Stefan Zerbe

Restoration of natural broad-leaved woodland in Central Europe on sites with coniferous forest plantations

Abstract The creation and restoration of natural woodland serving diverse socio-economic as well as nature conservation purposes has become a major objective of sustainable forestry throughout Europe. There is a main focus on the conversion of anthropogenous coniferous forests, which are widely spread in the Central European lowlands and mountain ranges, into natural broad-leaved forests. For ecological as well as economic reasons, the integration of natural regeneration processes into conversion management is considered an important task. Taking the woodland of the Menzer Heide (NE Germany), a typical Pleistocene landscape in the northern Central European lowlands as an example, a vegetation analysis of the Scots pine ( Pinus sylvestris L.) plantations dominating in this area is presented. As the main results, (1) two communities are differentiated within the present-day pine plantations on the oligotrophic and acidic sandy soils. Indicated by different species compositions, the Dicranum -community and the Oxalis -community occur, the latter growing on sites with higher nutrient availability. (2) The comparison of an historical with the present vegetation analysis reveals an increase of nutrient availability in recent decades, most probably strongly related to the natural soil regeneration of the formerly exploited forest sites. (3) From the results of the vegetation analysis, including records of species and individual numbers of naturally rejuvenated trees, future stand development scenarios can be derived. Thus, the Oxalis -community may directly develop into oak-beech and beech stands as natural forests. In the long term, the Dicranum -community will pass a regeneration stage with pine and oak, probably further developing towards natural oak-beech and beech forests. In conclusion, decisions regarding extensive or intensive management, aiming at the conversion of coniferous plantations into natural broad-leaved forests, can be made following observation of the natural regeneration processes in the present-day stands. By utilising the natural regeneration processes and by applying only a few controlling silvicultural measures, a low-energy and cost-effective conversion of the forests can be accomplished.

Biodiversity in Berlin and its potential for nature conservation

Selected habitats in Berlin (Germany) were investigated with a focus on the diversity of flora and land use patterns. On the one hand, the correlation between the number of plant species and the diversity of land use patterns is shown for a transection running from the center to the outskirts of Berlin. The greatest variety of land use patterns and the highest number of species per square kilometer can be found in the transition zone between the city center and the outskirts where urban structures are closely associated with open spaces like large parks, urban forests, and larger wastelands. In accordance with the intermediate disturbance hypothesis, the mosaic of land use patterns in the transition zone with moderate frequencies or intensities of disturbance positively affects habitat diversity, as well as overall species diversity on the landscape level. Furthermore, in residential areas built in the 1920s and 1930s, the flora was studied from both a historical and a present-day perspective in order to assess the diversity of wild-growing indigenous and non-native plant species, wild-growing ornamental plant species, and planted trees. The highest numbers of species were recorded in less intensively managed habitats. In addition to structural factors (e.g. land use patterns) determining the diversity of flora and vegetation in cities, this study also demonstrates the importance of the historical factor for biodiversity. The differences in land use throughout the last 70 years (pre- and post-World War II era) can be seen as an explanation for the relatively high diversity of the flora in the investigated residential areas. Cities have to be regarded as a new type of environment with species compositions and habitats peculiar to urban-industrial areas. Future research and planning of nature conservation and sustainable development of urban-industrial areas should take the biological diversity in cities fully into account. Recommendations are given for the maintenance and development of biological diversity in cities, focussing on landscape and habitat as well as species diversity.

Effects of Biological Soil Crusts on Seed Bank, Germination and Establishment of Two Annual Plant Species in the Tengger Desert (N China)

The presence of biological soil crusts can affect the germination and survival of vascular plants, but the reasons are not well investigated. We have conducted a field investigation and greenhouse experiments to test the effect of crusts on two desert annual plants, which occur on the stabilized dunes of the Tengger Desert in N China. The results showed that biological soil crusts negatively influenced the seed bank of Eragrostis poaeoides and Bassia dasyphylla. The important effect of biological soil crusts on seed germination and establishment were performed indirectly through reducing the amount of germinating seeds. Field investigation and experimental results with regard to the seed bank indicated that higher seedling density was found in disturbed crust soil and bare soil surface than in intact crust soils. Greenhouse experiments showed that the effects of biological soil crusts on germination and establishment of the two plants are not obvious in moist condition, while disturbed crusts are more favorable to seed germination in dry treatment. Significant differences in biomass were found between disturbed crust soil and bare soil. Survival and growth of the two annual plants were enhanced in both algal and moss crusts during the season of rainfall or in moist environment, but crusts did not affect seedling survival in the dry period. The small seeded E. poaeoides has higher germination than larger-seeded B. dasyphylla in crust soils, but B. dasyphylla has a relatively higher survival rate than E. poaeoides in crust soils.

