The assessment of naturalness and its role for nature conservation and forestry in Europe

Naturalness is one of the most important criteria in nature conservation. This paper examines the fundamental concepts underlying the definition and assessment of naturalness. Its role in nature conservation and forest management under conditions of global change is also discussed. The degree of naturalness may be defined in ordinal classes. The “static” concept of the potential natural vegetation (pnV), developed in the 1950ies, is mostly used as the reference state. In other cases, its reversed concept, the hemeroby (degree of articifiality) is assessed, based on the intensity and frequency of human impacts. Since the 1970ies, more attention has been given to natural dynamics than in earlier approaches, e.g. in forest succession models. At the end of the 1980ies, the previous importance was increasingly stressed of natural browsing by large herbivores and the role of predators. These large herbivors are extinct today in most cultural European landscapes. It is assumed, that they open up the canopy, and create park-like forest structures which contain a diversity of habitats for other types of organism (birds, insects). Changed and permanently changing environments and altering patterns of competition between species continue to modify natural processes today. Some of the more conspicuous effects are the extinction of native species and immigration of species to new regions. Long-lived ecosystems like forests are however not able to adapt quickly to such changes and may be unable to find a new balance with the environment. Today, such changes occur very rapidly, and are reducing the original naturalness of ecosystems. Because of this, the criterion “naturalness” must be downweighted. Conversely, more importance should be attached to other criteria: particularly originality (= original naturalness) and restorability. Forestry is contributing to this accelerated change of biocoenoses by increasing disturbances and introducing exotic tree species. Naturalisation of some exotic tree species modifies the natural processes and creates a “new allochthonous naturalness”. Because of this, forest planning should try to preserve or restore stands with attributes of the “original forest”. Exotic species should not be planted, or only in a very restricted way.Naturnähe ist eines des wichtigsten Bewertungskritierien im Naturschutz. Die vorliegende Arbeit untersucht die den gängigen Naturnähe-Konzepten zugrundeliegenden Definitionen und Bewertungsmaßstäbe. Auch wird die Rolle von Naturnähe für Naturschutz und Waldbewirtschaftung im „Globalen Landschaftswandel“ diskutiert. Die Einteilung von Naturnähe erfolgt in graduellen Abstufungen. Zumeist wird dazu das “statische” in den 1950 er Jahren entwickelte Konzept der Potenziellen natürlichen Vegetation Vegetation (pnV) verwendet. In anderen Fällen wird die zur Naturähe gegenläufige Hemerobie (Grad des Nutzungseinflusses) herangezogen. Seit den 1970er Jahren wurden verstärkt Aspekte der natürlichen Dyanmik berücksichtigt, z.B. sogenannte „Phasenmodelle“. Ende der 1980er Jahre wurde die ehemalige Bedeutung der Megafauna (große Pflanzenfresser und Prädatoren) hervorgehoben, die heute in den europäischen Kulturlandschaften weitgehend ausgestorben sind. Es wird vermutet, dass Megaherbivoren einst in der Lage waren, den Wald aufzulichten und teilweise parkartige Strukturen mit einer großen Habitatvielfalt für andere Tierartengruppen (Vögel, Insekten) zu schaffen. Veränderte und sich permanent ändernde Umweltbedingungen und sich wandelnde Konkurrenzmuster zwischen den Arten führen auch heute zu sich laufend ändernden Naturprozessen. Einige der auffälligsten Effekte sind das Aussterben heimischer Arten und die Einwanderung von „fremden“ Arten in neue Regionen. Langlebige Ökosysteme wie die Wälder sind nicht in der Lage, rasch ein neues Gleichgewicht mit den Umweltbedingungen zu finden, ihre Umstellung dauert viele Jahrzehnte. Heute finden Veränderungen von Standortsbedingungen sowie die Einwanderung von Tier- und Pflanzenarten sehr rasch statt. Diese Prozesse reduzieren die frühere Naturnähe („Ursprünglichkeit“) der Ökosysteme. Deshalb ist bei naturschutzfachlichen Bewertungen das Kriterium „Naturnähe“ aus heutiger Sicht tendenziell geringer zu wichten. Umgekehrt sollte anderen Aspekten größere Bedeutung beigemessen werden, insbesondere der Ursprünglichkeit (bzw. angestammten Naturnähe) und der Wiederherstellbarkeit. Die Forstwirtschaft trägt zu einem beschleunigten Wandel der Lebensgemeinschaften bei durch zunehmende Eingriffe (Häufigkeit, Intensität) und Einbringen von Gastbaumarten. Die Einbürgerung einiger exotischer Baumarten verändert die natürlichen Prozesse und kreiert eine “neue allochthone Naturnähe”. Deshalb sollte die Forstplanung versuchen, „angestammt naturnahe“ Bestände zu schützen oder wiederherstellen. Exotische Arten sollten nur in einem sehr begrenzten Umfang angepflanzt werden

