«Proceedings of the th 14 National Street Tree Symposium 2013 ISBN: 978-0-9806814-1-3 TREENET Proceedings of the 14th National Street Tree Symposium ...»
The other problem encountered with tissue culture is selection. If the plants are initiated into culture from seed, how do we select them for their ornamental characteristics? The first selection step is the actual initiation in culture – the line must multiply, root and survive acclimatisation in sufficient numbers to be economically viable. Then, plants are set out to field trials to wait for flowering. This is most likely to take 5 years from seed, and for that whole time the lines must be maintained in tissue culture, with regular subculturing to maintain the health of the plantlets. If you are very lucky, you might get a line that flowers early, say, within 2 and a half years from seed. And it might have a flower colour that you are looking for. And it might have a habit that is desirable for home gardens and urban forestry. This is when you would need to start large scale field trials, in pots and in ground, to more thoroughly determine the characters of the new variety and make sure it is stable.
The OEDP and collaborators are very happy to say that they were lucky that such a line was found, and we are progressing this little wonder plant through the field testing process as we speak.
The full report from this project is available from Horticulture Australia Ltd (http://www.horticulture.com.au/) But what has all this got to do with ‘Designer Trees’ and eucalypts in suburbia?
In Australia, our external environment is full of eucalypts. In the country areas, there are areas of remnant native vegetation, mixing with farmland with planted trees, some endemic, some from other parts of Australia.
They are part of the landscape, and give a sense of place. In urban environments, the trees are fewer, and less comfortable in their surrounds. Often, they are majestic large trees, memories of a time prior to white settlement, but now causing conflicting emotions and opinions as humans try to reconcile a huge tree and its importance for habitat, air quality and human happiness with the problems of sheer size, water-seeking roots, limb dropping, ‘messy’ flowers, and resident wildlife. Sometimes, the trees are the result of well-meaning Council planners and enthusiastic gardeners, planted 30-40 years ago, untried and untested, possibly with unrealistic expectations as to their growth and impact on the environment. These trees are now creating problems and ill feeling in the community.
Ironically, conversations along the lines of “we need to plant more eucalypt trees in our urban environment” precede “My neighbour planted a eucalypt and it’s too big and its shading/dropping leaves on my garden”.
How can these conflicting opinions be reconciled? Are ‘designer trees’ the answer?
Take a set of characters that a tree should have: the height, the architecture, the canopy density, the vigour.
Sometimes, the flower and leaf should be considered too. Now, look at all of the species (eucalypts in this case) and identify which species have what characters. Mix that with a good understanding of the relationships between species, the reproductive biology and genetic relatedness; develop a program to cross breed different species with desirable characters, and (hopefully) produce a new plant with the characters you want.
For example, Corymbia maculata grows well in the eastern states, has a good upright habit, minimal limb drop (reportedly), but the bark, while attractive, is grey. C. aparrerinja on the other hand, has a glorious white trunk, but is a spreading tree from the sub tropics. Can the two be bred together, to result in an upright tree with a white trunk that grows well in most locations in Australia? In this case yes, however, the process of breeding new trees isn’t quick; it can take 5-10 years to produce the new tree and road test it, and get it ready for wide spread use.
The 14th National Street Tree Symposium 2013 It’s easy to see that many of the trees, be they eucalypt or other, in our urban forests are in decline, or will be soon, from age, inappropriateness, climate change, disease. For example, the City of Melbourne Urban Forest Strategy 2012-2032 reports “Modelling shows that within the next ten years, 23% of our current tree population will be at the end of their useful lives and within twenty years this figure will have reached 39%.” (City of Melbourne Urban Forest Strategy Revised Draft, September 2012).
These trees will need to be replaced, and the choice of what will be used to increase, renew and revitalise the Urban Forest across Australia becomes important. The same varieties and species that are currently planted could be planted again, or, we could look to a new generation of trees. Designer eucalypts could find an increased presence in our cities, and if they are more suited, planting them could take precedence over exotic species.
