Alien invasions mean more bad news for the plants of Galapagos…

(c)Forest and Kim Starr/Creative Commons

A recent scientific publication by the Charles Darwin Foundation (CDF) found that the presence of the invasive plant species Cinchona pubescens (pictured above) in the highlands of Santa Cruz may be leading to an increase in local soil nutrients. Whilst this may not sound like a bad thing, it could in fact spell further trouble for the archipelago’s native flora.

Due to their volcanic origin, the Galapagos Islands have relatively nutrient-poor soils, severely limiting the plant species that are able to grow there. Despite this, over 500 plants are native to the islands, 30% of which are found nowhere else on Earth. The species that live there have adapted to survive on the naturally poor nutrient load of the soils and over thousands of years a balance between these species has developed. The introduction of alien species into an ecosystem can severely affect this natural balance.

A report published in 2007 estimated that the total number of introduced plants into Galapagos could be as high as 900 species. Some of these introduced species have had a direct effect on the native floral community. For example the hill raspberry, Rubus niveus, directly effects native species by out-competing them for space. Other species can cause additional indirect effects.

C.pubescens, a member of the Quinine genus which is native to Central and South America but not to Galapagos, has in recent years become a dominant species in the formerly shrub dominated Miconia zone on Santa Cruz. As with R.niveus, C.pubescens out-competes many native species for space, but the recent CDF publication provides evidence that it may also be responsible for causing significant indirect effects. By increasing the concentrations of several key nutrients within the soil, C.pubescens could be increasing both the speed of its own spread and the risk posed by other invasive species. 

The Galapagos National Park Service is acting to reduce the impact of C.pubescens using a variety of methods, but given its extensive range on Santa Cruz and the relative inaccessibility of the habitat in which it grows, control is constrained by financial limitation.

by Pete Haskell

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