Humans decide which plants win or lose, and most are losing

Although humans and their direct ancestors have been around on Earth for several million years, it is in the last one thousand years that we have interfered with and changed almost every aspect of the biosphere – that precious space on our planet that is inhabited by living organisms. Today, human activities change climates, alter and destroy natural habitats, move plants and animals to locations where they didn’t previously occur, pollute the air, sea, freshwater and land, and exploit natural resources. We are truly the “lords of the biosphere.”

And as lords of the biosphere, a term coined by John McNeil in a publication in the year 2000, we decide what shall live and what shall die. According to John Kress, botany curator emeritus at the Smithsonian’s National Museum of Natural History, and Gary Krupnick, head of the museum’s plant conservation unit, humans have favored species that they have found useful and desirable, while the useless or valueless species have been excluded or driven to extinction. 

The scientists combed through current environmental databases, ethnobotanical descriptions, and conservation assessments of green plants to survey and measure the impact of humans on today’s botanical diversity. They considered the characteristics of more than 86,000 different plant species in order to decide whether their survival was aided by human activities, in which case they were “winners,” or whether human activities relegated them to a state of irrelevance and potential extinction, in which case they were “losers.”

“I actually started this project from a place of optimism,” said Kress. “I had just planted all these trees around my house in Vermont and thought to myself that maybe there are actually more winners than losers, and we are just focused on everything that’s disappearing.”

In order to categorize the chances of survival of different plant species in a future world dominated by humans, Kress and Krupnick evaluated mountains of data on the economic uses, environmental tolerances, legal and illegal trades and conservation status of approximately 30 percent of all vascular plants on Earth (that is plants that transport water, dissolved nutrients and other substances within their bodies by means of specialized vessels). 

Based on this data, they divided all the plants into seven categories: those that are winners and are useful to humans; winners that are not useful; losers that are useful; losers that are not useful; species that seemed likely to win in the future; those that seemed likely to lose in the future; and those that had already become extinct (571 species).

When the categories were tallied up, the analysis showed that losers currently outnumber winners, and that losers are likely to be more numerous than winners in the future if human impact on the planet continues on its current course. Kress and Krupnick categorized 20,293 species of plants as losers, with the vast majority of them being identified as not useful to humans. In contrast, just 6,913 species were categorized as winners, with all but 164 of those species having some human use.

In the future, assuming that human behavior will not change substantially, losers are projected to continue to outnumber winners, with 26,002 species in the potential losers category compared to 18,664 species in the tentative winners category. 

The researchers also considered whether there were evolutionary relationships within the groups of clear winners and losers. They mapped these species onto evolutionary trees to see if some plant orders contained high numbers of winner species, or high numbers of losers. 

“The question was whether there were some lineages of plants that were more packed with winners or were full of losers we should be concerned about,” said Kress.

The findings, published today in the journal Plants People Planet, showed that winners and losers are distributed pretty evenly across plant orders. There were a few instances where branches of the plant evolutionary tree had few species but more losers than winners, and these branches had an increased risk of being lost altogether. Plant groups such as cycads, and cypresses (the family that includes redwoods and junipers) were among those that fell into this category. 

“Now and in the future, plants have to adapt to the environment humans have created or they will go extinct,” said Krupnick. “Our results suggest that this means the plant communities of the future will be more homogenized than those of today.”

This loss of plant diversity could have major negative consequences for ecosystems around the world in future. Losing plant diversity will be associated with losses in animal diversity, Kress said, and this will make ecosystems less resilient in the face of hardship or change. This would have serious implications for humanity as well.

“The list of winners shows that we’ve selected certain species that are useful to us, but as that pool of plants we have to select from decreases in the future, humanity will have many fewer options when we want to reforest the planet, find new medicines or foods, or develop new products,” said Kress.

According to Kress, he hopes that these lists will give other researchers opportunities to look more in depth at the reasons why certain species or lineages are winning or losing in the age of humans and to identify the plants that are most in need of conservation.

“It still looks green outside my window, and that can create the illusion that plants are doing well,” said Kress. “But this study suggests we’re on course for a big loss of plant diversity, and we better wake up.”

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By Alison Bosman, Earth.com Staff Writer