Light, temperature and soil moisture regimes following gap formation in a semi-natural beech-dominated forest in Denmark

A renewed interest in natural gap dynamics has developed from a recent focus on sustainable forestry in Europe. To improve. our understanding of the role of a canopy opening on the physical environment in a natural forest. a case study was undertaken in and around a gap in a semi-natural, beech-dominated (Fagus sylvatica L.) forest. spatial and temporal variations in photosynthetically active irradiance (I-P), soil and air temperature (T-S and T-A) and soil water content (SWC) were studied until the third growing season after natural formation of the gap. I-P was highest in the northern part of the gap and in the adjacent forest, particularly around mid-summer and on sunny days. when I-P was predominantly direct. Total Ip in the southern part of the gap and along Rap edges declined by about 19.6% from the first to the second year after gap formation, possibly due to growth of canopy and sub-canopy trees. Maximum and mean T-S were generally highest in the southern central part of the gap, and in late spring and summer also under the closed canopy east of the gap. The insulating effect of dense regeneration could to some extent explain the spatial variation of T-S. though this was not tested directly. SWC in the gap was near field capacity and generally higher than that under the closed canopy during summer. A decrease in SWC from the first to the second year after gap formation may have been attributed to released edge trees. although water use by the dense regeneration could not be ruled out. In general, the effect of this small irregular gap on light, soil and air temperature, and soil moisture was influenced by the considerable microsite variation. Furthermore, growth of regeneration and edge trees. resulting in increased interception, shading and water extraction by roots, may have modified the gap effect seen as early as the second year after gap formation. (C) 2004 Elsevier B.V. All rights reserved.