Saturday, 25 April 2015

How significant are soil bacteria to the gardener?

Just let them get on with their lives!

Relevance to manure and fertiliser
I had intended to put this post in my ‘myth’ series and wanted to decry the promotion of organic fertilisers as being beneficial because they encourage bacteria. I found myself in some difficulty!
How could I say that bacteria are hugely significant to the life of the soil and yet most things the gardener might consciously do to promote them be irrelevant? 
In the case of many fertilisers, they do have an effect on specific bacteria, it’s just that the overall benefit on the health of the soil is small and inconsequential. 

Any organic material added to the garden is food for bacteria. Nitrogenous organic fertiliser will stimulate those bacteria that degrade the fertiliser and beneficially make soluble its nutrient content. Although I do not generally recommend organic fertilisers, I admit they are of horticultural value in that they supply nutrients  - my issue is that the fact that bacteria are involved in nutrient release is quite incidental and not a reason to buy them.

Fertilisers versus manures

Farmyard manure is the very best bulky organic material to add to your soil. Because there is a lot of it, it will significantly increase soil bacterial action. 
Although its nutrients are NOT very concentrated because of the bulk the total nutrients added are significant too (provided they have not been leached out in a field!)

Fertiliser is quite different to bulky organic soil additives which are often described in the UK, not with strict accuracy, as ‘manures’. Unlike bulky organic additives, fertiliser is a concentrated source of nutrients and is applied to the soil in very small quantities. Dried blood, bonemeal, fishmeal and seaweed extracts are examples of organic fertilisers. 

Poultry droppings, although strictly a manure if you define ‘manure’ on the basis that it comes out of the back end of an animal, is best treated as a fertiliser because of its lack of bulk and exceedingly high nitrogen content.

Sulphate of ammonia, sulphate of potash and growmore are examples of inorganic fertilisers. They also effect soil bacteria when for example, ammonium fertilisers are converted by bacteria to nitrate.
When sulphate of ammonia is added to the soil, bacteria convert the ammonium to nitrate and and slightly acidify the soil in the process. In addition the sulphate content has an acidifying action. On my lawn I regard these effects as a very good thing!

Both organic and inorganic fertilisers do effect soil bacteria but in such a small way that such bacteria are unworthy of a gardener’s consideration

Bulky organics such as horse and cow manure, garden compost or ‘leaf mould’ are by definition both organic and bulky and do have substantial effects on soil bacteria. We add such ‘manures’ to the soil for many reasons including plant nutrition but perhaps most importantly for their physical effects on soil structure. It is a moot point whether their undoubted considerable effect on bacteria is a significant reason to chose them.

Bacterial myths the Canadian way.
Robert Pavlis writes a very fine blog about gardening myths. He has been doing a series on soil organisms which includes references to flagrant claims in advertisements for organic fertilisers being beneficial because they encourage bacteria. He gives many excellent references to real scientific research to support his conclusions. You might like to read them.
Am I just out of touch or are Canadian and US citizens more gullible than we are? Perhaps their advertising is even more cynical than our own. Apparently over the pond you can buy bacteria to add to your soil! How pointless! No real gardener would use them.

This is a very useful bacteria that you can buy in France. It is not a soil bacteria but is a very effective bacterial disease of caterpillars that you can spray on your brassicas. I will pluck up courage to write about it one day!

Significance of soil bacteria
There are many ways to convey the magnitude of the presence of soil bacteria. Not only are they not very accurate they are likely to change with the next piece of research. I can’t quite believe that the mathematical progression of a single bacteria surging to 16 million in 24 hours is actually true! I find it easier to believe that the weight of bacteria in an acre of typical soil weigh as much as two cows! Of course if you go deeper, to perhaps more than a mile you, will find that half of the world’s biomass is bacterial! 
I do find it impressive that there might be a billion bacteria in a single gram of soil and that hundreds of thousands may be different species. 

The real message to a gardener is that there is a huge number of soil bacteria and they reproduce very quickly and their numbers dependent on changing conditions may grow or decline by several orders of magnitude within just a few hours. So much for any thought of adding a few from a packet - and anyway they may not be the right ones!

