Influence of annually fluctuating seed‐cone production and climatic factors on the upper‐crown expansion of canopy trees of Abies mariesii Masters (Pinaceae)

Abstract

To understand the influence of seed-cone production on the upper-crown expansion of canopy trees of Abies mariesii Masters, the influence of the annually fluctuating number of seed cones on the terminal-leader length of the main stem and primary branches was analyzed using seed-cone rachises remaining on the terminal leaders of the primary branches. The influence of climatic factors during the period of vegetative-bud growth and shoot elongation was also analyzed. For the upper-crown expansion, factors influencing the number of horizontally elongating branches on the top of the main stem were also examined. According to model fitting, the terminal-leader length of the main stem was negatively influenced by seed-cone production 1 year before shoot elongation. In contrast, the terminal-leader length of the primary branches was not clearly influenced by seed-cone production, but was positively influenced by the mean temperature in September 1 year before shoot elongation and in July in the year of shoot elongation. The number of horizontally elongating branches on the top was positively influenced by the terminalleader length of the main stem 1 year before horizontal elongation on the top and negatively influenced by seed-cone production 2 years earlier. Thus, in the upper part of the crown, the allocation of photosynthate to seed cones mainly affects the arrangement of needles and seed cones up to the higher positions. This trade-off between seed-cone production and upper-crown expansion influences the canopy shape and reproductive strategy of A. mariesii.

Growth allocation between height and stem diameter in nonsuppressed reproducing Abies mariesii trees

“…7). In addition to this, a closer negative relationship between seed‐cone production and height growth than any other relationship between climatic factor and height growth (Seki 2008) is supportive of the trade‐off. However, the lesser height growth in trees of larger reproduction is not necessarily explained by the deficit of photosynthate.…”

“…a trait of population in the limit of distribution (Despland & Houle 1997), no influence of the amount of accumulated photosynthate and nutrients on stem‐diameter growth (Seifert & Müller‐Starck 2009), and a large amount of accumulated photosynthate at the beginning of mast seeding (Seifert & Müller‐Starck 2009). With regard to the first line of thought (Despland & Houle 1997), the study site is located at the lower part of a subalpine forest (Seki 1994, 2008), and thus the reproductive trait is not the one at the limit of distribution. For the latter two, the source of photosynthate for stem‐diameter growth in A. mariesii is an open question, as is the photosynthate for reproduction.…”

“…Among trees with various degrees of biomass increase, trees with a larger biomass increase may lower the growth allocation to competitive ability, as it is associated with the reproduction (Figs 7,8). For these trees, an increase in leaf mass through stem‐diameter growth, suggested by a relatively constant horizontal crown expansion (Seki 2008), may be more important than height growth after mast years, but it may not necessarily be associated with larger reproductive allocation (e.g. Figs 6,8).…”

“…After seed dispersal, seed‐cone rachises remain on the surface of shoots without abscission (Fig. 1; Kohyama 1982; Seki 1994, 2008; Sakai et al . 2003).…”

“…This reproductive trait might be associated with larger reproductive allocation under larger biomass increase. In canopy trees, which indicate a large biomass increase, a temporal depression occurred in height growth after seed‐cone production but not in elongation along the horizontally extending branch axis (Seki 2008), suggesting obvious depression of growth allocation to height in comparison with stem diameter after reproduction. However, in trees with a small biomass increase, allocation to height growth might be important for the acquisition of a sunlit space.…”