Effects of Snowfall Fluctuation on Tree Growth and Establishment of Subalpine Abies mariesii near Upper Forest-limit of Mt. Yumori, Northern Japan

Abstract

We examined effects of annual snowfall fluctuation on tree growth and establishment in a mature stand (ca. 200 yr old) of Japanese subalpine Abies mariesii Mast, near upper forest-limits at leeward site. Relatively tall and aged fir trees (>5 m, >100 yr old) retained various scars of past mechanical damage due to snow pressures, e.g., multiple-, tip dieback- and broken-stems, and canopy anomaly. Ring-width pattern analysis showed that these deformed trees mostly experienced abrupt growth reduction. Some events of such abrupt growth reduction occurred simultaneously just after winters with heavy snowfall (e.g., mid-1960s), indicating that the A. mariesii trees often suffered from snow damage due to settlement force of excess snowpack. Particularly, in snowy winters, mechanical breakage of branches was likely to occur intensively at the height of 1 to 3 m above the maximum snowpack level of normal snowfall winters (ca. 3 m). On the other hand, some aged, but suppressed, trees sharply enhanced their growth rates simultaneously after such period of the intensive snow damage. This indicated that the snow damage upon the relatively tall trees sometimes facilitated regeneration of nearby shaded-trees by creating small-scale gaps. The snow-induced disturbance events may have occurred at about 10-yr intervals during the last half of 20th century. Our findings suggested that population dynamics of A. mariesii near its upper forest-limit, especially located at leeward and snowy site, was closely affected by the repetitive events of snow damage following snowy winters: the event primarily acted as a major limiting factor for canopy development of individuals, and sometimes triggered growth of suppressed-trees.