Effects of Norway spruce cultivation on the ground vegetation of beech forest sites on limestone

Ziel dieses Beitrags ist, den Einfluss der überschirmenden Baumarten auf die Artenzusammen-setzung der Waldbodenvegetation zu klären, beginnend vom reinen Buchenwald über abgestufte Mischungsverhältnisse bis hin zum reinen Fichtenbestand. Das für die Untersuchungsbestände gültige Waldbaukonzept der Landesforstverwaltung Baden-Württemberg soll hinsichtlich seiner Auswirkung auf die Waldbodenarten geprüft werden. Anhand der Ergebnisse werden Schlussfolgerungen für die forstliche Praxis abgeleitet.Spruce forests are frequently thought of as species poor and associated with the suppression of natural forest species, in other words a loss of biodiversity. The effect of varying degrees of spruce admixture on the ground vegetation is the theme of this study. Research was carried out in 50-90 year old pure beech and spruce stands, as well as variously mixed stands in the central “Schwäbische Alb”. Few species appear to be strictly tied to pure beech stands. To preserve these species, pure beech forest should be maintained at least in some stands of managed forests. However, the majority of the beech forest species can also be found in spruce stands. Under spruce, the species number increases considerably, because many open land species can be found. Their occurrence can be explained by the higher light intensities under spruce canopies. The increased number of species under spruce canopies does not necessarily mean a higher value for nature conservation. Other criteria like naturalness or rarity, must be taken into consideration. A few rare species were found to be associated with pure spruce canopies. Therefore, the conversion of all pure spruce stands to mixed stands would result in a loss of rare species well worth conservation

Natural regeneration of the deciduous oak species Pedunculate Oak (Quercus robur L.) and Sessile Oak (Quercrus petraea Liebl.) – a literature review with focus on wood pasture

Auswertungen von Untersuchungen über frühere Waldnutzungen sowie Waldweide legen nahe, dass die Verjüngung der mitteleuropäischen laubabwerfenden Eichenarten Stieleiche (Quercus robur L.) und Traubeneiche (Quercus petraea Liebl.) ein episodischer Prozess ist, mit oft langen Phasen ausbleibender Verjüngung im Wechsel mit Phasen der erfolgreichen Etablierung einer neuen Generation. Eine Vielzahl von Faktoren wirkt sich auf die Verjüngung der Eichen aus. Als besonders bedeutsam werden genannt die Lichtversorgung; Prädation der Eicheln insbesondere durch Mäuse, Wildschweine und andere Tiere; Verbiss durch Wildtiere und Weidetiere; Befall der Blätter durch Mehltau (Microsphaera alphitoides); Konkurrenz durch die Bodenvegetation; Spätfrost; sowie der Wasserhaushalt des Standorts. All diese Faktoren wirken in einem komplexen Wechselspiel zusammen. Zur Ansamung und erfolgreichen Etablierung der Eichen im Wald sind eine Auflichtung des Kronendachs sowie eine niedrigwüchsige Bodenvegetation notwendig. Letztere können beispielsweise durch Beweidung erreicht werden. Verbiss wird bei guter Lichtversorgung durch die Jungeichen gut vertragen, es bilden sich bonsai-artige Krüppelbäumchen mit tiefreichendem Wurzelwerk heraus. Ein Höhenwachstum setzt jedoch erst dann ein, wenn der Weidedruck reduziert wird. Dies kann durch zeitliche oder räumliche Schwankungen des Verbissdrucks erreicht werden (Weideruhe). Die laubabwerfende Stiel- und Traubeneiche muss daher als Intermediärtyp zwischen Pionierbaumart und „stresstolerator“ sensu GRIME et al. (1978) eingestuft werden. In vielen Kulturlandschaften finden sich Bedingungen zur erfolgreichen natürlichen Eichenetablierung, also ohne unterstützende waldbauliche Maßnahmen, heute nur mehr an linienförmigen saum- und mantelartigen Randstrukturen von Wäldern, in Hecken und Gebüschen – dort trotz des Vorhandenseins von Wild. Naturschutzfachliche Gründe und zu erwartende Klimaänderungen legen jedoch eine stärkere Beachtung und Förderung der Eichenverjüngung nahe. Hierzu stellt Beweidung im Wechsel mit Weideruhe eine in Vergessenheit geratene und heute nur mehr wenig bekannte Möglichkeit dar.Studies of historic forest uses and wood pastures allow the conclusion, that the regeneration of the central European deciduous oak species Pedunculate oak (Quercus robur) and Sessile oak (Quercus petraea) is an episodic process. It must be assumed, that long-lasting phases without successful regeneration of young oaks change with phases of successful establishment of a new oak generation. A number of factors is influencing the regeneration of oaks. The literature mentions light supply; predation of acorns by rodents, wild pigs and other acorn eating animals; browsing pressure by wild and domestic animals; infection of leaves with the mildew fungus Microsphaera alphitoides; competition with ground vegetation; late frost; and water supply. All these factors are interrelated in a complex way. It seems, that germination and successful establishment of these oaks depend from an open canopy and a low ground vegetation. In cultural landscapes, the last can be facilitated through wood pasture. Browsing is tolerated by the young oaks, when light supply is high. Under browsing pressure, oaks on open sites are able to survive, forming “bonsai-like” dwarfed deeply rooting treelets. However, height growth only can start after the end of grazing. This can be achieved by temporal and spatial fluctuations of browsing pressure. In terms of their life form strategy, Quercus robur and Q. petraea can be classified as stress-tolerating pioneers. In many cultural landscapes today, optimal sites for a successful natural establishment of oaks, i.e., without silvicultural supporting measures, can be found only along forest edges, in hedges and shrubland, even under presence of browsing wildlife. Today, arguments of nature conservation and climate change recommend an increased effort to facilitate oak regeneration. For that, periods of grazing changing with periods of succession can be a successful approach, which was well known in the past, but is nearly forgotten today

