A walk in a rainforest

Sunday, 11 July 2010

Broadwater State Forest

During my recent trip away, I spent a pleasant day in the Broadwater State Forest in North Queensland (near Ingham). We went for a walk in a 'wet tropical' rainforest there, and the vegetation was such a contrast to that I'd seen during my walk several months ago in the dry sclerophyll bushland in Yengo National Park in Sydney. Whilst I admire and enjoy our Sydney bushland and its plants, the rainforest seemed to offer me more ideas for my own garden.

Roots of huge fig tree at Broadwater

Upon entering the rainforest, we were immediately enclosed by a lush canopy of towering trees, and the area was almost all in semi-shade. Most of the trees were huge soaring specimens such figs (such as Ficus macrophylla, ht 39m) with immense buttressed roots, majestic fan palms (Licuala ramsayi, ht to 15m) and black beans (Castanospermum australe, ht 40m) with their amazing woody seedpods, but they reminded me that many of the smaller native rainforest trees are actually very suitable for growing in our Sydney gardens. In general, these are sleek, evergreen, glossy-leaved trees often with striking, unusual-looking flowers and interesting seedpods or berries. Some have attractive bark; others have beautifully coloured new spring foliage growth. Often growing very tall and slim in their native rainforest environments, in an open garden setting where they do not have to compete for light and nutrients, they tend to be shorter (about a half to a third their natural size). Unless trained by the gardener to a single bare trunk, they are usually bushy to ground level, making them suitable as screens, hedges or windbreaks if preferred. They can be planted close together to form a cool, tranquil mini-rainforest plot, with a canopy of leaves, as they occur in their natural environment, to create a shady retreat for shade-loving smaller tropical plants.

These trees generally enjoy our Sydney climate, like humus-rich, well-drained and mildly acidic soil, prefer regular mulching, watering (especially in their early years) and fertilising - like most of the exotic plants which we grow in our gardens, so they mix quite well with these. Frost can be a problem for tropical rainforest trees, especially in their early years, so protection should be given to such specimens in very cold suburbs. Some need a little shade when young.

Pods of the rainforest tree Castanospermum australe, often called the black bean

Examples of these trees which do well in Sydney gardens include the various lillypilly (Syzygium) species and varieties, with their distinctive new growth and striking berries; lemon-scented myrtle (Backhousia citriodora, ht 6-8m) which has leaves with a strong lemon scent when bruised and a profusion of fluffy cream flowers in spring and summer; blueberry ash (Elaeocarpus reticulatus 8-9m) with racemes of dainty fringed, waxy, bell-shaped flowers pink or white from spring to early summer, followed by rounded dark blue fruit; native frangipani (Hymenosporum flavum, ht 6-9m), with highly fragrant creamy flowers which age to deep yellow, in profuse clusters in late spring; and macadamia trees (such as Macadamia tetraphylla, ht 8-12m) with long hanging spikes of fragrant starry small pink or white flowers in spring and edible nuts ripening in late summer/autumn.

Canes of Calamus australis on a host tree

Another aspect of the rainforest that struck me was the way that the plants interacted with one another, which to me gave a feeling of vibrant dynamism. The plants do this in order to compete for light and nutrients. Native orchids as well as bird's nest ferns (Asplenium australasicum) and staghorn ferns (Platycerium superbum) grew in the crevices of trees; and we also encountered the mysterious 'wait-a-while' or lawyer plant (Calamus australis, ht to 25m), which looks like an innocent palm tree when young but develops strange long canes that viciously hook onto other plants (or unsuspecting people), using these to hoist itself upwards into the canopy. The mature canes of this plant are used for rattan furniture. Strangler figs (Ficus species) show one of the most aggressive forms of plant interaction in a rainforest, taking over and finally killing the host tree in which they begin their lives as ephiphytic seedlings high in the canopy.

It made me determined to grow more epiphytic plants (not strangler figs, though!) in my own garden: something I had already started to do in a tentative way by tying bromeliads, zygocactus and orchids (such as the native Dendrobium speciosum) onto branches of trees to create an intriguing vertical garden effect. I hope to write more about these once they become more established.

Unusual fungus at Broadwater

I was also fascinated by the variety of spectacular fungi that abounded on dead trees and on the forest floor, manifesting the endless cycle of growth and decay in the rainforest. In our own gardens, we don't often see the organisms that break down our dead plants to create compost to nourish other plants - in the rainforest that drama was everywhere!