NSC pools Many studies ed to a significar n the and carbon assimilation .How many leaves/needles does a tree(the Experiment6 erms c Light gradient Hypotheses..... 化anaw se 30%of the full light in sed by a 9 9 Control trees 20 30 40 50 60 70 80 NSC fraction (%) May July September Treated trees (September) Defoliated Pruned Debudded NSC pools 0 10 Needles Branches Wood Roots Needles Branches Wood Roots Li MH et al. 2002. Trees 16, 331-337 Biomass fractions used (according to Li Mai-He, 1999, PhD thesis, Univ. BOKU, Vienna, & Bernoulli M, Körner Ch, 1999. Phyton 39, 7-12): Needles 21%, Branches 19%, Stem wood 47%, Roots 13% Many studies demonstrated that severe defoliation led to a significant reduction in the tree health, growth and productivity and productivity, and carbon assimilation Ericsson A. et al. 1980. J Appl Ecol 17, 747-769 Honkanen T. et al. 1994. Funct Ecol 8, 631-639 Li MH et al. 2001. Schweiz Z Forstwes 152, 389-393 Li MH et al. 2002. Trees 16, 331-337 • How many leaves/needles does a tree (the threshold of transparency) need to remain its "normal" life? • How trees respond to an age-dependent defoliation in terms of C- & N-physiology? Apr 2002 Apr 2002 7 years 4 years 3 years 2 years 1 year -0% -9% -27% -46% -71% Light gradient 30% of the full light intensity 70% of the full light intensity Hypotheses……. • (1) light defoliations of the oldest needles have no effects, whereas a severe defoliation decreases the availability of carbohydrates and, therefore, causes a significant decrease in growth Li MH et al. (in preparation) • (2) the effects caused by a severe defoliation will be detectable for several years • (3) the capability for a carbon compensation of defoliated trees depends on light conditions, being easier in trees growing in full-light conditions rather than in shade