Solling Mountains Research Articles

Long‐term change in understorey plant communities of conventionally managed temperate deciduous forests: effects of nitrogen deposition and forest management

AbstractQuestionsThe understorey vegetation of temperate forests may serve as an indicator of long‐term change in site conditions. We investigated vegetation change of the herb and moss layers during the last 50 yr in managed European beech (Fagus sylvatica) and sessile oak (Quercus petraea) forests under chronic N deposition. We tested the hypotheses that (1) the species richness of the understorey vegetation has increased in intensively managed forests because species gains due to increased light and nutrient supply are greater than species losses, and (2) shifts in species richness and community composition differ between beech and oak stands due to contrasting light regimes.LocationForests of the Solling Mountains, central Germany.MethodsWe re‐sampled 95 relevés of the herb and moss layers after 46/47 yr (1966/67 vs 2013) to analyse changes in cover and species composition. In the beech forests, two widespread types of production forest (selection cutting vs shelterwood management) were compared with unmanaged forest reserves. Trends in vegetation change were related to a long‐term record of N deposition and soil chemistry, shifts in EIV and changes in canopy structure.ResultsA decrease in cover of the uppermost tree layer and emerging lower tree and shrub layers have increased the heterogeneity of canopy structure and indicate a more heterogeneous light distribution on the forest floor of the beech and oak forests. Plot‐level species richness has increased in both forest types (except for beech stands under shelterwood management). Under chronic N deposition (~40 kg N·ha−1·yr−1 before 1990, 20–25 kg·ha−1·yr−1 since 1990), the organic layer N pool more than doubled between 1966 and 1993 with a decrease thereafter, and the EIV‐N scores have increased. The N score increase was not related to changes in the canopy.ConclusionsThis study presents evidence of an N deposition effect on the understorey vegetation, which acts independently from the recorded changes in canopy structure. We conclude that altered nutrient supply due to atmospheric N deposition, together with changes in light regimes and management‐related disturbance, are the main drivers of vegetation change in the studied stands.

Intraspecific functional trait variation and performance of Populous tremuloides

The fact that plant-trait and functional-trait syndromes can describe plant growth strategies, and as a result their ecological requirements, has gained considerable importance in ecology (Grime et al., 1997; Westoby et al., 2002). At the global scale, the existence of a major axis of specialization among plants has been determined by measuring leaf functional traits; this axis highlights a fundamental trade-off between rapid acquisition of resources and conservation of resources within well-protected tissues (Diaz et al., 2004; Wright et al., 2004). Diaz et al. (2004) demonstrated that water and nutrient stresses lead to trait-syndrome convergence, with conservative species most present in stressful growth conditions, while acquisitive ones most present in to non-stressful growth conditions. This result highlight the functional traits capacity to explain species adaptation to different growth conditions. Moreover, despite the evidence of a large functional traits differentiation within species and the importance of trait variability within a species to establish itself in different habitats (Violle et al., 2012), functional strategies generally have been identified at the species level and did not incorporate within species traits variability. The fact that functional traits measurement allowed the definition of plant strategies, and as a result their ability to develop biomass in a variety of growth conditions, led Garnier and Navas (2011) to recommend this approach for agricultural and forestry systems to maximize services of these types of production, and to reduce their environmental drawbacks. However, several questions remain: (i) Do the species used in forestry and agro-systems display different trait syndromes among genotypes?; (ii) Is trait-value variation among genotypes related to genetic differences? and (iii) Are the strategies related to performance of the genotype? To answer these questions Hajek et al. (2013) test if leaf as well as root functional traits are related to Populus varieties performance. In order to do that, they grew seven demes, i.e. an assemblage of closely related individuals (Gilmor and Gregor, 1939), of two conspecific subspecies, the European Populus tremula and one deme of the North American P. tremuloides in monoculture stands in a common garden in the Solling Mountains (Germany). For each deme, roots were collected in the upper 30 cm of the mineral soil at a stem distance of 15–30 cm from 18 to 20 randomly chosen juvenile trees. Root functional traits, including specific root length (SRL, m.g−1), specific root area (SRA, cm2 g−1), root tissue density (RTD, g cm−3), root tip abundance, root diameter, and N content were measured on fine roots (<2 mm) according to Cornelissen et al. (2003). Simultaneously with root sampling, leaves were collected from the same trees to measure leaf area (cm2), specific leaf area (SLA, cm2g−1), and N and C contents. Hajek et al. (2013) showed strong intraspecific variation in nearly all functional traits; only RTD did not vary among demes. These results highlight that although root traits can describe species' strategies well, they may also allow populations within a species to be differentiated. This interpretation is strengthened by the fact that despite the small number of demes considered, two roots traits (root tip abundance and RTD) and two leafs traits (leaf size and SLA) appeared to be linked to genetic variation among demes. Moreover, some demes showed particularly high within-deme trait variation, suggesting the existence of strong within-deme genetic diversity. This result challenge the idea that a species should be described by one trait value and opens interesting perspectives in plant breeding by highlighting the existence of strong within-species trait diversity linked to genetic differentiation, which is a prerequisite for breeding based on functional traits. The authors did not highlight links between above-ground relative growth rates (RGR) and root traits, while leaf traits appeared to be linked to the RGR but are poor predictors of it. They hypothesized that this was due to a stronger relation between root traits and below-ground RGR than above-ground RGR, showing the need for more whole-plant holistic studies to better understand plant functioning. These links were tested in a single growth environment. Root functional traits should be linked more to species performance under conditions where water and nutrient availability limits plant growth and thus where different root strategies should result in contrasting performance (Zhu et al., 2010). In summary, study by Hajek et al. (2013) demonstrated the existence of significant intraspecific trait variation linked to genetic differences among demes. They also demonstrated that our knowledge about the links between traits and plant performance must be improve. It is hoped that the Hajek et al. (2013) study will stimulate more research efforts to clarify the relations among trait values, plant relatedness, plant performance and environmental factors, in order to let the concept of functional traits be functional in forestry and agronomy.

