Archive for the ‘Concerns of World Resources & Population’ Category

Ivy – Hell Bent or Heaven Sent

August 24, 2011

Written as a blog in response to a letter by Lt Col Paul French (Rtd.) in the Daily Telegraph of Monday 28th March 2011.

Most of us who love trees for their timber and role in the landscape, regard Ivy as a foe.  The wild variety in the UK is named Hedera helix, though from its growth pattern it would be more aptly named Hedera rete i.e. Ivy net.  However, there are three views of  ivy: that of the tree; that of the birds, bats, insects and fungi that live in and on it; and that of humans and the browsing animals.  In past centuries: before the reign of plastic, huge human populations and high wages; all trees, farmland, woodland and forestry, were cared for by the humans who worked the land.  Ivy was left to grow only on those trees that were already misshapen, or of a species whose timber was not considered to be useful.  Even then Ivy was controlled by deer and cattle that were permitted to seek the shelter of the woods in winter, where they kept down the undergrowth.  Their grazing kept the glades open so that Wild Garlic and Bluebells could get enough sunshine to grow and flower ahead of the herbs and thin grasses in the spring.

Viewed from the tree’s perspective it is definitely a devil.
The creeping stems of Ivy are coated on one side with tiny suction rootlets that enable it to climb up the trunk and cling to the bark of  the tree.  Generally it does not attack until a young sapling has become too inflexible to fling off the unwanted guest as it bends in
the wind.  Then, when after several years the trunk has lost its whippy characteristic, and is suitably firm and steady, the Ivy colonizes.  Unless it is broken off by humans or browsers, ivy grows steadily upwards branching as it goes, until it reaches a level at
which the branches are still whippy enough to shake off the tendrils for the time being.

Like all evergreen species, although it does not shed its leaves seasonally, they gradually age and drop off.  They then cause even more trouble: by lodging in the angles of the boughs, and with other leaves they rot down leaving a black leaf mould that in turn plays host to epiphytes – mosses, nettles and ferns.  The bark beneath then starts to rot, thus weakening the branch, and allowing the rot to penetrate the heart wood of the tree.  The living Ivy leaves also cause problems by sheltering the bark from the rain, and the ‘rootlets’ absorb any water running down the surface of the bark.  This leaves the bark dry, brittle, and cracked so that it is easily penetrated by insects and fungal spores.  These often carry diseases, both bacterial and viral, which are, in turn, transported into the sap that runs in the living layers just beneath the bark.  In this way pathogens can be carried up into the leaves of the canopy or down into the root system.

Worse still Ivy keeps its leaves throughout the winter, thus adding weight to the branches and extra surface area to catch the winds.

The ivy here has climbed nearly to the top of the birch tree and the weight of its leaves is slowly pulling the tree over.

Slow felling of a Birch by Ivy

  This at a time of year when our deciduous trees have shut down and shed their leaves, thus protecting themselves not only from the cold, but also from damage by winter storms.  In a young sapling the situation is not so serious, as it is often both strong and flexible enough to carry the extra leaf area without cracking; especially so since the ivy is young too and equally flexible, but the story is very different for the older tree.  Veteran trees often have ivy stems of over 6cms diameter half buried in their bark; and these vast old creepers add substantially to the weight to be carried by the branches, made even more fragile by the lack of moving sap during the winter months.

The result is very visible damage.  Some unlucky trees are completely thrown and partially up-rooted; some escape; but most veteran trees suffer the breaking of large boughs and even smaller branches in the crown of the tree.  These breaks leave scars that not only spoil the visual shape of the tree, but may also unbalance the tree, making it more susceptible to wind damage in the future; not to mention the increased risk of disease entering the broken timber via rain and spores.  All this damage hastens the slow demise of the tree.  However . . . .

Viewed from the denizens of the tree the story is very different; for everything, that the tree could be expected to regard as negative, is positive to them.  In fact the more the tree is damaged, the better the better it becomes for them.  Though as it disintegrates, they will all have to move on, starting with the birds and insects and ending with the decomposers growing on the rotting wood.  This is the way that it has always been.

In regions where there are no convenient conifers, ivy-laden trees provide some of the only safe shelter for small birds throughout the winter months; besides providing an every ready larder of spiders, flies, beetles, millipedes and mites throughout the year.  Bats too, can be found sheltering under the ivy during the summer; though it is possible that they are really looking for suitable warm sheltered holes to use for winter hibernation.  As for the rest: the birds’ living larder and the fungal spores; the ivy provides warmth, shelter and nice little cracks in the bark with good access to sap – an ideal growth medium for the fungi and any pathogenic bacteria and viruses spread by the insects.  Finally . . . .

