2:20 PM - 2:35 PM
[MIS23-15] Comparison of hypotheses about formation of the pseudo-alpine zone in accordance with topo-climatological survey
Keywords:pseudo-alpine zone, mountains with heavy snowfall, Abies mariesii, GIS, historical botany
On some mountains from central to northeastern Japan, the subalpine area is mostly covered with grass, dwarf bamboo or shrubs instead of conifers. This area called a pseudo-alpine zone was firstly thought to develop because large snow pressure prevents coniferous trees growing in the mountains with heavy snowfall (snow hypothesis). Historical perspectives later added two popular hypotheses. Warmer climate in the early Holocene may have shifted the lower limit of the subalpine zone above the summits (kick-out hypothesis). Scarcity of Abies mariesii habitats under former climate has been possibly succeeded by the present pseudo-alpine zone (limited Abies mariesii hypothesis). This study tests these three hypotheses using digital geographic data which were recently provided.
Some topo-climatological conditions under the subalpine climate on 34 mountains in the Tohoku to Chubu regions were studied to know habitat segregation. On a GIS software, habitats including Abies mariesii were extracted from digital vegetation maps provided by the Ministry of Environments in Japan and the occupancy of these habitats were determined for each mountain. Then, altitudinal ranges, slope angles and the annual maximums of snow thickness were compared respectively to discuss differences between mountains having the pseudo-alpine zone and the other mountains.
In 3 mountains without thick snow cover, Abies veitchii - Abies mariesii community accounts for more than 30% of the total area. On the other hand, Abies mariesii community accounts for more than 30% of the total area in 9 mountains. Some of the latter mountains are covered with thick snow, whereas some mountains lack coniferous forests despite less snowfall. These cases are inconsistent with the snow hypothesis. The absence of Abies mariesii on some high mountains cannot be explained from the kick-out hypothesis. The mountains dominated by Abies mariesii community are considerably gentler than the other mountains, which corresponds to the limited Abies mariesii hypothesis. According to the hypothesis, the poorly drained gentle slopes provide the niche of Abies mariesii until the early Holocene before Abies mariesii becoming dominant.
Some topo-climatological conditions under the subalpine climate on 34 mountains in the Tohoku to Chubu regions were studied to know habitat segregation. On a GIS software, habitats including Abies mariesii were extracted from digital vegetation maps provided by the Ministry of Environments in Japan and the occupancy of these habitats were determined for each mountain. Then, altitudinal ranges, slope angles and the annual maximums of snow thickness were compared respectively to discuss differences between mountains having the pseudo-alpine zone and the other mountains.
In 3 mountains without thick snow cover, Abies veitchii - Abies mariesii community accounts for more than 30% of the total area. On the other hand, Abies mariesii community accounts for more than 30% of the total area in 9 mountains. Some of the latter mountains are covered with thick snow, whereas some mountains lack coniferous forests despite less snowfall. These cases are inconsistent with the snow hypothesis. The absence of Abies mariesii on some high mountains cannot be explained from the kick-out hypothesis. The mountains dominated by Abies mariesii community are considerably gentler than the other mountains, which corresponds to the limited Abies mariesii hypothesis. According to the hypothesis, the poorly drained gentle slopes provide the niche of Abies mariesii until the early Holocene before Abies mariesii becoming dominant.