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 moun- tains, 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- gations at the time, Bernhard Ulrich, postulated a destabilisation of the forest ecosystem on naturally poor soil substrates as in Solling due to excessive acidification of the soil (ULRICH 1972; ULRICH et al. 1979). This hypothesis was first much questioned and criticised, but from the beginning of the 1980s on, when large-scale forest damage spread in several consecutive waves over Germany, it became the basis of extensive forest decline research. The long extension of the Solling flux data time series is extremely valueable since it facilitates the recognition of long-term trends in environmental pollution with adequate confidence. Figure 3 shows the time courses of sulphate-S and inorganic nitrogen flux rates in throughfall of the F1 spruce forest. It can be seen that, when Ulrich postulated critical forest soil acidification and ecosystem destabilisation in the mid-1970s, sulphur input rates were in fact higher than 100 kg · ha-1 · a-1 for several years of observation. From that time on, however, a strong and continuous decline can be discerned in the sulphur input time series, with annual rates below 20 kg · ha-1 · a-1 in the most recent years. This tremendous change was brought about by several steps of clean air legislation in Germany, which was in turn fostered and scientifically supported by the results of forest ecosystem research. Figure 3 also contains the inorganic nitrogen fluxes in the spruce forest throughfall. No continuous or strong trends can be discerned here.The forest ecosystem still receives nitrogen inputs in excess of the annual requirement for permanent storage in biomass increment (which amounts to about 10 kg · ha-1 · a-1,BREDEMEIER et al. 1990). The excess nitrogen is partly stored in an accumulating humus layer, and partly lost as nitrate in seepage water.The reason why sulphur emmissions were cut back so efficiently and nitrogen was not, results from the different nature of the sources of the two constituents.While most sulphur emissions stem from few large sources such as power plants and large industrial facilities, where filters were installed, most of the nitrogen stems from either vehicles (oxidized N) or agriculture (reduced N). To tackle the former, catalytic converters were introduced as standard equip- ment in new cars, while hardly any control has so far been exerted over the latter. Only very recently has forest ecosystem research highlighted a potential problem brought about by reductions of atmospheric deposition. This concern can again be demon- strated very clearly on the basis of the long-term time series from Solling (Fig. 4). As a matter of fact, the input flux rates of nutrient cations decrease over time parallel to decreas-
45 40 35 30
-1 25 20 kg x ha 15 10 5 0 68 70 72 74 76 78 80 82 84 86 88 90 92 94 96 98 2000
Mg Ca
Fig. 4. Time courses of annual throughfall fluxes of calcium and magnesium in an old growth spruce for- est at Solling (stand age 2004 = 120 y). 38 Martin Jansen, Michael Bredemeier es of acidifying pollutants, since the cations originated largely from the same sources (dusts and fly ashes of power plants and industries). The strong decline of calcium and magnesium inputs may pose a serious problem to forest nutrition on acidified soils in the long run, since in such soils these nutrients are particularly scarce. There are first reports in the literature of apparent deficiency in response to lowered inputs (GULPEN and FEGER 1998). These findings support the argument to continue compensatory liming of acidified forest soils (BREDEMEIER 2002a; BREDEMEIER 2002b). The Solling long-term sites are patch scale studies, which means that the particular process rates quantified there apply in a strict sense only to that very patch where they were measured. An extrapolation to the forest landscape scale (regionalization) was a task to be undertaken in a later period of forest ecosystem research (see below).
4 Roof experiments
While the research program at the long-term sites at Solling was largely confined to measurements in unchanged, ambient forests, the roof experiments represent a further step in the methodology of forest ecosystem research, comprising experimental manipulation of hydrological and biogeochemical fluxes. The Solling roof facility and its experimental setup is described in detail elsewhere (BREDEMEIER 1995; BREDEMEIER et al. 1998a). In this paper, we only very briefly describe the installations, focus on some key results and indicate the general role that the roof experiments played in the integrated forest ecosystem research at Solling. The roof facility is depicted in the sketch in Figure 5. It consists of three roof construc- tions of 300 m2 surface area each underneath the canopy of a pure Norway spruce stand.The roofs are covered with plates of highly transparent polycarbonate. All throughfall reaching
gondola
D2 D1 D3
storage tanks
central cabin
Fig. 5. Sketch of the facili- ties at the Solling roof proj- ect (drawing: R. Grote). For. Snow Landsc. Res. 78, 1/2 (2004) 39 the roof surfaces is directed towards the central cabin, where part of the water is redistrib- uted to the plots by a sprinkler system, and another part is de-ionised and then re-supplied with elements in concentrations representing an average background (pre-industrial) throughfall (clean rain plot “D1”, in the foreground of the sketch in Fig. 5). Litterfall on the roofs and organic debris retained in the filters of the gutters is periodically redistributed onto the soil surface underneath the respective roofs in order to maintain the internal cycle of nutrients in the solid phase.The area underneath the roofs is intensively equipped with all kinds of samplers and sensors, such as lysimeters for soil water sampling at five different depths and continuously recording tensiometers for soil water potential determination at the same depths. There are also root observation pits from which endoscopes can be intro- duced in perspex tubes into the soil and permanent soil biota monitoring plots. The crane in the centre of the facility is equipped with a gondola for transportation of up to two people and instruments for physiological and growth measurements in the canopy, where all the trees of the roofed areas and many control trees outside the roofs can be reached. While on one of the roof plots the clean rain experiment was performed, a second one hosted a drought/rewetting experiment to investigate the possible biogeochemical and physiological effects of augmenting weather