Afforestation of low-productive peatlands in Sweden
1997
Sundstroem, E. (SLU, Umeaa (Sweden). Inst. foer Skogsskoetsel)
This thesis summarises the results of four studies analysing the conditions for forest production on low-productive peatlands in Sweden with respect to climate, and water and nutrient regimes. Data were collected from five experimental areas, established in 1969, all treeless low-sedge mires located along a south-north gradient between latitudes 56 deg-66 deg N and temperature sums ranging from 825-1400 deg C (TS5). An identical 4 x 6 factorial split-split plot design, four drainage and six fertilization treatments, were used in all areas. The first study focused on survival and growth of planted Scots pine. Survival was positively correlated to temperature sum, PK-fertilization and drainage intensity. Tree growth was not influenced by variation in climate after mere drainage but in combination with fertilization, growth was strongly correlated to temperature sum. Site preparation, i.e. planting in turned-over peat mounds had positive effects on survival and growth, especially in less intensively drained plots. A high proportion of damaged trees was observed. The second study compared survival and growth of planted seedlings of Scots pine, lodgepole pine, Norway spruce and silver birch. Neither of Norway spruce, due to poor growth, nor silver birch, due to high mortality, was found suitable for this site type. Lodgepole pine had better height and diameter growth but also higher mortality rates than Scots pine. Response to fertilization was only found in the three southernmost areas for both pine species. It was also found that spot fertilizer application, with a third of the fertilizer amount gave the same growth response as broadcast application. The third study showed that natural establishment by seeding from neighbouring forests can be a complement to planting, provided that downy birch is accepted as a dominant tree species. The amount of naturally established trees exceeded the number of living planted trees in all five areas. In the fourth study, soil nutrient conditions were investigated. In the topsoil (0-20 cm) of extensively drained and non-fertilized plots, pH and total contents of N, P and Ca increased with decreasing temperature sum in similar site types. Contents of K and Mg were not correlated to temperature. Tree growth was positively correlated to contents of P, K, and Ca, but not to N, and only for temperature sums greater than or equal to 950 deg C. It was suggested that the increased available/total ratios of Ca in the soil, found after PK-fertilization but only in the three southernmost areas, reflect post-drainage intensity of N-mineralization. Hence, the absence of increased Ca ratios indicate that three growth is limited by the microbial release of organically bound N.
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