Characteristics and habitats of non‐native plant species in the city of Chonju, southern Korea

Investigations on non-native organisms have become an important task of modern ecology throughout the world. The major objective of this study was to identify the characteristics and habitats of non-native plant species in Korean cities in order to derive conclusions on the success of biological invaders. The city of Chonju in southwest Korea was selected as a representative investigation area. All wild-growing vascular plants were recorded in the city on a total of 106 sample plots located in representative land-use types and within various distances of the city center. Frequency, origin, life forms, and plant families of non-native species were analyzed. Additionally, the percentage of non-native species along a gradient from the city center to the outskirts was investigated. We found that most common non-native species of the flora of Chonju are: (i) native to the Northern hemisphere; (ii) belong to the annuals; (iii) belong to the plant families of the Compositae or Leguminosae; and (iv) they perform best on sites that are continuously disturbed by human impact. In conclusion, non-native species play a significant role in enhancing biological diversity in urban areas.

Stellt die potentielle natürliche Vegetation (PNV) eine sinnvolle Zielvorstellung für den naturnahen Waldbau dar

ZusammenfassungIm vorliegenden Beitrag wird die Anwendung des Konzeptes der potentiellen natürlichen Vegetation (PNV) im naturnahen Waldbau als eine Zielvorstellung für die Bestandesentwicklung kritisch diskutiert. Im Hinblick auf eine an der PNV orientierte, forstlich beeinflußte Baumartenzusammensetzung im naturnahen Waldbau werden vier Kritikpunkte angeführt:1.Die Konstruktion der PNV bleibt, v. a. hinsichtlich der Folgen anthropogener Standortsveräderungen, immer mehr oder weniger mit Spekulation behaftet.2.Das Konzept der PNV schließt eine Sukzession explizit aus. Sukzession und möglichst unbeeinflußte Bestandesentwicklungen sind aber gerade im naturnahen Waldbau erwünscht.3.Naturnahe Vergleichsbestände, die zur Konstruktion der potentiellen natürlichen Vegetation herangezogen werden, sind immer mehr oder weniger stark anthropogen beeinflußt.4.Die reale Gehölzvegetation, die durch jahrhundertelange Kulturtätigkeit des Menschen geschaffen wurde, ist, was die unterschiedlichen Vegetationstypen betrifft, häufig vielfältiger als die konstruierte PNV. Aus den Kritikpunkten wird die Schlußfolgerung gezogen, daß die PNV keine sinnvolle Zielvorstellung für den naturnahen Waldbau darstellen kann. Dagegen lassen sich waldbauliche Entwicklungsziele in jedem Fall direkt oder indirekt aus der realen, aktuellen Vegetation ableiten, wobei sich fünf Entwicklungszieltypen mit unterschiedlichen forstlichen Eingriffsintensitäten unterscheiden lassen: Naturwaldtyp, Naturverjüngungstyp, Umwandlungstyp, Bestandserhaltungstyp und Aufforstungstyp.SummaryThe application of the concept of the potential natural vegetation (PNV) as an objective for the development of forest stands in silvicultural planning is critically discussed in this text. Four arguments are stated against the application of the PNV as an objective in natural silviculture, especially concerning the composition of woody species in the forest stands:1.The construction of the PNV is more or less speculative especially with regard to the consequences of anthropogeneous changes of site conditions.2.The concept of the PNV explicitly excludes succession. But succession and natural development of forests is one of the main targets of natural silviculture.3.The remnants of “natural” woodlands used as a model for the construction of the PNV are always more or less influenced by human beings.4.The different types of the actual vegetation created by lasting cultural impacts are often more diverse than the constructed types of the PNV. It is stressed that objetives for the developments of forest stands can be based directly or indirectly on the actual vegetation in every case. Five types of stand development in which the intensities of silvicultural management differ distinctly are differentiated: natural forest type, natural rejuvenation type, stand transformation type, stand maintaining type and afforestation type.

Vegetation and future natural development of plantations with the Black poplar hybrid Populus×euramericana Guinier introduced to Central Europe

