The effect of a protected area on the tradeoffs between short-run and long-run benefits from mangrove ecosystems
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Catherine G. McNally, Emi Uchida, and Arthur J. Gold


Protected areas are used to sustain biodiversity and ecosystem services. However, protected areas can create tradeoffs spatially and temporally among ecosystem services, which can affect the welfare of dependent local communities. This study examines the effect of a protected area on the tradeoff between two extractive ecosystem services from mangrove forests: cutting mangroves (fuelwood) and harvesting the shrimp and fish that thrive if mangroves are not cut. We demonstrate the effect in the context of Saadani National Park (SANAPA) in Tanzania, where enforcement of prohibition of mangrove harvesting was strengthened to preserve biodiversity. Remote sensing data of mangrove cover over time are integrated with georeferenced household survey data in an econometric framework to identify the causal effect of mangrove protection on income components directly linked to mangrove ecosystem services. Our findings suggest that many households experienced an immediate loss in the consumption of mangrove firewood, with the loss most prevalent in richer house holds. However, all wealth classes appear to benefit from long term sustainability gains in shrimping and fishing that result from mangrove protection. On average, we find that a 10% increase in the mangrove cover within SANAPA boundaries in a 5-km2 radius of the subvillage increases shrimping income by approximately twofold. The creation of SANAPA shifted the future trajectory of the area from one in which mangroves were experiencing uncontrolled cutting to one in which mangrove conservation is providing gains in income for the local villages as a result of the preservation of nursery habitat and biodiversity.

Main Results and Conclusions:
  • A major mangrove protection project in Saadathi National Park (SANAPA) in Tanzania is examined in order to assess the effects of mangrove protection efforts on local communities. The goal of the protection project is to reduce mangrove loss while continuing to support residents within the park who currently rely on mangroves as a source of income
    • “The loss of mangroves within SANAPA slowed considerably after the park’s establishment in 2005” (13947)
  •  SANAPA succeeded in slowing the loss of mangroves. At the same time, many households that previously used mangrove trees for cooking or heating fuel likely switched to using other species of trees, which may have unexpected impacts on biodiversity.
    • “Between 1990 and 2009, the use of mangroves as primary household fuel decreased from 42% to 34%, but the largest decrease took place between 2004 (39%; before SANAPA) and 2009 (34%; after SANAPA)…with SANAPA, a number of households in the area lost a key extractive ecosystem service…Most households that no longer use mangroves have switched to other trees, which may result in biodiversity impacts yet to be explored.” (13947)
  • SANAPA led to a significant increase in the income from shrimping for households by increasing mangrove cover
    •  “[Shrimping and fishing combined] were the most important income source in 2009 for nearly 40% of the sample.” (13947)
    • “Households engaging in shrimping increased from 16% of the sample in 2004 to 23% in 2009. Households engaging in fishing increased even more, from 27% in 2004 to 43% in 2009.” (13947)
    • “a 1-km2 increase in mangrove cover within SANAPA increased the shrimping income by 19.5 million Tsh (approximately $13,000) per year” (13947)
    •  “a 1-km2 increase in mangrove cover outside SANAPA increased shrimping income by only 626,000 Tsh (approximately $417; Table 4, row 2).” (13947)
    • “The changes in these incomes are a result of an increase in number of shrimping and fishing days, earnings per day, and, in the case of fishing, increase in consumption per day as well.” (13948)
  • The poorest households are not necessarily able to easily make a transition from using mangroves in unsustainable ways, so more can and should be done to assist these groups in the future. Nevertheless, a long-term protection strategy for mangroves has greater benefits for communities than rampant short-term exploitation of mangroves.
    • “Only 2% of the households in the poorer group changed to a different source of fuel since 2005, suggesting the need for some support to transition to alternative fuel sources.” (13948)
    • “Even if it were at a sustainable level, the long-term sustainability of shrimp and other fisheries is contingent not only upon the continued existence of nursery habitat, but also sustainable levels of harvest, which requires appropriate institutions and property rights to manage the fisheries effectively.” (13948-13949)


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