Interdisciplinary Forest Ecosystem Experiments at Solling, Germany – from Plot Scale to Landscape Level Integration

For. Snow Landsc. Res. 78, 1/2: 33–52 (2004) 33 Interdisciplinary forest ecosystem experiments at Solling, Germany – from plot scale to landscape level integration Martin Jansen1 and Michael Bredemeier2 1 Institute of Soil Science and Forest Nutrition, University of Göttingen, Büsgenweg 2, 37077 Göttingen, Germany. [email protected] 2 Forest Ecosystems Research Centre, University of Göttingen, Büsgenweg 2, 37077 Göttingen, Germany. [email protected] Abstract The Solling, a mountainous forested area in northwestern Germany, has been the location of interdisciplinary forest ecosystem research from the early 1960s on. The methodology developed and employed there was novel and pioneering at that time. It enabled the quantitative description of matter and energy budgets for entire ecosystems and the connection of such process rates to ecosystem structures such as species composition, age, and biotic communities.The flux monitoring methodology developed at Solling and other early case studies is nowadays routinely applied at forest monitoring sites worldwide, e.g., in the European Level-II network of ICP Forests (International Co-operative Programme on Assessment and Monitoring of Air Pollution Effects on Forests). Solling holds the longest complete and continuous biogeochemical flux records in forest ecosystems worldwide. Recently the scope of forest ecosystem research at Solling has been expanded from the plot scale to the entire forest landscape. The main motivation for this scaling up was the desire to transfer the wealth of forest ecological knowledge obtained from prior research into practical forest management. GIS-based models provide spatially explicit estimates of important indicators such as diversity of forest stand types and risk of wind throw at the forest management unit level, and are a good basis to support practical forest management decisions. Keywords: forest ecosystem research, case studies, forest landscape, matter budgets, Solling 1 Introduction Results from integrated forest ecosystem research conducted in the Solling mountain area in northwestern Germany are widely recognized and have stimulated forest monitoring and research methodology worldwide. The data sets from Solling are in many cases unique with respect to the duration of measurements and comprehensiveness of parameters investigat- ed.The beginnings of the investigations at Solling now date back almost four decades, during which an evolution of ideas, scopes and paradigms took place. In this paper, we describe the historical development of forest ecosystem research at Solling, recollect some of the most important results, and finally address the problem of scale and the new research strategies connected to that issue. 34 Martin Jansen, Michael Bredemeier IBP.Interdisciplinary Phase 1: Phase 2: Phase 3: ecosystem research + Stability of Dynamics of Indicators and strategies forest decline research forest ecosystems forest ecosystems for sustainable forest management since 1968 1989 1994 1999 2004 Fig.1. Phases of forest ecosystem research at Solling. 2 The Solling – a landscape with a long history of forest ecosystem research The Solling is a typical low mountain range south of the Pleistocene northern German flat plains, reaching about 550 m a.s.l. at its highest elevations (Fig. 2). There are only some small towns found around the central mountainous area and few very small villages in the interior, hence the population density is very low compared to urban and industrial areas in Germany. The forest cover, conversely, is comparatively high, amounting to 60%, or 44 000 ha out of 74 000 ha total area. Solling is also a typical “cultural landscape” where the land has been utilized for centuries in many different ways. Numerous rural settlements established in the medieval period were later abandoned in times of plague and famine and were subsequently covered again by forest. In later times, when the human population grew again and primeval industries emerged, over-exploitation and human livestock degraded the forest in the Solling mountains, and open, over-aged forests or degradational heathlands dominated the landscape. In the past two centuries, the forests at Solling and in other parts of Germany regenerated under scientifically based forest management. However, the forests created by this new method were often very different from the primary natural state, comprising a high pro- portion of conifer plantations. This development is also typical for many other regions and landscapes of Germany.A comprehensive and detailed record of the Solling forest history is given by FÖRSTER (2002). The history of forest ecosystem research at Solling started in the early 1960s, as part of the International Biological