This dataset provides information about the study design, topography, geographic location and climatic conditions of the research plots of the interdisciplinary research training group 'RTG2300: Enrichment of European beech forests with conifers'. In each of forty forest stands, plots of 0.25 ha in size (called regular measurement plots, RMPs) were established in fall 2017 across the federal state of Lower Saxony, northwest Germany. The plots are grouped in eight so-called 'quintets'. Each quintet comprises five plots representing different forest stand types: three pure plots (European beech (Fagus sylvatica), Douglas-fir (Pseudotsuga menziesii), Norway spruce (Picea abies)) and two beech-conifer mixtures (beech-Douglas-fir and beech-Norway spruce). Four of the eight quintets are located in the southern part of the study area in the Solling and Harz mountain ranges. The other four quintets are located in the northern part of the study area in the North German plain. The southern plots are located in higher altitudes with lower mean annual temperatures and a higher annual precipitation. Growing conditions on the northern plots are less favorable than on the southern sites, in particular with respect to precipitation. On a subset of twenty out of the forty plots, intensive surveys such as root growth measurements, nitrogen retention analyses, or experiments on regeneration dynamics are carried out, besides the regular measurements on all plots. These intensive measurement plots (IMPs) comprise two southern and two northern quintets. Permanent, highly intensive measurements are conducted on special measurement plots (SMPs) that are a subset of 10 out of the 20 IMPs.
This dataset contains information from a tree census on the plots of the interdisciplinary research training group 'RTG2300: Enrichment of European beech forests with conifers'. The tree cesus was carried out during winter 2017/2018 using a Field-Map system (software Version 5x; IFER - Monitoring and Mapping Solutions, Ltd.; Prague; Czech Republic). All living and dead trees with a diameter greater or equal than 7.0 cm were recorded in the 0.25 ha plots (https://doi.pangaea.de/10.1594/PANGAEA.923125) and in a ten meter buffer zone surrounding the plot border. Tree coordinates relative to the plot center were recorded with a laser range finder with an integrated electronic compass (TruPulse Laser 360 R, Laser Technology Inc, Centennial, USA). Tree diameters were measured with a diameter tape preferentially at 1.3 m height. If a diameter measurement at 1.3 m was not possible, the alternative height of the diameter measurement was recorded. Tree species, tree vitality (dead or alive) and tree condition ('normal', 'snag', 'hung_up', 'sloping', 'thrown', 'stump') of each tree and heights of snags were recorded.
Climate change will substantially alter native forest ecosystem dynamics. Increased storm frequencies and severities and longer summer droughts are major threats for the provision of ecosystem goods and services (EG&S) from forests. To adapt forests stands to climate change, two silvicultural measures have been proposed: (i) the promotion of mixed stands and (ii) the integration of exotic tree species that are expected to be adapted to future climatic conditions (in particular from areas with a drier and warmer climate). Non-native tree species as well as mixed stands may be better suited for the expected future climate due to a higher resistance and resilience against disturbances. The combination of mixed stands that consist of native and non-native tree species, may present a suitable compromise between the desired effects on growth and vitality of forests and potential undesired effects on the composition of native species associations and ecosystem processes such as nutrient cycling. Despite high potential benefits of mixed stands, planted forests around the globe are mainly monocultures. To foster the provision of EG&S, more knowledge about the mechanistic functioning of mixtures as well as trade-offs between the provision of different EG&S from mixed and pure stands is necessary. Interdisciplinary research projects are necessary that address effects of mixtures consisting of native and non-native tree species on the composition of various taxonomic groups, ecosystem processes and their consequences for the provision of EG&S. The interdisciplinary research training group 'RTG2300: Enrichment of European beech forests with conifers' addresses this knowledge gap by studying the mechanistic and supplying ecosystem functioning of forest stands of native European beech (Fagus sylvatica L.), Norway spruce (Picea abies L. KARST) and non-native Douglas-fir (Pseudotsuga menziesii MIRB. FRANCO) in Northern Germany. The stand types in this project include pure stands of all three species and mixed beech/spruce and beech/Douglas-fir stands. Each stand type is represented at eight locations resulting in a total of forty study plots. Twenty out of the forty research plots of 0.25 ha size are located in the southern part of the study area in the Solling and Harz mountain ranges, whereas the other twenty plots were selected in the northern part of the study area in the North German plain. The southern plots are located at higher altitudes with lower mean annual temperatures and a higher annual precipitation than those in the north. The stands on the northern plots have less favorable growing conditions than those on the southern plots, in particular due to less precipitation. Here, we provide basic datasets that were collected by the RTG2300. This includes data about location, topography and climate of the research plots, data of the tree inventories and data about the density and spatial structure of the stands that were derived from the tree inventory data.
Many human activities have repercussions that are profoundly altering natural ecosystems at large-scales. The physical interference by humans with the climate systems has been intensively studied and has become increasingly clear. Significant progress has also been made in assessing range shifts of species and various other ecological responses such as altered species interactions. However, the consequences for ecosystem functioning and possible feedbacks on climate are still poorly understood. This is particularly true for aquatic ecosystems. In addition, information is exceedingly scant on the interactive effects of multiple environmental factors that are changing simultaneously. The proposed project builds on our previous experiments in a freshwater marsh to assess the combined effects of elevated temperature and nutrient loading on litter decomposition, a critical component of carbon cycling at the local and global scale in a variety of ecosystems. The general hypothesis is that impacts of elevated temperature, nutrient loading and the interaction of both are not readily predictable from current theory or through simple laboratory experiments, and that the magnitude of effects is such that important ramifications for elemental flows both within wetlands and across their boundaries are likely to result. I propose testing at this stage a series of specific hypotheses derived from our previous findings and relating to the effects of temperature and nutrients on decomposition. The focus will be on three priorities: (1) testing whether the lack of stimulation of litter decomposition by nitrogen enrichment that we observed is due to the limiting role of phosphorus in the marsh; (2) testing whether a shift in life-history patterns of specific detritivore taxa is responsible for the observed dramatic acceleration of litter decomposition in spring under simulated global warming; and (3) assessing whether the observed lack of effects by elevated temperature and nutrient loading on stem litter decomposition may be related to changes in O2 regimes during long-term operation of enclosures. The backbone of the proposed experiments to address these questions is a unique manipulative field experiment in enclosures installed in a littoral marsh dominated by Phragmites australis. Enclosures are heated to 4 C above ambient water temperature or enriched with Ca(NO3)2 or both. The experiment is set up as a randomized block design (N = 4) with two factors (temperature and nitrate enrichment), each with two levels. An open-marsh control is also included. The first two questions will be addressed in combined field enclosure and laboratory microcosm experiments, while the third question will be addressed in a field enclosure experiment only. The processes considered in different experiments include litter decomposition, nutrient immobilization, microbial respiration and productivity, enzymatic activity, and various measures of detritivore performance.