvious to the school’s management – to remove the tree before the branches fell off and injured students. This reaction is reasonable as safety is paramount, but we could see that removing the tree would be detrimental to the landscape as it provided an excellent source of shade to an otherwise exposed area.

As modern day arborists, LTM are often required to provide solutions that both benefit the health and amenity of the tree but reduce the risk of tree failure to an acceptable level. Fortunately, we have a wide variety of tools and techniques that enable this, from various pruning work to installing different types of support systems.

In this case, we installed two stainless steel bracing systems between the co-dominant stems. This involved drilling and bolting threaded rod through the opposing stems securing flexible cable between them. Cable bracing systems allow the stems to sway as they would naturally in the wind while restricting violent sways that could lead to branch failure. The minor damage caused by drilling into the stem stimulates woundwood growth over the bolted ends of the rods, significantly strengthening the system and sealing the wound, preventing decay-causing fungi from getting in. Using this bracing technique enabled the school to keep the Spotted Gum, which will continue to be an integral part of the landscape and provide their students with shade for many more summers to come – all at a fraction of the cost of removing it.

Earlier in the year Tree Logic provided the arborist report to the Melbourne City Council in relation to issues around developing an exceptional tree register.  The report focused on issues surrounding the preservation of large trees in dense areas, regulations and problems associated with enforcement of such laws. This week the Melbourne Age ran a story about this council research that aims to identify trees on private land that are unique, old, rare or otherwise noteworthy.

WHEN Melbourne City Council’s Cathy Oke suggested the council develop a register of ”exceptional” trees on private land to prevent them from being chopped down, the last place she expected to find one was in the backyard of her childhood home.
But when council arborists presented her with photos of trees in North Melbourne – part of early research into the idea – Ms Oke discovered she was looking at a lemon-scented gum in the garden of the house where her parents still live on the aptly named Wood Street.
”I thought, ‘I know that back garden’!” the Greens councillor said.
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”It just shows how varied the definition of ‘exceptional’ might be. These might be included because of their height, or because they’re in a suburb where there aren’t many pockets of large trees on private land.”

Read the entire article online…

Whilst many metropolitan councils have varying approaches retaining significant trees on private land, it is clear that a one size fits all approach to tree regulations does not apply.  The report cites…

“In Canada and the United States, public enlightenment and negotiation with developers are considered by many to be the most effective tools for preserving existing trees. (Profous & Loeb, 1990).
Schmied and Pillmann (2003) found that a regulation (law) “concerning tree protection seems to make sense, if it can be implemented in a non-bureaucratic, professional and efficient way, respecting the protection and conservation of nature. It should be structured simply and equitably, and its administration and implementation should be simple and efficient.”
There has to be a clear outline of the goals that want to be achieved by tree controls. The fostering of community support is absolutely critical to ensure the tree protection controls effectiveness. The community needs to be involved in the tree protection process; the success of the controls relies on the community’s support.”

Tree Logic supports any initiative to protect exceptional trees on private and public land and concede that education around environmental and social benefits is the right way forward.

Case Study – Coles Building – Hawthorn East

The Coles  head office complex in Hawthorn East has long been held up as one of the finest examples of planter box and on-slab planting in Melbourne. Time and time again, Landscape Architects have given evidence in VCAT, stating that planter box and on-slab planting is possible. The Myer building is often used as the best example in Melbourne.

Tree Logic has been involved on this site for several years as the managers come to terms with the decline faced by the site vegetation. Several investigations have linked the cause of this decline to a range of issues but predominately limited soil root zone volumes and poor soil qualities are the issue.

The above images show the significant decline in areas with limited soil volumes (planter boxes) and poor quality soils and limited volumes (on-slab plantings).

The original plantings around the building included a range of planter box and on-slab sites with a range of tree species and other vegetation. Aerial photographs from 2004 and 2006 through to 2010 show a significant decline in vegetation areas and the loss of all the trees sited in planter boxes located along Toorak Road.