Programme (IBP) when ecosystems representative of the different biomes of the world were selected for investigation.A mature pure beech forest on the high Solling plateau at about 500 m elevation was chosen to represent the typical Luzulo-fagetum of the temperate humid environment at lower elevations and under naturally oligotrophic site conditions. Moreover, the site was considered pristine with respect to human environmental impacts, since it is situated several hundred kilometers from the big industrial centres of Germany. The research conducted at Solling was designed in an integrated and interdisciplinary manner from the very beginning, i.e., research groups from different disciplines concentrated on the same object (the beech stand, later designated as “B1”) and brought together their results in joint reports and publications. New methods to determine entire element budgets of the forest ecosystem were developed, which are nowadays the standard methodology in forest monitoring networks worldwide.Also new micrometeorological and tree physiological methods were elaborated, employing high measuring towers in the forest. Many new results and a number of surprises resulted from that novel research, and some of them will be high- For. Snow Landsc. Res. 78, 1/2 (2004) 35 lighted below. The area of experimentation was continuously expanded, first by a pure Norway spruce stand in the neighbourhood of B1 (designated as “F1”), and later by many more plots to address issues such as liming and fertilization, soil animal and ground vegetation dynamics, gap dynamics, and experimental manipulation of chemical inputs and transfers in the ecosystem. The history and progress of integrated forest ecological research at Solling are documented in detail in two consecutive book volumes (ELLENBERG 1972; ELLENBERG 1986) and a copious number of further journal and book publications. In the following sections, we set out to describe the evolution of the general research strategy in forest ecosystem research at Solling and highlight some important results in this context. Roof F1 B Fig. 2. Landscape “Solling mountains” with case studies ( ), test areas for site evaluation (white), stands of block design (greyscales), and other research plots ( ) 36 Martin Jansen, Michael Bredemeier 3 Long-term research plots Initially, the scientific approach at the long-term research plots in the mature pure beech and spruce stands was measurement of ambient matter and energy transfers at the entire forest ecosystem level. In the 1960s, when the measurements started, this methodology was absolutely novel. Now, over three decades later, the same methods are used in routine monitoring of forest ecosystems in many countries worldwide, e.g., the European Level-II monitoring network (MEESENBURG et al. 2002). However, since Solling was among the first places where they were developed and employed, no other location has such a long and continuous record of biogeochemical fluxes in a forest ecosystem. For measurement of liquid phase fluxes, precipitation collectors were installed inside and outside the forest, and porous suction cup or plate lysimeters were bedded in the soil at various depths. While in this way aboveground fluxes of water and dissolved constituents could be quantified directly per unit area (on the basis of the samplers’ surface area), soil water fluxes had to be assessed by model calculation, and the values obtained were then multiplied with the concentrations found in the lysimeter samples at the respective soil depths to provide chemical fluxes. The models used for soil water flux calculation are based on the Darcy or Richards equation for unsaturated flow in porous media. Detailed descriptions of the methodology can be found in (HAUHS 1985; SCHMIDT 1993; SCHMIDT 1997; XU et al. 1998). The first results from the biogeochemical flux investigations came as quite a surprise to the scientists at that time. Instead of the expected pristine environmental conditions the analyses of throughfall and soil solution revealed that these media were highly acidic. Furthermore, a large surplus of acidity and pollutants in throughfall and beech stemflow compared to open land precipitation was detected, indicating a high filtering efficiency of the forest vegetation surfaces for air pollutants, which in turn increased the input of these constituents to the forest soil. Throughfall Solling Spruce (F1) 120 100 80 -1 · a -1 60 kg · ha 40 20 0 year 69 71 73 75 77 79 81 83 85 87 89 91 93 95 97 99 SO4-S NH4-N + NO3-N Fig. 3. Time courses of annual throughfall fluxes of sulphate-S and inorganic N in an old growth spruce forest at Solling (stand age 2004 = 120 y) For. Snow Landsc. Res. 78, 1/2 (2004) 37 On the basis of these findings, the chief scientist in charge of the biogeochemical investi-

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