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Gardens can be havens for soil animals in towns and cities

December 12, 2019

The fifth edition of the Dutch Soil Animal Days saw earthworms almost grab top spot thanks to the wet autumn weather. But at the end of the day, woodlice once again emerged as the most-observed soil animal in Dutch gardens. Nearly 1000 'citizen scientists' sent in their observations this year. And a surprisingly high number of people tried to do something in return for the vital services these soil creatures provide for us.

People can't live without healthy soil full of soil life, yet it's not something you hear about very often. With today's announcement of the results of the 2019 Soil Animal Days, we're breaking the silence. "After five years", says lead researcher Gerard Korthals, "it's now clear that gardens and parks are important havens for common soil animals in the city, and even balconies can be of value. If they're maintained in a soil animal-friendly way."

So how is all that indispensible soil life doing in our cities and towns? Every year around World Animal Day, researchers led by the Netherlands Institute of Ecology (NIOO-KNAW) and the Centre for Soil Ecology (CSE) try to fill in the gaps in our knowledge by enlisting the help of citizen scientists. This year's results are now available:


Who's on top?

In the Soil Animal Top 3 for 2019, woodlice are once again the number one. But not for all garden types: in green gardens and schoolyards they've been overtaken by earthworms, and in paved gardens they're neck-and-neck with spiders and their relatives. In the Top 3, arachnoids and earthworms are now in joint second place, while snails are in third place having apparently recovered after a bonedry season the previous year.

One of the most striking findings of 2019's soaking wet Soil Animal Days is that ants were not spotted as often: only in less than 60% of gardens. In 2018, ants did very well: thanks to the warm, dry weather they were still quite active in the autumn. Meanwhile, centipedes were not easy to find in many places, but more millipedes were reported even though they're not so common. That's a good sign!

Raining cats and dogs... and soil animals?

For our citizen scientists, the wet weather during the 2019 Soil Animal Days was quite a challenge, but most soil animals didn't mind. With an average of 43 soil animals reported per participating garden, numbers were up and noticeably higher than the average over the past five years (37.5 soil animals per garden).

During the Soil Animal Days, many people in the Netherlands enthusiastically search their gardens, parks, schoolyards or balconies. 944 participants also helped out with the scientific part this year by handing in their results, covering 185 gardens across the country.

Grading gardens

Those who did were given a grade representing the 'soil animal-friendliness' of their own garden. Those grades varied wildly this year. There were also grades per general type of garden, indicating its potential to be a haven for soil animals. With an average of 8.8 out of 10 based on all participating gardens, that potential is definitely there. Green gardens and tiny forests raked in the highest scores in terms of their potential: 9.2.

Fifth anniversary

So are there any conclusions to be drawn after five years of Soil Animal Days in the Netherlands? Gerard Korthals and his fellow soil researcher Ron de Goede answer in the affirmative. "Green and half-green garden, and parks and public gardens, are eldorados for earthworms, snails, spiders and woodlice in particular." These groups of soil animals are found in more than 80% of the gardens belonging to one of those types.

Another conclusion is that the weather is indeed an important factor when it comes to the survival and level of activity of soil animals. In 2017, arachnoids came out on top after a wet season while in 2018 - a dry year - there were lots of woodlice and few slugs. "We can conclude that in dry years, in particular, the type of garden and the way in which it is maintained are key factors for the survival of soil animals in the city."

Don't ask what soil animals can do for you...

To mark the fifth edition of the Soil Animal Days, we published a festive booklet looking at some of the most unusual and surprising soil animals: Ondersteboven, with the velvet mite as our special 'ambassador'. The booklet is sent to anyone who tells what they are doing for soil animals, in return for all the services they provide for us. Like turning autumn leaves into food for next year's plants, purifying our water and suppressing pathogens.

The most popular options to do something in return were (1) treating soil animals to a 'soil animal snack' by not removing dead leaves, and (2) refraining from using chemical pesticides and fertilisers. In addition, many people came up with creative suggestions such as not winterising their gardens, and letting children discover soil animals.

Are you near a garden or park in the Netherlands and would you like to take part? The next edition of the Dutch Soil Animal Days will be from 25 September-7 October 2020!
With more than 300 staff members and students, the Netherlands Institute of Ecology (NIOO-KNAW) is one of the largest research institutes of the Royal Netherlands Academy of Arts and Sciences (KNAW). It is the organiser of the annual Soil Animal Days together with the Centre for Soil Ecology (NIOO & Wageningen UR). Soil animal experts from NIOO, Wageningen UR and VU Amsterdam have drafted the soil animal chart, and IVN, Stichting Steenbreek and NL Greenlabel are supporting partners. This year, the Soil Animal Days were also held in cooperation with NIBI (Netherlands Institute of Biology) as part of the nationwide Biology Week, and they were part of the annual national Science Weekend: quite an ecosystem!

Netherlands Institute of Ecology (NIOO-KNAW)

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