State of the World’s Plants and Fungi: 2 in 5 plants are threatened by extinction

Scientists highlight the state of the art in conservation science and point to current methods of assessment and future studies needed to mitigate species extinction.

State of the World’s Plants and Fungi report was compiled by 210 researchers from 42 countries to provide an in-depth look at how we can protect and sustainably use the world’s plants and fungi for the benefit of people and the planet. The number of assessed plant species has doubled recently due to the Global Strategy for Plant Conservation but many targets, including assessing the conservation status of all plant species, have not been met this year (read more in the Global Biodiversity Outlook 5, page 124).

Whilst previous research estimated that one in five plant species are at risk of extinction, the recent findings by Dr Eimear Nic Lughadha and 29 colleagues have found that two in five known plant species is likely to be threatened by extinction. The International Union for Conservation of Nature (IUCN) Red List of Threatened Species is the most comprehensive database of the conservation status of over 120,000 species. The researchers reviewed the IUCN Red List and ThreatSearch to identify biases and gaps in extinction risk assessments of plants and fungi. The researchers predicted the proportions of threatened plant species geographically, quantified the Red List Index of 400 species in Madagascar and Brazil and discussed processes and drivers of species extinctions. Currently, 43.7% of vascular plants are considered threatened and the odds of a plant species being threatened by extinction doubled in Africa. Plants targeted by specific conservation projects are well described whilst overall, plants from Southern America, Northern America and tropical Asia are greatly underrepresented in assessments. 

Lughadha and colleagues found that 73,081 plant species (21% of all known plants), were assessed globally in 2016. The proportion of assessed plants increased to 28.3% by the beginning of 2020. The coverage was extremely small for mosses (1.3%) and green algae (<1%) and there was a strong geographical bias. Some of the overrepresented plants were woody perennials that are targeted by the Global Tree Assessment, and plants used by humans. Surprisingly, some of the species-rich families (e.g. Orchidaceae, Poaceae, Asteraceae) were underrepresented in conservation assessments.

The proportion of plant species covered by a global assessment on the IUCN Red List in 2020. Source: Lughadha et al., 2020

Out of the 285 assessed fungi species, 234 are basidiomycetes and mainly included better known species in Europe. 

The researchers used a statistical model that is mostly used for predicting the outcomes from elections for unrepresentative polls and estimate the level of threat for these groups due to biases.  The model predicted an increase in the odds of a species being threatened that is endemic to a single country. The odds of a plant species being threatened by extinction doubled in Africa whilst the odds quartered in Australasia. The level of extinction threat is likely to be overestimated for Arecaceae (palms) but underrepresented for Fagaceae, Cyperaceae and Myrtaceae. 

Next, the scientists discussed the processes of extinctions and key drivers. The current rate of plant extinctions is approximately 500 times than the pre-Anthropocene extinction rates and the most disproportionately high numbers occur on islands (e.g. Hawaii, St Helena). Whilst random extinctions could have little effect overall in terms of evolutionary history, the more recent extinctions seem to be clustered in certain lineages. Lughadha and colleagues recommend considering phylogenetic diversity in conservation prioritisation (e.g. EDGE approach) and also highlight that most extinctions are delayed and there might be an outstanding extinction debt (i.e. future extinction of species due to events in the past) due to historical land uses. 

The extinction debt of obligate symbiotic fungi (e.g. mycorrhizas, endophytes) could be driven by land uses and also by the extinction of obligate plant partners, making it a more complicated, hard-to-predict process. It is well-documented that the distribution of a plant species has been changing due to iIncreasing temperatures driven by climate change. The researchers use the examples of the 500 m increase in the upper limits of mountain plant species along Ecuador’s Chimborazo volcano and fungi fruiting in the Alps at higher elevations since 1960. If climate change were to lead to a 50% decline in a species potential range size, almost half of all tree species could be evaluated as threatened species.

Plant and fungi species threatened by extinction or under assessment. Chorioactis geaster (a) is currently under assessment. Pleurotus nebrodensis (b) is an endangered fungi in Sicily and Greece. Koompassia genus (c) includes vulnerable and critically endangered tall tropical trees that can support bee hives. Syzygium genus (d) includes vulnerable and critically endangered tropical trees with cauliflory growth (including the edible water apples). Nepenthes jamban (e; left) is a critically endangered pitcher plant in northern Sumatra. Manihot gracilis (f) is a vulnerable, secondary genetic wild relative of cassava plants in South America. Sources: Tim Jones/tripsis/T. R. Shankar Raman/Toby Hudson/Alfindra Primaldhi/WikimediaCommons and Mauricio Mercadante/Flickr

Finally, the scientists evaluated the trends in the Red List Index (RLI) and whether changes of occupancy area of a species could trigger a change in conservation category. The analysis consisted of assessing the distribution of 400 species of legumes and monocots in Madagascar and Brazil over a 25-year period. Whilst there was a relatively a downward trend for Madagascar, suggesting that species there are moving towards extinctions, one species out of 12 experiencing a 10% range loss actually triggered a change in the Red List category. 

“[T]he coarse nature of the Red List category thresholds means that large losses in occurrence, including from common species, may go undetected by the RLI”, Lughadha and colleagues wrote.

The review by Lughadha and colleagues highlighted gaps in plant and fungi conservation status assessments and the importance of understanding the extinction processes. 

“Plants and fungi not on the Red List are overlooked in large‐scale biodiversity studies and invisible to funding agencies”, the scientists wrote. “Underrepresentation of plants and fungi on the Red List limits options to promote their conservation.”

“Extinction debt studies for fungi are few, reflecting major challenges: their cryptic nature, with mycelium hidden in the substrata, sometimes makes it difficult to define individuals; determining generation time is also problematic […]”,  Lughadha and colleagues added.

The researchers set out the future prioritisation of which plants and where should be assessed and discuss the process can be speeded up by environmental DNA (eDNA) sampling, remote sensing, IUCN Green Status of Species and Species Threat Abatement and Recovery (STAR) Metric approaches and the development of artificial intelligence and open access software (e.g. GeoCAT). 

Extinction risk assessments are needed for as many plant and fungi species as possible but it is also crucial to turn attention to underrepresented locations and families to take better care of global biodiversity.