Lars Bo Pedersen

A comparison of litterfall and element fluxes in even aged Norway spruce, Sitka spruce and beech stands in Denmark.

Litterfall was investigated in three even-aged Norway spruce (Picea abies), sitka spruce (Picea sitchensis) and beech (Fagus sylvatica) stands on a nutrient poor-soil in Southern Denmark. Dry weights and N, P, K, S, Mg, Ca, Na, Al, and Fe concentrations and fluxes were examined in litterfall fractions. Foliage litter amounted to 90% of total litterfall. The tree stands showed a similar mean annual litterfall. In the spruce stands, annual litterfall was correlated negatively with the current year increment and positively with the previous year increment. Annual litterfall in beech was constant during the 6 study years whereas Norway spruce and sitka spruce showed large fluctuations between years caused by drought, spruce aphid infestations and probably sea salt stress. Norway spruce responded with a long lasting elevated needle loss. Sitka spruce responded to infestations with premature needle loss during short periods. The presence of a large syrphid (Coccinellidae) population was important in regulating aphid (Elatobium abietinum) population density. The between-year variation in element concentrations of litterfall was small whereas variations during the year were large. Interspecific levels were recognized: Norway spruce>beech>sitka spruce. High concentrations in Norway spruce were ascribed to a combination of drought, sea salt stress and elevated transpiration. In sitka spruce, aphid infestations reduced the litterfall N content. Sitka spruce showed the smallest amount of base cation fluxes with litterfall. In contrast, spruce and beech exhibited even litterfall element fluxes. Litterfall studies revealed reduced vitality in the non-native spruce stands and underlined the perception of a healthy stand of native beech.

Effects of airborne sea salts on soil water acidification and leaching of aluminium in different forest ecosystems in Denmark

Studies on biogeochemical cycling of elements are performed in even aged forest ecosystems of Norway spruce, Sitka spruce and beech at several locations in Denmark. Episodes with high sea salt deposition and unusual low water surplus percolation caused extreme salt concentrations in the soil solutions. The changes were smallest beneath beech stands and most pronounced at the most salt-affected Sitka spruce stands. Contemporary, the pH drops and the Al3+ concentration increased above 20 mg L-1 owing to cation exchange with Na+. The Cl- and Al3+ concentrations reached levels reported as toxic for Norway spruce, but not for Sitka spruce and beech. The changes in the soil water chemistry must be considered as important factors for the reduced vitality in Norway spruce ecosystems in Denmark.

Leaching versus input of nitrogen, potassium and magnesium in different fertilizer regimens in Christmas tree stands of Abies nordmanniana in Denmark

Abstract The effects of nitrogen (N), potassium (K) and magnesium (Mg) fertilization and deposition on nutrient leaching were assessed in four Danish Nordmann fir Christmas tree stands on former arable land. NPK 23-3-7 fertilizer type was applied in doses between 0 and 1200 kg ha−1 year−1. Deposition of N, K and Mg varied between 16 and 21 kg N ha−1 year−1, 2 and 10 kg K ha−1 year−1, and 2 and 3 kg Mg ha−1 year−1. The concentration of NO3–N in the soil water on the sandy sites was characterized by notable pulses contrasting the mitigated peaks on the clayey site. In general, the soil water concentrations and leaching reflected the fertilization, except for K at one clayey site. Mean annual leaching of NO3–N ranged from approximately 6 kg ha−1 year−1 in the control treatment to 235 kg ha−1 year−1 in the 1200 kg ha−1 year−1 fertilizer treatment. In the treatment with the commonly used 300 kg NPK 23-3-7 fertilizer NO3–N leaching was estimated to be approximately 46 kg ha−1 year−1. Annual leaching of N was described in a general model based on the fertilizer input. K and Mg leaching were distinctly more site specific than was N leaching. The magnitude of NO3–N leaching caused by application of 300 kg NPK 23-3-7 fertilizer was between the leaching amounts observed in traditional Danish forestry and Danish agriculture.