How many soil animals are there in Britain? Where do you find the most soil animals in the UK? What affects their presence?
The answer to these any many other questions have been addressed in a Countryside Survey Soil Manual a few years back, carried out by CEH. Countryside Survey (2007) Chapter 8
This estimates that there are over 12 quadrillion little bugs in our soils. How many is that? ANS: 12 thousand trillions
Brian Cox could tell you what that means in terms of stars and galaxies, but it is a heck of a lot. When they gone about looking for life on other planets, I wish they would look at the life under our feet. I counted half a million of them in three years. To count all those in British Soils I would have to live twice as long as the Earth has existed - about 7 Billion years.
YET most people would not be able to name any soil invertebrate other than 'worms. People who give it a thought tend to then say that most of the soil animals have something to do with breaking down debris turning it into nutrients so plants can feed better, but have no real notion of who does what. Hence the page, where I try to start to tease out who does what and I divide soil creatures into two sorts - those that look after living plants and those that break down dead debris.
The soil survey analysed soil bugs - invertebrates together in the top 8cm of soil, in a range of different habitats, comparing them again ten years later. They found that the most fauna were found in woodland soils, followed by pastures ,and the least in arable land.
The sampling numbers went up significantly for most soi animal categories between the sampling dates. This increased number mt almost certainly be due to extraction inefficiencies. Otherwise the world would be changing a lot more than we think. It is noticeable, that despite this the number in arable soils did not increase. See 'Save our Arable Soil.
The CEH considered that the difference was due to more oribatids, which would make sense as they are the hardest to extract, and they didnt appear too much in first year.
There are 2-3 times more arthropods (ones with legs like mites and springtails) in pasture than arable land, and 3-4 times more in woodland. In the ten years following the original survey the number of animals, particularly mites, increased in most habitats significantly. Except arable stayed pretty well the same. Arable got worse in most criteria - like diversity. This corresponds with the declining carbon in arable soil.
From 'Soil Invertebrates' Chapter 8 in Soils Report by Countryside Survey 2007
The mean number of invertebrates collected from cores in CS in 1998 was 52.3 and 77 in 2007 ( Table 8.3). This represented an overall increase of 47% in total catch in CS in 2007. The highest catches of invertebrates were in woodland habitats, with high catches al so recorded in Acid Grassland and Dwarf Shrub Heath. Lowest numbers occurred in three habitats Arable and Horticulture, Improved Grassland and Neutral Grassland that are most frequently the subject of intensive management practices. Catches in Arable and Horticulture habitats in particular were notably low in both surveys.
The CS were trying to see if they could measure biodiversity in the soil, and whether it may be resilient or susceptible to changes.
Measured and calculated parameters that were used as inputs for the analysis were.
1. Total catch of invertebrates from all broad taxa to give a measure of overall abundance of invertebrates in CS cores..
The clear increase in total invertebrate catch was evident in all habitats and significant in most, except one.Arable and Horticulture areas. This is not the result of low sample numbers in the analysis, as Arable systems are the second best represented habitat,
2. Number of broad taxa represented by the presence of at least one individual in each CS core as a measure of community taxa richness.
Arable and Horticulture systems had relatively low taxa richness that is consistent with the low overall catch in these areas in both surveys. Analysis by LOI class indicated a reduction in taxa representation in all soil classes.
3. Total catch of mites and springtails only since these two mesofauna groups usually comprised the majority of the invertebrates present in each core.
4. The ratio of Mites : Springtails, since this parameter was found to change in relation to climatic conditions as indicated by annual precipitation (highest mite: springtail ratio was found in plots where annual precipitation was highest within GB) in the 1998 data-set.
The significant increase in the mite: springtail ratio found in the majority of habitats was largely the result of an increase in the total number of mites caught rather than a reduction in springtail catches. The increase in mi te numbers is also the major reason for the increase in both the combined number of mites and springtails and total invertebrate catch (since mites are a major contributor to overall invertebrate numbers).
5. Shannon Diversity calculated for each sample using counts of individual number within broad taxa,including counts for springtail superfamily, as available for all 1998 and 2007 samples.
Shannon diversity showed only a limited difference between different habitats. Broadleaved Woodland showed the highest Shannon statistic in both 1998 and 2007 (1.21 and 0.87 respectively); while Bogs showed lowest..Arable significantly lower – like most habitats.
The survey considered that the increase in numbers may be due to methodological variations but real increases could not be ruled out. I noticed the increases were particularly noticable with oribatid mites. These in turn masked Shannon diversity - which was the main point of the exercise - to decide whether soils could withstand climate change OK. Some of this was put down to the fact that the mites seem to get on better in wet soil, and 2007 had been a particularly wet year.
But I find that oribatids are harder to extract, living lower down, so coming down later and that they need a temperature gradient to do so (seethe role of a simple tin can in bringing soil to life) whereas collembola emerge quicker and easier. Oribatids
The Tullgren funnels need controlled monitoring - I used to have thermostat gauges controlling the temperature, on my 60 funnel set. Nowadays I would expect temperature probes on top/bottom of soil, to make sure there is a consistent gradient - recommended to be 14o C. SO any change in that gradient - perhaps caused by higher ambient temperatures as suggested, would be a reason to explain such changes in the number of animals extracted. It is otherwise hard to consider any environmental factors having such an effect in such a short time. These little bugs have been around for about 400 million years. Why on earth would they increase by nearly 50% in just ten years. There would have to be a lot of warming to do that. I think we would have seen the steam rising.
But we wont know till other studies are carried out. We need a lot more than one for something so important. Nevertheless, what is apparent is that Arable land is supporting less small soil creatures than any other habitat, and that fits with the change in carbon in UK soils. From Executive Summary Countryside Soils Report 2007
So there current policies are not doing their job to maintain soil quality in this land. Staggering. What are we doing about? Somebody should add up what this means in emitting carbon dioxide, and this contribution to UK GWP. (Has any other country done the calculation? My stab) Why isn't this discussed more? What may be causing such low levels of carbon. The obvious answer 'more ploughing'.
"Over the past several decades agricultural intensification led to enormous land-use changes resulting in dramatic losses of biodiversity . To counteract the loss of biodiversity agricultural land is converted to more natural ecosystems  like grassy arable fallows or wildflower areas, which are designed to enhance arthropod diversity and abundance of beneficial arthropods . The establishment of such semi-natural habitats targets mainly plants and above-ground invertebrates ,  and  neglecting the response of soil invertebrates . However, soil biodiversity is considerably higher than above-ground diversity at local scales . Yet, there is relatively little information about the development of soil biodiversity after cessation of agricultural practices "