Author(s)： Folke O. Andersson
Plant biomass, primary production and mineral cycling in the beech forest (Fagus sylvatica L.), Hestehave in Jutland, Denmark were studied over a 50-year period. The role of the forest as a carbon sink was also assessed. Aboveground tree biomass was 226 t·ha-1 in 1970 and after a 50-year 539 t·ha-1 in 2014, an unexpected increase with 313 t·ha-1. Annual production at those two points in time was 13.4 and 20.5 t·ha-1, respectively. It was apparent that the tree biomass was still acting as a sink for carbon, which was the dominant element in the aboveground parts. The concentration of other elements (N > K > Mg > P > S > Na > Mn > Zn > Fe > Cu) ranged from 495 to 0.4 kg·ha-1. Annual litterfall
restored 3.2 t·ha-1 to the soil as organic matter or 1.6 t·ha-1 as carbon. Over the year 53% of the litterfall was decomposed. A pH decrease of 0.95 units in the soil was observed between 1968 and 1993. This was attributed to fallout from a neighbouring thermal heating station affecting sulfur deposition and increasing soil acidification. After 1993, when filters were
fitted in the heating station, the pH decrease in the soil was smaller, only 0.09 pH-units up to 2011. The increased tree growth is an additional, likely explanation for the observed soil acidification. Deposition of the growth-limiting element nitrogen increased during later years and is now, most likely around 20 kg·ha-1 per annum, which may partly contribute to the increased production.
In this paper the original results from 1970 on tree biomass, production and mineral cycling are reported. Of particular interest has been to elucidate if the Hestehave forest today is a source or sink for carbon. It was concluded that it is still a sink. This was revealed trough a new analyse in 2014 of tree diameter and height. Unexpected high values for increased diameter, height, tree biomass and production were found. In comparison with
other data, the results seem most likely to be correct although a reservation has been given on methodological matters. A number of properties, which are changing in the forest dynamics today can be verified from the reported findings in the repeated Hestehave investigation. Financial resources were lacking for a more detailed analysis. New knowledge is needed on today’s forests for their management. The value of long-term experiments needs to be stressed.