Certain bacteria are essential for soil fertility. In contrast a few are actually plant diseases. 
There are two significant bacterial diseases of cherry - leaf spot and bacterial canker

One of the most significant bacterial pathogens is agrobacterium which can induce galls and tumours on plants by horizontal gene transfer!

Most of the huge number of bacteria in a soil are quite insignificant to the gardener. Perhaps this is untrue in that the good, bad and indifferent may compete together for resources in biocidal combat. Some that seemingly have no known useful function may do so in the future.

Examples of factors that massively and speedily effect bacterial numbers are soil temperature, aeration, drainage, pH, availability of water and carbonaceous material. 

Bacterial soil superstars
These are the ones you will learn about if you study soil science.

Ammonifying bacteria. These convert organic forms of nitrogen into inorganic ammonium. This fundamental process in the nitrogen cycle is known as mineralization. 

Nitrifying bacteria. These convert inorganic ammonium in a two stage process, first to nitrite and then on to nitrate.

Symbiotic nitrogen fixing bacteria. Examples are those that live in nodules on legume roots and enable the conversion of nitrogen gas into organic chemicals. They are one of the very few examples when it is sometimes worthwhile - via commercial seed treatment - to inoculate specific strains of bacteria into the soil

Free living nitrogen fixing bacteria act directly in the soil. They are not very significant in UK soils.

Denitrifying bacteria. These are associated with anaerobic waterlogged conditions and lead to polluting loss of nitrogenous gases to the atmosphere.

Thermophilic bacteria. These bacteria of decay can heat up a compost heap. Although desirable, they are not essential to the composting process.

Actinomycetes. These bacteria have characteristics of fungi - such as reproducing from spores. They are significant in the breakdown of tough chemicals such as lignin and cellulose. 

Cyanobacteria. These green photosynthesising and nitrogen fixing bacteria are of huge worldwide significance but are not commonly found in temperate soils. They also have an almost unique ability to ‘mop up’ high levels of nitrate from water. One to watch for the future!

Relevance of bacteria to gardening practice

Soil cultivation will aerate the soil, but not necessarily in the way you might wish. Aerobic bacteria will increase, which in turn increases the speed of breakdown of organic matter. For the gardener this conflicts the competing needs of release of nutrients and maintaining organic resource.
The other side of this coin is that the better pattern of oxygenation which results from minimum cultivation will usually lead to the highest bacterial populations yet retaining higher levels of organic matter.

Liming, fertilising  and manuring practice all effect bacterial action

Poor drainage leads to an increase in undesirable anaerobic bacteria

Good composting occurs when bacterial action is maintained by heat retention, sufficient nitrogen and application of lime.

Because temperatures have a fundamental effect on bacterial action, soil in winter will have next to no nitrate available to plants. In contrast a nitrate analysis in late summer will show greatly enhanced levels. 

It’s more important how fertiliser practice is effected by bacteria rather than how fertiliser practice effects bacteria!

A few less well known facts about soil bacteria

Thirty years ago growers would sometimes apply the systemic fungicide called Benlate as a soil drench. It was noticed each time it was used that its action diminished. It turned out that a soil bacteria could use the fungicide as a food and with each application the bacterial population population increased and gobbled up the fungicide.

In a similar vein, growers and farmers were permitted to dispose of washed out empty pesticide containers by burial. It was recommended that the holes were not too deep. Soil bacteria that degrade the chemical residues are far more numerous near the surface.

Thirty years ago it was routine practice for glasshouse growers to steam sterilise the soil. This was  primarily for soil pest and disease control. Most, but not all of the bacteria were also killed. In the absence of competition the first bacteria to colonise back - and without competition in greater numbers than before - were those bacteria that release soluble nutrients. The effect of planting in still warm soil with an increasing level of available nutrients over the first few weeks of the crop was highly valued by growers.

And I am sorry to spoil the party, but my beloved glyphosate has biocidal properties! In terms of how I use this herbicide the effect is insignificant!

On the brighter side it is now starting to be thought that a child’s exposure to soil and other outdoor bacteria greatly reduce future sensitivity to allergies.

