Articles
CHARACTERIZATION OF MODERATE HYDRIC STRESS ON ASH TREES (FRAXINUS AMERICANA) IN LANDSCAPED AREAS
During the transplantation in the definitive site, the tree leaves the major part of its root system in the nursery soil.
The first years after its transplantation dificulties of adjustment between transpiration and absorption can occur.
The transplantation conditions must be optimal to make it possible for the tree to regenerate a root system quickly.
The objective of this study is to follow the hydric alimentation conditions of 10 years old ash tree, which has been transplanted for two years, in April and November, in 4 m x2 m and 1.2 m deep plantation pits, where the reconstructed soils with arable earth are homogeneous.
Some trees are submitted to a moderate soil drying.
The measurements were taken in 1996. The trees were irrigated manually.
Measurements were taken on soils and trees : the soil water potential was measured with resistance probes "watermarck®" located at different depths and distances of the trunk in a range between -10 and -200 KPa; the leaf predawn water potential with pressure chamber and the branch diameter micrometric variations with displacement captors.
Comparisons between different parameters indicate, for the ash tree, a threshold of soil water potential for which a plant stress reaction and a branch diameter decrease were observed.
The micrometric study proved to be accurate to detect a hydric stress beginning of the tree.