Vertical foliage distribution determines the radial pattern of sap flux density in Picea abies
Alessandro Fiora (1, 2) and Alessandro Cescatti (1, 3)
1. Centro di Ecologia Alpina – Viote del Monte Bondone, 38100 Trento, Italy / 2. Corresponding author () / 3. EC, Joint Research Centre, Institute for Environment and Sustainability, Climate Change Unit, 21020 Ispra, Italy / Received May 15, 2007; accepted July 16, 2007; published online July 1, 2008
Summary
Understanding the causes determining the radial pattern of sap flux density is important both for improving knowledge of sapwood
functioning and for up-scaling sap flow measurements to canopy transpiration and ecosystem water use. To investigate the anatomical
connection between whorls and annual sapwood rings, pruning-induced variation in the radial pattern of sap flux density was
monitored with Granier probes in a 35-year-old Picea abies (L.) Karst tree that was pruned from the crown bottom up. Modifications in the radial pattern of sap flux density were quantified
by a shape index (SI), which varies with the relative contribution of the outer and inner sapwood to tree transpiration. The
SI progressively diminished during bottom up pruning, indicating a significant reduction in sap flow contribution of the inner
sapwood. Results suggest that the radial pattern of sap flux density depends mainly on the vertical distribution of foliage
in the crown, with lower shaded branches hydraulically connected with inner sapwood and upper branches connected with the
outer rings.
