A study published on June 10th in Nature Ecology & Evolution (authors: A.M. Humphreys, R. Govaerts, S. Ficinski, E.N. Lughadha, and M.S. Vorontsova) has indicated that over the past 250 years, 571 plant species have become extinct. Human activity is considered to be the primary reason for the vast majority of these extinctions.
The authors of the study were from the UK and Sweden. They relied heavily on an unpublished database originally created by one of the authors, botanist Rafael Govaerts, working at the Royal Botanic Gardens, Kew, in London.
They compared the Govaerts plant extinction database against a list of 1,234 plant species that had been declared extinct since the 1753 publication of Karl Von Linnaeus’s Species Plantarum, by the International Union for Conservation of Nature (IUCN) Red List of Threatened Species. The work of the authors began in 1988. It was far and away the largest analysis of plant extinction ever undertaken as they reviewed data on over 300,000 species. As a result of the analysis they determined that more than one half of the original 1,234 “extinct species” were either rediscovered or reclassified as living. The remainder makes up the 571 declared extinct in the June 10th Report.
A brief summary of the Report follows:
- The number of seed plan extinctions is more than four times that of the Red List.
- The extinction of seed plants is occurring at a faster rate than the normal rate for species; on average, 2.3 species have become extinct each year for the past 250 years. This is more than 500 times what would be expected from natural causes. Some prior studies had indicated that the number would be double that.
- The study compared extinction patterns using a measure of extinctions per million species years (E/MSY). The net result showed that 0.2% of plant diversity is extinct, mollusk extinction at 7%, and birds and mammals at 5%. The authors provide several explanations for the apparent difference in species extinction rates: “the extinction lag time is longer for plants than animals, and thousands of living plant species are thought to be functionally extinct.” What does that mean? They can’t reproduce either because the remaining population is either single sex or the carrier they need for pollination is no longer available.
- the extinction pattern for both animals and plants is “striking similar”. All of the areas with the highest proportion of extinctions are either islands or tropical areas.
- The authors point out Hawaii, parts of South Africa, Mauritius, Australia, Brazil, India and Madagascar as top extinction regions.
- Most extinct plants were hardwoods; a far lower proportion of herbaceous plants were prone to extinction.
- The main cause of the plant extinction is anthropogenic (i.e., us): the destruction of the natural habitat of the plants by human activity, such as deforestation, land use conversion, etc.
- There is no family pattern of plant extinction; meaning that it is “randomly distributed among evolutionary groups”. This is interesting because it is typical of prior studies with respect to plant extinction but atypical of those relating to mammals, where there are patterns.
- The number of plants that have become extinct is greater than the aggregate total of all extinct birds, mammals and amphibians.
- The number of actual extinctions is likely to be significantly higher.
Considering the importance of plant life to human life, this study should act as another provocative wake-up call. Human society is dependent on plant life as food sources – as are many, if not most, of the other species that, then, provide us with food sources. While climate change, per se, isn’t currently the direct cause of the plant extinction problem that is likely to change as the impact of climate change compounds and the environment becomes more hostile to plant life, and ultimately, to all life.
Complacency and business as usual must change.