Relationships Between Visual Obstruction and Aboveground Biomass in Shortgrass Steppe

Authors: Derner, Justin; Augustine, David

Submitted to: Society for Range Management Meeting Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: 9/25/2009
Publication Date: 2/22/2010
Citation: Derner, J.D., Augustine, D.J. 2010. Relationships Between Visual Obstruction and Aboveground Biomass in Shortgrass Steppe. In: Proceedings of the Society of Range Management and Weed Science Society of America joint annual meeting, "Working landscapes, providing for the future." Abstract PC-20. p. 316.

Interpretive Summary:

Technical Abstract: Visual obstruction is increasingly used by management agencies for decision-making and monitoring of remaining residue levels. Applicability of this technique for shortgrass steppe may be limited, however, given the dominance of short-statured vegetation such as blue grama [Bouteloua gracilis (Willd. Ex Kunth) Lag. ex Griffiths]. Our objective was to determine if relationships existed between visual obstruction and total aboveground biomass (current and prior year) and only current year biomass for shortgrass steppe. We recorded visual obstruction to the nearest 1 cm at the long ends of a 20 x 50 cm rectangular quadrat prior to clipping prior and current year biomass. Quadrats were sampled in early August in 2008 and 2009 from pastures that were ungrazed, light, moderate, heavy and very heavily grazed. Preliminary analyses indicate that visual obstruction accounts for about half of the variation in total and current year biomass when individual quadrat values were used (n=173), and 82-86% of the variation when pasture averages were used (n=16). Linear regressions of visual obstruction exhibited r2 values of 0.47 – 0.48 for the relationships of visual obstruction to total and current year aboveground biomass using individual quadrat data, and increased to 0.82-0.86 when pasture average values were used. Each 1 cm increase in visual obstruction was predicted to increase total aboveground biomass by 264-274 kg/ha and current year biomass by 252-274 kg/ha. Management applications of visual obstruction in shortgrass steppe for decision-making and monitoring have potential utility given the simplicity of this technique and application over large areas.