The impact on the Senjogahara ecosystem of extreme run-off events from the river Sakasagawa,Nikko National Park

Vegetational data from Senjogahara moor, Nikko National Park, Japan have been analysed using two contrasting but parallel multivariate approaches as a basis for future studies. The plant communities objectively defined using a divisive polythetic classificatory approach (TWINSPAN) have been successfully overlayed on an ordination of the same data using detrended correspondence analysis (DCA). The results reveal a vegetational mosaic reflecting differential levels of flood damage to the vegetation and its subsequent rates of recovery, in a space-time continuum. The results from the TWINSPAN classification show that 13 plant communities are present in the sample area and these correlate closely with complete absence, slight, or extremely heavy disturbance. The form of the disturbance as either channel erosion or alluvial depositional features is shown to also correspond quite closely with the vegetational types and is reflected in the ordination axes derived from DCA.     

The impact of extreme run-off events from the Sakasagawa river on the Senjogahara ecosystem, Nikko National Park. IV. Changes in tree and understory vegetation distribution patterns from 1982 to 1992

In this study, a survey was made of a sample area adjacent to Senjogahara moor, Nikko National Park, in central Japan, to discover the change of vegetation over the 10 years from 1982 to 1992. The sample area, which is dominated byMalus toringo, has often suffered alluvial deposition from flooding of the river. The accumulation depth of alluvial materials deposited for 1984–1987 were measured at 266 points in the area, and for 1987–1992 at 347 points. Each tree species showed its own changing pattern of distribution area in relation to the accumulation depth of alluvial deposits. For example,M. toringo showed an increase in the number of trunks, and extended its distribution area in spite of heavy deposition, whereasBetula platyphylla var.japonica andLarix kaempferi shifted their distribution to the area that suffered only light deposition. The distribution area of shrubby and herbaceous species of understory vegetation also showed different patterns of change. In addition, the recovery of bare ground by understory vegetation was by different species in heavily and in lightly deposited areas. These facts show that there is a difference in the tolerance of different species to burial by alluvial deposits, and this difference is an important factor in successional change and mosaic formation of vegetation in a repeatedly disturbed area.     

The impact of extreme run-off events from the Sakasagawa river on the Senjogahara ecosystem, Nikko National Park. V. The importance of adventitious root systems for burial tolerance of different tree species

We surveyed the morphological responses of tree species buried by alluvial deposits, and measured the physicochemical properties of alluvial materials which buried each of the individual trees, on Senjogahara moor, Nikko National Park, Japan. The results showed that these species had a different capcity to form adventitious roots.Malus toringo Sieb. individuals, which had survived in spite of heavy deposits over the past 10 years, developed many adventitious roots from the buried parts of their trunks. However,Larix kaempferi Carr. andBetula platyphylla Sukatchev var.japonica Hara, which both died in heavy deposit areas, were inferior toM. toringo in the formation of adventitious roots. From these facts, we presumed that the ability to develop adventitious roots contributed to the survival of trees and resulted in the difference in burial tolerance among each species. Adventitious roots tended to form in the depositional layers which consisted of fine particle size materials. It is thought that these layers prevent gas exchange between soil and air, causing a lack of oxygen to the rhizosphere. Thus, we concluded that adventitious roots have a physiological importance in reducing the obstruction, and in the survival of buried trees.     

The impact on the senjogahara ecosystem of extreme run-off events from the river Sakasagawa,Nikko National Park

During high run-off events the river Sakasagawa carries extremely large quantities of alluvial materials which are deposited in the north east corner of the Senjogahara moor. This study was initiated to examine the effects, both recent and historic, that this periodic and catastrophic inundation has had on the ecology of this area. It also questions the potential importance of alluvial deposition on the conservation of the moor as a whole. From the data presented it is clear that the present day vegetation of the north east corner of the moor represents a mosaic of vegetation reflecting differential levels of damage to the plants, deposition of alluvial material and the establishment of erosion channels in a space-time continum. The results indicate thatMalus Toringo andSalix integra can survive in the areas outside the heaviest flood damage, whereasUlmus Davidiana var.japonica, Betula platyphylla var.japonica andLarix Kaempferi are quite sensitive to flooding. SimilarlySasa nipponica var.nana is intolerant of even light alluvial deposition in contrast toLonicera caerulea var.emphyllocalyx andSpiraea salicifolia which are also still dominant beyond the zone of major alluvial deposition.     

Effect of flooding and temperature regime on growth and stomatal resistance ofBetula platyphylla var.japonica seedlings

Summary Both flooding and low temperature reduced height and stem diameter growth; leaf initiation; growth of leaves, stems, and roots; and lowered root-shoot ratios of 112-dayoldBetula platyphylla var.japonica seedlings. Flooding also induced leaf scorching and abscission. Growth was reduced much more by flooding than by low temperature. Interactive effects of flooding and temperature were shown on height growth, leaf initiation and expansion, and dry weight increment of leaves, stems and roots. The amount of growth reduction by flooding and low temperature was greater when based on analysis of dry weight increment of leaves, stems, and roots, than on their relative growth rates. The greater reduction of growth by flooding than by low temperature was associated with fewer and smaller leaves, more leaf injury, more stomatal closure, and greater decay of roots in flooded plants. Flooding and low temperature appeared to reduce growth by somewhat different physiological mechanisms. Research supported by the College of Agricultural and Life Sciences, University of Wisconsin, Madison, WI, USA and by Yamagata University, Tsuruoka, Japan. McIntyre-Stennis Project 2599.