extremes in the context of climatic change (LAMERSDORF et al. 1998a; LAMERSDORF et al. 1998b). The third roof in the array served as a control for roof effects alone, without further manipulation. Here, the water was immedi- ately re-sprinkled to the plot, without changing chemistry, amount or temporal distribution. The set of three roofs was completed by an unroofed ambient control plot, which was other- wise equipped in the same way as the roof plots. A highlight of the results from the Solling roof study was the time-lagged responses of the different ecosystem components to the decreased soil input fluxes brought about by clean rain application (TIETEMA et al. 1995; BREDEMEIER et al. 1998a; BREDEMEIER et al. 1998b). Soil solution chemistry responded rapidly to decreased input concentrations, particularly in the uppermost soil where less of the previously stored sulphates are available to counteract the dilution. But also at greater soil depths, decreases in concentrations soon became evident. Nitrate leaching ceased completely under reduced N inputs after weeks in the top soil and after several months in the deeper soil (Fig. 6). The quick and clear responses of soil water chemistry to the experimental manipulation were at first not reflected in the biological components of the forest ecosystem. But after
7 Nitrate-N 10 cm 6
5 Nitrate-N 100 cm 4 Aluminium-N 10 cm [mg/l] 3
2
1
0 Oct-89 Oct-90 Oct-91 Oct-92 Sept-93 Oct-94 Oct-95 Oct-96 Nov-97 Nov-98 Mar-01 Mar-02
Date
Fig. 6.Time courses of nitrate-N at 10 and 100 cm soil depth and aluminium at 10 cm. Begin of clean rain manipulation was in October 1991. 40 Martin Jansen, Michael Bredemeier about two to three years, the fine-roots in the soil started to respond by an increased living biomass and improved morphology (MURACH and BREDEMEIER 1999). This improvement in the fine-root vitality has been sustained until today. It can be interpreted as a reaction to decreased acidity stress, or to a decreased availability of dissolved organic nitrogen, or both (BREDEMEIER et al. 1998a; LAMERSDORF and BORKEN 2004).The aboveground parts of the trees in terms of growth, physiological parameters, and apparent vitality status, have not responded in a clear pattern so far. Hence, the overall result from this experimentation is that acidification of forest soils and nitrate leaching can be efficiently decreased under reduced anthropogenic atmospheric inputs. In this process, the soil solution as an abiotic equilibrium component responds fastest (while the soil solid phase due to its high stocks of previously stored acidity changes much slower). The fine-roots, in intimate contact with the soil water, respond to their changed chemical environment with a time lag, which is a quite common feature in biological systems in general. Aboveground physiology and growth are again buffered and delayed against these changes in the root zone and respond strongly delayed, if at all. The overall picture thus shows a potential of recovery, but with cascaded temporal buffers between the different ecosystem components. This buffered cascade of responses probably works both ways, under acidification as well as under de-acidification as in the clean rain experiment at Solling. The roof study can be regarded as an advance to new methodologies in forest ecosystem research at Solling. However, it is still a process study at the plot scale (at a very high level of intensity). The next step to take was to extrapolate the knowledge gained from plot level to the entire forested landscape.
5 Forest landscape research
Plot experiments are necessary to increase our knowledge about ecosystem processes and the impacts of natural and anthropogenic disturbances, as outlined above. However, the high levels of effort and investment connected to these investigations allow only the establishment of a small number of case studies. In Lower Saxony, only 8 plots are intensively monitored according to the LEVEL-II program (MEESENBURG et al. 2002). Therefore, a statistical analysis and interpretation of results from such studies is only possible on a broader scale like Europe (DISE et al. 1998; DE VRIES et al. 2002; LANGUSCH et al. 2003). Another specificity of the case studies F1, B1 and “roof” is that they are excluded from normal forest management. No usual forestry measures such as thinning and harvesting have taken place since their establishment in 1967 and 1971. Therefore the spatial, vertical and horizontal distribution of trees, their growth development and ecological impacts like light regime or temperature distribution are not comparable to common forest stands in the Solling area (MEYER et al. 2003). Moreover, LEVEL-II plots and case studies were fenced to prohibit the entrance for unauthorized people and wild animals in order to protect the experimental equipment. But the fences influence the ecological development on the plots, for example by the exclusion of megaherbivores like red deer, which occur in high densities in the Solling area. Another limitation of the traditional case studies in the Solling area is the experimental design was restricted to pure stands of spruce and beech only. However, because of the eco- logical and economic problems of pure coniferous stands during the last 100 years and the low value of these stands for nature conservation, the forest administrations nowadays favour mixed stands of coniferous and deciduous trees for future planning. For Lower For. Snow Landsc. Res. 78, 1/2 (2004) 41
Saxony the state government passed a bill in 1992 called LÖWE (Long term ecological forest development, OTTO 1989; OTTO 1991; NMELF 1992), which aims to reduce the proportion of coniferous trees in the state forest of Lower Saxony from about 70% to 30%. Summing up the limitations of the plot studies, it is obvious that the transfer of their results to managed forest sites is limited. A gap exists between the scientific knowledge for the plots (F1, B1, “roof”) and for neighbouring stands, which undergo regular forest management. The information available for these stands concerning soil, climate, floristic, and faunistic elements is restricted to the coarse mapping of site evaluation and forest management data. In the 3rd research phase (Fig. 1) the Forest Ecosystems Research Centre aims to close this information gap between case studies and managed forest stands and to develop a link between the different scales. In order to develop “indicators and strategies for a sustainable forest management”, a landscape approach was chosen to transfer ecological information and to improve the spatial database on forest stands.
