Ms. Jimenez et al., Radial variation in sap flow in five laurel forest tree species in Tenerife, Canary Islands, TREE PHYSL, 20(17), 2000, pp. 1149-1156
Variations in radial patterns of xylem water content and sap flow rate were
measured in five laurel forest tree species (Laurus azorica (Seub.) France
, Persea indica (L.) Spreng., Myrica faya Ait., Erica arborea L. and Ilex p
erado Ait. ssp. platyphylla (Webb & Berth.) Tutin) growing in an experiment
al plot at Agua Garcia, Tenerife, Canary Islands. Measurements were perform
ed around midday during warm and sunny days by the heat field deformation m
ethod. In all species, water content was almost constant (around 35% by vol
ume) over the whole xylem cross-sectional area. There were no differences i
n wood color over the whole cross-sectional area of the stem in most specie
s with the exception of E. arborea, whose wood became darker in the inner l
ayers. Radial patterns of sap flow were highly variable and did not show cl
ear relationships with tree diameter or species. Sap flow occurred over the
whole xylem cross-sectional area in some species, whereas it was limited t
o the outer xylem layers in others. Sap flow rate was either similar along
the xylem radius or exhibited a peak: in the outer part of the xylem area.
Low sap flow rates with little variation in radial pattern were typical for
shaded suppressed trees, whereas dominant trees exhibited high sap flow ra
tes with a peak in the radial pattern. Stem damage resulted in a significan
t decrease in sap flow rate in the outer xylem layers. The outer xylem is m
ore important for whole tree water supply than the inner xylem because of i
ts larger size. We conclude that measurement of radial flow pattern provide
s a reliable method of integrating sap flow from individual measuring point
s to the whole tree.