This data set provides unique empirical data from triplets of Scots pine ( Pinus sylvestris L.) and European beech ( Fagus sylvatica L.) across Europe. Dendrometric variables are provided for 32 triplets, 96 plots, 7555 trees and 4695 core samples. These data contribute to our understanding of mixed stand dynamics. Dataset access at http://dx.doi.org/10.5061/dryad.8v04m . Associated metadata available at https://metadata-afs.nancy.inra.fr/geonetwork/apps/georchestra/?uuid=b3e098ca-e681-4910-9099-0e25d3b4cd52&hl=eng .
During the last decade, empirical research often showed superiority of ecosystem functions of mixed forest stands compared to monocultures, e.g. productivity (Río and Sterba 2009; Pretzsch et al. 2010, 2013; Vallet and Perot 2011, Condés et al. 2013; Bielak et al. 2014; Liang et al. 2016), structural diversity (Río et al. 2016a) or stability (Knoke et al. 2008). However, the underlying processes are often still poorly understood. Moreover, generalizations require empirical data from different growing conditions, e.g. soil and climate. This unique data set includes 32 triplets across 16 European countries (Fig. 1) representing different ecoregions. Each triplet includes two pure stands and one with the two species in mixture, all with similar climatic and soil conditions. Effects of mixing these species can be analysed with respect to their corresponding pure stands. Under the umbrella of COST Action FP1206 EuMIXFOR (European Network on Mixed Forests), these triplets were established for the common European tree species, Scots pine and European beech. These species differ in their functional traits, and the data set provides a unique opportunity to develop a general understanding of the causes and patterns of mixing responses.
All stands (plots) represent mostly even-aged and mono-layered forests. Intra-specific age (species in pure vs species in mixed stand) within each triplet is always similar; however, inter-specific age may differ. Plots within a triplet are mostly rectangular in shape ranging from 0.01 to 1.6 ha in size. The geographical location, altitude, slope, aspect, mean annual temperature, annual precipitation and substrate are available for each plot (Table 1). Due to the established gradient, these variables differ between triplets but are similar within each triplet.
A standard protocol for data collection was established and applied for each triplet. For all trees exceeding diameter at breast height of 7 cm, mandatory attributes (Table 2) were defined and collected including tree number (Nr), tree species, diameter at breast height (dbh), tree height (h) and crown base height (cbh). In addition, on each plot, increment core samples for 10–20 dominant trees per species and angle count samples (acs) for the sampled trees were collected (Bitterlich 1952). Specific information is assigned to each tree indicating its status (alive, dead or damaged). Only standing trees were recorded. Spatial location (Cartesian coordinates) of individual trees was defined as an optional variable but was measured on most plots.
The tree numbering system is in ascending order starting from 1 for trees located within the plot and, if recorded, 901 for trees outside but with part of their crowns inside the plot. For all labelled trees, the corresponding species was determined. Diameter at breast height was measured for all trees using girth tape while a digital hypsometer was used for measuring tree height and crown base height. Increment cores aiming to reach the pith were taken at 1.30 m height in north and east directions from the stem using increment borers. Likewise, 1–2 angle count samples (acs) were recorded using a relascope with basal area factor 4 or 1 m2 ha−1. All data were stored using predefined templates. In total, 7555 trees were measured and 4695 core samples were taken.
For 24 triplets, optional data of individual tree location and crown radii were collected. Crown radii (m) were mostly measured in N, NE, E, SE, S, SW, W and NW cardinal directions with a minimum of four directions. Tree spatial information is given in Cartesian coordinates referring to a point of origin, e.g. the south west corner post of the corresponding plot.
Data processing—stand level data
Stand characteristics such as mean tree dimension, basal area (BA m2 ha−1) and volume stock per hectare (V m3 ha−1) were derived for each plot and species group, pine and beech. Additional coniferous and deciduous species within the mixed stands were grouped either as pine or beech, respectively. In pure stands, all additional species were assigned to the corresponding main species. Stand attributes are based on all surveyed living trees within the corresponding plot and are expressed per ha. A Petterson height curve function (Petterson 1955) was parameterized for each plot and species group. Missing tree heights and the height of quadratic mean diameter tree (hg) were calculated applying the corresponding height curve function. Stand volume was derived while taking into account each individual tree’s diameter at breast height, derived tree height and species-specific form factors (Franz 1971). All stand characteristics (Table 3) were calculated using standard evaluation software available at the Chair of Forest Growth and Yield Science, TU München (Biber 2013).
Access to data and metadata description
The data set is available from the Dryad Digital Repository http://dx.doi.org/10.5061/dryad.8v04m (Heym et al. 2017) and cover five files (Contact.txt, TripletInformation.txt, Trees.txt, Crowns.txt and Cores.txt). Contact.txt file includes all contact information of the specific data provider. Associated metadata available at https://metadata-afs.nancy.inra.fr/geonetwork/apps/georchestra/?uuid=b3e098ca-e681-4910-9099-0e25d3b4cd52&hl=eng.
