Effect of light and humus on survival and height growth of ash (Fraxinus excelsior L.) seedlings

In 1997, 300 three-month-old ash (Fraxinus excelsior L.) seedlings were removed out of the three different humus types (100 seedlings from each humus type) in the experimental forest of Aelmoeseneie (University of Ghent) with a closed canopy, in north of Belgium. Humus types were described as active mull with pH of 5.3-6.5, acid mull with pH of 4.4-5.2 and moder mull with pH of 3.8-4.3. Seedlings were transplanted in plastic pots, filled by the original soil, and placed under five levels of light intensity (2.5, 10, 18, 28 and 92/), inside and outside the forest. Only with 92/ light intensity seedlings were watered as necessary to avoid any appreciable water deficit. The results after one growing season revealed that seedlings attained a very high survival rate (95.3/). Survival was the highest when seedlings grew under semi-closed canopy (10, 18, and 28/) and also outside the forest at the 92/ light intensity, compared with those under closed canopy (2.5/). It also confirmed that ash seedlings are shade tolerant, but with little growth. Height growth indicated an increasing growth response to nutrient availability with increasing light intensity. In fact, minimum height growth was observed in lower light intensities (2.5 and 10/) and the maximum value in higher light intensities (28 and 92/). Height growth of ash seedlings increased at humus types of active and acid mull, compared with moder mull. At the end of the first growing season, lack of differences in survival rate and height growth, produced under 18, 28 and 92/ light intensity, revealed that training the seedlings under semi-closed canopy (18 and 28/) has a preference to those under relatively full daylight (92/) associated with watering. Therefore, the first year observations showed that ash seedlings, either in view of stem quality and growth or with regard to the facilities of maintenance, are preferable to be trained under intermediate light intensities (preferably 28/), at the high nutritional humus (active and acid mull).