Comparison of four different programs for the analysis of hemispherical photographs using parameters of canopy structure and solar radiation transmittance

There have been many studies involving the use of hemispherical photographs to indirectly estimate canopy structures and forest light environments. A variety of commercial and free software packages are available for the analysis of hemispherical photographs. The costs of investment might represent an advantage of the free programmes over the commercial, but as yet little has been documented about the differences in their outputs and in the technical applications from a user (ecologist and forester) perspective. The objective of the study was to compare the canopy structure variables (canopy openness and effective plant area index) and solar radiation transmission estimates (direct, diffuse and global solar radiation transmittances) from digital hemispherical photographs taken under two forest canopy conditions (gap and closed canopy) in three different broadleaf forest regions (Chile, Germany, Venezuela) and calculated using four different programmes. The hemispherical photographs were analysed using one commercial (HemiView) and three free programmes (Gap Light Analyzer, hemIMAGE and Winphot). The results obtained revealed that all of the programmes computed similar estimates of both canopy structures and below-canopy solar radiation. Only the results relating to the effective plant area index with an ellipsoidal leaf angle distribution made with HemiView and Winphot deviated significantly. Other user aspects are also discussed, such as costs, image formats, computer system requirements, etc.In vielen Studien werden Hemisphärenphotos genutzt um indirekt die Kronenstruktur und die Belichtungsverhältnisse zu schätzen. Verschiedene kommerzielle und kostenfreie Softwarepakete sind zu Analyse von Hemisphärenphotos verfügbar. Es gibt bisher keine umfassende Vergleichsstudie zu Ergebnissen oder technischer Handhabung aus Sicht der Nutzer dieser Programme (Ökologen und Forstwissenschaftler). Das Ziel dieser Studie war der Vergleich der Schätzungen von Kronenstrukturvariablen (Kronenöffnung und effektiver Pflanzenflächenindex) Solartransmission (direkte, diffuse und Global-Strahlung) aus digitalen Hemisphärenphotos berechnet mit vier verschiedenen Programmen (kostenpflichtig: Hemi- View und frei: Gap Light Analyzer, hemIMAGE and Winphot). Die verwendeten Photos stammen aus drei verschiedenen Laubwaldregionen (Chile, Deutschland und Venezuela) und repräsentieren jeweils Verhältnisse unter geschlossenem Kronendach und in Lücken. Die ermittelten Schätzungen für die verschiedenen Strukturvariablen und Einstrahlungsverhältnisse zeigten eine sehr hohe Übereinstimmung. Einzig der effektive Pflanzenflächenindex basierend auf ellipsoider Blattwinkelverteilung unterschied sich signifikant zwischen den Programmen. Weitere für Nutzer interessante Aspekte wie Kosten, Bildformate, Systemvoraussetzungen und mehr wurden verglichen und diskutiert

How does radial growth of water-stressed populations of european beech (Fagus sylvatica l.) trees vary under multiple drought events?

