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

Abstract

In  1997, 300 3-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 1 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 semiclosed    canopy (18 and 26%) 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).