Karl-Heinz Feger

Forest ecosystem research - priorities for Europe.

Abstract European Forest Ecosystem Research Network (EFERN), was set up in 1996 as one result of the Ministerial Conferences on the Protection of European Forests in Strasbourg 1990 and Helsinki 1993 with the aim of promoting ecological research for sustainable forest management. Three plenary meetings were held, each with a specific theme. The results of these meetings have been documented in 10 chapters in a volume with the title ‘Pathways to the wise use of forests in Europe’. The intention was also to give priorities for future forest ecosystem research. In accepting the idea that sustainability includes a multifunctional view of forests, there is a need to find ways of integrating classical forest ecosystem research with biodiversity, water quality and socio-economics. The balancing of the different interests in the forests can be done through planning. From this results also a choice of adequate management methods of the forest resources. The classical stand level in forestry requires now an additional scale — the landscape level. The aim with this paper is to present a concept which attempts to integrate the disciplines involved — ecosystem and landscape ecology and its components. Areas where research efforts are central are also mentioned.

Element budgets of two contrasting catchments in the Black Forest (Federal Republic of Germany)

Abstract Rainfall and throughfall inputs of all major cations and anions, via open-field bulk precipitation and canopy throughfall, are compared with streamwater outputs in two forested catchments at higher altitudes of the Black Forest. The sites differ considerably in terms of bedrock geology, soil type, soilwater characteristics, topography, and forest management history. Deposition at both sites is almost equal and, in contrast to other forest areas in Central Europe, of a low-to-moderate level. Dry deposition does not seem to play an important role. Distinct differences in the elemental output emerge owing to the differing site conditions. At Villingen, deposited nitrogen is almost totally retained, whereas at Schluchsee, nitrogen output and input are of the same order of magnitude. This is consistent with the different nitrogen nutrition level of the stands, microbial turnover in the soil, and former management practices (change of tree species, excessive nutrient export). Sulphur is not retained in either of the catchments. At Schluchsee, sulphur export exceeds input from canopy throughfall by a factor of 2.5. The higher output rates, both of nitrogen and sulphur at Schluchsee, are due to the much higher microbial mineralization of organic matter as shown by previous incubation tests. Differences in cation and proton export are mainly caused by a different drainage pattern. In contrast to the Schluchsee catchment, where vertical water pathways prevail, the streamwater solute output at Villingen is dominated by a shallow subsurface runoff. Atmospheric deposition is a contributing, but not the dominant, factor in the biogeochemical cycling at these sites. Hence, a generally applicable quantitative definition of ‘critical loads’, especially for nitrogen, is illusory and the use of such numbers will be misleading.

Nitrogen cycling in two Norway spruce (Picea abies) ecosystems and effects of a (NH4)2SO4 addition

Nitrogen cycling in two Norway spruce (Picea abies (L.) Karst.) ecosystems in the ARINUS experimental watershed areas Schluchsee and Villingen (Black Forest, SW Germany) and initial effects of a (NH4)2SO4 treatment are discussed. Although N reserves in the soils are similar and atmospheric N input is the same low to moderate level characteristic for many forested areas in SW Germany, N export by both seepage and streamwater differs considerably. At Villingen, deposited N is almost totally retained in the ecosystem, whereas at Schluchsee N export is the order of the input. This is explained by differences in forest management history. The Villingen site had been subject to excessive biomass export (e.g., litter raking) leading to unfavorable microbial transformations in the soil. In contrast, as a ‘relic’ of the former beech stand, the Schluchsee site is characterized by high biological activity in the soil with vigorous nitrification despite low pH values. Accordingly, the two ecosystems responded differently to the additional N input (150 kg NH4+ -N ha−1 as (NH4)2SO4). Nitrification starting immediately in the Schluchsee soils led to continued Al mobilization and leaching of basic cations and NO3−. The availability of Mg, already deficient before treatment, further decreased due to Mg leaching and marked N uptake by the stand. In contrast, most of the added N in Villingen was immobilized in the soil. Hence, uptake by the stand and leaching of NO3− and cations was correspondingly lower than at Schluchsee. The results emphasize the problems associated with the definition of generally applicable values for ‘critical loads’ of N deposition.

