Aim: To contribute to environmentally sound practices in the ACT region through environmentally responsible horticultural and site management.
The Gardens strives to ensure that its activities demonstrate sound environmental practices, consistent with its status as a national institution.
The development of the Gardens adjoining Canberra Nature Park has required particular attention to minimising the potential for plants grown at the Gardens to become weeds in the Park. A buffer zone is maintained around the site where it borders the Canberra Nature Park and this is regularly monitored. Cultivation of plants with known weed potential is carefully managed to limit the possibility of their spread. The Gardens has also advised organisations selling plants from the site about plants with weed potential.
The Gardens position as part of the Sullivans Creek catchment has implications for both the quality and quantity of water released from the site. Water is currently collected through a stormwater drainage system before being discharged into Sullivans Creek. Water use in the Gardens is discussed further in Section 7.4.
Building and horticultural developments at the Gardens are planned with consideration for direct and indirect environmental impacts. The use of recycled materials is encouraged where appropriate and preference is given to plantation-grown timber products. Contractors working on site are contractually obliged to meet current ACT and Commonwealth environmental regulations.
Recycling of waste from offices, the cafe and horticultural activities is also encouraged.
Aim: To retain healthy remnant and regenerating native vegetation on the Gardens site for conservation and wildlife habitat and as a buffer between the developed gardens and the surrounding Canberra Nature Park.
Large areas of remnant and regenerating native vegetation have been retained on the site managed by the Gardens. Many of these are adjacent to extensive areas of bushland in the Canberra Nature Park on the eastern slopes of Black Mountain. The natural vegetation in this area is primarily dry open eucalypt forest with some remnant woodland on the lower slopes. The dominant tree species in the open forest are Eucalyptus mannifera, E. rossii and E. macrorhyncha. The understorey is a relatively sparse mixture of shrubs and tufted grasses.
This vegetation provides a buffer zone for fire and weed control between the developed gardens and surrounding Canberra Nature Park. A fire control irrigation system exists within the buffer zone along the western and southern boundaries. Firebreaks are maintained along fence lines in these areas.
A weed eradication program along the Gardens boundaries prevents exotic and native plants spreading to the surrounding Canberra Nature Park. In 1996 much effort was devoted to removing dense infestations of Acacia baileyana growing in the southern precinct of the Gardens.
Many naturally occurring trees remain in the developed part of the Gardens, particularly the northerly and westerly parts. Some of these trees are in decline because of changes in soil moisture regimes, damage to their roots and trunks from earlier developments, or because of the effect of pathogens including Armillaria or Phytophthora (see also Chapter 3). Old, large trees with hollows are retained even when dead (if they do not pose a safety threat) for the benefit of wildlife. Other smaller trees, dead or in serious decline and without obvious habitat value, are removed to allow for development as well as for aesthetic and safety reasons.
A previously constructed nature trail and bark hut, situated in the undeveloped western part of the Gardens, were decommissioned because of lack of resources to maintain the trail or to prevent vandalism to the hut. Walking tracks have been constructed throughout the adjoining slopes of Black Mountain, and Canberra Nature Park manages these.
Aim: To maximise the value of the Gardens as habitat for native wildlife to the extent consistent with the Gardens botanical, horticultural and visitor services functions.
The cultivation of flora from many parts of Australia has provided a variety of habitats within the Gardens, resulting in a reliable, year-round food supply which wildlife, particularly birds, now exploit. For example, the construction of water and rock features has provided enhanced habitat for Eastern Water Dragons. The impact of developments at the Gardens includes consideration of the potential impact on native wildlife.
Wildlife in the Gardens has been the subject of a number of research studies by staff, students of the Australian National University and others. Guided tours focussing on native animals, particularly birds, have been provided. Nocturnal tours to locate and view arboreal mammals have also been conducted.
While it is not the charter of the Gardens to display native wildlife, the importance and value of wildlife in the Gardens is well recognised as is the need to manage various species to protect the living collection.
Some native species, such as ducks and kangaroos, have increased in number due partly to the modifications of the environment of the Gardens. Wood duck numbers, for example, build up very quickly over a breeding season and cause problems by grazing plants, spreading weed seeds and fouling areas of the site. Brown snakes are frequently sighted in the Gardens over the hottest months and cause particular concern when present around the busy carpark, cafe and Visitor Centre areas.