5.1 Experimental design
The experimental design of the landscape approach was based on two elements:
5.1.1 Randomized block design To investigate the influence of mixed stands on biodiversity and ecosystem functioning, a block design experiment was established in the Solling area (see Fig. 2). Neighbouring forest stands of similar characteristics (soil type, elevation, slope etc.) and different tree species composition in the same age class were selected. The stand types were pure spruce (>90%), pure beech (>90%), and beech/spruce mixed stands with dominating spruce (70%), dominating beech (70%) and almost equal proportions (50%). Preferential mixing type was a single tree or tree group mixture. The age classes were 30–60 years (young), 60–100 years (intermediate), and >100 years (old). Eight suitable blocks were established in 1999 (3 old, 3 intermediate, 2 young blocks).
5.1.2 Grid of 100 m · 100 m The whole Solling area was covered with a regular grid of 100 m · 100 m. The experimental grid is identical with the official forest inventory grid of the Lower Saxony forest adminis- tration. Experiments were to be placed on the points of this universal grid if practicable. The proposed experimental design and integrated analyses were realized with a strong and powerful Geographic Information System (GIS), containing the basic information of forest inventory, site evaluation, geological maps, digital elevation model, climatic maps, orthophotos etc. (DÖRING et al. 2002). The forest stands of the block design were identified with special database queries. In addition the areas for climatic research, assessment of wind throw risk, and nutrient element budgets were stratified by the digital geographic data base.
5.2 Results
Three different approaches are presented as an example of results for the biotic function of forest ecosystems: 1) Measurements of species diversity of understory vegetation in the areas of block design 2) Modelling tree species and stand type diversity 3) Wind throw risk 42 Martin Jansen, Michael Bredemeier
5.2.1 Diversity of understory vegetation The herb layer of forests reacts very differently to nutrient and water availability and changes of environmental conditions like climate change or canopy closure (e.g. SCHMIDT 1999; ELLENBERG 1996). One of the main hypotheses of the project was that mixed stands have higher species number (α-diversity) in the herb and moss layer than pure stands. The investigations were carried out on 100 m2 plots in the areas of the block design. A detailed description of the results can be found in SCHMIDT and WECKESSER (2002) and WECKESSER (2003). The lowest species number of herbs and mosses was found in pure beech forests of the Luzulo-Fagetum (Fig. 7). The species composition in pure beech forests showed the highest amount of characteristic plants of deciduous forests (Fig. 8), typical for this most important natural woodland community of the Solling mountains (GERLACH 1970). With an increasing amount of spruce, which is not part of the natural woodland communities in the Solling mountains, the number of species in the herb and moss layer increased. This was true for the plots in both younger and older stands. The highest number of species was found in the old pure spruce stands. The plant sociological characteristic showed a strong shift in species composition. Even a low amount of spruce in the tree layer reduces the abundance of typical species of deciduous forest in favour of species from coniferous forest and grassland, as well as indifferent species. Mixed stands of spruce and beech were closer related to the pure spruce stands than to the pure beech stands concerning the abundance of species in the herb and moss layer. Probably, the reasons for these results are the changing micro- and mesoclimatic con- ditions within the stands, mainly the light regime. Pure beech stands tend to develop closed canopies, strongly shading the forest floor. Spruce stands, especially old stands, are often damaged by stem rot or wind throw, enabling more light to penetrate the canopy and thus foster the appearance of grassland and ruderal species.
herb layer moss layer n=87/32 50/21 38/60 29/27 34/32 35/15 46/68 n=87/32 50/21 38/60 29/27 34/32 35/15 46/68 35 35
30 30 2 25 25
20 20
15 15
10 10
number of species/100 m 5 5
0 0
h S S S B B ce h S S S B B ce c > > = > u c > > = > > u ee > B B S >> ee > B B S > r b B d d d S pr b B d d d S p e d e e e d s e d e e e d s r e ix ix ix e re r e ix ix ix e re u ix m m m ix u u ix m m m ix u p m m p p m m p
stands > 90 years stands < 80 years
Fig. 7. Species number of herb and moss layer in beech-spruce mixed forests and pure stands in the Solling mountains. Evaluation of 100 m2 plots (median, 10th,25th,75th, and 90th percentile). Samples from mixed stands were divided into five classes representing different proportions of beech and spruce (from SCHMIDT and WECKESSER 2002, mod.). For. Snow Landsc. Res. 78, 1/2 (2004) 43
The interpretation of the results has to be differentiated. The number of species and derived indicators like Shannon or Simpson index alone are not appropriate for the assess- ment of forest stands with respect to biodiversity.They have to be discussed in the context of naturalness and their relevance for nature conservation. The increase of species numbers is clearly related to a decrease in naturalness of the stands. Additional herb species occurring in mixed stands or spruce stands are of minor relevance for nature conservation. They often represent non-forest species and indicate the anthropogenic disturbance of the system; see also V.OHEIMB et al. (1999), SCHMIDT (1999), JENSSEN and HOFMANN (2002).