Note the areas outlined in red. Now there has been significant removal of trees and other vegetation with no trees in the Toorak Road planter boxes and trees and vegetation completely removed form several internal courtyard areas.

These images it can easily be seen that while the trees and other vegetation planted around the building initially established, the trees only just established and then started to decline. Within a period of approximately six years the trees and other vegetation had declined so badly that it has been all removed and the design of planters and courtyard areas changed to reflect the difficulties of vegetation management.

The above photographs show the very poor condition of the declining trees in the Toorak Roadplanter boxes and alongside the main building prior to them all being removed.

This site should show a clear message to planting designers that limited root zone volumes for large trees just does not work and that while the trees may grow for several years after planting, ultimately the limited root zone volumes will see trees decline and require removal.

In terms of all the benefits of trees, including aesthetic, social and environmental benefits, most research suggests that the greatest benefit is derived from large trees. Sustainable tree growth requires space and large trees need more space. However, in terms of residential development space for trees is always a compromise..and it is the trees and space for trees that is compromised.

How did we get to the point where a new dwelling can have no real usable open space and no space for existing trees or even for the planting of new trees? The trend for larger dwellings on smaller blocks has been around for some time but who said this was a good idea? There does not appear to be a gradual change. Space was there and now its not!

Prior to a certain date suburban form still had back gardens of useful size and a significant covering of trees. Professor Tony Hall in a Griffith University paper Where have all the gardens gone? (2007) states “…after a certain point in time, the construction of one type of suburban form was almost
totally replaced by another.”

Hall states that “residential built form is a product of commercial forces operating within a regulatory framework”. The incentive is to now maximise floor area for the lowest cost resulting in square or rectangular forms with internal garages while forgoing amenity. Hall states that during the 1990s, a new suburban residential form emerged in Australia and the old one ceased to be built.
With the disappearance of the backyard there are significant disadvantages for the wider community:

Hall states “The design of both the house and the space around it presumes an entirely indoor lifestyle, insulated from the prevailing climate and with little propensity for exercise.”

With issues such as childhood obesity being a major nation-wide problem, the lack of outdoor recreation space is likely to be an additional factor at play.

Hall argues that built form is permanently changing the space for gardens (and trees). And….once its gone….its gone for good!

He states that the argument for the absence of private open space behind dwellings should not turn on what the current ‘trends’ are! If we let it, this argument rules out this open space permanently!

The suburban landscape has ceased to be one of large gardens with trees. These landscapes now tend to be confined to wealthier suburbs. Hall states that “This trend represents a loss that has serious ecological implications.” “The narrow dimensions of the space around buildings ……. Will lead to a substantial reduction in tree cover in perpetuity,..”

The implications for arboriculture is just as serious. Trees are being removed that will never be replaced. Not only is the tree gone but the space that was there to plant a replacement tree is now gone too!

Tree Soil Volume Requirements

Calculating the amount of soil required by a mature tree can assist in determining proper root zone volumes that provide a suitable growing environment for urban trees. The soil available to the roots needs a wide profile rather than deep. This is because roots proliferate in the first 500- 1000mm of soil. Soil at depths greater than this may not be utilized by the root system.

Several methods for calculating required soil volumes are available.

In this example we have used a modified version of the Crown Projection Method (CPM). This method uses the expected mature width of the canopy or half the expected mature height of the tree, whichever is greater, to provide a radial distance from the base of the tree used calculate the soil volume required. This method provides 0.6m3 for each 1m2 of ground space within this radial distance (crown projection).

