POSTED 31 OCT 2002
Passiflora loxensis, an endangered species from Loja Province, Ecuador. Courtesy C. Ulloa, Missouri Botanical Garden
According to the International Union for the Conservation
of Nature (IUCN), 13 percent of the world's plants are threatened. That
may sound like a lot of plants, but a new study indicates that far more
are actually facing extinction.
The study concerned "all plants that are likely to qualify for one of the IUCN's three threatened categories: critically endangered, endangered, and vulnerable," field biologist Nigel Pitman of Duke University e-mailed us from Peru. However, while IUCN counts species known to be in trouble, Pitman used logic to try to pinpoint species that may, in many cases, remain to be identified.
The twin starting points for the study were patterns in the distribution of threatened species, and an estimate of Earth's total plant wealth: 310,000 to 422,000 species.
If the total number of plants is known to such wobbly "accuracy," it may seem a fool's errand to pinpoint how many are threatened. But Pitman and colleague Peter Jorgensen of the Missouri Botanical Garden statistically massaged the numbers to reflect known distribution patterns of rare plants:
Large countries have more rare plants than small ones.
Mutisia magnifica, a vulnerable species from the
Loja Province. This species was discovered in 1994, in an area where charcoal
production could destroy the ecosystem.
Courtesy C. Ulloa, Missouri Botanical Garden
Depending on which of these relationships were included, Pitman and Jorgensen calculated that 22 to 62 percent of plant species are threatened. From five calculations, Pitman said the most convincing is the one that includes 141,974 threatened species - 34 percent to 45 percent of all plants. This estimate, says Pitman, takes into account the size of countries, the presence of hot spots, and the fact that threatened species are already well known from temperate zones.
Who cares?
While that's a lot of endangered plants, we don't
really need another study to highlight the ongoing biodiversity crisis
during this period of population growth,
habitat change, and economic expansion. Still, Pitman says ignorance does
not guarantee bliss, "We want to remind people that we seem to be on the
edge of a global extinction crisis, and that our abilities to document
the advance of that crisis are not yet up to the challenge, even for relatively
well-known groups of organisms, like plants," Pitman says.
Hibiscus fragilis is a critically endangered plant
on the island of Mauritius in the Indian Ocean. The 46 known, mature plants
are not regenerating due to competition from alien plant species. The
only hope for survival is to restock and manage the wild plants, and
to clear the invaders. © Wendy
Strahm
Eventually, he hopes, the study may attract money to the chronically under-funded fields of taxonomy, natural history and field ecology. "The paper puts a price tag on improving our global monitoring system for plants threatened with extinction. The cost is well within the budgets of several foundations and even conservation NGO's. So while the paper won't have an immediate impact on the ground -- apart from attracting more attention to the problem -- it may spur a large, much-needed investment to improve our monitoring system for plant extinction."
Pitman adds that it's "scandalous" that we have barely begun to count the forms of life on the only planet known to have life. "It boggles the mind that our best estimates for how many plant species there are on the planet vary by almost 30 percent. We know more about North American tree communities in the Pleistocene than we know about some South American tree communities today. And plants are a relatively well-studied group, so it gives you an idea how blind we are to the rest of life on Earth."
-- David Tenenbaum
Bibliography
Estimating the Size of the World's Threatened
Flora, Nigel Pitman and Peter Jorgensen, Science, 1 Nov. 2002, p. 989.
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