100 other species 90 80 indifferent 70 ruderal 60 50 grassland 40
% of abundance forest clearing 30 20 deciduous forest 10 coniferous forest 0 pure beechmixed stands pure spruce
Fig. 8. Plant sociological behaviour of herb layer species in pure and mixed stands of beech and spruce (older than 90 years) in the Solling mountains. Frequencies of species out of a total of 319 sample plots (100 m2 from SCHMIDT and WECKESSER 2002, mod.).
5.2.2 Trees species and stand type diversity In addition to the measurements of floristic diversity in the block areas, calculations of elements of biotic and economic functions were carried out at the landscape level. The main objective was to compare different silvicultural strategies according to their fulfilment of different forest functions. The data base for these calculations was derived from forest planning data. We calculated the α-diversity for the tree layer from tree parameters (species, age) for every forest stand in the Solling mountains according to the areal percent of the parameters (BÖHL 2001). This is the same concept as used for herb and moss layers. The α-diversity describes neighbourhood stand diversity and is based on the stand types of the neighbouring management units of a certain stand. According to the length of the boundary line of neighbouring stands, the Shannon or Simpson Index can be calculated for every management unit. Figure 9 shows on the left side a forest stand with neighbouring stands of the same stand type and therefore a lower Shannon-Index. On the right side the same stand is surrounded by different stand types, which results in a higher Shannon-Index. The present situation in the Solling area is characterized by a high amount of pure stands with low mean tree diversity (Shannon = 0.45) and age diversity (0.39) at the stand level (HILDEBRAND 2001). In contrast the β-Diversity showed high values (Fig. 10) indicating a highly variable mosaic of stand types. Fig. 10. Spatial representation of Simpson Index for present state stand type distribution according to the LÖWE-pro- gram. Fig. 9. of examples Theoretical of calculating stand diversity No 1. neighbourhoods for stand Martin Jansen,Martin Bredemeier Michael 6 7 5 8 1 9 4 3
2
2002).All older than spruce stands in the Solling mountains EDDE 6 7 5 8 1 9 4 3 Shannon = 0Shannon = 0Simpson = Shannon = 1.3 0.7 Simpson = 0–0.2 0.2–0.4 0.4–0.6 0.6–0.8 0.8–1 2 Within project phase 3 (see Fig. project phase Within 1) a study has been established to quantify wind throw Simpson-Index 5.2.3 risk throw Wind guideline, LÖWE The aims to achieve the large scale conversion of pure spruce stands into clearcutting.mixed stands of beech and spruce without favours management strategy The from old pure to mixed stand types.target diameter harvesting for the transition Target risk,diameter harvesting increases wind throw because the stability of the stand is probably reduced by harvesting the tallest trees with maximum diameter and best stability. risk for the Solling area (R 44 60 years were selected in the GIS, except stands on sites with impeded drainage. Based on the 100 m · 100 m grid, about 700 sample plots were stratified in the GIS for the selected 4000 ha of old spruce stands.were established in stands with hundred sample plots Four known wind throw (stratified sample plots), and 300 were set randomly. Soil characteristics like soil horizons and texture were examined as well as tree parameters like height, breast height diameter, and stem rot in a 7 m radius.A wind model and root excavations completed the data. For. Snow Landsc. Res. 78, 1/2 (2004) 45
The clay content in the upper soil layer significantly increased the probability of wind damage in the Solling mountains. Only 20% of the sample plots with low clay content (5–10%) showed wind damage in the stratified sample plots (Fig. 11; left). In the random set only 10% of the sample plots were affected. In both strata the frequencies of damages increased significantly with increasing clay content in the upper soil horizons. Clay contents of 15–20% lead to a probability of wind damage of 40 to 50%. Not only does the probability of damage increase with increasing clay content, but also the intensity of the damage as well (Fig. 11; right). Plots with clay contents below 10% showed little damage. More than 70% of the sample plots were in the two lowest damage classes 0.1 and 0.3. In contrast, if the clay content in the upper soil was above 20%, 35% of the sample plots had lost all trees, and on about 40% of the sample plots more than 80% of the trees had fallen. It is possible that the higher wind throw risk on soils with high clay content is caused by changes to the root system. Root excavations show that the anchoring of the trees in clay soils is not as strong as it is in soils with low clay content (REDDE 2002). Based on this statistical evaluation, recommendations can be given for the wind throw risk following a conversion of old spruce stands in the Solling mountains, as well as for the establishment of spruce in the next stand generation.
60 n=124 50 50 n=106 40 40 n=118 30 30 n=216 n=81 20 20 n=102 sample plots [%] 10 10
sample plots with wind damage [%] 0 0 5–10 10–15 15–20 0.1 0.3 0. 5 0.7 0.9 total clay [%] wind damages [%] stratified sample plot clay<10% random sample plot clay>20%
Fig. 11. Left: Relative frequencies of sample plots with wind damage affected by different clay content of the upper soil layer. Right: Degree of wind damages affected by different clay content of the upper soil layer (from REDDE 2002, mod.).
