Patterns of shrub expansion in Alaskan arctic river corridors suggest phase transition
Abstract
Recent increases in deciduous shrub cover are a primary focus of terrestrial
Arctic research. This study examined the historic spatial patterns of shrub
expansion on the North Slope of Alaska to determine the potential for a phase
transition from tundra to shrubland. We examined the historic variability of
landscape-scale tall shrub expansion patterns on nine sites within river valleys
in the Brooks Range and North Slope uplands (BRNS) between the 1950s and
circa 2010 by calculating percent cover (PCTCOV), patch density (PADENS),
patch size variability (CVSIZE), mean nearest neighbor distance (MEDIST) and
the multi-scale information fractal dimension (dI) to assess spatial homogeneity
for shrub cover. We also devised conceptual models for trends in these metrics
before, during, and after a phase transition, and compared these to our results.
By developing a regression equation between PCTCOV and dI and using universal
critical dI values, we derived the PCTCOV required for a phase transition
to occur. All nine sites exhibited increases in PCTCOV. Five of the nine sites
exhibited an increase in PADENS, seven exhibited an increase in CVSIZE, and
five exhibited a decrease in MEDIST. The dI values for each site exceeded the
requirements necessary for a phase transition. Although fine-scale heterogeneity
is still present, landscape-scale patterns suggest our study areas are either currently
in a state of phase transition from tundra to shrubland or are progressing
towards spatial homogeneity for shrubland. Our results indicate that the shrub
tundra in the river valleys of the north slope of Alaska has reached a tipping
point. If climate trends observed in recent decades continue, the shrub tundra
will continue towards homogeneity with regard to the cover of tall shrubs.
Description
The open access fee for this work was funded through the Texas A&M University Open Access to Knowledge (OAK) Fund.Department
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