Background
The authors write that "in snowpatch grasslands, plant distributions follow the contours of the snowmelt gradient around summer snowpatches," producing "similarly steep gradients in plant productivity and topsoil (e.g. Billings and Bliss, 1959; Helm, 1982; Kudo, 1991; Stanton et al., 1994.)" In fact, they say that "in the subalpine zone of northeastern Japan, sites where the snow cover disappears after July are usually occupied by 'snowpatch bare grounds' with extremely poor vegetation cover" that is "encircled by snowpatch grassland," citing Yamanaka (1979). As a result, they say that "litter fall and the organic content in topsoil decrease toward the center of a snowpatch because the period for plant growth becomes shorter with delay in the time of snow disappearance," so that in current "snowpatch grasslands, peaty topsoil is restricted to sites where snowmelt comes early." And as a result of this fact, the unique situation provided by a snowpatch can provide a good opportunity for paleoclimatic reconstructions based on vertical profiles of soil characteristics at various locations along transects moving outwards from summer snowpatches.

What was done
Working in a snowpatch grassland within a shallow depression of landslide origin on the southeastern slope of Japan's Mt. Zarumori (~39.8°N, 140.8°E), Daimaru et al. dug 27 soil pits at various locations in and around the central location of the snowpatch, carefully examining what they found and determining its age based on ¹⁴C dating and tephrochronology.

What was learned
The five researchers report that "peaty topsoils were recognized at seven soil pits in the dense grassland, whereas sparse grassland lacked peaty topsoil," and they say that "most of the buried peat layers contained a white pumice layer named 'To-a' that fell in AD 915." This observation, plus their ¹⁴C dating, led them to conclude that the buried peat layers in the poor vegetation area indicate "warming in the melt season," as well as "a possible weakened winter monsoon in the Medieval Warm Period," which their data suggest prevailed at the site they studied throughout the tenth century, i.e., AD 900-1000. And the fact that they write that "many studies have reported climatic signals that are correlated with the Medieval Warm Period from the 9th to 15th centuries in Japan," suggests that the possibly weakened winter monsoon of AD 900-1000 may also have been a consequence of the warmer temperatures of that period.

What it means
The evidence continues to mount for a global Medieval Warm Period that was warmer than the Current Warm Period has been to date. And since the atmosphere's CO2 concentration was so much lower a millennium ago than it is today, there is no compelling reason to attribute the lesser warmth of the present to the air's higher CO2 content.

References
Billings, W.D. and Bliss, L.C. 1959. An alpine snowbank environment and its effects on vegetation, plant development and productivity. Ecology 40: 388-397.

Helm, D. 1982. Multivariate analysis of alpine snow-patch vegetation cover near Milner Pass, Rocky Mountain National Park, Colorado, U.S.A. Arctic and Alpine Research 14: 87-95.

Kudo, G. 1991. Effects of snow-free period on the phenology of alpine plants inhabiting snow patches. Arctic and Alpine Research 23: 436-443.

Stanton, M.L., Rejmanek, M. and Galen, C. 1994. Changes in vegetation and soil fertility along a predictable snowmelt gradient in the Mosquito Range, Colorado, U.S.A. Arctic and Alpine Research 26: 364-374.

Yamanaka, H. 1979. Nivation hollows on the southeast slope of Mt Onishi, Iide Mountains, northeast Japan. Annals of the Tohoku Geographical Association 31: 36-45.