Long-term Observations in a Norway Spruce Forest at Lange Bramke, Harz (Germany)

Michael Hauhs1, Christina Bogner1, Henning Meesenburg2, Holger Lange3
1 Ecological Modelling, University of Bayreuth
2 Nordwestdeutsche Forstliche Versuchsanstalt, Grätzelstr. 2, Göttingen, Germany
3 Norwegian Forest and Landscape Institute, Postboks 115, N-1431 Ås, Norway

O 1.2 in Long term trends in the functioning of ecosystems

14.07.2014, 11:35-11:55, H18

The Harz mountains have an exceptionally well-documented history of mining and forestry. Starting in the 16th century this included irregular inventories and assessments of forest and water resources and covered also today’s monitoring sites at the Lange Bramke valley. In 1889 one of the first monitoring sites for forest yield in Germany was started in  the Bramke valley within 500 m of today’s sites. The 100-140-year old stand in the Bramke valley was harvested in 1946 in an exceptional  valley-wide clear cut by British occupation forces. Today the Norway spruce stand at this site is just a few years younger than the previous one at the time of its first monitoring. Besides catchment hydrology, the effect of deposition of air pollutants into the Bramke catchment has  been studied since the 1970ies. The main focus of research was on soil and water acidification including symptoms of forest decline (yellowing  due to Mg deficiency). Now the Bramke catchments have become part of national and international long-term monitoring programs (level II ICP Forest site).

The measured time series of meteorological variables, runoff,  throughfall, hydrochemistry and soil solution chemistry were used to develop and validate biogeochemical models of sulfate dynamics. However, no model has yet been able to reproduce the chemical  dynamics correctly. To the contrary, many simple model assumptions such as an effective sulfate adsorption process at the catchment scale turned out to be inconsistent with the long-term data set. Currently,  data in throughfall, soil solution and runoff water show the shifting  importance from sulfate to nitrate.

Prominent forms of human impact in this area are export of biomass, hunting, mining, deposition of air-pollutants and forestry operations  such as thinning and liming. During the first eight years, the nitrogen levels in runoff remained undistinguishable between an experimentally limed catchment (Steile Bramke in 1989 with 16 t CaMgCO3 ha−1 ) and  an untreated control (Dicke Bramke). From 1997 onwards, nitrogen  levels started to increase at Steile Bramke. In our contribution, we show the importance of this exceptional data set in revealing unexpected  effects in forest ecosystems. Long-term monitoring is a crucial  ingredient for understanding and sustainable use of ecosystems. However, this data set also demonstrates that the role of process-based models in explaining ecosystem behaviour and their ability to predict its dynamics have been overrated.

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last modified 2014-04-03