Biosoil soil data for Finland

The purpose of the Biosoil soil inventory (ICP Forests - level I - test plots) was to assess the chemical state of the soil and its changes, and secondly to assess the soil properties that affect the functioning of the forest land. In addition to the fact that the Biosoil data provides soil information for the study of the effects of atmospheric deposition on a larger scale, the soil inventory serves other purposes as it provides data for both research diciplines, climate change mitigation (e.g. the amount of carbon and its changes) and sustainable forest management (e.g., in addition to acidification, also, for example, studies on nutrient cycles and imbalances).

Soil profile data was collected as part of the BioSoil project, Natural Resources Institute Finland, Luke (former Finnish Forest Research Institute, METLA). The BioSoil project was implemented as part of ICP Forests (International Cooperative Program on the Assessment and Monitoring of Air Pollution Effects on Forests; icp-forests.net/) and the EU Forest Focus program (Tamminen and Ilvesniemi 2013). The aim of the project was to collect information on soil properties, composition and changes in carbon, nutrients, acidity and heavy metals in Finnish forest lands. The material was collected in the so-called From the network of ICP Forests Forest Focus Level I experimental area in 2006-2007, which were first sampled for soil samples in 1986-1995 (Tamminen and Starr 1994, Tamminen 2009). This network is part of the so-called 3,000 permanent sample plot data. In Finland, the BioSoil database contains 631 experimental plots, while the total number of the plots in Europe is around 6000 (icp-forests.net/). A detailed description of all the collected data and variables is given in BioSoil Kuvio- ja puusto-ohjeet (2006).

In the laboratory, the particle size categories (clay, silt and sand) of the soil profile samples were determined. Approximate content of soil organic matter for the mineral soils was determined for different layers based on loss on ignition at a temperature of 550 °C for about two hours. In addition, the concentrations of several elements were determined from the samples.

The basic data of the experimental area include: latitude, longitude, altitude from sea level, soil moisture, slope, topographical location, bare rock cover (%), soil type, parent material, coarse particle content (%), soil texture, site type and Sphagnum cover (%).

Information was collected from the mineral soils by the EU funded Biosoil project during 2006-2007 (Tamminen, 2006; Tamminen ja Ilvesniemi, 2013).

Data have been used in several research projects (Heiskanen ym. 2018, Heiskanen ym. 2020, Launiainen ym. 2022, Lehtonen ym. 2016, Mäkelä ym. 2022, Rantakari ym. 2012).

## 3,000 permanent sample plots established 1985-86

In connection with the 8th national forest inventory in 1985-1986, approximately 3,000 permanent experimental plots were established for the purpose of monitoring the nature of the forest and the state of the environment. The plots were located in a network of forest inventory covering the entire country. The distances between the clusters of plots in southern Finland are 16 km both in the south-north direction and in the east-west direction. In northern Finland, the distances are 24 km in the south-north direction and 32 km in the east-west direction. Each cluster has a group of plots in the direction from south to north including 4 plots every 400 meters in Southern Finland and 3 plots every 600 meters in Northern Finland.

For the BioSoil project, one plot was selected and measured from each cluster. The data collection of the forest inventories and the assessment of surface areas are based on the division of each plot on the forestry land into management units. Management units have been formed based on the properties of the tree stand. A management unit is a homogeneous area in terms of soil type and trees, as well as the forest management measures that have been carried out in the area. The 4-acre permanent circular sample plot area used in the inventory can be divided into several forest management units. For example, if a part of the test area belongs to a different land class, forest type, or sample plot locates to be on the border of a peatland and a forest or on the border of a tree development class, it is divided into different management units according to the stand properties.

If necessary, the biologists refined the management unit borders assessed by the inventory team by refining management units borders by the cover drawing made from the sample plot. The refinement of the management unit was based on the site types. The smallest distinguishable management unit had to be at least 5% of the area of the of the sample plot (4 acres). In the inventory, the coverage of field and understory species was estimated from four 2 m2 sample squares systematically placed in the 4-acre experimental area. The abundance of each plant species was evaluated as projected coverage, i.e. the percentage covered by aerial shoots and mixed stems on the sample plot. Coverages were estimated with an accuracy of 1%, coverage below 1% with an accuracy of 0.1%. The biologists of the inventory groups received uniform training for the field work. A large number of tree stand and growth location codes have been inventoried from the plots. Soil samples have also been taken from the inventory plots.