Dramatic diversity losses in epiphytic lichens in temperate broad-leaved forests during the last 150 years

Comparing data of epiphytic lichen diversity in semi-natural broad-leaved forests in north-western Germany from the 19th to early 20th centuries with recent inventories revealed strong changes, even though forest structure and tree species composition had changed only little. In three study areas, between 55% and 70% of the species became rarer during the 100–150-year long observation period. In the spatially extended study areas Weser-Ems Lowlands and Solling Mountains, 36% or 39% of the species, respectively, could not be rediscovered in the recent survey. Considering that species might have been overlooked during revisitation, the extinction rate was estimated to be 28% in the Weser-Ems Lowlands and 30% in the Solling Mountains based on a estimated probability for recovering the species of 75% in crustose lichens and 90% in foliose and fruticose lichens. The main causes of the species decline are thought to be forest management (especially the reduction of overmature and decaying trees), the reduction of soil moisture and, with it, air humidity due to drainage as well as the deposition of acidifying and fertilizing substances from the atmosphere. Lichens specialized on rain-sheltered bark furrows and cavities of old trees or smooth, shady bark or moist thick-stemmed deadwood in the forest interior have suffered the strongest declines, including the epiphyte flora of Fagus sylvatica, Central Europe’s most abundant native forest tree species. Only few lichens which benefit from nitrogen deposition, global warming or the acidification of bark due to sulphur dioxide pollution have spread.

Fine roots of overstory Norway spruce (Picea abies):

