Biodiversitäts-Forschung AFSV Waldökologie, Landschaftsforschung und Naturschutz Heft 11 (2011) S. 49–61 4 Fig., 2 Tab. + Anh. urn:nbn:de:0041-afsv-01157 Impact of the admixture of European beech (Fagus sylvatica L.) on plant species diver- sity and naturalness of conifer stands in Lower Saxony Auswirkungen der Einbringung von Buche (Fagus sylvatica L.) auf die Artendiversität und Naturnähe von Nadelholzbeständen in Niedersachsen Sabine Budde, Wolfgang Schmidt and Martin Weckesser Abstract Buche (Fagus sylvatica) in standortsfremden Nadelholz- Monokulturen die Bedingungen im Sinne des Naturschutzes The promotion and extension of continuous cover mixed und der Forstwirtschaft verbessert. Diese Hypothese wird stands with a simultaneous reduction of conifer-monocultures auf der Grundlage von drei unterschiedlichen Nadelholz- play a major role in current silvicultural practices in Cen- Buchen-Versuchsreihen geprüft. Im Mittelpunkt steht dabei tral Europe. It is assumed that the admixture of the natural die Bodenvegetation als wichtiger und sensitiver Indikator dominant beech (Fagus sylvatica) in pure non site-specific für den ökologischen Zustand von Wäldern. Jede Versuchs- conifer stands automatically indicates better conditions in reihe umfasst reine Nadelholz-Bestände (Picea abies, Pinus terms of nature conservation and forest management. To test sylvestris, Pseudotsuga menziesii), Nadelholz-Buchen- this hypothesis three different conifer-beech-comparisons of Mischbestände und reine Buchen-Bestände auf sauren pure and mixed stands in Lower Saxony are studied, analys- Mineralböden, auf denen von Natur aus nährstoffarme Buchen- wälder (Luzulo-Fagetum) vorherrschen würden. Das ing plant species diversity and naturalness of understorey Alter der Bestände variiert zwischen 50 und 150 Jahren. vegetation as one important indicator for the ecological Schwerpunkte der Analyse sind die Artenvielfalt und Naturnähe status of forests. Each comparison includes pure conifer- der Bodenvegetation. Um den Einfluss der Baumarten auf den ous stands (Picea abies, Pinus sylvestris, Pseudotsuga men- Standort und die Vegetation zu bewerten, werden die Licht- und ziesii), mixed coniferous-beech-stands, and pure beech stands Bodenverhältnisse der Bestände charakterisiert. on similar acidic mineral soils where the potential natural vegetation will be an oligotrophic beech forest (Luzulo- Es zeigt sich, dass mit der Beimischung der Buche in allen Versuchsreihen die Pflanzenartenvielfalt abnimmt und die Fagetum). The age of stands varies between 50 and 150 Naturnähe zunimmt. Unterschiedlich ist dabei die Intensität der years. To specify tree species influence on site conditions Veränderungen. Zwischen den Kiefern-Buchen-Mischbestän- and vegetation, the study also includes light climate and soil den und den Kiefern-Reinbeständen bestehen sehr deutliche data of the stands. Unterschiede im Aufbau der Bodenvegetation, so dass die It is observed that, with regard to all comparisons, the ad- Mischbestände den Buchen-Reinbeständen bereits sehr ähnlich sind. In den Douglasien- und Fichten-Versuchsreihen mixture of beech reduces plant species diversity but increases vollzieht sich der Artenwechsel vergleichsweise unauffällig naturalness of the stands. The intensity of beech admixture und kontinuierlich. Wenn man davon ausgeht, dass der effects differs. While in Scots pine stands the impact of ad- naturschutzfachliche und waldbauliche Status sich sowohl mixed beech is very noticeable, with the mixed stands being mit zunehmender Phytodiversität als auch bei zunehmen- nearly identical with pure beech stands, the species change der Naturnähe verbessert, so zeigen diese Ergebnisse auf in Douglas-fir and Norway spruce stands proceeds more Bestandesebene eine gegenläufige Entwicklung, da das in slowly. der Region der potenziell natürlichen Vegetation entspre- chende Luzulo-Fagetum von Natur aus sehr artenarm Assuming that the status in nature conservation and forest an Gefäßpflanzen ist. management is improving with increasing plant species diver- sity and increasing naturalness, the results of this study show Schlüsselwörter: Bodenvegetation, Luzulo-Fagetum, a contrary development on a stand scale, as the potential Picea abies, Pinus sylvestris, Pseudotsuga menziesii, Humus- natural vegetation of the L u z u l o - F a g e t u m is in its self akkumulation, Licht, pH-Wert, Naturschutz very species poor on vascular plants. 