The calculation is straightforward and is based on the expectation that tree roots will utilise the top 0.6m of soil.
The calculation is represented as: Soil Volume (m3) = 3.14 x r2(m) x 0.6(m).
Therefore a tree with a height of 10 m and a crown spread of 16m would require the following soil volume:

Soil Volume (m3) = 3.14 x 8m2 x 0.6m
Soil Volume (m3) = 121m3

However a tree with a height of 20 m and a crown spread of 5m would require the following soil volume:
Soil Volume (m3) = 3.14 x 10m2 x 0.6m
Soil Volume (m3) = 188m3             Adapted from Watson & Himelick (1997)

This diagram shows the relationship between tree size and the amount of soil volume required for establishment and ongoing growth. From: Urban, J. 2009 Up By The Root

Matching Tree Species to Volume

The following table highlights the potential ranges of rooting volumes for some of Melbourne’s most popular tree species.

Recent VCAT Decisions

Railway Parade, Murrumbeena:

19 dwellings over a significant basement (was 2 single-storey single dwellings) There are setbacks from the basement to the boundary fence lines of between 1.0 – 3.0 metres. The plan by the Landscape Architect shows a total of 42 individual trees to be planted (including 28 Capital Pears) and 151 shrubs (including 46 Lilly Pillys [clipped?]

One section where there are 9 Capital Pears shown measures 2.5 metres X 27.0 metres which equates to 67.5m3 of soil volume (assuming 1.0 metres depth of soil).

The table above indicates that Capital Pear is rated as being a ‘medium’ sized tree and requiring root zone volume for one tree of approximately 40-60m3. Yet we have a design that shows 9 trees in a space that is barely enough for 1 tree with the result being a short-term landscape solution.

The Chairman stated:

“The space available around the perimeter of the building is sufficient to establish a landscape setting for the building consistent with this planning context.

The submission that the layout of the basement does not provide sufficient space for the establishment of the canopy trees proposed in the landscape plan does not appear to be soundly based, and is in fact inconsistent with my experience of landscaping outcomes elsewhere in the metropolitan area;”

One can only ask what landscapes the Chairman was referring to and what his experience with landscape “outcomes” is ?

The Chairman stated that the argument that there was not enough space for new trees was not “soundly based”.

Why was the burden of ‘proof’ not on the Landscape Architect to show that there was enough space? What more did the Council opposing the development have to do?

Metaxas Architects Pty Ltd v Bayside CC [2007] VCAT 40 (15 January 2007)

I refer here to the landscaping report (by the LA), which provides details of this proposed planter bed approach. (This report refers) …to such use of raised planter beds as a “…commonly implemented planting technique which has been used in many built form landscapes in residential Melbourne”.

In contrast, (Council’s Arborist and the Objectors) criticised this proposed use of raised planter beds as providing an inadequate amount of soil for the relevant trees to grow properly and to be secured in the event of high winds. Hence their evidence was that these trees are likely to grow to a much lower height than shown in the relevant elevation plans….

The Chairman stated that:

“I am ultimately persuaded that the proposed use of raised planter beds is acceptable… I consider (the LA’s) evidence regarding the proposed use of the raised planter beds to be fundamentally credible.

On one side of the ledger, I accept that the totality of evidence before me indicates that the growth potential of the new trees in the raised planter beds will probably be somewhat less than the ‘best case scenario’ put forward by (the LA).

All in all, I see the probable scenario with the proposed central landscaping as being that it will not be as expansive as (the LA’s) evidence at its highest suggests, but this landscaping ultimately should still be acceptable.

To the extent that (Council’s Arborist & Objectors) evidence conflicts with my findings set out above, that evidence is rejected.”

Highland Properties Pty Ltd v Glen Eira CC [2007] VCAT 1032 (11 June 2007)

The Chairman stated that:

“We are satisfied that the proposed landscaping of the site is respectful of the neighborhood character and provides adequate opportunity for canopy tree planting. We reach this position having regard to the following:

A detailed landscape plan was part of the advertised plans and shows some 125 canopy trees planted throughout the site and this will improve the canopy cover on this site.

We accept (the LA’s) evidence in regard to the capability of planter boxes to support medium height trees. Our observations of existing planting in boxes on various sites together with examples provided by (the LA) support the contention that appropriate species planted in boxes can be healthy in the long term and contribute significantly to the landscape.