A story about bacteria from my friend Peter Williams

Microbiologist and maestro gardener Peter Williams played a very significant part in the greening of Northern coal mining slag heaps thirty years ago.
An important aspect of their restoration was the use of huge quantities of lime. A bacteria called thiobacillus acts on iron pyrites in the coal waste to release sulphates which form sulphuric acid. The acidity of the slag can become as low as a a remarkable pH 1.5! The most acid you will ever find a real soil is a very rare pH 3.5.
Peter tells me that in the reclamation they used lime at 200 ton per acre every two years. He remarked that a farmer might use lime at 10 tons per acre once in his lifetime! When they applied lime the colliery waste fizzed!

He went on to tell me that on a similar site in Wales when land engineers used concrete drains, to their surprise and consternation within a year they had dissolved away.

I hope the above arguments help to persuade you that gardeners should carry on with good gardening and forget about the bacteria. They will look after themselves!

Yesterday morning I discussed this post with Peter W. and the futility off adding bacteria to the soil. The conversation turned to adding mycorrhizal fungal spores from a packet! Mycorrhiza are of course fungi and not bacteria. As I have posted before mycorrhiza are highly beneficial and sometimes essential. I have previously shown doubt about adding them from a packet. 

Peter is a fine microbiologist with a special interest in mycorrhiza. He has been talking to colleagues even more knowledgable about fungi than he! After our conversation this morning I now feel emboldened to offer our opinion that adding spores from a packet is a complete waste of time. 

Monday, 20 April 2015

Blogger Page Views milestone for the No Dig Gardener!

Roger has a little Google Page View counter on the No Dig Gardener blog, just as an indicator for him to see if he gets any visitors. He is quite obsessed with both the counter and Google Analytics!

First, let me apologise to all the gardeners who read Roger’s blog. This post is not about gardening, although I’m sure all you other bloggers out there will understand.

I’m Cathi – Roger’s neighbor and long-suffering resident blog adviser! Roger is away on one of his jaunts to see family in France at the moment, and all the excitement has happened in his absence. He’ll be so disappointed!

The Page View counter reached half a million on Sunday morning!

Reaching the half a million page view mark

That is 500 000 pages looked at! His very first blog was published 26th June 2012. I find it more than a little amusing that the no dig gardener’s half million was reached on 19th April 2015 with this active pagewhich was published 1st November 2012! It’s a post about digging – oh, the irony!

Still, it was ever so exciting watching the counter hit half a million.

…and I just can’t resist posting this picture!

Sunday, 12 April 2015

Why does my new tree grow so slowly?

Trees and shrubs can be inhibited by grass and weed!

There are many reasons why woody plants fail to make healthy new growth and sometimes die! Causes are from the common place such as planting too deeply, failing to water or watering too often to the totally bizarre, such as strangulation and urination. Today I have only one focus: competition from grass.

Grassing up to the base of young trees stifles their growth.
The stunting of tree growth can be quite extreme and sometimes a woody plant fails to grow at all and may be more susceptible to pest and disease. Not always, some very vigorous plants such as the Norway maple might not miss a stride.

This vigorous Cedrus atlantica glauca tolerates the poor winter aeration in my deep wet soil and thrives

As a tree eventually achieves some stature it starts to outgrow inhibiting grass. 
In traditional fruit growing practice, reduction of vigour and promotion of fruiting was achieved by grassing down orchards. Such an effect might be an advantage to gardeners when in later years a tree threatens to outgrow its position.

My Acer griseum has made very little growth in twelve years
I often see inhibition of tree and shrub growth as a result of grass competition and have experienced it myself. Numerous trials by the landscaping industry have demonstrated dramatic effects. After several years in soil clear of vegetation a young tree might achieve double or treble the height of its grassed down neighbour. 
Sometimes gardeners plant shrubs in a lawn and they often die for lack of summer water.

To my amazement I have witnessed arboreta that don’t understand this phenomenon. I have seen young trees just standing still for years in coarse weed or grass. I think that their green credentials do not permit them to get out the knapsack and underspray.

Although grassed to the base I sometimes take out just a little grass to facilitate mowing
It’s all about competition
Horticultural students are taught weeds compete for light, water and nutrients. We can discount light unless very small saplings are planted in very rough grass. Shortage of tree nutrients is significant but it is lack of water that makes the real difference.

