Aim. The aim behind this work is: (i) to review the work on Scots pine needle litter in order to construct a model for the decomposition process, from litterfall until a stable fraction is left, (ii) suggest a simple regulating mechanism for its sequestration of carbon. Focus will be on foliar litter of Scots pine and the genus Pinus. Discussion. The chemical composition of newly shed pine litter is in part determined by climate, e.g. mean annual temperature (MAT). Thus concentrations of nitrogen (N) are higher -and those of manganese (Mn) lower -with higher MAT. This may also influence the decomposition process. Mass loss of newly shed pine needle litter is positively influenced by climate (e.g. MAT), as well as by N and phosphorus (P) concentrations. In the late stage (above c. 30% accumulated mass loss) the influence of climate fades and those of lignin (Acid Unhydrolyzable Residue -AUR), N, and Mn are regulating the decomposition process. As the degradation of AUR dominates the decomposition process important parameters are those that influence the degradation of AUR, thus N and Mn. In the humus-near organic matter limit values have been related to litter Mn concentration over a wide climate gradient. Thus, the higher the Mn concentration, the further the process goes and the smaller the stable fraction.Conclusions. It appears that factors regulating the size of the stable litter fraction may be used as a tool on a larger geographical scale to predict carbon sequestration rates in pine forests.

Boreal forest soils play an important role in the global carbon cycle by functioning as a large terrestrial carbon sink or source, and the alteration of fire regime through global change phenomena may influence this role. We studied a system of forested lake islands in the boreal zone of Sweden for which fire frequency increases with increasing island size. Large islands supported higher plant productivity and litter decomposition rates than did smaller ones, and, with increasing time since fire, litter decomposition rates were suppressed sooner than was ecosystem productivity. This contributes to greater carbon storage with increasing time since fire; for every century without a major fire, an additional 0.5 kilograms per square meter of carbon becomes stored in the humus.

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Knowledge of past fire regimes is crucial for understanding the changes in fire frequency that are likely to occur during the coming decades as a result of global warming and land-use change. This is a key issue for the sustainable management of forest biodiversity because fire regimes may be controlled by vegetation, human activities, and/or climate. The present paper aims to reconstruct the pattern of fire frequency over the Holocene at three sites located in the same region in the northern Swedish boreal forest. The fire regime is reconstructed from sedimentary charcoal analysis of small lakes or ponds. This method allows fire events to be characterized, after detrending the charcoal influx series, and allows estimation of the time elapsed between fires. The long-term fire regime, in terms of fire-free intervals, can thus be elucidated. At the three sites, the mean fire-free intervals through the Holocene were long and of similar magnitude (approximately 320 years). This similarity suggests that the ecological processes controlling fire ignition and spread were the same. At the three sites, the intervals were shorter before 8600 cal yr BP (calibrated years before present), between 7500 and 4500 cal yr BP, and after 2500 cal yr BP. Geomorphological and vegetation factors cannot explain the observed change, because the three sites are located in the same large ecological region characterized by Pinus sylvestris-Ericaceae mesic forests, established on morainic deposits at the same elevation. Archaeological chronologies also do not match the fire chronologies. A climatic interpretation is therefore the most likely explanation of the long-term regional pattern of fire. Although recent human activities between the 18th and the 20th centuries have clearly affected the fire regime, the dominant factor controlling it for 10000 years in northern Sweden has probably been climatic.

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Abstract. The occurrence of macrofossil charcoal (long axis > 0.5 mm) and Picea abies (Norway spruce) pollen in peat stratigraphies, in combination with size and age data from 2976 P. abies trees were used to analyse ecosystem continuity and stand‐structure in ten old‐growth swamp‐forests in northern Sweden. All stands were dominated by P. abies, a species whose abundance increased westwards in Sweden between 3000 and 2000 yr B.P. In three stands no macrofossil charcoal was found and the maximum age of the peat, determined by 14C dating, varied from 1800 to 3600 yr B.P. In the other seven stands the number of levels containing charcoal varied from 1 to 23, but only between 1 and 7 levels were found after the appearance of spruce. Here the maximum age of the peat varied from 400 to 7900 yr B.P. The ten stands had an all‐sized stand structure and a stand continuity of ca. 300 yr. The shape of the age structure was similar to an inverse J‐curve. This indicates a continuous recruitment over time in a self‐perpetuating ecosystem. In a short‐term perspective (< 300 yr), the swamp‐forests are characterized by individual trees continually emerging while others are dying. it is suggested that internal dynamics of continuous small‐scale disturbances in combination with local site‐specific factors determine the structure of these forests. in a long‐term perspective, some of the present spruce swamp‐forests within the northern boreal zone have functioned as true fire‐free refugia since the establishment of P. abies populations while others have been affected by recurring fires, although not as frequently as forests on surrounding drier sites. The hypothesis that Scandinavian spruce swamp‐forests in general have functioned as true longterm fire‐free refugia is thus modified by the present results.

1. Global wildfire activity and biomass burning have varied substantially during the Holocene in both time and space. At the regional to continental scale, macroclimate is considered to be the predominant control regulating wildfire activity. By contrast, the role of forest tree composition is often considered as a subsidiary factor in studies addressing temporal variation in regional wildfire activity.2. Here, we assemble a spatially comprehensive data set of 75 macroscopic charcoal records that reflect local burning and forest landscapes that are spread over a substantial part of the European boreal forest, spanning both oceanic and continental climates. 3. We show that the late-Holocene invasion of Norway spruce Picea abies, a new forest dominant in northern Europe, significantly reduced wildfire activity, thus altering forest disturbance dynamics at a subcontinental scale. 4. Synthesis. Our findings show that a biotic change in the local forest ecosystem altered the fire regime largely independent of regional climate change, illustrating that forest composition is an important parameter that must be considered when modelling future fire risk and carbon dynamics in boreal forests.