We are satisfied that the landscaping proposed through the centre of the site which includes a planting in a number of planter boxes is capable of contributing to the landscape character of the area, which we note is identified as low and medium scale. In this regard we agree with the findings of Member Martin in relation to planter boxes where he found that

…the growth potential of the new trees in the raised planter beds will probably be somewhat less than the “best case scenario’ put forward by (the LA).“

Sharp v Glen Eira CC & Ors [2009] VCAT 1812 (2 September 2009)

The Chairman stated that:

“The Responsible Authority was critical of the lack of landscaping opportunities due, it submitted, to the basement being located on the northern boundary and only 600mm off the southern boundary.

This is considered to be another area where there must be some balance brought with providing increased housing.

The ground level dwellings each have areas of private open space that provide for landscaping that will contribute to the amenity of the future residents. The setback to the rear of the site allows for planting along the rear boundary and planting can be accommodated along the side boundaries within the private open space areas.”

It should be understood that the VCAT Chairman is talking about tree planting in a 600mm wide gap next to a basement wall.

There is no doubt that there is a dichotomy between urban consolidation and retaining trees.  The strength of the argument often depends on which profession or interested party you talk to.  One clear difference is an understanding of tree growth and  physiology and the time trees take to achieve their optimum size to return maximum benefit. Urban consolidation is real and with a current demand and trend towards apartment developments, trees and space for trees will be lost on private land in the metropolitan area.  This will lead to changes in neighbourhood character and a reduction in canopy densities.  Providing tokenisitc space for trees on densely developed sites looks good in plan view, however this practice is not sustainable in the longer term and in no way compensates for the trees that have been lost.   Further reading and case study see our story on “You just can’t keep a plant in a pot forever”

Download the factsheet pdf

We all look forward to the seasonal spectacle as our deciduous trees change colour.  However, some years this display is great and some not so great!  Why is this and why do some tree species have better autumn colour than others?

On a scientific basis, the autumn leaf change is based upon a range of chemical processes that occur within the leaf as the climate changes from the hot summer to the cooler winter.

There are four leaf pigments that are responsible for leaf colour that occur in the autumn.  These are chlorophylls, carotenoids, anthocyanins and tannins.

Chlorophyll

Chlorophyll is located within the leaf plant cells and gives leaves and other plant parts their green color. Chlorophyll absorbs the sun’s energy and is a major factor in photosynthesis, the chemical reaction in which carbon dioxide and water are transformed to sugars which the tree uses for food. During the spring and summer for deciduous trees, chlorophyll is continually being produced and utilised and leaves appear green.

As day length gets shorter and temperatures cool in the autumn, the leaves stop this food- making process.  Trees then start to withdraw nitrogen and phosphorus from the leaves to be stored in twigs and branches during the dormant winter period. This change in chemical makeup and the reduced amount of sunlight on the leaves as day length gets shorter, gradually stops the production of chlorophyll. The green color of the leaves fade and other pigments present in the leaf are then exposed and this results in a change in leaf colour.  The timing of this leaf colour change varies dependent upon day length and temperature and within different tree species, with some trees having leaves that will remain green longer than others and a whole range of fading green colour changes.  This can typically be seen with such species as Birch, Elm, Poplar, Willows and some species of Maples.

Carotenoids

The chemical Carotene is responsible for the yellow and orange colors in leaves and also  in such plants as bananas, corn and carrots.  Carotenoids are also located in the chloroplasts and assist chlorophyll in the capture of sunlight for photosynthesis.  Caratenoids are always present in the leaves, but are generally not visible for most of the year because of greater amounts of chlorophyll present. As explained above, as the chlorophyll in the leaves degrades, these colors then become visible. Carotenoids are responsible for the yellow color of some Maples, some Oaks, Elms, Poplar and Ashes.

