Spatial variation and linkages of soil and vegetation in the Siberian Arctic tundra – coupling field observations with remote sensing data

Abstract

Abstract. Arctic tundra ecosystems will have 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 20 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) -bare soil, lichen tundra, shrub tundra, flood meadow, graminoid tundra, bog, dry fen, wet den and water -to classify the variation in our site. To characterize the LCTs, we sampled 92 study plots for plant (biomass and leaf area index, LAI) and soil 25 (organic matter OM%, bulk density, moisture, pH, litter layer depth, litter mass loss, temperature and active layer depth) 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 (QuickBird and WorldView-2, portraying vegetation at 180, 220 and 750 growing degree days, DD with 0 °C threshold) and a digital elevation model (derived from a WV-2 stereo-30 pair image). We found that soils in our site ranged from mineral soils in bare soil and lichen tundra (on average 3.9 % OM) to soils of high OM% in graminoid tundra, bog, dry fen and wet fen (38 %), with shrub tundra and flood meadow Vascular shoot mass and LAI were also positively associated with soil OM content, and LAI with active layer depth, but the amount of variation explained was significantly lower (6-15 %). NDVI captured variation in peak season vascular LAI better than variation in moss biomass, but the difference depended on the phase of the growing season in the image:180-DD, 220-DD and 750-DD NDVI captured 23, 17 and 7 % of moss mass variation and 25, 34 and 50% of vascular 5 LAI variation, respectively. For this reason, soil attributes associated with moss mass were better captured by early season NDVI and those associated with LAI by late season NDVI. Topographic attributes were related to LAI and many soil attributes, but not to moss biomass and they could not increase the amount of spatial variation explained in plant and soil attributes above that achieved by NDVI. 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 10 OM% and temperature, but variation in moss biomass is difficult to capture by remote sensing reflectance or topography.This suggests that using simple reflectance indices and DEM for spatial extrapolation of those vegetation and soil attributes that are relevant for regional ecosystem and global climate models warran...

Interpreting eddy covariance data from heterogeneous Siberian tundra: land cover-specific methane fluxes and spatial representativeness

“…The mean annual temperature and precipitation at Tiksi in 1981-2010 were -12.7 °C and 323 mm, respectively (AARI, 2018). The study area is within the continuous permafrost zone; the depth of the active soil layer typically varied within 0.2-0.4 m in early Julymid-August 2014 (Mikola et al, 2018). The landscape around the EC tower represents the coastal tundra zone of eastern Siberia with a high diversity of plant species and communities (Nyman, 2015;Juutinen et al, 2017;Mikola et al, 2018).…”

“…The land cover classification was based on seven visually judged plant community types (PCTs) augmented by two nonvegetated surfaces: (1) wet fen, (2) dry fen, (3) bog, (4) graminoid tundra, (5) flood meadow, (6) shrub tundra, (7) lichen tundra, (8) bare ground and (9) water (Mikola et al, 2018). The PCTs were identified within an area of 1 km 2 around the EC tower on the basis of an extensive vegetation and soil survey.…”

“…The internal and external classification accuracy of the land cover classification were 80 and 49 %, respectively. For details, see Mikola et al (2018).…”

“…TWI is defined as a function of the upslope contributing area and the local terrain slope, and thus it serves as a proxy for potential soil moisture. For details of the DEM and TWI data, see Mikola et al (2018). All maps have a 2 m pixel size, and in this study they were limited to a circle with a radius of 1.4 km from the EC tower, which defines the domain of the present study.…”

“…Arctic tundra serves as a prime example of a surface that is heterogeneous with respect to biogeochemical processes. The vegetation, soil and land cover structure of tundra areas are fragmented, the landscape typically comprising patches of different plant communities, water bodies and other land cover types (Stow et al, 2004;Virtanen and Ek, 2014;Mikola et al, 2018). Such heterogeneity concerns both the composition and configuration of surface properties.…”