Plant Migration: Wings, Hairs and Humans
Plants Migrate Via Oceans
Plants migrate in manifold ways, many of which are quite extraordinary. We have heard often one of our great aunts or grandma remark about a plant in the neighborhood as having a foreign origin. Cashew trees, though a native of Brazil, are now cultivated on a large scale in India and Africa. Rubber tree was originally found in the Americas but it could cross continents and develop into a valuable cash crop. Unlike animal fossils of ancient times, plant fossils are found in plenty in the very many archaeological layers of earth preserved by chance for the perusal of scientists. Hence Palaeobotany has evolved as a significant field. Still, there are many complex factors in action when one considers the history of plant migration. For example, consider a seed falling into the ocean. It will have a destiny decided by the ocean currents, its edibility to sea creatures, the hardness of its outer shell that enables it to float for many days without rotting, and the like. It is an intricate game of nature driven by the food chain and some degrees of chance.
Carriers that Help Plants Migrate
Trees have their own natural mechanisms for seed dispersal and migration and these are mainly, seeds having wings, having hairs, delicious and plump fruits to attract carrier animals, seeds having a shape and texture to be able to roll on the ground, having tasty nuts and sometimes the ability of the seedpods to explode! Mistletoes and sandbox trees have such exploding fruits. There are many insects and small animals that bury their fruit harvest and often forget about it. Obviously, another trick of nature is to preserve the nuts and let them germinate when the time comes. Though most animals carry seeds to distances unintentionally, humans do it wilfully as well.
How Migrated Plants Survive?
Do you know how difficult it is for a newcomer plant to get acceptance in a forest ecosystem? This is not because forest plants and trees are conservative or narrow-minded; the reason being there are many perennial trees in a forest that have well-developed root systems. All the roots of all the trees work as a single net covering the topsoil that prevents new saplings from taking root. Grasslands that have extensive root networks though much minuscule in scale, also resist new entries. Migrated plants also have to adapt to the climatic conditions where they are newly trying to take root. However, all the plant wealth that is distributed across the world irrespective of extreme climate differences stands proof of the resilience of the guest plants.
Over the Mountains, Above the Seas
The ferns migrate at the scale of a Siberian Crane or an Arctic Turn. Its spores travel thousands of kilometers, borne by air. The qualities that allow this magnitude of migration are more than one- the infinitesimal size of the spores, their ability to germinate many months after they are produced by the mother fern. Each spore after sprouting can grow into a bisexual fern and hence to reproduce on new land is not a problem at all.
Story of the Ocean as Told by Sea Lettuce
Sea lettuce grows on seashores and its seeds get carried forth by the ocean. Then, up to period of one year, the seeds may float in the sea. What things those seeds could tell about the life in the sea if only they have a voice! Imagine, a chronicle of sea lettuce about the sea inhabited by whales and pirate ships, ephemeral sunsets and the limitless sky! After experiencing (rather not experiencing) all these, the seeds settle on a shore and still retain their germination potential. On new land, they anchor their tiny roots. Coconuts and mangrove seeds also make amazing sea voyages seeking a chance to sustain the species.
The Winged Friends of Plant Migrants
There is a profound connection between migratory birds and seeding plants. The birds eat the fruits of the plants and then fly to far-off lands. The seeds thus carried to new lands in their stomachs usually have hard outer shells, the feature that helps them be safe from getting digested.
There is a big category of colonizing species to explore when we discuss plant migration. These are the plant species that have the adaptability to different geographies, climates, and long gestation periods. An example could be the Pond Apple, which is a small tree that is capable of invading a rain forest and turning it into just a species-thin patch of vegetation by growing into thick monocultures and suffocating all other plants.
Plant Migration by Agriculture
Plant migration through agriculture is another sub-topic of this discourse. Take the case of Barley. The earliest reported cultivation of Barley is from the region of the Middle East that is called the fertile crescent. That was 10000 years back in history. Gradually Barley migrated to South Asia, indeed with the help of the farmers, traders, and travelers of those times. One very popular Barley variety was found by scientists to have traveled from South Asia to Europe via human sea routes.
Nature has made many plants in such a way that they are pre-adapted to make use of human migration and other human activities for their dispersal over the planet. So, what do you think? Had nature also planned the kind and scale of ecological disturbances and habitat destruction that were to accompany the evolution of Homo Sapiens on earth? I leave it an open question.
Encyclopaedia Britannica: Falling Far from the Tree: 7 Brilliant Ways Seeds and Fruits are Dispersed.
Invasive Plant Species of the World, 2nd Edition: A Reference Guide to Environmental Weeds by Ewald Weber.
On the Origin and Domestication History of Barley (Hordeum vulgare) by A. Badret al., Molecular Biology and Evolution, Oxford Academic.
Plant Migration: The Dynamics of Geographic Patterning in Seed Plant Species by Jonathan D. Sauer.
Plant Migration Studies by Charles E. Bessy.
© 2018 Deepa