5.3 Integration of experiments at the forest landscape level
One of the main objectives of the 3rd phase was to integrate the results at the forest landscape level. Methods of regionalization and spatial modelling are helpful to provide informations at the level of forest management (JANSEN et al. 2002a). For example, climatic elements like monthly mean temperature and precipitation were regionalized for sloping landscapes of southern Lower Saxony, including the Solling moun- tains (MUES 2000; MUES et al. 2002). JUDAS and SCHAEFER (2002) showed for a 400 ha beech forest in the same area that the spatial distribution of carabid species was governed by moisture and temperature gradients. Soil chemical characteristics were predicted for regions of the Black Forest (ZIRLEWAGEN 2003) or forest soils in Austria (LEXER et al. 1999). In 46 Martin Jansen, Michael Bredemeier contrast, prediction attempts for the Solling or the Harz mountains failed, because the statistical models show only weak correlations between the soil chemical variables and the predictor variables derived from a DEM, site evaluation, and geology (JANSEN et al. 2002b). For the landscape of the Solling mountains we derived different indicators to assess the present state of the forest landscape and to analyze the consequences of strategic forest management decisions. Indicators were defined in compliance with the Ministerial Conference on the Protection of Forests in Europe as quantitative measures for the charac- teristic quality of forest functions. In the first step, spatially explicit indicators for biotic and economic forest functions were established. The naturalness of a forest landscape was derived from a model of natural woodland communities (NWC). Tabulated assignment of NWC to growth districts, geomorphological variables and site types of the forest site evaluation are important for the spatial prediction (JANSEN et al. 2002c). Naturalness was calculated by the comparison of tree composition of current management units with the modelled tree composition of the NWC for the same stand. In addition to diversity indices on the stand level and neighbourhood diversity indices, a third class of quantitative measures for diversity of forest landscapes can be calculated from the geometry of areas (DIAZ 1996; TURNER et al. 2003). The usefulness of these indices to describe changing landscape patterns caused by deforestation or fragmentation has been discussed by FITZSIMMONS (2003) and RICOTTA et al. (2003).
Table 1: Spatial indicators for biotic and economic functions of the Solling mountains. function aspect indicators biotic naturalness • amount of tree species from natural woodland communities diversity • tree species within the stand: Shannon, Simpson etc.. • neighbourhood of stand types: Shannon, Simpson, etc. • area diversity: contagion, core areas, maximum area, etc. economic sustainable • economic yield revenue
The assessment of forest landscapes is not restricted to the present state of the stand type pattern. Spatial simulation and scenarios of future stand type distribution support the analysis of consequences of strategic management decisions (VARMA et al. 2000; JANSEN et al. 2002d; PENNANEN and KUULUVAINEN 2002; SEELY et al. 2002). For the Solling mountains, a GIS-based scenario was calculated according to the manage- ment strategy of the LÖWE-program of the forest administration. Therefore, future stand types (Waldentwicklungstypen, WET) were assigned to site evaluation data. Information about young growth was included by the selection of WET. Special rules concerning the maintenance of deciduous forest types were considered in the system as well as preferential areas for stands with tree composition similar to the potential natural vegetation (PNV). The comparison of the percent area of the future scenario with the present stand type distribution shows a distinct shift towards deciduous trees in the future. Most spruce stands will be replaced by mixed forest stands of beech and spruce, whereas the amount of oak For. Snow Landsc. Res. 78, 1/2 (2004) 47
PNV
Dougl.
Spruce/Conif.
Spruce/Decid.
Dlrp
Dsrp
Beech/Conif.
Beech/Decid.
Oak
0 10 20 30 40 50 60 area [%]
present state WET LÖWE
Fig. 12. Percent area of present stand type distribution compared to a scenario of the future distribution of Waldentwicklungstypen (WET) according to the LÖWE-program of the forest administration of Lower Saxony. Dlrp: Deciduous trees with long rotation period (e.g. ash, maple); Dsrp: Deciduous trees with short rotation period (e.g. alder, birch).
stands remains constant. Percent area of deciduous trees with a long rotation period (e.g. ash, maple) or short rotation period (e.g. elder, birch) increase slightly. Based on maps of different spatial and temporal scales, it is possible to compare the results of long term planning in a spatially explicit way. Furthermore, it is possible to assess target stand type distributions by suitable indicators for different forest functions, such as diversity indices on a landscape scale, the naturalness of the vegetation, as well as economic indicators such as economic yield. Decisions about possible silvicultural strategies will there- fore be based on quantitative descriptions of multifunctionality. For the present scenario of the LÖWE-program it can be stated that because of the higher proportion of beech for the Solling area, the naturalness at stand level increases. The α-diversity also increases because the area percent of mixed stands is extended. Because of the dominating effect of a single WET (beech-spruce mixed forest), however, β-diversity at the landscape level decreases because only few stand types were planned in this area. The patches of different stand types are replaced by homogeneous areas of the same stand type (Fig. 13). The frequency distribution of Shannon- and Simpson-Index shows a distinct shift towards lower values. On the other hand, the practical conversion and application of a chosen strategy by forest management can be assisted by maps from the simulation system at the regional and local scale. Regional maps of long-term development can be helpful for optimizing the regional application of overall silvicultural strategies. Maps on the local scale are a supportive prep- aration for short term practical management decisions, e.g. the 10-year forest planning cycles. 48 Martin Jansen, Michael Bredemeier
Fig. 13. Spatial distribution of Waldentwicklungstypen (WET, stand development types) according to the LÖWE-program.
