Nils Malmer

Thawing sub‐arctic permafrost: Effects on vegetation and methane emissions

Ecosystems along the 0degreesC mean annual isotherm are arguably among the most sensitive to changing climate and mires in these regions emit significant amounts of the important greenhouse gas methane (CH4) to the atmosphere. These CH4 emissions are intimately related to temperature and hydrology, and alterations in permafrost coverage, which affect both of those, could have dramatic impacts on the emissions. Using a variety of data and information sources from the same region in subarctic Sweden we show that mire ecosystems are subject to dramatic recent changes in the distribution of permafrost and vegetation. These changes are most likely caused by a warming, which has been observed during recent decades. A detailed study of one mire show that the permafrost and vegetation changes have been associated with increases in landscape scale CH4 emissions in the range of 22-66% over the period 1970 to 2000.

Growth-limiting nutrients in Sphagnum-dominated bogs subjects to low and high atmospheric nitrogen supply

The effects of increased nitrogen or phosphorus supply on the productivity of Sphagnum-dominated ombrotrophic bogs in northern and southern Sweden were studied. Atmospheric nitrogen deposition in souther Sweden (high-N site) exceeds that in northern Sweden (low-N site) by about tenfold. Vertical height growth of the Sphagnum carpet was measured by the crankedwire method. Length growth of individuals was measured by autoradiography after labelling with 14 CO 2 . The results of both methods were significantly correlated, but the cranked-wire data were systematically lower. Productivity of Sphagnum at the low-N site increase almost fourfold after additional nitrogen supply (4 g N m −1 year −1 ), but no increase was found after additional phosphorus supply (0.4 g P m −2 year −1 ) (...)

Interactions betweenSphagnum mosses and field layer vascular plants in the development of peat-forming systems

The interactions between field layer vascular plants andSphagnum mosses in peat-forming systems are discussed in terms of differences in growth strategies, access to light, acquisition of mineral nutrients and water and the processes involved in the formation of the micro-topographical structures characteristic for these systems.To keep pace with the vertical growth ofSphagnum, the co-occurring vascular plants require a growth strategy involving continuous movement of the growing point and meristematic tissue upwards and a frequent formation of adventitious roots.The growth form and architecture of the vascular plants determine the occurrence and distribution of the structural units on a mire, the hummocks, lawns and hollows. Dwarf shrubs and other vascular plants with an orthotropic growth pattern characterise hummocks, where they form a firm matrix which reinforces and supports the spongy biomass ofSphagnum. In a similar way, clonal herbs stabilise the lawns because of the predominantly plagiotropic, or only weakly orthotropic, growth pattern of the rhizomes and coarse roots in the upper, oxic layers.Extended periods of drought often may have deleterious effects on the mosses but smaller impacts on the vascular plants because of their more efficient water conducting system. Different sources of mineral nutrients are used bySphagnum (atmospheric deposition) and the vascular plants (mineralisation of the organic matter). The presence ofSphagnum, therefore, reduces the supply of nutrient resources to the vascular plants.Sphagnum thereby gains a competitive advantage. A high rate of mineralisation would be beneficial to the vascular plants by increasing their growth rates causing shading of theSphagnum mosses and covering the moss layer by the above-ground litter fall. However, the slow decomposition ofSphagnum litter keeps the system in balance as it will reduce the nutrient supply to the vascular plants.

Patterns in the Growth and the Accumulation of Inorganic Constituents in the Sphagnum Cover on Ombrotrophic Bogs in Scandinavia

Three hummock species of Sphagnum mosses (S. fuscum, S. rubellum and S. russowii) and two hollow species (S. balticum and S. magellanicum), characteristic of the moss layer on ombrotrophic bogs in Scandinavia, have been analyzed for N, P, S, Na, K, Mg, Ca, Mn, Fe, Cu, Zn, Cd, Pb, Al and acid insoluble ash (AIA). The moss plants were divided into four segments of predetermined length which were weighed and analyzed separately. Moss weight increases mostly in the capitulum while the main length increase occurs further down. N, P, and K accumulate in the upper parts of the moss carpet, while the concentrations of AIA, Al, Fe, Zn, Cd and Pb increase with the age of the plants. The ion exchange capacity of the mosses determines the concentrations of Na, Mg and Ca; the sum of Ca+Mg being the same throughout the plant. Concentration differences among species result mainly from differences in growth pattern and site conditions. Concentrations in moss layer and underlaying peat are not correlated. A variation between sampling areas is demonstrated for six elements (N, S, Cu, Zn, Cd and Pb) due to a varying supply from man-made emissions, for two elements (Na, Mg) due to varying oceanic influence, and for four elements (P, Na, Mg, Ca) probably due to varying moss productivity. The supply of Al, Fe and AIA is greatest near agricultural and industrialized regions. The variation in Mn is explained by soil and bedrock conditions. Most of the supply of S, Na, Mg and Ca is drained from the moss layer. All other elements are contained in the moss layer and, with the exception of K and Mn, transferred to the peat by litter deposition. It is unlikely that differences in supply of plant nutrients influence the geographical distribution of the bog plants. Hummock species should serve better than hollow species for monitoring current

Variation in the C/N quotient of peat in relation to decomposition rate and age determination with ^,210>Pb

Variation in the C/N-quotient of peat in relation to decomposition rate and age determination with 210Pb.

