Pixel walking along the boreal forest-Arctic tundra ecotone: Large scale ground-truthing of satellite-derived greenness (NDVI).

In this Technical Advance, we describe a novel method to improve ecological interpretation of remotely sensed vegetation greenness measurements that involved sampling 24,395 Landsat pixels (30 m) across 639 km of Alaska's central Brooks Range. The method goes well beyond the spatial scale of traditional plot-based sampling and thereby more thoroughly relates ground-based observations to satellite measurements. Our example dataset illustrates that, along the boreal-Arctic boundary, vegetation with the greatest Landsat Normalized Difference Vegetation Index (NDVI) is taller than 1 m, woody, and deciduous; whereas vegetation with lower NDVI tends to be shorter, evergreen, or non-woody.

Arctic sea ice retreat fuels boreal forest advance.

Climate-induced northward advance of boreal forest is expected to lessen albedo, alter carbon stocks, and replace tundra, but where and when this advance will occur remains largely unknown. Using data from 19 sites across 22 degrees of longitude along the tree line of northern Alaska, we show a stronger temporal correlation of tree ring growth with open water uncovered by retreating Arctic sea ice than with air temperature. Spatially, our results suggest that tree growth, recruitment, and range expansion are causally linked to open water through associated warmer temperatures, deeper snowpacks, and improved nutrient availability.

Sufficient conditions for rapid range expansion of a boreal conifer.

Unprecedented modern rates of warming are expected to advance boreal forest into Arctic tundra, thereby reducing albedo, altering carbon cycling and further changing climate, yet the patterns and processes of this biome shift remain unclear. Climate warming, required for previous boreal advances, is not sufficient by itself for modern range expansion of conifers forming forest-tundra ecotones. No high-latitude population of conifers, the dominant North American Arctic treeline taxon, has previously been documented advancing at rates following the last glacial maximum (LGM).

Species turnover in ant assemblages is greater horizontally than vertically in the world's tallest tropical forest.

Abiotic and biotic factors structure species assembly in ecosystems both horizontally and vertically. However, the way community composition changes along comparable horizontal and vertical distances in complex three-dimensional habitats, and the factors driving these patterns, remains poorly understood. By sampling ant assemblages at comparable vertical and horizontal spatial scales in a tropical rainforest, we tested hypotheses that predicted differences in vertical and horizontal turnover explained by different drivers in vertical and horizontal space.

Using fractal self-similarity to increase precision of shrub biomass estimates.

We show that aerial tips are self-similar fractals of whole shrubs and present a field method that applies this fact to improves accuracy and precision of biomass estimates of tall-shrubs, defined here as those with diameter at root collar (DRC) ≥ 2.5 cm. Power function allometry of biomass to stem diameter generates a disproportionate prediction error that increases rapidly with diameter.

What color should glacier algae be? An ecological role for red carbon in the cryosphere.

Red-colored secondary pigments in glacier algae play an adaptive role in melting snow and ice. We advance this hypothesis using a model of color-based absorption of irradiance, an experiment with colored particles in snow, and the natural history of glacier algae. Carotenoids and phenols-astaxanthin in snow-algae and purpurogallin in ice-algae-shield photosynthetic apparatus by absorbing overabundant visible wavelengths, then dissipating the excess radiant energy as heat.

Shrubline but not treeline advance matches climate velocity in montane ecosystems of south-central Alaska.

Tall shrubs and trees are advancing into many tundra and wetland ecosystems but at a rate that often falls short of that predicted due to climate change. For forest, tall shrub, and tundra ecosystems in two pristine mountain ranges of Alaska, we apply a Bayesian, error-propagated calculation of expected elevational rise (climate velocity), observed rise (biotic velocity), and their difference (biotic inertia). We show a sensitive dependence of climate velocity on lapse rate and derive biotic velocity as a rigid elevational shift.

Metagenome sequencing of prokaryotic microbiota collected from Byron Glacier, Alaska.

Cold environments, such as glaciers, are large reservoirs of microbial life. The present study employed 16S rRNA gene amplicon metagenomic sequencing to survey the prokaryotic microbiota on Alaskan glacial ice, revealing a rich and diverse microbial community of some 2,500 species of bacteria and archaea.

Historical biogeography of the North American glacier ice worm, Mesenchytraeus solifugus (Annelida: Oligochaeta: Enchytraeidae).

North American ice worms are the largest glacially-obligate metazoans, inhabiting coastal, temperate glaciers between southcentral Alaska and Oregon. We have collected ice worm specimens from 10 new populations, completing a broad survey throughout their geographic range. Phylogenetic analyses of 87 individuals using fragments of nuclear 18S rRNA, and mitochondrial 12S rRNA and cyctochrome c oxidase subunit 1 (CO1) identified 18 CO1 haplotypes with divergence values up to ~10%.