Anthocyanins

Anthocyanins are responsible for the pink and purple leaves of tree species such as Red Maple, Scarlet Oak and Dogwoods along with many other woody plants.  They also give color to red apples, grapes, berries and plums.  This chemical is formed in the cell sap and is water soluble and is contained in the liquid of leaf cells.  There can be great variety in the pink to purple colors and this is influenced mainly by cell pH.  Anthocyanins are usually red, however, may become purplish to blue if cell sap pH increases due to a range of factors such as temperature, water availability, etc.  Anthocyanins are generally not present in the leaf until they are produced in the autumn.

Tannins

Tannins are responsible for the brown hues in the leaves of some Oaks and other trees. Tannins also combine with other leaf chemicals (typically Carotene) to produce the golden yellow in some leaves such as Beech. These compounds are always present in the leaves, but only become visible as chlorophyll and carotenoids disappear from leaves.

It is when there is the greatest difference between day time and night time temperatures that brings about the most spectacular leaf coloring.  During the hot/warm days at the end of summer, lots of sugars are produced in the leaf but the cool (but not freezing) nights and the gradual closing of veins going into the leaf prevent these sugars from moving out. These conditions favor anthocyanin production and brilliant red autumn color. However early frosts will significantly effect autumn colors by killing or severely injuring the leaves before the pigments reach their maximum development.  Rainy and overcast days will also decrease the intensity of autumn colors due to reduced daylight limiting photosynthesis and the sugars available for anthocyanin production.

The slow change into autumn that we typically expect in suburban Melbourne tends to lower the intensity of autumn colors.  A cold snap with the quick onset of winter will produce the most brilliant autumn colors.

Tree Logic was commissioned to survey another significant site in Sydney, which involved the assessment of historic trees. Tree Logic has previously assessed the trees in Centennial Parklands, the Royal Botanic Gardens and The Domain (in 2006). Tree Logic also assessed the trees at The Rocks and Darling Harbour (in 2007) for the Sydney Harbour Foreshore Authority. This latest project involved the assessment of approximately 4000 trees at Callan Park, Lilyfield.

Section of former Rozelle Hospital (now University of Sydney College of Arts)

Callan Park is a large tract (approximately 60ha) of state owned public land, which is approximately 4km directly west of Sydney. The site has and continues to be utilised for a variety of purposes, but the most significant role of the site was its association with the Rozelle Psychiatric Hospital (which closed in 2008). The site continues to be utilised for public health purposes and recreational activities, but significant changes might occur on the site as master planning continues (Refer to http://callanparkyourplan.com.au).

Horticulturally, the site has evolved over the last 160 years, seemingly with intensive periods of tree planting at different times. The site has developed a large collection of native and exotic trees, which will require constant and ongoing management. A total of 190 different species were recorded amongst individual trees and tree groups. The 34 most dominant tree species represent 82% of the total trees identified in the survey. The ten most frequently observed species were: 1, Casuarina glauca, 2, Lophostemon confertus, 3, Ficus microcarpa var. hillii, 4, Jacaranda mimosifolia, 5, Populus nigra ‘Italica’, 6, Casuarina cunninghamiana, 7, Corymbia citriodora, 8, Celtis sinensis, 9, Cinnamomum camphora & 10, Erythrina Xsykesii

A large number of significant mature trees and tree groups were observed and assessed throughout the course of the study. I believe that some of the trees would have some significance at a local level, at a state level and some trees may be of interest nationally. A number of the trees assessed during the survey were unusual (to say the least) and this resulted in a few headaches with tree identification. The following table lists some of the species of interest.

Callan Park is a valuable historic asset in very many respects. Horticulturally, the site has enormous value for its collection of trees, the variety of species and the way the plants have been arranged throughout the site. It is easy to understand why the community is seeking to preserve the site as open space and recreational pursuits.

There will be significant challenges ahead for those that manage the site and the vegetation on it. Improving access to the site will result in greater numbers of people and traffic. This is likely to trigger a wide range of changes; including the need for improvements to roads, paths and other infrastructure. Developments of this type usually result in some level of threat to existing trees, and these changes will need to be rigorously managed if the site is expected to retain historic trees.

