To settle or protect? A global analysis of net primary production in parks and urban areas

We test-at the global scale-the hypothesis that human beings tend to build settlements in areas of high biological productivity, and protect (as parks) areas of low productivity. Furthermore, we propose an alternative measure of the extent and effectiveness of the global protected areas network based on potential net primary production (NPP0). The average NPP0 in urban areas and parks is calculated and compared to the average NPP0 of the geopolitical regions and biomes containing these areas. Additionally, human appropriation of net primary production (HANPP) in parks is used as an indicator of the effectiveness of these protected areas. We find that in almost all regions of the world, humans have chosen to settle in the most productive areas. At the global scale, urban areas have considerably higher NPP0 (592 g Cm− 2 yr− 1) than the global average (494 g Cm− 2 yr− 1), while parks have roughly average NPP0 (490 g Cm− 2 yr− 1). Parks with an IUCN category of I-VI account for 9.5% of the planet's terrestrial NPP0, compared to 9.6% of its terrestrial area. Although protected area and protected NPP0 are nearly equal, this equivalence is diminished by HANPP within parks. Globally, the average HANPP in all protected areas is 14% of their NPP0, and HANPP within parks increases as the park management category becomes less restrictive. Moreover, we find a positive correlation between HANPP in parks and the extent of urbanization in the surrounding region and biome. Area-based targets for conservation provide no information on either the quality of the areas we choose to protect, or the effectiveness of that protection. We conclude that NPP0 and HANPP may provide an additional, useful tool for assessing the extent and effectiveness of the global protected areas network.