Dutch nature is eroding from the inside out

"There are many stories about how we are losing biodiversity, so I would like to start with the good news", says Naturalis researcher Kaixuan Pan. Like many biologists, his love for nature was born from visiting it, but his true strength lies in his talent with the analysis software on his laptop. Pan can make a dataset dance.

His latest analysis shows that Dutch grasslands are recovering after decades of continuous decline. "This means we are capable of reversing biodiversity loss. That is hopeful news for everyone! As we approach the 2030 milestone for global biodiversity targets, we need not only the bad news about what is being lost, but also positive examples that inspire action and help us understand what may work."

Decline

There's more bad news. First of all, the decline in biodiversity continues in other areas, particularly forests. Pan: "It is possible that grasslands can benefit faster from conservation measures because grass simply has a shorter life cycle than trees. We don't know exactly what is going on yet, and we would need to investigate that."

Another piece of bad news is that over decades, the surveyed areas have not only become poorer in species, but have also come to resemble each other more and more. Our nature is increasingly becoming homogenized.

Plots

Bad news number three is somewhat more complex. The database Pan used for his recent publication in Ecology Letters is the so-called National Vegetation Database, a compilation of plant surveys from hundreds of thousands of small areas. These were carried out sometimes by professional ecologists or students, but also through the indispensable dedication of voluntary citizen scientists.

Ecologists use what is called a Species Accumulation Curve to show how the number of discovered plant or animal species rises as you survey an area. In the beginning, you easily find more species, and the curve climbs steeply. After that, it flattens out because you keep finding plant species you have already counted. Pan plotted these curves for all the plots of land in that database. Over the years, these curves have been getting flatter: the number of species is decreasing—except, as mentioned, in the grasslands.

Correcting

Because nature reserves have often become fragmented or shrunk over the years, you cannot simply compare old data with data from today. By calculating how the curve progresses per square meter, the researchers were able to 'correct' the data for differences in surface area. And that is where the real bad news comes in: even when correcting for the changed size of areas, the curves flatten out faster nowadays than they used to. This means that across an identical surface area, structurally fewer different native species remain, even within nature reserves.

Consequently, merely protecting nature reserves is not enough to keep the biodiversity within them stable. The quality of nature is eroding, from the inside out. Pan therefore advocates for a 'Baseline Quality of Nature': environmental conditions for plants and animals must be improved, both inside and outside of nature reserves. "Simply looking at how many square meters of nature reserve there are is not sufficient to halt and reverse biodiversity loss and achieve the ambitious global biodiversity targets set by the United Nations for 2030."

More information

• Read the article A Century of Shifting Native Species-Accumulation Curves Reveals Long-Term Biodiversity Loss, published on 15 June in Ecology Letters.

Text: Naturalis Biodiversity Center
Images: Getty Images