Rokliden (Sweden) 1905-1926
Location and Scale
Rokliden, 26km west of Piteå in north Sweden at 65°19′N, 20° 59′E
A 8.64 ha plot
1905 - 1926
The yearly precipitation during the period 1906–1929 at Fagerheden, 2 km north of the research site, was 531 ± 98mm, including an increasing trend of 7mm per year. The monthly maximum was 81mm in August and minimum was 20mm in February (Malmström, 1931). Fagerheden is also the station in the official Swedish precipitation network that recorded the highest ever daily amount of precipitation – 198mm on 28 July 1997 (SMHI, 2013). During 1961–1990, the yearly precipitation was 640mm (SMHI, 2013), i.e. an increase by 20% from the first period. Air temperature data from the nearest climate station at Piteå was used to describe the local climate at Rokliden. The yearly mean temperature at Piteå for the period 1906–1927 was 1.9 +/- 0.8 °C (Malmström, 1931), and for 1961–1990, it was 1.7 °C (SMHI, 2013), but it was lower at Rokliden because of its higher elevation. The coldest month at Piteå was January (-9.6 °C) and the warmest July (16.2 °C). Run-off from the Råneå River at Niemisel, 90km NE of Rokliden (SMHI, 2013), was used together with precipitation data from Fagerheden to obtain the water balance for the hydrological years 1906/07–1915/16.
Geology and Soils
The bedrock consists of gneiss, frequently of granite character. Outcrops are found in many places north of the research site (Tamm, 1931). The soil consists of ordinary till (cf. Table I) sometimes somewhat worked by water at the surface, sand and peat. The sand has typically been washed down into sallow depressions in the till surface and is therefore often overlain by a thin peat layer, deeper than 0.3m in some patches, but never deeper than 0.7 m. The soil depth is from less than 1m to at least 3m (Tamm, 1931).
The plot was located located 2 km down a 3-km-long, gently sloping (~4%), north facing, till slope, interspersed with small mires, with an asltitude range 243–253.5m
Vegetation / Land Use
The Norway Spruce dominated forest was 150–220 years old in 1925 and to a large extent cut during the ensuing 5 years (Malmström, 1931). In the northeast corner of the site, 3400m2 was clear cut in 1908 to evaluate the effect of a forest stand and its removal on paludification (Hesselman, 1909).
During the last decades of the 19th century, a great worry arose about forest landscape paludification in Northern Sweden. This was the original impetus for forest hydrological research in Sweden. Because of the debate about whether ongoing paludification threatened forest productivity in northern Sweden, a scientific assessment of the situation was one of the first tasks given to the botanical section of the Swedish institute of Experimental Forestry. When G. Andersson got the position as the first botanist of the Swedish Institute of Experimental Forestry in 1902, he recruited Henrik Hesselman as an assistant.
After preliminary investigations (Andersson and Hesselman, 1907), it was clear that it was necessary to obtain time series of vegetation patterns and groundwater levels and the Swedish Institute of Experimental Forestry established the first field research site in 1905 at Rokliden, close to Piteå in North Sweden. By 1931, it was concluded that paludification was not spreading across Northern Sweden at an appreciable rate.
Within the Rokliden research site, 22 groundwater wells were installed and levels measured weekly until 1926. A map with 0.5m equidistance, ten vegetation classes, and soil profiles was established. Groundwater flow velocity was estimated by tracing added sodium chloride. Hydraulic conductivity was measured on undisturbed soil cores, while mechanical and chemical analyses were carried out on other samples. Groundwater was collected and analysed for dissolved compounds including oxygen.
The importance of hydrology for soil types and vegetation development is one of the main enduring legacies from Rokliden. This is still included in basic forest site classification in Sweden even though the origins at Rokliden are long since forgotten. The dominant but intermittent role of upper soil horizons for till soil drainage was also tested using experimental data at Rokliden. When developing the theory for podzol development in till soil, Tamm (1931) showed the importance of drainage from below in lowering groundwater below the conducting upper horizons using experience from Rokliden.
Modern measurements in the re-established groundwater observation network and reanalysis of old data confirmed the plausibility of these original conclusions. Partial catchment area could explain rates of both groundwater level rise and recession. Revisiting this field study reveals that many issues in contemporary hillslope hydrology were already established a century ago, even though the provenance of that knowledge is not generally recognized.
Much more detail on the site and the data collected are given in Grip (2015).
Grip, Harald, 2015, Sweden’s first forest hydrology field study 1905–1926: contemporary relevance of inherited conclusions and data from the Rokliden Hillslope, Hydrol. Process. 29: 3616–3631, DOI: 10.1002/hyp.10420
Andersson G, Hesselman H. 1907. Vegetation och flora i Hamra kronopark. Meddelanden från Statens Skogsförsöksanstalt 4: 35–102; Skogsvårdsföreningens tidskrift 5: 41–110.
Malmström C. 1931. Om faran för skogsmarkens försumpning i Norrland. En studie från Kulbäckslidens och Roklidens försöksfält. Meddelanden från Statens Skogsförsöksanstalt 26: 1–126. (Deutsches Resümee: Über der Gefahr der Versumpfung des Waldbodens in Norrland (Nordschweden), 127–162). Stockholm.
Tamm O. 1931. Studier över jordmånstyper och deras förhållande till markens hydrologi i nordsvenska skogsterränger. Meddelanden från Statens Skogsförsöksanstalt 26: 163–355. (Deutsches Resumé: Studien über Bodentypen und ihre Beziehungen zu den hydrologischen Verhältnissen in nordschwedischen Waldterrains, 356–408). Stockholm.