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

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.     

Impact of extreme run-off events from the River Sakasagawa on the Senjogahara ecosystem,Nikko National Park III. Pattern of alluvial deposition and effects on the growth ofMalus Toringo andBetula platyphylla var.japonica

In the study area at Senjogahara, there are 13 vegetational groups forming a space-time continuum in response to alluvial deposition from the River Sakasagawa. The pattern of deposition changes markedly from time to time, and the vegetation is thus a mosaic of recovery phases in different stages of development. There is marked zonation of layers of gravel, silt and organic matter in the soil profile, running sequentially from the mouth of the river back to the moor. Furthermore, there is a decrease in the depth of the water table with distance from the river mouth. The growth increment ofMalus Toringo is poor under the canopy ofUlmus Davidiana var.japonica forest, with maximum growth occurring in the areas of active alluvial deposition. The changing patterns ofMalus growth have been used to approximate the dates of major changes in the erosion channels and areas of alluvial deposition. There were five main channels in the study area. The oldest was on the west side and active ca. 35–40 yr prior to 1984, the year of sampling. Subsequently, adjacent areas further east became major drainage and erosion channels about 25–30 yr before 1984. However, after 1985 the erosion channels again showed a marked change in pattern, and currently flow into an entirely different sector, being responsible for the continuous dynamic patterns of vegetational change in this area.     

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.     

Spatially explicit population responses of crayfish Procambarus alleni to potential shifts in vegetation distribution in the marl marshes of Everglades National Park,USA

Hydropattern disturbance has had wide-ranging impacts on wetland communities of the Florida Everglades, especially on the habitats and the aquatic biota of the seasonally flooded marl marshes. We used the Everglades crayfish Procambarus alleni as a model to study the associations among hydrology, vegetation distribution, and population dynamics to assess the potential impacts of hydrological changes on the aquatic faunal community in Everglades National Park. To classify benthic habitats as sources or sinks for the crayfish population, we quantified vegetation community structure using GIS maps in which dominant vegetation types were weighted by local hydroperiod (length of inundation). Regression analysis showed that this habitat classification was associated with crayfish density distribution. We then used a spatially explicit, stage-structured population model to describe crayfish population fluctuations under current environmental conditions and to simulate the potential population-level responses to habitat changes that might occur following hydrological restoration. In habitat that was initially saturated with crayfish, the crayfish population size declined under current environmental conditions and then stabilized at about 13% of the initial density over a 50-year period. A 4-month increase in hydroperiod was then simulated by converting shorter-hydroperiod Muhlenbergia-dominated marsh habitat to longer-hydroperiod Cladium-dominated marshes. The model predicted a rapid 7-fold increase in crayfish density following the simulated habitat restoration. This indicated that several functional effects may result from the restoration of historical hydropatterns in marl marshes: (1) the areal extent of habitat sinks will be reduced to isolated patches, whereas the spatial distribution of aquatic source habitats will expand; (2) crayfish population size will increase and persist over time; (3) the minimum threshold needed to increase secondary aquatic productivity may be a 7-month hydroperiod over 90% of the marl marsh landscape. Restoration of historical hydropatterns could thus have cascading positive effects throughout the Everglades aquatic food web.