Thursday, October 23, 2014
Under the skin of a sycamore
Thursday's Guardian Country Diary is about the remarkable range of small invertebrates that live under the flaking bark of old sycamore trees.
When the bole of an old sycamore tree expands the old rigid bark cracks and begins to curl at the edges, while ....
.... a fresh, new layer of bark forms underneath. It might not look very attractive but these bark flakes, some as large as a slice of toast, take a long time to fall off and while they are still attached harbour a remarkable fauna of small invertebrates underneath. Here's a selection, most of which I've yet to ID.
Millipedes, a hatched moth pupa and some unidentified cocooons
Lots more millipedes - these were just a few from under two bark scales - if this sample is representative there must have been hundreds sheltering under the bark of this tree
A minute scarlet mite
A rather beautiful little money spider, Gonatium rubens
A huddle of earwigs ....
... that raised their tail forceps in defence when they were suddenly exposed to the light. Male left, female on the right.
A spider that lives in a silken tent under the bark
Lots of slugs in areas where the bark is permanently damp, where rain water trickles down the tree trunk ..
.... together with snails ......
...... and woodlice
Another moth pupa, that looks as though it hatched successfully.
Sycamore sits low in the league table for tree foliage that supports insect biodiversity - a 1961 research paper on the subject found only 15 species, compared with the 284 hosted by oak (click here for details). But a quick look under the flaky bark of old sycamores casts them in a more favourable light, as a sheltered habitat for a host of invertebrates.
The few examples shown here were just from a height that I could reach - there may well be a different array of species higher up the trunk and the hosted species most probably vary depending on the aspect (sunny & south facing or shaded & north-facing). Moisture must play a role too because there are well defined runnels where rainwater flows down the trunk from the branches and the bark there is always moist and often very wet. All in all, flaking sycamore bark is probably quite a complex habitat, with many interesting interactions between species that inhabit it.