An ancient UK oak woodland in summer
David Beeson. 21st June 2020
In the end the important thing is to add it all together.
Most of us enjoy spotting things. As a kid it happened to be steam locomotives and then, thankfully, young ladies. I didn’t keep a ‘black book’ but I can recall all the latter… there were precious few! (But, saved the best to last, of course.) I’m still at it … spotting things … but now it is the amazing fauna and flora that I encounter.
Most wildlife enthusiasts have their own specialities. Sure, I look out for butterflies and odonatan, invertebrates of all types and even birds – if they will stay still for long enough. However, it is only mammals and plants that will have me rushing off in pursuit. Luckily, most organisms have their advocates and sighting lists arrive at the offices of the various conservation bodies, so they can add it all up.
The adding up, in the end, is what we call ecology. The way the whole system works together.
The geologists tell us that under Harewood Forest, in North-west Hampshire, are layers of chalk – the inorganic remains of once-living organisms. Mixed in are the silts from the shallow seas in which those basic organisms lived. As naturally acidic rain (Carbon dioxide is an acidic gas that dissolves in water) chemically washes out the calcium carbonate the silts are mostly left behind … and these are what we now call ‘clay cappings’, that are naturally found over some of the chalk bedrock. Harewood is, in parts, clay-over-chalk in its geology. (Gravels have been deposited elsewhere.) A geology map will tell all, and I hope you have one in your library.
The geology of an area is the start to working out what is going on. Plants being the key organisms. Calcicoles are plants that can live with lime-rich soils. Calcifuges cannot cope. You’ll encounter few calcifuges in Harewood, although chalk-heaths do occur locally, and they support calcifuge heathers and gorse. (Always remembering that soil surface layers have a big leaf litter input in the autumn, and that has some acidity.)
With the chalk not far beneath the soil surface it is the calcicoles that dominate here.
Climate change, and more immediately, weather will have a huge impact of some organisms. We have good, bad, average and indifferent butterfly years – often driven by those atmospheric changes. Add all the yearly data together and we see trends that can be linked to other factors and so to the understanding of the population-change results.
Harewood has a great range of organisms. Sadly, we see only a minute percentage as ‘PRIVATE’ signs punctuate the place in increasing numbers, yet the overall ecology is clear even from public footpaths. This woodland is dominated by pedunculate oak trees that seem to be mostly planted or naturally seeded in Victorian times. Beneath them are a sad discontinuity of hazel that cries out for coppicing, and a limited mixture of other shrubs. Most of these plants are native species, although you will see non-native conifers and horse chestnuts.
The dominant trees form the huge bulk of the biomass that drives the local food chain and provides the closed environment in which all else depends. And, the conditions within a woodland are a contrast to those outside. Inside it is: less windy, more humid, may have less light at ground level and has a reduced temperature range. So, the organisms here will mostly be quite different to those encountered outside.
Where the soil has been disturbed, for example along the derelict railway cutting, the ecology abruptly alters. The best example being along Middleway. Here oak has given way to other trees … and a locally very rare bird cherry shrub. Change the geology and the ecology will be quite different too.
In summer the Harewood ground flora is mostly lacking as too little light energy arrives at the woodland floor. A few specialists look healthy, for example dog’s mercury, but most other plants are in hibernation or comatose. The great exception being the bracken that thrives where felling has opened the canopy.
(An understory of hazel appears sufficient to inhibit the fern’s expansion.)
As we have covered before, all woodland plants have their chemical protection and, so, summer invertebrates need to be specialists as free plant nectar and pollen are in short supply. The famous butterflies that the area hosts mostly feed off aphid honeydew high in the canopy, the aphids bypassing the plant’s toxicity by driving their penetrating mouthparts directly into the food delivery system (phloem) of leaves.
Aphids are critical to the adult butterflies. The aphids extract plant sap, a carbohydrate-rich concoction, extracting a small proportion of sugars and, importantly, the amino acids / proteins for their own needs and dumping the excess sugars as honeydew.
Looking up is what the smart woodland butterfly observes do – then you’ll spot the purple emperors, the purple hairstreaks, plus plenty of white admirals and silver-washed fritillaries resupplying their energy needs from the honeydew.
The butterflies will not have this resource to themselves. Ants, other invertebrates and microorganisms such as fungi and bacteria will likewise consume it.
So, adult butterflies, aphids and their allies avoid summer plant toxicity. The birds feast on the summer glut of insects gaining the protein needed to survive, grow or moult their feathers. Come autumn many insect-feeders must change their diet and also the detailed shape of their beaks or depart for ‘new pastures’ as the honeydew food chain feast is over.
Sadly, some woodland invertebrates also feed off me. Harewood has a thriving population of ticks. The human-liking type will be carried by mammal and birds. (Recent evidence demonstrates that wild birds are capable of actively transporting ticks and their associated diseases, even during migrations. Ground-dwellers, such as non-native pheasants, are likely candidates.) Other tick species occur, even on bumble bees.
Plant material is a good summer food source for many organisms. Some organisms can detoxify one plant poison – the Solomon’s seal cut-fly, for example. Some, like the leaf-miners, live between the upper and lower leaf margins that mostly contain the toxin. Other consumers will live off the resources in dead wood – especially fungi and bacteria. Deer, and there seem to be more muntjacs here every year, eat a bit of this and a bit of that and, thus, limit their toxin load.
Few people or organizations have the skills and resources to put everything together into a complete ecology of an area. The Wildlife Trusts, RSPB, Butterfly Conservation and Woodland Trust do their best, yet research work is difficult and time-consuming. University PhD candidates often do the legwork in ecological investigations and Oxford University has an enviable reputation here. Their research woodland, Wytham Woods, just to the west of the A34 by-pass around Oxford, is their key spot. So, if you fancy seeing what is going on … attempt to get a visit there. PTES sometimes offers courses there – I went on a badger research day some years back and return occasionally.
Keep sending in your data. If you haven’t yet the confidence to do that … just start in a small way. Look at the App Store on your smart phone, you’ll find some that suit your skills. Mammal Mapper is a good place to start recording data.
Meanwhile, have you tried out BirdNET yet? Or Google Lens? I have found both useful, as has the Woodland Trust tree identification App.
Now, I’m not great with birds, but I have seen and heard more warblers than ever this year. Is this because I’m taking more notice (and using BirdNET) or is this an upsurge because of global warming? Help!