Long-term monitoring of ecosystem functions at Solling, Germany: Recovery from acidification or new risks due to climate change?

Henning Meesenburg1, Bernd Ahrends1, Stefan Fleck1, Markus Wagner1, Heike Fortmann1, Birte Scheler1, Mascha Albrecht1, Uwe Klinck1, Karl Josef Meiwes1
1 Environmental Control, Northwest German Forest Research Station

Invited Talk 1 in Long term trends in the functioning of ecosystems

14.07.2014, 10:45-11:15, H18

For  almost  50  years  indicators  related  to  various  functions  of  forest  ecosystems  have  been monitored at spruce and beech stands at Solling, Germany. Today the monitoring sites are part of different monitoring activities such as ICP Forests Level II (European Intensive Monitoring of Forest Ecosystems) and LTER (Long Term Ecological Research Network).
The  major  findings  of  the  monitoring  at  Solling  are  related  to  acidification  by  atmospheric deposition, nitrogen saturation as well as effects of climate change and elevated CO2. The effects of changing emission rates on deposition are clearly detectable at Solling. Sulphur deposition  at  Solling  increased  until  the  mid  1970ties  and  was  reduced  by  more  than  80 % since  then.  Nitrogen  deposition increased  until  the  end  of  the  1970ties  and  has  decreased slightly since then, but is still exceeding the critical loads for nitrogen. Deposition of acidity drastically decreased as a consequence of changing deposition rates of sulphur and nitrogen. 

Sulphur output from the soil shows a delayed response to decreasing deposition rates with a decrease of about 50 %. Simultaneously, contents of base cations (Bc) and Al in soil solution decreased.  Bc/Al  ratio  within  the  rooting  zone  as  indicator  for  Al  toxicity  is  below  critical limits indicating actual stress for tree roots.

As a consequence of the introduction of mobile anions, pools of exchangeable nutrient cations decreased drastically during the last 40 years. Actual base saturation is only about 3 % in the main  rooting  zone  indicating  a  reduced  elasticity  of  the  ecosystems.  Simultaneously,  the thickness of the forest floor doubled with correspondent changes in carbon, nitrogen, and base cation pools.

Nutrition of the forest stands as indicated by foliar analyses has deteriorated with respect to base cations relative to nitrogen. In contrast, an accelerated forest growth has been observed.  Input-output  budgets  of  nutrients  show  that  forest  utilization  at  the  spruce  stand  cannot  be maintained sustainable without depletion of nutrient pools. The actual Mg budget is negative even with no biomass use. For the beech stand, sustainability can be achieved at a higher level of biomass utilization.

Time series of ecosystem fluxes and states are integrated using dynamic modelling to evaluate links  between  nitrogen  and  carbon  budgets  and  the  potential  impact  of  climate  change  on recovery  of  the  forest  ecosystems  from  acidification.  The  contribution  demonstrates  the findings, which can be conducted from long-term monitoring and emphasises the value of the respective programs.

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Letzte Änderung 09.04.2014