Can forest remnants in oil palm act as microclimate oases for biodiversity?

There is growing interest in the ecological value of set‐aside habitats around rivers in tropical agriculture. In their latest research, Williamson and colleagues investigate the capacity for riparian buffers to act as microclimatic refugia across an oil palm dominated landscape in Borneo.

In many ways, oil palm is a miracle crop – it is vastly more productive than its temperate and tropical counterparts and is a major contributor to tropical economies.

However, these benefits come at an environmental cost. Compared to lush tropical rainforests, oil palm plantations are barren deserts. As such, balancing the demand for palm oil with the need to protect the planet’s flora and fauna has become a hotly contested issue.

Clearly, oil palm is a hostile land for wildlife. How, then, can we make this desert more habitable for forest species, both now, and heading into a future overshadowed by anthropogenic climate change?

Riparian buffers are remnants of forest retained around rivers, which are afforded protection from development activities nearby, primarily to protect water quality. Studies reveal a diverse range of flora and fauna thriving in riparian buffers in farmland. However, what is less clear is the attributes a buffer needs to support biodiversity.

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A riparian buffer runs through a newly planted oil palm plantation. Photo: Dr Matthew Struebig

Technology is revolutionising the way that tropical ecologists undertake their research – we can now scan entire landscapes using aircraft-mounted lasers (LiDAR), creating 3D vegetation maps to scrutinise – and this enables us to study the importance of riparian buffers for protecting biodiversity.

When we combine these approaches with a new generation of dataloggers – USB sticks that can be left in the field to measure temperature and humidity for months on end – we are able to tease apart what riparian buffers are like in both a structural and microclimatic sense.

Our research shows that riparian buffers act as oases of cool, wet forest in a landscape dominated by the hot, dry oil palm plantations. We also demonstrate that buffers need to have a high vegetation quality, and therefore need to be protected from degradation via activities such as logging and grazing.

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An aerial shot of a typical riparian buffer in an oil palm plantation. Photo: Dr Sol Milne

How can we check that any of this even matters to the flora and fauna that we aim to protect? To find out, we need a bioindicator.

Dung beetles are arguably one of the best bioindicators in tropical forests – with some plastic bottles, a scrap of cloth and a bucket of freshly-mixed human dung (donated by charitable colleagues), you can catch thousands overnight.

When we combined our state-of-the-art techniques with the more rudimentary dung beetle sampling, we found some key relationships that govern biodiversity responses across palm oil landscapes.

First, wider riparian buffers are better for dung beetles than narrow ones. Riparian buffer width is one of the criteria that the Roundtable on Sustainable Palm Oil (RSPO) requires for their stamp of sustainability approval to be on palm oil products. Width is also mandated by many governments. However, these guidelines tend to vary among countries and are often 2.5-3 times lower than the 80 metres we recommend.

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The impressively-horned Proagoderus watanabei is one of the more charismatic dung beetles found in riparian buffers in Sabah, Malaysia. Photo: Dr Rob Knell

Second, the temperature of riparian buffers matters. In narrow buffers (20 metres width or less), higher temperatures had dire consequences on the beetles found there. Knowing that vegetation structure influences climatic conditions found in these buffers, we emphasise that we shouldn’t just focus on the mandatory widths to support biodiversity; habitat quality is vital too.

We therefore strongly advocate for further protection, restoration and replanting of degraded riparian buffers in tropical farmland. If we are to limit the loss of biodiversity across human-modified tropical landscapes, both now and in a warmer future, wildlife refuges like those provided in riparian buffers will become increasingly important.

Read the full article, Riparian buffers act as microclimatic refugia in oil palm landscapes, in Journal of Applied Ecology

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