Abstract

The Arctic is currently undergoing intense changes in climate; vegetation composition and productivity are expected to respond to such changes. To understand the impacts of climate change on the function of Arctic tundra ecosystems within the global carbon cycle, it is crucial to improve the understanding of vegetation distribution and heterogeneity at multiple scales. Information detailing the fine-scale spatial distribution of tundra communities provided by high resolution vegetation mapping, is needed to understand the relative contributions of and relationships between single vegetation community measurements of greenhouse gas fluxes (e.g., ~1 m chamber flux) and those encompassing multiple vegetation communities (e.g., ~300 m eddy covariance measurements). The objectives of this study were: (1) to determine whether dominant Arctic tundra vegetation communities found in different locations are spectrally distinct and distinguishable using field spectroscopy methods; and (2) to test which combination of raw reflectance and vegetation indices retrieved from field and satellite data resulted in accurate vegetation maps and whether these were transferable across locations to develop a systematic method to map dominant vegetation communities within larger eddy covariance tower footprints distributed along a 300 km transect in northern Alaska. We showed vegetation community separability primarily in the 450–510 nm, 630–690 nm and 705–745 nm regions of the spectrum with the field spectroscopy data. This is line with the different traits of these arctic tundra communities, with the drier, often non-vascular plant dominated communities having much higher reflectance in the 450–510 nm and 630–690 nm regions due to the lack of photosynthetic material, whereas the low reflectance values of the vascular plant dominated communities highlight the strong light absorption found here. High classification accuracies of 92% to 96% were achieved using linear discriminant analysis with raw and rescaled spectroscopy reflectance data and derived vegetation indices. However, lower classification accuracies (~70%) resulted when using the coarser 2.0 m WorldView-2 data inputs. The results from this study suggest that tundra vegetation communities are separable using plot-level spectroscopy with hand-held sensors. These results also show that tundra vegetation mapping can be scaled from the plot level (<1 m) to patch level (<500 m) using spectroscopy data rescaled to match the wavebands of the multispectral satellite remote sensing. We find that developing a consistent method for classification of vegetation communities across the flux tower sites is a challenging process, given the spatial variability in vegetation communities and the need for detailed vegetation survey data for training and validating classification algorithms. This study highlights the benefits of using fine-scale field spectroscopy measurements to obtain tundra vegetation classifications for landscape analyses and use in carbon flux scaling studies. Improved understanding of tundra vegetation distributions will also provide necessary insight into the ecological processes driving plant community assemblages in Arctic environments.

Highlights

  • IntroductionChanges in vegetation composition and productivity are predicted to occur due to a lengthening of the growing season [4,5,6], increases in air and soil temperature and active layer depth [7,8], increased shrub cover [9,10], and acceleration of below ground microbial activity and nutrient cycling [3,11,12]

  • The Arctic is currently undergoing dramatic changes in climate [1,2,3]

  • Scaling from plot (e.g., UniSpec) to landscape (WorldView-2) was challenging because of the difference in spatial resolution between the field spectroscopy narrow band reflectance data and the multispectral satellite imagery. These results indicate that multispectral satellite imagery having a spatial resolution of 2 m is not spatially adequate to represent the innate sub-meter vegetation heterogeneity found in these ecosystems as described by Muster et al [76]

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Summary

Introduction

Changes in vegetation composition and productivity are predicted to occur due to a lengthening of the growing season [4,5,6], increases in air and soil temperature and active layer depth [7,8], increased shrub cover [9,10], and acceleration of below ground microbial activity and nutrient cycling [3,11,12] These changes influence the terrestrial carbon cycle and alter the relationship between arctic ecosystems and global climate. Increasing temperatures may heighten methane (CH4 ) and CO2 release from thawing permafrost, enhancing plant-mediated transport of CH4 [14,15] and contributing to rising levels of greenhouse gases in the atmosphere.

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