Viewed from the requirements of humans and browsers the story becomes split.

On the ‘Up side’, the latter seem to regard Ivy as we would a tasty herb.  However, it is probable that their actions are related to self medication, as Ivy is a known anthelmintic that has been used as such in the past.  Animals may not be able to read books, yet many seem to either know or learn that certain ‘herbs’ are beneficial when eaten in small quantities.  So long as the plant is bitter they don’t exceed the safe dose; it is only when the plant is sweet, either alive or when dead e.g. Ragwort, that they over eat and poison themselves.

Humans too have used Ivy leaves as a medicine for thousands of years; though now-a-days its use is limited to external applications because of unpleasant side effects and its ability to destroy red blood cells if imbibed in excess.   However, externally the leaves still provide a useful herbal poultice for leg ulcers, enlarged glands, painful joints and other pains that can be reached from the outside!

This oak is completely encased in ivy, only the dead branches remain sticking out above the luxuriant growth.

Ivy engulfs its prey - a veteran oak dies

On the ‘Down side’ humans have always grown trees, not only because of their beauty, but also because of their many uses: for food and the energy to cook it; for medicines; for timber with which to make houses, tools, and all the plethora of things that are necessary for a good quality of life; and for ashes to make lye for soap making.  So overall, anything that affects the health of trees qualifies as a devil rather than an angel from the point of view of humans.

But that is not the full story and Ivy too has its uses.  Perhaps the solution is: to remove ivy* from all straight trunked trees and those that are suitable for structural or ornamental timber; then remove it from 25 – 50 percent of the remaining trees.  25% of trees with ivy is quite sufficient in our heavily treed areas e.g. Dorset and Devon; but in areas where trees are more scarce e.g. Northumberland then 50% of the remaining trees with ivy might be acceptable.  Let common sense prevail, and preferably prevent  our non-governmental public bodies and allied groups from removing all our conifers on the grounds that they are not native, or that their English names fail to suggest that they should live south of the border e.g. Scots Pine (Pinus sylvestris) which is prevalent right across Europe from North to South.  To my certain knowledge trees are totally unaware of geographical boundaries – unless they coincide with environmental attributes such as climate, aspect, rainfall and altitude!  However, the conifers do provide very good protection from inclement weather for wildlife and particularly for small birds, many of whom crowded into our group of Lawson Cypresses at dusk on a winters evening, and provided a chirrupy sort of concert for any who cared to stand under and listen!

*Ivy removal is simple.  Pull the small stems off young trees using fingers, before they become established.  For older, thick stems of ivy use a saw, billhook or chopper, to cut and remove a 5cm/2 inch segment from the base of the trunk.  Try to avoid damaging the bark where possible; but a little damage to a small piece of bark is preferable to much the much greater damage caused by the ivy.


Thoughts on Hugh’s Fish Fight

February 1, 2011

I have just signed Hugh Fearnley-Whittingstall’s petition to stop dead by-catch being thrown back into the sea. But pausing to think about this part of the catch, I realize that there are actually many problems associated with removing it from the marine environment.

Of course the real answer is not to take by-catch; nor to over fill the nets when bringing them to the surface. Having been out on a university research trawler in the 1990s, I am fully aware that the sonar scans and computer information from other boats  mean that the species of fish in a shoal, and its precise size, is known as the trawler approaches the region; and thus well in advance of the net being released in the first place.  Bottom trawls are a very different ‘kettle of fish’.

The number of fish that will die depends on several factors, amongst which, the way that they control buoyancy is probably the most important (see “Buoyancy Matters” end of this note).  Fish that cannot, or are slow to dive are the ones that become prey to the wake hugging gulls.  Those that have lost the ability to control their buoyancy, gradually sink through the water column, becoming dinner for scavengers on their journey to the bottom.  Other fish, krill, copepods and indeed bacteria and algae would normally expect to benefit from the extra nutrients that are thus released into the marine ecosystem – after all most marine organisms live and die in the sea.  If the by-catch came from the sea floor, then providing that they are still alive and don’t get caught by a gull, they don’t usually have swim bladders and will slowly drift down, be reunited with their food source and will survive the experience; though even for them the sudden pressure change may be a problem.  But normally, the ecosystem in which trawled fish live, is sustained by a rich mixed food source that contains some photosynthetic organisms and so moves up and down within the surface layers, stimulated by light and dark at the surface.  For these pelagic fish, it is the speed with which the trawl comes up to the surface and is hauled aboard that is the problem.  If it happened slowly enough most swimbladders could adjust, but too fast and they burst.  They can also become disconcerted when released to the surface and this may help to explain their slowness in swimming back down to their home level.  From the gulls’ point of view, the slower the better; as this allows them to attack the fish in the bag.  From the fishermen’s point of view, the faster the better; as this allows them to get the whole catch on board in an undamaged state – the customers tend to dislike battered fish with speared chunks taken out of their sides!  Arguably the seabirds do not rely on an abundance of fish deposited on the surface by a boat.  This happens naturally when prey species are hunted by faster hunters e.g. tuna who drive the shoals to the surface and coincidentally into the beaks of the gulls.  The only real problem here is that, without the trawler, these fish would probably have lived to see another day and even spawn, before becoming dinner for other marine inhabitants.