European beech (Fagus sylvatica L.) trees are becoming vulnerable to drought, with a warming climate. Existing studies disagree on how radial growth varies in European beech in response to droughts. We aimed to find the impact of multiple droughts on beech trees’ annual radial growth at their ecological drought limit created by soil water availability in the forest. Besides, we quantified the influence of competition and canopy openness on the mean basal area growth of beech trees. We carried out this study in five near-natural temperate forests in three localities of Germany and Switzerland. We quantified available soil water storage capacity (AWC) in plots laid in the transition zone from oak to beech dominated forests. The plots were classified as ‘dry’ (AWC 60 mL). We performed dendroecological analyses starting from 1951 in continuous and discontinuous series to study the influence of climatic drought (i.e., precipitation-potential evapotranspiration) on the radial growth of beech trees in dry and less-dry plots. We used observed values for this analysis and did not use interpolated values from interpolated historical records in this study. We selected six drought events to study the resistance, recovery, and resilience of beech trees to drought at a discontinuous level. The radial growth was significantly higher in less-dry plots than dry plots. The increase in drought had reduced tree growth. Frequent climatic drought events resulted in more significant correlations, hence, increased the dependency of tree growth on AWC. We showed that the recovery and resilience to climatic drought were higher in trees in less-dry plots than dry plots, but it was the opposite for resistance. The resistance, recovery, and resilience of the trees were heterogeneous between the events of drought. Mean growth of beech trees (basal area increment) were negatively impacted by neighborhood competition and positively influenced by canopy openness. We emphasized that beech trees growing on soil with low AWC are at higher risk of growth decline. We concluded that changes in soil water conditions even at the microsite level could influence beech trees’ growth in their drought limit under the changing climate. Along with drought, neighborhood competition and lack of light can also reduce beech trees’ growth. This study will enrich the state of knowledge about the ongoing debate on the vulnerability of beech trees to drought in Europe

Floristic Change at the Drought Limit of European Beech (Fagus sylvatica L.) to Downy Oak (Quercus pubescens) Forest in the Temperate Climate of Central Europe

An increase in drought could cause shifts in species composition and vegetation structure. In forests it limits the occurrence of drought sensitive tree species which become replaced by drought tolerant tree species and forest communities. Under temperate macroclimatic conditions, European beech (Fagus sylvatica L.) naturally dominates the forested landscape, except on extremely shallow soil in combination with high irradiation. On these sites beech reaches its drought limit, and is replaced by forests dominated by species like downy Oak (Quercus pubescens s.l.) and English Oak (Quercus petraea L). Phytosociological and ecological data were collected in the transition (ecotone) between European beach stands and stands of more drought tolerant species in order to quantify the drought intensity threshold, above which beech is replaced by drought tolerant species. It was shown that favourable topographic and soil conditions partially compensated the unsuitable climatic conditions for beech. The ecotone between these forest types was found to be characterized by shallow soils with an available soil water storage capacity of 73 l/m² or less, and an irradiation intensity of 6000 MJ/m2 or more during the growing season. This indicates that under conditions of climate change beech would naturally still remain the dominant tree species on the majority of central European forest sites

Carbon and oxygen dual-isotopes indicate alternative physiological mechanisms opted by European beech trees to survive drought stress

Poor drought tolerance of European beech trees raised concerns in Europe. We hypothesized that beech could show an opposite physiological response to the same level of climatic drought with change in edaphic drought. We performed a combined analysis of δ$^{13}$C and δ$^{18}$O in tree rings to reveal retrospective temporal physiological responses of trees to drought. The edaphic drought was assessed by quantifying the capacity of soil to store water in plots (classified as “dry” and “less-dry”) near the drought limit of the species in three near-natural oak-beech ecotones in Germany and Switzerland. Neighbourhood competition was quantified. A climatic drought index was calculated from meteorological records and related to the δ$^{13}$C and δ$^{18}$O values of the trees. Trees from dry plots showed a higher response to drought and climatic dependency than less-dry plots. Neighbourhood competetion increased δ$^{18}$O values significantly. Dual isotope analysis shows a tendency of greater stomatal resistance in dry plots and higher stomatal conductance in less-dry plots. We conclude that beech trees belonging to the same population under changing soil water availability can show different physiological responses under climatic drought stress. Our finding indicates the high plasticity of the beech trees to survive drought stress with changing site conditions