1 Introduction Keywords: Understorey vegetation, Luzulo-Fagetum, Picea abies, Pinus sylvestris, Pseudotsuga menziesii, humus In the 19th century in many parts of Central Europe there was widespread reforestation on degraded soils with non- accumulation, light, pH-value, nature conservation autochthonous coniferous tree species, such as Scots pine (Pinus sylvestris) or Norway spruce (Picea abies). These Zusammenfassung species were favoured because they were easy to establish Die Förderung und Ausweitung von Mischwäldern bei gleichzei- and to manage, and because these fast growing species tiger Reduktion reiner Nadelholz-Bestände spielt aktuell eine appeared to provide a solution to significant timber shortage große Rolle im mitteleuropäischen Waldbau. Gemeinhin wird at this time (SPIECKER 2003). Driven by a similar motivation angenommen, dass die Beimischung der standortsgemäßen for fast growing and high yielding timber crops, non-native Waldökologie, Landschaftsforschung und Naturschutz 11 (2011) 49 AFSV Biodiversitäts-Forschung Douglas-fir Pseudotsuga( menziesii) has also been introduced Lower Saxony (forest growth zone “Mitteldeutsches Trias-Berg- into many parts of Central Europe more recently (KOWARIK und Hügelland”, GAUER & AL DINGER 2005) and rise to 528 m 2010, KOWNATZKI et al. 2011). above sea level. The research area is characterized by a humid, sub-montane to montane climate (latitude: 51°40’ N–51°50’N, Today the use of these fast growing monocultures is still very longitude: 9°26’E–9°44’E, elevation: 300–450 m NN, annual common, but it is intensely debated because of their potential precipitation: 915–1,030 mm, mean annual temperature: instability and their negative impacts on biodiversity (SPIECKER 7.3 –7.8°C, GAUER & AL DINGER 2005). The parent rock of the 2003). A high level of biodiversity is thought to increase Solling plateau is red sandstone covered with loess. Therefore ecosystem stability, at least with respect to the diversity of the main soil type is an acid silty loam cambisol (FAO clas- overstorey tree species (SCHÜTZ 2001, SCHERER -LORENZEN et sification) with a high content of aluminium but a good water al. 2005, RÖHRIG et al. 2006, BAR B IER et al. 2008, PAQUETTE & ECKE ss ER ME ss IER 2011). Large-scale conversion of the existing even- supply (W 2003, with further details and maps of the aged coniferous stands into continuous cover mixed stands is research area and investigated stands). recognised as a solution to improve forest ecosystem stability and biodiversity. The main broadleaved tree species used in Investigations in the Pleistocene regions cover a much wider many forest conversions at present is European beech (Fagus geographic range, including three different forest growth sylvatica), which is one of the dominant native tree species of zones. The northernmost part is the coastal area of Lower Central European forests (BOHN & NEUHÄU sl 2000/2003). Saxony (forest growth zone “Niedersächsischer Küstenraum”, latitude: 53°24’ N–53°29’N, longitude: 9°00’E–9°20’E, eleva- Many studies have found unfavourable effects of conifer tion: 0–75 m NN, annual precipitation: 715–840 mm, mean plantations on vegetation, humus, soil etc. when compared annual temperature: 8.4–9.0°C, GAUER & AL DINGER 2005). to pure broadleaf stands (Norway spruce: ZER B E 1994, HÜTT L Following a climatic gradient from the Atlantic northwest to & SCHAAF 1995; Douglas-fir: KNOERZER et al. 1996, MARQUE S the more sub-continental affected southeast, the west-central & RANGER 1997; Scots pine: ZER B E et al. 2000, AUGU S TO et al. lowlands of Lower Saxony (forest growth zone “Mittelwestnied- 2002). Fewer studies have explicitly considered how conifer- ersächsisches Tiefland”, latitude: 52°33’ N–53°18’N, longitude: broadleaf mixtures influence biodiversity or site conditions 8°30’E–9°40’E, elevation: 75–150 m NN, annual precipitation: (Spruce/beech: LÜCKE & SCH M IDT 1997, MATTHE S 1998, LEIT L 650–810 mm, mean annual temperature: 8.5–9.3°C, GAUER & 2002, GÄRTNER 2003, ENGE L HARD & REIF 2004, Gr o d z i ń s k a et AL DINGER 2005) have a slightly lower annual precipitation and al. 2004, SCH M IDT et al. 2004; Douglas-fir/beech: VOR & SCH M IDT a higher mean annual temperature. Finally, at the end of the 2006; Pine/beech: SCH M IDT et al. 2004, VOR & SCH M IDT 2006, climatic gradient the eastern lowlands of Lower Saxony (forest DENNER & SCH M IDT 2008). The main objective of these stud- ies is often the analysis of biodiversity. The discussion of the growth zone “Ostniedersächsisches Tiefland”, latitude: 52°39’ results in context with naturalness or ecosystem functions is N–53°28’N, longitude: 9°45’E–10°40’E, elevation: 30–170 mostly lacking. m NN, annual precipitation: 560–810 mm, mean annual tem- perature: 8.1–9.1°C, GAUER & AL DINGER 2005) are situated. The It is assumed that stands of native forest trees automatically entire Pleistocene region is formed by glacial sedimentary entail a higher naturalness of the associated biotic communi- deposits resulting in sandy soils partly covered with loess. ties (FRITZ 2006, REIF & WA L ENTOW S KI 2008). However,