© 2003 Heron Publishing—Victoria, Canada
Shoot growth and crown development: effect of crown position in three-dimensional simulations
Eero Nikinmaa (1, 2), Christian Messier (3), Risto Sievänen (4), Jari Perttunen (4) and Mika Lehtonen (4)
1. Department of Forest Ecology, University of Helsinki, P.O. Box 24, FI-00014, Finland / 2. Author to whom correspondence should be addressed (eero.nikinmaa@helsinki.fi) / 3. Groupe de Recherche en Écologie Forestière interuniversitaire (GREFi),Université du Québec à Montréal, C.P. 8888, succursale
centre-ville, Montréal, Québec H3C 3P8, Canada / 4. The Finnish Forest Research Institute, Vantaa Research Centre, Jokiniemenkuja 1, P.O. Box 18, 01301 Vantaa, Finland / Received August 18, 2000; accepted May 5, 2002; published online January 2, 2003
Summary
Trees have been increasingly considered as modular organisms, with individual shoots forming autonomous units that respond
semi-independently to their surrounding environment. However, there is evidence for fairly strict hormonal control of tree
crown development. Studies on the hydraulic architecture of trees suggest a closer functional connection between shoots and
crown development than is postulated by the theory of branch autonomy. We studied how shoot growth pattern influences growth
and crown architecture in young Scots pine trees simulated by the LIGNUM model assuming that (a) the growth of a shoot mainly
depends on its light climate and (b) the growth of a shoot is influenced by its position within the crown. We determined shoot
position within the crown based on a recently developed vigor index. The vigor index compares the relative axis cross-sectional
area from the base of the tree to each shoot and gives a value of 1 to the pathway of the greatest cross-sectional area. All
other shoots attain values between 0 and 1 depending on their cross-sectional areas and the cross-sectional areas of the branches
leading there from the main axis. The shoot light climate is characterized by annually intercepted photosynthetically active
radiation. We compared the results from simulations (a) and (b) against an independent data set. The addition of a within-shoot
position index (the vigor index) to our simulation (simulation b) resulted in a more realistic tree form than that obtained
with simulation (a) alone. We discuss the functional significance of the results as well as the possibilities of using an
index of shoot position in simulations of crown architecture.
Keywords:
modeling, modularity, Pinus sylvestris, tree architecture, vigor index.
