Ecosystem Services To Suffer Under Invasive Impact?

Been a while since I've been able to pen a post, some inconvenient examinations took up a lot of time over the past couple of months (I learnt so much about carbon sequestration after wildfires that I didn't even get to write *cries*). I was planning to re-launch the blog on WordPress, but that hasn't happened yet and it probably won't for a while....

In any case, I've had time now to put something together, taking a look at the potential impact of invasive species on ecosystem services, using a recent example from Montserrat (Peh et al., 2015)

If you're thinking 'what is an ecosystem service?' it's a fairly straightforward concept, essentially referring to the benefits that an ecosystem provides to humans. A lot of these can be very important, both locally (like food provision) and on larger scales (such as carbon sequestration *painful memories*)

The term is being increasingly used in academic literature , having been popularised by the Millennium Ecosystem Assessment in the early 2000s. The Google Ngram graph below shows how it's usage has really taken off.

In addition to the term's growing usage, there is growing concern that invasive species may negatively impact ecosystem function, thus the services they provide.

So, to Montserrat! Located in the sunny Caribbean, Montserrat may seem like a great place for a holiday. However, half the island is an 'exclusion zone' following a devastating volcanic eruption in 1995. The island also has a growing problem controlling invasive species, which is what the recent study is more concerned with.

In Montserrat, local stakeholders at the Central Hills forest area (Fig.1) are concerned that invasive feral goats and pigs may trigger a chain of events that causes native vegetation to by replaced by alien plum and guava trees.

Fig.1 Map of Montserrat, highlighting the study area

This, of course, will have knock on impacts for the animals of the ecosystem. For example, consumption of native lobster claw plants causes the loss of nests for the Montserrat oriole, an endemic bird which attracts nature tourism (look how cute it is, I'd like to see one)

A Montserrat oriole. Straight up 10/10 but critically endangered.

Staying on the subject of nature tourism, the opportunity to view our feathered friend and walk in the cloud-shrouded tropical forest is a great attraction to international tourists. A survey was carried out on tourists to the Central Hills asking them if they would still visit if the ecosystem was substantially altered by invasive and endemic biota were lost.

In 2009, the reserve made an estimated $419,000 from nature based tourism. The survey revealed that only 54.3% of tourists said they would still visit the reserve if the invasion substantially altered the forest, representing a loss of income of $192,000 per year.

Central Hills. Worth a visit I'd say.

Another service that could be impacted in an invasive takeover is carbon sequestration (nooo not again...). It is estimated that the total carbon stock of the forest is currently 341,000Mg and would shrink to 302,000Mg under the invasive prevalent state.

Taking a Carbon price of $83.61 per tonne, the benefit of maintaining current forest structure would be over $3,000,000, and of course, there would be a little less carbon dioxide in the atmosphere. The resolution of the study is low though, so there is little confidence in this statement.

Trees: sucking up CO2, and savings

Overall, control of feral livestock and suppression of invasive plants in the Central Hills would result in a net benefit of $214,000 per year. Cessation of feral livestock control would reduce benefits to locals (via harvesting wild meat) and global beneficiaries (tourism, carbon sequestration) and would likely cause the disappearance of native species in the reserve. Basically, failure to control invasive species = everybody loses.

In an attempt to manage the 'all-round loser' situation, hunting of livestock has been undertaken since 2009. However, long term funding for this endeavor has not yet been secured. From an economic viewpoint, Peh et al have shown that it needs to continue.

Montserrat has been devastated by a recent volcanic eruption and its ecosystem services in the north of the country are threatened by invasive species. Control needs to be undertaken, the only issue now is who is going to pay for it.

Finally, if invasive species are threatening services in Montserrat, it makes it more likely that services will suffer elsewhere if similar disruption to ecosystem functions occur. Another reason to be wary of invasive species then...

Over and out

Rob