Monitoring of natural regeneration in a dense semi-natural mixed hardwood forest on the base of ash, beech, oak and sycamore occurred over 3 years in the Aelmoeseneie experimental forest, Belgium. 40 permanent plots (4 m x 5 m) were selected in three various humus types, located in an ash stand and in an oak - beech stand. In all plots abundance and top height of all broad leaved regenerated species were determined at the end of the growing seasons 1995 and 1998. In addition, the seedlings which appeared in the plots during 1996 and 1997 were identified and followed up. This study proves that in the investigated sites natural regeneration is drastically poor and diversity is low, in particular where the humus layer is more acidic (mull moder) and the litter layer is thick. No regeneration phase older than the seedling stage (h < 40 cm) is developed on the different humus types. On average, total number of seedlings in 1995 amounts to 38 units/are in the ash stand and to 63 units/are in the oak - beech stand. Survival rate over a 3- year period is 37% and 42% respectively in the ash and oak - beech stands. Total ingrowth during the growing seasons 1996 and 1997 is virtually poor, indicating 16 and 8 units/are respectively in above mentioned stands. Survival rate of occurring seedlings, as well as the ingrowth of new seedlings are notably different (P < 0.05) according to the soil conditions of the ash stand. Generally, the low presence of seedlings and the lack of regeneration older than the seedling stage reveal that the regeneration development encounters with a critical problem. The continuation of this process would likely result in a progressive succession by the invasive and the unwanted tree species.
