Measuring benefits of protected area management: trends across realms and research gaps for freshwater systems

Abstract

Protected areas remain a cornerstone for global conservation. However, their effectiveness at halting biodiversity decline is not fully understood. Studies of protected area benefits have largely focused on measuring their impact on halting deforestation and have neglected to measure the impacts of protected areas on other threats. Evaluations that measure the impact of protected area management require more complex evaluation designs and datasets. This is the case across realms (terrestrial, freshwater, marine), but measuring the impact of protected area management in freshwater systems may be even more difficult owing to the high level of connectivity and potential for threat propagation within systems (e.g. downstream flow of pollution). We review the potential barriers to conducting impact evaluation for protected area management in freshwater systems. We contrast the barriers identified for freshwater systems to terrestrial systems and discuss potential measurable outcomes and confounders associated with protected area management across the two realms. We identify key research gaps in conducting impact evaluation in freshwater systems that relate to three of their major characteristics: variability, connectivity and time lags in outcomes. Lastly, we use Kakadu National Park world heritage area, the largest national park in Australia, as a case study to illustrate the challenges of measuring impacts of protected area management programmes for environmental outcomes in freshwater systems.

Keywords: Kakadu National Park; freshwater ecosystems; impact evaluation; protected area management.

Figure 1.

Aquatic ecosystems and land uses within and adjacent to Kakadu National Park in northern Australia. Threats to natural ecological values within Kakadu are depicted, emphasizing connectivity issues that should be considered when designing impact evaluations (refer to text for detailed explanation).

Figure 2.

Potential experimental designs for measuring the impact of protected areas in terrestrial (a–c) and freshwater systems (d–f). (a) A directed acyclic graph (DAG) reflecting standard quasi-experimental design employed in many studies [9] in which the causal effect of protection on forest cover is measured while controlling for confounding variables. (b) Measuring the impact of protected area management may require more complex outcome measures such as species abundance. It may also require considering multiple mechanisms such that protection has a causal impact on the mechanisms (e.g. fire, poaching and logging) and the mechanisms have an effect on the outcome measure. (c) In terrestrial environments (grey shows forest habitat, outline shows protected area and black heavy outline shows sample units), the selection of sample units can rely on standard units such as grids while controlling for confounding variables such as slope and vegetation [9]. (d) A similar quasi-experimental design could be employed in freshwater systems to measure the causal effect of protection on river flow while controlling for confounding variables. (e) Measuring the impact of protected area management on freshwater ecosystems may require different outcome measures compared to those used in terrestrial environments, based on theories of change that account for the causal effect of protection on mechanisms (e.g. fire, invasive species, riparian management) and the mechanism effect on the outcome measure. (f) In freshwater environments, sample units may need to be irregular shapes and sizes to capture connected units (grey shows protected area and black heavy outline shows sample units). Here, we depict several catchments, one of which is protected (shown in grey shading). The full catchment may be an appropriate sample unit and thus a matched catchment would be required as a control (shown in black heavy outline).

Figure 3.

Map of historical mimosa density across water bodies in Northern Australia displayed at a 1 km resolution (based on reference [55]). Kakadu National Park boundary is shown to emphasize the difference in infestation levels within the park and on neighbouring floodplains to the east (East Alligator/Murgenella) and to the west (Mary River). Floodplains considered in our analysis are labelled with their initials (from west to east: MR, Mary River; WM, Wildman/West Alligator; SA, South Alligator; EA, East Alligator; EA/M, East Alligator/Murgenella).