Mitchell, Edward

2001, Mitchell, Edward, van der Knaap, W. O., van Leeuwen, Jacqueline F.N., Buttler, Alexandre, Warner, Barry G., Gobat, Jean-Michel

Stratigraphy, radiocarbon dating and analyses of pollen, plant macrofossils and testate amoebae were used to reconstruct the development and ecology of a small raised bog in a karst-dominated landscape in the Swiss Jura Mountains. Special focus was on past vegetation and on the history of Pinus rotundata in relation to anthropogenic and climatic influences. Testate amoebae were used to reconstruc-t past local soil pH and water-table depth. The inferred development of the Praz-Rodet bog typifies a classic hydroseral tefrestrialization of a small basin. Two features are specific for this site. First, the bog was much wetter than today for a long period; according to our hypothesis, this only changed as a consequence of human activities. Second, two hiatuses are present at the coring location (Younger Dryas--early Preboreal, and 4700-2800 cal. yr BP), the former probably caused by low lake productivity due to cold temperatures and the latter by the erosional activity of the adjacent small river. The date of 2800 cal. yr BP for renewed peat accumulation may be related to climatic change (Subboreal-Subatlantic transition). Pollen indicators failed to show one hiatus: an apparently complete pollen sequence is therefore no guarantee of an uninterrupted sediment accumulation. Evidence of early minor human impact on the vegetation in the Joux Valley dates back to c. 6850 calendar years, congruous with the early Neolithic in the Jura Mountains. The history of Pinuis rotindata appears to be more complex than previously believed. Human activity is clearly responsible for the present abundance of this species, but the tree was naturally present on the bog long before the first evidence of important human disturbance of the site (1500 cal. yr BP). It is suggested that, in karst-dominated landscapes, dense forests growing on mineral soils around raised bogs may significantly reduce summer evapotranspiration by acting as windbreaks. Forest clearance results in increased evapotranspiration, causing a lowering of the water table on the bog and a modification of the vegetation cover. This hypothesis has implications for the management of similar small raised bogs in karst-dominated landscape.

1999-5-2, Mitchell, Edward, Buttler, Alexandre, Warner, Barry, Gobat, Jean-Michel

Testate amoebae (Protozoa) living in Sphagnum peatlands are important environmental and paleoecological indicators. The distribution of these animals is closely related to soil moisture variables. This study examines the ecology of sphagnicolous testate amoebae near the southern limit of bogs in Europe. A total of 64 samples were collected for analysis of testate amoebae from six peatlands in the Jura region of Switzerland and France. Eleven site-specific ecological variables, six of which were soil-moisture related variables, were measured at each site. The data were subjected to weighted averaging, jack-knifing, cluster analysis, canonical correspondence analysis, and the indicator value method to model relationships between testate amoebae distributions and environmental variables. Testate amoebae abundance showed a direct relationship with pear pH and depth to water table. Strong relationships were with sites that had a water table less than 41 cm deep. In drier sites with water table depth greater than 41 cm, other factors such as soil porosity and water holding capacity were more important compared to the wetter sites. Though there was a strong relationship between restate amoebae faunas and soil moisture content and porosity, these two variables could not be confidently predicted. Testate amoebae in peatlands in this region appear to be sensitive to peat pH and water tables. Further work is needed to explore relationships between restate amoebae, soil moisture, and porosity.

1999, Mitchell, Edward, Gilbert, Daniel, Butler, Alexandre, Grosvernier, Philippe, Albinsson, Christer, Rydin, Hakan, Heijmans, Monique, Hoosbeek, Marcel, Greenup, Alisson, Foot, Jonathan, Saarinen, Timo, Vasander, Harri, Gobat, Jean-Michel, Visconti, Guido, Beniston, Martin, Iannorelli, Emilio D, Barba, Diego

To monitor global change, large scale long term studies are needed. Such studies often focus on vegetation, but most plant species have limited distribution areas. Micro-organisms by contrast are mostly cosmopolitan in their distributions. To study the relationships between organisation groups, we analysed the testate amoebae (Protozoa), vegetation, and water chemistry of five Sphagnum peatlands across Europe. Inter-site differences were more pronounced for the vegetation than for testate amoebae species assemblage. Testate amoebae represent a useful tool in multi-site studies and environmental monitoring of peatlands because: 1) the number of species is much higher than for plants, 2) most species are cosmopolitan and are therefore less affected by biogeographical distribution patterns than plants; thus differences in restate amoebae assemblages can be interpreted primarily in terms of ecology, 3) restate amoebae can be used to analyse and monitor small scale (cm) gradients that play a major role in the functioning of peatland ecosystems. We further studied the effect of elevated CO2 on microbial communities in the same peatlands. Elevated COL increased the biomass of heterotrophic bacteria and decreased the biomass of medium size protozoa (mostly small restate amoebae). These effects suggest changes in community functioning that may have feedback effects on other components of the ecosystem.