Microsites Influence the Light Response of Young Douglas-Fir (Pseudotsuga menziesii (Mirb.) Franco)

Abstract

Two comparable sites with uneven-aged mixed forest stands with more than 20% Douglas-fir in the growing stock at an altitude of 650 m a.s.l. were selected. The physiological response of young trees to different light intensities was measured during the main growing season in three consecutive years, and four different light categories, which were determined from hemispherical photographs. The four light intensity categories were defined according to Indirect Site Factor (ISF%): in the open (A-ISF > 35%), at the outer forest edge (B-25% < ISF < 35%), at the inner forest edge (C-15% < ISF < 25%), and under complete canopy under mature forest stand (D-ISF < 15%). Climate data were obtained from the Royal Netherlands Meteorological Institute ‘Climate Explorer’ website (http://climexp.knmi.nl). For the intensive micrometeorological observations, four monitoring sites were established along the elevation gradient at each site during summer and late fall to record relative humidity (RH%) and temperature (°C) with a 30 min recording interval sequence. Measured assimilation responses (A) and light use efficiency () at one site followed the expected pattern, while humidity combined with microsite conditions proved significant in explaining the specific response of young Douglas-fir to the different light intensity at the other site. For higher survival and optimal future development of Douglas-fir in the changing environment, microsites with higher capacity for storage moisture and favorable microclimate should generally be preferred to exposed and dry sites.

Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) in Europe: an overview of management practices

“…European experience indicates that Douglas-fir can grow on a range of soil types apart from heavy soils with pseudogley close to the surface, on dry or heavily waterlogged soils where rooting is restricted, leading to instability, and on calcareous soils. It grows best on deep, well-aerated, moderately acidic (pH 5 − 6), free draining soils of loamy-sand or sandy-loam texture which allow good root development (Rameau et al 1989;Horgan et al 2003;Perić et al 2011;Spellmann et al 2015;Novák et al 2018;Eckhart et al 2019;Čater 2021).…”

Tree-Ring Width Data of Tsuga longibracteata Reveal Growing Season Temperature Signals in the North-Central Pearl River Basin since 1824 AD

“…The climate sensitivity analysis of European beech (Fagus sylvatica) along an elevation gradient (110-1230 m) in south-western Germany showed that tree growth of F. sylvatica was strongly limited by low precipitation at lower elevations (110-300 m), but by low summer temperature at higher elevations (1230 m) [57]. In addition, different microsite environments and topographic conditions, such as soil microbes, soil depth and slope orientation, may also influence the sensitivity of tree growth [59][60][61]. At microsites with high moisture storage capacity, Douglas-fir (Pseudotsuga menziesii) in Slovenia favored the exposed and dry sites for optimal survival and development [61].…”

“…In addition, different microsite environments and topographic conditions, such as soil microbes, soil depth and slope orientation, may also influence the sensitivity of tree growth [59][60][61]. At microsites with high moisture storage capacity, Douglas-fir (Pseudotsuga menziesii) in Slovenia favored the exposed and dry sites for optimal survival and development [61]. Zhao et al [60] pointed that T. longibracteata located at a southeast-oriented hillside with a steep slope and shallow soil may experience severe water stress in summer due to having a low soil water-holding capacity and experiencing enhanced soil evaporation, while T. longibracteata growing on a northwest-oriented hillside with a flat slope and thick soil layer may be less water-restricted in summer due to a high soil water-holding capacity and experiencing low soil evaporation.…”