Weekly TV series feature specialist cops who understand the momentary expressions that pass across the features of their suspects at times of stress, and then nail them!  Guilt or fear? Anger or hope? Apparently there are such deeply coded reactions perceivable in our 52 facial muscles, that whether you are a war-like man in Papua New Guinea or a peace-loving woman from Thailand, the same groups of expressions occur in identical circumstances. We all smile with joy, and interestingly ‘smile-grimace’ in anger or fear too. Our eyes open wide with surprise, and we frown spontaneously when worried, confused or disorientated.  But under the surface of these obvious, well-known facial expressions, there are literally hundreds of combinations of muscle actions, which tell a far more complex and dependable story of what is happening within the heart and soul of a person.

Are we surprised that we are so deeply programmed as homo sapiens that we are all linked together with the same neurological circuits? And do we alone, amongst living things on Earth have visible predictable reactions to our surroundings, which can be successfully decoded by those in the know.  The answer is “no” to both questions; we should not be surprised, and we are not alone.  I am sure that horse-lovers, rose-growers, fishermen and butterfly-catchers will all tell stories substantiating how deeply the objects of their interest, respond to changes around them.

Now let us see how this idea relates to trees, which are after all, central to our blog.  Understanding how trees change and react to the world around them will add massively to our own enjoyment in Tree Spotting. It will also enhance our intrinsic knowledge of the local conditions where each individual tree lives. We humans, obviously being highly intelligent and emotionally charged to boot, transform our facial expressions in brief flashes of time, and we often have to respond appropriately within seconds. Trees are stationary, and adjustments they make are generally slow and for the long-term. These modifications lead to one of the conundrums we face when learning to identify different species: ie the same species does not always look identical, wherever you may find it.  The adaptations a tree has to make often alter its looks forever. My grandmother used to warn us, when we looked angry or sad, that if the wind should suddenly change direction, our faces would stay that way until we died! Well, with trees, this is true. The changes they make are very often permanent.

There are so many instances where trees respond to outside influences, that a simple list of interesting adaptations is probably the most space-efficient way to describe some of them.

1    We all know, but sometimes forget to interpret, the direction and strength of a prevailing wind, by the angle of the trunk of the local, taller, woody species, leaning away from the blast. This is especially obvious on high mountain-sides and along windy coasts but is never a factor in forests.

2    A second less obvious, but amazing ‘windy’ story is that trees ‘remember’ being blasted by a strong gale. When some trees have been severely buffeted, they often spend excessive energy the following year, thickening and strengthening their trunks in preparation for the next seasonal onslaught. The ability to carry the knowledge of this future need is a phenomenon, which, as far as I know, has not been explained by scientists.

3    Many types of trees that have faced fire and survived, are able to thicken their trunks with an outer, corky layer, ensuring greater protection against the possibility of burning in years to come. This characteristic is particularly prevalent in the Protea Family.


4    A short-term, temporary change occurs in most South African Acacias, virtually every day. Many of them are able to fold up the two sides of their leaflets as the sunlight fades, which helps to conserve moisture that might otherwise evaporate in the still warm, evening air.

5    Perhaps my most intriguing fact for this month is one that I have unashamedly taken from Colin Tudge’s Secret Life of Trees, the fascinating book I referred to a few months ago. Browsing through it (again) this week, I came across the following information that feels a little like a scientific miracle. Trees (and other plants) tend to grow towards a main, steady source of light. The initial ideas that explain how this happens, were first noted by Darwin in 1880, in his experimentation with oats. Most of us probably imagine that plants simply reach towards the light. It turns out however, that reaching light-ward is in fact ‘lateral thinking’ on the part of plants, taken to a very sophisticated level.  There is a common plant hormone called auxin, which has various essential functions in plant metabolism. One of its jobs is to stimulate the relatively rapid growth of various plant parts. Where auxin is present, growth speeds up in that specific area.  It is important to our story that this mobile hormone shows a preference for shade.  In the case of trunks, main branches and twigs, this means that auxin migrates to the cool side, away from the sunlight and “commands that section to grow faster”. As the ’back‘ of the branch thickens, the front is forced to bend forward ie towards the light!  I find this utterly amazing – as I have said above - because one would expect the plant to simply be growing towards the light source.  I enjoy trying to imagine that the craggy, gnarled tree species with such fascinating contortions of branches and twigs, are shaped that way because of the auxin hiding on the shady side!

