Best‐practice forestry management delivers diminishing returns for coral reefs with increased land‐clearing

Abstract

Protection of coastal ecosystems from deforestation may be the best way to protect coral reefs from sediment runoff. However, given the importance of generating economic activities for coastal livelihoods, the prohibition of development is often not feasible. In light of this, logging codes of practice have been developed to mitigate the impacts of logging on downstream ecosystems. However, no studies have assessed whether managed land‐clearing can occur in tandem with coral reef conservation goals. This study quantifies the impacts of current land use and the risk of potential logging activities on downstream coral reef condition and fisheries using a novel suite of linked land‐sea models, using Kolombangara Island in the Solomon Islands as a case study. Further, we examine the ability of erosion reduction strategies stipulated in logging codes of practice to reduce these impacts as clearing extent increases. We found that with present‐day land use, reductions in live and branching coral cover and increases in turf algae were associated with exposure to sediment runoff from catchments and log ponds. Critically, reductions in fish grazer abundance and biomass were associated with increasing sediment runoff, a functional group that accounts for ~25% of subsistence fishing. At low clearing extents, although best management practices minimize the exposure of coral reefs to increased runoff, it would still result in 32% of the reef experiencing an increase in sediment exposure. If clearing extent increased, best management practices would have no impact, with a staggering 89% of coral reef area at risk compared to logging with no management. Synthesis and applications. Assessing trade‐offs between coastal development and protection of marine resources is a challenge for decision makers globally. Although development activities requiring clearing can be important for livelihoods, our results demonstrate that new logging in intact forest risks downstream resources important for both food and livelihood security. Importantly, our approach allows for spatially explicit recommendations for where terrestrial management might best complement marine management. Finally, given the critical degradation feedback loops that increased sediment runoff can reinforce on coral reefs, minimizing sediment runoff could play an important role in helping coral reefs recover from climate‐related disturbances.

Cumulative impact assessments highlight the benefits of integrating land-based management with marine spatial planning

“…In addition to having large impacts in intensity, the footprint of land-based activities is widely distributed throughout the reef and across all municipalities. These findings underline the critical role that integrated "ridge-to-reef management" should play (Álvarez-Romero et al, 2011;Brown et al, 2019;Carlson et al, 2019;Wenger et al, 2020). However, the current marine spatial plan does not address landbased pressures, focusing instead exclusively on regulating marine activities, hence failing to protect its waters from its key pressures.…”

Global forest restoration opportunities to foster coral reef conservation

“…A next step consists of adapting this workflow to local planning by accounting for other data sources (Figure 6, also see Brown et al, 2017;Tulloch et al, 2021). The utility of modelling soil loss from watersheds to identify the potential management options has been demonstrated by several small-scale studies (Delevaux et al, 2018;Tulloch et al, 2021;Wenger et al, 2020). Follow-up analysis could address additional sources of sediment, for example, gully erosion or bank erosion to the river.…”

Assessing Effects of Sediment Delivery to Coral Reefs: A Caribbean Watershed Perspective

“…However, even if validated, models can still misrepresent actual sediment dynamics (Smith et al, 2011). Watershed models that are used to estimate sediment discharge are conceptualized in some form of the sediment budget framework in that they apply the principle of mass conservation (Equation 2) where erosion is allocated to either "storage" or "sediment discharge" (e.g., Bartley et al, 2007;Wenger et al, 2020). In essence, sediment budgeting analyses can lead to targeted mitigation strategies.…”