Shoot growth and crown development: effect of crown position in three-dimensional simulations

Abstract

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.

Crown architecture and its role in species interactions in mixed boreal forests

“…Accordingly, the branching hierarchy of the mother branch explained the shoot number and length in both studied species in this thesis. The decrease in shoot growth in relation to increased GO was also reported in B. pendula and in Pinus sylvestris by Maillette (1982) and Nikinmaa et al (2003), respectively. The effect of branching hierarchy on shoot number and length results in efficient resource allocation to a few branch axis and shoots, leading them to gain length, direct growth and reach for light (Trewavas 2005).…”

“…High shoot formation and growth at the top of the crown has previously been shown and associated with good light conditions (e.g. Mäkinen 1999;Goulet et al 2000;Takenaka 2000;Kaitaniemi and Ruohomäki 2003;Niinemets and Lukjanova 2003) and hydraulic preference (Goulet et al 2000;Nikinmaa et al 2003). The strongest growing shoot individuals are situated under better light conditions, i.e.…”

“…Interdependence between hydraulic and crown architectures may possibly exist, which means that hydraulic architecture also regulates the development of crown architecture as suggested by Nikinmaa et al (2003), especially in unfavourable environmental conditions. Maximum tree height at least is suggested to be restricted by water economy (Woodward 2004).…”

“…Crown architecture determines the local environmental conditions within tree crowns and influences the layout of contact surfaces between the environment and the physiological processes involved in resource acquisition, whereas physiology produces new materials for constructing the architecture (Ford 1992). Tree crown architecture is composed of subunits, individual branches and shoots that may have largely autonomous carbon economies, so the growth and survival of these crown units are sensitive to their local environments (Sprugel et al 1991;Nikinmaa et al 2003;Sachs 2004). This modular structure (Harper 1977) allows high structural plasticity at multiple hierarchical levels as a response to the changing growth environment (Sorrensen-Cothern et al 1993).…”

Application of the functional-structural tree model LIGNUM to growth simulation of short-rotation eastern cottonwood

“…Above-ground structural development and the C allocation are affected by branching, by the relative sizes of tree segments and radiation environment. The effect of the relative size of a segment is described by its vigor index (Perttunen et al 2001, Nikinmaa et al 2003. The greater the vigor index value, the more NPP is allocated on the segment.…”