DOI: 10.5061/dryad.f7m0cfz4b
title: Tundra plant communities along the mesotopographic gradient in NE Finland

description: We describe plant communities along the mesotopographic gradient in the
 low-elevation subcontinental mountains of NE Finland (Utsjoki region). We
 sampled vascular plants, bryophytes, and lichens along 18 mesotopographic
 ridge-snowbed transects comprising a total of 180 plots. We used
 non-metric multidimensional scaling (NMDS) ordination with envfit to
 explore the differentiation of plant communities in relation to
 mesotopography, elevation, rock cover, the cover of bare ground, snow bed
 size, and snowmelt time. The classification of communities was performed
 using DIANA clustering. Plant communities were differentiated
 along the mesotopographic gradient, snowmelt time, elevation, and rock
 cover. The DIANA analysis distinguished seven clusters corresponding to
 the following communities: Betula nana−Lichenes heath,
 Empetrum−Myrtillus−Stereocaulon heath, Empetrum−Pleurozium−Lichenes heath,
 graminoid-rich snow-protected heath, Oreojuncus trifidus–Avenella flexuosa
 snow-protected heath, Polytrichastrum sexangulare–liverwort snowbed, and
 Salix herbacea–Kiaeria starkei snowbed. Because of the strong impact of
 snowmelt time on plant community structure and distribution of
 communities, it is likely that climate change-induced changes in snow
 conditions are affecting tundra vegetation, and especially snow beds are
 threatened. Snowbed communities in the Utsjoki region roughly align with
 previously described vegetation associations of mountain areas in NW
 Europe. The assignment of the graminoid-rich snow-protected health
 community remains uncertain.
description: Vegetation data was sampled in the summer of 2019 along 18
 mesotopographical transects in NE Finland (Utsjoki). GPS coordinates of
 the transects were recorded using Garmin 64SX GPS. Transects were designed
 to cover the snow depth gradient at a 15−30 m distance from the top of the
 ridge to the depression with snowbed vegetation. Eight 0.8 m x 0.8 m plots
 were placed at regular intervals along each transect. In each plot,
 vascular plants, bryophytes, and macro lichens were identified, and their
 coverage was visually estimated. The coverage of each species was
 estimated using a modified logarithmic Hult−Sernander−Du Rietz scale
 consisting of 10 classes. The identifications were made at the species
 level, when possible, based on collected specimens (i.e. if specimens were
 large enough and contained all needed distinguishing
 characteristics).<em> Lophozia</em> spp., including
 <em>Barbilophozia sudetica</em>, were treated as collectives
 as were some lichens such as <em>Cladonia arbuscula</em> and
 <em>C</em>. <em>mitis</em>. The coverage classes
 were later converted to percentage values of each class center, which
 correspond to cover percentages of 71.2, 35.6, 18.9, 8.9, 4.4, 2.2, 1.1,
 0.5, 0.25, and 0.125. The coverage of bare soil and stones was also
 estimated using the same scale. Two extra plots were sampled for each
 snowbed, at a 1.5−5 m distance from the last plot at the snowbed end of
 the transect. Extra plots are marked in the data with the letter E. To
 render long-term monitoring of vegetation, both ends of the transects were
 marked in the field, and coordinates were collected using a GPS
 receiver. We estimated the mesotopography for each plot
 (1−8, which 1 = ridge, 8 = snow bed) along with the elevation, size (m²),
 and snowmelt time for snow beds. Snowmelt time was evaluated from Landsat
 and Sentinel 2 images from 3−5 summers, depending on the availability of
 cloud-free images. Based on snowmelt time, snow beds were divided into
 three classes (1−3) which of 1 represents early-melting, 2
 intermediate-melting, and 3 late-melting snowbeds. Early-melting snow beds
 were mostly snow-free at the end of June (range 8 June−16 July),
 intermediate-melting snowbeds at the beginning of July (range 24 June−28
 July), and late-melting snow beds at the end of July or beginning of
 August (range 10 July−17 August). There was considerable year-to-year
 variation in snowmelt times, while the order of snowmelt appeared to be
 quite constant. Thus, the estimates describe relative, but not exact, snow
 melting time.
