Functional specialization of current shoots as a reproductive strategy in Japanese alder (Alnus hirsuta var. sibirica)

Abstract

Current shoots, which form the crown of a tree, are specialized in various functions such as crown expansion, reproduction, and assimilation. We examined the temporal and spatial distribution of reproductive shoots in Alnus hirsuta Turcz. var. sibirica (Fischer) C.K. Schn., assessed their direct and indirect costs of reproduction, and explained their distribution in the crown as the reproductive strategy of a current shoot population. The upper and lower limits to the lengths of current shoots for reproductive growth (flower formation) were 40 and 10 cm, respectively. Reproductive 1-year-old shoots produced fewer shoots in the following year than non-reproductive 1-year-old shoots. In current shoots longer than 40 cm, the increment of reproductive output in the following year by abandonment of reproduction surpassed the decrement of reproductive output in the current year by abandonment of reproduction. This may be one reason for the upper limit of reproductive shoot length. Thus, the current shoot population of A. hirsuta var. sibirica may be divided into three functionally specialized subpopulations: reproductive, maintenance, and exploratory. This specialization is considered to be a reproductive strategy to maximize their lifetime reproductive success.Key words: current shoot population, reproductive ecology, functional specialization, cost of reproduction, Japanese alder.

Factors affecting cone production in Pinus pinaster Ait.: lack of growth-reproduction trade-offs but significant effects of climate and tree and stand characteristics

“…In forest trees, inverse correlations between size and cone production have been found for both conifers and angiosperms at the tree level (see, for instance, Eis et al, 1965;Selas et al, 2002;Monks & Kelly, 2006), but also at the branch level within trees (Tappeiner, 1969;Fox & Stevens, 1991;Hasegawa & Takeda, 2001). Moreover, a carry-over effect has been documented for the reduction of tree growth after intense fruit production (Thomas, 2011).…”

Spatial Distribution of Regenerated Woody Plants in <i>Alnus hirsuta</i> (Turcz.) var. <i>sibirica</i> Stand in Japan

“…In our study site, all the canopy trees were alders. The tree height was about 15 m, and the canopy of this stand was almost closed (Hasegawa & Takeda, 2001;Tobita et al, 2010). The mean (± SD) stem diameter at breast height (dbh) of trees was 12.4 (±3.8) cm in April 1995 and the frequency distribution of dbh was unimodal, indicating that this stand comprised trees of similar age (Tobita et al, 2010).…”

Current-year shoot based approach for annual variation in the reproductive output in Siberian alder (Alnus hirsuta var. sibirica)

“…Male flowers fall after flowering. The fertilized female flower matures to fruit on 1-year-old shoots, and then seeds are dispersed by wind in November (Hasegawa and Takeda 2001).…”

“…As carbon allocation is localized and current photosynthate is allocated to reproduction, annual variation is not explained, at least from the viewpoint of resource allocation. As shown by Hasegawa and Takeda (2001), there is a tight relationship between current-year shoot dynamics and reproduction of current-year shoots. Thus, there may be some ecological or other benefit which may account for the proximate causes in annual variation of reproductive output.…”