Definition of surface stoniness and its classification
Surface stoniness
Surface boulders are boulders that are partly visible or whose outlines are clearly discernible at the ground surface. A surface boulder must not be covered by mineral soil, but it may be covered by a continuous humus layer (however, it must not be covered by peat). The humus layer must be removable with a light kick of the foot, so that part of the boulder is exposed.
The number of boulders and their size are assessed within a circular plot with a radius of 10 metres, i.e. an area of approximately 314 m².
The map in the link below shows which surface stoniness class is most dominant within an area, as well as the strength of the degree of dominance. Consequently, a darker shade within each class indicates a stronger dominance.
The dominance map has been created by combining the classes for surface boulder diameter and surface boulder abundance according to the following scheme:
The frequency map in the link below shows the occurrence of the surface stoniness class small-boulder, boulder-poor, expressed in frequency classes, as well as their proportion of the forest land area. For the surface stoniness class small-boulder, boulder-poor, the surface boulders within an assessed area (approximately 314 m²) number 1–20 and have an average diameter of 2–6 dm.
The frequency map in the link below shows the occurrence of the surface stoniness class small-boulder, boulder-rich, expressed in frequency classes, as well as their proportion of the forest land area. For the surface stoniness class small-boulder, boulder-rich, the surface boulders within an assessed area (approximately 314 m²) number more than 20 and have an average diameter of 2–6 dm.
The frequency map in the link below shows the occurrence of the surface stoniness class large-boulder, boulder-rich, expressed in frequency classes, as well as their proportion of the forest land area. For the surface stoniness class large-boulder, boulder-rich, the surface boulders within an assessed area (approximately 314 m²) number more than 20 and have an average diameter greater than 6 dm.
The frequency map in the link below shows the occurrence of the surface stoniness class large-boulder, boulder-poor, expressed in frequency classes, as well as their proportion of the forest land area. For the surface stoniness class large-boulder, boulder-poor, the surface boulders within an assessed area (approximately 314 m²) number fewer than 20 and have an average diameter greater than 6 dm.
The figure below summarises the rules for which boulders within a plot are counted as surface boulders. Räknas = Counted. Ja = Yes. No = Nej. Räknas ej om det är torv över blocket = Not counted if peat above the boulder.
Surface boulders – number
The number of surface boulders within an area of approximately 314 m² is estimated, and the abundance class is recorded according to the following:
The diameter of a surface boulder is defined as the mean of its maximum and minimum width in the horizontal plane. That is, the surface of the boulder is projected onto the ground plane, and sight lines for the maximum and minimum width are drawn through the centroid of the projected area (the height of the boulder above the ground surface is therefore not taken into account).
If the assessed area (approximately 314 m²) contains surface boulders and the number is at most five, their mean diameter is recorded. If more than five surface boulders are present, a so-called typical boulder is selected, belonging to the most common size class, and the diameter of this boulder is recorded.
The diameter of surface boulders is recorded according to the following classes:
Surface boulders – diameter
Boulder-free/no surface boulders 2.0–3.0 dm 3.0–4.0 dm 4.0–5.0 dm … and so on up to 97.1–98.0 dm ≥98.1 dm
The surface stoniness classes shown in the maps have been created by combining the classes for surface boulder diameter and surface boulder abundance (see tables above) according to the following scheme:
