Oil roads have higher impact than expected on canopy-dwelling frogs

Scientists have found that oil roads running through remote tracts of primary forest in the Ecuadorian Amazon have a much greater effect on frogs living in the canopy than previously assumed. In fact the Ecuadorian government and oil companies have always argued that these oil roads have little to no effect on the environment, because they are well managed and no settlers are allowed to open up tracts of forest next to these roads, as is the case along other oil roads in the country. However, this first investigation of effects on life in the canopy shows that the number of frogs is severely affected by these oil roads even though the surrounding forest seems to be in good health and  these frogs are living at altitudes up to 50 meters above the forest floor. This means that biodiversity next to these ‘low-intensity’ oil roads might be more under threat than always thought.

In my own experience, walking through a rainforest you don’t see as many animals as you would expect from the most diverse terrestrial ecosystem on the planet. If I compare this to my snorkeling experience on the Great Barrier Reef there is a huge difference: on the reef you are overwhelmed by the number of fish, anemones and other creatures that are inhabiting it. No way you have to make a big effort to spot something. In the rainforest of course visibility is poorer and to the untrained eye many animals remain hidden among the trees and in the leaf litter, while the large ones are notoriously shy. But as well, a large percentage of the animals lives way up high in the canopy and therefore remains nearly invisible to us. Due to its inaccessibility the canopy and the creatures living there are poorly studied. Some scientists have figured that instead of going up they could make sure the creatures are brought down; by spraying insecticide into a tree top they were able to catch the arthropods on the ground that normally have their home in the canopy. According to these researches up to 50% of the known species in the rainforest live at height.  Anurans, frogs and toads, are found in the canopy in large numbers as well.

This large species diversity is explained by the very diverse ecological niches that exist in the canopy, where microclimatic conditions differ markedly from those in the forest and on the forest floor: the wind has a more pronounced impact here, temperatures are more extreme and humidity is very low. In a sense conditions here are more typical for a desert than for a rainforest. Epiphytes like bromeliads play a vital role in sustaining life in the canopy and act like oases in the desert by holding water (up to 4 liters for one bromeliad) in their leaf axils, creating water pools (for instance used by poison dart frogs to raise their tadpoles in). In this way up to 50.000 liters per hectare can be stored in these bromeliads. They harbor their own mini-ecosystems and seeing how many species they support and how sensitive they are to changing microclimatic conditions, studying them is of vital importance.

Lead scientist Shawn McCracken and his colleagues wanted to explore the effects of oil roads on the amphibians living in these bromeliads and therefore picked two oil roads in Ecuador’s Yasuni National Park, of which one was a ‘high-intensity’ oil road and the other a ‘low-intensity’ oil road. In the surroundings of the former considerable tracts of forest had been cleared, also because people had entered the area to colonize it and establish their own agricultural lands. In the latter there are only few clearings in the vicinity of the oil road and no people have been allowed to colonize the area. Unfortunately the data for the high-intensity road could not be collected, because the bromeliads in the vicinity of the road, of the species Aechmea zebrine, soon disappeared after the study had started. However they still collected interesting data in the control treatment and the low-intensity road.

Next to their findings, which I will discuss in a minute, the natural park in which they conducted their study has a peculiar recent history. The Yasuni National Park was made the focus of the ITT-Yasuni initiative, launched by the Ecuadorian government in 2008, that had the goal of collecting 3,5 billion dollars from the international community to compensate for leaving three remote blocs in the park (Ishpingo-Tambococha-Tiputini) untouched by oil development. The Yasuni National Park has been touted as the most biodiverse region in the world and also in terms of amphibian species, 150 in total, this park reigns supreme. The Ecuadorian president, Rafael Correa, wanted to preserve this area, but only if he would receive enough money, half of the estimated total revenue from the oil in this region, so that the Ecuadorian society did not have to bear the costs of preserving nature alone. As a side note, the money was destined to flow back to United Nations development projects and to community projects in the region.

It has been applauded as a bold initiative to conserve biodiversity, mitigate climate change and support indigenous people and can been seen as a form of payment for ecosystem services, because leaving the forest intact would provide many services to the human population as a whole.  On the other hand, some people felt like the president was effectively blackmailing the international community and simply trying to make money. However, I personally do sympathize with the initiative because it left the international community with the choice of preventing oil exploration in an ecologically highly valuable region, while in other countries that choice is mostly not even offered. Either way, after five years Rafael Correa decided to cancel the initiative, because until then only a fraction of the needed total had been collected, leading him to state that “The world has failed us”.

While the Ecuadorian president in my opinion was right to express his disappointment in the international community, he hardly has an impeccable reputation when it comes to environmental management in his country: Ecuador has the highest deforestation rate of any country in South-America and many rainforest areas have been affected severely by oil exploration. It is even the driving force in the Ecuadorian Amazon behind the deterioration of the forest; oil exploration leads to the construction of roads (and subsequent opening up of the forest for settlers) that have a severe negative impact on the flora and fauna through, among others,  the barrier effect, road kills, pollution and the edge effect. And now the research by McCracken et al. has shown that even the parts of the forest that were deemed unaffected by those ‘ low-intensity’ roads are significantly impacted.

In their study they sampled a total of 160 bromeliads, all Aechmea zebrine , by going up into the canopy and found in them 95 anurans from 10 different species.  For the undisturbed forest they found that 45% of the bromeliads were occupied by anurans, whereas only 25% of the bromeliads found close to the ‘low-intensity’ road provided a home to anurans. Moreover, they established that the number of individuals that were present within these bromeliads was also significantly lower near the oil road. This means that both species diversity and number of individuals that these bromeliads sustain, declined significantly in the vicinity of the ‘low-intensity’ oil road. A result that these scientists didn’t expect either, as they had noted that the habitat quality of the forest near to the road seemed to be good. Explaining this clear result therefore doesn’t seem that straight-forward, also because the habitat factors between the undisturbed canopy and that next to the road didn’t have any explanatory power, i.e. they didn’t differ significantly between these treatments.

Previous studies have shown however that linear clearings, like roads, can have a profound effect on forest structure and microclimate along the edge of the clearings. They can alter the microclimatic conditions and it is expected that these changes are exacerbated in the canopy, where the bromeliads  grow that are very sensitive to any change in these microclimatic conditions. The observation that communities of A. zebrine were smaller in the disturbed forest supports the idea that conditions are less favorable for them than in the undisturbed forest.  Fewer bromeliads means less suitable and more widely spread habitat for the anurans, while the scientists believe that the water in these bromeliads might be polluted as well by the nearby oil operations. The exact mechanism by which oil roads reduce the number of anurans in the canopy is still open for debate, but whatever may cause this decrease, the results are alarming nonetheless. This is why the scientists conclude their article by saying: “Based on these results, we support the recommendation […] to permit no new terrestrial access routes into Yasuni or its buffer zone and establish a moratorium on future exploration and extraction operations”. I fully agree with them, but the hunger for oil seems not to be satisfied yet and with governments only slowly implementing alternative ways of producing energy, a moratorium on oil extraction seems a far away dream.See also the article by Mongabay here