The horizontal and vertical distribution of live fine roots (diameter &lt; 2 mm) of overstory Norway spruce [Picea abies (L.) Karst.] and their influence on diameter and height growth of underplanted beech (Fagus sylvatica L.) and Douglas-fir (Pseudotsuga menziesii [Mirb.] Franco) saplings were studied on experimental plots in the Solling Mountains (Germany). The aims of this study were to investigate how overstory fine root density varies with stand density, and how it influences growth of the underplanted saplings to changes in belowground resources availability in connection with simultaneously changing light availability. Most fine roots were concentrated in the humus layer (more than 45%) and in the top mineral soil (0-5 cm, about 15%). Fine root biomass increases with overstory basal area and decreases with rising distance from the nearest overstory tree, reaching about zero within ca. 8 m distance. Over the whole two-year study period, light availability alone was the decisive factor for growth of the beech saplings (5 resp. 6 years of age) while growth of the Douglas-fir saplings in the first study year (6 years of age) was additionally affected by a shortage of belowground resources due to root competition in a season with less than average rainfall. This species-specific response of underplanted saplings to changes in above and belowground resources is of silvicultural importance for the establishment of a mixed stand beneath a mature canopy: the more sensitive Douglasfir should be planted on the central parts of openings with little or none belowground competition while the less sensitive beech can be placed below the denser parts of the overstory.

The Collembola community of a Central European forest: Influence of tree species composition

The present study investigates the response of the Collembola community to replacement of beech by spruce or by mixed stands of beech and spruce in the Solling mountains (Germany). The study was carried out in three beech ( Fagus sylvatica), spruce ( Picea abies) and mixed stands of beech and spruce arranged in three blocks. The density, diversity and community structure of Collembola as well as microbial and abiotic parameters in the organic layers and mineral soil of the three spruce, three beech and three mixed stands were investigated. Major results are: (i) Collembola communities did not differ strongly between stand types and were dominated by Folsomia quadrioculata and Mesaphorura species, (ii) neither total abundance of Collembola nor densities of the hemiedaphic species F. quadrioculata, Parisotoma notabilis and Isotomiella minor significantly responded to stand type, (iii) in the mixed stands the fungal biomass was increased leading to high densities of fungal feeding Collembola (e.g. Mesaphorura sp.) and high species numbers of Collembola, (iv) the density of the epedaphic and partly herbivorous group Entomobryidae/Tomoceridae in the spruce stands exceeded that in the mixed and beech stands; presumably this was due to the higher diversity of the ground vegetation in the spruce stands. Canonical correspondence analysis (CCA) of the collembolan communities of L/F and H/Ah horizons also indicated that most of the epedaphic species were associated with the spruce stands. Moreover, results of the CCA indicated that soil pH is an important structuring force for collembolan communities. Overall, results suggest that stand type impact collembolan communities, presumably via changes in the amount and quality of food resources, such as fungal biomass and living plant material. However, differences in collembolan community structure between the investigated stand types were moderate supporting earlier findings that Collembola generally respond little to changes in the vegetation structure.

Nutrient fluxes via leaching from coarse woody debris in a Fagus sylvatica forest in the Solling Mountains, Germany

To evaluate the importance of nutrient fluxes via leaching from coarse woody debris (CWD) in an area with high atmospheric nitrogen (N) inputs, throughfall and CWD leachate from logs at different stages of decomposition were investigated over a period of 14 and 27 months, respectively, in a 160-year-old European beech ( Fagus sylvatica L.) forest in northwestern Germany. Water samples, collected from 30 zero-tension lysimeters installed in pairs along 15 logs and from 27 neighboring raingauges, were chemically analyzed in the laboratory. Generally, as CWD decay advanced, the ratio of leachate to throughfall decreased, and the amount of dissolved nutrients in the leachate increased. With the exception of ammonium (NH4+) and dissolved inorganic carbon, the element concentrations in the CWD leachate were significantly higher than those in the throughfall. The concentrations of NH4+and nitrate (NO3–) in the CWD leachate, which were very high compared with values from North American studies, were caused by the continuously high atmospheric N inputs, and the resulting N saturation in the forest ecosystem investigated. The low concentrations of the cations calcium and magnesium indicate that at this site nutrients limiting plant and fungal growth are retained and accumulated in the CWD.

