Shigeto Ikeda

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

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.

Mechanical Damage on Abies mariesii Trees Buried below the Snowpack

Abstract On a gentle leeward slope in a snowy forest limit in northern Honshu Island, Japan, mechanical damage by snow settlement and creep on Abies mariesii trees buried below the snowpack was examined to detect signs of the snow-damage effect on future survival and crown development. Damage types were recorded based on direct observation of crowns in 1996, a year of high snow accumulation exceeding 4.5 m, and 1997, a year of moderate snow accumulation. Of 153 trees examined, 63% were damaged in 1996 and 15% were damaged in 1997. The most destructive damage type was breakage of stems ≥5 cm in diameter, which occurred on eight trees in 1996 and three in 1997, resulting in foliage loss and death of some trees. The prevalent damage type was branch tearing at branch-stem junctions primarily within a height range of 4–6 m, which occurred on 171 branches in 1996 and 5 in 1997. Under snowy and windy conditions, stem breakage and branch tearing, caused by forces active within restricted layers of the snowpack, may reduce the future survival and crown development of A. mariesii buried below the snowpack in years of heavy snowfall.

Vegetation patterns and their dependency on site conditions in the pre-industrial landscape of north- eastern Japan

We reconstructed the vegetational landscape of the pre-industrial era (the beginning of the twentieth century) in north-eastern Japan, and estimated the distribution patterns of traditional land-uses, as suggested from the vegetation. We found significant correspondence between the spatial patterns of vegetational landscape and site attributes, and hypothesized the underlying mechanisms. The study area was classified into three vegetation types: grasslands, secondary forests and old-growth forests. It was determined that the grasslands were formed and maintained by burning; secondary forests were derived from either charcoal woods or forests recovered on abandoned grasslands; and old-growth forests had suffered the least anthropogenic disturbance. Each past vegetation type showed significant dependency on site attributes such as altitude, slope angle, slope aspect, hydrological topography and distance from the nearest human habitation. The relative importance of these site attributes varied depending on the vegetation type. Grasslands and old-growth forests, which were the most and the least disturbed sites in the study area, respectively, showed clear contrasts in their dependencies especially on the slope aspect and on elevation. These site attributes were thought to have had influences on each vegetation type by determining the inflammability of the site. Satellite photographs indicated that north-facing valleys had been relatively wet throughout the fire-prone spring season. Hence, these areas would have been free from frequent fire, and more likely to preserve old-growth forests. Ground wetness in spring was thought to be the underlying factor determining the contrasts in past vegetation and land-use patterns in the area.

Paleoclimatic implication of buried peat layers in a subalpine snowpatch grassland on Mt. Zarumori, northern Japan

Abstract We reconstruct the paleoclimatic background of buried peat layers formed around the 10th century, which occur in a snowpatch grassland in a snowy mountain in northern Japan. In the snowpatch grassland, peat accumulation is presently restricted by the presence of a summer snowpatch. Thus, the buried peat layers imply that the summer snowpatch around the 10th century was smaller than it has been in recent times. Climatic control of the year-to-year variation of the present snowpatch was examined based on a snowpatch survey and analysis of meteorological data. The observed snowpatch profiles suggested that winter wind speed played an important role in controlling summer snowpatch size. The buried peat layers indicate not only warming in the melt season, but also a possible weakened winter monsoon in the Medieval Warm Period.

Climatic Change and Snowpatches, Revealed by Soil Stratigraphy Around the Nivation Hollows

This study tries to reconstruct past climatic conditions by means of alpine-subalpine meadow soil stratigraphy, which records past snow disappearance time in nivation hollows. Buried peat found on Mt. Zarumori indicates that the date of snow cover disappearance in approximately 1000 y.B.P., was earlier than in recent times. Calculations of the past snowmelt rate by the degree-day method, indicate that warming in summer and lower winter snowfall accumulation, hastened snowmelt and enabled the peat to deposit. This warmer climatic condition in north Japan corresponds to the so-called “Medieval Warm Period” of Europe and North America.