Bring Me The Soil Horizon

Up at my Mother-In-Law's place, there's some construction work going on, shoring up the house next door or some some such. We went to have a look at and there, where the soil had been dug away, was another of those wonderful times that the text book description that you've been looking at in various books for years is perfectly rendered in real life. In this case, a perfect example of soil horizons.

Here's the text book version:

And here's the real deal:

So yeah, looks like a load of dirt, huh? Well, on the top layer is, ya know, grass and stuff and you don't have to be a biologist to know that grass 'and stuff' is organic. Organic - i.e. living - matter dies and then decays, being broken down by microbes and fungi and stuff. This creates what gardeners call a 'rich humus', which is kind of food for plants. Not hummus, that's food for vegetarians.

Anyway, from the bottom of the picture up, is the underlying rock, which is chalk and is fairly typical of the south of England. Chalk is basically dead sea shells, built up over a very long time and is alkaline, if you remember the post I made a couple of weeks ago attempting to explain acid and alkaline soils: http://punkrockecology.blogspot.co.uk/2016/06/orchidorama.html 

Also, it doesn't hold water very well, as we can see as the darker brown soil at the top washes out very quickly to light brown and then the pure white of the chalk. This creates the alkaline and not very fertile chalk downland that I also attempted to explain here: http://punkrockecology.blogspot.co.uk/2016/06/over-hills-and-far-away.html

If you're a gardener, or a farmer, or indeed if you're a plant, then there is a 'perfect' soil, which is called loam and is a rich dark brown, very mildly acidic and a mixture of clay, sand and silt. Rusty coloured soil, incidentally, is coloured that way precisely because it is full of tiny particles of ferris oxide, or rust, and this rust is an indication of air and water being able to penetrate deep into the soil. White soil, grey soil and black soil (the latter being peat soils, such as that described in 'Orchidorama') show the opposite of this, usually that the iron and everything else is being washed away or that air is not able to penetrate.

If ya wanna get even more geeky, then look up 'munsell soil colour chart', or have a look at the following links:

Soil types explained for gardeners: https://www.rhs.org.uk/advice/profile?PID=179

A very tech description of soil horizons: http://passel.unl.edu/pages/informationmodule.php?idinformationmodule=1130447025&topicorder=4

Or you can just slack off and watch this. I like it. It's got a citroën van in it.

Orchidorama

Just to get everybody up to speed, I'm on holiday on the Isle Of Lewis in the outer Hebrides at the moment and am keeping my eye open for anything interesting. We'd already spotted porpoises, jellyfish and a dead monkfish before we'd even got there and, on arrival, we were not disappointed!

The western Isles, which are a very remote, wet and windswept place are renowned for their machair, or beds of wildflowers. This is from the gaelic for 'fertile plane' and represents a flat bit of coastal land, stuck at a fairly neutral pH level between the alkaline sea and the acid bog of the inland.

To expand briefly on that, all soil is either acid, neutral or alkaline. Soils such as chalk, which is the predominant soil type down where I live on the south coast, are alkaline while "good" soils tend towards either neutral or very slightly acid. It's one of those things you get a lot in ecology, where a healthy soil helps maintain a healthy soil. Plants die and are eaten by various critters, down to and including microbes, which creates a rich hummus that is ideal soil for plants to grow in.

It's one of those weird, chicken and egg type situations, where perfect harmony is perpetuated somehow. However, in some places, heavy and persistent rain will wash all these nutrients out of the soil. The western isles are all about heavy and persistent rain. And wind. This makes the soil very acid indeed and, as we know acid and microbes do not get along very well. The rain washes nutrients from the soil, making the soil more acidic, which inhibits microbial life in the soil and microbial life is basically the bottom of the pyramid that all life rests on. Without it, nothing happens.

Last time I was up here, it was February 2015 and I was moving stones around amongst other things. Down south, even in February, when you moved a stone, lots of little critters like woodlouse and centipedes would scurry out of your sight but here... nothing. Not even worms. It was one of the best illustrations of a line in a text book that I'd ever seen. Without microbes, stuff does not rot and so you get great, springy, squishy matts of peat building up over the centuries. Remove a core from these bad boys and you can bring up seeds going bucket just after the last ice age.

So, just to recap, rain washes out nutrients, creating a highly acidic soil. This creates a difficult environment for most plants - the interior of the Isle of Lewis is not thick with fields of wheat, for example - however, this makes it a just fantastic habitat for plenty of rare plants. Orchids, for example.

The four pictured are in the driveway of the place where we are staying. Just to confirm that: in the place where we are staying, there are at least four wild orchids IN THE DRIVEWAY. The one in the picture above is a good foot high. According to my research, it's a northern marsh orchid, on account of the fact that it looks like one, it's in the north (we're about 20 miles south of the most northerly point in the British isles) and it's on a marsh. Dactylorhiza praetermissa to give a species name, though be warned I am not an expert, just a bloke with a book on wild flowers.

