Biomass allometry for alder, dwarf birch, and willow in boreal forest and tundra ecosystems of far northeastern Siberia and north-central Alaska

Shrubs play an important ecological role in the Arctic system, and there is evidence from many Arctic regions of deciduous shrubs increasing in size and expanding into previously forb or graminoid-dominated ecosystems. There is thus a pressing need to accurately quantify regional and temporal variation in shrub biomass in Arctic regions, yet allometric equations needed for deriving biomass estimates from field surveys are rare. We developed 66 allometric equations relating basal diameter (BD) to various aboveground plant characteristics for three tall, deciduous shrub genera growing in boreal and tundra ecoregions in far northeastern Siberia (Yakutia) and north-central Alaska. We related BD to plant height and stem, branch, new growth (leaves+new twigs), and total aboveground biomass for alder (Alnus viridis subsp. crispa and Alnus fruticosa), dwarf birch (Betula nana subsp. exilis and divaricata), and willow (Salix spp.). The equations were based on measurements of 358 shrubs harvested at 33 sites. Plant height (r²=0.48-0.95), total aboveground biomass (r²=0.46-0.99), and component biomass (r²=0.13-0.99) were significantly (P<0.01) related to shrub BD. Alder and willow populations exhibited differences in allometric relationships across ecoregions, but this was not the case for dwarf birch. The allometric relationships we developed provide a tool for researchers and land managers seeking to better quantify and monitor the form and function of shrubs across the Arctic landscape.