An Approach to the Identification of Indicators for Forest Biodiversity—The Solling Mountains (NW Germany) as an Example

Abstract In this study, we present an approach for the identification of indicators for biodiversity within forest ecosystems. We analyze the data of stands of pure Norway spruce (Picea abies (L.) Karst) and European beech (Fagus sylvatica L.), as well as mixed P. abies–F. sylvatica forests in the Solling mountains (NW Germany). The analysis is based on 683 vegetation samples in total. For different plant groups, that is, vascular plants, bryophytes, Red List species, we investigate species numbers as a parameter of biodiversity. Species numbers are differentiated into three classes to describe low to high diversity. Plots are separately examined for the three different forest types. In order to take the species–area relationship into account, we only use relevés with a plot size of 100 m2. Our approach focuses on the probability to be in a defined range of species numbers, that is, class, if a certain species occurs. For the purpose of facilitating the differentiation of the classes, we use the presence values of species in the classes for further characterization of indicators. Few indicators were found for the low ranges of species numbers. In addition, there were only a small number of species groups and stand types having indicators for all three classes. Various species have multiple indicator functions, e.g., with regard to the investigated species groups. The focus on a few of these multi‐indicators allows a rapid assessment of forest biodiversity. The catalog of indicators resulting from the investigation helps to facilitate and accelerate biodiversity evaluations of forest stands, in particular with regard to nature conservation and the restoration of natural forests.

Measurements of the exchange of carbonyl sulfide (OCS) and carbon disulfide (CS2) between soil and atmosphere in a spruce forest in central Germany

Abstract The exchange of carbonyl sulfide (OCS) and CS 2 between the atmosphere and the pedosphere was investigated in a temperate zone spruce forest in the Solling Mountains (51°N), Germany during three field campaigns in 1999. Dynamic (flow-through) chambers were used to measure the OCS and carbon disulfide ( CS 2 ) exchange fluxes between the soil and the atmosphere. All measurements showed a net OCS flux from the atmosphere into the soil. On average ( ± standard error of the mean), the OCS uptake rate of the soil was 0.81 ( ± 0.03 ) pmol m - 2 s - 1 and the total range was between 0.23 and 1.38 pmol m - 2 s - 1 . CS 2 fluxes varied between an uptake of 0.11 pmol m - 2 s - 1 and an emission of 0.23 pmol m - 2 s - 1 . Therefore, CS 2 is emitted by the soil in a nearly balanced mean flux of 0.01 ( ± 0.01 ) pmol m - 2 s - 1 . Slight dependencies of the OCS flux on soil temperature and soil water content were detected. The fluxes varied by about a factor of 2 over a distance of 10 m. A comparison of the OCS fluxes between soil and atmosphere with the fluxes observed simultaneously above the canopies revealed that only 1% of the OCS which was taken up by the whole forest ecosystem is deposited in the soil. The impact of the CS 2 exchange between soil and atmosphere for the whole ecosystem flux of CS 2 was even more negligible.

Relationships between tree dimension and coarse root biomass in mixed stands of European beech (Fagus sylvatica L.) and Norway spruce (Picea abies[L.] Karst.)

Relationships between tree parameters above ground and the biomass of the coarse root system were examined in six mixed spruce-beech stands in the Solling Mountain region in northwest Germany. The selected stands were located on comparable sites and covered an age range of 44 to 114 years. Coarse roots (d \ge 2 mm) of 42 spruce and 27 beech trees were sampled by excavating the entire root system. A linear model with logarithmic transformation of the variables was developed to describe the relationship between the coarse root biomass (CRB, dry weight) and the corresponding tree diameter at breast height (DBH). The coefficients of determination (R2) attained values between 0.92 for spruce and 0.94 for beech; the logarithmic standard deviation values were between 0.29 and 0.43. A significantly different effect of tree species on the model estimates could not be detected by an analysis of co-variance (ANCOVA). For spruce, the derived relationships were similar to those reported in previous studies, but not for beech. Biomass partitioning in the tree compartments above and below ground differs significantly between spruce (coarse root/shoot ratio 0.16±0.06) and beech (coarse root/shoot ratio 0.10±0.03) in the mixed stands. These results are similar to those given in other studies involving pure spruce and beech stands on comparable sites in the region, although the ratios of pure stands in other regions growing under different site conditions are somewhat higher. Comparing trees of the same DBH classes, root/shoot ratios of spruce are 1.2 to 3 times higher than those of beech. Dominant spruce trees (DBH>60 cm) attained the highest ratios, suppressed beech trees (DBH<10 cm) the lowest. Site conditions of varying climate and soils and interspecific tree competition are likely to affect root/shoot ratio and DBH-coarse root biomass relationships. The greater variability in beech compared with spruce indicates a high 'plasticity' and adaptability of beech carbon allocation. Thus, the derived equations are useful for biomass estimates of coarse roots involving trees of different ages in mixed stands of spruce and beech in the Solling Mountains. However, application of these relationships to stands in other regions would need further testing.

