Editor’s Choice 57:12 – Best-practice forestry management delivers diminishing returns for coral reefs with increased land-clearing

Associate Editor, Dr Kiran Dhanjal-Adams, introduces the December Editor’s Choice paper, which demonstrates that sediment runoff from industrial logging can affect food security and livelihoods in the Solomon Islands.

Kolombangara is an island in the Western Province of the Solomon Islands in the South West Pacific. The island harbors a large variety of ecosystems, ranging from mangrove ecosystems at sea level to cloud forest ecosystems along the crater, with 16 endemic species – including the Kolombangara White Eye and the recently rediscovered New Georgia Monkey-faced Bat (endemic to the Solomons).

Kolombangara roughly translates to the ‘Water Lord’ – the island owes its name to the 75 river catchments that deck its flanks. Forests are informally protected above 400m altitude, leaving roughly one third of the island free from logging. However, logging still occasionally occurs above 400m.

Logging has repercussions for sediment runoff within the many river catchments of the island. Sediment not only reduces the quality of drinking water, but also causes indirect impacts much further downstream in the neighboring coral reefs, where sedimentation increases turbidity, decreases coral cover and reduces fish abundance. This is especially problematic because grazing coral reef fish constitute roughly 25% of subsistence fishing of Kolombangara, leading to a tradeoff between the benefits of coastal development and the benefits of coastal protection

In this month’s Editor’s Choice, Wenger and colleagues use a combination of land-sea modelling to quantify the influence of different logging scenarios on sediment runoff and coral reef health. This method is unique in that it links remote sensing, models of soil erosion, models of marine sedimentation and coral reefs field surveys. Importantly, the authors’ also quantify the potential impacts of logging above 400m on the surrounding coral reefs.

Logging codes of practice in the Solomon Islands currently require a 100m riparian buffer and forbid logging on a slope of more than 25 degrees. However, these best management practices, when compared with no management, had little benefit for reef sedimentation under high levels of logging (20-40% logged).

In fact, 40% logging put a shocking 89% of coral reefs around Kolombangara at risk of sedimentation. Only when less than 20% logging occurred, did best management practices provide a benefit when compared to no management. However, this ‘best case scenario’ still resulted in 32% of the reef experiencing an increase in sediment exposure.

Kolombangara fig 2
Sediment runoff on New Georgian (neighboring Kolombangara). Photo: Tim Adams

Though many coral species can deal with some degree of turbidity, this research confirms that shifts will occur in coral communities above a certain sedimentation threshold, with knock-on effects on for local fisheries. This study also highlights how rapidly this threshold is reached with only small amounts of logging. Maintaining protection above 400m in Kolombangara will therefore be beneficial to reef health and fisheries.

Finally, the results demonstrate the importance of integrating management across realms that are often not considered in unison – terrestrial and aquatic. Such an approach allows for spatially-explicit recommendations for managers to understand what management practice to perform where, with mapped impacts on the surrounding and downstream environment.

The full Editor’s Choice article, Best‐practice forestry management delivers diminishing returns for coral reefs with increased land‐clearing, is free to read for a limited time in Journal of Applied Ecology

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