Dynamics of aqueous aluminum species in a podzol affected by experimental MgSO4 and (NH4)2SO4 treatments

Chemistry of aqueous Al in a podzol on a Norway spruce (Picea abies [L.] Karst.) site in the Black Forest (SW Germany) and changes induced by experimental applications of MgSO4 were studied. Soil solution taken from the O, E and BC horizons were analyzed for the fractions ‘labile monomeric Al’, ‘non-labile monomeric Al’, and ‘acid-reactive Al’. The activities of ‘inorganic monomeric Al’ species and the saturation indices (SI) of the soil solution with respect to Al-bearing minerals were calculated using the equilibrium speciation model WATEQF. On the untreated plot, soil leachates are characterized by Altot concentrations of 0.1 mg L−1 (mineral soil). In the O horizon, the fractions ‘acidsoluble Al’ and ‘non-labile monomeric Al’ (mainly organically complexed Al) together comprise 80% of Altot. In the leachates from the mineral soil Al3+ prevails, being 50% of Altot. Al-F-complexes make up 5 to 10% in all horizons. MgSO4 and (NH4)2SO4 treatments resulted in an intense Al mobilization up to 50 mg L−1. In this situation, 60% of Altot is covered by Al3+ and 40% by non-phytotoxic Al-SO4-complexes. After rainfall events, mobilized Al is quickly translocated into the subsoil, with water flow through macropores then appearing to be an important mechanism. In both treatments, soil solution chemistry was favorable for the precipitation of the Al(OH)SO4-type minerals alunite and jurbanite. However, a control of Al solubility by this process is not likely due to kinetic restraints. Application of MgSO4 was followed by an increase of the Mg/Al molar ratio in the soil solution, whereas the Ca/Al ratio decreased. After treatment with (NH4)2SO4 both the Ca/Al and the Mg/Al ratios deteriorated.

Estimation of spatially distributed soil information: dealing with data shortages in the Western Bug Basin, Ukraine

Integrated watershed models require spatially differentiated soil information. However, in many regions of the world the limited availability of soil data hinders an appropriate simulation of hydro-ecological processes. Such circumstances lead to unsupported statements, poor statistics, misrepresentations, and, ultimately, to bad resource management. The Western Bug catchment in west Ukraine is an example of such a region. In the former Soviet Union, soil classification primarily focused on soils of agricultural importance, whereas, forested, urban, industrial, and shallow soil territories were left underrepresented in the classification and soil maps. Spatially differentiated soil texture data are required to predict soil hydraulic properties using pedotransfer functions (PTFs), along with soil maps. Furthermore, the Ukrainian soil texture scheme does not match the particle size classes commonly used with PTFs. To overcome these shortcomings, a fuzzy logic methodology was applied, based on terrain and vegetation/land use analysis and soil sampling, to close the information gaps. For the application of PTFs, a procedure was tested to estimate missing values of soil texture distribution. Applied methods were evaluated using recent soil surveys, measured soil texture, and water retention properties, while having in consideration the limitations brought by scarce soil data for integrated watershed modelling purposes.

Solute Fluxes and Sulfur Cycling in Forested Catchments in SW Germany as Influenced by Experimental (NH4)2SO4 Treatments

Results are presented from the research project Arinus which investigates biogeochemical cycling in Norway spruce (Picea abies KARST.) ecosystems in the Black Forest (SW Germany) and effects of experimental (NH42SO4 additions. The interaction of the terrestrial and aquatic system is assessed using an integrated approach which combines flux measurements in representative plots on the stand level with input-output budgets of small catchments. The approach, field installations and experimental manipulations are described. Results from element flux measurements in the untreated systems are presented and processes controlling N and S transformations are discussed for two catchments representing contrasting site conditions. Even though the S budget is negative for both systems there is a distinct difference in the relation between organicvs. inorganic S fractions in the soil. Sulfate mineralization and desorption, respectively are discussed as controlling processes. Sulfate retention is not only a function of soil properties, but also of water fluxes and pathways. The uptake of added SO42− was highly controlled by the counter-cation. Microbial N retention in the soil was highly influenced by the site management history. The extent of streamwater acidification was highly dependent on the transformations and mobility of N and S in the soils which in turn controlled cation leaching and alkalinity.

