Scientists say current IUCN Red List status may be an underestimation of risks for many tree species
Photo: iStock Scientists fear that over 17,000 tree species are facing increased exposure to human-induced global stressors that subsequently put them at a higher risk of extinction than indicated by their current status in the International Union for Conservation of Nature (IUCN) Red List of Threatened Species. It is a comprehensive list of species and critical health indicator of global world biodiveristy.
The scientists quantified the rates of change over the past two decades based on six major threats categorised by the Global Tree Assessment, an initiative to assess conservation of tree species mentioned on the IUCN Red List. These threats are: crop agriculture expansion, tree cover decline as a proxy for overexploitation in all vegetation types, urbanisation, deforestation as a proxy for land-use change threats in forested areas, changes in burnt area descaled as fire and fire suppression, and climate change measures in terms of changes in annual variation in figures of temperatures, precipitation and seasonality and vapour pressure deficit (VPD) and VPD seasonality.
The first four threats — crop agriculture expansion, tree cover decline, urbanisation, deforestation — under the ambit of land-use change can push any tree species to extinction, irrespective of its specific characteristics, according to the authors of the report published in Nature Communications titled More than 17,000 tree species are at risk from rapid global change.
The scientists studied 41,835 species, which include 72.2 per cent of all tree species occurring worldwide, and were able to calculate exposure threats for 32,090 species. Out of this, 54.2 per cent (17,393) were found to be exposed to “higher and increasing threats”.
Though these changes in exposure were likely to push the tree species’ extinction risk, about 8.7 per cent were only found to be listed as ‘threatened’ on the IUCN Red List.
“Due to the convergence of threats, these species will likely exhibit intensified responses as a result of synergistic effects. Consequently, these species may be at a higher risk of extinction than indicated by their current IUCN Red List statuses, implying a likely global underestimation of risks to tree species,” the authors noted.
Deforestation was the major reason for the largest changes in potential threats among species’ extent, the findings showed.
“The maximum annual tree cover decline was 6.67 per cent of species’ extent, and was found for Rhodolaena macrocarpa (native to Madagascar, Red List status: Endangered due to wood harvesting, mining, and fire), Arytera miniata and Syzygium sambo- gense (both native to New Guinea, Red List status: Endangered due to deforestation for settlement and agriculture activity, and Not Evaluated, respectively), Gluema korupensis (native to Cameroon, Red List status: Endangered due to deforestation and its low number of mature individuals) and Weberbauerocereus madidiensis (native to Bolivia, Not Evaluated on the IUCN Red List),” it added.
The analyses of tree species revealed that the highest annual deforestation rate was 5 per cent of species’ extent noted for Eucalyptus redimiculifera, native to Western Australia, having a Red List status as Data Deficient.
Lower rates of recent change in threat exposure were found among cropland agriculture, urban development and burnt areas.
The study pointed out that the recent climate change has, “Caused the species’ extents to become warmer, dried and more seasonal in precipitation and drought, affecting species from the tropics to the subarctic in the past 20 years.”
Regarding India, Coline CF Boonman, lead author of the study, said, “We have found that 240 tree species occurring in India are suggested by us to be needing prioritisation for IUCN Red List re-assessments. When we consider the 10 Indian tree species with the highest rates of change per threat, we find that 67 unique species are listed.”
Boonman said that of these 67 species, there are three tree species listed in the top 10 highest rates of change for three threats of the six climate-relate threats identified.
The species identified are Salix pycnostachya (non-native; high rates of change from deforestation, cropland expansion, urban expansion), Tamarix dioica (native; high rates of change from deforestation, tree cover change, change in drought or vapour pressure deficit), Tecomella undulata (native; high rates of change from deforestation, tree cover change, change in drought, or vapour pressure deficit, change in maximum temperature).
Further, the researchers said another 14 species are in the top 10 highest rates of change for two of the six climate-related threats.
The species identified are Aesculus indica, Aglaia oligophylla, Albizia amara, Antiaris toxicaria, Ehretia obtusifolia, Flacourtia indica, Gyrocarpus americanus, Hardwickia binata, Limonia acidissima, Salix turanica, Salix wilhelmsiana, Sorbus cuspidate (synonym is Griffitharia vestita), Stereospermum chelonoides, Wrightia tinctoria.
Jens-Christian Svenning, co-author of the study, said, species such as Tamarix dioica, Tecomella undulata and Aesuculus indica have cultural significance and socioeconomic uses.
The researchers recommend identified high priority species, which are at highest threat and re-evaluation of species, to reassess their IUCN Red List status and further suggest regularly to be conducted every 5-10 years.
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