Assessment, Conservation and Sustainable Use of Forest Biodiversity

Assessment, Conservation and Sustainable Use of Forest Biodiversity
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NHy - EMISSION DENSITY TRIGGERS DIVERSITY OF “TYPICAL”
FOREST VASCULAR PLANTS
Hermann Ellenberg* and Tobias Nettels**
*Institute for World Forestry, Federal Research Centre for Forestry and Forest Products, Hamburg,Germany;
** MSc-thesis, Faculty for Biology, University of Hamburg, Germany.
E-mail: ellenberg@holz.uni-hamburg.de
Keywords: plant species diversity, sustainable forest management, management intensity, ammonia emission
density, eutrophication, Northern Germany.
Introduction:
Eutrophicating and acidificating power of ammonia (NH3) and ammonium (NH4 + )deposition from the air is
well known scince the mid Eighties. It is considered one of the main causes for forest decline in Central
Europe. Forests are “combing” these substances from the air and concentrating by this means the deposition
load upon their areas. Trees and other plants are able to take up ammonia and ammonium directly from the
air via their stomata and assimilate them into their leaves. Also, algae or lichens in the canopy assimilate these
nitrogen compounds directly. Deposition and assimilation of NH3 and NH4 + trigger eutrophication of the
ecosystem with a nutrient that in the past has been in short supply at most places, naturally or as a consquence
of unsustainable use. This eutrophication occurs via leaf and litter fall and by the decomposition of this
organic material through the activities of soil organisms.
Question:
As forests are normally not/no longer supplied with nitrogen fertilizers, and as plant indicator species for poor
nitrogen supply are known to be most intensly threatened – does there exist a correlation or even a causal
connection between numbers of “typical” forest species (vascular plants: ELLENBERG 1998) and the emission
density of NHy ?
Approach:
For 28 counties (Landkreise) in the Northern German Lowlands – a quite homogenous macro-landscape over
hundreds of kilometres – emission densities of NH3 had been calculated from animal husbandry statistics and
provided to the CORINE data sample of the European Community. These data could be taken at the Federal
Agency for Nature Conservation in Bonn. – The number of “typical” forest vascular plant species have been
counted from this Agency’s data pool on the distribution of vascular plants in Germany. The species pool of
“typical” forest vascular plants for each county was defined as the cumulative species numbers for four map
sheets 1 : 25 000 (about 11 x 11 km, Messtischblatt). We concentrated on counties with approximately similar
forest cover percentages (between 12 and 25 % forest cover).
Results:
There exists a clear correlation: high NHy – emission densities go parallel with low numbers of “typical” forest
vascular plant species. This is especially evident for the counties on the poorer soils of the moraines of the last
but one glaciation (see Figure). Possibly this result is only due to a lack of a similar steep gradient in emission
densities for the counties in younger moraine landscapes. – This findings fit well with earlier published results
on “eutrophication – the most serious problem in nature conservation” (ELLENBERG et al., 1989).
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