To take into account the local size changes, resulting of space fluctuation of a physical parameter, leads to the general formulation of internal stresses induced in a continuous anisotropic medium. Assuming a linear mechanical behavior, a new mechanical problem can be presented as a generalisation of Duhamel method. The method is applied to the particular case of shrinkage, where wood is assumed to be linearly elastic, cylindrically orthotropic and homogeneous. The stress-shrinkage tensor components are calculated from the strain-shrinkage and elastic stiffness tensors, both characteristic of the high anisotropy of wood. Using various bibliographic references, concerning 21 species of trees, with specific gravity from. 25 to 1. 28, it is shown that the stress shrinkage can be considered as an isotropic characteristic of wood materials. Moreover a good approximation of the stress-shrinkage coefficient, for a given wood, is obtained multiplying the square of the specific gravity by the constants K₁₀₈ = 21.5 MPa/per thousandH that seems to be a specific constant of woods.