A UN conference on preserving the earth's dwindling resources opened Monday with grim warnings that the depletion of natural habitats and species was outpacing efforts to protect them.

Just a week after conservation group WWF said wildlife numbers had halved in 40 years, governments met in South Korea to analyse progress since they agreed four years ago on 20 targets for stemming the tide of biodiversity loss by 2020.

The opening of the UN Convention on Biological Diversity (CBD) conference saw the release of a comprehensive report showing those targets were not being met, with natural habitats still disappearing at an alarming rate, and animals facing increased extinction threats.

"It is a document that should make the whole world sit up. It is about all of life on earth," said the executive director of the UN Environment Programme Achim Steiner.

"We need to do more -- and do it fast -- to protect the very fabric of the natural world," Steiner said.

The so-called Aichi Biodiversity Targets -- drawn up in 2010 -- included halving the rate of habitat loss, expanding water and land areas under conservation, preventing the extinction of species on the threatened list, and restoring at least 15 percent of degraded ecosystems.

"Encouraging steps have been taken around the world to tackle biodiversity loss at many levels," the CBD said in its Global Biodiversity Outlook report.

"Nevertheless, it is clear from this mid-term review that, on their current trajectory, they will not be sufficient to meet most of the targets by the deadlines committed to."

-- 'Alarming' deforestation --

Global rates of deforestation are still "alarmingly high" despite a slowdown in the depletion of the Brazilian Amazon and gains in forest coverage in Vietnam and China, the report said.

Habitats of all types, including forests, grasslands, wetlands and river systems, continue to be fragmented and degraded.

In one striking example of long-term degradations, the report cited a 20 percent reduction since 1980 in the populations of wild birds specialising in habitats such as grasslands and forests in North America and Europe.

Short-term projections of the dangers facing animal species as a result of habitat loss generally predict a "worsening" situation, the report said.

"Despite individual success stories, the average risk of extinction for birds, mammals and amphibians is still increasing," it warned.

The most recent update of the International Union for Conservation of Nature's Red List of threatened species in July said a quarter of mammals, over a tenth of birds, and 41 percent of amphibians are at risk of extinction.

Last week, the WWF's 2014 Living Planet Report highlighted a 52 percent decline in mammals, birds, reptiles, amphibians and fish overall from 1970 to 2010.

It said humans were consuming resources at a rate that would require 1.5 Earths to sustain -- gobbling up animal, plant and other resources at a faster rate than nature can replenish them.

Nations have struggled to find common ground on funding for the Aichi Targets, especially for poor nations whose scarce resources are already committed elsewhere.

At the CBD's last meeting, in Hyderabad, India, in 2012, the world agreed to double biodiversity aid to developing countries by 2015.

But they did not quantify either the base amount or the target -- and the numbers are still far from being resolved.

In a study published last week in the journal Science, an international team of more than 30 scientists also concluded that the Aichi Targets were unlikely to be met.

"There is a collective failure to address the loss of biodiversity, which is arguably one of the greatest crises facing humanity," said Richard Gregory, one of the paper's authors and head of species monitoring and research at the British RSPB conservation group.

And the WWF's global policy director, Susan Brown, said Monday's report was a wake-up call for governments who now had to "supercharge efforts" to meet the 2020 goals.

"The CBD, its parties and all stakeholders cannot afford to fail," Brown said in a statement.

"This meeting must break down barriers to generate the willpower and resources to protect what little remains of our natural world," she added.