6 Conclusions
Solling was one of a small number of locations in the world where modern integrated inter- disciplinary ecosystem research was developed. With respect to biogeochemical flux records and budget datasets in forests it holds the longest complete time series worldwide. The pioneering research on element deposition to the forest soils revealed – in contrast to the initial expectations – that in spite of its remote location the Solling forest is subject to considerable inputs of air pollutants from long range transport originating from distant industrial areas to the east and to the west. In the 1970s, the scientists in charge of the biogeochemical studies postulated a destabilisation of the ecosystems owing to severe acidification of the soils by strong mineral acids from atmospheric deposition. In the following decade, the 1980s, widespread forest damage actually occurred in Germany at exposed sites, particularly in the intermediate mountain ranges. Following this development, forest eco- system research was intensified to assess consequences and perspectives, and air pollution legislation measures were taken to reduce emissions. Today, another 20 years later, it can be For. Snow Landsc. Res. 78, 1/2 (2004) 49 stated that these measures were successful with respect to the initiation of recovery from acidification. The issue of excess atmospheric nitrogen input to forest ecosystems, on the other hand, could not be solved so far. New problems with forest nutrition may arise from the decreases in base cation inputs, which occurred parallel to the reduction in acid depo- sition. To counteract such potential problems in the future, compensatory liming of acid forest soils with dolomitic substrates should be continued (besides of other desired effects from liming). Forest ecosystem research at Solling was interdisciplinary from the beginning. The inter- disciplinary approach was intensified and extended in a new generation of ecosystem manipulation experiments by roof installations from the 1990s on. The results from the Solling roof project, also in connection with European partner projects, allowed for a much improved quantification of biogeochemical process rates and better calibration of forest ecosystem process models. The successful analysis of ecosystem processes at Solling was feasible only on the basis of interdisciplinary collaboration and integration of single scientific disciplines such as soil science, zoology, botany and climatology. Particularly the crucial interfaces soil/plant and plant/atmosphere demanded for an interdisciplinary approach, in order to describe a com- prehensive set of system-related processes and their rates on the basis of the intensively investigated plot case studies. The extrapolation from those studies to the bulk of “normal”, regularly managed stands in the forest landscape required a new methodological orientation. Inventories with high density of sampling points for spatial representativeness but much lower intensity of measurements at the single point were needed in order to facilitate good regionalisation. However, the “old” methods which were developed in the intensive plot studies are still applied – with reduced intensity – in the new landscape-oriented approach (e.g., inventories of soil biota and ground vegetation as well as soil nutrient inventory and acidification status). New tools for analysis on the landscape scale are geographical information systems (GIS), which allow for spatial integration of all observations performed. Furthermore, they are the interface between the base data layers from the forest administration (e.g., site mapping, forest planning) and the scientific information added from ecosystem research. The GIS interface facilitates integration of the ecological knowledge base into practical forest management strategies. The expansion of scale from plot to forest landscape went parallel to a modification of scope of the investigations. Besides of continued measurements on biogeochemical dynamics, sustainable multi-functionality of forest management was emphasized more strongly (i.e., the ecosystem- and landscape level consequences of different forest management options). Example topics in this regard are biodiversity in pure and mixed forest stands or the risk of wind throw in differently structured stands. This research addresses an actual change of paradigm in German forest management, where since the 1980s conversion of monoculture forest to mixed stands increasingly is a silvicultural goal of the public forest administrations.
Acknowledgements Forest Ecosystem Research at Solling was and is funded by the German Federal Ministry of Education and Research (BMBF), the German Research Foundation (DFG), and the European Commission, Directorate for Research and Technology (EU-DGXII). 50 Martin Jansen, Michael Bredemeier