Trees of the Month April 2010

This month we are looking at various trees that have easy-to-identify unusual shapes or features. In each case, I try to explain some of the reasons for their recognisable uniqueness.


Bushveld
Large-leaved Rock Fig
Ficus abutilifolia
 
This tree is easily recognisable in rocky areas of the Bushveld and Lowveld.  You can see the thick, white, snake-like roots of the tree curl and probe between clefts and cracks towards the moisture and soil below.  The Rock fig has large, rather coarse, almost quilted, heart-shaped leaves and, like all figs, has milky latex.  The unusual shape is determined by the trees’ ability to find even the smallest crevices in the rocks and to send sinewy roots into the gaps.  As these roots thicken and grow stronger, they are part of the natural forces such as water, heat and cold, which gradually split the rock apart.
 
 
 
Cape South
Kamassi
Gonioma kamassi
 
In most instances where you will recognize Kamassi, it is a small forest tree and one of my personal favourites, both in the wild and in my garden.  It is personified by the enigma of being a very orderly tree with all its leaves in perfect whorls of three; yet at the same time its lower twigs have an easy-to-distinguish habit of trailing sideways in the shape of a thin, cup-like curve, carrying the whorls of green outwards and upwards into any available spot of sunlight!  The tree’s precise, repetitive nature, combined with its adventurous creativity, fascinate me wherever, and whenever I encounter it!
 
Cape North
Quiver-tree Aloe
Aloe dichotoma
 
A Tree Spotting trip to the North-western Cape would not be possible without recognising a Quiver-tree Aloe.  It is a favourite along the streets of Springbok as well as Upington, and therefore you do not even need to venture into the wilderness of the Richtersveld, or the Namaqua National Park to admire the unusual leaves, trunk and flowers.  Essentially the shape of most Aloes is a successful response to arid, harsh conditions where years can pass with little rain, and yet (in times past) the tree would have had to outwit massive herds of would-be-browsers.  The thick succulent leaves retain moisture, while the thorny leaf edges deter mammalian nibbles of any kind!
 
 
Highveld
Common Cabbage-tree
Cussonia spicata
 
The outer corky bark of the Cabbage-tree Family is a response to the potential hazard, or actual presence of fire; its thickness offers an extra layer of protection to the precious cambium that carries the liquids and food of life for the tree. Perhaps the wide-spreading branches attracted animals that sought shade and then left behind their organic gifts of urine and faeces to feed the tree.  I have no explanation for the curiously shaped, sculptured leaves that characterise the genus and I would love input from any bloggers.
 
KwaZulu-Natal
Flat-crown Albizia
Albizia adianthifolia
 
Of all our South African trees that have magnificent, sturdy, straight trunks, carrying exquisitely branched, flat crowns, the Flat-crown Albizia is surely the most beautiful. Theories abound as to why there are so many flat-topped Acacias and Albizias in Africa.  The most obvious, is the inter-link between the shade and the mammal herbivores that, while keeping cool, deposit urine and faeces beneath the tree, feeding the roots.  In addition, I was told that the Acacias half way up the mountainside, outside the Ngorogoro Crater in Tanzania (Acacia lahai locally called Red Thorn, Melelek and Ormelelek), have wide-spreading branches with canopies actually touching, in order to break the thundering fall of heavy raindrops; the deluge would otherwise pound the soil below, loosen it and then wash it away downhill. Perhaps all flat-crowned trees protect their own precious topsoil in this way?
 
Lowveld
Fever-tree Acacia
Acacia xanthophloea
 
The striking greeny-yellow bark of the Fever-tree Acacia, covered by a thin layer of fine powder, which rubs off on your fingers, makes this tree instantly recognisable.  The green is not purely for looks, as this is one of the few ‘real’ woody trees where some photosynthesis takes place in the bark itself. Another advantage of the bark colour, for the Tree Spotter, is that it becomes easy to see contrasting dark ‘sacrificial limbs’, on most adult specimens. In fact most trees use a couple of lower branches as a dump-site, into which they pump excess minerals, leading to the death of that branch and its twigs. However in brown-barked species the dying process is not as noticeable as on the glowing green of the Fever-tree.