headshot of a kaka, a parrot species from New Zealand

Slowing biodiversity loss by designating half the world as a nature reserve

Slowing biodiversity loss is more than a desire, it is an imperative if we are to feed everyone well. The problem is that the ideas to slow extinction rates often involve a compromise with food production and other land use.

Slowing biodiversity loss is essential.

There is an idea that we might need to designate half the world as a nature reserve to achieve this outcome. Yep, half the landmass and presumably half the oceans as well.

This idea comes about because of extraordinary levels of biodiversity loss that are way above rates in the fossil record, which researchers term the background rate.   

This background extinction rate refers to organisms that go extinct over time. And they do because this is how evolution works. Types of organisms evolve, but other types are lost as the local and sometimes global conditions change beyond their ability to cope. Extinction is both natural and inevitable. 

This natural attrition can also be used to estimate the average duration of a species in the fossil record. For mammals, this is roughly 1 million years. 

Humans still have over 700,000 years to go to achieve the average. And despite, or perhaps because of, our extraordinary numerical, distribution, and energetic success, we are doing our utmost to die young as a species. Human activity is messing with the planet, hence the idea to designate half of it as a reserve.

First, let’s look at the current extinction event.

The Anthropocene mass extinction

Nature is in the midst of a significant global extinction event. This is the sixth mass extinction, as it is now called by the evolutionary biologists who study patterns of species gain and loss. 

Based on historical estimates of species extinctions, rates of biodiversity loss are way above background from a range of factors, particularly the uniquely human ability to convert land to agricultural production. 

Humans appropriate at least a quarter of the net primary production on the planet into various foods from crops and livestock. This happens directly and through the disruption of the natural vegetation, such as when forests are cut down to grow crops or cows.

This appropriation of net primary production reduces the amount of energy and space available to other organisms. Rare species that are often already few can succumb to this resource loss. Shortages affect individuals’ survival, growth and reproductive capacity, causing population numbers to decline. 

We call the human use of primary production by many names: habitat change, deforestation, land clearing and related emotive words. But the reality is that human population size, our fantastic ability to grow food and therefore to keep increasing our population size, is altering the landscape and has been done since agriculture was invented 12,000 years ago. 

The significant changes began with the industrial revolution when we put power into our agricultural processes through fossil fuels. 

All of these things are well known. 

Human manipulations of the landscape, changes to the atmosphere, impacts on the oceans and biodiversity loss combine for changes that geologists estimate would be recognizable in the future stratigraphic record. In other words, humans have instigated a new geological epoch, the Anthropocene. 

All of these things are truly dramatic in the grand scheme of things. 

Being alive at the changing of an epoch is miraculous, given they only come along every 5 million years plus. 

Wow, go us.

Make half the world a reserve for slowing biodiversity loss.

OK, we made a bit of a mess, enough to start a new epoch. 

The difference between humans and all other living organisms is that we have cognition and agency. We recognize what has happened and what is happening now. We also believe there are also things we can do about it. And that spirit of agency brings us to the reserve idea.

As an alternate to the rewilding concept, the idea going around is that the only way to prevent further degradation of the environment and loss of biodiversity is to make half the world a reserve

That’s the number researchers reached when analyzing the available data. There are challenges enough in rewilding 30% of the earth, not least being how to feed everyone well, but reserving all that land is another thing.

It is hard to imagine what the world would look like if half of the landmass became a national park, nature reserve, conservation area or whatever we call them. 

Presumably, they would have to be multiple-use parks like conservation areas in parts of Europe where people live in national parks and even undertake agricultural practices. But those practices are limited, as is development, so the native vegetation is encouraged to return to something like its original form; if that is even possible.

Rewilding, a return to the wild by removing human influences and letting nature take care of itself, would be one of the mechanisms for rehabilitation to make the new reserves look like reserves. 

Is there enough land?  

The habitable land area on Earth is about 106 million km, roughly 71% of the total land area.  

About half the habitable land is used for agriculture; the rest is forest, shrubland and freshwater. About 1% is used for towns, cities and other human infrastructure.

The 48 million km2 of agricultural land is divided between livestock and cropping—the animals use 37 million km2, and the crops 11 million km2.

Here is a bit more detail on the numbers from Our World in Data.

graphic of global land use to illustrate how hard it will be slowing biodiversity loss

Humans already use most of the available land for production purposes. The rainforests make the news because we continue to cut down to convert to agriculture as the lazy source of new agricultural opportunities.

The land in use provides enough food for 8 billion people and their pets, even when a third of production is wasted along the supply chain. But problems with distribution and access to that food mean that nearly a billion people are underfed and another three billion suffering one or other form of malnutrition.

In other words, there is no buffer in the current food production system. Insufficient land exists to retire a significant proportion from food production without increasing starvation risk.