7 References
BÖHL, J., 2001: Dynamik der Waldstrukturdiversität. Masterarbeit Forstliche Fakultät, Universität Göttingen, 65 pp. BREDEMEIER, M., 1995: Experimental manipulations of the water and nutrient cycles in forest ecosystems (patch scale roof experiments EXMAN). Agric. For. Meteorol. 73: 307–320. BREDEMEIER, M., 2002a: Anthropogenic effects on forest ecosystems at various spatio-temporal scales. The Scientific World Journal 2: 827–841. BREDEMEIER, M., 2002b: Nachhaltigkeit der Regelungsfunktion von Waldböden – Kriterien und Indikatoren. In:Tagung “Wald und Boden”. Berichte des Forschungszentrums Waldökosysteme der Universität Göttingen B 65: 10–16. BREDEMEIER, M.; BLANCK, K.; DOHRENBUSCH, A.; LAMERSDORF, N.; MEYER, A.C.; MURACH, D.; PARTH,A;XU, Y.-J., 1998a: The Solling Roof Project – Site Characteristics, Experiments and Results. For. Ecol. Manage. 101: 281–293. BREDEMEIER, M.; BLANCK, K.; XU,Y.-J.; TIETEMA, A.; BOXMAN, A.W.; EMMETT, B.A.; MOLDAN, F.; G UNDERSEN, P.; SCHLEPPI, P.;WRIGHT, R.F., 1998b: Input-output budgets at the NITREX sites. For. Ecol. Manage. 101: 57–64. BREDEMEIER, M., MATZNER, E., ULRICH, B., 1990: Internal and external proton load to forest soils in northern Germany. J. Environ. Qual. 19: 469–477. DIAZ, N.M., 1996: Landscapes Metrics. A new tool for forest ecologists. J. For. 94, 12: 12–16. DISE, N.B.; MATZNER, E.; GUNDERSON, P., 1998: Synthesis of nitrogen pools and fluxes from European forest ecosystems. Water Air Soil Pollut. 105: 143–154. DÖRING, C.; JANSEN, M.; HENTSCHEL, S.; SLOBODA B., 2002: Der Einsatz forstlicher Geo- informationssysteme in der ökologischen Forschung am Beispiel der Fallstudie “Waldland- schaft Solling”. Dt. Verband Forstl. Versuchsanstalten, Sektion Forstliche Biometrie und Informatik 14. Tagung, Tharandt, 2002. 34–44. ELLENBERG, H., 1972: Integrated experimental ecology: methods and results of ecosystem research in the German Solling Project. Berlin, Heidelberg, New York, Springer. ELLENBERG, H., 1986: Ökosystemforschung: Ergebnisse des Sollingprojekts 1966–1986, Stuttgart, Eugen Ulmer. ELLENBERG, H., 1996: Vegetation Mitteleuropas mit den Alpen in ökologischer, dynamischer und historischer Sicht. Stuttgart, Verlag Eugen Ulmer. 1095 pp. FITZSIMMONS, M., 2003: Effects of deforestation and reforestation on landscape spatial structure in boreal Saskatchewan, Canada. For. Ecol. Manage.174: 577–592. FÖRSTER, M., 2002: 1500 Jahre Waldnutzung im Solling und ihre Auswirkungen auf Wald und Boden. In: BLANCK, K. (ed) Tagung “Wald und Boden” in Göttingen, 18. und 19. Oktober 2001, Berichte des Forschungszentrums Waldökosysteme der Universität Göttingen B 65: 27–37. GERLACH, A., 1970: Wald- und Forstgesellschaften im Solling. Schriftenr. Veg.kd. 5: 79–98. GULPEN, M.; FEGER, K.H., 1998: Magnesium and calcium nutrition of spruce on high altitude sites – yellowing status and effects of fertilizer application. Z. Pflanzenernähr. Bodenkd. 161: 671–679. HAUHS, M., 1985: Wasser- und Stoffhaushalt im Einzugsgebiet der Langen Bramke (Harz). Berichte des Forschungszentrums Waldökosysteme der Universität Göttingen A 17: 1–206. HILDEBRANDT, T., 2001: Vergleichende Diversitäts- und Strukturanalyse der Waldlandschaft Solling und der Lüneburger Heide. Diplomarbeit, Universität Kiel, 70 pp. JANSEN, M.; JUDAS, M.; SABOROWSKI J., 2002a: Spatial modelling in Forest Ecology and Management - A case study. Berlin, Heidelberg, New York, Springer. 225 pp. JANSEN, M.; EBERL, C.; BEESE F., 2002b: Regionalization of soil chemical variables in the Harz mountains. In: JANSEN, M.; JUDAS, M.; SABOROWSKI J. (eds) Spatial modelling in forest ecolo- gy and management – A case study. Berlin, Heidelberg, New York, Springer. 68–86. JANSEN, M.; SCHMIDT, W.; STÜBER, V.;WACHTER, H.; NAEDER, K.; WECKESSER, M.; KNAUFT F.J., 2002c: Modelling of natural woodland communities in the Harz mountains. In: JANSEN, M.; JUDAS, M.; SABOROWSKI J. (eds) Spatial modelling in forest ecology and management – A case study. Berlin, Heidelberg, New York, Springer. 162–175. For. Snow Landsc. Res. 78, 1/2 (2004) 51
