Reviews and syntheses : Greenhouse gas exchange data from drained organic forest soils - a review of current approaches and recommendations for future research

Drained organic forest soils in boreal and temperate climate zones are believed to be significant sources of the greenhouse gases (GHGs) carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O), but the annual fluxes are still highly uncertain. Drained organic soils exemplify systems where many studies are still carried out with relatively small resources, several methodologies and manually operated systems, which further involve different options for the detailed design of the measurement and data analysis protocols for deriving the annual flux. It would be beneficial to set certain guidelines for how to measure and report the data, so that data from individual studies could also be used in synthesis work based on data collation and modelling. Such synthesis work is necessary for deciphering general patterns and trends related to, e.g., site types, climate, and management, and the development of corresponding emission factors, i.e. estimates of the net annual soil GHG emission and removal, which can be used in GHG inventories. Development of specific emission factors also sets prerequisites for the background or environmental data to be reported in individual studies. We argue that wide applicability greatly increases the value of individual studies. An overall objective of this paper is to support future monitoring campaigns in obtaining high-value data. We analysed peer-reviewed publications presenting CO2, CH4 and N2O flux data for drained organic forest soils in boreal and temperate climate zones, focusing on data that have been used, or have the potential to be used, for estimating net annual soil GHG emissions and removals. We evaluated the methods used in data collection and identified major gaps in background or environmental data. Based on these, we formulated recommendations for future research.Peer reviewe

Carbon stocks and fluxes in a young Siberian larch (Larix sibirica) plantation in Iceland

The understanding of how forests function with respect to carbon (C) balance and its interaction with the climate system is a fundamental question in climate change research. Another important question is how large the sink for CO2 is in northern forests and how it varies with forest type, management, stand age and with external factors, such as climate variability. According to the Kyoto Protocol, C sequestration of all afforested areas since 1990 is to be deducted from the national GHG emissions. It is however highly uncertain when such young plantations become net sinks for CO2, especially if some major site preparation has been applied. The main aim of the present thesis was to evaluate the effect of afforestation on ecosystem C dynamics. For this, eddy covariance measurements of net ecosystem exchange (NEE) were made during three years over a Siberian larch (Larix sibirica) plantation with typical site conditions for afforestation in Iceland; previously grazed heathland that was site-prepared and planted in 1991-1992 and was therefore a ‘Kyoto-forest’. Additional studies took place in a comparable treeless sites and in different age-classes of Siberian larch, Sitka spruce (Picea sitchensis) and lodgepole pine (Pinus contorta), which are all commonly used in afforestation in Iceland. The young Siberian larch plantation acted as a relatively strong sink for CO2, with NEE of -375, -566 and -245 g CO2 m-2 for years 2004, 2005 and 2006, respectively. The observed annual variation in NEE was more related to variation in the carbon efflux (Re) than in the carbon uptake (GPP). Air temperature and soil water potential showed the strongest correlation to annual changes in Re. The GPP was lower in 2005, when the plantation experienced severe spring frost damage, but that was also the year with the highest NEE. Stock-change measurements supported the results of the eddy covariance flux measurements, indicating a mean annual sequestration of -673 g CO2 m-2, year-1. They indicated largest change in belowground C-stocks, in the fine root biomass and soil organic matter, not in aboveground C-stocks that generally is the main focus of carbon inventories. The chronosequences in 10-50 year old plantations showed similar increase in soil C stocks following afforestation as the main study site

A young afforestation area in Iceland was a moderate sink to CO2 only a decade after scarification and establishment

This study reports on three years (2004-2006) of measurements of net ecosystem exchange (NEE) over a young Siberian larch plantation in Iceland established on previously grazed heathland pasture that had been scarified prior to planting. The study evaluated the variation of NEE and its component fluxes, gross primary production (GPP) and ecosystem respiration (R-e), with the aim to clarify how climatic factors controlled the site's carbon balance. The young plantation acted as a relatively strong sink for CO2 during all of the three years, with an annual net sequestration of -102, -154, and -67 g C m(-2) for 2004, 2005, and 2006, respectively. This variation was more related to variation in carbon efflux (R-e) than carbon uptake (GPP). The abiotic factors that showed the strongest correlation to R-e were air temperature during the growing season and soil water potential. The GPP mostly followed the seasonal pattern in irradiance, except in 2005, when the plantation experienced severe spring frost damage that set the GPP back to zero. It was not expected that the rather slow-growing Siberian larch plantation would be such a strong sink for atmospheric CO2 only twelve years after site preparation and afforestation

Biomass and composition of understory vegetation and the forest floor carbon stock across Siberian larch and mountain birch chronosequences in Iceland

Changes in understory biomass, forest floor carbon (C) stock and vegetation composition were studied in six age-classes of Siberian larch (Larix sibirica) and two age-classes of native birch (Betula pubescens) in Iceland. The ground vegetation was less in the larch during the thicket stage and in the old-growth birch compared to a treeless pasture. Understory biomass was strongly related to canopy gap fraction across forest stands (P < 0.001), but not to soil pH or soil C/N ratio. Increased mass of dead wood and alterations in vegetation composition increased the forest floor C-stock of older forests. The forest floor had reached as high C-stock as the pasture's ground vegetation in ca. 50 years in the managed larch plantations and in ca. hundred years in the unmanaged birch forest. This study clearly shows the importance of which time-step is used when changes in forest floor C-stocks are computed for afforestation areas

Cultural ecosystem services provided by the biodiversity of forest soils : a European review

Soil is one of the most species-rich habitats and plays a crucial role in the functioning of terrestrial ecosystems. It is acknowledged that soils and their biota deliver many ecosystem services. However, up to now, cultural ecosystem services (CES) provided by soil biodiversity remained virtually unknown. Here we present a multilingual and multisubject literature review on cultural benefits provided by belowground biota in European forests. We found 226 papers mentioning impact of soil biota on the cultural aspects of human life. According to the reviewed literature, soil organisms contribute to all CES. Impact on CES, as reflected in literature, was highest for fungi and lowest for microorganisms and mesofauna. Cultural benefits provided by soil biota clearly prevailed in the total of the reviewed references, but there were also negative effects mentioned in six CES. The same organism groups or even individual species may have negative impacts within one CES and at the same time act as an ecosystem service provider for another CES. The CES were found to be supported at several levels of ecosystem service provision: from single species to two or more functional/taxonomical groups and in some cases morphological diversity acted as a surrogate for species diversity. Impact of soil biota on CES may be both direct % by providing the benefits (or dis-benefits) and indirect through the use of the products or services obtained from these benefits. The CES from soil biota interacted among themselves and with other ES, but more than often, they did not create bundles, because there exist temporal fluctuations in value of CES and a time lag between direct and indirect benefits. Strong regionality was noted for most of CES underpinned by soil biota: the same organism group or species may have strong impact on CES (positive, negative or both) in some regions while no, minor or opposite effects in others. Contrarily to the CES based on landscapes, in the CES provided by soil biota distance between the ecosystem and its CES benefiting area is shorter (CES based on landscapes are used less by local people and more by visitors, meanwhile CES based on species or organism groups are used mainly by local people). Our review revealed the existence of a considerable amount of spatially fragmented and semantically rich information highlighting cultural values provided by forest soil biota in Europe

Cultural ecosystem services from belowground

International audienc