The world is edging toward a major conservation target for protected land and oceans, but there are concerns over how safeguarded areas are managed and whether they are effectively protecting endangered species, according to a new report.

Nearly 15% of the Earth’s land, covering around 20m sq km, is contained in national parks or other protected areas. This figure has flatlined over the past year, largely because of improved data collection, but is close to an internationally agreed goal to protect 17% of the land surface by 2020.

There has been a faster rate of progress in ocean conservation, albeit of a low base. Around 4% of the total surface of the ocean, covering 15m sq km, is now protected. This area, roughly the size of Russia, has quadrupled in size over the past decade.

But the progress report by the UN Environment and the International Union for Conservation of Nature (IUCN) warns that some of the most biodiverse ecosystems are not being protected and that the management of many protected areas is deficient.

Less than 20% of areas considered crucial hubs for species are fully protected, the report states, with countries routinely failing to assess the effectiveness of their national parks nor provide wildlife corridors that allow animals to roam between protected areas.

Restricting hunting, mining and other development helps species’ overall survival chances, with the report stating that global populations of terrestrial species in protected areas suffered an average decline of 18% from 1970 to 2010, compared to a 39% loss for species when unprotected areas are included.

“Ecological factors such as park size, fragmentation and connectivity are fundamentally important in the long term, but are often superseded by short-term social and economic factors,” the report, presented at the IUCN congress in Hawaii, found.

“Protected areas can have positive impacts on species extinction risk and population trends, but they need to be properly sited and managed to realize their full potential.”

Erik Solheim, head of UN environment, said that “huge gains” have been made in the quantity of protected areas, but this had to be matched by their quality.

“The world needs to do more to effectively protect our most biologically diverse spaces,” he said. “Protected areas need to be better connected, to allow populations of animals and plants to mix and spread. Also important is ensuring local communities are involved in protection efforts. Their support is fundamental to long-term conservation.”

Countries in South America and the Caribbean protect the largest portion of their land, with Brazil accounting for the world’s largest safeguarded system, spanning 2.47m sq km. Countries in the Middle East, by contrast, protect just 119,000 sq km, or around 3% of the area’s landmass.

Some nations are moving towards including biodiversity values in their national accounts, such as the UK, which has accounted for the value of air quality and recreation in areas such as the Lake District. But other nations continue to subsidize ecologically harmful practices, such as Thailand’s support for a shrimp farming industry that is resulting in the destruction of mangroves.

Marine reserves have grown thanks to new measures taken by countries including Australia, New Zealand, the UK and Spain. The report does not include the recent creation of the world’s largest ocean reserve by the US, off the north-western islands of Hawaii.

Conservationists are pushing for far greater efforts to protect marine life, with a resolution put to the IUCN congress that nations aim for 30% of the oceans to be protected. While terrestrial ecosystems are affected by climate change, poaching and mass land conversion for agriculture, the warming, acidifying oceans are possibly faring even worse with less protected area.

Dan Laffoley, a marine adviser for the IUCN, said the 30% target is “important, absolutely critical, but we need to think beyond those targets. We need to protect much more of the ocean, only about 1% is strictly protected.

“With the knowledge we have, we need more than that. We need a far more strategic, connected approach if we are going to get out of this mess.”