The Callan Park tree assessment was a great project to be involved with and Tree Logic has been fortunate with its involvement with so many historic tree assessments in the broader Sydney area. The process of undertaking assessments of significant trees in mature landscapes, and recommending management strategies, is an ever-increasing aspect of Treelogic’s business. The focus on managing mature trees and landscapes has been a common theme in recent newsletters (see September and December 2010)

Healthy soil differs from dirt in the myriad of life forms it contains.  Soil organisms (the biological properties of a soil) aerate, decompose plant material, assist nutrient absorption, build soil structure, reduce water requirements and play a vital role in the nitrogen cycle.
A proper balance of nutrients and pH obviously play a significant role in healthy plant growth.  Biological activity can also affect the pH of the soil and subsequent impacts on the utilisation of of nutrients.
The biological properties of a soil decompose the organic matter in the form of litter falling on the soil surface and subsequently incorporates it into the soil profile.  Nutrients are released as by-products, including the mineralization of nitrogen and nitrogen fixation (making nitrogen available to plants).  The soil’s physical properties, including moisture content, temperature, aeration (bulk density) pH and nutrient content are necessary for a diverse soil organism population and a high level of activity.  Limiting any of these factors limits soil organism activity, organic matter cycling and subsequently reduces soil fertility.
The undisturbed forest soil has organic layers in it’s profile.  These organic layers comprise leaf litter at the surface, a decomposition layer and a humus layer. These large, high-molecular-weight molecules are made up of carbon, nitrogen, soil minerals and soil aggregates. The resultant humus is a stable, inseparable part of the soil matrix that can remain intact for hundreds of years.
When OM is incorporated into the surface soil it forms the topsoil (A horizon) and this horizon has the most optimum conditions for plant growth.
Urban soils are generally highly disturbed soil environments that do not mimic the soil conditions of natural forest soils.  Human activity is the predominant agent in the formation of urban soils. Urbanisation also contributes unique amendments and contaminants to the urban soil.
Disturbing soil profiles, mixing and filling, and contamination lead to variability. This can also lead to compaction; restricted aeration and water drainage, crusting and bare, often hydrophobic surfaces.  Importantly, interrupted nutrient cycling and modified soil organism activity result in unhealthy (low vigour) growth and predisposes plants to other environmental and biological stresses.
Tree decline is as a result of several interacting factors, such as prolonged drought, competition with adjacent trees, pest and disease infestation and generally depleted soil environments.  Poor soil structure is a significant predisposing stress factor for plants.  Poor soil structure affects water infiltration and permeability, water holding capacity, aeration status and loss of pore space.  If plants do not have access to sufficient water and oxygen they will decline.
Healthy soil requires organic matter (OM); it aids in aggregation (soil structure), cation exchange (storehouse of nutrients) and water holding capacity. But most importantly, it sustains biological life in the soil; the greater amount and diversity of biological life there is in a soil the greater potential for healthier plant growth.  Soil health is the basis for plant health and by extension, healthy plants can help develop healthy humans.
Tree Logic has commenced a trial to incorporate humus into urban soils. Ninety established Plane (Platanus spp.) street trees exhibiting decline symptoms, were treated using liquid humus, Seasol® and urea.  A number of trees in parks and reserves within an eastern Melbourne municipality were also treated.
A sample of the trees to be treated along with controls in close proximity that included healthy Planes and Planes displaying similar malaise were established prior to the commencement of treatments. The samples looked at current season shoot tip extension and leaf size. In addition, leaf samples were fluoresced and data captured on short and long term stress indicators. This data will be compared against future samples to determine the efficacy of the treatments over a 2 year period.
Injecting liquid humus into urban soils will start to build up the organic content of the soils which will aid water holding capacity, cation exchange capacity, and reduce leaching. Organic matter can also buffer effects of any pesticides and stabilise pH.  Treatments are carried out in autumn and spring (before bud burst). Humified carbon differs physically, chemically and biologically from the labile pool of organic carbon that typically forms in agricultural soils. Labile organic carbon arises principally from biomass inputs (such as leaf litter) which are readily decomposed.
In conjunction with the liquid humus the soils can also be injected with liquid nitrogen. In degraded urban soils the major nutritional limitation on plant growth is lack of nitrogen (Pulford, 1991). Without an adequate pool of organic nitrogen, which microbial activity breaks down into forms (NH4+ & NO3-), mineral nitrogen is quickly depleted in soils and nitrogen deficiencies develop. Low organic matter content is typical of urban soils consequently nitrogen is the nutrient most limiting to growth (Roberts, Jackson, Smith, 2006).
The other consideration is the on-going nature of the applications, that is, to be successful a number of applications will be required. Products, application timing and rates and costs could be developed upon request.