Eastern grey kangaroos have on occasions caused extensive damage to the Gardens living collections by trampling and grazing plants. In conjunction with wildlife authorities, it has been necessary to manage kangaroo numbers. A kangaroo management plan has been developed in consultation with ACT Government authorities, which is consistent with the EPBC Act.
The use of chemicals in the Gardens is recognised as a potential threat to wildlife, particularly birds and beneficial invertebrates, and there has been a considerable reduction in the use of chemical pesticides in recent years.
Exotic animals such as cats, foxes, rats, dogs and blackbirds are found in the Gardens. All such animals pose various threats to native wildlife through predation, competition for food and shelter and transmission of disease.
Aim: To provide reliable, efficient and cost-effective water and power supplies to Gardens facilities and provide safe, efficient and environmentally sensitive reticulation of services throughout the site.
The Gardens is serviced by electricity, gas and water supplies from the local distribution systems.
Three major electricity supply lines service the site. Two overhead power lines service the northern area. The southern area is serviced by an underground supply service, which is partly reticulated through the site by overhead lines. A further supply line services the Franklin Building in the southern part of the Gardens.
Gas is supplied to both northern and southern areas and is separately metered for each area.
Water supply is vital to the management of Gardens collections and it is all currently supplied from the ACT water supply. An extensive irrigation system, controlled by a number of isolated electronic irrigation controllers, covers the site to support the Gardens extensive plant collections. This accounts for around 98 per cent of Gardens water use.
The Gardens has investigated the potential for using water from alternative sources such as Lake Burley Griffin, and groundwater from bores. To date they have not been considered feasible or suitable for horticultural use. A water audit of the Gardens was conducted in 1997 to determine ways in which the Gardens could more efficiently use water, particularly in relation to irrigation practices and technology.
As a result of the 1997 study, training was provided to all horticultural staff on modern irrigation practices and some new irrigation technology was installed for trials. Investigation of water losses from the system also resulted in the location and repair of a number of leaks from the ageing water reticulation system.
While water use in buildings is low in comparison to irrigation use, a program of water efficiency measures such as the installation of dual flushing cisterns in toilets and preventive maintenance of plumbing fittings is conducted on an ongoing basis.
The quantity and quality of stormwater released from the site is a matter of concern because of its potential effect on the surrounding environment. Limited opportunities exist on site to retain stormwater, and the quantity of water released has implications for stream flow beyond the site. The use of fertilisers as part of the horticultural management of the plant collections is carefully controlled to minimise the potential for excessive nutrient release from the site.
The most energy intensive sector of the Gardens is the nursery, where glasshouses are used to hold collections of tropical and sub-tropical plants and heated beds provide the necessary conditions for plant propagation. Several glasshouses at the Gardens have been renovated to include thermally efficient materials. Energy savings of around 40 per cent are expected from these works but further work is required to enhance the energy efficiency of nursery operations.
Air-conditioning, heating and cooling in buildings also accounts for significant energy use. The age and quality of construction of some site buildings does not promote energy efficiency. Remedial works have been undertaken where practical.
The Gardens aims to operate in an environmentally responsible manner.
Aim: To adopt management practices that minimise waste generation and promote recycling of waste materials.
The Gardens produces waste products related to horticultural management, site development, visitor use and office based activities.
General waste collection and disposal services are managed under contract. Bulk materials and non-recyclable plant waste are delivered to authorised waste disposal sites by Gardens staff.
The bulk of waste generated at the Gardens is related to sound horticultural management and consists largely of plant material. Where possible, and giving consideration to horticultural hygiene practices, waste plant materials are chipped and composted on site for reuse as mulch. Limited release of waste plant material for firewood, or for use in craft activities, is also undertaken from time to time. Material that cannot be reused is sent to landfill sites in the ACT.
Site developments including new landscape features, buildings and infrastructure requirements generate waste products such as concrete and excavation spoil and building materials. Contractors are encouraged to comply with the Development Control Code for Best Practice Waste Management in the ACT.
The Gardens has, wherever possible, adopted the waste management strategy outlined in the ACT Governments waste strategy for Canberra No Waste by 2010. The ANBG has instituted a no bins policy to encourage visitor awareness of waste disposal issues. The policy has been largely successful, with very little litter being generated by public use of the site. Recycling collection facilities are available for public use. The cafe also separates glass and metal products for recycling.
Most offices at the Gardens are provided with paper recycling facilities and staff are encouraged to sort high quality paper products for this purpose.