Surface terrière

The surface terrière (noted " G") is a term of Sylviculture used in the field of the ecology and forest sciences.

Definition

This index corresponds, for a Arbre given, in France with the sectional surface of a tree measured to 1,30 meter of the ground (approximately 4.5 feet height for the english-speaking, and formerly “with height of shoulder” ). But, according to the countries and times this measurement can be made or to be made with a height ranging between 1 and 1,5 with the top of the level of the ground. It is a measurement often more approximate in zone Tropicale for the large trees, because for certain species, their “buttresses” can still with this height prevent " cercler" the tree to measure the perimeter of it.

surface total terrière or average , of a given surface (dispersed, aligned trees or forest settlement, Agrosylviculture, Scrap-metal, Orchard, city park, etc) can be calculated by the sum of the surfaces terrières of all the Arbre S of this surface; it is usually expressed in m ² /ha. The number calculated for one ha allows an approximate extrapolation for a larger homogeneous surface. Thus a surface average terrière can be calculated for a country. For example;
In France' , the surface terrière moyenne' in 2005 was estimated at 22,5 m2/ha for the public forest of metropolis. On a country scale, this figure should not evolve/move theoretically much in time, except following major fires, major epidemics or important Tempête S, which can also be indices of the first total impacts of climatic Modifications. Thus in France, 19.690.000 m3 of Chablis resulting from the two storms of December 1999 represented sleon the ONF more than 7% of wood the total resource of the national forests;

Note:
La surface terrière of a tree is all the more high as the tree is large;
la surface terrière of a settlement is all the more high as the settlement is dense.
Pour of the reasons of time and because most of the young trees will be eliminated the first years at the time of the competition for the light, one generally measures surface terrière only for the stems of more than 10 cm in diameter.

Use

It one of the indicators is used for forestry management or at the time of the study of forest settlements. The follow-up in the time of this measurement indeed gives a precise index of the woody Productivité of a piece, via the speed of growth (in diameter) of the trees. The surface terrière is also an indication of occupation of the ground and space by the trees. To be more realistic this index must be cross with the height of the trees, in particular for the species which grow little in width and quickly in height, particularly in dense forest.
C' is an indicator sometimes used for the ecocertification (FSC by ex), to follow the evolution of a peuplemnet in time. (A management known as near to ecological nature or of the type Prosilva seeks to preserve little a surface terrière total optimal and high and variable, whereas management by close-cropped cuts results in a curve into teeth of saws.
Cette surface “G” gives an index of the volume of wood when it is calculated for only one tree. When it is total expresses anything the age of the trees, neither their height, nor of their diversity or quality but gives a precise index of the space occupied by the trees, proportionally on a surface.

This index also can, within the framework of a impact study or of a Public survey to be used to calculate be to carry out compensatory measures more " justes" , continuation for example with installations requiring the destruction of a wooded piece; Instead of retimbering two or four hectares per hectare of forest crossed, the author of work having required a compensation must then replant trees so as to immediately restores surface lost terrière. This last with the choice between planting many tree or diameter shafts low, less, but of larger diameter. This compensation does not restore all the functions ecological of the lost forest, but it at least makes it possible to find an equivalent raised biomass more quickly. This is made with “obligation of result” , i.e. that the trees which die in the first years following a failure of plantation must be replaced)

Measure surface terrière of a settlement:

Two techniques, possibly complementary are used

measurement of the circumference with 1,30m of each tree; and addition for the calculation of the total area (or averages and extrapolation in the case of large surfaces)
estimate using a Relascope (or measures angle).

See too

External bonds

August 1st

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