Author Graeme Lyons
Itís very hard to find invertebrates as you walk around in the winter. That is, unless you know where to look! One of the best places to look is in grass tussocks. I have recently discovered just how many different invertebrates you can find in tussocks after a conversation with Patrick Roper. So, last week Penny Green and I headed up to the valley field one lunch time armed with nothing more than a bow saw and a couple of white trays...
...I sawed of a cockís-foot tussock low to the ground and inverted it into the white trays (you could just as easily use a white sheet). I then shook the tussock for 30 seconds or so. I was surprised at just how many invertebrates there were in just a single tussock. You can also find similar numbers of invertebrates in large patches of moss. There were lots of spiders, woodlice, beetles and moth larvae. The beetles, being my current area of interest, were mostly made up of over-wintering ground beetles, rove beetles and ladybirds with the odd leaf beetle in there too. What surprised me even more though was that many of the species I keyed out proved to be species that I had not seen before. Upon consulting the texts, none of them could be considered rare or even scarce, but I was obviously seeing a group of invertebrates that were difficult to find in the summer months using more conventional means. There are thousands of tussocks of grass at Woods Mill and sampling a small number adds greatly to our understanding of the siteís fauna without having a negative impact on the invertebrates themselves.
In the Little Meadow at Woods Mill it became very clear that a tussock growing on a patch of ground that is slightly higher (and drier) than the surrounding wetland will have even more invertebrates wintering in it. It must appear to a tiny invertebrate as a vast citadel of sanctuary upon a hostile plain filled with dangerous winged beasts (birds). Tussocks of grass then are of great value to invertebrates, particularly within a wetland complex and/or relatively flat and exposed areas. Cattle-grazing tends to produce a more tussocky sward than sheep grazing but of course, the density and duration of grazing animals greatly effects how much structure is left over the winter. It is important for many nutrient poor sites that they remain so, and therefore removing biomass and nutrients is crucial. This should however not remove all over-wintering structure and a fine balance is needed if plants and invertebrates are both to be catered for.