Southern Beech

One genus typical of the Gondwanan flora is Nothofagus - the ‘southern beech’ or the ‘black birch’ trees. Southern beech can be found in broadleaf forests of Tasmania, New Zealand, and South America. The leaves of these trees are smaller than those of the northern-beech, a little glossier and slightly more serrated. Only on young trees does the bark resemble that of oak or beech. The large lenticels are more like those of a birch tree. The small nuts are encased in an involcre that opens like those of a beech. The southernmost species are deciduous and fairly winter hardy. Winters in Patagonia and Tasmania are not quite as chilling as those in Canada. Nevertheless, these southern forests are subject to both snow and frost.

Metasequoia or Dawn Redwood

Meatsequoia, dawn redwood or shui shan (Metasequoia glyptostroboides) is a conifer in the baldcypress family (Taxodiaceae). It is a forest tree with a broad tapering crown. Its needles are arranged in a plane like those of the coast redwood or the baldcypresses. Twig are arranged oppositely in flat splays. Like baldcypress it is deciduous, dropping needles and small twigs in the autumn. Its cone is round and globular, like a redwood's. The bark is orange-reddish. Like both baldcypresses and the redwoods it is a fast growing tree. In less than fifty years it can reach 30 metres in height.

Metasequoia has been known to the people of the Hupeh region of China for centuries. Surprisingly, the genus was not catalogued by scientists until 1941, when a Japanese paleobotanist, Shigeru Miki, distinguished it from other redwood fossils. Before that time, the Metasequoia genus was only known from fossils! Then, in 1944-45, a Chinese forestry professor, Gan Duo, recognised that here were living specimens in the Hupeh region!

Metasequoia was much more common before the current set of ice ages. The genus was once native to both Asia and North America. Metasequoia during the Eocene lived as far north as Axel Heiberg Island, as the fossil record clearly indicates. The ranges of both the redwoods and metasequoias have shrunk back drastically since that time. Now all redwoods are native to the Americas, and wild metasequoia occur only in Asia. Perhaps they could not adjust well to the climatic fluctuations during the last set of ice ages.

In the late 1940s specimens of this so-called living fossil dawn redwood were shipped to gardens all over the world. In many temperate regions of Europe and North America plantings have grown to over 30 metres in less than fifty years. In its growth rate it is much like the redwoods, which grow rapidly in the first few decades. Redwoods and baldcypresses can live for a millennium or more if they are not disturbed. No one knows how long the metasequoia can live. The specimens in China are not particularly ancient.

Metasequoia is fairly tolerant of cooler temperate climates such as occur near Toronto. It is a rather peculiar looking tree. Like baldcypress and tamarack it is bald in the winter, and looks like a 'dead pine'. Yet it is a curious conifer of medium hardiness. If one appreciates conifers it is a good arboretum choice.

Redcedar & Junipers

Eastern redcedar, redstick cedar, pencil cedar, Virginia juniper or baton rouge (Juniperus virginiana) is a conifer in the Cupressaceae family. Redcedar can be up to 16 metres tall, with a very pointed dense crown. The foliage often has a dark reddish cast. The evergreen has short pointed needles tightly appressed to the three to four-sided twig. The leaves are prickly, unlike arbor-vitae or cypress leaves. Like most junipers it is usually dioecious, but monoecious (hermaphrodite) trees do occur. Juniper cones have fleshy cone scales, which make them superficially berry-like. When mature the 'berries' turn bluish or purplish and are eaten by birds, which can pass and disperse the seeds. The wood is soft, reddish and excellent for carving and woodcraft. The bark is fibrous and reddish. The redcedar is native to the Carolinian forest, and it is most common in the drier upland regions.

Eastern redcedar has two main 'races'. J. virginiana var. crebra has a pointed crown, and grows mostly in the north-east. The variety south-west of the Mississippi and Great Lakes has a broader sprawling crown. They are definitely the same species, as they hybridise where the ranges overlap.

Juniperus is a genus common to North America, Eurasia and Africa. Junipers generally grow in dry well-drained soils in the uplands. Often they grow where other trees cannot survive. There are at least 70 juniper species in the world. The small Utah juniper (J. osteosperma) graces the dry hilltops in the Great Basin and the Sierras. The larger Rocky Mountain juniper (J. scopulorum) grows mostly in the southern Rockies. One-seed juniper (J. monosperma) is a juniper of the semi-arid American south-west and Mexico. The strangest juniper is the most common species. The common juniper (J. communis) grows from the boreal forest, to the northern Rockies, across to north-temperate Eurasia, and in montane North Africa. Common Juniper is circumpolar in distrubution, with racial variations from flat-shrub to full tree size. This genévrier is the species from which gin gains its flavour. Without the 'berries' gin would be a sort of bland whisky.

