Effects of the gypsy moth defoliation on growth and mortality of oak stands
Investigations were carried out in Rumania in three oak stands (Quercus pedunculata) situated in two different phytoclimatic regions where the defoliation was observed one year or more consecutive years. In four other forests were used artificial defoliations in young (15–20 years) stands.
The growth (ig) was estimated in permanent trial plots (with minimum 150 trees each plot) in defoliated stands and in control stands where gypsy moth were controlled. p ]Radial growth (ir) was measured by microauxometer and by increment cores sampled with Pressler borer.
The results show that one year defoliation influenced the stands growth in that year and in the next two years. In this case the whole growth difference — as compared with control stands — was almost similar to the equivalent of one year growth. If the defoliation occurred two consecutive years, the whole growth difference was similar to 1.3–2.2 years growths, in old stands and in young stands respectively.
Oak stands defoliation, unassociated with other limitative factors, does not lead to oak mortality but only to increase of natural elimination process.