Tuesday, 24 May 2016

Rare redwood at dawn


Some time ago a reader, Rob Dabal, encouraged me to write more on plants in the Royal Botanic Gardens Victoria collection that are extinct in the wild, or nearly so. Rob was responding to a post on my South American botanic garden trip where I mentioned (in passing) the extremely rare Easter Island pea, Sophora toromiro.

I've already provided some background to the Ginkgo or Maidenhair Tree, Ginko biloba, now either extinct in the wild or represented outside gardens by a few trees in China. And much has been written about the Wollemi Pine, Wollemia nobilis, and the discovery of 100 or so trees north of Sydney in 1994.

The Dawn Redwood, Metasequoia glyptostroboides, is worth a separate post. It's also timely, as we head towards the end of autumn. The Dawn Redwood is one of a handful of conifers (pine relatives) that looses its leaves for winter. That is, it's deciduous (as is its close relative, the Montezuma Bald Cypress, Taxodium distichum, one of which is our tallest tree in Melbourne Gardens).

We have two specimens of Dawn Redwood in Melbourne Gardens, one in about the middle of Eastern Lawn (the big expanse of grass dotted with trees and those fantastic forked Grass Trees), the other (photographed here) near to Gardens House and the perennial border. The image at the top was taken last week, at dawn. This next one in early April, later in the day.


It's a tree you'll find all over the world in botanic gardens, and some major parks and even private gardens, but it's extremely rare in its native habitat, now persisting in only a few small stands. Unlike the ginkgo, we are confident the Dawn Redwood has maintained this foothold (roothold?) without human intervention, although now it's human rice cultivation in addition to poor reproductive success that threatens its survival in 'nature'. 

The story of the Dawn Redwood is very similar to that of the Wollemi Pine in that it was known from the fossil record and thought to be extinct until a small population was brought to the attention of the scientific community. In the case of the Dawn Redwood it was a young forester, Wang Zhan, who made the first botanical collection, in 1943 (branches of the Wollemi Pine were first collected by a Park ranger, David Noble, in 1996).

The tree was well known, and respected, by the local village who had erected a simple temple in its honour. We now know there are a number of small populations near the border of Hubei and Sichuan provinces in western-central China. Both the Wollemi Pine and the Dawn Redwood were rushed into cultivation, first in botanic gardens and public parks, and then a few years later commercially. 


According to our horticultural historian, Roger Spencer, seed arrived at Royal Botanic Gardens Victoria in 1947, and the first trees were seven metres tall by 1961. The two alive today I presume came from that original batch, so the one photographed here near Gardens House (above again in early April) could be just under 70 years old (although it looks younger than the other). It's probably 20 metres tall.

Like the Wollemi Pine there is only one species of Metasequoia extant today. I gather the common name 'Dawn Redwood' is actually an oblique reference to its fossil record, and it's presence at the 'dawn' of conifer time. It's commonly thought to be a simple reference to the red-bronze foliage at this time of year. I like to think of it as recognition of the time of day when Wang's first saw his tree, at dawn, on 21 July 1943.

While superficially like the Coast Redwood (Sequoia sempervirens) and Giant Redwood (Sequoiadendron giganteum), and other members of the Taxodiaceae family (including, more closely, the Montequma Bald Cypress) it can be distinguished by the deciduous leaves arising opposite one another from the stem in a feather-like arrangement. Reminiscent in fact of our Wollemi Pine.


Like the Wollemi Pine, it has separate female and male cones. These next photos (taken just after dawn in mid April, as the leaves were turning) show the ladies first. The female cones were higher in the tree, like the Wollemi Pine...


Also like the Wollemi Pine, we grow this species in our gardens, and particularly in botanic gardens, to preserve the species. At the same time we encourage conservation in its native habitat, so that all the organisms that depend on this tree and the tree depends on itself, can survive the human epoch.

3 comments:

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