Literature Review: Giant Trees

by Carl Strang

Today’s posting is a literature review entry that relates to a lesson from travels. The topic is giant trees. Let’s begin with a recently published study.

D. Y. P. Tng, G. J. Williamson, G. J. Jordan, D. M. J. S. Bowman. Giant eucalypts – globally unique fire-adapted rain-forest trees? New Phytologist, 2012; DOI: 10.1111/j.1469-8137.2012.04359.x

This study was described in a ScienceDaily article. Only 50 species of trees worldwide exceed 50m in height. Many live in the Pacific Northwest of North America, and on Borneo, in rainforest ecosystems. In contrast, 13 are eucalypts in Australia. How to think of the latter ecologically has been problematic, because they live in rainforest environments, but are fire-adapted. One of them is the tallest flowering plant in the world, Eucalyptus regnans, Australian mountain ash. According to co-author Bowman, “Our research suggests gigantism in eucalypts evolved opportunistically within the last 20 million years when the ideal environmental conditions for rapid tree growth were combined with the presence of wildfire.” The researchers conclude that the trees belong as part of the rainforest, ecologically, because their large size is made possible by the rainforest environment. They live in the edges of rainforests, however, where fires reach on rare occasions, and these trees have become dependent upon fire for successful reproduction. Though the fire kills the trees, it also opens up the environment, releases nutrients to the soil, and removes seed predators, resulting in favorable conditions for reproduction.

Have you seen any of the giant trees? If not, I urge you to put that experience on your bucket list. I have had the good fortune to meet two such species, as I covered in an earlier Lessons from Travels post.

This is Eucalyptus regnans, which is known in Tasmania as the swamp gum, but in the paper cited above is called the Australian mountain ash.

The giant redwood was the other species featured in that post. The study cited today points to the rainforest environment as the factor that makes such large tree size possible. That contrasts to our local much lower rainfall, limiting the size our trees can attain. The other emphasis in this paper is on fire. Many of these eucalypts have adaptations that encourage fires.

Many of the eucalypt trees actively shed their bark in strips, building a layer of litter that supports fire.

Perhaps such encouragement is necessary in a rainforest environment where fire may need help. In our local environment, the climate is dry enough that fire has no such trouble.

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