Phytomass patterns across a temperature gradient of the North American arctic tundra

Only a few studies to date have collectively examined the vegetation biomass and production of arctic tundra ecosystems and their relationships to broadly ranging climate variables. An additional complicating factor for studying vegetation of arctic tundra is the high spatial variability associated with small patterned‐ground features, resulting from intense freeze‐thaw processes. In this study, we sampled and analyzed the aboveground plant biomass components of patterned‐ground ecosystems in the Arctic of northern Alaska and Canada along an 1800‐km north‐south gradient that spans approximately 11°C of mean July temperatures. Vegetation biomass was analyzed as functions of the summer warmth index (SWI–sum of mean monthly temperatures > 0°C). The total absolute biomass (g m −2 ) and biomass of shrubs increased monotonically with SWI, however, biomass of nonvascular species (mosses and lichens), were a parabolic function of SWI, with greatest values at the ends of the gradient. The components of plant biomass on patterned‐ground features (i.e., on nonsorted circles or within small polygons) were constrained to a greater degree with colder climate than undisturbed tundra, likely due to the effect of frost heave disturbances on the vegetation. There were also clear differences in the relative abundances of vascular versus nonvascular plants on and off patterned‐ground features along the SWI gradient. The spatial patterns of biomass differ among plant functional groups and suggest that plant community responses to temperature, and land‐surface processes that produce patterned‐ground features, are quite complex.