USING NATIVES TO AN ADVANTAGE

The difference between drought-tolerant natives and heat-tolerant natives lies in how they manage environmental stress.

Not all natives are the same. Trees that have evolved in a hotter climate will generally handle heat better. While their systems have acclimatised or adapted to withstand higher stress brought on by heat, they may still require adequate moisture to thrive. These adaptations over time include producing lighter coloured foliage and thicker reflective leaf surfaces as a way of preventing overheating.

Native trees such as Tristaniopsis laurina (Water Gum), Waterhousea floribunda (syn Syzygium floribunda) (Weeping Lilly Pilly), Lophostemon confertus (Queensland Brush Box) and Corymbia maculata (Spotted Gum) have wider leaves and a denser structure. They create a thicker canopy for shade but require moisture for their transpiration system to work effectively.

Natives for Heat Tolerance Left to Right: Tristaniopsis laurina ‘Luscious,’ Waterhousea floribunda ‘Whisper,’ Lophostemon confertus, Corymbia maculata ‘Lowanna’

Similar to how we sweat as humans, water is used to regulate temperature and if too hot, moisture vapour transpires through thousands of little holes in their leaves called stomata, cooling the leaf surface and air around them. Stand beneath these trees on a hot day and it is noticeably cooler.

Consider heat tolerant trees if you experience hot temperatures in your area, or spasmodic periods of dry but have adequate water supply either via irrigation or rainfall. Heat tolerant natives are high on Council agendas as they suit plantings in built up areas, in cities for example, in and around roads and footpaths which attract and absorb heat. These areas are cooled due to the shade and the trees acting as evaporative coolers.

Drought-tolerant trees on the other hand suit planting in dryer spaces, hot, dry climates and in areas that are heavily reliant on rainfall for water. Drought-tolerant trees are often those trees used in low-maintenance landscapes. A great example is with the Brachychiton species with its bottle-shaped trunk for water storage.

Natives for Drought Tolerance: Left to Right: Corymbia citriodora, Eucalyptus Scoparia, Banksia integrifolia, Allocasuarina littoralis

A tell-tale sign that a native tree is more suited in drought is the presence of smaller and narrower leaves, sometimes waxy, silver or grey in colour which helps to reflect sunlight. These natives are also characterised by deep-root systems with an evolved ability to store water in roots, leaves and stems. The stomata on these types of trees close due to the intense light on hot days, so they don’t transpire as readily. While they will provide shade it is often light shade and with the lack of transpiration, the cooling these trees provide, is less.

Examples of drought-tolerant trees include Banksia integrifolia (Coastal Banksia) with its waxy leaves, Eucalyptus sideroxylon ‘Rosea’ (Ironbark) with thick bark hence its name, Allocasuarina species (Sheoak) with its fine needle-like leaves, Eucalyptus Scoparia (Wallangarra White Gum) and Corymbia citriodora (Lemon-scented Gum) with its long slender leaves.

For more information, visit Speciality Trees at the links below