In today’s world, habitats disturbed by landslides, shifting rivers, forest fires, or humans, are rapidly taken up by pioneer plants, whose motto seems to be ‘live fast, die young’. The pioneers, such as fireweed, willows, and dandelions, flourish for only a few years before being pushed away by species that represent more mature phases of succession. Here in Finland, that usually means first birches and rowens, and after a few decades, thick dark forests of spruce.
In the time of the dinosaurs, things were slightly different.
From Late Cretaceous all the way to Miocene there was a distinct community of plants in disturbed sites – such as empty river channels, collapsed riverbanks, and wildfire sites all around the temperate climates of Northern Hemisphere. At the heart of this community was the maidenhair tree (Ginkgo).
Most commonly associated with ginkgoes were katsura trees (Cercidiphyllum). Dawn cypress (Metasequoia), sycamore (Platanus), and delta cypress (Glyptostrobus) were also parts of this community. The specific species change through time, though sometimes mostly because paleobotanists haven’t been comfortable assigning plants separated by ten of millions of years to the same species, even though they look apparently identical.
In a 2003 study on the ecology of these plant communities, 48 fossil sites spanning all the way from Late Cretaceous to Middle Miocene were sampled. The locations were in North America, Axel Heiberg Island in the Canadian Arctic, Spitsbergen, and Scotland. Same or similar communities also existed in Asia, and until the earliest Cenozoic, on the Southern Hemisphere.
Logically for a pioneer plant, the seedlings of these trees have a bolting phase, in which they rapidly grow large enough to withstand competition. Unlike the weedy plant communities of today’s disturbed habitats however, all of these trees live to be very, very old. The ‘temporary’ pioneer vegetation did not endure for mere years, but centuries or millenia before being slowly replaced by the area’s mature vegetation.
On modern standards, these trees were lousy pioneers. They reproduce extremely slowly (for example, ginkgo trees only start producing fruit around the age of 20 to 30 years) and are less effective dispersers than today’s weedy flowering plants. It’s therefore somewhat surprising all of these genera are actually still alive. Plants take a long time to die.
Time has thrown these old friends apart on different continents. Ginkgoes, katsuras, dawn cypress and delta cypress hang on, mostly as small relict populations, in different parts of East Asia. Sycamores are seemingly better suited to modern plant communities and are represented by some ten species on three continents.
Incidentally, all of these old friends also have beautiful autumn colours, which may give additional inspiration to paleoartists, as depicted on the top picture of this article.
Old trees are odd
In most areas of the developed world, forests have been strongly influenced by humans for a long time. The main consequence is a rapid disturbance cycle: trees are rarely allowed to reach an old age. In everyday life, many people will never see truly natural stands of trees. It may, then, be missed by paleoartists how plain weird old and unmanaged forestlands sometimes look.
Ginkgoes grow up to be particularly grotesque. Mature ginkgo trees start sprouting aerial root-like growths called chi chi (which is apparently Japanese for breasts, as that’s what they look like, if you have a lively imagination). When chi chis touch the ground, they sprout roots and start acting as a holdfasts for new trunks. Trees full of chi chis of different sizes look oddly like they have started to melt. Very old trees have multiple trunks growing from a huge underground tangle the size of a small house. These can still be seen today on a few wild or semi-wild stands in China, such as the one on Tiamnu Mountain.
Very old sycamores (which can survive two thousand years or more) are often hollow, with huge spaces inside them, while conifers like dawn cypress become knotty like an old man’s arm. Trees growing in windy locations will bend into odd shapes, while those damaged by herbivores will often grow secondary trunks to get around the damage.
While some wild forests truly are composed of fairly straight tree trunks growing at regular distances, there is plenty more space for imaginative forest scenes in paleoart. And for Ginkgo’s old friends.
First part: Not all Ferns Look Like Ferns.
Second part: Fruit for the Dinosaurs.
Third part: On Grasses and not Exactly Grasses.
Fourth part: Flora in the Time of Chasmosaurs.
Fifth part: Things I Saw in Madeira.
References and Further Reading:
Royer et al. (2003) Ecological conservatism in the ‘living fossil’ Ginkgo. Paleobiology 29(1).