Evaluation of sulphur cycling in managed forest stands by means of stable S-isotope analysis

Sulphur cycling was evaluated in a 20 to 60 year old Norway spruce (Picea abies L. Karst) ecosystem in the Black Forest near Schluchsee, SW Germany, by means of stable sulphur isotope analysis.Soil and plant material were analysed for S-content and S-isotopic composition to gather information on the S-distribution in the ecosystem. Two out of three adjacent watershed areas, highly comparable to each other were fertilized with MgSO4 and (NH4)2SO4 respectively, where sulphate was enriched in the 34S-isotope compared to the sulphur present in the ecosystem. As the fertilizer S served as a tracer, comparison of the S-isotopic composition of total and inorganic S in the soil and S in spruce needles from both the treated and the control sites led to new information of S-turnover processes.The S-isotopic composition of spruce needles changed markedly after the fertilizer application. Within half a year a shift towards the S-isotopic composition of the fertilizers sulphate indicated uptake of the sulphate by the trees, although this uptake did not become visible with the S content of the needles.Regarding the soil, a shift in the S-isotopic composition of the total sulphur was not that striking as with the needles, although the phosphate extractable sulphate showed a clear shift towards the S-isotopic composition of the fertilizer sulphate.

Assessment of the ecological effects of forest fertilization using an experimental watershed approach

In the research project ARINUS, the effects of restabilization measures (fertilization with readily soluble MgSO4) on the element cycling of Norway spruce ecosystems in the Black Forest (SW Germany) are studied. The objective is to quantify the natural and anthropogenic components of element cycling. Interrelations between the terrestrial and aquatic subsystem are assessed using an integrated approach which combines flux measurements in representative plots with input/output balances of small experimental watersheds. The paper discusses the initial effects of a whole-watershed treatment with Kieserite (750 kg ha−1 MgSO4 · H2O) based on the Mg and S cycling in the control watershed. With the fertilizer, 130 kg ha−1 Mg and 170 kg ha−1 S were introduced into the system. Fertilization resulted in increased levels of Mg and S in the needles. Despite high inorganic Al concentrations and extremely low Ca/Al ratios in soil solution, there was no evidence for ‘Al toxicity’. Since fertilizer losses from the system 1 1/2 years (2 growing seasons) after the treatment have been modest, surface water was hardly been affected. More than 75% of the applied Mg has remained in the ecosystem, primarily in the intensively rooted upper soil layer. Also S has been retained to a considerable extent. The mobility of fertilizer sulfate in acidic forest soils is substantially lower than has been hitherto assumed from laboratory experiments. Therefore, fertilization with readily soluble sulfate-based Mg fertilizers is recommended as an efficient and — in comparison to liming — less risky restabilization measure on sites with a high potential for nitrification.

An integrated watershed/plot-scale study of element cycling in spruce ecosystems of the Black Forest

The research project ARINUS is the study of the effects of restabilization measures (fertilization with rapidly soluble Mg salts) and atmospheric deposition on the element cycling of typical spruce ecosystems in the Black Forest. The objective is to quantify the natural and anthropogenic components of element cycling at these sites which will provide a better estimation of the effects induced by external perturbations,e.g. increasing atmospheric deposition, fertilization, or biomass export. Interrelations between the terrestrial and aquatic system are assessed using an integrated approach which combines flux measurements in representative plots with balances of small experimental watersheds. This paper describes the approach, treatments, field installations, methods, and site conditions of one of the two research areas. Furthermore, preliminary results from element inventories and watershed input-output budgets are discussed. According to the distribution of Mg in the ecosystem, the experimental area Schluchsee is a typical Mg deficient site. Magnesium losses result from leaching both from the canopy and the superficially rooted top soil. Since atmospheric deposition is low, cation export is primarily controlled by the ecosystems internal production of acids. This excess mineralization in the soil is attributed to a change from the original mixed forest to the present spruce monoculture.

Importance of natural soil processes relative to atmospheric deposition in the mobility of aluminium in forested watersheds of the Black Forest

The dynamics of aqueous aluminium in the ARINUS experimental watersheds at Schluchsee (granite) and Villingen (quartz sandstone), Black Forest (South-west Germany), were studied in order to detect the processes and factors controlling its mobility. Aluminium speciation was performed in the seepage of typical soils (podsol, acidic brown earth, stagnogley) at 3 depths (organic layer, 30 cm and 80 cm of the mineral soil) as well as in streamwater. The studies concentrated on the variability in time and space of inorganic monomeric Al (Ali), and organic monomeric Al (Alo). Furthermore, the equilibrium speciation model WATEQF was used to calculate the distribution of inorganic Al species. Natural soil properties and processes, such as DOC mobilization and excess mineralization of NO3(2-) and SO4(2-), appeared to have great influence and outweigh the deposition effects upon Al mobilization in these systems which receive only low to moderate loads of acidic deposition.