Growth and fructification of a Norway spruce (Picea abies L. Karst) forest ecosystem under changed nutrient and water input

In the mountainous region of a low mountain range (Solling mountains) an ecosystem manipulation experiment with roof constructions underneath the canopy of a 60-year old Norway spruce stand is run since 1991. The responses to artificially prepared, pre- industrial through fall and to extended summer droughts with intensive rewetting are investigated in two parallel roof experiments and evaluated against a roof control and an ambient control plot. After long terms of drought distinct reactions of the trees were visible in growth. The reactions of height-increment were more distinct than the effects on diameter-increment. Furthermore, the trees of the domi- nating social classes (Kraft I and II) reacted more on low water-supply than the dominated trees. So it is probable that a long lasting stress by drought effects changes the stand structure, too: the vertical structure of a stand would get more homogeneous and the diversity in the stand structure would decrease. Reduced input of sulphur and nitrogen did not show any distinct growth reactions within the 9-year ob- servation period. roof-project / nitrogen / drought / growth / fructification

A spreadsheet-based biogeochemical model to simulate nutrient cycling processes in forest ecosystems

A Nutrient Cycling Spreadsheet (NuCSS) model was developed to simulate nutrient cycling in forest ecosystems. This model is intended to provide a tool for nutrient management and is intermediate in complexity between simple budget calculations and complex, process-based ecosystem models. NuCSS simulates biomass production, organic matter decomposition, N mineralization, cation adsorption, weathering and leaching (hydrology not included) using empirical relationships and simple mechanistic process descriptions. The model calculates a target biomass production and associated nutrient uptake. By reviewing soil nutrient pools the user can assess whether available soil nutrients can sustain the targeted biomass production. NuCSS was calibrated to a Norway spruce site in the Solling Mountains, Germany. The model performance was evaluated using long-term data on deposition, vegetation, water quality and soil nutrient inventories. Long-term predictions were made using a ‘business as usual’ and two reduced deposition scenarios. Results from NuCSS were compared with simulations from other biogeochemical models. The element distribution over soil, forest floor and vegetation closely matched measurements both after one and 15 years. Forest floor nutrients were underestimated but data on forest floor accumulation proved to be unreliable. NuCSS overestimated N uptake, N mineralization and leaching but not enough data on these fluxes were available to determine whether NuCSS was wrong. Simulated base cation leaching agreed well with the measurements but K leaching was overestimated most likely due to an underestimation of the selectivity coefficient for K adsorption. The reduced deposition scenarios caused N and base cation leaching to decrease with time. When N deposition was reduced by 95%, a N deficit occurred and N mineralization and deposition could not sustain the (fixed) uptake. For most simulated parameters NuCSS agreed well with more detailed, process-based, biogeochemical models. In general, NuCSS simulated a higher N leaching and N mineralization than most other models. Trends in base saturation and base cation leaching simulated by NuCSS agreed well with other models. The model proved to be helpful in addressing some of the uncertainties in nutrient cycling regarding vegetation uptake, weathering rates and N mineralization. Given the uncertainties in description of certain processes, a quantitative use of NuCSS may not be justified. These uncertainties also apply to more complex nutrient cycling models, however.