JANSEN, M.; SCHULZ, R.; KONITZER A.; SLOBODA B., 2002d: Scenarios of long-term forest stand development in the Harz mountains. In: JANSEN, M.; JUDAS, M.; SABOROWSKI J. (eds) Spatial modelling in forest ecology and management – A case study. Berlin, Heidelberg, New York, Springer. 177–193. JENSSEN, M.; HOFMANN, G., 2002: Pflanzenartenvielfalt, Naturnähe und ökologischer Waldumbau. Allg. Forst Z. Waldwirtsch. Umweltvorsorge. 402–404. JUDAS, M.; SCHAEFER, M., 2002: Regionalization of macrofauna populations. In: JANSEN, M.; JUDAS, M.; SABOROWSKI J. (eds) Spatial modelling in forest ecology and management – A case study. Berlin, Heidelberg, New York, Springer. 87–110. LAMERSDORF, N.; BORKEN, W., 2004: Clean rain promotes fine root growth and soil respiration in a Norway spruce stand. Glob. Chang. Biol. (in press). LAMERSDORF, N.; BEIER, C.; BLANCK, K.; BREDEMEIER, M.; CUMMINS, T.; FARRELL, E.P.; KREUTZER, K.; RASMUSSEN, L.; RYAN, M.; WEIS, W.; XU, Y.-J., 1998a: Effect of drought experiments using roof installations on acidification / nitrification of soils. For. Ecol. Manage. 101: 96–109. LAMERSDORF, N.; BLANCK, K.; BREDEMEIER, M.; XU, Y.-J., 1998b: Drought experiments within the Solling roof project. Chemosphere 36: 1161–1166. LANGUSCH, J.J.; BORKEN, W.;ARMBRUSTER, M.; DISE, N.B.; MATZNER E., 2003: Canopy leaching of cations in Central European forest ecosystems – a regional assessment. Z. Pflanzenernähr. Bodenkd. 166: 168–174. LEXER M.J.; HÖNNINGER,K;ENGLISCH M., 1999: Schätzung von chemischen Bodenparametern für Waldstandorte am Beispiel der Österreichischen Waldinventur. Forstwiss. Cent.bl. 118: 212–227. MEESENBURG, H.; SCHULZE, A.; MEIWES K.J., 2002: Dauerbeobachtung von Waldböden als integraler Bestandteil des forstlichen Umweltmonitorings in Niedersachsen. UBA-Texte 66/02, Boden-Dauerbeobachtung in Deutschland: Ergebnisse aus den Ländern. 55–65. MEYER, P.; VATH, T.; LÜPKE,B.VON, 2003: Die Struktur albanischer Rotbuchen-Urwälder – Ableitungen für eine naturnahe Buchenwirtschaft. Forstwiss. Central.bl. 122: 47–58. MUES, V., 2000: GIS-Gestützte Regionalisierung von Klima- und Depositionsdaten in Nieder- sachsen. Dissertation Forstliche Fakultät, Universität Göttingen,
REDDE, N., 2002: Risiko von Sturm und Folgeschäden in Abhängigkeit vom Standort und von waldbaulichen Eingriffen bei der Umwandlung von Fichtenreinbeständen. Berichte des Forschungszentrums Waldökosysteme, A 179: 171 pp. RICOTTA, C.; CORONA, P.; MARCHETTI, M., 2003: Beware of contagion! Landsc. Urban Plan. 62: 173–177. SCHMIDT, W., 1999: Bioindikation und Monitoring von Pflanzengesellschaften – Konzepte, Ergebnisse, Anwendungen, dargestellt an Beispielen aus Wäldern. Ber. Reinh.-Tüxen-Ges. 11: 133–155. SCHMIDT, W.; WECKESSER, M., 2002: Structure and species diversity of forest vegetation as indicators of forest sustainability. In: SPELLMANN, H. (ed) Presentation of the 5th international Workshop of the EU-Live-Project: Demonstration of methods to monitor sustainable forestry 2001-05-05 – 2001-05-08 Germany, Göttingen, Cuvillier. 68–78. SCHMIDT, J.P., 1993: Eine Einführung in die hydrologischen Untersuchungen von Waldöko- systemen. Forstarchiv 64: 158–163. SCHMIDT, S., 1997: Zusammenhang von Wasser- und Stoffhaushalt in der Langen Bramke – Vergleich unterschiedlicher zeitlicher und räumlicher Massstäbe. Berichte des Forschungs- zentrums Waldökosysteme der Universität Göttingen A 146: 1–188. SEELY, B.; WELHAM, C.; KIMMINS, H., 2002: Carbon sequestration in a boreal forest ecosystem: results from the ecosystem simulation model FORECAST. For. Ecol. Manage. 169: 123–35. TIETEMA, A.; WRIGHT, R.F.; BLANCK, K.; BOXMAN, A.W.; BREDEMEIER, M.; EMMETT, B.A.; GUNDERSEN, P.; HULTBERG, H.; KJONAAS, O.J.; MOLDAN, F.; ROELOFS, J.G.M.; SCHLEPPI,P.; STUANES,A.O.;VAN BREEMEN, N., 1995: NITREX: the timing of response of coniferous forest ecosystems to experimentally-changed nitrogen deposition. Water Air Soil Poll. 85: 1623–1628. TURNER, M.G.; GARDNER, R.H.; O’NEILL, R.V., 2003: Landscape Ecology in Theory and Practice. Heidelberg, Berlin, New York, Springer. 404 pp. ULRICH, B., 1972: Chemische Wechselwirkungen zwischen Waldökosystemen und ihrer Umwelt. Forstarchiv 43: 41–43. ULRICH, B.; MAYER, R.; KHANNA, P.K., 1979: Die Deposition von Luftverunreinigungen und ihre Auswirkungen in Waldökosystemen im Solling. Sauerländer Verlag, Göttingen. VARMA, V.K.; FERGUESON, I.; WILD, I., 2000: Decision support for the sustainable forest manage- ment. For. Ecol. Manage. 128: 49–55. VRIES DE,W.;REINDS,G.J.;VAN DOBBEN, H.; DE ZWART, D.;AAMLID, D.; NEVILLE, P.;POSCH, M.; AUE, J.; VOOGD, J.C.H.; VEL, E.M., 2002: Intensive monitoring of forest ecosystems. 2002 Technical report EC, UN/ECE, Brussels, Geneva. 175 pp. WECKESSER, M., 2003: Die Bodenvegetation von Buchen-Fichten-Mischbeständen im Solling – Struktur, Diversität und Stoffhaushalt. Göttingen, Cuvillier Verlag. 157 pp. XU,Y.-J.; BLANCK, K.; BREDEMEIER, M.; LAMERSDORF, N., 1998: Hydrochemical input-output budgets for a clean rain and drought experiment at Solling. For. Ecol. Manage. 101: 295–306. ZIRLEWAGEN, D., 2003: Regionalisierung bodenchemischer Eigenschaften in topographisch stark gegliederten Waldlandschaften. Schr.reihe. Freibg. Forstl. Forsch. 19: 154 pp.
Accepted April 9, 2004