Relationships between Arctic shrub dynamics and topographically derived hydrologic characteristics

Abstract

Shrub expansion is a global phenomenon that is gaining increased attention in the Arctic. Recent work employing the use of oblique aerial photographs suggested a consistent pattern of positive change in shrub cover across the North Slope of Alaska. The greatest amounts of change occurred in valley slopes and floodplains. We studied the association between shrub cover change and topographically derived hydrologic characteristics in five areas in northern Alaska between the 1970s and 2000s. Change in total shrub cover ranged from −0.65% to 46.56%. Change in floodplain shrub cover ranged from 3.38% to 76.22%. Shrubs are preferentially expanding into areas of higher topographic wetness index (TWI) values where the potential for moisture accumulation or drainage is greater. In addition, we found that floodplain shrub development was strongly associated with high TWI values and a decreasing average distance between shrubs and the river bank. This suggests an interacting influence of substrate removal and stabilization as a consequence of increased vegetation cover.

UAV photogrammetry for mapping vegetation in the low-Arctic

“…Fine-scale topographic characteristics can also be quantified using SfM processing of UAV surveys to model hydrological flow paths and areas of concentrated flow (Lucieer et al 2014). These characteristics have an important control on tundra vegetation distribution and growth (Naito and Cairns 2011;Cameron and Lantz 2016).…”

Tall Deciduous Shrubs Offset Delayed Start of Growing Season Through Rapid Leaf Development in the Alaskan Arctic Tundra

“…First, higher nitrogen of taller shrubs may be related to the fact that tall deciduous shrubs tend to grow in areas where soil conditions facilitate their growth (Tape et al, 2012). For instance, increased subsurface water flow in naturally occurring deciduous shrub-dominated tundra compared to graminoid-dominated tundra increases nutrient flow (Giblin et al, 1991;Shaver and Chapin, 1991) and access to nitrogen (Naito and Cairns, 2011;Bonfils et al, 2012;Chapin et al, 1988). Second, their inherently thicker snowpack insulates soils from freezing air temperatures during the winter, thereby enabling higher rates of winter soil mineralization (Schimel et al, 2004;DeMarco et al, 2011), which would enable higher leaf nutrient contents.…”

“…Expansion of deciduous shrubs into primarily graminoid-dominated tundra in the Alaskan Arctic is evident in comparative historical photo interpretation (Tape et al, 2006) and has been quantified in field surveys . Deciduous shrub expansion has been attributed to increases in air temperature (Walker et al, 2006), subsurface water flow (Naito and Cairns, 2011;Tape et al, 2012), and soil nutrient mineralization . Findings from experimental manipulation studies suggest that deciduous shrubs will continue to expand and grow taller as arctic warming continues (Chapin et al, 1995;Wahren et al, 2005;Walker et al, 2006).…”

Woody Plant Encroachment: Causes and Consequences

“…Runoff and runon relationships and their substantive influences on woody plant abundance are also evident on gently sloping landscapes (Tongway et al 2001). Landscape-scale variation in rates and patterns of WPE in recent decades are therefore related to and constrained by topoedaphic variation (Wu and Archer 2005;Naito and Cairns 2011;Browning et al 2012;Rossatto et al 2014 Fig. 2.4, but sites on the landscape with a subsurface clay content of 17 % at 33 cm depth reached this cover asymptote about 30 years sooner than sites where the subsurface clay content was 25 % at 23 cm depth (Browning et al 2008).…”