Many gardeners are surprised how most tree roots grow in the top 30cm. That is the  most fertile place in respect of air and availability of nutrients. A significant proportion of rainfall comes in small doses and just wets the surface. Shallow roots get first bite of the cherry.
Grass is a past master at making strong surface roots. It has evolved that way to survive on savannah. It is a moot point how the deeper roots made by un-mown taller grass compare with the dense matted roots of mown grass. Mown grass is usually the worst competitor because constant mowing keeps it constantly green and transpiring compared with tired old leaves on uncut plants. Dead grass might even give temporary benefit to the trees by mulching!

A particular problem of tall un-mown grass is at the base of a tree trunk when wet conditions prevail and wet leaves and humidity facilitates fungal infection.

I had intended to speculate about allelopathy where one plant chemically inhibits another. I knew that couch grass produces organic toxins that act as natural herbicides. I wondered whether such an effect might occur with other grasses. I found this site which claims allelopathy has a huge inhibiting effect on trees. Not all the allelopathic grasses quoted are relevant to UK lawns! 
Kentucky bluegrass, red fescue, perennial ryegrass, Bermuda, and bahia grass all produce toxins. As much as 50% inhibition has been suggested. I have no idea how such a figure is derived!

Another danger is when closely grassed  trees are damaged by mowers.

So where do trees grow best?
Trials have shown that they establish best in soils clear of vegetation. After planting such soil is best left undisturbed and kept weed free by shallow hoeing, hand weeding or spraying. The very best results of all are when weed free soil has a thick mulch. Most research into this has used materials such as bark mulch. If appropriate, don’t overlook loose gravel or stone.
In real gardens you will want to underplant the trees with plants!

This tuberous corydalis is only above ground for ten weeks in winter and  provides zero competition.

Winter bulbs generally thrive under deciduous trees
So what can a gardener do to grow trees in the lawn?
Short of avoiding grass altogether to plant in clear soil circles is the usual solution. A meter or so diameter, although not perfect, will make a huge difference for the first few years. There will come a time that you can dispense with the circles. (and any ugly  stakes - but that is another story).

Whoops - I have just noticed the ugly stake. As Cathi’s gardener I need to remove it. These trees have sprayed out circles to facilitate safe mowing. I have already removed several decapitating branches to protect Cathi when she charges round on her ride-on mower!

I hate seeing trees planted in excavated depressions with deep edges that catch all the litter. Worse, if winter drainage is poor the sunken soil catches the rain. Best for your plants to be level with the lawn or in wet gardens slightly raised.

Personally if I want to plant a tree in grass I kill out the circles with glyphosate and plant direct into the lovely fibre-rich soil. I cringe when I see gardeners moving good turf - their very best soil - to plant trees!

What about ornamental borders under trees?
It’s probably not a good idea to grow grass under a grove of  trees. You will get a load of green moss as a result of their shade!
Most of we gardeners will wish to grow mixed plantings of ornamental plants. To varying degrees such plants will compete for the trees’ water but dehydration will be much less than that caused by a lawn. 
For most of us as trees become well established our new worry will be that the trees will dehydrate our plants!

In terms of a beautiful garden most of us will opt for tree plantings with a ‘natural’ looking understory of nice plants.

Most of my own trees are planted in mixed borders

A couple of caveats
Wise gardening words are often redundant in unusual circumstances. My own garden is a deep coarse silt  - I have previously wrongly described it as fine sand - overlying sticky clay about two metres down. My perched water table ensures deep roots can always find water. My own trees are grassed up to their bases. It was a surprise how much the grass suppressed my Acer griseum and ginkgo but all my other trees have grown very well.

My advice to plant trees in clean soil applies to climates like here in the UK where dry periods in summer are rather frequent. My advice will not apply in places with high all year round rainfall. I saw a shrub border in Eire and another in Costa Rica where the complete planting was in mown grass and grew very well.

A tree planting scheme remembered
The promotion logo was …
‘Plant a tree in 73’
The next year it became…
‘Plant some more in 74’
A wag added…
‘None alive in 75’

The cynic had noted that the public were encouraged to plant trees in the countryside without any indication that without after care their chances of survival were small.
I saw many trees after planting invaded by coarse grass, ground elder, bindweed and all manner of dehydrating vegetation. No wonder many died or at best stood still for many years.