But let’s dig deeper anyway and see if half of the world could become a reserve. 

Half the world

If land covers 29% of the planet and a third is uninhabitable, there is not much land for people and all the other organisms. It’s already a tight squeeze.

Currently, half the habitable land is used for agriculture, with roughly a quarter of that used for crops.

So where is the half for nature reserves?

graphics to show the relative area of arable land compared with the land area of the planet

Forests are 38% of habitable land, so they could all be turned over to reserves. This would mean no paper, construction timber, firewood, or charcoal. 

Almost 2.8 billion people still rely on coal, charcoal, and wood to cook food. Where charcoal is the primary cooking fuel, yearly usage per person is roughly 150 kg.

But even if all the forests became reserves, there is still another 12% of habitable land area to find, roughly 13 million km2. We could get this from the shrublands that are mostly semi-arid or at temperature extremes that prevent tree or grass growth. These are relatively unproductive lands, so why not make them reserves?

Building up ‘the half’ from forests and shrubland would mean the agricultural land could stay as a food source. This would be essential for future food security and avoid the complication of convincing the people living on the land of their new status as reserve residents with its constraints on tillage, harvest and fertilizer use. And while we are at it, take the ground that they have managed for decades is no longer theirs but is, in fact, a custodianship for a greater good. 

Of course, people would not allow this to happen. And even if it did, the real question, similar to the affliction hidden in the climate change story, is if we were to allocate half the global land area and half the oceans to reserve or conservation values status, would that solve the problem of slowing biodiversity loss? 

If we picked the forests and the shrublands and stayed clear of the agricultural lands, what about the loss of diversity in those lands, such as the insect apocalypse? What about all the species that do not live in forests or dry shrublands?

Would species loss slow down and stop? 

Here we come to the main flaw in the ‘half the world’ idea which is also a problem for the similar suggestion to rewild 30% of the planet. Species loss might slow, but it would not stop because the extinction process is already in train running at multiple times the background rate. It won’t stop just because we decide to declare a reserve, even if that comes with a side of revegetation or rehabilitation of large parcels of land. 

Many species have already lost enough habitat to fragment populations that become smaller and vulnerable to further disturbance. Their innate viability is already compromised. Some of these species are the walking dead. 

Extinction is forever, as the famous saying goes. So if the extinction events have happened, no amount of revegetation or reserve status will bring those extinct animals and plants back. 

The nature reserve

There’s an additional problem. The status of many current reserves is that they only exist on paper. 

Inside the land area drawn on maps are weeds, pest animals and feral species that are altering and changing those environments dramatically from what they might have been if they were pristine reserves. 

In other words, there must be active management to achieve biodiversity outcomes. Lock it and leave it can work, but in most instances, there is a requirement to manage feral animals, weeds and pollution, even the people who visit. 

Reduce disturbance and vegetation will recover along with some of its associated biodiversity. However, natural regeneration is not guaranteed to support the vulnerable species you aim to protect. They might need more directed help through plantings, reintroductions, vegetation thinning, etc. 

Imagine the cost of managing half the global land surface as reserves. 

Of course, this could be a welcome cost because it would give people work to do, and many people would be delighted to go and spend time in nature improving its quality and performance for future generations. 

The question then becomes, who pays?

The cheaper alternative is to lock away the land and hope all the biodiversity will return. Some of it will, but not all. 

Again slowing biodiversity loss is possible, but it won’t stop.

What sustainably FED suggests

As you can see, it is easy to debunk radical ideas like half the world as a nature reserve. By definition, they are outside normality and most of us are suspicious of such things.

This particular idea is unrealistic for many reasons. Not least, it is unlikely to deliver the expected results even if it is possible to implement. Recall that we have tried many times to reverse biodiversity loss through treaties and agreements with a spectacular lack of success. We suggest that it is wise not to get carried away.

However, it is wise to consider the possibility. 

In radical ideas, there is often a kernel of opportunity. Instead of reserves, we redesign landscapes around catchments, managing land based on natural hydrological units. This idea has a long history. But what if we also said that these catchments and sub-catchments were also designated as no net loss areas where loss refers not to biodiversity but to nutrients?

Agriculture must become circular to recycle everything in these areas, and whatever leaves the fields, forests, and streams must return. This is how nature works, and we could mimic what she does.

Not new ideas, but they are much more likely to achieve a result than designating half the world as a nature reserve.

Hero image from photo by Tomas Sobek on Unsplash


Mark is an ecology nerd who was cursed with an entrepreneurial gene and a big picture view making him a rare beast, uncomfortable in the ivory towers and the disconnected silos of the public service. Despite this he has made it through a 40+ year career as a scientist and for some unknown reason still likes to read scientific papers.

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