title: 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 (d I ) 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 d I and using universal critical d I 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 d I 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.
authors: Department of Geography, Texas A&M University 810 Eller O&M Building, Mailstop 3147 TAMU, College Station, Texas, 77843-3147.
authors: Adam T
authors: AT
authors: Naito
authors: Department of Geography, Texas A&M University 810 Eller O&M Building, Mailstop 3147 TAMU, College Station, Texas, 77843-3147.
authors: David M
authors: DM
authors: Cairns
keywords: Alaska; Arctic; landscape analysis; phase transition; shrub expansion; tundra
references: Acta Biotheor. 2002;50(3):141-54
references: 12211328
references: Ecol Lett. 2007 Jul;10(7):619-27
references: 17542940
references: Proc Natl Acad Sci U S A. 2012 Dec 26;109(52):21384-9
references: 23236159
references: Ecol Evol. 2013 Oct;3(11):3683-700
references: 24198933
references: Ecol Lett. 2012 Feb;15(2):164-75
references: 22136670
references: Proc Natl Acad Sci U S A. 2005 Sep 20;102(38):13521-5
references: 16174745
references: Nature. 2001 May 31;411(6837):546-7
references: 11385559
references: New Phytol. 2010 Jun;186(4):890-9
references: 20345642
references: Proc Natl Acad Sci U S A. 2006 Jan 31;103(5):1342-6
references: 16428292
references: Science. 2005 Oct 28;310(5748):657-60
references: 16179434