Taking the plunge: waterfall plants under threat

Today marks the publication of the latest update of the International Union for Conservation of Nature Red List for Threatened Species™ (IUCN Red List) to include 142,577 species in total and 58,343 plant species.

In this update, the plight of freshwater and wetland systems has been specifically highlighted by IUCN.

While the conservation status of freshwater animals is well documented to be precarious, freshwater plants are often widespread and comparatively resilient to extinction risk.

In fact, about 75% of freshwater plants published on the Red List have been assessed as Least Concern, compared to just 50% for other freshwater taxa.

A notable exception to this generalisation are plants growing in and around waterfalls in tropical areas.

Members of the “orchids of the falls” or Podostemaceae family, in particular, are often restricted to just a single set of falls or rapids.

These narrow distributions inherently increase the risk of extinction for these species, which is only exacerbated by human activity.

For freshwater and wetland systems on the whole, unsustainable agriculture and urbanisation are the key drivers of species decline; for waterfall plants growing in tropical areas, it is the construction of dams for hydroelectric power that often poses the most significant threat and has already resulted in global extinction of several species in Africa.

The dam at Memve’ele is far from an isolated example: Inversodicraea koukoutamba, known only from the Koukoutamba falls on the Bafing River in Guinea, is also included on the IUCN Red List for the first time and is assessed as Critically Endangered.

The same reason, different hydroelectric project.

In this case, it’s the planned Koukoutamba Hydroelectic Power Station threatening the species’ survival.

It is essential, therefore, that hydroelectric dam projects are undertaken with due consideration for the fragile ecosystems their construction will impact.

Stemming the flow

Fortunately, all of the falls mentioned lie within sites recently designated as Tropical Important Plant Areas (TIPAs) in Cameroon and Guinea.

The TIPAs project helps to prioritise conservation by focussing on sites of particular importance for threatened, endemic and other valuable species.

Sites proposed in Cameroon so far, including Memve’ele and Lobé, accommodate around 70% of threatened species across approximately 4% of the area of Cameroon.

As well as documenting species presence at TIPA sites, Kew scientists are working with local partners to protect species through further monitoring, dissemination of knowledge, promotion of sustainable livelihoods, restoration of habitat, and propagation in local nurseries.

In areas targeted for hydroelectric projects in Cameroon, such as Memve’ele, we are investigating the possibility of transplanting some species from affected sites, though this is not expected to be easy or straightforward.

This activity would complement existing ex situ conservation involving collection of seed for storage in the seedbank of the Cameroon National Herbarium and Kew's Millennium Seed Bank.

Through the publication of these species on the IUCN Red List, and the implementation of in situ and ex situ conservation measures, we hope to protect this unique flora of rheophytes, and to raise the profile of these fascinating plants to those attracted to the less conspicuous of nature’s wonders.