Hugh Fearnley-Whittingstall is correct in that it is daft to throw dead fish/sea creatures back into the sea, in terms of human food.  However, if one brings the by-catch ashore, then another very real problem springs to mind, concerning what it is right to do with it i.e.  If the fishermen land this extra catch and sell it, then they are benefitting from the fish that they should not have caught in the first place!  With our huge population, it is difficult enough as it is to maintain fish stocks with enough adult fish, of mature size, to optimise breeding.  I fear that if the fishermen find that they can actually earn an income from the extra catch, then they will do so – after all the human population is now so huge that all that they catch will be eaten.  Unfortunately, the likely result is that even more species of fish and marine organisms will end up on the critical list.

Perhaps the answer is to ensure that any extra catch is taken into custody on the dock and distributed to local fishmongers for the cost of the distribution exercise only.  That would actually have the benefit of providing more jobs for humans, but then of course they would have to be paid out of the sale of the by-catch, with the result that they too would be hoping that the by-catch was as large as possible.  If the fishermen are fined, then they will simply dump the catch at sea as before!

It’s a difficult question.

Buoyancy Matters: Fish in general have a specific gravity of 1.07 and so will tend to sink in water, unless they keep swimming.  This is no problem for predator fish such as mackerel, sharks and indeed rays; but for those that feed in the plankton, neutral buoyancy is an advantage meaning they can stay at the same level as the plankton without having to expend extra energy on maintaining their level in the water column – plankton move up and down according to the light levels.  This neutral buoyancy is achieved by the presence of a swimbladder (air filled bladder) whose pressure can be adjusted to suit the feeding requirements.  Most young fish can adjust the volume of their swim bladders by actually swallowing air from the surface, and in some species this ability is retained in adulthood.  However, in many species of adult fish this duct closes and the volume is adjusted by the removal of gases from the blood.  Since most fish can survive out of water for a short while, provided that they are kept wet and cool; most are returned to the sea alive.  However, whether they will survive or not, depends on the factors mentioned above; plus whether the benthic species can survive the sudden decompression from several atmospheres up to the surface at an air pressure of only 1 atmosphere.  Some fish with swimbladders have been found at depths of over 4000m depth.  For each 10 metres of depth, the pressure increases by 1 atmosphere; so at a feeding depth of 100 metres the water exerts a pressure of 10 atmospheres.  This means that when these pelagic fish surface, the gas in a closed swimbladder expands 10 times and will definitely burst the organ before it reaches the surface.  Even a swimbladder that is connected to the mouth relies on the fish being able to burp out gas fast enough to avoid bursting the swimbladder.  Non-ducted swimbladders are filled with gas from the blood, which implies that their adjustment is normally slight/slow; and big changes in the volume of gas required would take a long time to achieve.

Once on the surface, another problem arises as the fish has to refill its swim bladder adjusting the fill to the increasing pressure as it moves back down.  If only the surface air were available, then obviously as the fish swam down this would be compressed leaving a very deflated swimbladder.  In turn this could cause displacement and abnormal compaction of the internal organs.

Apart from these problems, the swim bladder of some species contains the normal gas mixture of nitrogen, oxygen and carbon dioxide in ratios that differ not only from the air, but also from those in the water at their living depth.  Thus the ratio of nitrogen in a cod’s swimbladder may vary from 7.6% to 56% with associated percentages of oxygen of 76.6% and 30.1%; and carbon dioxide of 15.8% and 13.9%.  All this is managed by a specialized rete mirabile type structure of the supplying blood capillaries – a similar structure is used to cool the blood going to the feet of penguins and to warm the returning blood so that the core temperature is not affected unduly.  Nature is very good at re-using good ideas.


Wilderness to Farmlands to Towns – can we afford this change to be inevitable?

October 14, 2010

Wilderness to Farmlands to Towns – can we afford this change to be inevitable?

This topic is often on my mind and it was recently magnified when I read “Among the Elephants” by Iain and Oria Douglas-Hamilton.   Iain’s study sets out to establish how best the African elephant can be managed in the limited areas of the National Parks.  In the final chapter, he comes to the crux of the problem.

