Forest photology
Considerations, rather general, above, suggest that the natural radiation
emitted by the sun and the sky, must act in multiple ways on plants in general
and especially on trees of all sizes, including Culture is the main goal pursued
by the foresters.
We alluded earlier to photosynthesis, his role is extremely important since
it is assumed, generally, that this feature is characteristic of plants with
chlorophyll is the basis of life on our globe. With water and dissolved minerals
in the soil with carbon dioxide from the air (where it exists in a very low
average rate of about 0.03%), with the energy that the sun, plants "to
build" themselves from these simple elements. They say they are autotrophic.
The tonnage they produce, has been a very rough, estimated for the whole land,
80/100 billion tons per year. Of course, trees are no exception to this rule
and influence, its intensity, its composition and its duration also determines
their growth closely. The mineral content of the wood extracted periodically
from the forest is generally very low (often less than 1% of dry weight) and
can therefore say, a somewhat simplified, that trees are made of Water, air
and light. They are considered in ecology, as true "producers" of
organic matter.
But on they will develop into a kind of parasitism complicated (this term being understood in a broad sense), consumers order varied - the lignivorous (many insects) - the granivorous (particularly birds)
- strict herbivores who eat shoots and
leaves (insects and many mammals) - as saprophytes, which feed on dead
plant material, often fell to the ground (microflora and microfauna varied
and many mushrooms), etc. ... In addition, these consumers 1st order,
living populations of carnivores, consuming 2 order (birds to insects,
winged or terrestrial predators to herbivores, as the man who, forester,
hunter or mycologist, intervenes in this complex cycle).
The forest is characterized by competition,
soil and air, between the various hosts that inhabit this body. From
a strictly forestry, it is necessary to consider, in particular, the
sharp reduction of natural radiation received at the lower forest. However,
there are formed mostly by seed, many young trees that can develop favorably
than if the forester is helping them. By the mid-16th century, there
are texts which mention, in a precise way, then what were the concerns
of forest this time. In 1548, Louis Petit, "Maistre des Eaux et
Forêts du Val de Saint Dizier, prescribed, for example," not
to let the oak and beech trees so that one does too umbrage to the and
another new release. In the 19th century, foresters ranked species after
they claimed, very soon, lots of light (such as oak and pedunculate oak,
or pine, Scots, Austrian black or sea, which were considered " tree
of light ") - or they endured long enough, dense enough shelter
(this was the case of silver fir, or beech, known as" shade tree ").
But they were hardly gone away, and had only very little attention to
quantifying requirements of these various species.
Moreover, they have long been hampered by the opinion of some botanists who, with the most serious reasons, and based on experiments indisputable professed "that light slows growth." The young oaks and young Beech, born on the edge of the forest stand, bend sharply toward the light (or heliotropism phototropism). If we try to keep them vertical by tutors attached to their stems, phototropic influence is so strong that curve, or even that it breaks these tutors. This unilateral light, which inhibits the growth of some trees, it does not when it is distributed to slow the elongation? How to reconcile the undeniable need shade, which is characteristic of many woody species, considering their growth in length, for example, with the light requirements resulting from considerations on the useful role of natural radiation in nutrition? That claim ultimately in this area, various kinds of forest trees?
But radiation does not only natural
light, it also brings heat. But if the moderate rise in temperature
certainly favors the performance of various physiological functions
of trees (such as photosynthesis, or growth ), it can, once it exceeds
the optimum, varying with species, future nutrition curb accelerating
the phenomenon of respiration, which reuses, often a significant,
material produced by photosynthesis. Too high, it dries the leaves,
with stomata closed, stopping all gas exchange essential to the life
of the tree and can even burn the young stems and thus destroy in
a definitive way. At ground level, it dries the surface layers, increasing
the water imbalance, and decreases the relative humidity of air.
We can understand how difficult it is to determine a priori the result
of these actions, positive or negative. And that's not all: quite
recently, it has revealed a new type of phenomenon, "photoperiodic
induction". Depending on the length of days and nights, varying with
latitude and time of year, some woody species exhibit profound reactions,
affecting their germination, growth, flowering and fruiting in particular
the effects of which can overlap and interfere with those already
very complicated, as described above.
The growth of the tree, found almost
by foresters, is conditioned by natural radiation in an extremely
complex and, assuming that each partial physiological effects described
could be characterized with great precision, programming and use
a computer would be the only solution currently possible to obtain
indications of overall value. Unfortunately, much of this research
are far from being pushed forward enough. Only the theoretical study
of photosynthesis is attempted in this way. As the human brain is
incapable of doing alone, such a synthesis.
Fortunately there are researchers
for another possibility: that of questioning the trees themselves,
and we shall see in a subsequent chapter how, with relatively simple
experiments, one can detect among the many effects of natural radiation,
which are practically the most important how to bring them into play
in promoting those that are most useful, and inhibiting those that
seem the most harmful way to achieve rapid growth and balanced variety
of woody species, characterizing a forest production and quality.
To facilitate reading this booklet, we will appoint most of the time, the trees which are mentioned by their common names (in French).
To enable accurate determination, here, for some, the correspondence with the scientific names (in Latin):
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A study photological complete forest should normally extend to research the influence of natural radiation on animal species that are usually found there. It should be noted, first, that this influence is less pronounced in animals than in plants more closely related to the microclimate of their station. Much has studied the phenomena of vision, in various animal species, mammals, molluscs and insects. The influence of photoperiod regime on reproduction has been the subject of various experiments: insects (MARCOVITCH, 1924, LEES - 1959), birds (ROWAN-1925) some mammals (BISONETTE-1932). Research on the influence of ultraviolet (cell damage, genetic mutations) were also performed. We can see these issues A. GIESE (1964) and Y. LE GRAND (1967) - (See the Bibliography final).