Abstract Plantations of the Black poplar hybrid Populus×euramericana Guinier, introduced to Europe, are widely spread especially in floodplains. Within the Spree forest (NE Germany) as a representative investigation area, poplar stands were investigated with regard to stand history, stand structure, species composition, and spontaneous tree rejuvenation. The study presented here, follows the hypothesis, that from the investigation of vegetation, structure, and history of anthropogenous forest stands, dominated by alien tree species, future development scenarios with regard to natural forest stands can be derived. As the main results, (1) two poplar forest communities are differentiated, the Salix cinerea–Populus×euramericana community (SPC) and the Calamagrostis canescens–Populus×euramericana community (CPC). Although these forest communities have several vegetation characteristics in common (e.g. low canopy cover, occurrence of alien species in the herb layer), their different species composition indicates different soil water conditions, similar to the naturally occurring swamp (Alnion) and floodplain forests (Alno-Ulmion). (2) Different site conditions of the poplar forest communities are not only reflected by the different total species compositions but also by the different species pool and frequency of the tree rejuvenation. (3) Within the SPC, different soil water conditions are also indicated by different species compositions on the level of sub-communities. On the contrary, former land use, stand age and stand structure are closely correlated with different species compositions within the CPC, thus indicating different stages of succession at the level of sub-communities. From the stand history and the results of vegetation analysis, including records of species and individual numbers of naturally rejuvenated trees, scenarios of the future natural development of these anthropogenous poplar forests can be derived. It is concluded, that vegetation changes as an effect of former (e.g. grassland) and present day land use (cultivation of alien poplar) are reversible with regard to the future development of natural forests.

Indicators for plant species richness in pine (Pinus sylvestris L.) forests of Germany

Forestry is obliged to record as well as maintain and/or enhance biological diversity in forests due to national and international agreements. Accordingly, it is necessary to work out methodological approaches for the assessment of biodiversity in forests. In the study presented here, we focus on the total plant species pool (563 vascular plant and bryophyte species) of pine (Pinus sylvestris L.) forests in NE Germany to identify indicators for plant species richness. We distinguished several groups like “herb”, “grass-like”, “woody”, “endangered”, and “exotic species”, for which we detected indicators for low (class #1), intermediate (class #2), and high (class #3) species numbers. From a total of 84 species, which were identified by a three-step procedure, most indicators were found for class #3. Only few indicators have been revealed for intermediate species numbers, i.e. class #2. With help of Ellenberg’s ecological indicator values and information on the main occurrence in Central European vegetation types and plant communities, respectively, we characterized the indicator species ecologically. The ecological site preferences of the indicator species in general reflect the fact that species richness is highest in base-rich, light, and anthropogenically disturbed pine forests. On the contrary, species-poor forests were revealed by indicators, which mainly occur on acidic sites. It is concluded that a considerable set of indicators for species richness can help facilitate biodiversity assessments in forestry and ecosystem restoration practice.

Zum Einfluß von Weichlaubhölzern auf Vegetation und Auflagehumus von Fichtenforsten — Untersuchungen in einem zwei Jahrzehnte alten Birken-Ebereschen-Vorwald im Hoch-Solling

ZusammenfassungIn einem Birken-Ebereschen-Vorwald auf Mittlerem Buntsandstein im Hoch-Solling wurden die Vegetation, die Bestandesstruktur und die Humusauflage untersucht. Das Ergebnis einer ca. 20jährigen, weitgehend ungestörten Entwicklung nach Fichtenwindwurf und Holzräumung wird im Hinblick auf den Einfluß von Weichlaubhölzern auf mit reiner Fichte bestockte Waldstandorte analysiert und diskutiert. Im Vergleich zum benachbarten Restbestand des heute ca. 100jährigen Fichtenaltholzes weist der Birken-Ebereschen-Vorwald eine mechrschichtige Gehölzstruktur und eine höhere Artenvielfalt auf. Wesentliche Veränderungen konnten im Inventar und in der Häufigkeit der Arten in der Krautschicht ermittelt werden. Während unter Fichte die Drahtschmiele(Avenella flexuosa) dominiert, hat sich im Vorwald deren Deckungsanteil deutlich zugunsten von Rotem Straußgras(Agrostis tenuis) verringert. Die im Vorwald gegenüber dem Fichtenaltbestand häufigeren Arten weisen nicht nur auf den im Mittel höheren Lichtgenuß am Boden des Birken-Ebereschen-Vorwaldes hin, sondern auch auf eine höhere Nitrifizierungsrate im Oberboden und frische bis wechselfeuchte Standortsverhältnisse. Humusformen und -qualitäten im Vorwald und Fichtenaltholz weichen deutlich voneinander ab. Die Untersuchungsergebnisse geben Hinweise auf die unter den Aspekten eines naturnahen Waldbaus positiven Einflüsse einer vorübergehenden Weichlaubholzbestockung auf Auflagehumus und Bodenvegetation von Nadelholzforsten.SummaryVegetation, stand structure, and organic soil layer of a birch-rowan forest on sand-stone in the upper Solling (NW-Germany) were studied at a site where 20 years ago the spruce stand had been thrown by storm and cleared afterwards. The result of a largely undisturbed softwoods stand development lasting approximately 20 years is analysed and discussed in order to find out about the influence of softwoods on the vegetation, structure and organic layer of stands with Norway spruce. Compared with the neighbouring remnant of the now approximately 100-year-old spruce stand, the birch-rowan forest is more diverse in terms of stand structure and number of species. Significant changes were found in composition and dominance of species in the herb and moss layer. High cover values ofAvenella flexuosa in the spruce stand were displaced withAgrostis tenuis in the birch-rowan forest. The species which are more frequent in the birch-rowan forest than in the spruce stand indicate the relatively higher light intensity on the forest floor, a higher nitrification rate in the upper soil and moist site conditions or temporarily stagnating wetness. Qualities of the organic layers in the spruce stand and the birch-rowan forest differ significantly. In view of near-natural silviculture the results show positive effects of a temporary softwood stand on the organic soil layer and vegetation of coniferous stands.