TripletInformation.txt provides plot and stand characteristics. The first two columns (Triplet and Plot) identify each plot. Plot characteristics cover year and month of the survey (year and month), plot size (area), location (longitude and latitude), elevation above sea level (altitude), inclination (slope), exposition (aspect), temperature (t), precipitation (p) and substrate (substrate). Stand characteristics cover tree species (species), age (Age), number of trees (N), quadratic mean diameter (dg) and corresponding height (hg), basal area (BA) and merchantable stand volume over bark (V). All variables refer to 1 ha and the main species (species) pine or beech, respectively. Additional species are assigned either as pine or beech as described in methods.
Trees.txt includes all measured tree attributes. Each row describes one tree and can be identified by columns Triplet, Plot and Nr. Tree information covers scientific species name (species), tree’s spatial information (x and y), diameter at breast height (dbh), tree height (h), crown base height (cbh) and two angle count measurements for the cored trees (acs_1 and acs_2). Column cored distinguishes cored trees (1) and non-cored trees (0). Any additional information is given in column remarks.
Crowns.txt contains all measured crown radii (distance) with its corresponding cardinal direction (azimuth). Column Triplet, Plot and Nr ensure the link to the corresponding tree in Trees.txt. In addition y_axis_to_north describes the deviation of the y-axis to north direction.
Cores.txt file contains all year ring width values (rw) for each year (year) and the two different directions (azimuth). Column Triplet, Plot and Nr ensure unique tree identification and link the corresponding tree attributes.
Missing information is always described using NA. All tables can be linked based on the columns Triplet, Plot and Nr. Detailed description of the metadata can be found in the supplementary material (EuMIXFOR Scots pine - European beech data.xlsx).
Validation of each data set was performed including crosschecks by hand, graphical and numerical tests. First, the unit of tree attributes and year ring width was carefully validated. Tree and corresponding core labels were compared manually and corrected where needed. Cross-dating of radial increment was performed by each collaborator and inconsistent cores were dropped. The relationship of individual tree height to its corresponding diameter at breast height, expressed by a Petterson height curve, was analysed for each triplet, shown as an example for triplet 1032 in Fig. 2.
Crown base height was validated by visualizing cbh and corresponding tree height. If spatial information was available, visual inspection was applied to validate tree position and crown measurements. In addition, allometric relationships between diameter at breast height and crown projection area (cpa), calculated based on mean squared crown radii, cpa = a ∗dbhb , were validated visually (Fig. 3).
Location of border trees was inspected by means of graphical output. Core data were also compared with species-specific variation of basal area increment in pure and mixed stands within each triplet (Fig. 4).
All data were imported into an access database and technical plausibility checks were applied, e.g. data types or duplicates.
Reuse potential and limits
The original data set covers attributes at the tree level, increments cores, stand and triplet characteristics and has been used for different purposes by Pretzsch et al. (2015, 2016), Río et al. (2016b, 2017), Dirnberger et al. (2016) and Forrester et al. (2017). The data set presented here describes the original data, but ongoing projects can complement the published data by additional measurements of resource supply, nutritional status and wood properties. Furthermore, it has the potential to reveal the effect of site conditions on the mixing responses at the stand, species and individual tree level. Available spatial information allows analyses of crown projection (Dirnberger et al. 2016), crown architecture or light regimes. The available core data allow retrospective analyses and can be linked to corresponding tree attributes, e.g. Pretzsch et al. (2016) or Río et al. (2017). Reconstructing stand characteristics provides temporal stand level information, e.g. Pretzsch et al. (2015). Moreover, spatial information of most of the plots allows for distance dependent analysis at small scales.
However, for specific analyses, some plot sizes could be too small. Tree and stand characteristics are only available for the year of survey. Therefore, temporal analyses require reconstructions at the tree and stand levels.
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This article is based upon work from COST Action FP1206 (EuMIXFOR), supported by COST (European Cooperation in Science and Technology). All contributors thank their national funding institutions and the woodland owners for agreeing to establish, measure, analyse and reuse data from the triplets. Many thanks to the anonymous reviewer and data paper handling editor Marianne Peiffer for their helpful comments to improve the early draft of the manuscript.
Networking for the design and discussion of the transect study was supported by COST Association during FP1206 COST Action (EuMIXFOR: European mixed forests – Integration Scientific Knowledge in Sustainable Forest Management). Funding for the establishment of the plots and collection of the data belonged to co-author.
Contribution of the co-authors
All co-authors contributed to the data set with establishing the triplets, supervising and undertaking field campaigns, data providing, synchronizing core data. M.H. wrote the data paper, all coauthors reviewed it and H.P. coordinated the transect study.
Handling Editor: Marianne Peiffer
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Heym, M., Ruíz-Peinado, R., Del Río, M. et al. EuMIXFOR empirical forest mensuration and ring width data from pure and mixed stands of Scots pine (Pinus sylvestris L.) and European beech (Fagus sylvatica L.) through Europe. Annals of Forest Science 74, 63 (2017). https://doi.org/10.1007/s13595-017-0660-z
- EuMIXFOR data
- Mixed and monospecific stands
- Mixed stand dynamics
- Scots pine
- European beech