Input rates, decay losses and accumulation rates of carbon in bogs during the last millennium: internal processes and environmental changes

In peatlands the balance between litter input and decay loss in the oxic acrotelm determines the rate of carbon input to the anoxic catotelm with carbon lost at very slow rate. In the acrotelm the C/N-quotient decreases with depth and indicates the loss of carbon from the acrotelm. On one boreo-nemoral and three subalpine ombrotrophic bogs in Sweden the carbon losses in the acrotelm plus the apparent carbon-accumu lation rates in the catotelm for the last millennium revealed a constant carbon-sequestering rate up to the end of the nineteenth century equalling that in recent Sphagnum-dominated communities. On the boreo-nemoral bog the carbon-accumulation rate in the catotelm decreased by 50% over the same period while it remained constant on the subalpine bogs. A catotelm with permafrost may have provided more constant conditions for the carbon accumulation than a rising water level creating anoxic conditions. Due to vegetation changes, the recent carbon sequestering in the peat-forming communities is lower than previously and only just enough to compensate for the integrated losses. It is argued that because of internal processes the bogs up to the end of the nineteenth century had obtained or were approaching a steady-state with regard to the carbon input to the catotelm and the supply of mineral nutrients. In contrast, an increased climatic humidity around 1000 cal. BP resulted in high carbon-accumulation rates in the boreo-nemoral bog. Climate could have triggered the recent vegetation changes, but an increased nitrogen deposition is also a probable reason.

STRATIGRAPHIC AND PALEOCLIMATIC STUDIES OF A 5500-YEAR-OLD MOSS BANK ON ELEPHANT ISLAND, ANTARCTICA

Analyses of a core from the deepest known moss peat bank in Antarctica, on Elephant Island, South Shetlands, show that this Chorisodontium aciphyllum-dominated bank began to grow ca. 5500 14C yr BP. Combined with other studies in the region the present study indicates more extensive glaciation before 5000 to 6000 BP than today on some of the South Shetland Islands. The main hypothesis is that these frozen moss banks contain important paleoclimatic information. The stratigraphic parameters analyzed included degree of humification, organic and mineral matter content, bulk density, chronology, volumetric growth and organic accumulation rates, carbon and nitrogen concentrations, C/N ratios, nitrogen accumulation rates, and finally magnetic analyses to detect tephra horizons. A discussion of the interrelationships between these parameters is followed by theoretical calculations of annual net primary productivity combined with multivariate analysis of the data set. Results of the analysis show that three calculated productivity peaks coincide with three periods of milder and more humid summers, at 4150-3900, 3180-3030, and 2030-1840 BP. However, the period with possibly the warmest summers, 3180-3030 BP, is interpreted also to have been characterized by cold winters. The data suggest that the periods with the coldest summers (and possibly also winters) prevailed at the earliest stage of the moss bank development, at ca. 3500 BP, and 2500 BP.

Vegetational Succession in a South Swedish Deciduous Wood

In 1918 the small area of woodland, Dalby Soderskog, in southwestern Skane was designated as a national park. It was regarded as ‘the only remaining representative of the type of deciduous forest, that during periods long ago commonly occurred in the southernmost province of our country’ (translation from Lindquist 1938, p. 61).

Total nutrient accumulation and seasonal variation in resource allocation in the bog plant Rhynchospora alba

Mass allocation and allocation of minerals (N, P, K, C, Ca, Mg, Mn, Fe, Zn and Na) to different component organs of the perennial Rhynchospora alba were studied in plants taken from an ombrotrophic bog area.

Leaf litter fall and soil acidity during half a century of secondary succession in a temperate deciduous forest

Vegetation, leaf litter fall and soil pH were sampled repeatedly within semipermanent plots in a South-Swedish deciduous forest, 1935–1983. Leaf litter fall was summarized in a litter quality index. Vegetation types were differentiated along similar gradients in soil pH and leaf litter quality. The greatest shifts in dominance among field layer species were found in those plots where the quality of the leaf litter had improved. These plots also showed a halt in the general tendency towards a decreasing pH in the top soil.