Bolton Percy Parish Council were informed that they would receive fifteen trees the following week. A planting committee was immediately convened. As the only horticulturist I was made chairman. In practice the committee was never quorate and I chose the sites and did the planting and all subsequent maintenance. 
The trees that arrived were a curious selection. No wonder the nursery industry loved the scheme, they could sell all their surplus. It was proclaimed that each tree would have a ‘tree preservation order’. How stupid - any administration and preparation of plans would take a much greater time than planting and maintenance. I was not only too lazy I did not want to saddle people with future trees that might be in the wrong place, outgrow their space or even prove to be eyesores when perhaps not very healthy. The only plan of the whereabouts of these trees is in my head!

It is very difficult to suddenly find places for extra trees in a well wooded country village. My choices were rather desperate. It was the year before I started to maintain the then rather wild Bolton Percy Cemetery. Five trees were planted there. Twenty years later I was rather relieved when three by then large Sorbus aria, were chopped down when part of the old churchyard wall needed rebuilding. Every time I make my monthly maintenance visit I curse myself for the deep shade under a wretched huge sycamore I planted. On the other hand a beautiful Amelanchier canadensis in the parish room yard has thrived and produced beautiful blossom and autumn colour for the past forty years.
Last month I took it into my head to see how many trees have survived. I was pleased to find ten including a fine copper beech that will grace the village for the next hundred years.

Planted in 1973 this copper beech is starting to make a fine tree. If you look carefully through it you will see another tree planted at the same time across the road. Sadly it is being strangled by ivy

Now worthy of a tree preservation order - hint to Parish council

In these links I discuss the theory of water conservation by mulching and dehydration by planting.

Saturday, 4 April 2015

Kabschia saxifrages at Waterperry Gardens

Ice diamonds are forever.

Now at the beginning of April is a chance for anyone living near Oxford to visit the National Collection of these silver gems.

Anytime is a good time to visit Waterperry Gardens the old home of  Waterperry School of Gardening for Girls. The garden and grounds are superb all the year round and the end of the season reaches a crescendo with fantastic michaelmas daisies. The spacious gardens are superbly maintained with a wide range of high quality plants.
It’s a wonderful place for a visit. It includes an unusually well managed ‘up market’ garden centre. The extensive garden facilities are superbly organised and  serve excellent food.  There is even a small gardening museum.
If Beatrix Havergal could see it today she would be proud.

Miss Havergal’s  gardening school for girls
A formidable vicar’s daughter. Hugely eccentric she was loved – and I suspect feared – by many generations of girls who attended the two year residential gardening course. There is nothing like that college today that teaches hands on practical technical horticulture. The girls were taught in an upright godly manner and grew the crops and maintained the grounds from dawn until dusk. There was time left for gentile parties and play. For most of the students it was the best time of their lives. Girls from Waterperry  have over the years made a huge contribution to gardening. ‘Trix’ considered their education too good to be wasted on marriage!
‘Old girl’ Mary Spiller has worked and made a huge contribution to Waterperry’s  high standards for more than fifty years. I was myself privileged to work with a lovely colleague who was a former pupil. She was also a vicar's daughter and devoted her life to her students.
If you want to get a better flavour of the history of Waterperry read this delightful article in the Oxford post.

Silver saxifrages were the girl’s best friend

Kabschia saxifrages
 Miss Havergal loved ice diamonds and the tradition has been continued in a kabschia collection curated by Adrian Young, alpine grower and saxifraga sage extraordinaire.
Kabschia saxifrages are one of fifteen classification sections of saxifraga and are difficult to grow. As high alpen plants they grow in very different conditions to here on low ground. They are covered by winter snow and do not experience the vagaries of the UK winter. In spring in the mountains melting snow, wind, intense sunshine and deep nutrient-poor rocky scree terrain contribute to a very special habitat. 

At ground level they are likely to be too wet in winter even in very well drained rubble. In summer they suffer from periods of drought and excessive heat.

