Abstract
Abstract. Upscaling plant biomass distribution and dynamics is essential for estimating carbon stocks and carbon balance. In this respect, the Russian Far East is among the least investigated sub-Arctic regions despite its known vegetation sensitivity to ongoing warming. We representatively harvested above-ground biomass (AGB; separated by dominant taxa) at 40 sampling plots in central Chukotka. We used ordination to relate field-based taxa projective cover and Landsat-derived vegetation indices. A general additive model was used to link the ordination scores to AGB. We then mapped AGB for paired Landsat-derived time slices (i.e. 2000/2001/2002 and 2016/2017), in four study regions covering a wide vegetation gradient from closed-canopy larch forests to barren alpine tundra. We provide AGB estimates and changes in AGB that were previously lacking for central Chukotka at a high spatial resolution and a detailed description of taxonomical contributions. Generally, AGB in the study region ranges from 0 to 16 kg m−2, with Cajander larch providing the highest contribution. Comparison of changes in AGB within the investigated period shows that the greatest changes (up to 1.25 kg m−2 yr−1) occurred in the northern taiga and in areas where land cover changed to larch closed-canopy forest. As well as the notable changes, increases in AGB also occur within the land-cover classes. Our estimations indicate a general increase in total AGB throughout the investigated tundra–taiga and northern taiga, whereas the tundra showed no evidence of change in AGB.
Highlights
Estimated global mean surface temperature has increased by 0.87 ◦C since pre-industrial times and continues to rise (IPCC, 2018)
In the larch closed-canopy forest L. cajanderi makes the highest contribution to above-ground biomass (AGB) (92 % or 10.20 kg m−2 (IQR = 5.09 kg m−2) on average of the total of 11.04 kg m−2 (IQR = 4.98 kg m−2), Fig. 5)
Total AGB in the tundra focus area has not changed over the time studied (0 kg m−2, interquartile range (IQR) = 0.2 kg m−2), while in the northern tundra–taiga it has increased by 0.69 kg m−2 (IQR = 0.69 kg m−2) and in the southern tundra–taiga by 0.44 kg m−2 (IQR = 0.91 kg m−2)
Summary
Estimated global mean surface temperature has increased by 0.87 ◦C since pre-industrial times and continues to rise (IPCC, 2018). The Arctic is warming 2 to 3 times faster than the global annual average. In the course of global warming, positive feedbacks can be observed: for example, encroachment of deep-rooted vegetation due to shrubification can lead to deeper carbon deposition and act as a potential carbon sink (Jobbágy and Jackson, 2000). Estimation of above-ground biomass (AGB) stocks and detailed knowledge about the individual taxa contributing to it is of prime interest in understanding whether the northernmost forests and tundra change in biomass in analogy to the widespread observed shrubification. This information is essential for modelling terrestrial carbon cycling in vulnerable high-latitude
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