Key factors controlling the size, biomass, and sprouting of Japanese alder swamp forest in Kushiro Mire, Hokkaido, Japan

Abstract

The interrelation among size, biomass, and sprouting of alder trees was studied to extract the most important hydrochemistrical factors controlling the growth of alder forest in Kushiro Mire, northern Japan. The gradient was mostly explained by chemical variables such as pH, ash content, and P 2 O 5 , which showed strong positive correlation with each other, and secondarily by fluctuation of the water table (WL, i.e., water level range). These variables are more important than other hydrochemical ones, because neutral and turbid flood water replaces acidic mire water and conveys fine sediment with adsorbed phosphorus, which in turn could regulate the pH and amount of phosphorus. Also, the number of sprouts showed negative correlation mainly with tree size and redox potential (Eh), which suggested a flooded environment. Because of this, the size of alder was suppressed by hydrochemical variables; however, alder individuals producing new sprouts were maintained. We conclude that variation in size, biomass, and sprouting of alder was mainly controlled by acidity and phosphorus availability, and was significantly influenced by water fluctuation.

Hydrological influences on the distribution of vegetation and tree height of Alnus japonica (Thunb.) Steud. in the Kushiro Mire, Japan

“…Fluctuations of the water table under a peat surface layer would be controlled by the sediment content, as represented by the ash content in another study on the Kushiro Mire (Negishi, 2008(Negishi, , 2009. A decline in the water table would supply air to the soil, which would promote the decay of peat.…”

“…Site 20, a patch of alder forest in a reed community, had fewer alder trees compared with the other alder tree sites, which suggests that seed survival was difficult at this site. Although alder trees differ in their height and survive by sprouting (Negishi, 2008), they may be able to survive in waterlogged sites for long periods. On the other hand, river shortcutting changes the flow regime of rivers, for example, by shortening the duration of flooding and decreasing the base flow (Wongsa et al, 2004;Nakayama, 2008a,b), which may promote alder survival.…”

“…The growth of alder seedlings is inhibited by a flood treatment in vitro, altering the trees' size and morphological features (Terazawa and Kikuzawa, 1994;Yamamoto et al, 1995;Nagasaka, 2001), and mature alder forests are also affected in situ (Negishi, 2008). For the in situ case particularly, it is clear that a tree's size is determined by environmental factors and not by its age (Shinsho, 1982).…”