The redevelopment of the Hyatt’s Foyer is complete and the five Ficus hilli var. ‘Flash’ installed by Tree Logic are prospering in their purpose built habitat.

The project presented many challenges none less demanding than balancing the horticultural requirements of the plants against engineering constraints, interior design requirements and construction schedules.

Tree Logic was involved with the designers from the outset providing advice that ensured adequate soil volume was designed into the floor space, specifying soil media appropriate for growth that meet ?oor load restraints, securing appropriate species of a large enough size to create an impact and advising on appropriate artifcial lighting requirements to sustain the three trees that were located within the building.

That was the easy part.

The installation of the trees was undertaken in conjunction with the construction process which was demanding to say the least. Getting the materials we required including almost 70 cubic meters of soil media and five 6 meter tall trees weighing 1.2 tonne each into the site from Collins and Russell Street was a challenge in itself that was compounded by tight deadlines, even tighter access and the need to protect expensive floor coverings. Once we were in, drainage had to be installed, the soil media had to be carefully layered within the pits, the trees set, irrigation installed, moisture and temperature monitoring equipment fitted all completed whilst a myriad of other construction activities went on around us in close proximity.

In the final phases of the construction process, Tree Logic also had to ensure that the trees and the pits were kept free of building debris such as plaster and stone dust whilst monitoring and testing our systems.

With that all behind us, Tree Logic is now charged with the responsibility of maintaining the trees over the expected life of the design and developing their form to suit the space and, in time; create spectacular indoor trees.

Tree Logic would like to thank our staff, GHG, Bar Studios, Billard Leece, May Horticultural, Kanes Construction and Irene Gosney to mention a few for their patience and support through the delivery of this project.

In October, Tree Logic was set the task of transplanting a large maturing Azarole Hawthorn (Crataegus azarolus) located in old Salvation Army site where it had been planted 60 years earlier, to Victory Park in the very heart of Traralgon which is literally across the road.

The tree is listed on the Victorian Heritage Register as being of state botanical significance as the only known example of this specie or hybrid in Victoria. With the help of Rob Bodenstaff (Arbor Centre, WA), BS Callow, Gyra Engineering and various local sub-contractors including P & D Cranes, Maffra Trenching and RTL Transport; Tree Logic set about process for transplanting the 40 tonne tree.

How we did it

A root ball of over 5 meters in diameter was carefully excavated, roots were trimmed and the ball framed. A steel raft frame was constructed under the tree so that it may be lifted with a crane and placed on a transport vehicle. The base lift method of transplant was chosen over the more common practice of pin lifting, to reduce damage to the tree and to take a much larger root ball. Once lifted on to transport the tree was driven across the Princess Highway into Victory Park. The tree was planted proud of existing site grade to avoid any potential water logging of the root ball, was mulched and the site cleaned up.

The job was completed within 5 days. LaTrobe City Council will look after the tree for the next 2 – 5 years until it becomes re-established in the landscape. Parks and Gardens staff lead by Mick Cantwell were trained by Tree Logic in the nuances of managing and maintaining the tree over this critical period and we will be dropping in from time to time to see how the tree fares. Early indications are that it’s a happy team at Hawthorn.