THE INFLUENCE OF SITE PREPARATION ON GROWTH IN QUERCUS-ROBUR L. SEEDLINGS IN A SOUTHERN SWEDEN CLEAR-CUT AND SHELTERWOOD

Natural regeneration of Quercus spp. is regarded as a method with majo r problems for establishing new stands. A number of factors like quant ity and quality of acorn production, heavy predation and browsing on a corns and seedlings and low growth rate of oak seedlings contribute in regeneration failures. To study the influence of light, nutrients and water on growth in Quercus robur I,. seedlings in relation to site pr eparation, a field experiment was established. The experiment was carr ied out in a clear-cut and a shelterwood in southern Sweden from 1992 until 1995. Five different treatments were applied and acorns were the n planted. The treatments were: herbicide, herbicide and mixing of the humus layer and the top 10 cm of the mineral soil, herbicide and remo val of the humus layer, herbicide and deep cultivation down to 40 cm w ith the humus layer in the bottom and undisturbed control. Irrespectiv e of the method, the different site preparation treatments after three years equally well prevented the growth of ground vegetation and incr eased the seedling growth. PPFD (photosynthetic photon flux density) a t seedling level was about 20% of full light in the shelterwood and in the undisturbed control plots in the clear-cut. PPFD at the seedling level were about 60% of full light in the different site preparation t reatments in the clear-cut. The mean cumulative soil water potential w as about the same in undisturbed control plots in the clear-cut and sh elterwood. In the different site preparation treatments, mean cumulati ve soil water potential indicated lower values in the clear-cut compar ed to the shelterwood. According to measurements of the leaf water pot ential, seedlings seemed to be more affected by water stress in the cl ear-cut. Nitrogen concentration in leaves was about the same in all tr eatments. Longer periods with shelterwoods in combination with the add itional site preparation for ground vegetation control was recommended for practical forestry for improved growth of oak seedlings during na tural regeneration. It does not seem to be important which method of a dditional ground vegetation control is chosen as long as the amount of ground vegetation is reduced. It was concluded that light level alone is not the key factor controlling growth of oak seedlings during natu ral regeneration. However, light and soil water content may interact a nd influence the growth of oak seedlings. (C) 1998 Elsevier Science B. V.