Regeneration of compacted soil aggregates by earthworm activity

Soil compaction is a problem of modern agriculture, caused by heavy machinery when used in unsuitable, especially moist, conditions. Some regeneration processes in compacted loess soil were studied in a field experiment near Relliehausen, at the edge of the Solling mountains in Lower Saxony, Germany. Conventional tillage (CT) and conservation tillage (CS) systems were compared. The compaction was induced by the use of different wheel loads. The influence of earthworms was determined by comparing soil aggregates and casts with respect to dry and moist porosity, swelling, and water stable aggregation. For visualisation of the microstructure, a scanning electron microscope was used. The casts were obtained from two earthworm species living for 6 months in the laboratory in monoliths, taken on the plots after the wheeling procedure. The casts showed 10–20% higher values for porosity and about 50% higher swelling values than comparable soil aggregates, while the relative water stability was ca. 10% lower. We conclude that casts are looser and less stable than aggregates from the soil the earthworms ingested. To show the ecological relevance of the changes in the casts, the cast production per hectare per year was calculated. It was especially high in the most loaded soil under CS with endogeic species.

The inoculation of Lumbricus terrestris L. in an acidic spruce forest after liming and its influence on soil properties

At a formerly limed study site in a spruce forest on acidic soil in the Solling mountains, Central Germany, adult or near adult specimens of Lumbricus terrestris were inoculated. The establishment of a reproducing population was monitored for four years. Burrowing activity was detected down to 50 cm, with locally marked incorporation of organic matter to a depth of 20 cm. Chemical changes due to lime particles were restricted to earthworm burrows and a thin surrounding soil layer. A random sample of soil cores revealed no differences in soil chemical characteristics between limed plots with or without L. terrestris.

Root respiration and its importance for the carbon balance of beech saplings (Fagus sylvatica L.) in a montane beech forest

Root respiration of 10-year-old beech saplings (Fagus sylvatica L.) grown in the understorey (UND) and in a natural gap (GAP) of a mature beech forest in the Solling mountains, FRG, was investigated from April until December, 1990. Respiration rates of fine, medium and coarse roots were measured in situ by a PC-controlled cuvette system. Fine root respiration rates were in the range of 0.5–9.8 nmol CO2 gDW−1 s−1 at both sites, but respiration rates of UND saplings were higher, compared to those of GAP saplings. The dependence of respiratory activity on soil temperature proved to be highly significant (p<0.001) for both plots, following a quasi-Arrhenius type curve. Fine root respiration rates of UND saplings were highly significantly, negatively correlated with the water content of the attached organic material, whereas respiration rates of GAP saplings did not show such a correlation. Further, a significant correlation (p<0.01) between mycorrhizal biomass and respiration rate was detected at the UND site, but not at the GAP site. Medium and coarse root respiration rates were very similar and no significant differences between the two sites were detected. Maximum respiration rates of 3.1 nmol CO2 gDW−1 s−1 were reached in the middle of July. Due to low light intensities in the under storey, daily net CO2 assimilation rates of UND saplings were much smaller than those of GAP saplings. At both sites, net CO2 assimilation rates varied more than respiration rates and thus the carbon balance of beech saplings was more affected by the rate of carbon fixation than by the rate of respiratory carbon loss.

Physikalische Eigenschaften von Schluffdecken

Physical properties of silt crustsThe physical properties of silt crusts of two locations within the eastern part of the Solling mountains in Western Germany were investigated. They were formed downhill on top of sloping grey brown podzolic soils derived from loess during heavy rainfall, which caused aggregate breakdown and erosion. The crusts were several cm in thickness. They consist of 80% coarse silt (20–60μ), of 12% medium silt (6–20μ) and of 5% clay (&lt;2μ). The content of organic matter is low. Porosity of the silt crusts is 47–51 vol.%. Compressed silt crusts with 40% porosity contain only 2,5 vol.% of large pores &gt; 15μ, According to this the unsaturated hydraulic conductivity remains almost constant when tensions are increasing, but it drops immediately, when the 15μ pores drain at 200cm H2O pressure. The saturated conductivity varies with porosity in the range of 10–50 cm/day. But in the Ap‐horizon of a grey brown podzolic soil with higher contents in clay and organic C the saturated conductivity varies with porosity in the range of 10–10 000 cm/day. Only during rainstorms with high intensity silt crusts will impede rapid water infiltration into the underlying grey brown podzolic soil.