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United States Department of Agriculture

Agricultural Research Service

Title: A Visual Obstruction-Based Technique for Photo Monitoring of Willow Clumps

Authors
item Boyd, Chad
item Svejcar, Anthony

Submitted to: Journal of Range Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 7, 2004
Publication Date: July 1, 2005
Citation: Boyd, C.S., Svejcar, A.J. 2005. A visual obstruction-based technique for photo monitoring of willow clumps. Journal of Range Management. 58(4):434-438.

Interpretive Summary: Quantifying woody plant abundance has often proven difficult in the field for reasons that include irregular plant morphology, between observer variability, and lack of standardized techniques. One potential solution to these challenges is the use of ground-based photographic technology. Our objective was to develop a photo-based technique could be used to monitor changes in willow (Salix spp.) abundance over time and estimate changes in abundance associated with herbivory. We focused on young willows (< 2m in height) because this size class represents a critical life history stage for establishment of willow clumps. In August of 2000 and 2001 we harvested 25 willow (Salix boothii Dorn.) clumps and clamped them in front of a 150 x 200cm fluorescent orange photoboard. Clumps were defoliated of photosynthetically active tissue (leaves and tips of current annual stem growth ' PAT) by hand in 4 to 7 increments and photographed before and after each removal. Images were scanned to digital format and the degree of photoboard obstruction was determined using Adobe Photoshop 4.0 software. Regression analysis indicated that visual obstruction of the photoboard was a good predictor of both total clump PAT weight (r2 = 0.89, p < 0.01) as well as PAT weight remaining following sequential defoliations (r2= 0.92, p < 0.01). These results suggest our technique provides a reliable index of both willow abundance and utilization within the size class of willow tested. Results may differ using larger willows with increased woody biomass. Research is needed to determine inter-species variability in the relationships described above.

Technical Abstract: Quantifying woody plant abundance has often proven difficult in the field for reasons that include irregular plant morphology, between observer variability, and lack of standardized techniques. One potential solution to these challenges is the use of ground-based photographic technology. Our objective was to develop a photo-based technique that could be used to monitor changes in willow (Salix spp.) Abundance over time and estimate changes in abundance associated with herbivory. We focused on young willows (<2m in height) because this size class represents a critical life history stage for establishment of willow clumps. In August of 2000 and 2001 we harvested 25 willow (Salix boothii Dorn.) Clumps and clamped them in front of a 150 x 200cm flourescent orange photoboard. Clumps were defoliated of photosynthetically active tissue (leaves and tips of current annual stem growth - PAT) by hand in 4 to 7 increments and photographed before and after each removal. Images were scanned to digital format and the degree of photoboard obstruction was determined using Adobe Photoshop 4.0 software. Regression analysis indicated that visual obstruction of the photoboard was a good predictor of both total clump PAT weight (r2=0.89, p<0.01) as well as PAT weight remaining following sequential defoliations (r2=0.92, p<0.01). These results suggest our technique provides a reliable index of both willow abundance and utilization within the size class of willow tested. Results may differ using larger willows with increased woody biomass. Research is needed to determine inter-species variability in the relationships described above.

Last Modified: 10/21/2014
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