The solution at Waterperry is clever, efficient and elegant but does require you to forget the growing contraption and imagine yourself there in among miniature mountains composed of three tons of white Canadian tufa. 
Tufa is limestone rock with a kind of perforated ‘aerobar’ structure. Not only can plants grow on it they can also root into it.

An ingenious system to provide ideal growing conditions in this country
Adrian has created raised beds filled with well drained ‘ballast’. His growing mixture is sharp sand and up to 20mm grit mixed half with peat. Peat is a highly water retentive yet well aerated ingredient infinitely superior to any trendy ‘green’ alternative.

In winter the beds are protected from excessive rain by transparent vinyl sheets. In summer they receive fifty percent shade from wood slats. Overhead permanent spray lines supply regular rain all the year round. 

You can see from the pictures how well Adrian Young’s saxifragas grow.
You can read more about Adrian’s work here

These gorgeous varieties grow together in gentle competition. Note the closely packed leaves characteristic of kabschia saxifrages

They just love this mossy tufa and so do I 

Imagine these as cliffs and note that saxifrages love bright shade 

March and April is perhaps the best time for alpines 

Kabschias have  a lovely range of colours achieved by very skilled hybridisation 

 The gravel mulch looks good and conserves water
I myself grow as many as twenty different saxifrage species and varieties but have forgotten their names. I confess I cannot say with certainty whether any are kabschias! I know some are merely ‘mossy’ ones. Kabschias are small ‘hard’ leaved, silvery and  bloom early. I know over the years I have lost several that have just faded away. The ‘saxs' that do well for me are the lovely encrusted type. 

I am a sucker for any saxifrage

Waterperry saxifrages love the rain from the overhead watering system. Here in Tigne in the French Alps encrusted saxifrages receive wet spray from the cliff springs 

Tucked close to an encrusted saxifrage this is the only kabschia I am sure of! It has perhaps survived because the well drained ground retains summer moisture and one of my dwarf pines provides light shade.

I think the advantage of the trough is that I don’t forget to water in Summer

Saxifrages grow together with my hardy cacti and  self seeded Scilla biflora in my gravel garden

Wednesday, 1 April 2015

Hybridity’s contribution to evolution: featuring fossil trees

Part 4

Most of our garden plants have been created or hugely modified by hybridisation. Most farm and domestic animals do not exist in nature. Even those that do occur naturally have been ‘improved’ by mixing diverse forms together. Plant and animal breeders routinely find hybridisation to be a quick and easy tool to create new forms. Crossing of even quite diverse species and ‘varieties’ is relatively easy.
I reported last time how cycads are potently promiscuous. In my research for my post on horsetail, I found the several species of equisetum - that most ancient of plants - mix their genes very readily indeed. Clearly prehistoric plants and animals hybridised too. Why don’t evolutionists recognise the implications?

The Dawn Redwood, Metasequoia glyptostroboides and its later relations

My twelve year old metasequoia will soon get too big
Living metasequoias were identified for the first time in China in 1941 and in the same year its fossils were first found. An expedition to China in 1948 found a remote forest of a thousand more trees. Like those other fossil trees ginkgo and the Wollemi pine it was easy to propagate and specimens were very soon planted all round the world. Ginkgo and metasequoia are now relatively common here in the UK. Known to rapidly grow into a large tree the early specimens have not been here long enough to know how large they will get.

I do not want to use these relics of former forest in the time of the dinosaurs to merely argue my case for hybridity. I want to also consider them as fascinating plants. In terms of hybridity’s place in evolution they probably raise more questions than answers. I have allowed myself to be tempted to also discuss the Dawn Redwood’s very close relations, Sequoiadendron giganteum, Sequoia sempervirens (the coast redwood) and Taxodium distichum (the swamp cypress). They are all very big, exceedingly long lived trees and in terms of plant classification are placed close together.

The dawn redwoods clock-in as fossils ninety million years old. Even on an evolutionary timescale this is not small, albeit compared with ginkgo, relatively recent. Unlike ginkgo it can be classified together with well known younger relations. In common with ginkgo it has provided enough puzzles to lead some botanists to suggest it might  be a hybrid. In common with ginkgo modern specimens are almost identical to the earliest known fossils. It is truly amazing how so many plants and animals appear as fossils ‘out of nowhere’ and then continue to be found in succeeding strata that show sequences over millions of years with very little change until extinction or the present day.

