Who would believe that forests hold within them the secrets of landmasses lost to time? It’s difficult to digest. How can continents break up, and come together, only to split apart, again? How can trees that survive only for a few thousand years, help us understand those episodes, unfolding over millions of years? However, there is a family of trees with a very unusual distribution that does just that. I am talking about the Dipterocarps (of the family Dipterocarpaceae). A report has been published, in the Proceedings of the National Academy of Sciences, that reveals the existence of tropical forest types revealing links between the likes of South America and Africa, or Madagascar and India. I will be discussing this in detail, later. Here is the report as published by Science Daily – ‘Mapping the First Family Tree for Tropical Forests’ (dated February 5, 2018):
The results, culled from almost 1 million different tree samples from 15,000 tree species, have uncovered a shared ancestry between tropical forests thousands of miles apart and previously believed to be unrelated. Published this week in the Proceedings of the National Academy of Sciences, the study describes an international, grassroots effort to collect and analyze data from more than 400 geographic coordinates across the tropics, a region that comprises 40 percent of the Earth’s surface.
The study was led by Ferry Slik, an associate professor at the Universiti Brunei Darussalam in Brunei. Janet Franklin, a distinguished professor of biogeography at the University of California, Riverside, coordinated the interpretation and reporting of the data, which is publicly available as an open access article. Franklin said the new classification scheme’s value comes from the inclusion of ancestral information about the tree samples (gleaned from DNA analyses), rather than the “snapshot” of tree biodiversity that is obtained from recording a plant’s species.
“When ecologists study biodiversity, they look at the present day by identifying the range of species in a particular forest. However, without going deeper into a plant’s history by looking at its family tree, each species is considered separate and unrelated,” Franklin said. “By adding the evolutionary relationships between species, however, we suddenly have a measure of how similar species are to each other. This means that we were able to do a much more detailed and realistic comparison between forest sites than previously possible.”
The study revealed five major tropical forest regions: Indo-Pacific, Subtropical, African, American, and Dry Forests, which are found at the boundaries between tropical and dry climates. The study also showed the evolutionary relationships between the forests. One surprising finding was that tropical forests in Africa and South America are closely related, with most of the differences between them occurring within the last 100 million years. “An African tropical forest is evolutionally more similar to tropical forests in the New World than to forests in the Indo-Pacific,” Franklin said. “While this was somewhat unexpected, it likely reflects the breaking apart of South America and Africa resulting in the formation of the Atlantic Ocean that started approximately 140 million years ago.”
Researchers also found that related subtropical forests exist in two distinct regions: East Asia and Central/South America. “These regions share the same temperate climate and, even though they are not geographically close, their forests share common ancestors, which is a bit of a mystery,” Franklin said. “However, it may be that we are actually looking at remnants of the once extensive tropical forests that ranged from North America all the way to Europe and Asia. When Earth’s climate cooled down these forests mostly disappeared, but parts seem to have survived in Asia and America.”
The researchers hope an understanding of the diversity and composition of the tropical forests will help them anticipate region-specific responses to global environmental change. “Different forests may be more vulnerable or resilient to climate change and deforestation, so if we understand the similarities and differences between forests it will help inform conservation efforts,” Franklin said.
An Indian newspaper, ‘The Hindu’, focused on the implications of the report for India’s bio-geography and evolutionary history. Appearing on February 6, 2018, the article ‘First Family Tree for Tropical Forests’, (by Aathira Perinchery) described the link between India and Madagascar as follows:
Indian scientists from the Indian Institute of Science, Pondicherry University, Delhi University, Jawaharlal Nehru University, Bharathiar University, International Institute of Information Technology, Sigur Nature Trust (SNT) and the Kerala Forest Research Institute also contributed to this data. Another finding is that dry forests found in India, America, Africa and Madagascar are also closely related to each other.
“India plays a central role in this story because many of the plant species in the Asian tropics reached Asia via India about 45 million years ago, including the very important tree family of Dipterocarpaceae (Asia’s main timber group),” Slik wrote in an e-mail to The Hindu.
“In terms of fundamental science, these are important results in botanical research,” said India-based ecologist Jean-Philippe Puyravaud of Masinagudi’s Sigur Nature Trust, who contributed to the study. “Forests and vegetation are uniquely shaped by their history, and we need to make more efforts to conserve them.”
This story of how the Dipterocarps traveled from the rapidly disintegrating southern supercontinent of Gondwanaland to the northern supercontinent of Laurasia via the Indian landmass is nothing short of magical. Today, the family is found in the tropical forests of South America, Africa, Madagascar, South and Southeast Asia. Evidence of this is to be found in amber deposits recovered from the state of Gujarat in Western India. I will take that up in another post.
Image Attribution: The image above, sourced from Wikimedia Commons, shows a double winged Dipterocarp Fruit (Shorea species) in Sarawak, Malaysia. It was uploaded by Bernard Dupont. The name of the family comes from the wings which the trees use to disperse their seeds.
- ‘First Family Tree for Tropical Forests’, (dated February 7, 2018, by Aathira Perinchery), The Hindu
- ‘Mapping the First Family Tree for Tropical Forests’ (dated February 5, 2018, originally written by Sarah Nightingale), Science Daily
- ‘Prehistoric Creatures Discovered in Huge Indian Amber Haul’ (dated October 25, 2010, by Ian Sample), The Guardian