Winter CO2 fluxes in a sub-alpine grassland in relation to snow cover, radiation and temperature

Carbon dioxide (CO2) emissions were measured over a period of 3 years at the sub-alpine Swiss CARBOMONT site Rigi Seebodenalp. Here we show, that winter respiration contributes larger than expected to the annual CO2 budget at this high altitude, rich in belowground organic carbon grassland (7-15% C by mass). Furthermore the contribution of winter emissions to the annual CO2 budget is highly dependent on the definition of "winter” itself. Cumulative winter respiration determined over a 6 month period from 15th of October until 15th of April contributed 23.3±2.4 and 6.0±0.3% to the annual respiration during the years under observation, respectively. The insulation effect of snow and a lowering of the freezing point caused by high concentrations of soil organic solutes prevented the soil from freezing. These conditions favored higher soil temperatures resulting in relatively high respiratory losses. The duration of snow cover and micrometeorological conditions determining the photosynthetic activity of the vegetation during snow-free periods influenced the size and the variability of the winter CO2 fluxes. Seasonal values are strongly influenced by the days at the end and the beginning of the defined winter period, caused by large variations in length of periods with air temperatures below freezing. Losses of CO2 from the snow-covered soil were highest in winter 2003/2004. These high losses were partially explained by higher temperatures in the topsoil, caused by higher air temperatures just before snowfall. Thus, losses are not a consequence of higher soil temperatures registered during the summer heat wave 2003. However, water stress in summer 2003 might have caused an increment in dead organic matter in the soil providing additional substrate for microbial respiration in the following winter. Although considerable day-to-day fluctuations in snow effluxes were recorded, no conclusive and generally valid relationship could be found between CO2 losses from the snow pack and snow depth, rate of snow melt, wind speed or air pressure. This suggests that time lags and hysteresis effects may be more important for understanding winter respiration than concurrent environmental conditions in most ecosystems of comparable typ

Management and site effects on carbon balances of European mountain meadows and rangelands

We studied carbon balances and carbon stocks of mountain rangelands and meadows in a network of 8 eddy covariance sites and 14 sites with biomass data in Europe. Net ecosystem exchange of pastures and extensively managed semi-natural rangelands were usually close to zero, while meadows fixed carbon, with the exception of one meadow that was established on a drained peatland. When we accounted for off-site losses and inputs also the carbon budget of meadows approached zero. Soil carbon stocks in these ecosystems were high, comparable to those of forest ecosystems, while carbon stocks in plant biomass were smaller. Since soil carbon stocks of abandoned mountain grasslands are as high as in managed ecosystems, it is likely that the widespread abandonment of mountain rangelands used currently as pastures will not lead to an immediate carbon sink in those ecosystems

Winter CO2 fluxes in a sub-alpine grassland in relation to snow cover, radiation and temperature

ISSN:0168-2563ISSN:1573-515

Funding

CARBOMONT is a project within Framework 5 of th

The analysis of spatio-temporal forest changes (1775-2000) in Flanders (northern Belgium) indicates habitat-specific levels of fragmentation and area loss

Spatio-temporal forest changes can have a progressive negative impact on the habitat of species that need forest continuity, i.e. the continuous presence of forest. Long-term species data that demonstrate such an impact are often not available. Instead we applied a spatial analysis on maps of the historical and present-day forests, by calculating landscape indices that explain forest plant species diversity. We digitized for this purpose, forests in Flanders (northern Belgium, similar to 13,500 km2) at four time slices (1775, 1850, 1904-1931, 2000) and created a map of forest continuity in 2000. The ecological relevance of the analysis was further enhanced by a site classification, using a map of potential forest habitat types based on soil-vegetation relationships. Our results indicated that, between 1775 and 2000, forests occupied 9.7-12.2 % of the total study area. If continuity was not taken into consideration, forest fragmentation slightly increased since 1775. However, only 16 % of the forest area in 2000 remained continuously present at least since 1775 and is therefore called ancient forest (AF). Moreover, connectivity of forest that originated after 1775, called recent forest, was low and only 14 % was in physical contact with AF. The results were habitat-specific as forest on sites that are potentially suitable for a high number of slow-colonizing species, e.g. ancient forest plants, were affected most. We discuss that a GIS analysis of this kind is essential to provide statistics for forest biodiversity conservation and restoration, in landscapes with a dynamic and heterogeneous forest cover

Application of the ancient forest concept to potential natural vegetation mapping in Flanders, a strongly altered landscape in Northern Belgium

Construction of potential natural vegetation (PNV) poses particular challenges in landscapes heavily altered by human activity and must be based on transparent, repeatable methods. We integrated the concept of ancient forest (AF) and ancient forest species (AFS) into a four-step procedure of PNV mapping: 1) classification of forest vegetation relev,s; 2) selection of those vegetation types that can serve as PNV units, based on AF and AFS; 3) merging of selected vegetation types into five PNV units that can be predicted from a digital morphogenetic soil map; 4) mapping of three additional PNV units based on additional environmental data. The second step, concerning the selection of reference forest vegetation, is of particular interest for PNV construction in Flanders (northern Belgium), where forest cover has been subject to temporal disruption and spatial fragmentation. Among the variety of extant forest recovery states, we chose as PNV units those vegetation types for which a high proportion of relev,s had been located in AF and that contained many AFS. As the frequency of AFS depends on site conditions, we only compared and selected vegetation types that are found on similar sites according to average Ellenberg indicator values. While succession is irrelevant for the definition of PNV, colonization rates of AFS can be used to estimate the time required for PNV to be restored in a site

Management and site effects on carbon balances of European mountain meadows and rangelands

We studied carbon balances and carbon stocks of mountain rangelands and meadows in a network of 8 eddy covariance sites and 14 sites with biomass data in Europe. Net ecosystem exchange of pastures and extensively managed semi-natural rangelands were usually close to zero, while meadows fixed carbon, with the exception of one meadow that was established on a drained peatland. When we accounted for off-site losses and inputs also the carbon budget of meadows approached zero. Soil carbon stocks in these ecosystems were high, comparable to those of forest ecosystems, while carbon stocks in plant biomass were smaller. Since soil carbon stocks of abandoned mountain grasslands are as high as in managed ecosystems, it is likely that the widespread abandonment of mountain rangelands used currently as pastures will not lead to an immediate carbon sink in those ecosystems