BioSoil土壤调查（ICP Forests-一级-试验样地）的目的在于评估土壤的化学状态及其变化，其次是评估影响林地功能的土壤特性。除了为大尺度研究大气沉降效应提供土壤信息外，该调查还服务于其他目的：为气候变化减缓（如碳储量及其变化）和可持续森林管理（如酸化研究之外，还包括养分循环与失衡研究等）两大研究领域提供数据支撑。

土壤剖面数据由芬兰自然资源研究所（Luke，前身为芬兰森林研究所METLA）的BioSoil项目收集。BioSoil项目是ICP森林空气污染影响评估与监测合作计划（ICP Forests，官网：icp-forests.net/）及欧盟Forest Focus计划的一部分（Tamminen和Ilvesniemi，2013）。该项目旨在收集芬兰林地土壤特性、组成及碳、养分、酸度和重金属变化的相关信息。研究材料取自2006-2007年ICP Forests Forest Focus一级试验区网络，这些样地首次土壤采样时间为1986-1995年（Tamminen和Starr，1994；Tamminen，2009）。该网络是所谓“3000个永久样地”数据的一部分。芬兰BioSoil数据库包含631个试验样地，而欧洲范围内的样地总数约为6000个（icp-forests.net/）。所有收集数据及变量的详细描述见《BioSoil Kuvio- ja puusto-ohjeet》（2006）。

实验室中测定了土壤剖面样品的粒径分类（黏土、粉砂和砂）。矿质土壤不同土层的有机质近似含量通过550℃下约两小时的烧失量（loss on ignition）测定。此外，还测定了样品中多种元素的浓度。

试验区的基础数据包括：纬度、经度、海拔、土壤湿度、坡度、地形位置、裸岩覆盖率（%）、土壤类型、母质、粗颗粒含量（%）、土壤质地、立地类型及泥炭藓覆盖率（%）。

矿质土壤的相关信息由欧盟资助的BioSoil项目于2006-2007年收集（Tamminen，2006；Tamminen和Ilvesniemi，2013）。

该数据已应用于多项研究项目（Heiskanen等，2018；Heiskanen等，2020；Launiainen等，2022；Lehtonen等，2016；Mäkelä等，2022；Rantakari等，2012）。

1985-1986年建立的3000个永久样地

在1985-1986年第八次全国森林调查期间，为监测森林特征与环境状况，建立了约3000个永久样地（permanent sample plot）。这些样地分布于覆盖全国的森林调查网络中。芬兰南部样地集群的南北向与东西向间距均为16 km；芬兰北部样地集群的南北向间距为24 km，东西向间距为32 km。每个集群包含一组样地，从南到北排列：芬兰南部每400米设4个样地，北部每600米设3个样地。

BioSoil项目从每个集群中选取并测量1个样地。森林调查的数据收集及面积评估基于林地样地划分为经营单元的方式。经营单元根据林分特性划分，是土壤类型、林木特征及经营措施均一致的均质区域。调查中使用的4英亩永久圆形样地可划分为多个经营单元。例如，若样地部分区域属于不同土地类别、森林类型，或样地位于泥炭地与森林边界、林木发育阶段边界，则需根据林分特性划分为不同经营单元。

必要时，生物学家会通过样地覆盖图修正调查团队评估的经营单元边界，修正依据为立地类型。最小可区分经营单元面积需至少占样地（4英亩）的5%。调查中，在4英亩样地内系统设置4个2 m²样方，用于估算草本及林下植物的覆盖率。每种植物的丰度以投影盖度（即样地上气生枝条与混合茎秆覆盖的百分比）评估，盖度≥1%时精度为1%，<1%时精度为0.1%。调查团队的生物学家接受了统一的野外工作培训。样地中还调查了大量林分及生长位置编码，并采集了土壤样品。