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

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 P₂O₅, 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.