Armed with over 15 years of experience, the OEDP is about to embark on a new breeding program, to ‘design’ the ‘right eucalypt for the right place’. We aim to develop a range of trees that are suitable to a range of climates, or for more specific ones; that have the shape, size, flowering, trunk colour, that is sought by designers; that will be disease resistant, low maintenance, non-invasive and ‘safer’; that will increase city biodiversity and keep humans happy and healthy. It’s a long term project and will not succeed without input from nurseries, advanced tree producers, landscape architects, councils and arborists, so expect to hear more from the OEDP soon.
Acknowledgements The OEDP would like to acknowledge the contributions of many organisations and people, without whose
contribution this work would not have made it this far:
Horticulture Australia Limited, Rural Industries Research and Development Corporation, The Playford Trust, the Frank and Hilda Perry Trust, Don and Margaret Laidlaw and the University of Adelaide.
Humphris Nursery (Vic), Narromine Transplants (NSW), Yuruga Nursery and Clonal Solutions (FNQ), Longford Flowers (VIC), Redlands Farming (QLD) and AUSBUDS (NSW/QLD).
Professor Margaret Sedgley; Drs John Conran, Andreas Klieber and Graham Collins; Drs Michelle Wirthensohn, Cassandra Collins and Justin Rigden Drs Erminawati Wuryatmo, Pauline Glocke, Jenny Guerin, Leanne Pound, Toby Knight, Meredith Wallwork, Chockpisit Channuntapipat, Carol Walker, and Sunita Ramesh; Ms Kirsty Neaylon, Ms Di Smit, Mr Narhoja Omarhoja, Ms Susan Bankes, Ms Sonali Mookerjee, Ms Alex Freebairn, Mr Sam Freeman, Ms Jan Nei Hing, Mr Jeremy Prater, Ms Kelly Swain, Mr David Sinclair and Master Edison Sinclair.
Mr David Lawry OAM and Mr Glenn Williams TREENET
For further reading about Sue O’Keefe’s subject matter refer to the following publications:
“Water management and healthy ageing in rural Australia: economic, social and cultural considerations.” Environment and Behaviour, accepted 31 July 2013 (in press) Maureen Rogers, Rachel Winterton, Jeni Warburton, Suzanne O’Keefe
Abstract Recycled water is one of the main water resources with substantial contribution to increase the security of future water supplies. Scientific and technical studies are required to maximize this contribution through developing water recycling opportunities and reuses particularly for green space irrigation to provide environmentally, socially and economically sustainable environments. The use of municipal recycled water for green space plants is a valuable attempt to use the easily available water resources but it requires a monitoring system to mitigate the possible inverse impacts on the soil, plants and water systems. Variables such as climate, irrigation methods and frequency, plant species and soil can have a profound effect on the sensitivities of plants to salts and toxicity. Soil drainage, irrigation application rate, water quality, rainfall characteristics and plant canopy shade can influence the long-term effects of salinity, and toxic effects of chemical compounds on the vegetation health. It is, therefore, important to have information specific to each individual plant species, as well as information on all the above-variables, specific to each locality, in order to properly plan and manage water requirements of specific landscapes. In this paper the main potential inverse impacts of reuse of recycled water for irrigation is discussed and Adelaide parklands as a case study is briefly reviewed.
