Spatial variation and linkages of soil and vegetation in the Siberian Arctic tundra – coupling field observations with remote sensing data
Authors: Mikola Juha , Virtanen Tarmo , Linkosalmi Maiju , Vähä Emmi , Nyman Johanna , Postanogova Olga , Räsänen Aleksi , Kotze D. Johan , Laurila Tuomas , Juutinen Sari , Kondratyev Vladimir , Aurela Mika 
Published: May 2018

Abstract. Arctic tundra ecosystems will play a key role in future climate change due to
intensifying permafrost thawing, plant growth and ecosystem carbon exchange,
but monitoring these changes may be challenging due to the heterogeneity of
Arctic landscapes. We examined spatial variation and linkages of soil and
plant attributes in a site of Siberian Arctic tundra in Tiksi, northeast
Russia, and evaluated possibilities to capture this variation by remote
sensing for the benefit of carbon exchange measurements and landscape
extrapolation. We distinguished nine land cover types (LCTs) and to
characterize them, sampled 92 study plots for plant and soil attributes in
2014. Moreover, to test if variation in plant and soil attributes can be
detected using remote sensing, we produced a normalized difference vegetation
index (NDVI) and topographical parameters for each study plot using three
very high spatial resolution multispectral satellite images. We found that
soils ranged from mineral soils in bare soil and lichen tundra LCTs to soils
of high percentage of organic matter (OM) in graminoid tundra, bog, dry fen
and wet fen. OM content of the top soil was on average 14 g dm−3 in bare
soil and lichen tundra and 89 g dm−3 in other LCTs. Total moss biomass
varied from 0 to 820 g m−2, total vascular shoot mass from 7 to 112 g m−2
and vascular leaf area index (LAI) from 0.04 to 0.95 among LCTs. In
late summer, soil temperatures at 15 cm depth were on average 14 ∘C in bare soil and lichen tundra, and varied from 5 to 9 ∘C in
other LCTs. On average, depth of the biologically active, unfrozen soil layer
doubled from early July to mid-August.
When contrasted across study plots,
moss biomass was positively associated with soil OM % and OM content and
negatively associated with soil temperature, explaining 14–34 % of
variation. Vascular shoot mass and LAI were also positively associated with
soil OM content, and LAI with active layer depth, but only explained 6–15 %
of variation. NDVI captured variation in vascular LAI better than in
moss biomass, but while this difference was significant with late season
NDVI, it was minimal with early season NDVI. For this reason, soil attributes
associated with moss mass were better captured by early season NDVI.
Topographic attributes were related to LAI and many soil attributes, but not
to moss biomass and could not increase the amount of spatial variation
explained in plant and soil attributes above that achieved by NDVI. The LCT
map we produced had low to moderate uncertainty in predictions for plant and
soil properties except for moss biomass and bare soil and lichen tundra LCTs.
Our results illustrate a typical tundra ecosystem with great fine-scale
spatial variation in both plant and soil attributes. Mosses dominate plant
biomass and control many soil attributes, including OM % and temperature,
but variation in moss biomass is difficult to capture by remote sensing
reflectance, topography or a LCT map. Despite the general accuracy of
landscape level predictions in our LCT approach, this indicates challenges in
the spatial extrapolation of some of those vegetation and soil attributes
that are relevant for the regional ecosystem and global climate models.