EnriCo: Enrichment of European beech forests with conifers: impacts of functional traits on ecosystem functioning

The societal demands for ecosystem goods and services are globally increasing. One possibility to meet this challenge is to manage forests in such a way that aspects of wood production and forest conservation are combined. Against this background, mixed forest stands composed of locally occurring native tree species and highly productive tree species growing outside of their native range are of particular interest. Despite the importance of native-non-native tree species mixtures, their impact on ecosystem functioning has rarely been studied. It is generally assumed that presence, abundance, distribution, and diversity of functional traits are more important for ecosystem functioning than species diversity per se. To study this assumption in further detail, EnriCo aims at identifying the functional traits and associated mechanisms that control ecosystem functioning in pure and mixed stands of European beech (Fagus sylvatica, a deciduous tree species which would be the dominant tree species in Central Europe under natural conditions), Norway spruce (Picea abies, a native conifer species mainly cultivated outside its natural range) and Douglas-fir (Pseudotsuga menziesii, a non-native conifer species, which originates from the Pacific Northwest of North-America). It is hypothesized that mixtures of European beech with conifers show higher functional diversity than pure European beech stands and that the effects of admixed conifers on ecosystem functioning are more pronounced in mixtures with Douglas-fir.

40 forest stands differing in tree species composition and site quality have been selected. The set of plots is based on 40 preselected forest stands (called regular measurement plot, RMPs) across the federal state of Lower Saxony that contain series of mixed species plots (Douglas-fir and European beech, Norway spruce and European beech, respectively) and pure species plots. The RMP stands are older than 60 years and comprise 8 ‘quintets’ each with three pure plots (European beech, Douglas-fir, Norway spruce) and two beech-conifer mixtures (beech-Douglas-fir and beech-Norway spruce). The quintets will be used to avoid bias due to regional clustering of stand types. The RMPs will cover a range of nutrient and water conditions. The stands have been managed according to the currently best practice guidelines of the lower Saxony state forest enterprise. Species in a mixed RMP stand contribute > 20 % to the basal area. Each plot is 50 m x 50 m in size. Depending on the ecosystem level under investigation, additional measurements of different intensity will take place on the plots. Very laborious measurements will be conducted on a sub-set of 20 plots out of the total number of 40 plots. On these 20 intensive measurement plots (IMPs, 4 quintets along the range of nutrient and water conditions of the RMPs), intensive measurements will be carried out beside the regular measurements of all subprojects. Permanent, highly intensive measurements will be done on special measurement plots (SMPs) which are a subset of 10 out of the 20 IMPs. Thus, the experimental layout is a nested design.

Eleven closely linked subprojects focus on key functional traits of the tree species and associated biota and the mechanisms that link them with ecosystem functioning. The interdisciplinary research approach requires close cooperation between students and supervising scientists which will be facilitated by different team building activities. The concept of qualification is based on an ambitious and clearly structured programme of intensive interdisciplinary research and supervision, which will support top-class PhD studies. Special options for further qualification and support for career planning are offered to a postdoctoral researcher. The comprehensive programme will expose the students to a broad array of methods, ranging from molecular genetics, over ecophysiology and isotope analyses to sophisticated regression modelling. The systematic and profound research-oriented qualification will generate highly skilled natural resource managers with topical knowledge and skills that cross disciplinary boundaries and provide key qualifications for careers in academia, the public sector and enterprises.