Global forest restoration opportunities to foster coral reef conservation

Abstract

Sediment runoff from disturbed coastal catchments is a major threat to marine ecosystems. Understanding where sediments are produced and where they are delivered enables managers to design more effective strategies for improving water quality.A management strategy is targeted restoration of degraded terrestrial areas, as it provides opportunities to reduce land-based runoff from coastal areas and consequently foster coral reef conservation. To do this strategically, a systematic approach is needed to identify watersheds where restoration actions will provide the highest conservation benefits for coral reefs. Here, we develop a systematic approach for identifying global forest restoration opportunities that would also result in large decreases in the flux of sediments to coral reefs. We estimate how land-use change affects sediment runoff globally using high-resolution spatial data and determine the subsequent risk of sediment exposure on coral reefs using a diffusion-based ocean transport model. Our results reveal that sediment export is a major issue affecting 41% of coral reefs globally. The main coastal watersheds with the highest sediment export are predominantly located in Southeast Asian countries, with Indonesia and the Philippines accounting for 52% of the sediment export in coastal areas near coral reefs. We show how restoring forest across multiple watersheds could help to reduce sediment export to 63,000 km 2 of coral reefs. Although reforestation opportunities in areas that discharge onto coral reefs are relatively small across watersheds, it is possible to achieve large sediment reduction benefits by strategically targeting watersheds located in regions with a high density of corals near to the coast. Thus, reforestation benefits on coral reefs do not necessarily come from the watersheds that produce the highest sediment export. These analyses are key for generating informed action to support both international conservation policy and national restoration activities.

Global rarity of intact coastal regions

“…Alleviating threats to coastal regions under high levels of human pressure will therefore require comprehensive assessments of the specific drivers of change within and beyond the 50‐km radius we applied. Results of such assessments will inform development of and identify the challenges of implementing targeted management strategies, such as managing run‐off, to reduce impacts to coastal ecosystems (Suárez‐Castro et al., 2021; Wenger et al., 2020). Our methods have the same limitations inherent to all cumulative pressure mapping efforts—other anthropogenic pressures that affect coastal regions could not be included due to incomplete spatial or temporal coverage, such as changes in sedimentation and freshwater input (Ezcurra et al., 2019; Halpern et al., 2019; Venter et al., 2016b).…”

Modelling the spatial extent of post‐fire sedimentation threat to estimate the impacts of fire on waterways and aquatic species

“…The RUSLE model can be applied on any land use, including areas of modified vegetation. It was first introduced in the USDA Soil and Water Conservation Service in 1993 and has been used extensively to explore soil loss in many countries (Renard et al, 1997; Suárez‐Castro et al, 2021; Teng et al, 2016). The RUSLE calculates the annual soil loss by water on a hillslope using a linear equation that is the product of six environmental factors:where RUSLE is the average annual soil erosion at each cell (t ha −1 year −1 ); R is the rainfall‐run‐off erosivity factor (MJ mm ha −1 h −1 year −1 ); K is soil erodibility factor (t ha h ha −1 MJ −1 mm −1 ); L is the slope length factor; S is the slope steepness parameter; C is the cover management factor (representing the ratio of soil loss from land cropped under specific conditions to the corresponding loss from a tilled, continuous fallow condition); and P is the erosion control support practice factor (which provides a ratio between the soil loss expected for a certain soil conservation practice to that with increasing and decreasing surface slope) (Table 2) Teng et al (2016) have calculated the RUSLE values for all of Australia at a scale of 1 km.…”

“…The RUSLE model can be applied on any land use, including areas of modified vegetation. It was first introduced in the USDA Soil and Water Conservation Service in 1993 and has been used extensively to explore soil loss in many countries (Renard et al, 1997;Suárez-Castro et al, 2021;Teng et al, 2016). The RUSLE calculates the annual soil loss by water on a hillslope using a linear equation that is the product of six environmental factors:…”

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

“…3. Relying on specific land cover types as proxies for sediment delivery tends toward generic policy recommendations, like reforestation (e.g., Suárez-Castro et al, 2021), with questionable levels of success (e.g., Basher, 2013;Ramos-Scharrón and Figueroa-Sánchez, 2017). On small-to medium-sized watersheds like those draining the USVI and PR, relatively small sources are responsible for a sizable portion of the sediment yield (e.g., Ramos-Scharrón and MacDonald, 2007b;Stock et al, 2014;Labrière et al, 2015;Carlson et al, 2019), and depending on previous uses, forested lands can produce similar amounts of sediment as those that are actively used (Ramos-Scharrón et al, 2021).…”