Ginkgo

Ginkgo biloba, also called ginkgo or gingko, is a gymnosperm in the Ginkgoaceae family. It is a deciduous gymnosperm, which is not totally unusual, several other conifer species loose their leaves in the winter. However, the ginkgo leaf is broad and fan-shaped, with bifurcating veins that radiate out from the leaf petiole. Superficially, the leaf form looks like a maidenhair fern leaflet. Only a few 'conifers' have broad leaves nowadays, but in the Mesozoic era many gymnosperms had broad leaves.

Ginkgo biloba is the last species of the Ginkgoaceae to survive to modern times. Apparently, the number of ginkgo species declined over the millennia until only one remained. Seven million years ago ginkgoes of various species grew in the Americas and Eurasia. Today ginkgo apparently grows wild only in the Tian Mu Shan reserve in eastern China. In the 1800s ginkgo survived predominantly as a cultivated tree. Chinese and Japanese gardeners planted ginkgo as an urban tree and garden ornamental. Most of the wild ginkgo stands in China have long ago been cleared for farmland or logged over. If not for human cultivation the plant would have become extinct. The scarcity of wild ginkgo is remarkable, considering how very hardy the tree is. Today the ginkgo is planted all over the temperate world as an stress tolerant urban tree.

Ginkgo has a pyramidal crown, like many other gymnosperms. It can grow to at least 30 metres in height. In the autumn its leaves turn a beautiful bright yellow, before they fall. Ginkgo is dioecious, male and female sporophylls are on separate trees. The male strobilus is catkin-like and produce windborne pollen. The sperm cell in each pollen grain is flagellated, like the sperm of ferns. Female sporophylls contain only a few ova each. After pollination these grow into plum-like seeds. Usually only one or two seeds develop fully on each raceme. A fleshy husk covers each seed. The husk becomes fetid and has a rancid odour when the seed matures. Wild foxes, racoon-dogs and sometimes squirrels, eat the 'fruit', even though it is slightly toxic. These animals do not seem to be effective seed dispersers.

Ginkgo diaspores may originally have utilised a dispersal strategy similar to the walnuts. The rather poor tasting husk may discourage most casual fruit eaters, but does not deter animals that horde nuts, like squirrels. Such creatures leave a portion of the surplus nuts or diaspores that they bury. Indeed squirrels do plant ginkgo seeds, given the chance. This raises and interesting question: what horded the ginkgo diaspores during the Mesozoic? (That is, if the berries were similar in taste back then.) During the Mesozoic the closest analogues of the squirrels were the multituberculates. Did these rodent-like mammals horde seeds?

Nowadays ginkgo trees tend to reproduce by cloning. Coppice sprouts swell up from the lignotubers of old trees. Often aerial 'roots' extend downward from old trees. If these touch the ground they take root, and send up shoots. The Japanese named these adventitious sprouts chichi, or 'breasts'. Because under older trees the chichi swell up into pointed masses, and the chichi that hang down can thicken into masses like sagging breasts. If the parent tree dies, or a chichi touches the soil, the chichi sprout into new clones. The Tian Mu Shan ginkgo trees do not reproduce with great frequency. Seeds seldom form new trees, and chichi coppice out only when a clearing forms in the forest canopy. Possibly the slow reproductive rate of ginkgo disadvantaged them relative to angiosperms. One would think that there must be some ecological weakness that accounts for the decline of the wild ginkgo. Although, the exact explanation is a not known.

Ginkgo makes a very hardy urban tree. Ginkgo is surprisingly tolerant of air pollution and water stress. Adventitious sprouts form from stressed and nearly dead branches, and if crown die-back occurs, coppice shoots almost always sprout from the tree base. Ginkgo is very drought resistant. A ginkgo can loose all of its leaves in a dry spell, and re-grow a new set after a rain! Since the 'fruit' is smelly, slightly toxic and an allergen, the planting of female ginkgo trees is generally avoided by urban foresters. In the last few decades of the twentieth century urban forester have planted only the male trees as ornamentals. Although, in many cities the older planting still have many female trees among them. Because of its hardiness, the ginkgo is fast becoming a preferred ornamental. As long as a region is temperate, but not too dry, ginkgo trees will prosper. They are therefore planted all across most of temperate North America. Boulevards all over New York City are lined with male ginkgo trees. And significant number of ginkgo trees have been planted in Toronto, including those outside the Art Gallery of Ontario, and on the grounds of the University of Toronto.

Yews