To me, the startling and significant thing is that the coast redwood, Sequoia sempervirens, that giant of all trees, achieving more than 350ft high, is thought by more enlightened botanists to be a hybrid. Metasequoia is thought to be one of the parents, the other probably Sequoiadendron giganteum or perhaps another now extinct sequoia. Taller than either purported parent it is a supreme example of hybrid vigour.

Taxodium distichum
My own swamp cypress Taxodium distichum 

Although the swamp cypress is not thought to be a hybrid - but who knows - its fossil ancestry and an unusual characteristic make it a very interesting plant.
It’s a plant with a mystery. It possesses upright ‘pneumatophores’ that grow from the ground or from the muddy floor of a lake. Its not called ‘swamp cypress’  for nothing and I am privileged to have seen this phenomenon on many fine trees in the US Everglades. The pneumatophores look rather like wooden traffic cones and may elongate to several feet long.
I learnt on my metaphorical mother’s knee that their function is to facilitate oxygen uptake - and pneumatophores truly fill this role on trees such as mangroves. The strange thing is that despite very extensive study in the case of the swamp cypress they have no obvious function at all.

A rather tall tale
Taxodium distichum might very well be a hybrid. A property of organisms that arise from ‘more distant’ hybrid crosses is that they have not been directly shaped by the pressures of conventional natural selection. They arise as a new organism and are a result of thousands of genes in new combinations. They ‘sink or swim’ in the place that they find themselves or if animals any suitable niche they can find.
Taxodium has formidable characteristics that have enabled its survival over millions of year. Should useless pneumatophores have no selective disadvantage they might very well stay.
This is analogous to conventional ‘genetic drift’ where many characteristics such as hair colour or the shape of a nose or the kind of twirl on an ammonite has no selective pressure to remain or go.
It is well known that where animal and plant organs and tissues are no longer useful that natural selection will select against them. Evolutionary theory recognises that many organs are vestigial. Some organs such as the human appendix and tonsils were thought to be so. It is now known that this is incorrect and it would seem that they both bear a role in our immune systems.
One can perhaps better explain ‘useless’ pneumatophores in terms of having evolved in conditions where in the past they did incur advantage. In which case they would be truly vestigial in Darwinian terms.

As is usual  on tricky botanical issues I consulted scientist Peter. He reminded me that any  biological attribute comes at a ‘cost’ in terms of resources. Natural selection would tend  to remove anything that failed to contribute to survival.

With regard to taxodium’s funny stumps we find it very hard to  believe they have no function at all!

Like metasequoia, taxodium is a deciduous tree

Taxodium fossils
Petrified forests have been found in several locations. A famous one is in 65million year Cretacious deposits in Prince William Forest in Virginia. Such fossils are of course made of stone.

Scuba divers made a fascinating find of submerged taxodium forest sixty foot deep off the coast of Mobile two years ago. The trees were seemingly so fresh that the you could smell their characteristic resin. It would seem that they only have a very short time left to observe and record these trees  before they succumb to predation and decay. Research findings I believe have not yet been published. I presume the sea floor must have elevated to expose these ancient pristine trees?

The Soviet connection
Writing these posts have led me down some fascinating avenues. This article written by A.S. Yablokov on wide hybridisation and translated in 1960 gave me both interesting material and a chill shudder. It covers work in the USSR in the period dominated by that misguided man Lysenko. Lysenko promoted the Lamarckian view of the inheritance of acquired characteristics. Such ideas complemented Stalin’s ambitions and Lysenko rose to high status and dominated Soviet genetics for several decades. Not only did many distinguished geneticists die in the gulags, Lysenko’s crackpot ideas led to several failures in Soviet agriculture and the death of millions.

