Terrestrial invasion

Last week we put aside our stinky wetsuits and scuba gear to explore terrestrial Galapagos for a few days. We went out into the highlands of Santa Cruz with Heinke, a postdoc at Brown, and her two Ecuadorian field assistants. Heinke studies the impacts of an tree species (Cinchona pubescens, the quinine tree) that was introduced to Galapagos from mainland Ecuador, and has been doing research here for many years.

Introduced/invasive species are a particularly big concern in island ecosystems like the Galapagos. In the Galapagos National Park, there have been huge efforts to control the spread of invasive species and protect native Galapagos species. The results of these control efforts can be clearly seen where the national park borders private/agricultural land.

National park land on the left, agricultural land on the right. The plot on the left is full of the native Galapagos miconia plant, while you can see plenty of non-native elephant grass on the right.

Miconia robinsoniana, an endemic shrub that grows at high elevations. The 'miconia zone' at ~600m is named for it.

We had a beautiful, mostly clear day at Media Luna, which is unusual - the highlands have been rainy even when the coastal areas are clear and sunny. But when they are not shrouded in clouds, the view from the highlands is incredible - 180º of ocean - and you can see all the way to Puerto Ayora!

A clear view all the way to the ocean, with Puerto Ayora and Tortuga Bay in the south.

The Cinchona trees are very conspicuous against the native shrubs of the highland 'miconia zone' - they tower over everything else. Equally conspicuous is the park management's aggressive attempts to control it - around the Media Luna crater itself, they have cut most of the Cinchonas and locally applied chemical herbicides, leaving behind bare trunks.

Cinchona trunks as far as the eye can see.

One of the big questions that people tend to ask when looking at an invasive species is: what effects does it have on the ecological community? It is a question I have been asking as well, with respect to my own algal invader. Because Cinchona is a tree in a community that previously had no trees, it has the potential to shade out other plants and limit the light available to them for photosynthesis. Heinke's experimental set-up aims to figure out exactly what the effects of Cinchona shading are, using artificial shades to control the amount of light available to the native shrubs. It will be cool to see how this affects the species diversity and composition of the plant community.

Two different shade treatments: total shade in the centre and partial shade on the left. On the right you can see a Cinchona forest that hasn't been managed by the national park - a really different-looking plant community compared to the short, shrubby one in the foreground.

For the past year, I've thought of invasive species mostly in terms of the marine algal species I study. It was interesting to look at it in a terrestrial system, particularly an island one. It gives me a slightly broader perspective on things before I return to the invasion happening in the shallow subtidal zone of New England.