Using geomorphology to map plant community distribution in complex polygonal tundra landscapes

Abstract:

Climate change over the next century is expected to substantially alter Arctic ecosystem structure and function, resulting in important feedbacks to global climate. Representing Arctic landscapes in the carbon cycle and climate models, however, is challenging because vegetation and soils vary over small spatial scales. Robust approaches are needed for identifying distinct plant communities for fine-scale model parameterizations, and for mapping the distribution of these communities to enable scaling from plot to grid-cell.

Here, we demonstrate how a novel technique using LiDAR-derived metrics to delineate micro-topographic features can also be applied to mapping plant community distribution in a polygonal tundra landscape on the Barrow Environmental Observatory (BEO), Alaska. We recorded species composition in 48, 1 x 1 m plots located across contrasting ice-wedge polygon types on the BEO in July 2012. One-way cluster analysis and non-metric multidimensional scaling identified four major plant communities, namely i) tall Carex (sedge) dominated communities, ii) mixed tall graminoid-forb-moss communities, iii) dry graminoid-lichen communities and iv) low-stature, lichen dominated-communities. These communities were strongly linked to micro-topography, corresponding with i) low centers ii) troughs, iii) rims and transitional polygon centers, and iv) high centers. We therefore combined plant community type with geomorphological analyses using high-resolution LiDAR-derived metrics (e.g. slope, curvature, flowpath distances) to delineate micro-topographic features to produce a vegetation map. The map was verified using 24 field survey transects in which plant community boundaries were mapped using DGPS. The approach performed well, with only a small (5%) over-estimate of the extent of trough communities and a corresponding under-estimate of rim and transitional center communities.

Overall, these analyses provide a framework which can be used for parameterizing fine-scale ecosystem models of the tundra at Barrow, including the vital component of determining fractional coverage of vegetation communities within the broader landscape. Future work will include incorporating soil variables, and determining the extent to which soil and vegetation classifications are coupled.