This one was probably a common spotted orchid, although according to this same book, they tend to grow on lime soils, which this very much is not. But putting all that aside, isn't it pretty? And they're all over the place. Literally: you look in a roadside verge and think 'oh, another orchid'. Back home, I got quite excited when I saw a few on a roadside verge that had specifically been planted for wildlife. Here... they just grow.

Anyway, just to wrap up, this is not the machair that I described above. That is mostly buttercups and daisy as far as I can tell. This is on the acid bog that covers most of the island. More to follow... stay tuned.

The Petrified Forest

Right next to the beautiful chalk downland meadow that I described yesterday is a yew forest, which remains one of the freakiest places I have ever been to. Seen from the other side of the valley, it looks much as a wood should do, but get inside and the place and it's a monochrome scene of bare ground and leafless branches. 

To me, it always brought to mind the seventh circle of hell in Dante's Inferno, written in the 1300s about a (hopefully fictional) walking tour through hell. One of the circle is called the 'wood of suicides', where the souls of those who commit suicide are transformed into a wood full of brittle, dead trees. 

Or possibly, the petrified forest on Skaro, the home planet of the Daleks, as explored by William Hartnell and friends in the first series of Dr Who.

What it really is, is a forest of yew trees, possibly dating back to the bronze age and definitely from at least the middle ages. Yew trees are evergreen, meaning that they never shed their leaves and evergreen woodland tends to be less biodiverse than broadleaf for just this reason. In broadleaf woodland, the trees shed their leaves in the autumn and regrow them in the spring, giving several months in which light will penetrate to the forest floor. This is why these woods have thick matts of bluebells and other flowers in March and April.

Evergreens do not do this and, while conifers are tall and thin, yews spread out  up and sideways and, in an established yew forest such as this, barely any light penetrates.

Without light, photosynthesis cannot happen and, without photosynthesis, barely anything else happens, so there is no matt of vegetation on the forest floor, just a thin layer of leaf litter and, below that, bare earth. This makes the topsoil very vulnerable to erosion, with only really the roots of the trees holding it in place.

Chalk soil is already free draining, and therefore not the most fertile (as described yesterday). So, altogether, the place is hardly the most fecund environment for new growth. 

That said, the place is not entirely dead of life. Where there is a break in the canopy, there will be a little oasis of green, while the outer edges are dotted with ash saplings and inch or so high. We saw a couple of badger setts and some deer, both of which probably appreciate the cover and the relative peace that the woods gives them, while the canopy was full of the twittering of birds and the floor covered in snail shells.

It just goes to show that nature will find a way and, just because you don't see anything, it doesn't mean that there is nothing there.

Some more info on these woods and other yew forests around the country: http://www.ancient-yew.org/mi.php/yews-at-sites-of-antiquity/104

The Seventh Circle Of Hell in Dante's Inferno: https://en.wikipedia.org/wiki/The_Wood_of_the_Self-Murderers:_The_Harpies_and_the_Suicides

A Yew Forest that you're allowed to visit (and don't have to clamber over a barbed wire fence to get into) plus some more florid prose on yew trees:http://www.theguardian.com/travel/2000/oct/07/unitedkingdom

Dr Who episode  'The Dead Planet', first series December 1963:
https://vimeo.com/108169426

...and show notes:
http://www.bbc.co.uk/doctorwho/classic/episodeguide/daleks/detail.shtml

Over The Hills And Far Away

Another day, another nature photography expedition with the missus. This time to Hambledon Hill, an iron age hill fort near Blandford. 

This is classic calcareous grassland. Chalky soil, so alkaline, free draining and with a very thin soil layer. This makes it good wildflower habitat, as we can demonstrate:

This is Bird's Foot Trefoil. Also known as 'bacon and eggs' for some inexplicable reason. Although bird's foot trefoil is hardly the most obvious name either. Also 'granny's toenails', although I'm seriously wondering at this point whether whoever wrote my wildflower ident book was taking the mickey.

Read more: http://www.wildlifetrusts.org/species/birds-foot-trefoil

This is classic grassland. As mentioned above, due to the thin soil and chalk beneath, it's not very fertile. Basically, if you are grazing cattle and sheep on these hills, there is a limit to how much it can be grazed, as the grass will have to recover. It's all about how many animals you can have on how large a patch of land.
Then some time around the early twentieth century, artificial nitrate fertilisers were invented and suddenly, you could take a patch of thin soil such as this, plough it up and seed it with rye grass or something similar, fertilise it regularly and graze cattle much more intensively. This was called 'improved grassland' and was great for farmers, great for cheap lamb and beef but not so great for wildflowers.

The flowers and plants that had traditionally grown on this sort of soil had adapted to a marginal, very frugal, environment. So, if you then suddenly made that environment less marginal and invited an extremely virulent grass onto the scene, those marginal plants found themselves crowded out.

 

And so now we roll onto grassland restoration, which attempts to return these areas to their previous species-rich status. It mostly involves not fertilising the soil and maintaining grazing on the land but at a much less intense level. On this evidence, it seems to be working. 

Read more about calcareous grassland restoration HERE

Have a look yourself sometime if you're in the area. It's a beautiful place and has some fine views of the county. Reminds me of a song, in fact.