Influence of historical land use on present-day forest patterns: A case study in south-western Germany

Two major questions were investigated in this study: (1) What are the contributions of historical in comparison with natural factors to the development of present-day forest patterns? (2) What implications can be drawn from an understanding of forest patterns and historical land-use development with regard to landscape planning and nature conservation? The Sandstein-Spessart, a natural unit in south-western Germany, served as an example to show the influence of different types and intensities of land use on the differentiation of the natural landscape. The methodological approach to this study was a synthesis of previously available information. It was shown that different initial site conditions within the natural unit such as geology and climate led partly to the spatial differentiation of the present-day landscape. However, economic and political factors such as the glasswork industry and hunting activities also played a major role in the development of different forest patterns. Examples are given of how this synthesis of landscape ecology and landscape history can provide a useful basis for nature conservation and landscape planning.

The influence of softwood broadleaves on vegetation and the soil organic layer in Norway spruce stands - investigations in a two-decade old birch-rowan forest in the upper Solling area, Lower Saxony, NW Germany.

ZusammenfassungIn einem Birken-Ebereschen-Vorwald auf Mittlerem Buntsandstein im Hoch-Solling wurden die Vegetation, die Bestandesstruktur und die Humusauflage untersucht. Das Ergebnis einer ca. 20jährigen, weitgehend ungestörten Entwicklung nach Fichtenwindwurf und Holzräumung wird im Hinblick auf den Einfluß von Weichlaubhölzern auf mit reiner Fichte bestockte Waldstandorte analysiert und diskutiert. Im Vergleich zum benachbarten Restbestand des heute ca. 100jährigen Fichtenaltholzes weist der Birken-Ebereschen-Vorwald eine mechrschichtige Gehölzstruktur und eine höhere Artenvielfalt auf. Wesentliche Veränderungen konnten im Inventar und in der Häufigkeit der Arten in der Krautschicht ermittelt werden. Während unter Fichte die Drahtschmiele(Avenella flexuosa) dominiert, hat sich im Vorwald deren Deckungsanteil deutlich zugunsten von Rotem Straußgras(Agrostis tenuis) verringert. Die im Vorwald gegenüber dem Fichtenaltbestand häufigeren Arten weisen nicht nur auf den im Mittel höheren Lichtgenuß am Boden des Birken-Ebereschen-Vorwaldes hin, sondern auch auf eine höhere Nitrifizierungsrate im Oberboden und frische bis wechselfeuchte Standortsverhältnisse. Humusformen und -qualitäten im Vorwald und Fichtenaltholz weichen deutlich voneinander ab. Die Untersuchungsergebnisse geben Hinweise auf die unter den Aspekten eines naturnahen Waldbaus positiven Einflüsse einer vorübergehenden Weichlaubholzbestockung auf Auflagehumus und Bodenvegetation von Nadelholzforsten.SummaryVegetation, stand structure, and organic soil layer of a birch-rowan forest on sand-stone in the upper Solling (NW-Germany) were studied at a site where 20 years ago the spruce stand had been thrown by storm and cleared afterwards. The result of a largely undisturbed softwoods stand development lasting approximately 20 years is analysed and discussed in order to find out about the influence of softwoods on the vegetation, structure and organic layer of stands with Norway spruce. Compared with the neighbouring remnant of the now approximately 100-year-old spruce stand, the birch-rowan forest is more diverse in terms of stand structure and number of species. Significant changes were found in composition and dominance of species in the herb and moss layer. High cover values ofAvenella flexuosa in the spruce stand were displaced withAgrostis tenuis in the birch-rowan forest. The species which are more frequent in the birch-rowan forest than in the spruce stand indicate the relatively higher light intensity on the forest floor, a higher nitrification rate in the upper soil and moist site conditions or temporarily stagnating wetness. Qualities of the organic layers in the spruce stand and the birch-rowan forest differ significantly. In view of near-natural silviculture the results show positive effects of a temporary softwood stand on the organic soil layer and vegetation of coniferous stands.