Keywords: Recycled wastewater, reuse wastewater, Irrigation, Adelaide Parklands Introduction Rapid urbanization and industrialization have increased the pressure on limited existing fresh water to meet the growing needs for food production and keeping environment in a healthy condition. Utilizing efficient irrigation systems and using alternative sources of water, such as recycled wastewater, to meet the growing demands would be a positive response to this concern (Hassanli et al, 2010). The majority of urban water supplies for irrigation are used to maintain vegetation health, appearance and municipal amenity (Nouri et al, 2012). Climate change is also threatening Australian urban water supplies through increasing evapotranspiration and decreasing precipitation. The most severe climate change impact is expected in the southern and eastern regions of Australia (Collett and Henry, 2011).Increasing water use efficiency and also water efficiency in urban landscapes are achieved by supplying only the amount of water that the plants require to maintain healthiness and aesthetic appearance. The water demand of urban landscapes is quite different from agricultural crops and turf grasses due to the specific conditions in urban green spaces (Costello et al., 2000).The use of recycled wastewater has been identified as a potential sustainable irrigation practice and one of the management approaches. Recycled wastewater may potentially contain pathogens and levels of chemicals deleterious to vegetation and the environment. Although low concentrations of certain chemicals may not have immediate and obvious toxic effects on vegetation or the structure of the soil, bioaccumulation may occur, causing long-term chronic effects(Salgot et al., 2006). Continued irrigation using recycled water, in long term could exceed the soil’s adsorption capacity for salts (Nable et al., 1997). Particularly during dry seasons when there are few rainfall events which could leach the salts from the soil. Soil structure can be affected by excess sodium in irrigation water (Hassanli et al, 2007) which reduces soil aeration and water filtration rates. This, in turn, leads to water logging, excess runoff and restricted root growth. In this paper the potential inverse impact of reuse of recycled wastewater for landscape irrigation is discussed and Adelaide parkland as a case study would be reviewed.
The 14th National Street Tree Symposium 2013 Salinity and general toxic effects of recycled wastewater The level of salt accumulation within the soil depends on a number of different factors: physical and chemical characteristics of the soil;
annual precipitation; evapotranspiration; the annual water application and most importantly, the concentration of salts in the irrigation water(Lazarova and Bahri, 2005).When the levels of dissolved salts are high in the soil, additional energy is required for plants to take up water from this medium. The increased osmotic pressure of salty soil water is the reason for this higher demand on the plant’s energy resources. Symptoms of salinity stress are similar in most plant species. These symptoms include leaf scorching, (Fig. 1) mottling or shedding and twig dieback in angiosperms (Azza Mazher et al., 2007).
Each plant species has a specific salinity tolerance level above which the growth and productivity of the plant is affected ( Azza Mazher et Fig.1: Toxic effects of salinity on al., 2007). The salt tolerance variation of different plants and a typical leaves(Las Pilitas Nursery, n.d.) crop response to salinity are shown in Fig. 2.
Figure 2. Salt tolerance variation of different plants (a) and a typical crop response to salinity (b) Halophytes which occur naturally in saline conditions are often not as badly affected as non-halophytes which may die more readily under excessively saline conditions.
Environmental conditions may also have an effect on each species’ response to salinity. In general excessive salinity inhibits vegetative and reproductive growth and sometimes induces changes to plant morphology and anatomy. The most common toxic elements in wastewater are Sodium (Na), Chloride (Cl) and Boron (B). For landscaping and agricultural purposes, the most important components are those chemical elements that have an effect on the growth of plants and the structure and permeability of the soil (Pedrero et al., 2010). Different soils, drainage, irrigation methods and amount of shade will influence the long-term effects of salinity, and chemical elements on the vegetation.
Ongoing foliar irrigation can lead to toxic levels of Na, Cl and B in the leaves of plants. Although all species respond differently to foliar irrigation application, generally, the amount of foliar damage has been in direct proportion to the frequency of sprinkler treatment (Devitt et al., 2003). An excess of any irrigation can cause water logging and secondary salinity.
The 14th National Street Tree Symposium 2013 Toxic effects of sodium on plants Soil with excess sodium may exhibit changes in soil structure. These changes could reduce the rate of water infiltration and aeration of the soil. This in turn reduces the water available for uptake by plants and could also increase the amount of sodium taken up in the water by plants. The toxic effects of sodium accumulation in plants are evidenced by leaf mottling and necrotic patches (Fig.3) on the leaves (Stevens et al., 2008). High levels of sodium also cause damage to the root cells and can interfere with the photosynthetic processes of the plant. Woody plants are particularly vulnerable to the toxic effects of sodium as the symptoms are not seen for some time (Stevens et al., 2008) since the Figure3. Necrotic patches caused excess sodium accumulates in the roots and trunk. The uptake of essential by sodium toxicity on a grape vine macronutrients by the plant can also be affected when high levels of (PIRSA, n.d.) sodium are present in the soil (Stevens et al., 2008).