In their new study, Gabriela Montejo-Kovacevich and colleagues consider whether riparian zones provide biodiversity conservation benefits for Butterflies.
Selectively logged tropical forest is now more widespread than old-growth primary forest, except in the Amazon and Papua New Guinea. Logging forests for timber is less devastating for biodiversity than other types of land-use change that are ravaging through tropical regions, such as conversion to agriculture or cattle pastures. However, the demand for timber is on the up and, in many regions, secondary forests are the only refuge left for biodiversity. How, then, can we make the best out of these remnants of degraded forest?
Protecting intact forest around streams is often the only legal requirement enforced when it comes to selective logging in the tropics. These ‘riparian reserves’ (or buffers) were initially designed to protect the all-important water supply of forests, but they can also act as safe havens for biodiversity. In highly degraded landscapes such as oil palm plantations, riparian reserves have been found to protect microclimates and biodiversity. What is less clear, and what we tackle in this study, is whether these set-asides of untouched forest have an important role in biodiversity conservation when the surrounding forest is less degraded, such as in selective logging concessions.
Studying butterflies in the Brazilian Amazon
One of the easiest groups of insects to collect systematically is the fruit-feeding butterflies (Family: Nymphalidae). To do this, you need, as the name suggests, lots of fruit. Rotting, fermenting banana is full of volatiles that attract all sorts of insects, but butterflies have a particular soft spot for it. We used around 40kg of old bananas a week to replenish 48 butterfly traps every two days, which rotated between habitat types. All butterflies trapped were photographed, marked, and released in situ, helping us track butterfly dispersal within the forest.
We focused on sampling butterflies within riparian reserves, near ephemeral or permanent streams, and paired sites 200 m towards the forest interior that had been recently selectively logged. Similarly, we sampled primary forest areas that have not yet been logged, also near streams or in interior forests. This design allowed us to test whether butterfly communities in riparian reserves were more similar to primary forest than to interior logged forest, in other words, assess the value of riparian reserves in protecting primary forest-like assemblages.
Riparian reserves within logging concessions are doing their job – to an extent
We found that the butterfly communities in the riparian reserves within logged areas were similar to those communities found in primary forest, whereas the communities inside logged forest had a slightly different set of butterflies. We even found that butterfly communities inside the riparian reserves were often much more similar to the butterflies in primary forests many kilometres away than the butterflies trapped inside logged forest only 250m away.
Maintaining taller trees inside the riparian reserves, so that a high canopy is maintained, was a key predictor of retaining a primary forest-like community. Generally, there were no specific groups of butterflies that disproportionally benefitted from riparian reserves, but we did find that primary forest was irreplaceable for some species such as Magneuptychia analis or Opsiphanes cassina.
So, what now?
We found that riparian reserves inside logged forest were providing an important refuge for primary forest butterflies, although they cannot fully replicate the conditions of large areas of primary forest. This is in line with other animals in tropical landscapes, such as for birds in oil palm plantations and mammals found on riparian strips embedded in cattle pastures Riparian buffers are also likely to be an important corridor increasing connectivity between primary forest patches, helping to maintain their diversity (see here).
In Brazil, legal requirements require riparian buffers of 60m (30m either side) around small streams which seems sufficient for most butterfly species. However, in southeast Asia requirements are much narrower, and so work is required to explore the biodiversity-financial trade-offs for optimal buffer widths. Riparian strips are likely to become increasingly important refuges for biodiversity in the face of land-use and climate change, so future studies should also assess to what extent these corridors protect other taxa.
Read the full paper Riparian reserves protect butterfly communities in selectively logged tropical forest in Journal of Applied Ecology.