On further investigation I learnt that up to about 1925 Soviet geneticists were the best in the world and many things taken for granted in breeding and genetics today were discovered in Russia.
You need to read between the lines when reading the Yablokov link. Mindful of the fate of many colleagues they had to be careful.
It does seem to me that Yablokov’s associates were fine breeders of forest trees and fruit and many of them were proud to be called horticulturists. The link describes their work with distant hybridisation which they define as either crosses between different species or crosses within a species but from diverse geographic sources. The article contains references to many successful intergeneric crosses between different conifers including sequoia, sequioadendron and taxodium. Had metasequoia been discovered they would have hybridised it too!
Consistent with Lysenko doctrine the article also refers to grafting as a special case of hybridisation. This is of course nonsense! Never-the-less the Russians were skilled grafters and the results they report do not in most cases conflict with the known benefits of grafting. We recognise today that rootstocks do exert powerful effects on the scions but in no way interfere with their genes.

Could it be that because hybridisation was a tenet in Lysenko’s poisonous doctrine, that as a force in evolution this concept has been tarnished?

Metasequoia and Taxodium as garden plants

I group them together as both these close deciduous relations can easily be grown and share similar features. Both can grow in poorly drained conditions but also in almost any normal garden soil.
Potentially too big for many sites, dwarf and more slender forms are available. For example Metasequoia ‘Sheridan’s Spire’ is more slender than the usual form. Taxodium ‘Celeste’ is slow growing and spreads to make a low shrub. Even that giant of all trees, sequoia comes as ‘Little Ted’ in an exaggerated dwarf form.

I find it amazing that plants are so ‘plastic’ that trees with the genetic constitution to be so huge, with tiny genetic tweaks can be so small. In the case of bonsai trees their diminution requires no genetic change at all.
My own two metasequoias and lone taxodium are the normal vigorous quick growing kind. RHS quote 25 metres as the eventual height of metasequoia in the UK. It could be very much more!
Initially quite slender my own dawn redwood will do me for perhaps twenty years. Should I still be around I will chop it down and plant another. I wonder if the stump has the capacity to regenerate?

I find it quite fascinating that a simple mutation can change the leaf colour
Nikolai Vavilov 
Radio Four recently made a programme about how old wheat varieties such as emmer and durum had been preserved and were now maintained as a genetic resource for the future. I learnt for the first time about one of the world’s greatest geneticists, Nikolai Vavilov who travelled the world, building up the greatest ever collection of seeds, roots and tubers. He could talk to local peasants and farmers in fifteen different languages. A giant amongst geneticists and evolutionists he was a world authority on the evolution of plants and ourselves. He dreamed of breeding  – no doubt exploiting hybridisation - high yielding nutritious plants that would feed the world. He rose from peasant stock to become for many years the director of the Lenin Academy of Agricultural Science.

He sponsored a young peasant named Lysenko….
In 1940 Valilov was sentenced to death by Stalin for opposing Lysenko’s views. This was commuted to 20 years hard labour and he died in a prison camp in 1943.
His former staff at the Institute maintained his collection and although several of them died of hunger in the Russian famine they refused to eat their valuable store. Seized in the Nazi advance the collection went to Germany.
Posthumously pardoned, the Vavilov Institute was named in his honour. He lives on today together with his equally brilliant physicist brother in the names of a minor planet, a crater on the far side of the moon and Vavilov II, the name of a ‘Siberian wheatgrass’ widely planted in North America.
In 2010 the Putin regime was in the process of selling for housing development hundreds of acres where The Vasilov Institute’s vast collection of fruits and trees were preserved…. 

A footnote on Sequoia giganteum
Rather like the the three fossil trees the giant sequoias came late to Europe and in the UK became widely known in 1853. When seed raised plants became available every gentleman’s estate had to have one. 
The new introduction was named Wellingtonia! How Victorian to name a fine American tree after a British general. In the UK wellingtonia is still widely used as a  ‘common name’.
Some have grown very quickly and several specimens are now fifty metres high. For a tree that can live for thousands of years their potential UK height is unknown.

We visited an old country estate in Oxford this weekend and I was thrilled to find two fine sequoias.

The wellingtonia towers over other trees at the entrance

The lovely soft red bark is fibrous and fire resistant. In ‘less refined gardens’ the bark is worn where visitors have punched it!

Look carefully and spot the male and female cones
To read my previous posts in this series click 'hybridity' in the side bar
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