Spatial planning for a green economy: National-level hydrologic ecosystem services priority areas for Gabon

<div><p>Rapidly developing countries contain both the bulk of intact natural areas and biodiversity, and the greatest untapped natural resource stocks, placing them at the forefront of “green” economic development opportunities. However, most lack scientific tools to create development plans that account for biodiversity and ecosystem services, diminishing the real potential to be sustainable. Existing methods focus on biodiversity and carbon priority areas across large geographies (e.g., countries, states/provinces), leaving out essential services associated with water supplies, among others. These hydrologic ecosystem services (HES) are especially absent from methods applied at large geographies and in data-limited contexts. Here, we present a novel, spatially explicit, and relatively simple methodology to identify countrywide HES priority areas. We applied our methodology to the Gabonese Republic, a country undergoing a major economic transformation under a governmental commitment to balance conservation and development goals. We present the first national-scale maps of HES priority areas across Gabon for erosion control, nutrient retention, and groundwater recharge. Priority sub-watersheds covered 44% of the country’s extent. Only 3% of the country was identified as a priority area for all HES simultaneously, highlighting the need to conserve different areas for each different hydrologic service. While spatial tradeoffs occur amongst HES, we identified synergies with two other conservation values, given that 66% of HES priority areas intersect regions of above average area-weighted (by sub-watersheds) total forest carbon stocks and 38% intersect with terrestrial national parks. Considering implications for development, we identified HES priority areas overlapping current or proposed major roads, forestry concessions, and active mining concessions, highlighting the need for proactive planning for avoidance areas and compensatory offsets to mitigate potential conflicts. Collectively, our results provide insight into strategies to protect HES as part of Gabon’s development strategy, while providing a replicable methodology for application to new scales, geographies, and policy contexts.</p></div

The portfolio of combined hydrologic ecosystem services priority areas.

<p>(A) “All population” scenario. (B) “Rural-weighted” scenario. (C) Overlap between these scenarios. For (A) and (B), percentage areas (of the total country area) are reported for each unique combination of the HES objectives. For (C), the percentage area of overlap and separation is reported across the two scenarios.</p

Spatial biophysical inputs for hydrologic ecosystem services modeling.

<p>Data sources are described in the main text.</p

Land use/land cover map for Gabon used in the analysis.

<p>Land use/land cover map for Gabon used in the analysis.</p

Servicesheds for erosion control, nitrogen retention, and phosphorus retention weighted by downstream beneficiary population size.

<p>(A) “All population” serviceshed. (B) “Rural-weighted” serviceshed. Pixel values represent the number of downstream people within each serviceshed that would benefit from a watershed conservation activity on that pixel. Therefore, pixels with the highest values are those with the largest downstream population.</p

Priority areas of sub-watersheds (top 20% by area) for each hydrologic ecosystem service.

<p>(A-C) Erosion control, nitrogen retention, and phosphorous retention for the “all population” scenario. (D-F) Erosion control, nitrogen retention, and phosphorous retention for the “rural-weighted” scenario. (G) Groundwater recharge for the single scenario (i.e., not weighted by population distribution). Grey lines show the boundary of all the sub-watershed polygons.</p

Overlap of hydrologic ecosystem services priority areas with other indicators of conservation value.

<p>Overlap with national parks (shown in black outline) for (A) “all population” and (B) “rural-weighted” scenarios. All other colors represent portfolio sub-watersheds as described in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0179008#pone.0179008.g005" target="_blank">Fig 5</a>. Overlap with forest carbon stocks below or equal to (orange color) or above (purple color) the average sub-watershed total carbon stock across the country (154 MgC ha^-1) for (C) “all population” and (D) “rural-weighted” scenarios.</p