The role of epicormic shoot production in maintaining foliage in old Pseudotsuga menziesii (Douglas-fir) trees

Abstract

Shoots and foliage on branches of old Pseudotsuga menziesii (Mirb.) Franco var. menziesii (coastal Douglas-fir) trees are constantly renewed by epicormic shoot production. Epicormic shoots are produced in all parts of the crown, and epicormic buds remain dormant for 5 or 6 years on average. Epicormic shoot production results in reiteration of shoot cluster units (SCUs), an architectural unit of shoot organization within branches. Five phases of SCU development were identified based on relative age structures of regular and epicormic shoots. SCUs produce epicormic branchlets as early as 3 or 4 years of age, and peak production occurred around 6-13 years. Epicormic branchlets occur toward the proximal end of main axes of SCUs, where regular lateral branchlets are no longer producing new shoots. In some lower-crown branches, nearly 50% of shoots and foliage are epicormic shoots. Demographic analysis of SCUs showed that upper-crown branches are still growing in size, while mid- and lower-crown branches have reached maximum size, and are being maintained by reiteration of SCUs. Epicormic shoot production maintains shoots and foliage of old P. menziesii trees after height growth and crown expansion have stopped and may contribute to prolonging tree longevity.Key words: aging, branch growth, epicormic shoots, longevity, Pseudotsuga menziesii, reiteration.

The relationship between tree height and leaf area: sapwood area ratio

“…After cutting, branches were lowered to the ground using a second rope. We randomly collected 10% of the foliated shoots from each branch as measured by visual cluster measurements (Ishii and Ford 2001). Leaf samples were collected from each of these shoots and analyzed for S. Both S and total branch leaf weight were measured using identical methods to those used for the younger stands.…”

Développement de rejets épicormiques sur des séquoias californiens : intensité de l’élagage, génotype, caractéristiques des rejets

“…Several studies report increasing sprout production with increasing pruning severity (Collier and Turnblom, 2001;Eckstein, 1974;O'Hara et al, 2008;Stein, 1955;Waring and O'Hara, 2005) and greater sprout numbers/sizes on the exposed sides of tree boles (Collier and Turnblom, 2001;Deal et al, 2003;O'Hara et al, 2008). These are evolutionary adaptions that allow trees to quickly rebuild crowns after disturbances such as defoliations and branch damage (Begin and Filion, 1999;Ishii and Ford, 2001;Ishii et al, 2002). In contrast to crown disturbances such as fire, wind, or ice damage, typical forest pruning provides a much more uniform reduction in lower crowns and causes relatively uniform sprout reactions in susceptible species.…”

“…For some species, the rapid increase in leaf area with the production of epicormic sprouts can help regain photosynthetic area or help mitigate the cost of inefficient older branches with new small branches (Bégin and Filion, 1999;Ishii and Ford, 2001;Ishii et al, 2002). For pruned trees, pruning severity was cited as a primary cause of epicormic sprout development in many studies with greater severity leading to increased sprouting and greater persistence of sprouts (Deal et al, 2003;O'Hara et al, 2008;Waring and O'Hara, 2005).…”

Radiative transfer, interception and scattering in coniferous forests: models and applications for production ecology and remote sensing

“…However, it is also possible that some buds form along the length of a shoot, and new shoots can start to grow from these. The buds can even stay dormant for several years before a new shoot starts to elongate from them (Ishii and Ford 2001). The grouping of shoots into spatially distinct branches can be very pronounced, with empty spaces between the branch volumes, as in many spruces.…”