Want A Rainforest Garden? Then Plant Dry, Not Wet…

Queensland Lacebark, Brachychiton discolor

Queensland Lacebark, Brachychiton discolor

The word rainforest makes you think of hot, humid, dense, leafy, evergreen forest, such as the Daintree, the world’s most ancient rainforest in far northern Queensland (FNQ).

The Daintree is famous for its curious trees, ferns, palms, cycads, mosses, epiphytes, vines and orchids. FNQ is about tropical, wet rainforest but that  isn’t the only rainforest type.

Tasmania has cool temperate rainforest, the Sydney basin has warm temperate rainforest, and the Scenic Rim of Queensland has subtropical rainforest. Each different climate has produced its own version of rainforest, but each has a wet climate for at least some of the year.

For inspiration, the most diverse collection of wet rainforest trees grows at the Royal Botanic Gardens, Sydney. For many FNQld species, the RBGS is the most southerly location they are grown. Some specimens, such as Ribbonwood (Idiospermum australiense), are also the oldest or largest examples of their kind in cultivation.

The rainforest display at the National Botanical Garden in Canberra is a special place where rainforest plants thrive in a drier climate with a frosty winter. Here inspiration comes from they way they are grown in a hostile climate – in a gully, sheltered by trees and coddled by irrigation. That display is a fine example of how microclimates can be modified to suit special plant collections.

But what happens to wet rainforest plants during drought? They either need watering of they suffer, sometimes severely. Watering restrictions in the 1990’s made keeping the rainforest displays at the RBGS quite testing. Lacking fresh water bores, or sufficient stored rainwater, those rainforest displays didn’t always cope well with drought. It was tough for the gardeners who cared for those displays to watch them suffer.

Plant Dry Rainforest

When gardeners plan or plant a rainforest garden, a slice of the Daintree is usually what they visualise. One type of rainforest that seems to be almost always overlooked is dry rainforest. To help visualise dry rainforest, imagine  Hoop and Bunya pines rising through the canopy of a forest where trees have smallish leaves. Typically for rainforest, there are vines and epiphytes, including orchids, and ferns.

The basket fern (Drynaria rigidula) and Elkhorn (Platycerium bifurcatum) have adapted to seasonal drought by dropping their fronds, remaining dormant until growth resumes after rain. Lichen too remains dormant until sufficient mist, fog or rain reawakens growth.

Some species are exceptionally rare, like the endangered Ormeau Bottle tree (Brachychiton ormeau). Several trees, like figs, shed their leaves to avoid dehydration during the hot, dry, windy springs and the long wait between brief, wet summers. Leafless Brachychiton trees also flower, often spectacularly. The Crown of Gold, (Barklya syringifolia), the town of Gladstone’s floral emblem, is another spectacular flowering tree.

For the gardener, the benefits of growing dry rainforest plants are they are more forgiving, need less water, and can be more colourful in bloom. Little Kurrajong and Crown of Gold are ideal flowering trees to develop a suburban dry rainforest garden. Dry rainforest species establish faster if well watered, however they are more drought-resistant if watered sparingly. Once established, dry rainforest species survive longer, hotter, drier spells and erratic rainfall better than wet rainforest.

So why not plant a dry rainforest instead? Some plants are already familiar, like macadamia, bunya and finger lime. (Yes, these species also occur in wet rainforest. Rainforest is more complicated than most of us realise, dry rainforest especially so).

When I worked at the RBGS, we highlighted differences between Australian rainforest types. Community Education and sometimes I offered interpreted tours to schools, VIP’s and the Friends of the RBGS. Here’s some of our interpretive information on drought-tolerant, water saving, dry rainforests:

Dry rainforests

Not all rainforests grow in areas receiving evenly distributed, abundant supplies of rainfall. Lesser known are the tiny remnants of Dry Rainforests scattered across the Kimberley, Top End, Cape York, and down the east coast of Australia.

Since they occur in regions with a distinct wet and dry season, the more northerly monsoonal forests survive in sheltered gullies and along the banks of rivers. Under moister, past climatic conditions, their ancestors were widespread across the continent. As the climate became less suitable for rainforests, those species best fitted for the arid conditions survived. They replaced species less able to survive in the new conditions and evolved to deal with the changing environment.

Along the east coast, marginal rainfalls or poorer soils support Dry Rainforests in sheltered locations. They often grow on rocky sites that are rarely subject to fire. Because some Dry Rainforest trees have a greater tolerance of arid conditions, communities can be found up to 300 km inland where suitable shelter exists.

The ability of some species to shed leaves in dry conditions is an advantage for Dry Rainforest trees, enabling them to survive temporary water shortage. Common species include Lacebark (Brachychiton discolor), Australian Teak (Flindersia australis), Hoop Pine (Araucaria cunninghamii), and figs (like Ficus superb var. henneana).

Characteristic features of dry rainforests

* Small to large number of tree species forming the low to medium canopy layer;

* Scattered, larger trees, with emergents rising above the canopy;
* Trees include semi-deciduous species (Brachychiton species) or conifers (Callitris species);

* Small average leaf size of canopy trees. Leaves are often hard and blunt-tipped;
* Palms are absent;
* Large vines are common and diverse;
* Vascular epiphytes (flowering plants, like orchids) either rare or common, but with few species;
* Mosses and ferns scarce, lichens abundant”;

Last autumn, I visited the Quaker Arboretum which participates in Open Gardens Australia, to see how their collection of dry rainforest plants is coping after two dry years (2013, 2014).

That garden is looking great. It’s certainly dry, but all the plants are coping well. They are mulched, but receive no irrigation.

Here is a consolidated list of Dry Rainforest Species, your introduction to the diversity of Australia’s mosaic of dry rainforest communities, many of which can be obtained from Greening Australia’s The Gap Nursery, or from Kumbartcho Nursery.

I’ve included a gallery of dry rainforest plants. Surprisingly, there are more beautiful blossom trees in Australian dry rainforests than in our wet rainforests.

If you want a successful rainforest, one that will stand the test of time and our continually surprising climate, plant dry not wet rainforest species.

Jerry Coleby-Williams

18th March 2014, revised 12th August