Why are plants all over the world becoming woody

Newswise – Why do some plants grow into large woody shrubs or huge trees, while others remain small and never produce wood on their stems? It’s an evolutionary mystery that has already puzzled Charles Darwin for more than 160 years. Now, scientists from the Netherlands and Germany are providing the first global overview of the evolution of timber on the islands, which will finally help solve the mystery.

“The first woody trees on Earth evolved about 400 million years ago, but we still know very little about why they developed wood in the first place,” says Frederic Lins, a researcher at the Naturalis Center for Biodiversity and Leiden University. All of these early woody trees are now extinct and originated in unknown climatic conditions, so it’s impossible to understand the evolution of wood based on their fossils, but islands may offer the solution.

Timber evolution still occurs today, particularly in these areas known as the natural laboratories of evolution: the islands. One of the surprising aspects of isolated plants is that they are relatively more woody than those on neighboring continents. Charles Darwin described this phenomenon as isolated wood. It occurs when a non-woody continental colony reaches an island and subsequently develops into a woody shrub or even a tree on the same island after tens or hundreds of thousands of years.

Insular woods are known only from a few distinct breeds, such as the Hawaiian silver words (Fig. 2). To better understand why plants turned into wood during evolutionary history, the Dutch-German research team compiled a new database of more than a thousand isolated wood species and their distribution (Fig. 2), allowing them for the first time to accurately test a number of these species. existing hypotheses. With promising results. “We have identified a link between increased drought and increased wood formation in stems of plants on islands. I am convinced that the relationship between drought and wood will be much stronger on the continents,” says Lins. This is something the team will want to test soon when analyzing their entire database, also including about 6,000 additional wood species that developed their woods on the continents.


The researchers not only identified all of the world’s isolated wood species, but also determined their distribution and number of metamorphoses globally (Fig. 3), and tested which evolutionary hypothesis was the most likely. “It was really crazy to put together such data in the first place,” says Frederic Lins. “It took me over 10 years to finish the database, but fortunately it all pays off in the end.”

The new timber database has found more than three times the number of isolated wood species known to date. These more than 1,000 species are the result of at least 175 independent transitions. “This clearly confirms that islands are remarkable biodiversity hotspots in the world, with unique flora urgently in need of protection,” says first author Alexander Zizka, from the University of Marburg in Germany. The exhaustive research also offers an interesting glimpse into the future. “With the dry European summer of 2022 in mind, the fact that drought is emerging as one of the most likely factors for wood formation, provides promising research avenues in agriculture to help protect our food production,” explains Friedrich Lenz. “Supposing that we will be able to convert every non-wood crop into a woody one, we will not only have larger crops with a higher yield per plant, but more importantly, we will also be able to increase the drought tolerance of these timber crops… in a world facing climate change and growing world population, this is simply necessary.”