Very simply the rapidly increasing human population has resulted in the spread of rural and urban development into areas that were once solely the territory of wildlife and nomadic tribes.  This is actually a worldwide problem; however, this book highlights the problem in Africa.

For millennia elephants have roamed all over Africa from the Mediterranean to the Cape and from East to West. Between 11,000 and 5,000 BC, humans were observing them and they were featured in rock etchings, some of which have been found in Algeria.  Wherever the right mix of grass and trees existed, there too were the elephants.  As they passed, they ate the bark, young branches, fruits and seeds together with grass which they cut with their toe nails i.e. they do not normally pull it up in chunks and if this happens accidentally, they avoid eating the soil and roots. Many of the tree species in particular have seeds that will only germinate if passed through an herbivore’s gut; and since the elephant then deposits the seeds with a liberal amount of dung, the young trees germinate into an ideal growth medium, rather than into the frequently nutrient poor surrounding soil.  When the elephants have opened up an area of woodland so that there is no-longer an ideal mix, and grassland starts to take over, they move on – providing there is the space to do so.  The spreading grassland areas become savannah and can then support vast herds of grazers e.g. the Wildebeest and associated species.  Eventually, droughts and wildfires thin the grass, returning the essential trace elements to the soil, and the grazers turn to a fresh swathe of savannah.  Meanwhile the seeds that have remained dormant in the soil get a chance to germinate, usually in the vicinity of the few remaining trees, and gradually woodland builds up again.  Finally the cycle restarts with the return of the elephants.  In other words, the elephants act just like early humans with their practice of ‘slash and burn’, crop and move on, agriculture.

The problem for elephants now is not that they are hunted by humans per se; it is simply the level of hunting and the restriction of their ancient ranges by human infrastructure.  The African elephant has been hunted, for both ivory, meat and even domestication, for many centuries.  As far back as the 3rd century BC, Ptolemy set up a school for African elephants beside the Red Sea, for the specific purpose of using them with his armies!  However, in those days the population of Africa was very low and scattered, there were none of the huge urban developments and areas of cultivation that exist and are still extending to-day.  This meant that the elephant herds had the run of a whole continent to manage in their own way.

However, from the Douglas-Hamiltons’ book, it is quite clear that even in the Africa of 1975, cultivated crops were being planted right up to the boundaries of the National Parks wherever there was sufficient water for crop growth.  This conflict of land use had been started in past decades by the white settlers, but now that many were leaving, the conflict was being continued to an even greater extent by the ever growing local tribes.  It is an inconvenient fact that if land grows good woodlands, then there is enough water initially for humans to grow good crops.  Where crops can be grown, then towns arise to process them, transport them and provide the necessary infrastructure for a growing non-nomadic culture.  At this point the phrase “enough water initially” becomes crucial.  Inevitably, artesian wells have to be sunk and if water is found then the community continues to grow, if not it eventually moves on.  Unfortunately, the aquifers thus tapped are finite reserves, and their very use may hasten the draw down time for surface waters, thus threatening any remaining surface flows and the wildlife and ecosystems that depend on it.  Where the townships thrive, both the wild animals and indeed the native nomadic tribal peoples become regarded as nuisances; and their lives, harmonious with nature, are restricted to ever smaller areas in the interests of Growth – or should that be Greed.

So, if the change posed in the title is inevitable, then modern humans are faced with yet another dilemma; presuming that they are all agreed that they wish ALL the species on the planet to be able to survive.  Creating a habitat for one species, does not serve the vast mosaic of species that normally co-exist symbiotically.  The best solution is to let wild animals and their vegetation have sufficiently large areas to cycle naturally, in all parts of the globe.  However, this poses the question of how many humans the planet can actually support.  If we and all the other species are to live in harmony, with enough space to be able to enjoy our lives, then we do as individuals need to control our populations.

Traditionally, having long got the better of our carnivorous predators, our population has been controlled by disease and frequent and bloody wars.  However, this latter is a very unpleasant way of behaving and it is to be hoped that diplomacy will always prevail.  But even now, while this happy state of affairs is being established, all national, ethnic and religious groups need to consider how to prevent over population by humans, whilst preserving our varied gene pool and our diversity of thought and culture.  The more numerous we become, the more we encroach on wilderness areas, the scarcer our resources become and the more each diminishing resource costs to use.  In the 1960s water in the UK was still free.  Now we have to pay an ever increasing amount for this commodity so essential to life.  As our population rises so does the cost of living – for how long can we support these increasing costs that actually do nothing to save the species on this planet.