description: # **Tundra plant communities along the mesotopographic gradient in NE
 Finland**
 [https://doi.org/10.5061/dryad.f7m0cfz4b](https://doi.org/10.5061/dryad.f7m0cfz4b) The data was collected to study plant communities along mesotopographic ridge-snowbed gradients. Vegetation data were collected along 18 mesotopographic transects comprising a total of 180 plots. In each plot, vascular plants, bryophytes, and macro lichens were identified, and their coverage was visually estimated. Taxa identifications were made to species level always when it was possible. The length of the transect varied from 15 to 30 meters. The size of the vegetation plots was 0.8 x 0.8 m. Eight plots were placed at regular intervals along the transects. In addition, two extra plots were sampled for each snowbed, at a 1.5−5 m distance from the last plot at the snowbed end of the transect. The coverage of each species was estimated using a modified logarithmic Hult−Sernander−Du Rietz scale consisting of 10 classes. These classes were later converted to percentage values of each class center, which correspond to cover percentages of 71.2, 35.6, 18.9, 8.9, 4.4, 2.2, 1.1, 0.5, 0.25, and 0.125. ## Description of the data and file structure File name: Data_snowbed_Utsjoki_Finland Environmental data fields, rows 1-17: Plot: plot ID, extra plots are marked with E Site: Transect ID Mesotopography: The position of the plot along mesotopographic transect (1−8, which 1 = ridge, 8 = snow bed) Snowmelt time: Snowmelt time of the snowbed. Three classes (1−3) which of 1 represents early-melting, 2 intermediate-melting, and 3 late-melting snow beds. Early-melting snow beds were mostly snow-free at the end of June (range 8 June−16 July), intermediate-melting snow beds at the beginning of July (range 24 June−28 July), and late-melting snowbeds at the end of July or beginning of August (range 10 July−17 August). This was evaluated from Landsat and Sentinel 2 images, from 3−5 summers, depending on the availability of cloud-free images. Elevation: Approximatively elevation of the transect, m a.s.l. Aspect: Slope aspect (where 0 is north-facing, 90 is east-facing, 180 is south-facing, and 270 is west-facing estimated as degrees) Size: Size of the snow bed (m²) x: x-coordinate of the transect y: y-coordinate of the transect Vegetation_zone: Vegetation zone of the transects. Two categories: 1) hemioroarctic and 2) lower oroarctic Date: Date when data was collected Transect_direction: Direction of the transect from snow bed to ridge Transect_lenght: Lenght of the transects (m) Vegetation_community_DIANA: Vegetation community of the plot based on DIANA clustering. Divided to seven communities: 1 = *Oreojuncus trifidus*–*Avenella flexuosa snow-protected heath*, 2 = *Empetrum*−*Pleurozium*−*Lichenes heath*, 3 = *Empetrum−Myrtillus−Stereocaulon heath*, 4 = *Graminoid-rich snow-protected heath*, 5 = *Betula nana−Lichenes heath*, 6 = *Salix herbacea–Kiaeria starkei snowbed*, 7 = *Polytrichastrum sexangulare–liverwort snowbed.* Herbivory: the amount of droppings of small rodents in a plot. Three categories: abundant, some, and none Stones: Coverage of stones in the plot. Values are percentage values of the class center of a modified logarithmic Hult−Sernander−Du Rietz scale classes (10 classes). Bare_ground: Coverage of bare ground in the plot. Values are percentage values of the class center of a modified logarithmic Hult−Sernander−Du Rietz scale classes (10 classes). Species data, rows 18-229: Species observed on the plots. Values are percentage values of the class center of a modified logarithmic Hult−Sernander−Du Rietz scale classes (10 classes). The nomenclature of species follows the FinBIF checklist (FinBIF 2024).